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Life Cycle Cost Analysis of a Novel Cooling and Power Gas Turbine Engine

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PAGE 1

LIFE-CYCLE COST ANALYSIS OF A NOVEL COOLIN G AND POWER GAS TURBINE ENGINE By VAIBHAV MALHOTRA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2005

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Copyright 2005 by Vaibhav Malhotra

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This thesis is dedicated to my beloved fa mily for their continuous love, support and encouragement.

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ACKNOWLEDGMENTS I wish to express my gratitude towards the members of my supervisory committee, Dr. Joseph P. Geunes, Dr. William E. Lear, and Dr. S.A. Sherif, for their expertise, encouragement and support provided throughout this research. I would also like to thank Mr. John F. Crittenden of Triads Research Corporation for his continuous guidance and support. Lastly, I would like to thank all the members of the HPRTE group, especially Mr. Jameel Khan, for all their cooperation and encouragement. iv

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TABLE OF CONTENTS ACKNOWLEDGMENTS .................................................................................................iv LIST OF TABLES ............................................................................................................vii LIST OF FIGURES .........................................................................................................viii NOMENCLATURE ..........................................................................................................ix ABSTRACT ......................................................................................................................xii CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................7 Life Cycle Cost Analysis..............................................................................................7 High Pressure Regenerative Turbine Engine (HPRTE)...............................................8 Small Gas Turbine Technology....................................................................................9 Thermoeconomic Analysis.........................................................................................10 3 LIFE CYCLE COST ANALYSIS GUIDELINES.....................................................13 4 LCCA OF THE HPRTE AND THE MICROTURBINE...........................................18 Capital Investment Costs............................................................................................18 High-Pressure Compressor..................................................................................22 Combustor...........................................................................................................24 High-Pressure Turbine.........................................................................................25 Recuperator..........................................................................................................26 Power Generator..................................................................................................28 Gas Compressor...................................................................................................29 Heat Exchanger-HPRTE.....................................................................................29 VARS-HPRTE....................................................................................................30 Turbocharger-HPRTE.........................................................................................30 Air Bearings.........................................................................................................31 Energy Costs...............................................................................................................31 Fuel Costs............................................................................................................32 v

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Revenue from Refrigeration................................................................................33 Maintenance Cost.......................................................................................................35 5 RESULTS AND DISCUSSION.................................................................................37 6 SUMMARY AND CONCLUSIONS.........................................................................51 LIST OF REFERENCES...................................................................................................55 BIOGRAPHICAL SKETCH.............................................................................................57 vi

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LIST OF TABLES Table page 4-1 Base case design parameters and ambient conditions assumed in the computer code for the HPRTE/VARS and the microturbine...................................................20 4-2 Base-case values of the economic parameters used for the LCCA of the HPRTE and the microturbine.................................................................................................20 4-3 Coefficients of the gas turbine cost functions (large engine)...................................22 vii

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LIST OF FIGURES Figure page 1-1 A recuperated microturbine cycle..............................................................................3 1-2 HPRTE-VARS combined cycle.................................................................................6 5-1 Effect of increase in the HPT inlet temperature on LCCR and PCR.......................40 5-2 Effect of increase in the LPC pressure ratio on LCCR and PCR.............................40 5-3 Effect of increase in the HPT exit temperature on LCCR and cycle efficiency......42 5-4 Effect of increase in the HPT exit temperature on the revenue ratio of the HPRTE.....................................................................................................................42 5-5 Effect of ambient temperature on LCCR and PCR..................................................44 5-6 Effect of increase in HPC inlet temperature (ambient temperature for the microturbine) on cycle efficiency of the engines.....................................................44 5-7 Effect of increase in the recuperator effectiveness on LCCR and PCR...................46 5-8 Effect of increase in the cost coefficient fraction (CCF) on LCCR and PCR..........46 5-9 Effect of increase in the DOE discount rate on LCCR.............................................48 5-10 Effect of increase in the cost rate of natural gas on LCCR......................................48 5-11 Effect of increase in the electricity price rate on LCCR and PCR...........................50 viii

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NOMENCLATURE A heat transfer area COP coefficient of performance C E present value of energy cost C I present value of initial capital investment costs C RES present value of residual value C OMR present value of operations, maintenance and repair costs CCF cost coefficient fraction E 0 annual energy costs of the base period F c correction factor for heat exchangers F 0 future cost I fuel price index based on DOE projections I MS Marshall and Swift cost index LCC life cycle cost LCCR life cycle cost ratio LHV lower heating value MC heat exchanger-HPRTE P/P percentage pressure drop PV present value of any cost PCR plant cost ratio ix

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Q excess refrigeration, kW R gas constant R R recirculation ratio R Rev revenue ratio SIR savings to investment ratio T temperature W power d DOE discount rate e energy price escalation rates f friction factor m mass flow rate v specific volume Greek Symbols pressure ratio (HPC/HPT) efficiency effectiveness R angle of the wave pattern for recuperator foil folds equivalence ratio surface compactness capital cost x

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Subscripts C compressor CM combustor GEN generator HX heat exchanger R recuperator REF refrigeration T turbine VC vapor compression system comb combined cr critical in inlet out outlet poly polytropic ref reference xi

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science LIFE CYCLE COST ANALYSIS OF A NOVEL COOLING AND POWER GAS TURBINE ENGINE By Vaibhav Malhotra August 2005 Chair: Joseph P. Geunes Cochair: William E. Lear Major Department: Industrial and Systems Engineering Life Cycle Cost Analysis (LCCA) was performed to compare life cycle costs of a novel gas turbine engine to that of a conventional microturbine with identical power capacity. This engine, called the High Pressure Regenerative Turbine Engine (HPRTE) operates on a pressurized semi-closed cycle and is integrated with a Vapor Absorption Refrigeration System (VARS). HPRTE uses the heat from its exhaust to power the absorption refrigeration unit which cools the high pressure compressor inlet of the HPRTE to below ambient temperatures and also produces some external refrigeration, thus forming a cogeneration application. Life Cycle Cost Analysis procedure is based on the principles specified in the Federal Energy Management Program (FEMP) drafted by the Department of Energy (DOE). The costs evaluated for this analysis include the equipment costs, total plant costs, energy costs and maintenance costs, determined for both technologies. Effect of different design and economic parameters on the cost of the two technologies is analyzed in terms of life cycle cost ratio (LCCR), i.e. the ratio of life xii

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cycle costs of the HPRTE to that of a microturbine and plant cost ratio, i.e. the ratio of total plant costs (PCR) of the HPRTE to that of a microturbine. The life span for these technologies is assumed to be 80000 hours and assuming an operation span of 8000 hours in a year, the life time of the engines is calculated as 10 years. The pressurized nature of the HPRTE leads to compact components resulting in significant savings in equipment costs versus that of a microturbine. Revenue obtained from external refrigeration offsets some of the fuel costs for the HPRTE thus proving to be a major contributor in cost savings for the HPRTE. For the base case, with high-pressure-turbine (HPT) inlet temperature of 1373 K and HPT exit temperature of 1073 K, the HPRTE showed life cycle cost savings of 7% over a microturbine for similar power capacity. From the results of this analysis, the payback period to recover the additional investments made in the HPRTE in comparison to a microturbine is 3. 9 years, well within the engine life span of 10 years. For this analysis, the Savings to Investment Ratio (SIR) for the HPRTE is calculated as 2.15, significantly higher than 1 which, according to the FEMP guidelines is the minimum qualifying criterion for any effective project alternative to be selected. Based on the results of this analysis, the economic performance measures look favorable for the HPRTE, in comparison to a microturbine. xiii

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CHAPTER 1 INTRODUCTION For the past 60 years, electricity production and supply in the United States has been performed by centralized, regulated electric utilities that own and operate power generation facilities as well as the transmission and distribution lines. However, changes in the federal and state public policies have encouraged the opening of the electric power generation system to other alternatives like the Distributed Generation (DG) technologies. Distributed energy resources are parallel and stand-alone electric generation units located within the electric distribution system at or near the end user. Some of the benefits of distributed generation include greater local control of electricity delivery and consumption, cost savings obtained from reducing the peak demand, efficient utilization of waste heat in CHP applications, and reduced emissions versus other power generation technologies. This study is focused on the comparison of life cycle costs of two technologies that are particularly attractive for distributed generation applications. The first technology considered in this analysis is that of a microturbine. Microturbines are small gas turbines that burn gaseous and liquid fuels to create a high-energy gas stream that turns an electrical generator. Like the large gas turbines, microturbines also operate on a brayton thermodynamic cycle. In this cycle, atmospheric air is compressed, heated at constant pressure through combustion with a fuel, and then expanded in a turbine, which drives a generator. Most of the microturbines are integrated with a recuperator to utilize the heat of the exhaust stream, enabling an increase in the cycle efficiency and reduction in fuel 1

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2 consumption. Apart from possessing the other advantages of distributed generation, microturbines also have low to moderate initial investment costs and flexibility in terms of the fuel on which they can be operated. Figure 1-1 shows the block diagram of a recuperated microturbine. The second technology considered in this analysis is based on a novel cooling and power cycle that combines a semi-closed pressurized gas turbine engine called the HPRTE with a Vapor Absorption Refrigeration System (VARS) to form a cogeneration system. A schematic diagram of the HPRTE-VARS cycle is shown in Figure 1-2. Inlet air at State 1 is compressed by the low-pressure compressor (LPC, labeled C1). This compressed air then mixes with the recirculated combustion products from the recuperator at State 2.9. The combined stream is then passed through the generator (GEN) of the VARS where it acts as the heat source for the VARS unit. After exiting the generator, the combined air-gas stream passes through a heat exchanger (MC) where it is cooled further. The stream then goes through the evaporator of the VARS where it loses more heat and comes out at a temperature below that of the ambient. It is then compressed in the high-pressure compressor (HPC, labeled C2), heated in the recuperator R and combustor (CM), and then expanded in the high-pressure turbine (HPT, labeled T1). The exhaust stream is then passed through the recuperator where it loses some of its heat to the gases entering the combustor. At the exit of the recuperator, some portion of the exhaust is recirculated while the remaining portion is passed through a low-pressure turbine (LPT, labeled T2) and finally to the atmosphere. In a real sense, the HPRTE-VARS cycle is similar to the cycle of a recuperated microturbine except for the fact that the former is pressurized using a low-pressure compressor-turbine spool, uses highly

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3 dilute air, and has additional components; namely the VARS unit, low-pressure compressor/turbine system and the heat exchanger (MC). The VARS unit and the heat exchanger reduce the HPC inlet temperature and produce external refrigeration. FuelRCTInlet airExhaust streamCMGENPCETurbineRecuperatorCombustorGeneratorPower Conversion EquipmentCCompressorTR GENCMPCE Figure 1-1. A recuperated microturbine cycle Considering the fact that cogeneration technologies form an important part of the energy future of the world [1], the combined cooling and power generated from the HPRTE make it a very attractive distributed generation technology of the future. The waste heat of the HPRTE can also be utilized for combined heat and power generation. An earlier study conducted on the HPRTE has shown that the HPRTE has reduced thermal NOx levels by roughly five orders of magnitude versus open cycles. Apart from

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4 low thermal NOx, the HPRTE also has reduced emissions of Carbon Monoxide (CO) and other unburned hydrocarbons, in comparison to the open cycles. Other studies conducted on the HPRTE have demonstrated the water extraction capability of the engine. This water is obtained as a product of combustion and is recirculated with other exhaust gases, and almost the entire amount of water generated during the combustion process of the HPRTE, can be extracted for different applications. These applications include human consumption, process cooling or combined cycle operations. The objective of this study is to determine whether the HPRTE has economic benefits to complement its other advantages, by performing a cost analysis of the HPRTE and comparing the costs with the life cycle costs of a conventional microturbine, another attractive technology for distributed generation. A LCCA procedure based on the guidelines of the FEMP is applied to compare the potential savings in life cycle costs of an HPRTE-VARS combined system, to that of a microturbine, for identical power capacity and operating conditions. Major costs evaluated in this analysis include the equipment costs, total plant costs, energy costs, and maintenance costs incurred during the lifespan of engine operation. To reflect the comparative nature of this analysis, the results of this analysis are expressed in terms of life cycle cost ratio (LCCR) and plant cost ratio (PCR) of the two technologies. Additionally a term called revenue ratio (R Rev ) for the HPRTE is defined to analyze the ratio of revenue from refrigeration obtained for a particular set of operating conditions and input parameters to the revenue obtained for the base case. This ratio is equivalent to the ratio of net refrigeration produced for a particular case to that for the base case. As a

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5 part of this analysis, the sensitivity of the cost ratios (and revenue ratio of the HPRTE) to changes in design and economic parameters is evaluated for both technologies. Chapter 2 gives a brief insight into the previous research and studies performed on small gas turbines, primarily the HPRTE. It also discusses some of the previous work conducted on economic evaluations of thermodynamic cycles. Chapter 3 mentions the basic framework of the LCCA, as laid out in the FEMP guidelines. Chapter 4 discusses the approach followed for conducting a comparison of life cycle costs (LCC) of the HPRTE with those of a microturbine. Chapter 5 discusses the sensitivity of the LCC of both technologies with changes in design and economic parameters. Chapter 6 discusses some of the conclusions that can be drawn from this analysis.

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6 7.210971 2 34 5 68 C1EVAP C2 RT2C1Low-Pressure CompressorC2High-Pressure CompressorT1High-Pressure TurbineT2MCHeat Exchanger RCMCombustorCONDABSAbsorber-VARSEVAPGENGenerator-VARSEvaporator-VARSLowPressure TurbineRecuperatorCondenser-VARS GEN MC CM T1 2.9 2.9.1 2.9.2 7r 6r 5r 4r 3r 2r 1r 8r 2.9 2.9.1. 2.9.2 3.0 GEN EVAP COND ABS Figure 1-2. HPRTE-VARS combined cycle

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CHAPTER 2 LITERATURE REVIEW Life Cycle Cost Analysis As mentioned in the introduction, the primary aim of this study is to compare the life cycle costs of the HPRTE to that of a microturbine. This cost comparison is performed using the life cycle cost analysis procedure based on the FEMP guidelines established by the U.S. Department of Energy. These rules are effective in economic evaluation of energy and water conservation projects. The guidelines for applying the LCCA are clearly stated in the Life Cycle Costing Manual, NSIT handbook 135 [2]. Apart from covering the life cycle costing procedure, this manual also specifies the guidelines to determine supplementary economic measures like the savings to investment ratio (SIR), net savings (NS) and net payback period. Annual supplement to the NIST handbook 135 [3] published by the DOE, lists the projected energy price escalation rates, DOE discount rates and the corresponding discount factors to determine the present value of the future costs incurred during the life span of a system or a technology. Future costs include annually recurring non uniform costs like the energy costs and annually recurring uniform costs like the maintenance costs. Energy price escalation rates are listed for four census regions and also for the U.S. Average. For this analysis, the annual supplemented published for the year 2004 is used and the fuel escalation rates are taken to be that of the U.S. average. 7

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8 High Pressure Regenerative Turbine Engine (HPRTE) As described earlier, the HPRTE operates on a pressurized semi-closed, intercooled and recuperated cycle. Initial studies on semi-closed cycles were performed by the Sulzer brothers, Westinghouse and the U.S. Navy in the 1940s and 50s. The results of these studies indicated that the semi-closed cycle had certain advantages in terms of their thermal efficiencies, high specific power, lower emissions and system compactness as compared to the open cycles [4]. Despite these advantages, the research on semi-closed cycles was restricted due to operational and technological constraints. With the advancement of technology, interest in the semi-closed cycles has been revived. Significant research on the HPRTE is being conducted at University of Florida and several studies performed on the engine have delivered promising results. Nemec and Lear [5] analyzed the combined cycle of the HPRTE with a Rankine bottoming cycle and the results showed that the combined cycle could achieve thermal efficiencies in excess of 60%. MacFarlane [6] demonstrated that the HPRTE, because of its pressurized, semi-closed, and intercooled nature, had the capability to extract water from combustion products. The extraction of water had little effects on the rest of the cycle though the overall performance of the engine was improved due to an increase in the specific power. The water generated could be used for applications like process cooling, combined cycle systems and human consumption. This water could also be reinjected to the burner for power augmentation and reduction in NO x levels without much reduction in the engines performance. Muley and Lear [7] showed that the recirculation of the exhaust gases led to a reduction in thermal NO x formation rates by roughly five orders of magnitude versus typical open cycles. This was due to the fact that the recirculated gases reduced the oxygen concentration in the inlet air, thus leaving less oxygen to react with nitrogen.

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9 Presence of high-heat capacity inert gases like CO 2 and H 2 O also led to a reduction in the adiabatic flame temperature. Lear and Laganelli [8] demonstrated that the HPRTE produced a constant efficiency curve at part power over a wide range and that the HPRTE generated reduced emission levels versus open cycles. Boza et al. [9] conducted a thermodynamic performance analysis of the combined cooling and power cycle formed by integrating the HPRTE with a vapor absorption refrigeration system (VARS). The combined cycle was modeled for a small engine with power output of 100 kW and for a large engine having an output power of 40 MW. The results were presented in terms of thermal efficiency, refrigeration ratio and combined cycle efficiency and significant advantages over the state-of-the-art were predicted. Khan et al. [10] analyzed the combined HPRTE-VARS cycle for water extraction and showed that more than one kg of water can be extracted per kg of fuel for cases with high recirculation. Small Gas Turbine Technology As mentioned in the introduction, this analysis compares life cycle costs of the HPRTE to a conventional microturbine. Both these technologies come under the category of small gas turbines. Small gas turbine engines are gas or fuel fired turbine generator units with a power range of less than 500 kW. Compared to the other small scale power generation technologies, small gas turbines offer a number of potential advantages. These gas turbines have a compact size, flexibility of operating on liquid or gaseous fuels, small number of moving parts, extremely low emissions and the potential to be used for distributed generation applications. However these gas turbines have lower efficiency in their basic configuration as compared to the other small scale power generation technologies. An addition of a recuperator or a regenerator leads to significant increases in cycle efficiencies of small gas turbines. Romier [11] performed a parametric study to

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10 compare three different cycles for small gas turbines. The first cycle was a recuperative cycle, the second a recuperative-intercooled cycle and the third cycle was a recuperative-underpressurized cycle. The results were analyzed in terms of the cycle electrical efficiency as it is one of the most critical factors while determining the return on investment of a power generation system. Of the three cycles, the recuperated intercooled cycle had the highest electrical efficiency for a gas turbine co-generation system at a nominal power output of 350 kW. Thermoeconomic Analysis As per the guidelines mentioned in the life cycle costing manual, the life cycle costs of any technology can be determined by evaluating the equipment costs, process capital costs, energy costs, maintenance costs and the residual value. In this analysis, the equipment costs of both technologies are determined using the component cost functions, which were developed on the basis of exergoeconomic evaluation of gas turbine cycles. Exergoeconomics combines the exergy analysis with the economics of a system by assignment of costs based on the exergy content of an energy carrier. An energy carrier is any system or substance used for carrying and transforming energy. Exergy is defined as the maximum work attainable from an energy carrier under conditions imposed by the environment and expresses the maximum capability of the energy carrier to cause changes. It is closely related to system economics as the energy user pays for the potential of energy to cause changes [12]. Application of exergoeconomic analysis for thermodynamic systems was initiated by M. Tribus, R. B. Evans, R. A. Gaggioli and E.F. Obert in the late 1950s. These applications were further developed by Y.M. EL-Sayed, G. Tsatsaronis and C. Frangopoulos in the 1970s and 80s. Tsatsaronis [12] discussed the exergy analysis for components of an energy system and the application of exergy

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11 costing to evaluate the economics of the system. As a part of the exergy costing principles, a cost is assigned to every material and stream in the energy system, based on its exergy flow rate. This cost can be determined using exergy balances between the input and output streams of each component, after taking into account the exergy losses. Themoeconomic optimization of systems can be achieved by minimizing the cost of exergy for every component of the system. Initially the concept of thermoeconomic analysis was applied only to simple cycles but further developments led to its application for advanced and complex cycles. Franco and Casarosa [13] compared the results obtained from thermodynamic and thermoeconomic optimization of a brayton cycle with intercooling, reheating, regeneration and optimized heat recovery stream generator. The results from thermoeconomic optimization showed some shift in the cycle efficiency in comparison to that obtained from thermodynamic optimization, thus indicating a compromise between high cycle efficiency and engine economics. Massardo and Scialo [14] performed the thermoeconomic analysis of gas turbine cycles using a modular computer program TEMP, which can conduct thermodynamic, exergy and thermoeconomic analysis for several gas turbine cycle configurations. This tool uses the cost functions for the cost of compressor, combustor, turbine, power generator and intercoolers to determine the purchased equipment cost. These cost functions are developed as a result of exergoeconomic analysis of different components, performed in the initial study of thermoeconomics. Traverso et al. [15] have modified the cost coefficients used in the TEMP code by using the latest cost information available. A web based user friendly interface of the TEMP code has also been developed with the help of

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12 WIDGET. For this analysis, the equipment costs for both the technologies are calculated using the cost functions mentioned in reference 15.

