Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: P3.28 - Experimental study on effects of different inlet conditions on iron ore pellets drying process
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 Material Information
Title: P3.28 - Experimental study on effects of different inlet conditions on iron ore pellets drying process Droplet Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Zhang, Y.
Feng, J.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: iron ore pellet
drying
experimental study
grate-kiln
energy-saving
packed bed
 Notes
Abstract: The drying of iron ore pellet is a bottleneck for pellet quality and increasing production in pelletising process. An energy balance test was systematically carried out on a grate-kiln in China. And the results show that energy consumption resulting from drying accounts for 28% in the total amount of energy required for pellet induration. Therefore, any small improvement in the drying performance of grate-kiln can lead to considerable energy-savings. We set up an experimental facility to simulate the real industrial flow states. Series of experiment have been performed to investigate the drying characteristics of iron ore pellet packed bed between 200 and 300℃. And the effects of different inlet conditions on the drying process are studied. Also, the regressions of drying rate and time are obtained. In a word, this study provides a better understanding of the objective law of iron ore pellet drying process in the grate-kiln or straight-grate and helps to economize energy.
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
 Record Information
Bibliographic ID: UF00102023
Volume ID: VID00522
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: P328-Zhang-ICMF2010.pdf

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Paper No 7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Experimental study on effects of different inlet conditions on iron ore pellets drying process



Yu Zhang, Junxiao Feng

Thermal Science and Energy Engineering Department, School of Mechanical Engineering, University of Science and
Technology Beijing
No.30 Xueyuan Road, Haidian region, Beijing, P.R. China




Keywords: iron ore pellet, drying, experimental study, grate-kiln, energy-saving, packed bed




Abstract

The drying of iron ore pellet is a bottleneck for pellet quality and increasing production in pelletising process. An energy
balance test was systematically carried out on a grate-kiln in China. And the results show that energy consumption resulting
from drying accounts for 28% in the total amount of energy required for pellet induration. Therefore, any small improvement
in the drying performance of grate-kiln can lead to considerable energy-savings. We set up an experimental facility to simulate
the real industrial flow states. Series of experiment have been performed to investigate the drying characteristics of iron ore
pellet packed bed between 200 and 300"C. And the effects of different inlet conditions on the drying process are studied. Also,
the regressions of drying rate and time are obtained. In a word, this study provides a better understanding of the objective law
of iron ore pellet drying process in the grate-kiln or straight-grate and helps to economize energy.


Introduction

Iron ore pellet is an important agglomerated feedstock
for blast and DRI processes. And pelletising is the first step
in the production of these pellets. There are three kinds of
pelletising process: the straight-grate, shaft, and
grate-kiln-cooler (GKC). Compared to the shaft or
straight-grate furnace, the GKC furnace is more promising
partly because of advantages in low consumption of high
temperature-resistant alloy steel and apt for larger scale
production, partly because of characteristics of better pellet
quality and low electric power consumption. Due to these
advantages, the GKC process has attracted more and more
attention (Croft & Cross et al. 2009; Liu & Li et al. 2009).
And The GKC process has been widely used in China
recently.
The drying process is a bottleneck for pellet quality and
increasing production in pelletising process. An energy
balance test was systematically carried out on a grate-kiln in
China. The results show that energy consumption resulting
from drying accounts for 28% in the total amount of energy
required for pellet induration. Therefore, any small
improvement in the drying performance of grate-kiln can
lead to considerable energy-savings.
Many pioneers in modeling of complete GKC systems
established the energy balance models of iron ore pellet
induration (Young & Cross et al. 1979; Thurlby 1988a:
Thurlby 1988b: Thurlby 1988c). Also, in pilot scale
pot-grate, Kililikada & Thibault et al. (1994) paved the way
for induration modeling. Recently, Tsukerman & Duchesne
et al. (2007) studied the drying kinetics of individual iron
oxide pellet, and Forsmo & Forsmo et al. (2008)


