4018
Ind. Eng. Chem. Res. 2008, 47, 4018–4024
Voidage and Pressure Profile Characteristics of Sand-Iron Ore-Coal-FCC Single-Particle Systems in the Riser of a Pilot Plant Circulating Fluidized Bed M. Das, B. C. Meikap,* and R. K. Saha Department of Chemical Engineering, Indian Institute of Technology (IIT), Kharagpur, Dist. Midnapur (W), West Bengal, 721 302, India
Hydrodynamic behaviors of single system of particles were investigated in a circulating fluidized bed (CFB) unit. Particles belonging to Geldart groups A and B like sand of various sizes (80, 300, 417, 522, 599, and 622 µm), FCC catalyst (120 µm), iron ore (166 and 140 µm), and coal (335 and 168 µm) were used to study the hydrodynamic characteristics. Superficial air velocity used in the present study ranged between 2.01 and 4.681 m/s and corresponding mass fluxes were 12.5-50 kg/(m2 s). A CFB needs the creation of some special hydrodynamic conditions, namely a certain combination of superficial gas velocity, solids circulation rate, particle diameter, density of particle, etc. which can give rise to a state wherein the solid particles are subjected to an upward velocity greater than the terminal or free fall velocity of the majority of the individual particles. The hydrodynamics of the bed was investigated in depth and theoretical analysis is presented to support the findings. Based on gas-solid momentum balance in the riser, a distinction between apparent and real voidage has been made. The effects of acceleration and friction on the real voidage have been estimated. Results indicated a 0.995 voidage for higher superficial gas velocity of 4.681 m/s. Introduction Fast fluidized bed (FFB) is an emerging technology, having application in chemical, mineral, and metallurgical industries as well as in the power sector units. It assumes importance where high specific transfer rates, large solid throughputs, and thermal uniformity within the reactor are required.1,2 Fast fluidized bed is described as a dense entrained suspension, characterized by an aggregative state in which much of the solid is segregated in relatively large and densely packed group of particle.3 The solid is highly turbulent and displays extensive backmixing. As high-velocity gas is used to circulate an appropriate quantity of solid particles during the operation, it is possible to maintain almost all hydrodynamic regimes of a fluidized bed system, from bubbling to pneumatic conveying, with FFB lying in between. Fast bed consists of a dense phase region near the bottom, a dilute phase at the top, and a transition regime in between.4 With gradual increase in gas velocity, for a fixed solids circulation rate, the dense phase at the bottom further expands and slowly transforms into a dilute bed. Again with the increase in the solids circulation rate, at a constant gas velocity, the height of the dense zone at the bottom steadily rises and the system is said to be converted into a dense bed transport regime.5 Li et al.6 obtained extensive data on pressure drop and voidage in a fast fluidized bed, while using a wide range of materials such as alumina powder (54 µm), FCC catalyst (56 µm), iron pyrites, fly ash (56 µm), and iron ore powder (105 µm). A series of plots of voidage versus height of the riser was presented from the axial voidage distribution; they demonstrated the coexistence of the dense and dilute phases. They have also investigated the effects of operating pressure on axial voidage profile in FFB. Kojima et al.7 measured the velocity and static pressure profile in a CFB8 and observed that the local particle velocity at the axis of the bed increased with an increase in the gas velocity. Choi et al.9 measured the axial voidage profile in a cold model * To whom correspondence should be addressed. E-mail: bcmeikap@ che.iitkgp.ernet.in.