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CHAPTER 3 LIFE CYCLE COST ANALYSIS GUIDELINES Life cycle cost analysis (LCCA) is an economic method of project evaluation in which all the costs from owning, operating, maintaining and ultimately disposing of a technology are evaluated to compare different project alternatives. Life cycle cost analysis is particularly helpful when there are more than one competing alternatives for the same objective. The alternative with the lowest value of life cycle costs is usually considered to be the most effective. The costs primarily considered in the life cycle cost analysis include: initial investment costs, energy costs, cost of operations, maintenance and repair and finally the residual value of the system. While evaluating the life cycle costs of a system or technology, all the future costs, including the energy costs and the cost of operations, maintenance and repair are discounted to their present value as of the base date. The residual value of any system is its economic value at the end of the study period or assumed life span. The formula to evaluate life cycle costs of an alternative can be stated as follows: LCC = C I + C E + C OMR C RES (3.1) where C I is the present value of the capital investment costs, C E is the present value of the energy costs, C OMR is the present value of operations, maintenance and repair costs, and C RES is the residual value of the system, discounted to the base date. The residual value can also be considered as the final resale (or scrap) value of the system minus the disposal cost. Costs which are similar for all alternatives considered in the analysis do not contribute in the final decision process of selecting an alternative and hence can be 13

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14 ignored. As mentioned earlier, all the future costs incurred during the life span of an alternative, need to be discounted to their present value for inclusion in the LCC analysis. The discount rate of future costs for energy and water conservation project is established every year by the DOE. Future costs can further be classified as one time costs, uniform annually recurring costs and non uniform annually recurring costs. The present value (PV) of a one time future cost F 0, can be determined using the relation ndF PV 10 (3.2) where d is the discount rate and n is the time duration between the base period and the period in which this cost is incurred. Similar expression can be obtained for calculating the life cycle costs of uniform annually recurring costs like the annual maintenance cost. If F 0 is the uniform annually recurring cost, then the present value (PV) of the life cycle costs can be determined using the relation nnddd FPV11110 (3.3) Here d is the discount rate and n denotes the total life span of a system or the time period over which these costs are incurred. The term nnddd1111 is used by the DOE to calculate the discount factors or the Uniform Present Value (UPV) factors based on a fixed discount rate for different values of n (expressed as number of years). Hence, the present value of an annual uniform cost incurred for a period of n years can be determined by just multiplying the annual cost by the UPV factor listed for that particular value of n. For the calculation of energy costs, the escalation rates of the fuel prices also have to be taken into account. These escalation rates are generally non-constant and are

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15 based on the projections made by the DOE. The present value of life cycle costs of the fuel (or any other source of energy with non uniform annual costs) required for a systems operations, considering the base-year as 2004, is determined using the relation ntttOEdIEC120041 (3.4) where E 0 is the annual cost of energy as of the base date; t is the index used to designate the year of energy usage; n is the number of periods (generally years), over which energy costs or savings accrue; I (2004+t) is the projected average fuel price index specified by the DOE for the year 2004+t (where I, for the year 2004 2 = 1.00); and d represents the discount rate. The term ntttdI120041 is evaluated by the DOE for various fuels based on their respective escalation rates for different values of n, assuming a fixed discount rate d. The resulting number is referred to as the UPV factor for fuel costs. Fuel costs for any value of n, can be determined by simply multiplying the fuel cost for the base date by the UPV factor corresponding to that value of n. These UPV factors are calculated based on price escalation rates of fuels for four census regions and also for the U.S. average. Another critical factor to be considered in the LCCA is the rate of inflation. As per the FEMP guidelines, the LCCA procedure can be applied using two different approaches for dealing with inflation. The first approach deals with stating the cash flows in constant dollars while the second approach states the cash flows in current dollars. Constant dollars are dollars of uniform purchasing power, exclusive of the rate of inflation and indicate what the same goods or services will cost at different times if there is no change in the general price level. Current dollars on the other hand are inclusive of inflation and reflect changes in the purchasing power of dollars from year to year. The constant dollar

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16 approach has the advantage of avoiding the need to project future rates of inflation or deflation. The discount rates published by the DOE follow a constant dollar approach and the same approach is followed in this analysis. Apart from the LCC, there are supplementary methods of evaluating economic performance based on the LCCA procedure. These include the savingstoinvestment ratio (SIR), net savings (NS) and net payback period. The net savings (NS) for an alternative, relative to a designated base case, can simply be calculated by subtracting the LCC of an alternative from the LCC of the base case. While evaluating multiple, mutually-exclusive alternatives, the alternative with the highest value of NS will also have the lowest value of LCC. Hence LCC and NS can be used interchangeably. The SIR is defined as the ratio of present value of savings obtained from an alternative (with respect to the base case) to the additional investments made to implement the alternative. An alternative is considered economically justified with respect to the base case if it has a value of SIR greater than 1. Another economic performance measure that can be determined using the LCCA procedure is the net payback period. The payback period is expressed as the number of years between the base period and the time when the cumulative savings obtained from an alternative are just sufficient to recover the incremental initial investment. Since the payback period does not include all cost or savings, or even the residual value after the payback date, it s not a valid method for selecting among multiple, mutually-exclusive project alternatives. As per the FEMP guidelines, the payback period should just be used as a screening measure for the LCC analysis. However, the SIR and the NS always give results consistent with those obtained from the life cycle costs. The sensitivity of life cycle costs of a system to changes in

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17 design and economic parameters is usually evaluated to determine the trends in life cycle costs for different operating and economic conditions.

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CHAPTER 4 LCCA OF THE HPRTE AND THE MICROTURBINE The primary aim of this analysis is to compare the life cycle costs of the HPRTE integrated with a VARS to that of a conventional microturbine. This analysis is based on the guidelines established by the DOE in the FEMP. The major costs evaluated in this analysis include the equipment costs, total plant costs, energy costs and maintenance and repair costs. The sum of equipment costs, labor costs, material costs and installation costs is categorized as the process capital cost. Adding soft costs like project supervision costs and contingency fees to the total process capital gives the total plant cost or the capital investment costs The residual value for both the technologies is assumed to be similar and hence ignored in the analysis. This cost analysis is performed for a base power load of 250 kW for both technologies. The life span for both technologies is assumed to be 80,000 hours, and assuming an operation span of 8000 hours in a year, the life time for both technologies is calculated as 10 years. In the following sections, the major costs evaluated for the analysis are discussed starting with the capital investment costs. Capital Investment Costs Capital investment costs primarily include the equipment costs, installation costs, costs of electrical instrumentation and other materials, and project supervision and contingency fees. The installation costs can be assumed to be 30% of the total equipment costs, while the costs of electrical instrumentation is usually assumed to be 20% of the equipment costs. Project contingency fees and project management fees usually account for 15% each of the equipment costs. These percentages are assumed to be similar for 18

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19 both technologies and taken from previously published data [16]. The cost of land is not included in this analysis. As mentioned earlier, equipment costs for both technologies are calculated using the component cost functions developed on the basis of thermoeconomic analysis of gas turbine cycles. These functions were modified by Traverso et al. [15], by changing the cost coefficients of these functions, making them representative of current equipment cost. The cost functions were developed for gas turbine engines with a power range of 1 to 300 MW. Though the cost functions were developed for medium-to-large sized gas engines, they can also be used to determine the equipment costs for small gas turbine engines (like the HPRTE and the microturbines), just by changing the cost coefficients. As the cost information of equipments is proprietary and difficult to obtain, the cost coefficients for small engines were taken to be a parameterized fraction of the cost coefficients of large engines. This fraction is referred to as the Cost Coefficient Fraction (CCF) in this analysis. The assumption of cost coefficients of small engines being a fraction of that of the large engines is based on the relatively inexpensive radial technology of small engines in comparison to the relatively expensive axial technology for the large engines. The fact that the same cost functions and coefficients were applied both for the HPRTE and the microturbine ensured a fair comparison even with the uncertainty in the values of the cost coefficients. For the present study, the design parameters for the cost function are obtained from a computer code developed for thermodynamic analysis of the HPRTE-VARS cycle [10]. This code assumes a fixed value of the equivalence ratio by changing the recirculation ratio R R which is defined as the ratio of mass flow rate of the exhaust stream to that of fresh air. The equivalence ratio, on the other hand, is defined as the fuel-air ratio at the actual condition to that under

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20 stoichiometric conditions. The code developed for the HPRTE-VARS cycle can also be used to simulate a microturbine cycle by neglecting any recirculation of the exhaust stream and not including any of the additional components present in the HPRTE. Table 4-1 shows the base case design parameters and ambient conditions used in the computer code, for both the HPRTE-VARS cycle and the microturbine. The different economic parameters assumed for the base case are listed in Table 4-2. Table 4-1. Base case design parameters and ambient conditions assumed in the computer code for the HPRTE/VARS and the microturbine Design Parameters Values Turbine Inlet Temperature K 1373 Turbine Exit Temperature K 1073 Turbomachinery Polytropic efficiencies 85% Recuperator Effectiveness 0.84 HPRTE Heat Exchanger Effectiveness 0.8 Pressure Drop in Combustor 0.05 Pressure Drop in HPRTE-Heat Exchanger 0.03 Pressure Drop in VARS Generator (HPRTE) 0.03 Pressure Drop in VARS Evaporator (HPRTE) 0.03 Pressure Drop in Recuperator (Gas side) 0.06 Pressure Drop in Recuperator (Air side) 0.02 Generator Temperature K (HPRTE-VARS) 373 Evaporator Temperature K (HPRTE-VARS) 288 Ambient Conditions Ambient Temperature K 303 Relative Humidity of Fresh Air 90% Ambient Pressure (atm) 1.0 Table 4-2. Base-case values of the economic parameters used for the LCCA of the HPRTE and the microturbine Economic Parameters Values DOE Discount Rate 3% Cost Rate of Natural Gas ($/MMBTU) 5 Price Rate of Electricity (cents/kWh) 8 Cost Coefficient Fraction (CCF) 0.5

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21 The main components common for both the HPRTE and the microturbine include the high-pressure compressor, combustor, the high-pressure turbine, recuperator, and the power generator. The HPRTE also includes additional components in terms of a VARS unit, a heat exchanger for inlet air cooling, and a turbocharger that works as a low-pressure compressor/ turbine system. The design parameters for the components common to both technologies are assumed to be of similar values. Considering the rapid advancement in gas turbine technology, the assumed values of HPT inlet and exit temperatures of both engines are reflective of the future technology levels of the gas turbines. On the other hand, the values assumed for pressure drop across the heat exchanger and the VARS unit of the HPRTE are significantly high, with a total pressure drop of almost 9% across the heat exchanger-VARS section (Table 4-1). High values of pressure drop across the heat exchanger-VARS section lead to a noticeable decrease in the HPRTE-VARS cycle efficiency. However, if the pressure drop across the heat exchanger and the VARS unit is ignored, the cycle efficiency of the HPRTE is very similar to that of a microturbine. Table 4-3 lists the coefficients of gas turbine cost functions for large engines as mentioned in reference 15.This table also lists the cost coefficients for the main components of a gas turbine These cost coefficients are denoted by c 1 cc 1 t 1 and g 1 (all cost coefficients are represented in $) for the high-pressure compressor, combustor, the highpressure turbine, and the generator, respectively. As discussed earlier, the base-case cost coefficients for small engines (HPRTE, microturbine) are assumed to be 50% of those of large engines, or in other words, the cost coefficient fraction (CCF) is assumed to be 0.5 for the base case. The equipment costs for both technologies are discussed in details in the next section.

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22 Table 4-3. Coefficients of the gas turbine cost functions (large engine) Constant Value c 1 ($) 5095.9 c 2 0.15 c 3 0.85 c 4 0.3 cc 1 ($) 1857 cc 2 0.995 cc 3 5.479 cc 4 34.36 cc 5 0.6 P ref [Pa] 101325 T ref [K] 288.15 t 1 ($) 5979 t 2 0.29 t 3 4.185 t 4 23.6 t 5 0.75 g 1 ($) 1030.9 g 2 0.72 m ref [kg/s] 1 POW ref [kW] 1 refcrm, 0.9586 Traverso, A., Massardo, A.F., Cazzola, W., and Lagorio, G., 2004, WIDGET-TEMP: A Novel Web-Based Approach for Themoeconomic Analysis and Optimization of Conventional and Innovative Cycles, Proc., 2004 ASME TURBO EXPO, Vienna, Austria, June 14-17, 2004, ASME Paper 2004-GT-54115. High-Pressure Compressor Both the HPRTE and the microturbine use a centrifugal or a radial compressor to compress the inlet air and raise its temperature and pressure. The cost of the high-pressure compressor of both technologies is calculated using the cost function for compressors capital cost defined by Traverso et al. [15]. This relationship is expressed as:

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23 2,1)ln(431cCpolyccrefcrminPinTinRairmcrminPinTinRairmcC (4.1) The cost equation uses a corrected expression of mass flow rate for different pressure and temperature conditions. Here, T airm in and P in represent the mass flow rate, temperature, and pressure of the incoming air. represents the critical mass flow rate at choking conditions (Mach number = 1) and is a constant in this analysis. The expression crm crminPinTinRairm represents the corrected mass flow rate, which is also normalized with respect to the reference conditions. The constants for the cost functions are taken from reference 15 and are listed in Table 2. As mentioned earlier, the value of cost coefficient c 1 is taken to be 50% of that of the large engine. The cost of the compressor is dependent on the corrected mass flow rate, its pressure ratio and polytropic efficiency poly, C The coefficient c 3 demonstrates the scaling effect of compressor size (and hence cost) with power. An increase in the output power capacity leads to an increase in compressors size and cost, but in a non linear fashion. The mass flow rates, temperatures and pressures are obtained from the computer code simulating the two cycles. The inlet air coming into the high-pressure compressor of the HPRTE is at an elevated pressure after being compressed in the low-pressure compressor. This results in a lower corrected mass flow rate for the HPRTE in comparison to that of a microturbine for a similar power output, thus reducing HPRTEs compressor cost relative to that of a microturbine. Similar

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24 pressure ratios for the high-pressure compressor (HPC) can be achieved for both technologies as the turbine inlet and exit temperature for the HPRTE are assumed to be same as that of a microturbine. The polytropic efficiency of the compressor is also assumed to be same for both technologies. Combustor The capital cost of the combustor chamber, where the fuel-air mixture is burned at constant pressures, to achieve the desired turbine inlet temperature, is determined by the following cost relationship defined in [15]. 24,35/111ccCMccTTccccrefoutoutoutoutCMPPevmvmccrefoutout (4.2) Here, v outm out and T out represent the mass flow rate, specific volume and temperature of the gas stream exiting the combustor. The values of these parameters are determined by the computer code developed for both technologies. From the perfect gas law relation, the specific volume of the gases is directly proportional to the temperature, at constant pressures. Since the temperature of the gases passing through the combustor is maximum at the combustors exit, the specific volume of the gases also attains its maximum value at combustors exit. The cost of the combustor is thus calculated using the mass flow rate and the specific volume at its exit. This cost expression is also nondimensionalized using reference conditions. For this analysis, since the combustor exit temperature of the gases is same for both the HPRTE and the microturbine, their specific volumes and hence the costs are dependent on the pressure of the gases at the exit of the combustor. Because of the initial compression in the low-pressure compressor, the gases exiting the combustor of the HPRTE are at higher RTPv

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25 pressures than those of the microturbines. Thus the cost of the HPRTE is reduced by a factor proportional to the pressure ratio of its LPC/LPT, in comparison to that of a microturbine. The cost relation also demonstrates an inverse relationship between combustors cost and its pressure drop CMPP/ For this analysis, an equal value of the pressure drop is assumed for both engines. Also, the primary zone temperature in the combustor of the HPRTE is reduced due to increased dilution of the inlet-air stream of the HPRTE by the recirculated stream. This may allow the combustor of the HPRTE to be made with relatively inexpensive material, in comparison to that of a microturbine. However, for this analysis, no economic credit is claimed for savings in material cost of the combustor of the HPRTE High-Pressure Turbine After exiting the combustor, the gases are expanded in the high-pressure turbine. The cost of the turbine is determined from the cost function relationship developed by Traverso et al. [15] and represented by Equation 4.3. 24,35,11)ln(1tTpolytTTttrefoutoutoutoutTrefininevmvmt (4.3) Here, v outm out and T out represent the mass flow rate, specific volume and temperature of the gas stream exiting the high-pressure turbine. T in represents the turbine inlet temperature. As in the case of the combustor, the cost of the turbine is dependent on the volume of the gases at the exit of the turbine. This is due to the fact that since the gases undergo an expansion process in the turbine, they attain their maximum volume for the turbine section at the exit, where the pressure of the gases is the lowest for the entire section. The exit turbine pressure of the gases for a microturbine is less than that for the

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26 HPRTE, again by a factor proportional to the LPC/LPT pressure ratio of the HPRTE. This leads to larger specific volumes of the gases and hence larger costs for the highpressure turbine of the microturbine, relative to that of the HPRTE, assuming the same turbine inlet and exit temperatures for both technologies. The cost function also shows a logarithmic proportionality with the pressure ratio of the turbine and an inverse relationship with the polytropic efficiency poly, T. As in the case of the high-pressure compressor, the polytropic efficiency of the high-pressure turbine of the HPRTE is assumed similar to that of the microturbine. Recuperator A recuperator facilitates heat exchange between hot exhaust gases and compressed air going into the combustor. This reduces the amount of fuel needed to heat the compressed air to the turbine inlet temperature, thus helping in a significant increase in the cycle efficiency and the specific power of the engine. The cost of the recuperator is evaluated using the following expression derived for the volume of the recuperator by McDonald [17]. RRRRRfPPmV1/11 (4.4) This expression relates the recuperator volume with its mass flow rate, pressure ratio of the engine cycle, recuperators effectiveness and pressure drop, and the surface geometry of the recuperator. The factor RRf1 represents the surface geometry of the recuperator and this factor is assumed to be same for both technologies. For a recuperated microturbine, the cycle pressure ratio determines the temperature of the compressed air stream going into the recuperator. The pressure of the exhaust stream of the engine,