investigated the mechanisms in oxidation and sintering of
magnetite iron ore green pellet. Other research mainly
involves pellet strength predictions (Batterham 1986:
Dwarapudi & Gupta et al. 2007), computational fluid
dynamics (CFD) analyses (Croft & Cross et al. 2009), gas
leakages problem (Afzal & Cross 1994), thermo-physical
properties of iron ore pellet (Sundarmurti & Rao 2002),
effects of partial melting and melt phase formation on the
induration energy balance (Firth & Manuel 2005), and
control (Pomerleau & Pomerleau 2003). Thurlby and
Batterham (1980) is the only paper showing measurements
of pellet temperature during drying (Tsukerman &
Duchesne et al. 2007). Tsukerman & Duchesne et al. (2007)
studied the single iron ore pellet drying behaviour by
measuring the pellet temperature and mass. To our
knowledge, there is no open literature published for
investigating the drying behaviour of iron ore pellet packed
bed by measuring the pellet temperature and mass
simultaneously.
In the paper, we set up an experimental facility to
simulate the real industrial flow states. Series of experiment
have been performed to investigate the drying
characteristics of iron ore pellet packed bed between 200
and 300"C. And the effects of different inlet conditions on
the drying process are studied.

Nomenclature


height of pellet packed bed (layer number)
moisture content (dry basis) (%)
pellet mass (dry basis) (kg)





































Level 1 10 200 1.0 8 2
Level 2 12 250 1.5 10 3
Level 3 14 300 2.0 12 4

Table 5 Drving conditions
Condition Diameter Air Air Water Bed
(mm) temperature velocity (\vt oo) height
( c) (m s) (layer)
1 10 200 2.0 8 2
2 10 250 1.0 10 3
3 10 300 1.5 12 4
4 10 200 1.0 10 3
5 12 250 2.0 12 3
6 12 200 1.0 10 4
7 12 200 1.5 8 3
8 12 300 1.0 10 2
9 14 300 2.0 10 3
10 14 200 1.0 12 2
11 14 200 1.5 10 3
12 14 250 1.0 8 4
13 12 200 2.0 10 4
14 12 300 1.0 8 3
15 12 250 1.5 10 2
16 12 200 1.0 12 3

The moisture content can be written as:
m
M (%d.b) (1)
m,
The drying rate of pellet can be expressed as:
dMll
y, =(2)
dt
The experimental direct measurement error is shown in
Table 6. And the indirect measurement error of the moisture
content is 0.37%, whereas that of the drying rate 23.12%.

Table 6 Direct measurement error
Items Instnuments Accuracy Relative error (oo)
Diameter Calipers 0.05mm 0.625
Alass Electric balance 0.001g 0.0164
Temperature thermo couples l o 4.347

Flow mte Rtmet r 0.1m3/h .5


Experimental Facility

The drying experimental facility is shown in the Fig.1. It
consists of 9 main components: the fan, valve, flow meter
heating section, resistance heater, experimental section,
thermocouples, temperature controller, and fixing stand.
And it can simulate flow states which temperature ranging
from environmental temperature to 300 oC and velocity
from 1 to 3 ms '.











Figurel: The schematic diagram of the drying facilitV.
1-experimental section 2-heating section 3-resistance
heater 4-fixing stand 5-fan 6-valve 7-flow meter
8-thermocouples 9-temperature controller

The resistance heater consists of 12 resistance wireS
that are installed in 12 quartz glass tubes respectively. And
its power is 9kW. In order to minimize the current of
circuit, the star connection is used for the 12 resistance
wires, which is divided to 3 groups. The outer diameter of
the quartz glass tubes is 8mm. The quartz glass tubes are
bundled with asbestos ropes, and installed within an outer
steel pipe. The role of the asbestos ropes lies in fixing the
quartz glass tube and isolating the tube and outer pipe.
Further, roots blower is used, and its model
L11x14LD-1. And the measurement of flow rate has been
preformed by glass rotameter (LZB-25). And temperature
controller consists of temperature indicator (XMTA-2201)
and relay. The inner diameter of experimental section is
48mm.

Results and Discussion

The drying behavior of iron ore pellet packed bed was
investigated using the experimental facility. And the recipe
of the pellet is presented in Table 1, 2, and 3. The pellets
were balled to an average diameter between 10 to 14 mm
(Table 5).