CFB of sand particles. Correlations were presented to predict solids circulation rate and axial voidage profile in the bed. Kato et al.10 investigated the local structure of gas particle flow in a CFB in three typical fluidization modes from the pressure measurements. They further observed that the particle hold-up distribution was affected by the superficial gas velocity and solids circulation rate. Literature survey also reveals that studies on the hydrodynamics of circulating fluidized bed for reduction of Fe ores with CO and H2 have been reported. The particle size distribution of the ore was degraded at high gas velocity and by turbulent.11 A detailed summary of the work carried out by various investigators for single systems is given in Table 1. Literature survey also reveals that the work carried out in the past few decades includes particles in border narrow range. The studies were mainly carried out for the noncatalytic processes on CFB. Few studies have been reported for catalytic systems with very high solid circulation. However, the wide range of particles in CFB has not been reported. Therefore, in the present studies an attempt has been made to study the hydrodynamic characteristics of a CFB with wide range on a single type of particle (coal, FCC, iron ore, sand). Experimental Setup and Technique A circulating fluidized bed made of Plexiglas was used as the experimental apparatus. It consisted of a riser, a cyclone, and a bag filter to separate the fines, a downcomer, a slow bed, and the transfer line connecting the slow and fast bed. The solids, after passing through the fast bed in the riser, get separated in the cyclone and bag filter, descend downward through the downcomer, and are collected in the slow bed and then transferred back into the riser. The CFB system being used here is schematically shown in Figure 1 and the detailed equipment characteristics is same as that reported by Das et al. (2007). Air at controlled rates is supplied to the fast bed (0.1015 m diameter and 5.83 m in height) from a root blower through a multihole distributor plate having 12% open area. A small amount of air from a bypass line is also sent to the slow bed to keep it at minimum fluidizing condition. For smooth transfer
10.1021/ie800282f CCC: $40.75 2008 American Chemical Society Published on Web 05/09/2008
Ind. Eng. Chem. Res., Vol. 47, No. 11, 2008 4019 Table 1. Summary of Experimental Conditions Related to Hydrodynamic Study of FFB (Single Type of Particle System) group of workers Yerushalmi et al.
D. Bai et al.15
Zhu et al.8
Xu et al.5
3
details of experimental conditions
remarks
riser: 0.15 m i.d. × 3.5 mL inclined transfer line solid used: FCC catalyst (Geldart group A) dp ) 49 µm, Fp ) 1450 kg/m3 riser: 0.097 m i.d. × 3 mL loop seal pneumatic valve type transfer line solids used: FCC catalyst (Geldart group A) dp ) 74 µm, Fp ) 1.77 g/cm3 riser: 0.076 m i.d. × 10 mL inclined transfer line solids used: Geldart group A; FCC (dp ) 45-125 µm, Fp ) 2.54 g/cm3) riser: 0.09 m i.d. × 11 mL solids used: Geldart group A; FCC catalyst (dp ) 54 µm, Fp ) 0.9295 g/cm3)
of aerated solids into the riser back, a transfer line inclined at 60° with the horizontal and having a control valve to regulate the flow of solids independently was used. In most of the work reported earlier, an L valve was used; this, however, used to give a large variation in the pressure drop compared to the smooth flow reported here. Various procedures have been reported in the literature to measure the solids circulation rate but in the present case a butterfly valve is used for obvious reasons like simplicity in operation and no loss in the solids that are circulated back into the riser. For pressure drop measurements 21 pressure taps are located along the CFB loop. A photographic view of the experimental setup is shown in Figure 1. The superficial gas velocities into the riser and slow beds are measured by pressure drop measurements across standard calibrated orifice meters installed in the air supply lines. The apparent voidage was calculated from the measured pressure gradient, assuming negligible acceleration effect and shear stress at the wall. Thus ∆P ⁄ z ) Fp(1 - ε)g
(1)
hydrodynamic studies: • voidage profile • flow and mixing • pressure fluctuation • proposer of cluster theory hydrodynamic studies: • core-annulus structure • fractal characteristics of fast bed hydrodynamic studies: • solids holdup distribution and flow development using optic probes • slip velocity hydrodynamic studies: • radial voidage profile for dense phase bubbling flow and dilute phase clustering flow has been estimated for the first time
Experiments were carried out with four different bed materials whose particle properties are listed in Table 2. Results and Discussion Experiments were conducted for loop pressure profile, static pressure profile, and voidage profile in the velocity range 2.01-4.02 m/s and solid circulation rate 12.5-50.0 kg/(m2 s). Longitudinal Pressure Profiles. The FFB was provided with a large number of pressure taps. Measurements were made for each gas velocity at different solid flow rates. Before each experimental run, the column was operated for about 25 min to establish the steady state. Thereafter, the pressure profile along the column was noted. The solid flow rate was measured again at the end of each run. The acceleration section (developing zone) at the bottom of the column consisted of (i) a section of constant pressure gradient which is the characteristics of a fully developed flow and (ii) a disengagement section where the pressure gradient is lower than that in the fully developed flow region.