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27 entering the recuperator of a microturbine is close to the ambient (1 atm) after going through the expansion in the turbine. The relationship between the volume of the recuperator and the cycle pressure ratio (Equation. 4.4) works fine in the case of a microturbine. This is due to the fact that cycle pressure ratio of a microturbine corresponds to the pressure ratio of its HPC/HPT as there is just one compression/expansion stage, with the exhaust stream entering the recuperator at ambient pressures. However, in the case of the HPRTE, there is an extra stage of compression for the inlet air as it is compressed in the LPC, before being compressed in the HPC. Thus the compressed air stream discharged from the HPC and the exhaust stream exiting the HPT of the HPRTE are at elevated pressures, by a factor proportional to the LPC/LPT pressure ratio, as compared to a microturbine. To include the effect of elevated pressures of both the streams entering the recuperator of the HPRTE, it was decided to use a corrected expression for the mass flow rate of the streams. The corrected mass flow rates were also applied for both streams entering the recuperator of a microturbine. To calculate the recuperator cost estimate for both technologies, the following equation developed by Douglas [18] relating the heat exchanger cost to its area was used. HX = cMSFIA29.22803.10166.0 (4.5) where HX is the heat exchanger capital cost, A is the heat transfer area, I MS is the Marshall and Swift cost index, which is 1280 for year 2004 and F c is the correction factor for different design pressures and construction materials. For this case, the correction factor was assumed to be 1. The heat transfer area is calculated using the thermodynamic code developed for the two cycles. The pressure drop across the recuperator and the recuperator efficiency were assumed to be similar for both technologies. Since the

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28 HPRTEs recuperator has lower corrected mass flow rates of both the streams as compared to a microturbine, it can be stated that for the same power output, the recuperator of the HPRTE is compact in comparison to that of a microturbine. The area and hence the cost of the recuperator of the HPRTE is less than that of a microturbine recuperator by a factor proportional to the LPC/LPT pressure ratio of the HPRTE. Power Generator Micro-or mini-turbines (30 to 500 kW) produce power either via a high-speed generator rotating on a single compressor/ turbine shaft or on a separate power turbine driving a gearbox and a conventional 3600 rpm generator. The high-speed generator of a single shaft requires a rectifier to convert its high frequency AC output into 60 Hz for general use. The cost of the generator is calculated using the cost relationship developed by Traverso et al. [15] for large engines by taking a modified cost coefficient, with CCF of 0.5. The cost of power conversion equipment is also included in the cost of the generator. This cost comes out to be similar for both the microturbine and the HPRTE as the power output for both engines is the same. The cost relationship is given by Equation. 4.6. 2,1grefTTGWWg (4.6) where is the electrical power generated by the engine. This expression is normalized with a reference power capacity. This equation depicts a direct but nonlinear relationship between the generator cost and the generated power. TW

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29 Gas Compressor Small gas turbines operating on gaseous fuel require the fuel to be delivered at pressures ranging from 50 psig to 80 psig for effective combustion. This requirement is much higher than the usual pipeline delivery pressure of 1-2 psig. To deliver the fuel at the required pressures for effective combustion, a gas compressor is used for both the HPRTE as well as the microturbine. The cost of the gas compressor is expected to add somewhere in the vicinity of 50-100 $/kW to the total equipment cost [19]. Though the fuel pressure of the HPRTE is higher as compared to a microturbine, the cost of the gas compressor is assumed to be insensitive to the pressure of the fuel. Heat Exchanger-HPRTE As discussed in the cycle configuration of the HPRTE, a heat exchanger (MC, Figure 1-1) is placed in the gas path before the high-pressure compressor to reduce the inlet temperature of the air entering the compressor. Reducing the temperature of the air before the compressor inlet reduces the work required for compressing the air to the desired temperature and pressure. Reduction in the compressor work increases the net work output from the system, thus increasing the overall efficiency of the engine. In this analysis, the heat exchanger is coupled to the evaporator of the VARS unit. The cost of this heat exchanger is also calculated using Equation (4.6). The heat transfer area for this heat exchanger is calculated using the thermodynamic code developed for the HPRTE cycle. Since the gas stream entering this heat exchanger is at elevated pressure after being compressed in the LPC, a corrected expression for mass flow rate (as done in the case of the recuperator) is used to determine the area and hence the cost of this heat exchanger. The value of the correction factor used in the cost equation of the heat exchanger is equal to the value of the correction factor used in the case of a recuperator. This value of the

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30 correction factor for the heat exchanger is highly conservative, considering the relatively expensive materials used for the recuperator, as compared to the heat exchanger. This difference in materials is due to the fact that the gas streams flowing through the recuperator are at higher temperatures, as compared to the gases flowing through the heat exchanger, thus resulting in expensive-material usage for the recuperator, in comparison to the heat exchanger. VARS-HPRTE The HPRTE is integrated with a vapor absorption refrigeration system (VARS). This unit is driven by the recirculated exhaust stream of the HPRTE and serves the dual purpose of cooling the inlet air going into the compressor and producing some external refrigeration. This VARS unit could either be based on a water/lithium bromide or an ammonia/water, refrigerant/absorbent pair. The cost of this unit is calculated using the cost per tonnage figure mentioned in reference 20 for a single-stage absorption unit. The code developed for thermodynamic analysis of the HPRTE/VARS cycle determines the cooling capacity of the VARS unit based on the cooling load required to cool the gas path and the external refrigeration generated. Turbocharger-HPRTE As discussed earlier, the HPRTE utilizes a low-pressure compressor-turbine system for pressurizing the fresh air to increase the specific power and fluid densities, thus making the system compact for a fixed power capacity. In this analysis, an automobile turbocharger is chosen as the LPC/LPT system. The cost of the turbocharger is assumed to be similar to that of automobile turbochargers. This cost is based on optimal values of the LPC pressure ratio and air mass flow rate. The optimal value of turbocharger pressure ratio is determined from the thermodynamic code that ensures that the work output

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31 obtained from the low-pressure turbine is equal to the work required for compressing the fresh air [10]. In place of a turbocharger, separate LPC and LPT can be used to generate additional work output, apart from pressurizing the inlet air. Air Bearings Small turbines can operate either on oil bearings or air bearings but air bearings are beneficial in terms of life, parasitic losses and lubricating flow. Air bearings do not require any oil or pump and thus provide cost advantages with simplicity of operation. The cost of bearings is assumed to be similar for both the HPRTE as well as microturbine and estimated directly from one of the bearing manufacturers website (http://www.lasermotion.com/Airbearings.html), based on load capacity and rpm values. After calculating the costs of major equipments used in the two technologies, the total plant cost is evaluated. As discussed earlier, this cost is the sum of equipment costs, installation costs, cost of electrical instrumentation and other materials, project supervision and contingency fees. As mentioned in the earlier part of this chapter, the installation costs, electrical instrumentation and other materials costs, project supervision costs and contingency fees are evaluated as a percentage of the equipment costs. These percentages are assumed to be the same for both technologies and are stated in the initial part of this chapter. The total plant cost is one of the critical factors in this analysis as some of the results of this analysis are expressed in terms of plant cost ratio (PCR), i.e., the ratio of the total plant cost of the HPRTE to that of the microturbine. Energy Costs One of the main elements of the total life cycle costs of both technologies is the cost of energy sources required for engines operation. The energy costs for this analysis primarily include the fuel costs incurred during the total life span of the engines. The fuel

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32 assumed in this analysis, for both technologies, is natural gas. For the case of the HPRTE, as mentioned earlier, there is some external cooling obtained from the VARS unit. This excess refrigeration has a definite economic advantage that is determined by converting the excess refrigeration into equivalent power as explained by Boza et al. [9] and discussed in the next section of this chapter. The excess refrigeration generated from the HPRTE is considered to be a source of revenue which apart from recovering the initial investment for the VARS unit also offsets some of the fuel cost of the HPRTE over the life span of the engine. Fuel costs for both engines and revenues from refrigeration for the HPRTE are discussed in the next section. Fuel Costs Fuel costs are categorized as non uniform annually recurring costs as the fuel prices might undergo an escalation or a descalation during the life span of the engine. The future costs of fuel required have to be discounted to their present value for LCC analysis. As mentioned earlier, the DOE determines the uniform present value (UPV) factors for all the major fuels. These factors are based on a fixed discount rate and include the projected escalation rates, for a specified duration for different fuels. DOE calculates the UPV factors for the four census regions and also for the U.S. average. In this analysis, the UPV factors developed for the U.S. average are considered. For the natural gas, taking a DOE discount rate of 3% and a time span of 10 years (life span for both technologies), the UPV factor is calculated as 7.87. Hence, to calculate the total life cycle fuel costs for both technologies, the annual fuel cost for the base year (2004, for this analysis) is multiplied by the UPV factor of 7.87. The annual fuel cost is determined using the average price rate of natural gas as of the base date (May 1 st 2004), the lower heating value (LHV) of natural gas and the annual fuel consumption. Average fuel price rate as of the base date

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33 are taken directly from the website of DOE. This price corresponds to the rate for the industrial sector and is exclusive of any state or federal taxes. The LHV of a fuel is defined as the net energy released during oxidation of a unit of fuel excluding the heat required for vaporization of the water in the exhaust stream. For natural gas, its value is approximately 47000 BTU/kg, where BTU is a standard unit of energy and is equivalent to the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. The annual fuel consumption is calculated by multiplying the per-hour fuel consumption by total number of operating hours of the engine. Fuel consumption per-hour is determined from the thermodynamic code developed for the cycles. The annual fuel cost is then calculated by multiplying the fuel price (expressed in $/BTU) with the LHV (BTU/kg) of the fuel and the annual fuel consumption (kg). The annual fuel cost, when multiplied by the UPV factor gives the life cycle fuel costs for both technologies. Revenue from Refrigeration As mentioned earlier, the VARS unit integrated with the HPRTE produces some excess refrigeration, apart from cooling the inlet air to the compressor. As discussed by Boza et al. [9], this excess refrigeration can be converted to equivalent power. The refrigeration produced by the VARS system of the HPRTE can be considered as a source of economic credit. This economic credit is estimated by considering the refrigeration as the amount of power required by a power-driven source of refrigeration, to generate an amount of refrigeration equivalent to that generated by the VARS unit of the HPRTE, operating under similar conditions. The total revenue from refrigeration is calculated by assuming that the equivalent power can be sold at the average price rate of electricity. For the purpose of estimating the power equivalent of the refrigeration, a vapor compression

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34 system is considered. This equivalent power is referred to as and calculated using the following relation REFW VCREFCOPQW REF (4.7) Here represents the excess refrigeration produced by the VARS unit and denotes the coefficient of performance of the vapor compression unit. The value of is determined from the computer code developed for thermodynamic analysis of the HPRTE-VARS cycle. The COP of the vapor compression system is obtained by using energy efficiency ratios (EERs) for appropriate sized air conditioning units and employing the ARI rating conditions under which the units are tested to determine the respective refrigeration efficiencies (COP/COP REFQ VCCOP REFQ Carnot ). The COP of the system is then calculated using COP Carnot and the refrigeration efficiencies. The equivalent power can also be represented in terms of the combined efficiency of the power and cooling cycle of the HPRTE-VARS expressed by the relation LHVmWWfuelREFHPRTEcomb (4.8) where represents the net power generated by the HPRTE, without the VARS unit. HPRTEW Like the fuel cost, the revenue generated from refrigeration is a future cost that needs to be discounted to the present value as of the base date. This is done by multiplying the annual revenue produced by refrigeration, with the UPV factor determined by the DOE for electricity. For the base case, taking a DOE discount rate of 3% and a time span of 10 years (life span for both technologies), the UPV factor for electricity is calculated as 8.38. Annual revenue from refrigeration is evaluated by

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35 multiplying the equivalent power generated from refrigeration by the average U.S. price rate of electricity for industrial sector as of the base date. For the base date of May 1 st 2004, the price rate of electricity is taken as 8 cents/kWh. This is a highly conservative rate, considering the fact that the HPRTE-VARS is a cogeneration system, producing both power and cooling, and this cooling can be of significant advantage in hot seasons and hot regions of the country. The revenue obtained from refrigeration offsets some of the fuel cost for the HPRTE after recovering the initial investment for the VARS unit. Maintenance Cost Since the HPRTE is a novel concept, its maintenance cost is estimated from the data available for maintenance cost of other small gas turbines like the microturbine. The microturbine, itself is a relatively new technology and there isnt much published data available for the maintenance cost incurred throughout the life span of the engine. Most manufacturers offer service contracts for specialized maintenance priced at about $0.01-0.02/kWh [21]. For This analysis, the maintenance cost of the microturbine is assumed to be 0.013 $/kWh. These service inspections include periodic inspections of the combustor (and associated hot section parts) and the oil bearing in addition to regular air and oil filter replacements. A gas microturbine overhaul is needed every 20,000 to 40,000 hours depending on manufacturer, design, and service. A typical overhaul consists of replacing the main shaft with the compressor and turbine attached, and inspecting and if necessary replacing the combustor. Since the HPRTE has additional components as compared to the microturbine, its maintenance cost is estimated at a rate of $0.015/kWh. The sum of capital investment costs, energy costs and maintenance costs gives the total life cycle costs of both technologies. These costs are then evaluated for different

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36 design and economic parameters, and the results are expressed in terms of cost ratios of the two technologies.

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CHAPTER 5 RESULTS AND DISCUSSION As this study is primarily focused on life cycle cost comparisons of the HPRTE with that of a microturbine, the majority of the results of this analysis are expressed in terms of the ratio of life cycle costs of the two alternatives for various design and economic parameters. Expressing the results as cost ratios and using the same cost functions and cost coefficients for both technologies ensures fairness of this analysis. The design and environmental parameters used for evaluating the life cycle costs of the two technologies include the HPT inlet and exit temperatures, LPC pressure ratio of the HPRTE, effectiveness of the recuperator and the ambient temperature. The HPT inlet and exit temperatures, and the recuperator effectiveness are independent variables limited by material and technology constraints. Ambient temperature is also an independent variable and is used to evaluate the sensitivity of cost ratios with changes in regional and seasonal conditions. The LPC pressure ratio (for this analysis, the pressure ratio of the turbocharger) of the HPRTE is directly dependent on the ratio of the LPT inlet temperature to the LPC inlet temperature (which also is the ambient temperature). The LPT inlet temperature is influenced by design parameters like the HPT inlet and exit temperatures, and recuperator effectiveness. Higher values of the ratio of the LPT inlet temperature to LPC inlet temperature increase the LPC pressure ratio, which has a significant influence on the system compactness and hence the plant costs of the HPRTE. The values of design, economic and environmental parameters common to both technologies are assumed to be the same. 37

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38 As discussed earlier, the HPRTE is similar to a microturbine except for the addition of an LPC/LPT system (a turbocharger, for this analysis) to pressurize the inlet air resulting in system compactness and an increase in power and fluid densities, and a heat exchanger-VARS section to cool the inlet air to the HPC and to produce some external refrigeration. The investments made for the additional components of the HPRTE are evaluated against savings in equipment costs due to system compactness of the HPRTE, and the revenue that can be generated from external refrigeration. After evaluating the life cycle costs of a conventional microturbine, the results of this analysis are expressed in terms of cost ratios, i.e., the ratio of life cycle costs of the HPRTE to the costs of a microturbine. These cost ratios include the life cycle cost ratio (LCCR) and the plant cost ratio (PCR) of the two technologies, and the revenue ratio (R Rev ) of the HPRTE, as defined in the earlier sections. The cost ratios are evaluated for different design, environmental and economic parameters. Figure 5-1 shows the effect of increasing the high-pressure turbine (HPT) inlet temperature on the LCCR and the PCR, keeping the other design, economic and environmental parameters fixed and retaining their base-case values. The figure shows that the LCCR and PCR decrease with increasing HPT inlet temperature. This trend can be explained on the basis of an increase in the HPT pressure ratio, with increasing HPT inlet temperature. The pressure ratio of the HPT has a direct dependence on the ratio of the HPT inlet temperature to the HPT exit temperature. Increasing the HPT inlet temperature, keeping the HPT exit temperature constant, increases the HPT pressure ratio. An increase in the HPT pressure ratio leads to an increase in the net refrigeration produced by the HPRTE. This is due to the fact that the gas at the HPC exit is at higher

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39 temperatures due to higher pressure ratios, thus reducing the amount of heat extracted from the exhaust stream in the recuperator and increasing the amount of heat available to power the absorption unit for refrigeration. Also, with an increase in the high-pressure turbine inlet temperature, the pressure ratio of the low-pressure compressor/turbine system of the HPRTE increases. This is due to the fact that a portion of the exhaust stream from the recuperator exit drives the low-pressure turbine whose pressure ratio depends on the temperature of the exhaust stream. This increase in the LPC pressure ratio reduces the corrected mass flow through the components for a fixed power output, thus resulting in system compactness and hence lower plant cost of the HPRTE in comparison to that of a microturbine. The decrease in PCR and LCCR with increasing LPC pressure ratios is demonstrated by Figure 5-2. Figure 5-3 shows the effect of increasing the HPT exit temperature on the LCCR, keeping all the other design, economic and environmental parameters fixed and retaining their base-case values. The figure show that the LCCR increases with an increase in the HPT exit temperature. As mentioned earlier, the HPT pressure ratio is directly dependent on the ratio of the HPT inlet temperature to the HPT exit temperature. Increasing the HPT exit temperature, keeping the HPT inlet constant, decreases the temperature ratio and hence the pressure ratio of the HPC/HPT spool. At reduced pressure ratio of the HPC/HPT spool, the exhaust stream going through the recuperator loses more heat to the compressed air stream, which enters the recuperator at lower temperatures because of the low pressure ratio of the HPC. This reduces the net heat available for refrigeration

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40 0.850.900.951.001.051.101.151.201250130013501400145015001550HPT Inlet Temperature (K)PCR 0.900.910.920.930.940.950.960.97LCCR PCR LCCR Figure 5-1.Effect of increase in the HPT inlet temperature on LCCR and PCR. Except for the HPT inlet temperature, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2) 0.850.900.951.001.051.101.151.201.522.533.54LPC Pressure ratio (atm)PCR0.900.910.920.930.940.950.960.97LCCR LCCR PCR Figure 5-2.Effect of increase in the LPC pressure ratio on LCCR and PCR. The LPC pressure is increased by increasing the HPT inlet temperature, retaining the base case values of other design and economic parameters (Tables 4.1, 4.2)

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41 produced from the VARS. However, beyond a certain temperature limit, the refrigeration actually starts increasing. This is due to the fact that an increase in the HPT exit temperature, with the HPT inlet temperature held constant, increases the recirculation ratio, to maintain the value of constant. This increase in the recirculation ratio makes more heat available to power the absorption unit, thus increasing the refrigeration and the revenue associated with it. Figure 5-4 demonstrates the change in refrigeration and hence the revenue from refrigeration expressed in terms of R Rev with an increase in the HPT exit temperature of the HPRTE. Since the exhaust stream exits the recuperator at lower temperatures, for an increasing HPT exit temperature, the LPC pressure ratio of the HPRTE is reduced due to a reduction in the net compression work for the LPC. This leads to an increase in the equipment cost and hence the plant cost for the system, thus increasing the LCCR. Figure 5-3 also shows the effect of increasing the HPT exit temperature on the cycle efficiencies of the HPRTE and the microturbine. The cycle efficiency of both technologies increases initially and, after reaching an optimal point, tends to start decreasing because of the decrease in the HPC/HPT pressure ratio. As both engines are expected to be designed for the temperature regime that is optimal in terms of cycle efficiencies, this optimal point occurs at moderate-to-low values of the HPT exit temperature. There, a good amount of refrigeration is generated and the low-pressure compressor ratio would be significantly higher to reduce the plant cost of the HPRTE, thus enabling the HPRTE to maintain its cost advantages over a microturbine. Figure 5-5 shows the effect of increasing ambient temperatures on the LCCR and the PCR, with all the other design, environmental and economic parameters fixed. As

