Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: P3.41 - Application of supercritical water Fluidized bed reactor in the process of coal gasification for hydrogen production
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 Material Information
Title: P3.41 - Application of supercritical water Fluidized bed reactor in the process of coal gasification for hydrogen production Experimental Methods for Multiphase Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Jin, H.
Lu, Y.
Guo, L.J.
Ge, Z.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: fluidized bed
supercritical water
hydrogen production
coal gasification
 Notes
Abstract: Hydrogen production by supercritical water gasification is a promising way for efficient and clean utilization of coal (Bermejo, 2004). Meanwhile, the blockage problem existing in the tubular reactor hinders the development of the supercritical water gasification technology (Lu, 2008). A novel supercritical water gasification system with a fluidized bed reactor was a good alternative to solve the problem. Supercritical water within the temperature region of 540℃~600℃ and pressure region of 23.5MPa~26.5MPa was used as fluidized medium and coal particles smaller than 96μm was used as both bed material and reactant for gasification. The minimum fluidization velocity and terminal velocity in certain experimental conditions were determined by the correlation equations introduced by Matsumura (2004). The flow rate of supercritical water was determined by evaluating the minimum fluidization velocity of coal particles with the thermodynamics properties of supercritical water. Hydrogen peroxide was selected as oxidant. Water-coal-slurry with the concentration of 30wt% was continuously stably gasified with no plugging observed. H2 occupied the largest part in the gaseous product in most conditions, followed by CO2 and CH4, and small amount of CO, C2H4 and C2H6 were also detected. The effects of parameters such as temperature, pressure, superficial velocity and concentration of water-coal-slurry were experimentally investigated. The gasification characteristics discipline of coal in supercritical water with a fluidized bed reactor was gained and the optimal parameters were selected. The yield of hydrogen was 14.99mol per kg of coal and the gasification efficiency was 92.60%. Supercritical water fluidized bed reactor demonstrated a bright future in the coal gasification technology for hydrogen production.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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Bibliographic ID: UF00102023
Volume ID: VID00529
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: P341-Jin-ICMF2010.pdf

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7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010



Application of supercritical water Fluidized bed reactor in the process of coal
partial oxidative gasification for hydrogen production


Hui Jin, Youjun Lu, Liejin Guo, and Zhiwei Ge

State Key Laboratory of Multiphase Flow in Power Engineering, Energy and Power Engineering, Xi'an jiaotong University
Xianning West Road 28#, Xi'an, 710049, China
lj-guo~mail.xitu.edu.cn

Keywords: fluidized bed, supercritical water, hydrogen production, coal gasification




Abstract

Hydrogen production by supercritical water gasification is a promising way for efficient and clean utilization of coal (Bermejo,
2004). Meanwhile, the blockage problem existing in the tubular reactor hinders the development of the supercritical water
gasification technology (Lu, 2008). A novel supercritical water gasification system with a fluidized bed reactor was a good
alternative to solve the problem. Supercritical water within the temperature region of 540"C~600"C and pressure region of
23.5MPa~26.5MPa was used as fluidized medium and coal particles smaller than 96 p m was used as both bed material and
reactant for gasification. The minimum fluidization velocity and terminal velocity in certain experimental conditions were
determined by the correlation equations introduced by Matsumura (I r I4,1. The flow rate of supercritical water was determined
by evaluating the minimum fluidization velocity of coal particles with the thermodynamics properties of supercritical water.
Hydrogen peroxide was selected as oxidant. Water-coal-slurry with the concentration of 30wt% was continuously stably
gasified with no plugging observed. H2 occupied the largest part in the gaseous product in most conditions, followed by CO2
and CH4, and small amount of CO, C2H4 and C2H6 WeTC 81So detected. The effects of parameters such as temperature, pressure,
superficial velocity and concentration of water-coal-slurry were experimentally investigated. The gasification characteristics
discipline of coal in supercritical water with a fluidized bed reactor was gained and the optimal parameters were selected. The
yield of hydrogen was 14.99mol per kg of coal and the gasification efficiency was 92.60%. Supercritical water fluidized bed
reactor demonstrated a bright future in the coal gasification technology for hydrogen production.