Table 1 Chemical components of the magnetite concentrateS
Chemical
comonnt TFe FeO SiO
Content 66.79% 27.1% 4.65%


Paper No


pellet mass (wet basis) (kg)
pellet diameter (m)
flow temperature (K)
time (s)
flow velocity (m's')
initial moisture (wt%)
ordinal number of pellet layer
drying rate (kg-s-'kg' dry basis pellet)
drying time (s)


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

Table 2 Chemical components of the bentonite
Chmial SiO? CaO MgO AlaO3
component
Content 60% 1.75% 3.17% 13.37%
Grain size 100% 0-74 pm


Table 3 Chemical components of the coke
Chemical Fixed Volatile
component carbon Ah matter Wae
Content 78.45% 6.88% 13.84% 0.83%

We applied the orthogonal experimental method to
study the drying behaviour of pellet packed bed. According
to the orthogonal experimental method, 16 kinds of drying
conditions are set, and temperature ranging from 200 oC to
300 oC, flow velocity ranging from 1.0 m/s to 2.0 m/s, and
moisture content ranging from 8% to 12%. And
arrangement of the experiment is presented in Table 4 and 5.


Table 4 Drving factor level
Diameter Air
(mm) temperature


Air
velocity
(m s)


Water
(\vt o)


Bed
height
(laver)




































. . .


-m- 1st layer pellet
-*-2ndlayer ple
3rd layer pellet
-v- 4thlaeplet



*- --i


-. - a


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


Paper No


Figure 2 shows the pellet surface temperature as
function of time under do ing condition 3. It can be seen
from the picture that the temperature of first layer pellet is
higher than that of others layers pellet, except for the initial
time. And after 1000s, curves of pellet surface temperature
flatten out gradually.


S0 0000.
.


S0 0004 -



00002-
0 00-


\, -a-1-st layer pellet
d--2dlaayeerrpe
g -7- 4t layer pellet








0 200 400 600 800 1000 1200 1400
Time (s)


-m-1- st layer pellet
-*-2nd layer ple
-Y- Maye pellet


Figure 4: Experimental pellet doing rate under doing
condition 3.


Figure 5 shows that the do ing rate as function of
moisture under do ing condition 3. The do ing rate
increases at first, and then its trend flattens out, and at last
decreases sharply. Due to few experimental points, the
drying characteristics are not seen obviously at moisture
ranging from 0.75 to 2.25.


0 200 400 600
Time


800 1000 1200 1400


Figure 2: Experimental pellet surface temperature under
do ing condition 3.


Figure 3 shows the pellet mass as function of time
under do ing condition 3. It can be seen from the figure that
the pellet mass decreases dramatically in the first duration of
400s. And after which, the curves flatten out gradually.


S0 0006 -



>`0 0002-



--0 0000 -


--- 1st layer pellet
-*- 2nd layerple
3rd layer pellet
--7- 4th layer pellet


00 05 10 15 20 25 30 35
Moisture (kg)


Figure 5: Experimental
under do ing condition 3.


pellet do ing rate vs moisture


S200 400 600
Time


800 1000 1200 1400


Figure 6 shows that the experimental pellet surface
temperature as function of time under condition 6. The
pellet surface temperature increases dramatically at first,
and then its trend flattens out, and after which increases
sharply again, and after 1000s its trend flattens out
gradually.


Figure 3: Experimental pellet mass under do ing condition



Figure 4 shows the pellet do ing rate as function of
time under do ing condition 3. The do ing rate of the first
layer pellet is higher than the second one, because the
temperature difference between the pellet and flow of first
layer pellet is higher than that of the second one. And the
curve of second layer pellet lags behind the first one.
Similar trend is also observed in other layers. Further, no
constant do ing rate phase is found obviously. And the trend
is similar to the trend that was shown in Test 1 of the
literature (Tsukerman & Duchesne et al. 2007). It can be
seen from the figure that the duration of first do ing stage
for the first, second, third, and fourth pellet layer is about
100s, 130s, 150s, and 240s respectively. And after 900s,
curves of do ing rate flatten out gradually, and
correspondingly that of temperature (Fig.2).


0 2b00 4~00 600 8 b 'l00 1000 120 1400
Time (s)


Figure 6: Experimental pellet surface temperature under
do ing condition 6.


s aee petlet
" t-nlae
























-m- 1st layer pellet
-*- -2nd layerpelt
3rd layer pellet
-r- 4thlaeplet



m-m-a---a-a--m


-m-1- st layer ple
-*-2nd layer ple
3rd layer ple
-v- 4th lyrple








'' 'm'a-. W=---'


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


Paper No


Figure 7 shows that the pellet mass as function of time
under condition 6.