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42 0.900.910.920.930.940.950.960.9795010001050110011501200HPT Exit Temperature (K)LCCR0.300.310.320.330.340.350.360.370.38Cycle Efficiency LCCR Cycle efficiency-HPRTE Cycle efficiency-Microturbine Figure 5-3 Effect of increase in the HPT exit temperature on LCCR and cycle efficiency. Except for the HPT exit temperature, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2) 0.900.951.001.051.101.151.201.251.3095010001050110011501200HPT Exit Temperature (K)Revenue Ratio Figure 5-4 Effect of increase in the HPT exit temperature on the revenue ratio of the HPRTE. Except for the HPT exit temperature, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2)

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43 observed from the figure, the LCCR and PCR decrease with increasing ambient temperature. An increase in ambient temperature decreases the amount of excess refrigeration produced by the VARS unit of the HPRTE and this leads to a reduction in the revenues generated from refrigeration. An increase in the ambient temperature also lowers the value of the LPC pressure ratio, because of the increase in LPC compression work with higher ambient temperatures. Reduction in the LPC pressure ratio increases the component cost of the HPRTE due to reduced compactness in the higher cost high-temperature components. As observed from the figure, at lower temperatures, the plant cost for the HPRTE is less than that of a microturbine (PCR less than 1). However, beyond a certain value of the ambient temperature, reduction in the LPC pressure ratio makes the value of the plant cost ratio exceed unity. This creates an unattractive regime for the HPRTE, though the revenue obtained from refrigeration still maintains the value of the LCCR below one. Additionally, the effect of increasing the ambient temperature on the cycle efficiencies of the two technologies is a critical factor for this analysis. Since the inlet air to the HPC of the HPRTE is cooled below ambient by the heat exchanger and the VARS unit, the HPRTE is able to sustain constant efficiencies even at high ambient temperatures. A microturbine, on the other hand, experiences a drop in cycle efficiency with increasing ambient temperatures due to increased compressor work. Changing the ambient temperature from 288 to 313 K decreases the microturbine cycle efficiency from 0.385 to 0.36, a drop of almost 7%. The fact that the HPRTE can maintain constant efficiencies at high ambient temperatures gives it a definite advantage over the microturbine. However, as mentioned earlier, the HPRTE can be regarded as a

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44 0.900.910.920.930.940.950.960.97285290295300305310315Ambient Temperature(K)LCCR0.850.900.951.001.051.101.151.20PCR PCR LCCR Figure 5-5.Effect of ambient temperature on LCCR and PCR. Except for the ambient temperature, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2) 0.320.330.340.350.360.370.380.39285290295300305310315HPC Inlet Temperature (K)Eta-Cycle HPRTE Microturbine Figure 5-6 Effect of increase in HPC inlet temperature (ambient temperature for the microturbine) on cycle efficiency of the engines. Except for the HPC inlet temperature, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2)

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45 microturbine operating on a pressurized loop and with additional components for inlet air cooling and excess refrigeration. If the HPC inlet temperature of the HPRTE is increased, there is a drop in its cycle efficiency similar in magnitude to the drop in the efficiency of a microturbine with the same increase in the ambient temperature. Figure 5-6 demonstrates this effect of change in cycle efficiencies of the two technologies with an increase in the HPC inlet temperature, which also is the ambient temperature for the microturbine. Figure 5-7 shows the effect of increasing recuperator effectiveness on the LCCR, with all the other design, economic and environmental parameters held constant. As the recuperator effectiveness is increased, the temperature of the exhaust stream exiting the recuperator is reduced, thus resulting in a decrease in excess refrigeration and hence an increase in the LCCR. A curve depicting changes in refrigeration revenue is also plotted to demonstrate this effect. Any decrease in exhaust stream temperature also lowers the LPC pressure ratio, reducing the HPRTE compactness and hence increasing the equipment cost of the HPRTE, in comparison to a microturbine, as explained in the earlier sections. The effects of changes in economic parameters on the life cycle costs of both technologies are also evaluated in this analysis. As mentioned earlier, the cost coefficients of small gas turbines components like the HPC/HPT, combustor and the power generator are taken to be a parameterized fraction (CCF) of the cost coefficients modified by Traverso et al. [15] for components of large engines. Figure 5-8 shows the effect of different values of the cost coefficient fraction (CCF) on the LCCR and PCR, retaining the base-case values of other parameters. As observed from the figure, the effect

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46 0.910.920.930.940.950.960.970.980.810.820.830.840.850.860.870.88Recuperator EffectivenessLCCR0.800.850.900.951.001.051.101.15Revenue Ratio LCCR Revenue Ratio Figure 5-7.Effect of increase in the recuperator effectiveness on LCCR and PCR. Except for the recuperator effectiveness, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2) 0.900.910.920.930.940.950.960.970.20.30.40.50.60.70.8Cost Coefficient FractionLCCR0.850.900.951.001.051.101.151.20PCR PCR LCCR Figure 5-8.Effect of increase in the cost coefficient fraction (CCF) on LCCR and PCR. Except for the CCF, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2)

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47 of changing the value of CCF does not have a very significant effect on the LCCR, with just a small decrease in the LCCR with increasing values of cost fraction. This decrease is due to the fact that for lower values of cost fraction, the difference between the costs of gas turbine components common for both technologies, though in favor of the HPRTE, is not very significant. Considering the fact that the HPRTE has additional components which are independent of cost fraction, the total plant cost of the HPRTE becomes greater than that of a microturbine for lower values of cost fraction. However as the cost fraction increases, the difference in the costs of components common to both technologies increases, offsetting the cost of additional equipments of the HPRTE and thus reducing the PCR and hence the LCCR by a small value. Most importantly, these results demonstrate the fact that the uncertainty associated with the value of cost coefficients, because of the proprietary nature of cost information does not have a significant effect on the cost ratios of the two technologies. Figure 5-9 shows the effect of an increase in the discount rate specified by the DOE, on LCCR, holding all the other design, environmental and economic parameters constant. As seen from the figure, the LCCR is fairly insensitive to changes in the discount rate, having a constant value with increasing discount rates. This discount rate determines the UPV factors for calculating life cycle fuel costs and maintenance costs of both technologies. The UPV factor to determine the life cycle revenues obtained from refrigeration generated by the HPRTE-VARS combined system also depends on the DOE discount rate. Figure 5-10 shows the effect of change in the cost rate of natural gas on LCCR, holding all the other parameters fixed. With an increase in the cost rate of natural gas,

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48 0.900.910.920.930.940.950.960.9701234567DOE discount rate (%) LCCR Figure 5-9.Effect of increase in the DOE discount rate on LCCR. Except for the DOE discount rate, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2) 0.900.910.920.930.940.950.960.9733.544.555.566.57Cost rate of natural gas ($/MMBTU)LCCR Figure 5-10. Effect of increase in the cost rate of natural gas on LCCR. Except for the cost rate of natural gas, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2)

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49 there is a small increase in the value of LCCR. As observed for the base case, the cycle efficiency of the microturbine is slightly higher than that of the HPRTE (Figure 5-3). Hence for the same power, microturbine has lower fuel consumption as compared to the HPRTE, resulting in lower fuel costs for the life cycle. With an increase in the cost rate of natural gas, the difference between the life cycle fuel costs of both technologies increases, in favor of the microturbine and this leads to an increase in the LCCR. However, this increase is not very significant, thus showing almost constant values of LCCR, even with uncertainty in fuel prices Figure 5-11 shows the effect of change in the price rate of electricity on LCCR and revenue ratio (R Rev ), keeping all other design, economic and environmental parameters fixed and retaining their base-case values. As expected, the LCCR decreases with increase in the price rate of electricity because of the increase in the revenues obtained from the HPRTE-VARS combined system. However, this decrease is not very significant and the value of LCCR can be considered to be in a fairly constant regime. Apart from evaluation of the cost ratios, supplementary economic methods like the net savings (NS), savings to investment ratio (SIR) and payback period are also evaluated in this analysis. As explained earlier, the SIR and NS evaluated for a particular analysis are consistent with the life cycle costs. The payback period, on the other hand does not include the costs incurred after the payback time span is reached and hence is not considered an effective measure of economic performance. For the base case parameters, the net savings obtained from the HPRTE in comparison to a microturbine, is approximately $76000. The SIR is calculated to analyze the effectiveness of the HPRTE, over a microturbine and for the base case, its value is 2.15. This value is significantly

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50 higher than 1, which is the qualifying value for any alternative in comparison to the base case. The discounted payback period for recovering the additional investment made for the HPRTE is a little less than four years. The results of this analysis indicate that, though the cost ratios are influenced by the change in design parameters, they are more or less insensitive to the uncertainty associated with the economic parameters 0.900.910.920.930.940.950.960.970.0650.0700.0750.0800.0850.0900.0950.100Price rate of electricity ($/kWh)LCCR0.850.900.951.001.051.101.151.201.25Revenue Ratio LCCR Revenue Ratio Figure 5-11. Effect of increase in the electricity price rate on LCCR and PCR. Except for the price rate of electricity, all design and economic parameters are fixed and their base-case values retained (Tables 4.1, 4.2)

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CHAPTER 6 SUMMARY AND CONCLUSIONS The primary aim of this analysis has been to compare life cycle costs of two technologies, the HPRTE and the conventional microturbine, by evaluating costs like the capital investment costs, energy costs and maintenance costs, incurred throughout the lifespan of the engine. Since the cost information, particularly for the equipment costs of the engines, is proprietary and hard to obtain, it is difficult to calculate a highly accurate life cycle costs estimate of both technologies. However, for this analysis, same cost functions, particularly for the equipment costs are used for both engines and the results of this analysis are expressed in terms of cost ratios rather than the actual costs, ensuring fairness of the cost comparison, even with the uncertainty in actual cost estimations. These cost ratios are evaluated for different design, environmental and economic parameters and cost ratios with values less than one indicate that the HPRTE is economically beneficial in comparison to a microturbine. One of the major factors that was found to influence the savings obtained from using the HPRTE, in comparison to a microturbine, is the pressurized nature of this engine. This leads to an increase in fluid density and makes the expensive, high temperature components of the HPRTE compact as compared to those of a microturbine, for the same power generated. The second major factor influencing the savings obtained from the HPRTE is the revenue generated from excess refrigeration, which, for this analysis, is converted into equivalent power for the purpose of revenue estimation. The revenue from refrigeration is analyzed in terms of the revenue obtained from selling the 51

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52 equivalent power Cost ratios determined for different design and economic parameters may be analyzed in terms of these two factors. The following is a summary of the major findings of this analysis: An increase in the HPT inlet temperature, keeping the other parameters unchanged decreases the LCCR. This is due to an increase in refrigeration and hence revenue from refrigeration with increasing HPT inlet temperatures. The LPC pressure ratio of the HPRTE also increases, with increasing HPT inlet temperatures, making components compact and reducing the total plant costs of the HPRTE. An increase in the HPT exit temperature increases the LCCR because of the decrease in refrigeration. However, the cycle efficiency of both systems increases initially with an increase in the HPT exit temperature, reaches a maximum and then starts decreasing due to the decrease in the HPC pressure ratio. An increase in the HPT exit temperature also reduces the LPC pressure ratio, thereby increasing the HPRTE equipment costs. Another effect that is associated with the HPT exit temperature of the HPRTE is the rise in the value of external refrigeration, after an initial decrease. This is due to an increase in the recirculation ratio to maintain a constant value of thus generating more revenue from refrigeration for the HPRTE. An increase in the LCCR is also observed with increases in recuperator effectiveness and ambient temperature. This is attributed to decreases in refrigeration revenue and LPC pressure ratios at higher recuperator effectiveness and ambient temperature for the HPRTE. Apart from calculating the LCC of the two technologies, supplementary economic measures like the savings to investment ratio (SIR), net savings (NS) and investment payback period were also evaluated for this analysis. For the base case analysis, the LCCR is 0.93, with a SIR of 2.15, NS of $ 76000 and a payback period of 3.92 years. As discussed earlier, the main cost coefficients of the equipment costs of both technologies were taken as a parameterized fraction (CCF) of the cost coefficients of large engines. This is done to account for the relative inexpensive radial technology of small gas turbines, as compared to the expensive axial technology of large engines. However, the results indicate that the cost ratios are fairly insensitive to the value of CCF as the same cost coefficients and cost functions are applied for both technologies. Changes in economic parameters like the DOE discount rate, cost of natural gas and cost of electricity showed little influence on the cost ratios. The LCCR showed an almost constant value with changes in the DOE discount rate. Increase in the cost of natural gas resulted in a small increase in the LCCR due to relatively higher fuel costs of the HPRTE, in comparison to a microturbine. As expected, increase in

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53 the cost of electricity resulted in a small decrease in the LCCR, because of the increase in the revenue from refrigeration for the HPRTE. Overall, the results indicate the fairly insensitive nature of the cost ratios to the uncertainty in economic conditions. For this analysis, the revenue obtained from refrigeration, converted into equivalent power, is calculated using a conservative price rate of electricity. However, this price rate can be substantially higher for comparatively hot seasons and regions of the country, where the external cooling produced will be of high importance, thus coming at a higher price. This will increase the revenues from refrigeration of the HPRTE resulting in a reduction in the LCCR. As in the case of the HPRTE, a microturbine could also be integrated with a VARS unit for cogeneration applications, thus generating external refrigeration along with power. However, the fact that the HPRTE is a high-pressure engine would help it maintain its cost advantage over a microturbine, as the higher cycle pressure will make the expensive, high-temperature components of the HPRTE compact in comparison to those of a microturbine. Since the gases of the HPRTE passing through the VARS unit are at higher pressures, in comparison to those for the microturbine, the heat exchangers of the VARS unit of the HPRTE would be compact, versus those for microturbine-VARS system. This would reduce the equipment costs and hence the total life cycle costs of the HPRTE, in comparison to a microturbine. Also, the additional investment required for the VARS unit will offset some of the refrigeration revenue generated by a microturbine-VARS system. Furthermore, additional technical advantages may favor the HPRTE economically for specific applications: compactness; fresh water production; reduced air/exhaust flow rate and low emissions. Previous studies point out that water can be extracted naturally in the HPRTE/VARS evaporator due to the high water vapor partial pressure and lower condensation temperatures. This fresh water can be used for additional process cooling,

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54 combined cycle applications, or human consumption, but in this analysis, there is no economic credit claimed for the water extracted. In another study related to the HPRTE, it has been demonstrated that the HPRTE has significantly reduced CO, unburned hydrocarbons and NOx as compared to open cycles. This can be reflected in terms of savings from environmental costs but also not included in this analysis. Reduced air/exhaust flow of the HPRTE would also lead to reduction in size of equipments like the exhaust duct and filtration system, though the economic advantage gained from this is also ignored in this analysis. Although the present results are encouraging for the HPRTE, further study is required in order to account for additional factors that can be a potential source of economic benefit, like the water extraction capability of the HPRTE. For future work, a detailed thermo-economic analysis of the HPRTE-VARS combined cycle and a microturbine-VARS combined cycle is recommended for more accurate estimation of actual system costs. Effort should be made to make the cost coefficients of the cost functions used in thermoeconomic analysis to be representative of the current equipment cost, by getting some cost estimates from the manufacturers. This cost comparisons can also be carried out by considering fuels other than natural gas like diesel.

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LIST OF REFERENCES 1. Scott, S.J., Holcomb, F.H., and Josefik, N.M., 2003, Distributed Electrical Power Generation: Summary of Alternative Available Technologies, Construction Engineering Research Laboratory, Engineering Research and Development Center, Champaign, Illinois, ERDC/CERL SR-03-18 2. Fuller, K.S., and Petersen R.S., 1996, Life-Cycle Costing Manual for the Federal Energy Management Program, NIST Handbook 135, National Institute of Standards and Technology, Gaithersburg, Maryland. 3. Schultz, L.I., Rushing, A.S., and Fuller, K.S., 2004, Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis-April 2004, Annual Supplement to NIST Handbook 135 and NBS Special Publication 709, National Institute of Standards and Technology, Gaithersburg, Maryland, NISTIR 85-3273-19. 4. Gasparovic, N., 1968, The Advantage of Semi-Closed Cycle Gas Turbines for Naval Ship Propulsion, Naval Engineers Journal, Vol. 80, pp. 275-281. 5. Nemec, T.S., and Lear, W.E., 1998, Thermodynamic Performance of a Semi-Closed Gas Turbine Combined with a Rankine Bottoming Cycle, 36 th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 1998, AIAA Paper 98-0361. 6. MacFarlane, R.S., 1997, A Study of the Impact of Water Extraction on the Regenerative Feedback Turbine Engine Cycle, M.S. Thesis, Department of Mechanical Engineering, University of Florida, Gainesville, Florida. 7. Muley, N.S., and Lear, W.E., 2003, Effect of Exhaust Gas Recirculation (EGR) on Thermal NOx Formation Rate, 41st AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 6-9, 2003, AIAA Paper 2003-0503. 8. Lear, W.E., and Laganelli, A.L., 1999, High Pressure Regenerative Turbine Engine: 21 st Century Propulsion, Final Technical Report for Contract No.NAS3-27396, University of Florida, Gainesville, Florida. 9. Boza, J.J., Lear, W.E., and Sherif, S.A., 2003, Performance of a Novel Semi-Closed Gas Turbine Refrigeration Combined Cycle, Proc., 2003 ASME TURBO EXPO, Atlanta, Georgia, U.S.A, June 16-19, 2003, ASME Paper GT2003-38576. 55

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56 10. Khan, J.K., Lear, W.E., and Sherif, S.A., 2004, Performance of a Novel Combined Cooling and Power Gas Turbine with Water Harvesting, Proc., 2004 ASME TURBO EXPO, Vienna, Austria, June 14-17, 2004, ASME Paper GT2004-53013. 11. Romier, A., 2004, Small Gas Turbine Technology, Journal of Applied Thermal Engineering, Vol. 24, pp. 1709-1723. 12. Tsatsaronis, G., 1993, Thermoeconomic Analysis and Optimization of Energy Systems, Prog. Energy Combust. Sci. Vol. 19, pp. 227-257. 13. Franco, A., and Casarosa, C., 2004, Thermoeconomic Evaluation of the Feasibility of Highly Efficient Combined Cycle Power Plants, Journal of Energy, Vol. 29, pp. 1963-1982. 14. Massardo, A.F., and Scial, M., 2000, Thermoeconomic Analysis of Gas Turbine Based Cycle, Journal of Engineering for Gas Turbine and Power, Vol. 122, pp. 664-671. 15. Traverso, A., Massardo, A.F., Cazzola, W., and Lagorio, G., 2004, WIDGET-TEMP: A Novel Web-Based Approach for Themoeconomic Analysis and Optimization of Conventional and Innovative Cycles, Proc., 2004 ASME TURBO EXPO, Vienna, Austria, June 14-17, 2004, ASME Paper 2004-GT-54115. 16. Onsite Sycom Energy Corporation, 2000, The Market and Technical Potential for Combined Heat and Power in the Commercial/Institutional Sector, Prepared for the US Department of Energy, Energy Information Administration, Washington DC. 17. McDonald, C.F., 2000, Low-Cost Compact Primary Surface Recuperator Concept for Microturbines, Applied Thermal Engineering, Vol. 20, pp. 471-497 18. Douglas, D.Q., 1998, Conceptual Design of Chemical Processes, McGraw Hill Books, New York. 19. Energy Nexus Group, 2002, Technology Characterization: Microturbines, Prepared for the Environmental Protection Agency, Washington DC. 20. Federal Energy Management Program, 2000, Integrated Systems, U.S. Department of Energy, Washington, DC, DOE/EE-0234. 21. Gas Research Institute, National Renewable Energy Laboratory, 2003, Gas Fired Distributed Energy Resources Technology Characterizations, National Renewable Energy Laboratory, Golden, Colorado, NREL/TP 620-34783.