Introduction

Coal, as a traditional fossil fuel, will still be the major
energy resource in the foreseeable further. According to the
estimation of primary energy resources in the world crude
oil and natural gas are likely to be exhausted in the next
several decades. Unlike these two fossil fuels, coal can still
be utilized over the next 200 years. At present, coal is a
major source of energy, accounting for ~25% of the world
energy supplies and 40% of the world electricity
generation (Dry 2002). It is suggested that coal will
continue to play an important role in meeting the world's
increasing energy demands in the future. However, in order
to exploit its use it is necessary to reduce the considerable
emissions of CO2, SOx, NOx, particulate matter, and
hydrocarbons generated by coal-based processes, which lead
to air pollution and climate change (Sudiro& Bertucco,
2008). In response to increasing enviromnent concerns, the
development of cleaner and more efficient coal conversion
is necessary (Chen&Chen, 2007).
Regarding the utilization of coal, clean coal technology has
become a noticeable topic. Hydrogen is an important raw
material in the chemical industrials such as in the
manufacture of ammonia and methanol. The possibility of
H2 as a future energy source in the heating, electric power,
and transportation sectors will cause a huge increase in the


H2 demand. Hydrogen would be produced from a very
diverse base of primary energy feedstocks using the
resources and processes that are most economical or
consciously preferred. Hydrogen produced from coal will
play an important role during the transition to a
hydrogen-based energy economy (Mondal & Piotrowski,
2005). The hydrogen production from coal is one of the
clean coal technologies.
Fluidized bed gasifier with air, steam or oxygen as oxidant
is useful for gasifying coal due to high rates of heat and
mass transfer (Pohorely & Vosecks, 2006, Wang & Jin,
2009). Supercritical water can also be a ideal oxidant in
fluidized bed gasifier, Supercritical water has special
physical and chemical properties, high diffusion rates, low
viscosity, and the complete miscibility with gases and
organic, make it an excellent medium for homogeneous,
fast, and efficient reactions (Kruse & Dinjus, 2005).
Supercritical water has sound handling capacity for coal
gasification, because supercritical water can enhance the
hydrolysis reaction of ether bond, ester bond, and
heteroatom structure. What's more, supercritical water can
swell and soften the matrix of coal structure and enhance the
removal of the products (Li & Egiebor, 1992, Adschiri &
Sato, 2000). Relatively low temperature of SCW conversion
impedes formation of NOx and SOx, and closeness of the
system excludes emissions of fine ashes (Savage, 1999,




































































350 400 450 500 550 600
Temperature(oC)


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

complete oxidation by stoichiometry calculation
Greek letters
p Density (kg/m )
&u Viscosity (Pas)
Subscripts
p Particle
mf Minimum fluidization velocity
t Terminal velocity
f Fluid
g Gas

Determination of fluidization parameters

Minimum fluidization velocity
The minimum fluidization velocity can be obtained by
balancing two forces acting on the particle bed, namely, the
gravitational force and drag force from the fluid. And the
property of water is calculated based on Thermodynamic
and Transport Properties of Water (IAPWS-95). The
calculation method is based on the correlation equations
introduced by Matsumura (I r 4,1

Re, ,= (3j3.7) + 0.04084r) -33.7

4r =

uRe

Sd,p,
Coal particle is used as the fluidization particle with the
density as 1400kg/m and it is assumed that it can be
treated as a sphere with a diameter of 96 m. Minimum
fluidization velocity in different operational parameters are
shown in Figure 1. It can be seen that when temperature
increases, minimum fluidization velocity increases first and
then decrease. As pressure increases, minimum fluidization
velocity decreases. Within the typical operational region
(23-27MPa, 450-600 C ), the minimum fluidization velocity
is typical within the region of 0.6-1.5mm/s.


Vostrikov & Dubov. 2007). Bermejo reported that coal
gasification in supercritical water has higher energetic
efficiency than pulverized coal power plants and pressurized
fluidized bed power plant (Bermejo & Cocero, 2004).
Requirement is arisen for coal gasification in
supercritical water fluidized bed reactor; however, report
concerning fluidized bed gasifier operating in such severe
condition is quite limited. Matsumura (lrlt14, used alumina
particles with a diameter of 100 m and density of
3400kg/m3 behaving in a manner similar to the B particles
in Geldart's classification in supercritical water, and
introduce the calculation of minimum of fluidization
velocity and terminal velocity. Potic (2005) introduced the
concept of micro-fluidized bed and established a cylindrical
quartz reactor with an internal diameter of only 1 mm for
process conditions up to 500 C and 244 bar. Lu (2008)
established a supercritical water fluidized bed reactor
system in SKLMF (State Key Laboratory of Multiphase
Flow in Power Engineering) and realized continuous
gasification of 30wt% glucose and 18nt% corn cob
feedstock experiments to investigate the effects of solution
concentration, temperature, pressure and oxidant
concentration. Jin (2010) investigated coal gasification
characteristics in the supercritical water fluidized bed
reactor and realized stable gasification of 24wt% coal slurry
and proved the possibility of hydrogen production from coal
by supercritical water fluidized bed system and solved the
slugging problem existing in the tubular reactor(Li &
Guo,2010, Antal & Allen, 2000).
Hydrogen peroxide can also be added as oxidant to
further enhance the carbon gasification efficiency and
realize the stable gasification of coal slurry (Savage, 1999-
Matsumura & Minowa, 2005, Watanabe & Mochiduki-
2001). The aim of this article is the determination of the
minimum fluidization velocity and terminal velocity of coal
particle in certain experimental condition and the effects of
operational parameters upon gasification characteristics of
coal in supercritical water fluidized bed reactor were
experimentally investigated to prove the effectiveness of
supercritical water fluidized bed reactor in coal gasification
technology.