Figure 1. Diagram of the experimental setup. Photographic view of the experimental setup.
4020 Ind. Eng. Chem. Res., Vol. 47, No. 11, 2008 Table 2. Characteristics of Bed Material used bed materials FCC sand
iron ore
coal sand
sand
sand sand
density, kg/m3
bed composition, %
Umf, m/s
Ut, m/s
εmf
18
1672
100
0.05
0.40
0.38
471
17
2668
100
0.131
4.01
0.44
166
20
5192
100
0.034
2.21
0.44
215
18
1150
100
0.078
2.08
0.45
300
17.5
2635
100
0.063
1.2
0.44
417
18
2549
100
0.122
1.2
0.45
522 622
18 19.5
2549 2590
100 100
0.122 0.122
2.86 1.4
0.45 0.45
particle size distribn
particle dia, µm
-30 + 52 ) 7% -52 + 72 ) 20.61% -72 + 120 ) 72.39% -30 + 52 ) 7.61% -52 + 72 ) 23.46% -72 + 100 ) 16.54% -100 + 200 ) 52.39% -300 + 240 ) 9.63% -240 + 200 ) 12.36% -200 + 150 ) 3.01% -150 + 120 ) 13% -120 + 100 ) 62% -30 + 52 ) 65.87% -52 + 72 ) 20% -72 + 100 ) 14.13% -30 + 36 ) 30.67% -36 + 52 ) 29.33% -52 + 60 ) 19.04% -60 + 72 ) 6.31% -72 + 100 ) 6.2% -30 + 52 ) 7.61% -52 + 72 ) 23.46% -72 + 100 ) 16.54% -100 + 200 ) 52.39% -22 + 25 ) 100% -16 + 22 ) 7.61% -22 + 30 ) 20.13% -30 + 44 ) 21.64% -44 + 60 ) 29.22% -60 + 72 ) 10.17% -72 + 100 ) 3.9% -100 + 200 ) 2.38%
120
CFB inventory, kg
For most of the runs reported here, only two zones (accelerating and fully developed zone) were found to be present. The third zone did appear in cases where solid circulation rate was very high. In the developing flow region (at the bottom of the riser), the up-flowing core particles experience a relatively large upward drag force and vigorous interaction with other particles (“clumps” or “clusters” formation). The steep decline in the pressure profile with height is possibly due to the combined effects of particle acceleration and net radial movement of solids from the upflowing core suspension to the predominantly down flowing wall region. In the developed flow region, the decay in the pressure profile is small as the solids concentration and the variation in the particle velocity with height are relatively low. Effect of Air Velocity on Pressure Profile. Figure 2 shows the effect of air velocity on pressure profiles. At a constant solids circulation rate (Gs) of 45.38 kg/(m2 s), as the air velocity is increased for the air-FCC system from 2.907 to 4.681 m/s, there is a considerable decrease in the static pressure. By comparing the data with other single systems like air-sand, air-coal, and air-iron ore, it is observed that the static pressure shows a decreasing trend as Ug increases. This occurs possibly due to large carryover of particles at higher velocity. Effect of Solid Circulation Rate on Pressure Profile. Figure 3 shows the effect of solid circulation rate on the longitudinal pressure profiles for four sets of systems for air-FCC. It is generally observed that the decay in pressure profile is rather steep at the bottom as compared to the top of the riser (where the decay is slow). With the increase in solid circulation rate, this decay in the pressure profile at the bottom of the riser is more and steep. Further, the level of static pressure is also higher along the height of the riser when the solid circulation rate
increases. Thus, the shape of the pressure profile changes with the solids circulation rate. When it increases, the length of the acceleration zone also increases and there might be a deviation from a linear pressure profile occurring at low solids circulation rate. Effect of Particle Diameter on Pressure Profile. Figure 4 shows the effect of particle diameter on the longitudinal
Figure 2. Static pressure profile along the riser: effect of superficial gas velocity (system: air-FCC).