PAGE 70

BIOGRAPHICAL SKETCH The author obtained a bachelor's degree in mechanical engineering with honors, in the year 2002. After working in a leading manufacturing firm for one year, the author joined the masters degree program in the industrial engineering department at University of Florida. After his post graduation in industrial engineering, the author hopes to combine his technical and managerial skills in his future professional endeavors. 57


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Full Text












LIFE-CYCLE COST ANALYSIS OF A NOVEL COOLING AND POWER GAS
TURBINE ENGINE














By

VAIBHAV MALHOTRA


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2005

































Copyright 2005

by

Vaibhav Malhotra




























This thesis is dedicated to my beloved family for their continuous love, support and
encouragement.















ACKNOWLEDGMENTS

I wish to express my gratitude towards the members of my supervisory committee,

Dr. Joseph P. Geunes, Dr. William E. Lear, and Dr. S.A. Sherif, for their expertise,

encouragement and support provided throughout this research. I would also like to thank

Mr. John F. Crittenden of Triads Research Corporation for his continuous guidance and

support. Lastly, I would like to thank all the members of the HPRTE group, especially

Mr. Jameel Khan, for all their cooperation and encouragement.
















TABLE OF CONTENTS



A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES ............... ................... ...................... .... ...... ........vii

LIST O F FIG U R E S ......... ........................... .... ......................... ............. viii

N O M E N C L A T U R E .......................................................................................................... ix

ABSTRACT .............. ............................................. xii

CHAPTER

1 IN TRODU CTION ................................................. ...... .................

2 LITER A TU R E REV IEW ............................................................. ....................... 7

Life Cycle Cost Analysis .............. ............................. ... .... ... .. ........ ..
High Pressure Regenerative Turbine Engine (HPRTE) ............................................8
Small Gas Turbine Technology ........... ............. ....................9
Therm oeconom ic A analysis .......................................................... ...............10

3 LIFE CYCLE COST ANALYSIS GUIDELINES.................................. ...............13

4 LCCA OF THE HPRTE AND THE MICROTURBINE .....................................18

C capital Inv estm ent C o sts ......... ................. ............................................................ 18
High-Pressure Compressor..................................................22
C o m b u sto r ..................................................................................................... 2 4
H igh -P ressu re T u rb in e.............................................................. .....................2 5
R ecu p erator .............................................................. ..................................2 6
Power Generator....... ........ ......... ... .................. ............ 28
Gas Com pressor ............. ........................ ........ .... .... .. ........ .......... 29
Heat Exchanger-HPRTE .................................. .....................................29
VARS-HPRTE ...................................... ............ .............. 30
T urb ocharger-H P R T E .............................................................. .....................30
Air Bearings .................... ........ .......................31
E n e rg y C o sts ...................... .. ............. .. .................................................. 3 1
F u el C o sts ................................................................ 3 2



v









R revenue from R efrigeration ............................................................ ...... ......... 33
Maintenance Cost ................................. ..... .. .. ... ....... ......... 35

5 RESULTS AND D ISCU SSION ............................................ ........................... 37

6 SUMMARY AND CONCLUSIONS.......................................................................51

L IST O F R EFE R E N C E S ............................................................................ ...............55

B IO G R A PH IC A L SK E T C H ...................................................................... ..................57
















LIST OF TABLES


Table


4-1 Base case design parameters and ambient conditions assumed in the computer
code for the HPRTE/VARS and the microturbine................................................20

4-2 Base-case values of the economic parameters used for the LCCA of the HPRTE
and the microturbine................ ...... ......... ......... .......... 20

4-3 Coefficients of the gas turbine cost functions (large engine)............... ...............22


page
















LIST OF FIGURES


Figure page

1-1 A recuperated m icroturbine cycle ........................................ ........................ 3

1-2 HPRTE-VAR S combined cycle ........ ........................ .....................6

5-1 Effect of increase in the HPT inlet temperature on LCCR and PCR ..................40

5-2 Effect of increase in the LPC pressure ratio on LCCR and PCR...........................40

5-3 Effect of increase in the HPT exit temperature on LCCR and cycle efficiency. .....42

5-4 Effect of increase in the HPT exit temperature on the revenue ratio of the
H PR T E .............................................................................42

5-5 Effect of ambient temperature on LCCR and PCR ............................................44

5-6 Effect of increase in HPC inlet temperature (ambient temperature for the
microturbine) on cycle efficiency of the engines. ............................................... 44

5-7 Effect of increase in the recuperator effectiveness on LCCR and PCR.................46

5-8 Effect of increase in the cost coefficient fraction (CCF) on LCCR and PCR..........46

5-9 Effect of increase in the DOE discount rate on LCCR .......................................48

5-10 Effect of increase in the cost rate of natural gas on LCCR .................. ........ 48

5-11 Effect of increase in the electricity price rate on LCCR and PCR........................50
















NOMENCLATURE


A heat transfer area

COP coefficient of performance

CE present value of energy cost

CI present value of initial capital investment costs

CRES present value of residual value

COMR present value of operations, maintenance and repair costs

CCF cost coefficient fraction

Eo annual energy costs of the base period

F, correction factor for heat exchangers

Fo future cost

I fuel price index based on DOE projections

IMS Marshall and Swift cost index

LCC life cycle cost

LCCR life cycle cost ratio

LHV lower heating value

MC heat exchanger-HPRTE

AP/P percentage pressure drop

PV present value of any cost

PCR plant cost ratio












R

RR

RRev

SIR

T

W

d

e

f


Greek Symbols

P pressure ratio (HPC/HPT)

nr efficiency

g effectiveness

OR angle of the wave pattern for recuperator foil folds

D equivalence ratio

Y surface compactness


capital cost


excess refrigeration, kW

gas constant

recirculation ratio

revenue ratio

savings to investment ratio

temperature

power

DOE discount rate

energy price escalation rates

friction factor

mass flow rate

specific volume










Subscripts

C

CM

GEN

HX

R

REF

T

VC

comb

cr

in

out

poly

ref


compressor

combustor

generator

heat exchanger

recuperator

refrigeration

turbine

vapor compression system

combined

critical

inlet

outlet

polytropic

reference















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

LIFE CYCLE COST ANALYSIS OF A NOVEL COOLING AND POWER GAS
TURBINE ENGINE

By

Vaibhav Malhotra

August 2005

Chair: Joseph P. Geunes
Cochair: William E. Lear
Major Department: Industrial and Systems Engineering

Life Cycle Cost Analysis (LCCA) was performed to compare life cycle costs of a

novel gas turbine engine to that of a conventional microturbine with identical power

capacity. This engine, called the High Pressure Regenerative Turbine Engine (HPRTE)

operates on a pressurized semi-closed cycle and is integrated with a Vapor Absorption

Refrigeration System (VARS). HPRTE uses the heat from its exhaust to power the

absorption refrigeration unit which cools the high pressure compressor inlet of the

HPRTE to below ambient temperatures and also produces some external refrigeration,

thus forming a cogeneration application. Life Cycle Cost Analysis procedure is based on

the principles specified in the Federal Energy Management Program (FEMP) drafted by

the Department of Energy (DOE). The costs evaluated for this analysis include the

equipment costs, total plant costs, energy costs and maintenance costs, determined for

both technologies. Effect of different design and economic parameters on the cost of the

two technologies is analyzed in terms of life cycle cost ratio (LCCR), i.e. the ratio of life









cycle costs of the HPRTE to that of a microturbine and plant cost ratio, i.e. the ratio of

total plant costs (PCR) of the HPRTE to that of a microturbine. The life span for these

technologies is assumed to be 80000 hours and assuming an operation span of 8000 hours

in a year, the life time of the engines is calculated as 10 years. The pressurized nature of

the HPRTE leads to compact components resulting in significant savings in equipment

costs versus that of a microturbine. Revenue obtained from external refrigeration offsets

some of the fuel costs for the HPRTE thus proving to be a major contributor in cost

savings for the HPRTE. For the base case, with high-pressure-turbine (HPT) inlet

temperature of 13730 K and HPT exit temperature of 10730 K, the HPRTE showed life

cycle cost savings of 7% over a microturbine for similar power capacity. From the results

of this analysis, the payback period to recover the additional investments made in the

HPRTE in comparison to a microturbine is 3. 9 years, well within the engine life span of

10 years. For this analysis, the Savings to Investment Ratio (SIR) for the HPRTE is

calculated as 2.15, significantly higher than 1 which, according to the FEMP guidelines is

the minimum qualifying criterion for any effective project alternative to be selected.

Based on the results of this analysis, the economic performance measures look favorable

for the HPRTE, in comparison to a microturbine.














CHAPTER 1
INTRODUCTION

For the past 60 years, electricity production and supply in the United States has

been performed by centralized, regulated electric utilities that own and operate power

generation facilities as well as the transmission and distribution lines. However, changes

in the federal and state public policies have encouraged the opening of the electric power

generation system to other alternatives like the Distributed Generation (DG)

technologies. Distributed energy resources are parallel and stand-alone electric generation

units located within the electric distribution system at or near the end user. Some of the

benefits of distributed generation include greater local control of electricity delivery and

consumption, cost savings obtained from reducing the peak demand, efficient utilization

of waste heat in CHP applications, and reduced emissions versus other power generation

technologies.

This study is focused on the comparison of life cycle costs of two technologies that

are particularly attractive for distributed generation applications. The first technology

considered in this analysis is that of a microturbine. Microturbines are small gas turbines

that bum gaseous and liquid fuels to create a high-energy gas stream that turns an

electrical generator. Like the large gas turbines, microturbines also operate on a brayton

thermodynamic cycle. In this cycle, atmospheric air is compressed, heated at constant

pressure through combustion with a fuel, and then expanded in a turbine, which drives a

generator. Most of the microturbines are integrated with a recuperator to utilize the heat

of the exhaust stream, enabling an increase in the cycle efficiency and reduction in fuel









consumption. Apart from possessing the other advantages of distributed generation,

microturbines also have low to moderate initial investment costs and flexibility in terms

of the fuel on which they can be operated. Figure 1-1 shows the block diagram of a

recuperated microturbine.

The second technology considered in this analysis is based on a novel cooling and

power cycle that combines a semi-closed pressurized gas turbine engine called the

HPRTE with a Vapor Absorption Refrigeration System (VARS) to form a cogeneration

system. A schematic diagram of the HPRTE-VARS cycle is shown in Figure 1-2. Inlet air

at State 1 is compressed by the low-pressure compressor (LPC, labeled Cl). This

compressed air then mixes with the recirculated combustion products from the

recuperator at State 2.9. The combined stream is then passed through the generator

(GEN) of the VARS where it acts as the heat source for the VARS unit. After exiting the

generator, the combined air-gas stream passes through a heat exchanger (MC) where it is

cooled further. The stream then goes through the evaporator of the VARS where it loses

more heat and comes out at a temperature below that of the ambient. It is then

compressed in the high-pressure compressor (HPC, labeled C2), heated in the recuperator

R and combustor (CM), and then expanded in the high-pressure turbine (HPT, labeled

Tl). The exhaust stream is then passed through the recuperator where it loses some of its

heat to the gases entering the combustor. At the exit of the recuperator, some portion of

the exhaust is recirculated while the remaining portion is passed through a low-pressure

turbine (LPT, labeled T2) and finally to the atmosphere. In a real sense, the HPRTE-

VARS cycle is similar to the cycle of a recuperated microturbine except for the fact that

the former is pressurized using a low-pressure compressor-turbine spool, uses highly










dilute air, and has additional components; namely the VARS unit, low-pressure

compressor/turbine system and the heat exchanger (MC). The VARS unit and the heat

exchanger reduce the HPC inlet temperature and produce external refrigeration.


Figure 1-1. A recuperated microturbine cycle

Considering the fact that cogeneration technologies form an important part of the

energy future of the world [1], the combined cooling and power generated from the

HPRTE make it a very attractive distributed generation technology of the future. The

waste heat of the HPRTE can also be utilized for combined heat and power generation.

An earlier study conducted on the HPRTE has shown that the HPRTE has reduced

thermal NOx levels by roughly five orders of magnitude versus open cycles. Apart from


C Compressor

T Turbine

R Recuperator

CM Combustor

GEN Generator
Power Conversion
PCEEquipment
Equipment









low thermal NOx, the HPRTE also has reduced emissions of Carbon Monoxide (CO) and

other unburned hydrocarbons, in comparison to the open cycles. Other studies conducted

on the HPRTE have demonstrated the water extraction capability of the engine. This

water is obtained as a product of combustion and is recirculated with other exhaust gases,

and almost the entire amount of water generated during the combustion process of the

HPRTE, can be extracted for different applications. These applications include human

consumption, process cooling or combined cycle operations. The objective of this study

is to determine whether the HPRTE has economic benefits to complement its other

advantages, by performing a cost analysis of the HPRTE and comparing the costs with

the life cycle costs of a conventional microturbine, another attractive technology for

distributed generation.

A LCCA procedure based on the guidelines of the FEMP is applied to compare the

potential savings in life cycle costs of an HPRTE-VARS combined system, to that of a

microturbine, for identical power capacity and operating conditions. Major costs

evaluated in this analysis include the equipment costs, total plant costs, energy costs, and

maintenance costs incurred during the lifespan of engine operation. To reflect the

comparative nature of this analysis, the results of this analysis are expressed in terms of

life cycle cost ratio (LCCR) and plant cost ratio (PCR) of the two technologies.

Additionally a term called revenue ratio (RRev) for the HPRTE is defined to analyze the

ratio of revenue from refrigeration obtained for a particular set of operating conditions

and input parameters to the revenue obtained for the base case. This ratio is equivalent to

the ratio of net refrigeration produced for a particular case to that for the base case. As a









part of this analysis, the sensitivity of the cost ratios (and revenue ratio of the HPRTE) to

changes in design and economic parameters is evaluated for both technologies.

Chapter 2 gives a brief insight into the previous research and studies performed on

small gas turbines, primarily the HPRTE. It also discusses some of the previous work

conducted on economic evaluations of thermodynamic cycles. Chapter 3 mentions the

basic framework of the LCCA, as laid out in the FEMP guidelines. Chapter 4 discusses

the approach followed for conducting a comparison of life cycle costs (LCC) of the

HPRTE with those of a microturbine. Chapter 5 discusses the sensitivity of the LCC of

both technologies with changes in design and economic parameters. Chapter 6 discusses

some of the conclusions that can be drawn from this analysis.






















C1 GEN MC EVAP C2 R CM T1 T2


COND

3r





EVAP


2.9.2


C1 Low-Pressure Compressor
C2 High-Pressure Compressor
T1 High-Pressure Turbine
T2 Low- Pressure Turbine
MC Heat Exchanger
R Recuperator
CM Combustor
COND Condenser-VARS
ABS Absorber-VARS
EVAP Evaporator-VARS
GEN Generator-VARS

Figure 1-2. HPRTE-VARS combined cycle


2.9.1.














CHAPTER 2
LITERATURE REVIEW

Life Cycle Cost Analysis

As mentioned in the introduction, the primary aim of this study is to compare the

life cycle costs of the HPRTE to that of a microturbine. This cost comparison is

performed using the life cycle cost analysis procedure based on the FEMP guidelines

established by the U.S. Department of Energy. These rules are effective in economic

evaluation of energy and water conservation projects. The guidelines for applying the

LCCA are clearly stated in the Life Cycle Costing Manual, NSIT handbook 135 [2].

Apart from covering the life cycle costing procedure, this manual also specifies the

guidelines to determine supplementary economic measures like the savings to investment

ratio (SIR), net savings (NS) and net payback period. Annual supplement to the NIST

handbook 135 [3] published by the DOE, lists the projected energy price escalation rates,

DOE discount rates and the corresponding discount factors to determine the present value

of the future costs incurred during the life span of a system or a technology. Future costs

include annually recurring non uniform costs like the energy costs and annually recurring

uniform costs like the maintenance costs. Energy price escalation rates are listed for four

census regions and also for the U.S. Average. For this analysis, the annual supplemented

published for the year 2004 is used and the fuel escalation rates are taken to be that of the

U.S. average.









High Pressure Regenerative Turbine Engine (HPRTE)

As described earlier, the HPRTE operates on a pressurized semi-closed, intercooled

and recuperated cycle. Initial studies on semi-closed cycles were performed by the Sulzer

brothers, Westinghouse and the U.S. Navy in the 1940s and 50s. The results of these

studies indicated that the semi-closed cycle had certain advantages in terms of their

thermal efficiencies, high specific power, lower emissions and system compactness as

compared to the open cycles [4]. Despite these advantages, the research on semi-closed

cycles was restricted due to operational and technological constraints. With the

advancement of technology, interest in the semi-closed cycles has been revived.

Significant research on the HPRTE is being conducted at University of Florida and

several studies performed on the engine have delivered promising results. Nemec and

Lear [5] analyzed the combined cycle of the HPRTE with a Rankine bottoming cycle and

the results showed that the combined cycle could achieve thermal efficiencies in excess

of 60%. MacFarlane [6] demonstrated that the HPRTE, because of its pressurized, semi-

closed, and intercooled nature, had the capability to extract water from combustion

products. The extraction of water had little effects on the rest of the cycle though the

overall performance of the engine was improved due to an increase in the specific power.

The water generated could be used for applications like process cooling, combined cycle

systems and human consumption. This water could also be reinjected to the burner for

power augmentation and reduction in NOx levels without much reduction in the engine's

performance. Muley and Lear [7] showed that the recirculation of the exhaust gases led to

a reduction in thermal NOx formation rates by roughly five orders of magnitude versus

typical open cycles. This was due to the fact that the recirculated gases reduced the

oxygen concentration in the inlet air, thus leaving less oxygen to react with nitrogen.









Presence of high-heat capacity inert gases like CO2 and H20 also led to a reduction in the

adiabatic flame temperature. Lear and Laganelli [8] demonstrated that the HPRTE

produced a constant efficiency curve at part power over a wide range and that the HPRTE

generated reduced emission levels versus open cycles. Boza et al. [9] conducted a

thermodynamic performance analysis of the combined cooling and power cycle formed

by integrating the HPRTE with a vapor absorption refrigeration system (VARS). The

combined cycle was modeled for a small engine with power output of 100 kW and for a

large engine having an output power of 40 MW. The results were presented in terms of

thermal efficiency, refrigeration ratio and combined cycle efficiency and significant

advantages over the state-of-the-art were predicted. Khan et al. [10] analyzed the

combined HPRTE-VARS cycle for water extraction and showed that more than one kg of

water can be extracted per kg of fuel for cases with high recirculation.

Small Gas Turbine Technology

As mentioned in the introduction, this analysis compares life cycle costs of the

HPRTE to a conventional microturbine. Both these technologies come under the category

of small gas turbines. Small gas turbine engines are gas or fuel fired turbine generator

units with a power range of less than 500 kW. Compared to the other small scale power

generation technologies, small gas turbines offer a number of potential advantages. These

gas turbines have a compact size, flexibility of operating on liquid or gaseous fuels, small

number of moving parts, extremely low emissions and the potential to be used for

distributed generation applications. However these gas turbines have lower efficiency in

their basic configuration as compared to the other small scale power generation

technologies. An addition of a recuperator or a regenerator leads to significant increases

in cycle efficiencies of small gas turbines. Romier [11] performed a parametric study to









compare three different cycles for small gas turbines. The first cycle was a recuperative

cycle, the second a recuperative-intercooled cycle and the third cycle was a recuperative-

under-pressurized cycle. The results were analyzed in terms of the cycle electrical

efficiency as it is one of the most critical factors while determining the return on

investment of a power generation system. Of the three cycles, the recuperated -

intercooled cycle had the highest electrical efficiency for a gas turbine co-generation

system at a nominal power output of 350 kW.

Thermoeconomic Analysis

As per the guidelines mentioned in the life cycle costing manual, the life cycle

costs of any technology can be determined by evaluating the equipment costs, process

capital costs, energy costs, maintenance costs and the residual value. In this analysis, the

equipment costs of both technologies are determined using the component cost functions,

which were developed on the basis of exergoeconomic evaluation of gas turbine cycles.