290 -
28 5-
28 0 -
27 5-
27 0 -
265-
~i260-


245-
240 -
$23 5
230-
22 5
22-
220-


--1Ist layer pellet
-*- -2ndlayer ple
3rd layer pellet
--7- 4th lyrple



r---T--


0 200 400 600 800
Time (s)


1000 1200 1400


S2000 4000 6000 8000
Time (s)


10 00 12000


Figure 10: Experimental pellet mass under drying
condition 12.


Figure 11 shows the pellet drying rate as function of
time under drying condition 12. And after 1100s, curves of
drying rate flatten out gradually, and correspondingly that of
temperature (Fig.9). The transition is a little longer than that
under drying condition 3.


Figure 7: Experimental pellet mass under drying condition




Figure 8 shows that the pellet drying rate as function of
time under drying condition 6. And after 4000s, variation of
drying rate is negligible. The transition is about 4 times than
that under drying condition 3.


S0 0004 (
-

,00003 -


,0 0002 -


910 0001 -


~0 0000-


S0 00040 -
0 00035s-
1000030 -






y0 00000 -

-0000005-


--- 1st layer pellet
-*- -2nd layerpelt
3rd layer pellet
-v- 4thlaeplet









0 2000 4000 6000 8000 10000 12000
Time (s)


-200 200 400 600 800 1000 1200 1400
Time (s)


Figure 11: Experimental pellet drying rate under drying
condition 12.


Figure 12 shows the pellet surface temperature as
function of time under drying condition 13.


Figure 8: Experimental pellet drying rate under drying
condition 6.

Figure 9 shows the pellet surface temperature as
function of time under drying condition 12.


-m st layer pellet
-*-2ndlayerpelt
3rd layer pellet
-r- 4thlaeplet




800 1000 1200 1400


0 200 400 600
Time


0200 400 600 800 1000 1200 1400
Time (s)


Figure 9: Experimental pellet surface temperature under
drying condition 12.


Figure 10 shows the pellet mass as function of time
under drying condition 12.


Figure 12: Experimental pellet surface temperature under
drying condition 13.


Figure 13 shows the pellet mass as function of time


-a-1- st layer pellet
-*-2nd layer ple
3rd layer pellet
-r- 4th lyrple





















































00006


-m- 1st layer pellet
--*- ndlaayeerrpet
-v-4t layer pellet



9 5 M=-W T-'




) 0 200 400 600 800 1000 1200 1400 1600
Time (s)


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

2 2
2'2=-151+4.87500r -0.18750r -17,, +4,, +0.11750T 4

-0.00025T +20.6875 ,+23.625h, 5h2


Last, several drawbacks are in the experiment. First,
the inner diameter of the experimental section is 48mm,
which is only about 4 times than the pellet diameter. So, the
wall effect is negligible. Second, we only measured the
pellet surface temperature and not got the inner temperature
prOfile of individual pellet. Therefore, further improvement
in experimental facility needs to be preformed.

COnclusions

From the study, the following conclusions can be
drawn:
(1) The experimental study has been conducted to
investigate the drying characteristics of iron ore pellet
packed bed.
(2) The effects of different inlet conditions on drying
characteristics of the pellet packed bed are studied. And
the results reveal that the constant drying rate phase
arises in condition 13, whereas does not in condition 3,
6 and 12.
(3) The regressions of drying rate and time are obtained.
(4) There are several drawbacks in the experimental facility,
and further improvement needs to be carried out.

Acknowledgements

The authors gratefully acknowledge the High-Tech
Research and Development Center of the China Ministry of
Science and Technology. And this work is fully financed by
the National High-Tech Research and Development 863
prOgram of China under Grant No.2007AAO5Z215.