Ind. Eng. Chem. Res., Vol. 47, No. 11, 2008 4021
Figure 3. Static pressure profile along the riser: effect of solids circulation rate (system: air-FCC).
Figure 5. Static pressure profile along the riser: effect of particle density.
Effect of Particle Density on Pressure Profile. The effect of bed material density is shown in Figure 5. At a constant air velocity (Ug) of 2.01 m/s and solids circulation rate (Gs) of 20.858 kg/(m2 s), the profiles for air-iron ore (density 5192 kg/m3) system, air-coal (density 1150 kg/m3), air-FCC (density 1672 kg/m3), air-sand (density 2668 kg/m3) system indicate that the static pressures are higher for denser systems, i.e., air-iron ore. Acceleration Length
Figure 4. Static pressure profile along the riser: effect of particle diameter (system: air-sand-FCC).
pressure profile for four different diameters of the air-sand system. At a constant solid circulation rate and superficial gas velocity, pressure profile is being compared for particle diameters 622, 522, 417, and 300 µm. It is found that at the bottom of the riser, decay in pressure is steeper for larger size particles. It is also observed that the length of acceleration zone decreases with increase in particle diameter.
The pressure profile analysis has shown the existence of an acceleration section at the bottom of the riser, the particle velocity being raised from zero to its value in the fully developed flow. Therefore, an additional term (∆Pa) in the pressure drop is incorporated. Monceaux et al.12 defined this term as the difference between the actual pressure at a reference point upstream from the solid injector and the pressure obtained when the fully developed flow straight line is extrapolated. In the present work, the variation of ∆Pa with the mean particle concentration in the fully developed flow section has been studied. Experimental results obtained under different operating conditions for air-coal, air-iron ore, air-FCC, and air-sand systems. At low concentration, corresponding to a similar profile regime, ∆Pa varies linearly with (1 - ) at a given air velocity and the slope increases with the air velocity. In the dense region, ∆Pa seems to remain constant. This value of ∆Pa in the “similar profile region” can be quite substantial. It appears therefore that, in the particular CFB system, the acceleration section cannot be neglected, not only because of its length (may vary from 0.9 to 3.1 m) but also because of additional pressure drop specially in the “similar profile region” operating conditions. Correlation for Acceleration Mixing Length. In the present work, the accelerating lengths have been found from the plots of pressure drop per unit height versus riser height. The data so obtained have been correlated as below:
4022 Ind. Eng. Chem. Res., Vol. 47, No. 11, 2008
Figure 6. Comparison of experimental and predicted Lacc/Dt (system: air-FCC).
Figure 7. Voidage profile along the riser: effect of superficial gas velocity (system: air-FCC).