Exergoeconomics combines the exergy analysis with the economics of a system by

assignment of costs based on the exergy content of an energy carrier. An energy carrier is

any system or substance used for carrying and transforming energy. Exergy is defined as

the maximum work attainable from an energy carrier under conditions imposed by the

environment and expresses the maximum capability of the energy carrier to cause

changes. It is closely related to system economics as the energy user pays for the

potential of energy to cause changes [12]. Application of exergoeconomic analysis for

thermodynamic systems was initiated by M. Tribus, R. B. Evans, R. A. Gaggioli and E.F.

Obert in the late 1950s. These applications were further developed by Y.M. EL-Sayed, G.

Tsatsaronis and C. Frangopoulos in the 1970s and 80s. Tsatsaronis [12] discussed the

exergy analysis for components of an energy system and the application of exergy









costing to evaluate the economics of the system. As a part of the exergy costing

principles, a cost is assigned to every material and stream in the energy system, based on

its exergy flow rate. This cost can be determined using exergy balances between the input

and output streams of each component, after taking into account the exergy losses.

Themoeconomic optimization of systems can be achieved by minimizing the cost

of exergy for every component of the system. Initially the concept of thermoeconomic

analysis was applied only to simple cycles but further developments led to its application

for advanced and complex cycles. Franco and Casarosa [13] compared the results

obtained from thermodynamic and thermoeconomic optimization of a brayton cycle with

intercooling, reheating, regeneration and optimized heat recovery stream generator. The

results from thermoeconomic optimization showed some shift in the cycle efficiency in

comparison to that obtained from thermodynamic optimization, thus indicating a

compromise between high cycle efficiency and engine economics. Massardo and Scialo

[14] performed the thermoeconomic analysis of gas turbine cycles using a modular

computer program TEMP, which can conduct thermodynamic, exergy and

thermoeconomic analysis for several gas turbine cycle configurations. This tool uses the

cost functions for the cost of compressor, combustor, turbine, power generator and

intercoolers to determine the purchased equipment cost. These cost functions are

developed as a result of exergoeconomic analysis of different components, performed in

the initial study ofthermoeconomics. Traverso et al. [15] have modified the cost

coefficients used in the TEMP code by using the latest cost information available. A web

based user friendly interface of the TEMP code has also been developed with the help of






12


WIDGET. For this analysis, the equipment costs for both the technologies are calculated

using the cost functions mentioned in reference 15.














CHAPTER 3
LIFE CYCLE COST ANALYSIS GUIDELINES

Life cycle cost analysis (LCCA) is an economic method of project evaluation in

which all the costs from owning, operating, maintaining and ultimately disposing of a

technology are evaluated to compare different project alternatives. Life cycle cost

analysis is particularly helpful when there are more than one competing alternatives for

the same objective. The alternative with the lowest value of life cycle costs is usually

considered to be the most effective. The costs primarily considered in the life cycle cost

analysis include: initial investment costs, energy costs, cost of operations, maintenance

and repair and finally the residual value of the system. While evaluating the life cycle

costs of a system or technology, all the future costs, including the energy costs and the

cost of operations, maintenance and repair are discounted to their present value as of the

base date. The residual value of any system is its economic value at the end of the study

period or assumed life span. The formula to evaluate life cycle costs of an alternative can

be stated as follows:

LCC = CI + CE + COMR CRES (3.1)

where CI is the present value of the capital investment costs, CE is the present value of the

energy costs, COMR is the present value of operations, maintenance and repair costs, and

CRES is the residual value of the system, discounted to the base date. The residual value

can also be considered as the final resale (or scrap) value of the system minus the

disposal cost. Costs which are similar for all alternatives considered in the analysis do not

contribute in the final decision process of selecting an alternative and hence can be









ignored. As mentioned earlier, all the future costs incurred during the life span of an

alternative, need to be discounted to their present value for inclusion in the LCC analysis.

The discount rate of future costs for energy and water conservation project is established

every year by the DOE. Future costs can further be classified as one time costs, uniform

annually recurring costs and non uniform annually recurring costs. The present value

(PV) of a one time future cost F0, can be determined using the relation

PV = F (3.2)
(1+d)

where d is the discount rate and n is the time duration between the base period and the

period in which this cost is incurred. Similar expression can be obtained for calculating

the life cycle costs of uniform annually recurring costs like the annual maintenance cost.

If Fo is the uniform annually recurring cost, then the present value (PV) of the life cycle

costs can be determined using the relation


PV = Fo -ld) l 1 (3.3)
d (1 + d) "

Here d is the discount rate and n denotes the total life span of a system or the time period


over which these costs are incurred. The term (I + d) is used by the DOE to
d( + d)"

calculate the discount factors or the Uniform Present Value (UPV) factors based on a

fixed discount rate for different values of n (expressed as number of years). Hence, the

present value of an annual uniform cost incurred for a period of n years can be

determined by just multiplying the annual cost by the UPV factor listed for that particular

value of n. For the calculation of energy costs, the escalation rates of the fuel prices also

have to be taken into account. These escalation rates are generally non-constant and are









based on the projections made by the DOE. The present value of life cycle costs of the

fuel (or any other source of energy with non uniform annual costs) required for a

system's operations, considering the base-year as 2004, is determined using the relation

nI
E (2004+t) (3.4)
S(1 + d)t

where Eo is the annual cost of energy as of the base date; t is the index used to designate

the year of energy usage; n is the number of periods (generally years), over which energy

costs or savings accrue; I(2004+t)is the projected average fuel price index specified by the

DOE for the year 2004+t (where I, for the year 20042= 1.00); and d represents the

n I
discount rate. The term (2004t) is evaluated by the DOE for various fuels based on
(1 +i d)

their respective escalation rates for different values of n, assuming a fixed discount rate d.

The resulting number is referred to as the UPV factor for fuel costs. Fuel costs for any

value of n, can be determined by simply multiplying the fuel cost for the base date by the

UPV factor corresponding to that value of n. These UPV factors are calculated based on

price escalation rates of fuels for four census regions and also for the U.S. average.

Another critical factor to be considered in the LCCA is the rate of inflation. As per

the FEMP guidelines, the LCCA procedure can be applied using two different approaches

for dealing with inflation. The first approach deals with stating the cash flows in constant

dollars while the second approach states the cash flows in current dollars. Constant

dollars are dollars of uniform purchasing power, exclusive of the rate of inflation and

indicate what the same goods or services will cost at different times if there is no change

in the general price level. Current dollars on the other hand are inclusive of inflation and

reflect changes in the purchasing power of dollars from year to year. The constant dollar









approach has the advantage of avoiding the need to project future rates of inflation or

deflation. The discount rates published by the DOE follow a constant dollar approach and

the same approach is followed in this analysis.

Apart from the LCC, there are supplementary methods of evaluating economic

performance based on the LCCA procedure. These include the savings- to- investment

ratio (SIR), net savings (NS) and net payback period. The net savings (NS) for an

alternative, relative to a designated base case, can simply be calculated by subtracting the

LCC of an alternative from the LCC of the base case. While evaluating multiple,

mutually-exclusive alternatives, the alternative with the highest value of NS will also

have the lowest value of LCC. Hence LCC and NS can be used interchangeably. The SIR

is defined as the ratio of present value of savings obtained from an alternative (with

respect to the base case) to the additional investments made to implement the alternative.

An alternative is considered economically justified with respect to the base case if it has a

value of SIR greater than 1. Another economic performance measure that can be

determined using the LCCA procedure is the net payback period. The payback period is

expressed as the number of years between the base period and the time when the

cumulative savings obtained from an alternative are just sufficient to recover the

incremental initial investment. Since the payback period does not include all cost or

savings, or even the residual value after the payback date, it s not a valid method for

selecting among multiple, mutually-exclusive project alternatives. As per the FEMP

guidelines, the payback period should just be used as a screening measure for the LCC

analysis. However, the SIR and the NS always give results consistent with those obtained

from the life cycle costs. The sensitivity of life cycle costs of a system to changes in






17


design and economic parameters is usually evaluated to determine the trends in life cycle

costs for different operating and economic conditions.














CHAPTER 4
LCCA OF THE HPRTE AND THE MICROTURBINE

The primary aim of this analysis is to compare the life cycle costs of the HPRTE

integrated with a VARS to that of a conventional microturbine. This analysis is based on

the guidelines established by the DOE in the FEMP. The major costs evaluated in this

analysis include the equipment costs, total plant costs, energy costs and maintenance and

repair costs. The sum of equipment costs, labor costs, material costs and installation costs

is categorized as the process capital cost. Adding soft costs like project supervision costs

and contingency fees to the total process capital gives the total plant cost or the capital

investment costs The residual value for both the technologies is assumed to be similar

and hence ignored in the analysis. This cost analysis is performed for a base power load

of 250 kW for both technologies. The life span for both technologies is assumed to be

80,000 hours, and assuming an operation span of 8000 hours in a year, the life time for

both technologies is calculated as 10 years. In the following sections, the major costs

evaluated for the analysis are discussed starting with the capital investment costs.

Capital Investment Costs

Capital investment costs primarily include the equipment costs, installation costs,

costs of electrical instrumentation and other materials, and project supervision and

contingency fees. The installation costs can be assumed to be 30% of the total equipment

costs, while the costs of electrical instrumentation is usually assumed to be 20% of the

equipment costs. Project contingency fees and project management fees usually account

for 15% each of the equipment costs. These percentages are assumed to be similar for









both technologies and taken from previously published data [16]. The cost of land is not

included in this analysis. As mentioned earlier, equipment costs for both technologies are

calculated using the component cost functions developed on the basis of thermoeconomic

analysis of gas turbine cycles. These functions were modified by Traverso et al. [15], by

changing the cost coefficients of these functions, making them representative of current

equipment cost. The cost functions were developed for gas turbine engines with a power

range of 1 to 300 MW. Though the cost functions were developed for medium-to-large

sized gas engines, they can also be used to determine the equipment costs for small gas

turbine engines (like the HPRTE and the microturbines), just by changing the cost

coefficients. As the cost information of equipment is proprietary and difficult to obtain,

the cost coefficients for small engines were taken to be a parameterized fraction of the

cost coefficients of large engines. This fraction is referred to as the Cost Coefficient

Fraction (CCF) in this analysis. The assumption of cost coefficients of small engines

being a fraction of that of the large engines is based on the relatively inexpensive radial

technology of small engines in comparison to the relatively expensive axial technology

for the large engines. The fact that the same cost functions and coefficients were applied

both for the HPRTE and the microturbine ensured a fair comparison even with the

uncertainty in the values of the cost coefficients. For the present study, the design

parameters for the cost function are obtained from a computer code developed for

thermodynamic analysis of the HPRTE-VARS cycle [10]. This code assumes a fixed

value of the equivalence ratio P by changing the recirculation ratio RR, which is defined

as the ratio of mass flow rate of the exhaust stream to that of fresh air. The equivalence

ratio, on the other hand, is defined as the fuel-air ratio at the actual condition to that under









stoichiometric conditions. The code developed for the HPRTE-VARS cycle can also be

used to simulate a microturbine cycle by neglecting any recirculation of the exhaust

stream and not including any of the additional components present in the HPRTE. Table

4-1 shows the base case design parameters and ambient conditions used in the computer

code, for both the HPRTE-VARS cycle and the microturbine. The different economic

parameters assumed for the base case are listed in Table 4-2.

Table 4-1. Base case design parameters and ambient conditions assumed in the computer
code for the HPRTE/VARS and the microturbine
Design Parameters Values
Turbine Inlet Temperature K 1373
Turbine Exit Temperature K 1073
Turbomachinery Polytropic efficiencies 85%
Recuperator Effectiveness 0.84
HPRTE Heat Exchanger Effectiveness 0.8
Pressure Drop in Combustor 0.05
Pressure Drop in HPRTE-Heat Exchanger 0.03
Pressure Drop in VARS Generator (HPRTE) 0.03
Pressure Drop in VARS Evaporator (HPRTE) 0.03
Pressure Drop in Recuperator (Gas side) 0.06
Pressure Drop in Recuperator (Air side) 0.02
Generator Temperature K (HPRTE-VARS) 373
Evaporator Temperature K (HPRTE-VARS) 288

Ambient Conditions
Ambient Temperature K 303
Relative Humidity of Fresh Air 90%
Ambient Pressure (atm) 1.0


Table 4-2. Base-case values of the economic parameters used for the LCCA of the
HPRTE and the microturbine
Economic Parameters Values
DOE Discount Rate 3%
Cost Rate of Natural Gas ($/MMBTU) 5
Price Rate of Electricity (cents/kWh) 8
Cost Coefficient Fraction (CCF) 0.5









The main components common for both the HPRTE and the microturbine include

the high-pressure compressor, combustor, the high-pressure turbine, recuperator, and the

power generator. The HPRTE also includes additional components in terms of a VARS

unit, a heat exchanger for inlet air cooling, and a turbocharger that works as a low-

pressure compressor/ turbine system. The design parameters for the components common

to both technologies are assumed to be of similar values. Considering the rapid

advancement in gas turbine technology, the assumed values of HPT inlet and exit

temperatures of both engines are reflective of the future technology levels of the gas

turbines. On the other hand, the values assumed for pressure drop across the heat

exchanger and the VARS unit of the HPRTE are significantly high, with a total pressure

drop of almost 9% across the heat exchanger-VARS section (Table 4-1). High values of

pressure drop across the heat exchanger-VARS section lead to a noticeable decrease in

the HPRTE-VARS cycle efficiency. However, if the pressure drop across the heat

exchanger and the VARS unit is ignored, the cycle efficiency of the HPRTE is very

similar to that of a microturbine. Table 4-3 lists the coefficients of gas turbine cost

functions for large engines as mentioned in reference 15.This table also lists the cost

coefficients for the main components of a gas turbine These cost coefficients are denoted

by cl, cci, ti and gi (all cost coefficients are represented in $) for the high-pressure

compressor, combustor, the high- pressure turbine, and the generator, respectively. As

discussed earlier, the base-case cost coefficients for small engines (HPRTE,

microturbine) are assumed to be 50% of those of large engines, or in other words, the cost

coefficient fraction (CCF) is assumed to be 0.5 for the base case. The equipment costs for

both technologies are discussed in details in the next section.









Table 4-3. Coefficients of the gas turbine cost functions (large engine)


ci($) 5095.9
c2 0.15
c3 0.85
c4 0.3
cci($) 1857
cc2 0.995
cc3 5.479
cc4 34.36
cc5 0.6
Pref [Pa] 101325
Tref [K] 288.15
ti($) 5979
t2 0.29
t3 4.185
t4 23.6
t5 0.75
gi($) 1030.9
g2 0.72
mref 1
[kg/s]
POWref 1
[kW]
mr,ref 0.9586
Traverso, A., Massardo, A.F., Cazzola, W., and Lagorio, G., 2004, "WIDGET-TEMP: A
Novel Web-Based Approach for Themoeconomic Analysis and Optimization of
Conventional and Innovative Cycles," Proc., 2004 ASME TURBO EXPO, Vienna,
Austria, June 14-17, 2004, ASME Paper 2004-GT-54115.


High-Pressure Compressor

Both the HPRTE and the microturbine use a centrifugal or a radial compressor to

compress the inlet air and raise its temperature and pressure. The cost of the high-

pressure compressor of both technologies is calculated using the cost function for

compressor's capital cost defined by Traverso et al. [15]. This relationship is expressed

as:


Constant


Value










C 3
m2 R. T.

air in in
P. Ih C
incr P c4 ln() (4.1)
ni r -- T i n p o ly C
in r reCT


The cost equation uses a corrected expression of mass flow rate for different pressure and

temperature conditions. Here iz,,,, Tin and Pin represent the mass flow rate, temperature,

and pressure of the incoming air. mzcr represents the critical mass flow rate at choking

conditions (Mach number = 1) and is a constant in this analysis. The expression


S in i represents the corrected mass flow rate, which is also normalized with
P. m
In Cr

respect to the reference conditions. The constants for the cost functions are taken from

reference 15 and are listed in Table 2. As mentioned earlier, the value of cost coefficient

ci is taken to be 50% of that of the large engine. The cost of the compressor is dependent

on the corrected mass flow rate, its pressure ratio p and polytropic efficiency rlpoly, c. The

coefficient c3 demonstrates the scaling effect of compressor size (and hence cost) with

power. An increase in the output power capacity leads to an increase in compressor's size

and cost, but in a non linear fashion. The mass flow rates, temperatures and pressures are

obtained from the computer code simulating the two cycles. The inlet air coming into the

high-pressure compressor of the HPRTE is at an elevated pressure after being

compressed in the low-pressure compressor. This results in a lower corrected mass flow

rate for the HPRTE in comparison to that of a microturbine for a similar power output,

thus reducing HPRTE's compressor cost relative to that of a microturbine. Similar









pressure ratios for the high-pressure compressor (HPC) can be achieved for both

technologies as the turbine inlet and exit temperature for the HPRTE are assumed to be

same as that of a microturbine. The polytropic efficiency of the compressor is also

assumed to be same for both technologies.

Combustor

The capital cost of the combustor chamber, where the fuel-air mixture is burned at

constant pressures, to achieve the desired turbine inlet temperature, is determined by the

following cost relationship defined in [15].

SIcc5 I Tt 7 cc4 1
(ic C out +e Tt o,,,e 1 (4.2)
C 1 otVot )ref (AP/P)cMc

Here hou,, vout and Tout represent the mass flow rate, specific volume and temperature of

the gas stream exiting the combustor. The values of these parameters are determined by

the computer code developed for both technologies. From the perfect gas law

relation(Pv = RT), the specific volume of the gases is directly proportional to the

temperature, at constant pressures. Since the temperature of the gases passing through the

combustor is maximum at the combustor's exit, the specific volume of the gases also

attains its maximum value at combustor's exit. The cost of the combustor is thus

calculated using the mass flow rate and the specific volume at its exit. This cost

expression is also nondimensionalized using reference conditions. For this analysis, since

the combustor exit temperature of the gases is same for both the HPRTE and the

microturbine, their specific volumes and hence the costs are dependent on the pressure of

the gases at the exit of the combustor. Because of the initial compression in the low-

pressure compressor, the gases exiting the combustor of the HPRTE are at higher









pressures than those of the microturbines. Thus the cost of the HPRTE is reduced by a

factor proportional to the pressure ratio of its LPC/LPT, in comparison to that of a

microturbine. The cost relation also demonstrates an inverse relationship between

combustor's cost and its pressure drop (AP/P)cM For this analysis, an equal value of

the pressure drop is assumed for both engines. Also, the primary zone temperature in the

combustor of the HPRTE is reduced due to increased dilution of the inlet-air stream of

the HPRTE by the recirculated stream. This may allow the combustor of the HPRTE to

be made with relatively inexpensive material, in comparison to that of a microturbine.

However, for this analysis, no economic credit is claimed for savings in material cost of

the combustor of the HPRTE

High-Pressure Turbine

After exiting the combustor, the gases are expanded in the high-pressure turbine.

The cost of the turbine is determined from the cost function relationship developed by

Traverso et al. [15] and represented by Equation 4.3.


E =t, (motot) +e ln() (4.3)
T out out )ref 1 ( 7polT (4.3)


Here iho,t, vout and Tout represent the mass flow rate, specific volume and temperature of

the gas stream exiting the high-pressure turbine. Tin represents the turbine inlet

temperature. As in the case of the combustor, the cost of the turbine is dependent on the

volume of the gases at the exit of the turbine. This is due to the fact that since the gases

undergo an expansion process in the turbine, they attain their maximum volume for the

turbine section at the exit, where the pressure of the gases is the lowest for the entire

section. The exit turbine pressure of the gases for a microturbine is less than that for the









HPRTE, again by a factor proportional to the LPC/LPT pressure ratio of the HPRTE.