Nomenclature


0.0016.

0.0014.

0.0012.

o.oolo.

0.0008.

0.0006.


Reynolds number
Diameter (m)
Archimedes number


-23MPa
-24MPa
-25MPa
-26MPa
-27MPa


u Velocity (m/s)
g Acceleration of gravity (m1 i'
GE Gasification efficiency, mass of gaseous product
/ mass of dry matter in the water-coal-slurry
CE Carbon gasification efficiency, mass of carbon
element in gaseous product / mass of carbon in
dry matter in the water-coal-slurry
HE Hydrogen gasification efficiency, mass of
hydrogen gas / the mass of hydrogen in dry
matter in the water-coal-slurry
YH2 Yield of hydrogen, the mass of certain gas
product divided by the mass of dry matter in
feedstock
ER Oxidant equivalent ratio, amount of oxidant
added divided by the required amount for


Figure 1: Minimum
operational parameters


fluidization velocity in different


Terminal velocity
When the fluid velocity is high enough to carry away the
particles in the bed, the terminal velocity is achieved. Coal
particle is used as the fluidization particle with the density
as 1400kg/m and it is assumed that it can be treated as a
sphere with a diameter of 96 m. The calculation method is










































U..LD .. .. ..


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

the typical operational region (23-27MPa, 450-600%), the
minimum fluidization velocity is typical within the region
of 26-38mm/s, it is several dozens times of minimum
fluidization velocity.

Experimental Facility

Figure 3 shows the scheme of system for hydrogen
production in supercritical water with a fluidized bed reactor.
The fluidized bed reactor is made of 316 stainless steel. The
inside diameter of the fluidization part and suspension part
are 30mm and 40mm respectively. The whole length of the
fluidized bed reactor is 915mm. The designed temperature
and pressure are 65C9Cand 30MPa respectively. Five
K-armored thermocouples are equipped along the axial
direction of the reactor to measure the fluid temperature in
the reactor.
Coal particle is used as both reactant and bed material. The
distributor is located in the bottom of the reactor, and water
preheated to the desired temperature flows through the
distributor at the bottom to form a fluidization state. Coal
slurry flows into the reactor from the input above the
distributor. A metal foam filter is installed at the exit of the
reactor in order to prevent the bed material escaping from
the fluidized bed reactor. Detailed experimental device and
operational method can be seen in the literature (Lu & Jin,
2009).
The bituminous coal was produced from Shenmu, Shaanxi,
China, and the elemental analysis and proximate results can
be seen in Table 1. Pulverized coal was mixed with CMC
(sodium carboxymethyl cellulose) to realize continuous
delivery under high pressure. CMC was purchase from
Shanghai Shanpu chemical Co., Ltd.. 30wt% analytically
pure H2O, was purchased from Nanjing Specialty Gas Co.,
Ltd..


based on the correlation equations introduced by Matsumura


Re, = P~


u, = Re, <2
S18pu


2 < Re, < 500



500









-23MPa


-26MPa
-27MPa


0.038

0.036.

0.034.

0.032.

0.030.

0.028


350 400 450 5~00
Temperature(oC)


550 600


Figure 2: Terminal velocity in different operational
parameters

Terminal velocity in different operational parameters is
shown in Figure 2. It can be seen that when temperature
increases, terminal velocity increases first and then Within
decreases. As pressure increases, terminal velocity decreases.