For group A particles
( )( )( ) []( )
Lacc Gs ) 0.538 Dt UgFg
0.3
µg dpUgFg
4.2
gdp
Ug
2
-2.3
Dt dp
1.9
Iv
-0.8
Fgdp
3
(2) Correlation coefficient is 0.90; 1.63 e Gs/Gg e 62.804, 8.4 × 10-2 e µg/dpUgFg e 1.2 × 10-1, 9.3 × 10-5 e gdp/Ug2 e 7.12 × 10-4, 511.06 e Dt/dp e 1022.33, 2.37 × 1012 e Iv/Fgdp3 e 1.97 × 1013. The experimental accelerating lengths have been compared with those predicted according to eq (2) and are shown in Figure 6. It can be seen that there is satisfactory agreement between the two sets of values. Apparent Voidage Profile in Fast Fluidized Bed. Several investigators have studied axial voidage profile in a fast fluidized bed which has been found to be dependent, apart from the specific CFB system used, on the gas velocity, solids circulation rate, and particle size and their distribution. The term “S” represents the shaped axial voidage profile with two regions: a dense zone at the bottom and a dilute region at the top of the riser. Between these two regions, there exists a transition region with an inflection point. It has been observed two regions (dense and dilute) in the riser of a FFB. There are also mathematical models to describe their “S”-shaped voidage profile. Generally, the interface between the dense and dilute zone is different. Yang13 established analytically that the level of the interface is dependent on the total solids inventory. Monceaux12 observed from the pressure drop data that the solids circulation rate and riser height determine the length of dense zone at the bottom and the slope of the voidage profle. Most of the above workers used Geldart group A materials (FCC catalyst, dp ) 50-100 µm) in their studies. Data on Geldart group B material are, however, lacking. Accordingly, in the present work, both group A (FCC catalyst) and group B (coal, iron ore, and sand) materials have been used to study the voidage variation as a function of air velocity and solids circulation rate.
Figure 8. Voidage profile along the riser: effect of solids circulation rate (system: air-FCC).
Effect of Air Velocity on Voidage Profile. The effect of air velocity on voidage profile is apparent in Figure 7 at constant solids circulation rate. It shows that as velocity increases from 2.907 to 4.681 m/s, voidage increases from the rage 0.897 to 0.9996 and 0.906 to 0.9998, respectively. This type of effect is observed because, as the air velocity increases, there will be a large carryover of particles and hence voidage increases. Effect of Solids Circulation Rate on Voidage Profile. The effect of solids circulation rate on voidage is apparent in Figure 8 at constant velocity. As the solids circulation rate is increased from 24.75 to 50 kg/(m2 s), voidage profiles showed a decreasing trend along the riser height. This can be explained possibly as
Ind. Eng. Chem. Res., Vol. 47, No. 11, 2008 4023
follows: as the solid circulation rate increases, more amount of solid is present along the riser height and hence voidage decreases. Effect of Particle Size on Voidage Profile. At constant solid circulation rate and constant fast bed air velocity, voidage profile has been compared for particle diameters 300, 417, 521, and 622 µm. It is found that the bottom of the riser is denser for larger size particles. This can be explained as follows: at the riser bottom both the large and fine particles are present and fine particles are embedded in large diameter particles and hence the voidage decreases. Effect of Particle Density on Voidage Profile. At a constant fast bed velocity and solid circulation rate, the voidage profile has been compared for three systems, with iron ore being the densest of the three. It is found that with iron ore the riser bed is less dense as the riser height rises. This can be explained that dense particles are heavier enough to move along the riser and as a result voidage is more pronounced for them. Real Voidage Profile in Fast Fluidized Bed. It has been stated in an earlier section (experimental pressure and apparent voidage profiles) that the riser can be divided into three sections: an acceleration zone, a developed flow zone, and a deceleration zone. The deceleration zone is normally present when the riser is equipped with an abrupt exit configuration. In the present case, the riser was fitted with a smooth elbow-type of exit and so the deceleration zone is absent. The developed flow zone is considered to be extended up to the exit end. Neglecting gas inertia and gravitation, the gas-solid mixture momentum equation can be written as
( )
dUS dP 4τw + - Fp(1 - ε)g + ws )0 dL Dt dL
(3)
Expressing the wall shear stress in terms of solid and gas component wall friction factors, fs and fg, eq 3 can be integrated between two points of the riser and written in final form: ∆PT )
∫
L
0
[
2
Gs FP(1 - ε)g dL + Fp(1 - ε)
]
∫
Lacc
0
Fp(1 - ε)g dL +
∫
Lacc
0
∫
Lacc
0
+ 0 2 L 2fgGg dL 0 F εD g t
∫
(4)
2fs(1 - ε)FpUs2 dL + Dt
2fgεFpUg2 dL + FP(1 - ε)US2 (5) Dt
The acceleration pressure drop thus consists of four terms: solid particle gravity, gas friction, solid friction, and kinetic energy of solid particles at the accelerating length. The voidage (real) in the above equation can be evaluated if the particle velocity Us is known. The solid particle velocity in the present case is obtained from the relationship: Gs Us ) FP(1 - ε)
fs
(6)
Further, to solve for the evaluation of real voidage in the acceleration zone of the riser using eq 5, the solid friction factor
[ [
] ]
Re t ε3 ) 0.0126 (1 - ε) (1 - ε) Re p
fs
Voidage in the Accelerating Zone. At the riser bottom, in the present case, an acceleration zone persists up to a considerable portion of the riser length. Upto the length of acceleration zone (Lacc), the total pressure drop can be written on simplification of eq4 as ∆PT )
fs and the gas friction factor fg are required. Yang13 proposed the following empirical equation for vertical pneumatic conveying:
L
fsGs2 L dL + 0 F (1 - ε)D p t
∫
Figure 9. Comparison of experimental and predicted voidage (system: air-coal).