This leads to larger specific volumes of the gases and hence larger costs for the high-

pressure turbine of the microturbine, relative to that of the HPRTE, assuming the same

turbine inlet and exit temperatures for both technologies. The cost function also shows a

logarithmic proportionality with the pressure ratio of the turbine P and an inverse

relationship with the polytropic efficiency rjpoly, T. As in the case of the high-pressure

compressor, the polytropic efficiency of the high-pressure turbine of the HPRTE is

assumed similar to that of the microturbine.

Recuperator

A recuperator facilitates heat exchange between hot exhaust gases and compressed

air going into the combustor. This reduces the amount of fuel needed to heat the

compressed air to the turbine inlet temperature, thus helping in a significant increase in

the cycle efficiency and the specific power of the engine. The cost of the recuperator is

evaluated using the following expression derived for the volume of the recuperator by

McDonald [17].


V {jO R 1 3CI -R (4.4)
J8 -R E (AP/P5;TR R

This expression relates the recuperator volume with its mass flow rate, pressure ratio of

the engine cycle, recuperator's effectiveness and pressure drop, and the surface geometry


of the recuperator. The factor represents the surface geometry of the


recuperator and this factor is assumed to be same for both technologies. For a recuperated

microturbine, the cycle pressure ratio determines the temperature of the compressed air

stream going into the recuperator. The pressure of the exhaust stream of the engine,









entering the recuperator of a microturbine is close to the ambient (1 atm) after going

through the expansion in the turbine. The relationship between the volume of the

recuperator and the cycle pressure ratio (Equation. 4.4) works fine in the case of a

microturbine. This is due to the fact that cycle pressure ratio of a microturbine

corresponds to the pressure ratio of its HPC/HPT as there is just one

compression/expansion stage, with the exhaust stream entering the recuperator at ambient

pressures. However, in the case of the HPRTE, there is an extra stage of compression for

the inlet air as it is compressed in the LPC, before being compressed in the HPC. Thus

the compressed air stream discharged from the HPC and the exhaust stream exiting the

HPT of the HPRTE are at elevated pressures, by a factor proportional to the LPC/LPT

pressure ratio, as compared to a microturbine. To include the effect of elevated pressures

of both the streams entering the recuperator of the HPRTE, it was decided to use a

corrected expression for the mass flow rate of the streams. The corrected mass flow rates

were also applied for both streams entering the recuperator of a microturbine. To

calculate the recuperator cost estimate for both technologies, the following equation

developed by Douglas [18] relating the heat exchanger cost to its area was used.


EHX= 101.3A 66 iMS(2.29+F) (4.5)


where EHX is the heat exchanger capital cost, A is the heat transfer area, IMS is the

Marshall and Swift cost index, which is 1280 for year 2004 and F, is the correction factor

for different design pressures and construction materials. For this case, the correction

factor was assumed to be 1. The heat transfer area is calculated using the thermodynamic

code developed for the two cycles. The pressure drop across the recuperator and the

recuperator efficiency were assumed to be similar for both technologies. Since the









HPRTE's recuperator has lower corrected mass flow rates of both the streams as

compared to a microturbine, it can be stated that for the same power output, the

recuperator of the HPRTE is compact in comparison to that of a microturbine. The area

and hence the cost of the recuperator of the HPRTE is less than that of a microturbine

recuperator by a factor proportional to the LPC/LPT pressure ratio of the HPRTE.

Power Generator

Micro-or mini-turbines (30 to 500 kW) produce power either via a high-speed

generator rotating on a single compressor/ turbine shaft or on a separate power turbine

driving a gearbox and a conventional 3600 rpm generator. The high-speed generator of a

single shaft requires a rectifier to convert its high frequency AC output into 60 Hz for

general use. The cost of the generator is calculated using the cost relationship developed

by Traverso et al. [15] for large engines by taking a modified cost coefficient, with CCF

of 0.5. The cost of power conversion equipment is also included in the cost of the

generator. This cost comes out to be similar for both the microturbine and the HPRTE as

the power output for both engines is the same. The cost relationship is given by Equation.

4.6.

92
EG = g1 (4.6)
T^ref)

where Wf is the electrical power generated by the engine. This expression is normalized

with a reference power capacity. This equation depicts a direct but nonlinear relationship

between the generator cost and the generated power.









Gas Compressor

Small gas turbines operating on gaseous fuel require the fuel to be delivered at

pressures ranging from 50 psig to 80 psig for effective combustion. This requirement is

much higher than the usual pipeline delivery pressure of 1-2 psig. To deliver the fuel at

the required pressures for effective combustion, a gas compressor is used for both the

HPRTE as well as the microturbine. The cost of the gas compressor is expected to add

somewhere in the vicinity of 50-100 $/kW to the total equipment cost [19]. Though the

fuel pressure of the HPRTE is higher as compared to a microturbine, the cost of the gas

compressor is assumed to be insensitive to the pressure of the fuel.

Heat Exchanger-HPRTE

As discussed in the cycle configuration of the HPRTE, a heat exchanger (MC,

Figure 1-1) is placed in the gas path before the high-pressure compressor to reduce the

inlet temperature of the air entering the compressor. Reducing the temperature of the air

before the compressor inlet reduces the work required for compressing the air to the

desired temperature and pressure. Reduction in the compressor work increases the net

work output from the system, thus increasing the overall efficiency of the engine. In this

analysis, the heat exchanger is coupled to the evaporator of the VARS unit. The cost of

this heat exchanger is also calculated using Equation (4.6). The heat transfer area for this

heat exchanger is calculated using the thermodynamic code developed for the HPRTE

cycle. Since the gas stream entering this heat exchanger is at elevated pressure after being

compressed in the LPC, a corrected expression for mass flow rate (as done in the case of

the recuperator) is used to determine the area and hence the cost of this heat exchanger.

The value of the correction factor used in the cost equation of the heat exchanger is equal

to the value of the correction factor used in the case of a recuperator. This value of the









correction factor for the heat exchanger is highly conservative, considering the relatively

expensive materials used for the recuperator, as compared to the heat exchanger. This

difference in materials is due to the fact that the gas streams flowing through the

recuperator are at higher temperatures, as compared to the gases flowing through the heat

exchanger, thus resulting in expensive-material usage for the recuperator, in comparison

to the heat exchanger.

VARS-HPRTE

The HPRTE is integrated with a vapor absorption refrigeration system (VARS).

This unit is driven by the recirculated exhaust stream of the HPRTE and serves the dual

purpose of cooling the inlet air going into the compressor and producing some external

refrigeration. This VARS unit could either be based on a water/lithium bromide or an

ammonia/water, refrigerant/absorbent pair. The cost of this unit is calculated using the

cost per tonnage figure mentioned in reference 20 for a single-stage absorption unit. The

code developed for thermodynamic analysis of the HPRTE/VARS cycle determines the

cooling capacity of the VARS unit based on the cooling load required to cool the gas path

and the external refrigeration generated.

Turbocharger-HPRTE

As discussed earlier, the HPRTE utilizes a low-pressure compressor-turbine system

for pressurizing the fresh air to increase the specific power and fluid densities, thus

making the system compact for a fixed power capacity. In this analysis, an automobile

turbocharger is chosen as the LPC/LPT system. The cost of the turbocharger is assumed

to be similar to that of automobile turbochargers. This cost is based on optimal values of

the LPC pressure ratio and air mass flow rate. The optimal value of turbocharger pressure

ratio is determined from the thermodynamic code that ensures that the work output









obtained from the low-pressure turbine is equal to the work required for compressing the

fresh air [10]. In place of a turbocharger, separate LPC and LPT can be used to generate

additional work output, apart from pressurizing the inlet air.

Air Bearings

Small turbines can operate either on oil bearings or air bearings but air bearings are

beneficial in terms of life, parasitic losses and lubricating flow. Air bearings do not

require any oil or pump and thus provide cost advantages with simplicity of operation.

The cost of bearings is assumed to be similar for both the HPRTE as well as microturbine

and estimated directly from one of the bearing manufacturer's website

(http://www.lasermotion.com/Airbearings.html), based on load capacity and rpm values.

After calculating the costs of major equipment used in the two technologies, the

total plant cost is evaluated. As discussed earlier, this cost is the sum of equipment costs,

installation costs, cost of electrical instrumentation and other materials, project

supervision and contingency fees. As mentioned in the earlier part of this chapter, the

installation costs, electrical instrumentation and other materials costs, project supervision

costs and contingency fees are evaluated as a percentage of the equipment costs. These

percentages are assumed to be the same for both technologies and are stated in the initial

part of this chapter. The total plant cost is one of the critical factors in this analysis as

some of the results of this analysis are expressed in terms of plant cost ratio (PCR), i.e.,

the ratio of the total plant cost of the HPRTE to that of the microturbine.

Energy Costs

One of the main elements of the total life cycle costs of both technologies is the

cost of energy sources required for engine's operation. The energy costs for this analysis

primarily include the fuel costs incurred during the total life span of the engines. The fuel









assumed in this analysis, for both technologies, is natural gas. For the case of the HPRTE,

as mentioned earlier, there is some external cooling obtained from the VARS unit. This

excess refrigeration has a definite economic advantage that is determined by converting

the excess refrigeration into equivalent power as explained by Boza et al. [9] and

discussed in the next section of this chapter. The excess refrigeration generated from the

HPRTE is considered to be a source of revenue which apart from recovering the initial

investment for the VARS unit also offsets some of the fuel cost of the HPRTE over the

life span of the engine. Fuel costs for both engines and revenues from refrigeration for the

HPRTE are discussed in the next section.

Fuel Costs

Fuel costs are categorized as non uniform annually recurring costs as the fuel prices

might undergo an escalation or a descalation during the life span of the engine. The future

costs of fuel required have to be discounted to their present value for LCC analysis. As

mentioned earlier, the DOE determines the uniform present value (UPV) factors for all

the major fuels. These factors are based on a fixed discount rate and include the projected

escalation rates, for a specified duration for different fuels. DOE calculates the UPV

factors for the four census regions and also for the U.S. average. In this analysis, the UPV

factors developed for the U.S. average are considered. For the natural gas, taking a DOE

discount rate of 3% and a time span of 10 years (life span for both technologies), the

UPV factor is calculated as 7.87. Hence, to calculate the total life cycle fuel costs for both

technologies, the annual fuel cost for the base year (2004, for this analysis) is multiplied

by the UPV factor of 7.87. The annual fuel cost is determined using the average price

rate of natural gas as of the base date (May 1st, 2004), the lower heating value (LHV) of

natural gas and the annual fuel consumption. Average fuel price rate as of the base date









are taken directly from the website of DOE. This price corresponds to the rate for the

industrial sector and is exclusive of any state or federal taxes. The LHV of a fuel is

defined as the net energy released during oxidation of a unit of fuel excluding the heat

required for vaporization of the water in the exhaust stream. For natural gas, its value is

approximately 47000 BTU/kg, where BTU is a standard unit of energy and is equivalent

to the amount of heat required to raise the temperature of one pound of water by one

degree Fahrenheit. The annual fuel consumption is calculated by multiplying the per-hour

fuel consumption by total number of operating hours of the engine. Fuel consumption

per-hour is determined from the thermodynamic code developed for the cycles. The

annual fuel cost is then calculated by multiplying the fuel price (expressed in $/BTU)

with the LHV (BTU/kg) of the fuel and the annual fuel consumption (kg). The annual

fuel cost, when multiplied by the UPV factor gives the life cycle fuel costs for both

technologies.

Revenue from Refrigeration

As mentioned earlier, the VARS unit integrated with the HPRTE produces some

excess refrigeration, apart from cooling the inlet air to the compressor. As discussed by

Boza et al. [9], this excess refrigeration can be converted to equivalent power. The

refrigeration produced by the VARS system of the HPRTE can be considered as a source

of economic credit. This economic credit is estimated by considering the refrigeration as

the amount of power required by a power-driven source of refrigeration, to generate an

amount of refrigeration equivalent to that generated by the VARS unit of the HPRTE,

operating under similar conditions. The total revenue from refrigeration is calculated by

assuming that the equivalent power can be sold at the average price rate of electricity. For

the purpose of estimating the power equivalent of the refrigeration, a vapor compression









system is considered. This equivalent power is referred to as WR and calculated using

the following relation

REF C(4O7)


Here QREF represents the excess refrigeration produced by the VARS unit and COPvc

denotes the coefficient of performance of the vapor compression unit. The value of QREF

is determined from the computer code developed for thermodynamic analysis of the

HPRTE-VARS cycle. The COP of the vapor compression system is obtained by using

energy efficiency ratios (EERs) for appropriate sized air conditioning units and

employing the ARI rating conditions under which the units are tested to determine the

respective refrigeration efficiencies (COP/COPcamot). The COP of the system is then

calculated using COPcarnot and the refrigeration efficiencies. The equivalent power can

also be represented in terms of the combined efficiency of the power and cooling cycle of

the HPRTE-VARS expressed by the relation
W + W
SHPRTE + WREF
I comb = (4.8)
mh uel LHV

where WHPRTE represents the net power generated by the HPRTE, without the VARS unit.

Like the fuel cost, the revenue generated from refrigeration is a future cost that

needs to be discounted to the present value as of the base date. This is done by

multiplying the annual revenue produced by refrigeration, with the UPV factor

determined by the DOE for electricity. For the base case, taking a DOE discount rate of

3% and a time span of 10 years (life span for both technologies), the UPV factor for

electricity is calculated as 8.38. Annual revenue from refrigeration is evaluated by









multiplying the equivalent power generated from refrigeration by the average U.S. price

rate of electricity for industrial sector as of the base date. For the base date of May 1st,

2004, the price rate of electricity is taken as 8 cents/kWh. This is a highly conservative

rate, considering the fact that the HPRTE-VARS is a cogeneration system, producing

both power and cooling, and this cooling can be of significant advantage in hot seasons

and hot regions of the country. The revenue obtained from refrigeration offsets some of

the fuel cost for the HPRTE after recovering the initial investment for the VARS unit.

Maintenance Cost

Since the HPRTE is a novel concept, its maintenance cost is estimated from the

data available for maintenance cost of other small gas turbines like the microturbine. The

microturbine, itself is a relatively new technology and there isn't much published data

available for the maintenance cost incurred throughout the life span of the engine. Most

manufacturers offer service contracts for specialized maintenance priced at about $0.01-

0.02/kWh [21]. For This analysis, the maintenance cost of the microturbine is assumed to

be 0.013 $/kWh. These service inspections include periodic inspections of the combustor

(and associated hot section parts) and the oil bearing in addition to regular air and oil

filter replacements. A gas microturbine overhaul is needed every 20,000 to 40,000 hours

depending on manufacturer, design, and service. A typical overhaul consists of replacing

the main shaft with the compressor and turbine attached, and inspecting and if necessary

replacing the combustor. Since the HPRTE has additional components as compared to the

microturbine, its maintenance cost is estimated at a rate of $0.015/kWh.

The sum of capital investment costs, energy costs and maintenance costs gives the

total life cycle costs of both technologies. These costs are then evaluated for different






36


design and economic parameters, and the results are expressed in terms of cost ratios of

the two technologies.














CHAPTER 5
RESULTS AND DISCUSSION

As this study is primarily focused on life cycle cost comparisons of the HPRTE

with that of a microturbine, the majority of the results of this analysis are expressed in

terms of the ratio of life cycle costs of the two alternatives for various design and

economic parameters. Expressing the results as cost ratios and using the same cost

functions and cost coefficients for both technologies ensures fairness of this analysis. The

design and environmental parameters used for evaluating the life cycle costs of the two

technologies include the HPT inlet and exit temperatures, LPC pressure ratio of the

HPRTE, effectiveness of the recuperator and the ambient temperature. The HPT inlet and

exit temperatures, and the recuperator effectiveness are independent variables limited by

material and technology constraints. Ambient temperature is also an independent variable

and is used to evaluate the sensitivity of cost ratios with changes in regional and seasonal

conditions. The LPC pressure ratio (for this analysis, the pressure ratio of the

turbocharger) of the HPRTE is directly dependent on the ratio of the LPT inlet

temperature to the LPC inlet temperature (which also is the ambient temperature). The

LPT inlet temperature is influenced by design parameters like the HPT inlet and exit

temperatures, and recuperator effectiveness. Higher values of the ratio of the LPT inlet

temperature to LPC inlet temperature increase the LPC pressure ratio, which has a

significant influence on the system compactness and hence the plant costs of the HPRTE.

The values of design, economic and environmental parameters common to both

technologies are assumed to be the same.









As discussed earlier, the HPRTE is similar to a microturbine except for the addition

of an LPC/LPT system (a turbocharger, for this analysis) to pressurize the inlet air

resulting in system compactness and an increase in power and fluid densities, and a heat

exchanger-VARS section to cool the inlet air to the HPC and to produce some external

refrigeration. The investments made for the additional components of the HPRTE are

evaluated against savings in equipment costs due to system compactness of the HPRTE,

and the revenue that can be generated from external refrigeration. After evaluating the

life cycle costs of a conventional microturbine, the results of this analysis are expressed

in terms of cost ratios, i.e., the ratio of life cycle costs of the HPRTE to the costs of a

microturbine. These cost ratios include the life cycle cost ratio (LCCR) and the plant cost

ratio (PCR) of the two technologies, and the revenue ratio (RRev) of the HPRTE, as

defined in the earlier sections. The cost ratios are evaluated for different design,

environmental and economic parameters.

Figure 5-1 shows the effect of increasing the high-pressure turbine (HPT) inlet

temperature on the LCCR and the PCR, keeping the other design, economic and

environmental parameters fixed and retaining their base-case values. The figure shows

that the LCCR and PCR decrease with increasing HPT inlet temperature. This trend can

be explained on the basis of an increase in the HPT pressure ratio, with increasing HPT

inlet temperature. The pressure ratio of the HPT has a direct dependence on the ratio of

the HPT inlet temperature to the HPT exit temperature. Increasing the HPT inlet

temperature, keeping the HPT exit temperature constant, increases the HPT pressure

ratio. An increase in the HPT pressure ratio leads to an increase in the net refrigeration

produced by the HPRTE. This is due to the fact that the gas at the HPC exit is at higher









temperatures due to higher pressure ratios, thus reducing the amount of heat extracted

from the exhaust stream in the recuperator and increasing the amount of heat available to

power the absorption unit for refrigeration. Also, with an increase in the high-pressure

turbine inlet temperature, the pressure ratio of the low-pressure compressor/turbine

system of the HPRTE increases. This is due to the fact that a portion of the exhaust

stream from the recuperator exit drives the low-pressure turbine whose pressure ratio

depends on the temperature of the exhaust stream. This increase in the LPC pressure ratio

reduces the corrected mass flow through the components for a fixed power output, thus

resulting in system compactness and hence lower plant cost of the HPRTE in comparison

to that of a microturbine. The decrease in PCR and LCCR with increasing LPC pressure

ratios is demonstrated by Figure 5-2.