Figure 3: Scheme of system for hydrogen production in supercritical water with a fluidized bed reactor 1 feedstock tank: 2,3
feeder; 4 fluidization bed reactor; 5 heat exchanger; 6 pre-heater; 7 cooler; 8,9,10 back pressure regulator; 11 high pressure
separator; 12 low pressure separator; 13,14 wet test meter: 15,16,17,18 high pressure metering pump; 19,20,21,22 mass flow
meter; 23 water tank


uP =~ ) d' j
225pP,

3.03g p, p, )d
u,=









Table 1 Analysis data of the Shenmu coal
Elemental analysis (wt %) Proximate analysis (wt %) Qb, ad
C H N S O"a M A V FC (MJ/kg)
69.63 3.75 0.80 0.41 12.25 5.31 7.85 30.92 55.92 27.826
*a Dl~ference


120


100 C
~GE
YH, 12
~-80
S60 8,

S40 a
c 4
20

0.0 0.1 0.2 0.3 0.4
ER(1)
(b)
Figure 5 Influence of ER upon gasification characteristics.
(580 C, 25MPa, 150g/min +15g/min, 4+2wt% coal + CMC)
(a) Gas Fraction (b) GE,CE,HE,YH2


90 120 150 180
Flow rate(g/min)

(b)
Figure 4 Influence of flow rate upon gasification
characteristics.(580 C 25MPa, ER=0.1, 4+2wt%
coal+CMC)(a) Gas Fraction (b) GE,CE,HE,YH2

and the terminal velocity is 35.12mm/s. The superficial
velocity is within the region between the minimum
fluidization velocity and the terminal velocity.
It can be seen from Figure 4 that, as the flow rate increases
from 90 g/min to 180g/min, both GE and CE increases,
because higher flow rate means higher superficial velocity


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


and lead to more intense fluidization state, in this situation,
the heat and mass transfer was more intensely enhanced, so
better gasification result was achieved. However, due to the
violent mixing caused by higher superficial velocity,
hydrogen produced by gasification reaction can easily react
with the oxidant, so from figure 4 it can be seen that, when
the superficial velocity is higher, hydrogen fraction is lower.
It is interesting to find that as flow rate increases, HE and
YH2 inCTreSes first and then decreases. Because when the
flow rate is low, the factor of enhance of heat and mass
transfer dominates, so it favours hydrogen production, while
when the flow rate is high, the reaction between hydrogen
and oxidant dominants.

Effect of ER
It can be seen from Figure 5 that ER influences the
gasification characteristics from two points of view. (1)As
ER from 0.0 to 0.4, GE increases from 47.01% to 92.59%.
Because oxidant in supercritical water can generate in-situ
heat and enhance the gasification to prevent the heat
resistant. Hydrogen peroxide in supercritical water can
generate active free radical and help decompose the
intermediate from the reaction, so gasification is enhanced.
(2) In fluidized bed reactor, oxidant and hydrogen produced
mixes and reacts, so certain amount of hydrogen is
COHSumed, as we can see from figure 5 that as ER increases,
hydrogen fraction decreases while carbon dioxide fraction
increases. When ER equals 0.0, HE is 107.52%, more that


The composition of the gaseous phase was measured by
Agilent 7890A gas chromatograph, which is equipped with
thermal conductivity detector and capillary column C-2000
that was purchased from LanZhou Institute of Chemical
Physics in China. High purity He was used as carrier gas
with a flowrate of 30ml/min.

Results and Discussion

Effect of fluidizing velocity
The flow rate of plunger metering pump was adjusted from
90 g/min to 180g/min to investigate the effect of various
fluidizing velocity. As the flow rate of the preheated water
increases from 90 g/min to 180g/min, the superficial
velocity increases from 16.2mm/s to 32.4mm/s. The
property of water is based on 580 0, 25MPa, using the
Thermodynamic and Transport Properties of Water
(IAPWS-95). Meanwhile as for the coal particle applied in
the reactor, the minimum fluidization velocity is 1.22mm/s


me

eco
IH


mc,
O CO,
SCH,
Sco
WH


Flow rate(g mn)

(a)


HE
tCE.
GGE
YH,


S60

03 30


ER(1)























































1 0


80 t j
GE
YH2 18E
S60

S40 4


20C ,---- -
6 12 18 24 30
Concentration(wt%)

(b)
Figure 7 Influence of concentration upon gasification
characteristics (25MPa, ER=0.1, 150g/min +15g/min, 580 C)
(a) Gas Fraction (b) GE,CE,HE,YH2

supercritical water within the experimental region
investigated. As mentioned above, ionic reaction pathway
was favoured in higher pressure, so gas production reaction
is inhibited (Buhler & Dinjus, 2002). In addition, higher
preSsure leads to higher water density and higher ionic
product, leading to the acceleration of the rate of hydrolysis
reactions and the improvement of extraction of volatile
component from coal. Higher pressure is not favourable
for gas formation according to the Le Chatelier's principle
because the volume expansion during the gasification. Due
to the combination of the mentioned above, pressure in fact
had no significant effect upon gasification characteristics of
coal in supercritical water seen from the experimental
results.