Re t ε3 ) 0.041 (1 - ε) (1 - ε) Re p
-0.98
,
Ut/Us > 1.5
(7)
,
Ut/Us < 1.5
(8)
-1.02
Equations 5–8 were solved iteratively to evaluate (real). Voidage in Fully Developed Zone. Above the accelerating zone, the kinetic energy of solid particles can be neglected. Incorporating the static head for gas, eq 7 is modified to ∆PT )
∫
L
Lacc
FP(1 - ε)g dL + 2fs(1 - ε)FpUs Lacc Dt
∫
L
∫
L
Lacc
Fgεg dL +
2
dL +
2fgεFgUg2 Lacc Dt
∫
L
dL
(9)
The fully developed zone in the riser section (indicated by apparent voidage profile) of a circulating loop appears to behave like a dilute phase vertical pneumatic transport line and so the correlation developed by Yang13 and Das14 for such beds can be employed. Thus, the particle velocity, beyond the acceleration region, can be expressed as
US ) Ug - Ut
(
1+
)
fsUs2 4.7 ε 2gDt
(10)
Equation 9 in conjunction with eqs 7, 8, and 10 are solved iteratively for the evaluation of voidage (real) in the developed zone. It is evident that there is perceptible difference between the apparent and real voidages. This is more evident when the data are plotted as shown in Figure 9. As can be seen, above 1.76 to 2.26 m riser height, the apparent and real voidage profiles
4024 Ind. Eng. Chem. Res., Vol. 47, No. 11, 2008
merge together. A similar results were reported by Das et al.16 for prediction of cluster diameter calculation. Conclusions In the present investigation, the hydrodynamics of fast fluidization have been studied thoroughly by using Geldart’s group A as well as group B type of particles in a typical N-type CFB system which has not been studied yet. The fast bed consists of dense phase region at the bottom and a dilute phase region at the top of the riser with unclear bed surface in between. The measured longitudinal pressure profiles in the fast bed riser indicate the existence of two different sections: an accelerating section and a constant pressure gradient section. The axial pressure profiles for the gas-solid suspension depend on various parameters like gas velocity, solid circulation rate, and solid properties The longitudinal voidage profiles exhibit an exponential decay nature. Using the experimental data the accelerating length has been correlated with reasonable accuracy. Based on the momentum analysis of gas-solid mixture along the riser, an attempt has been made to predict the “real” voidages at both the bottom and top of the riser. The difference noted between the apparent and real voidages at the bottom of the bed has been attributed to the accelerating particle pressure drop. Nomenclature Dt ) column diameter, m dp ) particle diameter, m jdp ) average particle diameter, m FCC ) spent FCC catalyst particles fg ) gas friction factor fs ) solids friction factor Gg ) gas mass flow rate, UgFg, kg/m2s Gs ) solids circulation rate, kg/m2s g ) acceleration due to gravity, m/s2 gc ) conversion factor, 9.81 (kg mass)(m)/(s2)(kg force) L ) height of the column, m Lacc ) accelerating (or mixing) length, m ∆PT ) total pressure drop in riser, Pa R ) radius of the riser, m Re ) Reynolds number, dpUgFg/µg Rep ) particle Reynolds number, dpUpFg/µg Ret ) Reynolds number at terminal settling velocity, dpUtFg/µg t ) time, s Ug ) superficial gas velocity, m/s Us ) solid velocity, m/s Ut ) terminal settling velocity, m/s