Figure 5-3 shows the effect of increasing the HPT exit temperature on the LCCR,

keeping all the other design, economic and environmental parameters fixed and retaining

their base-case values. The figure show that the LCCR increases with an increase in the

HPT exit temperature. As mentioned earlier, the HPT pressure ratio is directly dependent

on the ratio of the HPT inlet temperature to the HPT exit temperature. Increasing the HPT

exit temperature, keeping the HPT inlet constant, decreases the temperature ratio and

hence the pressure ratio of the HPC/HPT spool. At reduced pressure ratio of the

HPC/HPT spool, the exhaust stream going through the recuperator loses more heat to the

compressed air stream, which enters the recuperator at lower temperatures because of the

low pressure ratio of the HPC. This reduces the net heat available for refrigeration













1.20

1.15

1.10

1.05

1.00

0.95

0.90


0.85 --
1250


1300 1350 1400 1450
HPT Inlet Temperature (K)


1500


0.97

0.96

0.95

0.94 a

0.93 -J

0.92

0.91


- 0.90
1550


Figure 5-1.Effect of increase in the HPT inlet temperature on LCCR and PCR. Except for
the HPT inlet temperature, all design and economic parameters are fixed and
their base-case values retained (Tables 4.1, 4.2)


1.20


1.15-

1.10


1.05
C-,

1.00


0.95

0.90


0.85


0.97


-0.96

-0.95


-0.94


0.93


-0.92

-0.91


0.90


2 2.5 3 3.5


LPC Pressure ratio (atm)

Figure 5-2.Effect of increase in the LPC pressure ratio on LCCR and PCR. The LPC
pressure is increased by increasing the HPT inlet temperature, retaining the
base case values of other design and economic parameters (Tables 4.1, 4.2)


- PCR
- LCCR


- LCCR
- PCR


r
r
4









produced from the VARS. However, beyond a certain temperature limit, the refrigeration

actually starts increasing. This is due to the fact that an increase in the HPT exit

temperature, with the HPT inlet temperature held constant, increases the recirculation

ratio, to maintain the value of D constant. This increase in the recirculation ratio makes

more heat available to power the absorption unit, thus increasing the refrigeration and the

revenue associated with it. Figure 5-4 demonstrates the change in refrigeration and hence

the revenue from refrigeration expressed in terms of RRev, with an increase in the HPT

exit temperature of the HPRTE. Since the exhaust stream exits the recuperator at lower

temperatures, for an increasing HPT exit temperature, the LPC pressure ratio of the

HPRTE is reduced due to a reduction in the net compression work for the LPC. This

leads to an increase in the equipment cost and hence the plant cost for the system, thus

increasing the LCCR.

Figure 5-3 also shows the effect of increasing the HPT exit temperature on the

cycle efficiencies of the HPRTE and the microturbine. The cycle efficiency of both

technologies increases initially and, after reaching an optimal point, tends to start

decreasing because of the decrease in the HPC/HPT pressure ratio. As both engines are

expected to be designed for the temperature regime that is optimal in terms of cycle

efficiencies, this optimal point occurs at moderate-to-low values of the HPT exit

temperature. There, a good amount of refrigeration is generated and the low-pressure

compressor ratio would be significantly higher to reduce the plant cost of the HPRTE,

thus enabling the HPRTE to maintain its cost advantages over a microturbine.

Figure 5-5 shows the effect of increasing ambient temperatures on the LCCR and

the PCR, with all the other design, environmental and economic parameters fixed. As













0.97

0.96

0.95

t 0.94

-J 0.93

0.92

0.91

0.90
950


1150


S0.38

0.37

0.36

0.35 .

0.34
IL
0.33 *

0.32

0.31

-0.30
1200


HPT Exit Temperature (K)

Figure 5-3 Effect of increase in the HPT exit temperature on LCCR and cycle efficiency.
Except for the HPT exit temperature, all design and economic parameters are
fixed and their base-case values retained (Tables 4.1, 4.2)


1000 1050 1100 1150


1200


HPT Exit Temperature (K)

Figure 5-4 Effect of increase in the HPT exit temperature on the revenue ratio of the
HPRTE. Except for the HPT exit temperature, all design and economic
parameters are fixed and their base-case values retained (Tables 4.1, 4.2)


1100


LCCR
- Cycle efficiency-HPRTE .
Cycle efficiency-Microturbine

0 \

Ile


1000


1050


1.30

1.25

1.20

S1.15
w

S1.10
w,

S1.05

1.00

0.95

0.90


-
-
- -









observed from the figure, the LCCR and PCR decrease with increasing ambient

temperature. An increase in ambient temperature decreases the amount of excess

refrigeration produced by the VARS unit of the HPRTE and this leads to a reduction in

the revenues generated from refrigeration. An increase in the ambient temperature also

lowers the value of the LPC pressure ratio, because of the increase in LPC compression

work with higher ambient temperatures. Reduction in the LPC pressure ratio increases

the component cost of the HPRTE due to reduced compactness in the higher cost high-

temperature components. As observed from the figure, at lower temperatures, the plant

cost for the HPRTE is less than that of a microturbine (PCR less than 1). However,

beyond a certain value of the ambient temperature, reduction in the LPC pressure ratio

makes the value of the plant cost ratio exceed unity. This creates an unattractive regime

for the HPRTE, though the revenue obtained from refrigeration still maintains the value

of the LCCR below one.

Additionally, the effect of increasing the ambient temperature on the cycle

efficiencies of the two technologies is a critical factor for this analysis. Since the inlet air

to the HPC of the HPRTE is cooled below ambient by the heat exchanger and the VARS

unit, the HPRTE is able to sustain constant efficiencies even at high ambient

temperatures. A microturbine, on the other hand, experiences a drop in cycle efficiency

with increasing ambient temperatures due to increased compressor work. Changing the

ambient temperature from 288 to 313 K decreases the microturbine cycle efficiency from

0.385 to 0.36, a drop of almost 7%. The fact that the HPRTE can maintain constant

efficiencies at high ambient temperatures gives it a definite advantage over the

microturbine. However, as mentioned earlier, the HPRTE can be regarded as a













0.97


0.96


0.95


0.94


0.93


0.92


0.91


0.90 -
285


1.05


1.00


0.95


0.90


-0.85
315


Ambient Temperature(K)

Figure 5-5.Effect of ambient temperature on LCCR and PCR. Except for the ambient
temperature, all design and economic parameters are fixed and their base-case
values retained (Tables 4.1, 4.2)




0.39


- ,
.


--HPRTE
- Microturbine


HPC Inlet Temperature (K)


Figure 5-6 Effect of increase in HPC inlet temperature (ambient temperature for the
microturbine) on cycle efficiency of the engines. Except for the HPC inlet
temperature, all design and economic parameters are fixed and their base-case
values retained (Tables 4.1, 4.2)


- PCR
-LCCR


S0


.0 r
,.1
Iii
111
iii


0.38

0.37

0.36

0.35


0.34

0.33

0.32
285









microturbine operating on a pressurized loop and with additional components for inlet air

cooling and excess refrigeration. If the HPC inlet temperature of the HPRTE is increased,

there is a drop in its cycle efficiency similar in magnitude to the drop in the efficiency of

a microturbine with the same increase in the ambient temperature. Figure 5-6

demonstrates this effect of change in cycle efficiencies of the two technologies with an

increase in the HPC inlet temperature, which also is the ambient temperature for the

microturbine.

Figure 5-7 shows the effect of increasing recuperator effectiveness on the LCCR,

with all the other design, economic and environmental parameters held constant. As the

recuperator effectiveness is increased, the temperature of the exhaust stream exiting the

recuperator is reduced, thus resulting in a decrease in excess refrigeration and hence an

increase in the LCCR. A curve depicting changes in refrigeration revenue is also plotted

to demonstrate this effect. Any decrease in exhaust stream temperature also lowers the

LPC pressure ratio, reducing the HPRTE compactness and hence increasing the

equipment cost of the HPRTE, in comparison to a microturbine, as explained in the

earlier sections.

The effects of changes in economic parameters on the life cycle costs of both

technologies are also evaluated in this analysis. As mentioned earlier, the cost

coefficients of small gas turbines components like the HPC/HPT, combustor and the

power generator are taken to be a parameterized fraction (CCF) of the cost coefficients

modified by Traverso et al. [15] for components of large engines. Figure 5-8 shows the

effect of different values of the cost coefficient fraction (CCF) on the LCCR and PCR,

retaining the base-case values of other parameters. As observed from the figure, the effect













0.98


S- LCCR
Revenue Ratio


1.10

1.05
o

1.00 n

0.95

0.90

0.85


0.80


0.81 0.82 0.83 0.84 0.85 0.86 0.87 0.88
Recuperator Effectiveness

Figure 5-7.Effect of increase in the recuperator effectiveness on LCCR and PCR. Except
for the recuperator effectiveness, all design and economic parameters are
fixed and their base-case values retained (Tables 4.1, 4.2)


0.97

0.96

0.95

n 0.94

-J 0.93

0.92

0.91

0.90


1.20

1.15

1.10

1.05

1.00

0.95

0.90

0.85


0.3 0.4


0.6 0.7 0.8


Cost Coefficient Fraction

Figure 5-8.Effect of increase in the cost coefficient fraction (CCF) on LCCR and PCR.
Except for the CCF, all design and economic parameters are fixed and their
base-case values retained (Tables 4.1, 4.2)


0.97

0.96

n 0.95

-1 0.94

0.93

0.92


0.91


I- PCR
LCCR






-


I


1.15


, **


c









of changing the value of CCF does not have a very significant effect on the LCCR, with

just a small decrease in the LCCR with increasing values of cost fraction. This decrease is

due to the fact that for lower values of cost fraction, the difference between the costs of

gas turbine components common for both technologies, though in favor of the HPRTE, is

not very significant. Considering the fact that the HPRTE has additional components

which are independent of cost fraction, the total plant cost of the HPRTE becomes greater

than that of a microturbine for lower values of cost fraction. However as the cost fraction

increases, the difference in the costs of components common to both technologies

increases, offsetting the cost of additional equipment of the HPRTE and thus reducing

the PCR and hence the LCCR by a small value. Most importantly, these results

demonstrate the fact that the uncertainty associated with the value of cost coefficients,

because of the proprietary nature of cost information does not have a significant effect on

the cost ratios of the two technologies.

Figure 5-9 shows the effect of an increase in the discount rate specified by the

DOE, on LCCR, holding all the other design, environmental and economic parameters

constant. As seen from the figure, the LCCR is fairly insensitive to changes in the

discount rate, having a constant value with increasing discount rates. This discount rate

determines the UPV factors for calculating life cycle fuel costs and maintenance costs of

both technologies. The UPV factor to determine the life cycle revenues obtained from

refrigeration generated by the HPRTE-VARS combined system also depends on the DOE

discount rate.

Figure 5-10 shows the effect of change in the cost rate of natural gas on LCCR,

holding all the other parameters fixed. With an increase in the cost rate of natural gas,












0.97

0.96

0.95

0.94

0.93

0.92

0.91

0.90


DOE discount rate (%)


Figure 5-9.Effect of increase in the DOE discount rate on LCCR. Except for the DOE
discount rate, all design and economic parameters are fixed and their base-
case values retained (Tables 4.1, 4.2)



0.97

0.96

0.95


0.94

0.93

0.92

0.91

0.90


3 3.5 4 4.5


5 5.5 6 6.5


Cost rate of natural gas ($/MMBTU)

Figure 5-10. Effect of increase in the cost rate of natural gas on LCCR. Except for the
cost rate of natural gas, all design and economic parameters are fixed and
their base-case values retained (Tables 4.1, 4.2)


- -, --









there is a small increase in the value of LCCR. As observed for the base case, the cycle

efficiency of the microturbine is slightly higher than that of the HPRTE (Figure 5-3).

Hence for the same power, microturbine has lower fuel consumption as compared to the

HPRTE, resulting in lower fuel costs for the life cycle. With an increase in the cost rate

of natural gas, the difference between the life cycle fuel costs of both technologies

increases, in favor of the microturbine and this leads to an increase in the LCCR.

However, this increase is not very significant, thus showing almost constant values of

LCCR, even with uncertainty in fuel prices

Figure 5-11 shows the effect of change in the price rate of electricity on LCCR and

revenue ratio (RRev), keeping all other design, economic and environmental parameters

fixed and retaining their base-case values. As expected, the LCCR decreases with

increase in the price rate of electricity because of the increase in the revenues obtained

from the HPRTE-VARS combined system. However, this decrease is not very significant

and the value of LCCR can be considered to be in a fairly constant regime.

Apart from evaluation of the cost ratios, supplementary economic methods like the

net savings (NS), savings to investment ratio (SIR) and payback period are also evaluated

in this analysis. As explained earlier, the SIR and NS evaluated for a particular analysis

are consistent with the life cycle costs. The payback period, on the other hand does not

include the costs incurred after the payback time span is reached and hence is not

considered an effective measure of economic performance. For the base case parameters,

the net savings obtained from the HPRTE in comparison to a microturbine, is

approximately $76000. The SIR is calculated to analyze the effectiveness of the HPRTE,

over a microturbine and for the base case, its value is 2.15. This value is significantly










higher than 1, which is the qualifying value for any alternative in comparison to the base

case. The discounted payback period for recovering the additional investment made for

the HPRTE is a little less than four years. The results of this analysis indicate that, though

the cost ratios are influenced by the change in design parameters, they are more or less

insensitive to the uncertainty associated with the economic parameters.



0.97 1.25


0.96 1.20
LCCR 1.15
0.95 -- Revenue Ratio
1.10o
0.94 M
0 1.05
0.93
S* 1.00
0.92 *
0.95

0.91 0.90


0.90 .. 0.85
0.065 0.070 0.075 0.080 0.085 0.090 0.095 0.100
Price rate of electricity ($/kWh)



Figure 5-11. Effect of increase in the electricity price rate on LCCR and PCR. Except for
the price rate of electricity, all design and economic parameters are fixed
and their base-case values retained (Tables 4.1, 4.2)














CHAPTER 6
SUMMARY AND CONCLUSIONS

The primary aim of this analysis has been to compare life cycle costs of two

technologies, the HPRTE and the conventional microturbine, by evaluating costs like the

capital investment costs, energy costs and maintenance costs, incurred throughout the

lifespan of the engine. Since the cost information, particularly for the equipment costs of

the engines, is proprietary and hard to obtain, it is difficult to calculate a highly accurate

life cycle costs estimate of both technologies. However, for this analysis, same cost

functions, particularly for the equipment costs are used for both engines and the results of

this analysis are expressed in terms of cost ratios rather than the actual costs, ensuring

fairness of the cost comparison, even with the uncertainty in actual cost estimations.

These cost ratios are evaluated for different design, environmental and economic

parameters and cost ratios with values less than one indicate that the HPRTE is

economically beneficial in comparison to a microturbine.

One of the major factors that was found to influence the savings obtained from

using the HPRTE, in comparison to a microturbine, is the pressurized nature of this

engine. This leads to an increase in fluid density and makes the expensive, high

temperature components of the HPRTE compact as compared to those of a microturbine,

for the same power generated. The second major factor influencing the savings obtained

from the HPRTE is the revenue generated from excess refrigeration, which, for this

analysis, is converted into equivalent power for the purpose of revenue estimation. The

revenue from refrigeration is analyzed in terms of the revenue obtained from selling the









equivalent power Cost ratios determined for different design and economic parameters

may be analyzed in terms of these two factors.

The following is a summary of the major findings of this analysis:

* An increase in the HPT inlet temperature, keeping the other parameters unchanged
decreases the LCCR. This is due to an increase in refrigeration and hence revenue
from refrigeration with increasing HPT inlet temperatures. The LPC pressure ratio
of the HPRTE also increases, with increasing HPT inlet temperatures, making
components compact and reducing the total plant costs of the HPRTE.

* An increase in the HPT exit temperature increases the LCCR because of the
decrease in refrigeration. However, the cycle efficiency of both systems increases
initially with an increase in the HPT exit temperature, reaches a maximum and then
starts decreasing due to the decrease in the HPC pressure ratio. An increase in the
HPT exit temperature also reduces the LPC pressure ratio, thereby increasing the
HPRTE equipment costs. Another effect that is associated with the HPT exit
temperature of the HPRTE is the rise in the value of external refrigeration, after an
initial decrease. This is due to an increase in the recirculation ratio to maintain a
constant value of 0, thus generating more revenue from refrigeration for the
HPRTE.

* An increase in the LCCR is also observed with increases in recuperator
effectiveness and ambient temperature. This is attributed to decreases in
refrigeration revenue and LPC pressure ratios at higher recuperator effectiveness
and ambient temperature for the HPRTE.

* Apart from calculating the LCC of the two technologies, supplementary economic
measures like the savings to investment ratio (SIR), net savings (NS) and
investment payback period were also evaluated for this analysis. For the base case
analysis, the LCCR is 0.93, with a SIR of 2.15, NS of $ 76000 and a payback
period of 3.92 years.

* As discussed earlier, the main cost coefficients of the equipment costs of both
technologies were taken as a parameterized fraction (CCF) of the cost coefficients
of large engines. This is done to account for the relative inexpensive radial
technology of small gas turbines, as compared to the expensive axial technology of
large engines. However, the results indicate that the cost ratios are fairly insensitive
to the value of CCF as the same cost coefficients and cost functions are applied for
both technologies.

* Changes in economic parameters like the DOE discount rate, cost of natural gas
and cost of electricity showed little influence on the cost ratios. The LCCR showed
an almost constant value with changes in the DOE discount rate. Increase in the
cost of natural gas resulted in a small increase in the LCCR due to relatively higher
fuel costs of the HPRTE, in comparison to a microturbine. As expected, increase in









the cost of electricity resulted in a small decrease in the LCCR, because of the
increase in the revenue from refrigeration for the HPRTE. Overall, the results
indicate the fairly insensitive nature of the cost ratios to the uncertainty in
economic conditions.

* For this analysis, the revenue obtained from refrigeration, converted into equivalent
power, is calculated using a conservative price rate of electricity. However, this
price rate can be substantially higher for comparatively hot seasons and regions of
the country, where the external cooling produced will be of high importance, thus
coming at a higher price. This will increase the revenues from refrigeration of the
HPRTE resulting in a reduction in the LCCR.

As in the case of the HPRTE, a microturbine could also be integrated with a VARS

unit for cogeneration applications, thus generating external refrigeration along with

power. However, the fact that the HPRTE is a high-pressure engine would help it

maintain its cost advantage over a microturbine, as the higher cycle pressure will make

the expensive, high-temperature components of the HPRTE compact in comparison to

those of a microturbine. Since the gases of the HPRTE passing through the VARS unit

are at higher pressures, in comparison to those for the microturbine, the heat exchangers

of the VARS unit of the HPRTE would be compact, versus those for microturbine-VARS

system. This would reduce the equipment costs and hence the total life cycle costs of the

HPRTE, in comparison to a microturbine. Also, the additional investment required for the

VARS unit will offset some of the refrigeration revenue generated by a microturbine-

VARS system.

Furthermore, additional technical advantages may favor the HPRTE economically

for specific applications: compactness; fresh water production; reduced air/exhaust flow

rate and low emissions. Previous studies point out that water can be extracted naturally in

the HPRTE/VARS evaporator due to the high water vapor partial pressure and lower

condensation temperatures. This fresh water can be used for additional process cooling,









combined cycle applications, or human consumption, but in this analysis, there is no

economic credit claimed for the water extracted.

In another study related to the HPRTE, it has been demonstrated that the HPRTE

has significantly reduced CO, unburned hydrocarbons and NOx as compared to open

cycles. This can be reflected in terms of savings from environmental costs but also not

included in this analysis. Reduced air/exhaust flow of the HPRTE would also lead to

reduction in size of equipment like the exhaust duct and filtration system, though the

economic advantage gained from this is also ignored in this analysis.

Although the present results are encouraging for the HPRTE, further study is

required in order to account for additional factors that can be a potential source of

economic benefit, like the water extraction capability of the HPRTE. For future work, a

detailed thermo-economic analysis of the HPRTE-VARS combined cycle and a

microturbine-VARS combined cycle is recommended for more accurate estimation of

actual system costs. Effort should be made to make the cost coefficients of the cost

functions used in thermoeconomic analysis to be representative of the current equipment

cost, by getting some cost estimates from the manufacturers. This cost comparisons can

also be carried out by considering fuels other than natural gas like diesel.















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BIOGRAPHICAL SKETCH

The author obtained a bachelor's degree in mechanical engineering with honors, in

the year 2002. After working in a leading manufacturing firm for one year, the author

joined the master's degree program in the industrial engineering department at University

of Florida. After his post graduation in industrial engineering, the author hopes to

combine his technical and managerial skills in his future professional endeavors.