References

Afial, M. & Cross, M. GASFLO--Airflow
distribution evaluation software tool for ducting systems of
pellet induration processes. Appl Math Model, Vol. 18,
408-414 (1994)

Batterham, R.J. Modeling the development of strength
in pellets. Metall Trans B, Vol. 17B, 479-485 (1986)

Croft, T.N. & Cross, M. Slone, A.K. Williams, A.J.
Bennett, C.R. Blot, P. Bannear, M. Jones, R. CFD analysis
of an induration cooler on an iron ore grate-kiln pelletising
process. Miner Eng, Vol. 22, 859-873 (2009)

Dwarapudi, S. & Gupta, P.K. Rao, S.M. Prediction of
iron ore pellet strength using artificial neural network
model. ISIJ Int, Vol. 47, 67-72 (2007)

Firth, A.R. & Manuel, J.R. Thermal implications of
phase transformations during induration of iron ore pellets
produced from hematite. ISIJ Int, Vol. 45, 1561-1566
(2005)

Forsmo, S.P.E. & Forsmo, S.-E. Samskog, P.-O.
Bjdrkman, B.M.T. Mechanisms in oxidation and sintering


Paper No


under drying condition 13.


275-
270-
265-

S250-
S245-
1240-




-230


*\
*
g
*
*- *-


.


-m-1- st layer pellet
-*-2ndlayerple
3rd layer pellet
-r- 4thlaepeet
-- --


. --


0 200 400 600 800 1000 1200 1400 1600


Time (s)


Figure 13: Experimental pellet mass under drying
condition 13.


Figure 14 shows the pellet drying rate as function of
time under drying condition 13. The picture shows that there
is a constant drying rate phase obviously. And the phase is
similar to the trend in Test 5 of literature (Tsukerman &
Duchesne et al. 2007). It can be seen from the figure that the
duration of first drying stage for the first, second, third, and
fourth pellet layer is about 80s, 150s, 200s, and 220s
respectively. And after 1000s, curves of drying rate flatten
out gradually, and correspondingly that of temperature
(Fig.12). The transition is compared to that under drying
condition 12.


S00004-

Y~00003-
000-
000-


00000-


Figure 14: Experimental pellet drying rate under drying
condition 13.


We applied the method of Levenberg-Marquardt and
general global optimization, and the following regression
equations are gained.
The drying rate expression is as follows:

'1 = -16.3472 +0.0088T -0.0007T2 -2.7837h+0 .6926h
2 2 (3)
8.1743 -12.2616x + 4.0872x + 0.0007t 0.0002t


1-1.4863x+0.4971x2+ 0.0024t


The expression of drying time is written as:






Paper No 7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

of magnetite iron ore green pellets. Powd Tech, Vol. 183,
247-259 (2008)

Kililikada, K. & Thibault, J. Hodouin, D. Paquet, G
Caron, S. Modelling of a pilot scale iron ore pellet
induration furnace. Can Metall Q, Vol. 33, 1-12 (1994)

Liu, J.Y. & Li, F. Liu, J. Zhang, Y. and Wang, Y.L.
Micro-analysis of high-temperature oxidation-resistance of
a new kind of heat-resistant grid plate in grate-kiln. Int J
Miner Metall Mater, Vol. 16, 632-639 (2009)

Pomerleau, D. & Pomerleau, A. Hodouin, D. Poulin,
E. A procedure for the design and evaluation of
decentralized and model-based predictive multivariable
controllers for a pellet cooling Process. Comput CH E, Vol.
27, 217-233 (2003)

Sundarmurti, N.S. & Rao, V Thermal conductivity
and diffusivity of iron ore pellet having low porosity. ISIJ
Int, Vol. 42, 800-802 (2002)

Thurlby, J.A. A dynamic mathematical model of the
complete grate/kiln iron-ore pellet induration process.
Metall Trans B, Vol. 19B, 103-112 (1988a)

Thurlby, J.A. Gas flow and pressure balancing in
modeling grate/kiln induration. Metall Trans B, Vol. 19B,
113-121 (1988b)

Thurlby, J.A. Energy cost minimization in grate/kiln
induration. Metall Trans B, Vol. 19B, 123-132 (1988c)

Thurlby, J.A. & Batterham, R.J. Prediction of drying
and spelling behaviour of hematite pellets. Trans Inst Min
Metall, Vol. 89C, C125-C131 (1980)

Tsukerman, T. & Duchesne, C. Hodouin, D. On the
drying rates of individual iron oxide pellets. Int J Miner
Process, Vol. 83, 99-115 (2007)

Young, R.W. & Cross, M. Gibson, R.D. Mathematical
model of grate-kiln-cooler process used for induration of
iron ore pellets. Ironmak Steelmak, Vol. 6, 1-13 (1979)




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