Ut ) single-particle terminal velocity, m/s Ws ) solids rate, kg/s Greek Letters τw ) wall shear stress, Pa Fp ) solid density, kg/m3 Fs ) solid density, kg/m3 ) voidage
Literature Cited (1) Arena, U.; Cammarota, A.; Pistane, L. High Velocity Fluidization Behavior of Solids in a Laboratory Scale Circulating Bed. CFB Technol. 1986, 1, 119. (2) Das, M.; Banerjee, M.; Saha, R. K. Segregation and Mixing Effects in the Riser of a Circulating Fluidized Bed. Powder Technol. 2007, 178, 179. (3) Yerushalni, J.; Turner, D. H.; Squires, A. M. The Fast-Fluidized Bed. Ind. Eng. Chem. Process Des. DeV. 1976, 15, 47. (4) Han, G. Y.; Lee, G. S.; Kim, S. D. Hydrodynamics of a CFB. Korean J. Chem. Eng. 1985, 2, 141. (5) Xu, G.; Sun, G.; Gao, S. Estimating Radial Voidage Profiles for all Fluidization Regimes in CFB Risers. Powder Technol. 2004, 139, 186. (6) Li, Y.; Chen, B.; Wang, F.; Wang, Y.; Guo, M. Rapid fluidization. Inst. Chem. Eng. 1981, 21, 670. (7) Kojima, T.; Ishihara, K. I.; Guilin, Y.; Furusawa, T. Measurement of Solids Behavior in a FFB. J. Chem. Eng. Jpn. 1989, 22, 341. (8) Zhu, J. X.; Zhang, H.; Bergougnou, M. A. Hydrodynamics in Downflow Fluidized Beds: Solids Concentration Profiles and Pressure Gradient Distribution. Chem. Eng. Sci. 1997, 54, 5461. (9) Choi, J. H.; Yi, C. K.; Son, J. E. Axial Voidage Profile in a Cold Model CFB. Proc. 3rd Int. Conf. CFB 1990, 4. (10) Kato, K.; Tamura, T.; Nishino, K.; Takarada, T. Particle Hold-up Distribution in a CFB. CFB Technol. 1991, III, 145. (11) Sun, G.; Grace, J. R. The Effect of Particle Size Distribution on the Performance of a Catalytic Fluidized Bed Reactor. Chem. Eng. Sci. 1990, 48, 2187. (12) Monceaux, L.; Azzi, Y.; Molidstof, Y.; Large, J. F. Overall and Local Characterization of Flow Regimes in a Circulating Fluidized Bed. CFB Technol. 1986, I, 185. (13) Yang, W. C. Characterization of a CFB. J. Powder Bulk Solids Technol. 1977, 1, 89. (14) Das, M.; Meikap, B. C.; Saha, R. K. Dry beneficiation of iron ore and coal in a fast fluidized bed- a case study. Int. J. Chem. Sci. 2007, 5, 1691. (15) Bai, D.; Shibuya, E.; Masuda, Y.; Nakagawa, N.; Kato, K. Flow Structure in Fast Fluidized Bed. Chem. Eng. Sci. 1996, 51, 957. (16) Das, M.; Meikap, B. C.; Saha, R. K. Prediction of cluster diameter for a wide rage of gas-solid dispersed phase in a fast fluidized bed. Asia Pacific J. Chem. Eng., in press.
ReceiVed for reView February 18, 2008 ReVised manuscript receiVed March 18, 2008 Accepted March 20, 2008 IE800282F