540 560 580 600
Temperature(oC)
(b)
Figure 6 Influence of temperature upon gasification
characteristics (25MPa, ER=0.1, 150g/min +15g/min,
4+2wt% coal+CMC) (a) Gas Fraction (b) GE,CE,HE,YH2

Concentration
Figure 8 showed that when the concentration of the slurry
equaled 6wt%, the hydrogen fraction and the GE were
44.82% and 51.24% respectively. The HE was 88.15%. If
the concentration of coal slurry increases, the hydrogen
fraction decreases while the methane fraction increases. It
can be seen the competition of hydrogen element between
H2 and CH4, Which is similar to the regulation obtained by


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Antal (2000) As the concentration increased, the
gasification efficiency decreased.
The slurry of 28wt% coal and 2wt% CMC could be
continuously gasified in the fluidized-bed reactor without
plugging problems. High concentration means high
handling capacity but high concentration usually leads to
incomplete gasification and plugging problem (Antal &
Allen, 2000). So it is meaningful to find out the optimal
concentration of coal slurry.

Pressure
23.5MPa, 25MPa and 26.5MPa were selected to investigate
the effect of pressure. The experimental results are shown in
Figure 7. The hydrogen fraction and HE peaked when the
pressure was 25MPa, but the deviation was not obvious. As
for CE and GE, there are on significant difference in
different pressure. So, generally speaking, pressure had no
significant effect upon coal gasification characteristics in


unity. Because hydrogen produced was not only released
from coal but also from supercritical water.

Temperature
lonic pathway preferred at higher pressures and/or lower
temperatures and free radical degradation reaction pathways
preferred at lower pressures and/or higher temperatures are
two competing reaction pathways in supercritical water, and
gas is the typical product from the latter (Buhler & Dinjus,
2002). High temperature means higher reaction rate which
favours gasification reaction. However, higher temperature
means lower density of water when the pressure is kept
constant and lower density of water inhibits the extraction
reaction of volatile and hydrolysis reaction.
It is can be seen from Figure 6 that as the temperature of
reaction fluid increased from 540 C to 600 0, the fraction
of hydrogen increased from 41.66% to 48.26%. The yield of
hydrogen increased from 8.83mol to 13.66mol per kilogram
of coal. GE increased from 48.48% to 59.16%. It is obtained
that HE was more than unity. It was proven that hydrogen
element in water was released to gaseous products.
Temperature has a significant enhancement on coal
gasification result in supercritical water.


m c,
O co
O CH
Sco
mH,


IC2
O CO2
OCH,
OCO
M H,


Concentration(wt%)


Temperature(oC)


HE
eCE
~GE
YH,






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


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mH2
OCO
O CH4
O CO2
mC2


25
Pressure(MPa)


20 HE
O CE
mGE
15 UYH
150



5


Pressure(MPa)
(b)
Figure 8 Influence of pressure upon gasification
characteristics (580 0 ER=0.1, 150g/min +15g/min-
4+2wt% coal+CMC) (a) Gas Fraction (b) GECE,HE,YH2

Conclusions

A novel supercritical water gasification was established in
SKLMF to realise the clean and efficient coal conversion-
and the gasifier was a supercritical water fluidized bed
reactor. Coal particle smaller that 96 p m was selected as
both the bed material and reactant. The fluidization
parameters such as minimum fluidization velocity and
terminal velocity were determined by the correlation
equations introduced by Matsumura so as to select the flow
rate of superficial velocity. Experimental results showed that
hydrogen peroxide proved to be an effect oxidant. 30wt%
coal slurry was continuously gasified. Coal gasification
efficient reached 92.60% in only 580 0. Hydrogen faction
in gaseous product reached 55.49%. Different operational
parameter influences the gasification result differently.
Temperature has the most significant enhancement upon
gasification characteristics and higher superficial velocity
favours and higher oxidant equivalent ratio favours
gasification efficiency. Supercritical water fluidized bed
reactor proved to be an efficient apparatus for coal partial
oxidative gasification.

Acknowledgements

This work is currently supported by the National Key
Project for Basic Research of China through Contract No.
2009CB220000 and the National High Technology Research
and Development Program of China (863 Program) through
contract No. 2007AAO5Z147.






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


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