In order to improve the spoutability for fine particles, a new type of spout-fluid bed with an enlarged column section was proposed. Comparison of flow regime maps for the new design with a conventional spout-fluid bed showed that the range of stable spouting regime was extended when an enlarged column section was employed

Bao, Xiaojun, Dr.

Gong, Lei

Wei, Weisheng

Xu, Jian

English

Engineering Conferences International

Refereed ProceedingsThe 13th International Conference onFluidization - New Paradigm in FluidizationEngineeringEngineering Conferences International Year 2010HYDRODYNAMICS OF ASPOUT-FLUID BED WITH ANENLARGED COLUMN FOR FINEPARTICLESJian Xu∗ Lei Gong†Xiaojun Bao Dr.‡ Weisheng Wei∗∗∗China University of Petroleum†China University of Petroleum‡China University of Petroleum, Beijing, baoxj@cup.edu.cn∗∗China University of PetroleumThis paper is posted at ECI Digital Archives.http://dc.engconfintl.org/fluidization xiii/88HYDRODYNAMICS OF A SPOUT-FLUID BED WITH AN ENLARGED COLUMN FOR FINE PARTICLES  Jian Xu, Lei Gong, Xiaojun Bao*, Weisheng Wei The Key Laboratory of Catalysis, China National Petroleum Co., China University of Petroleum, Beijing 102249, China   ABSTRACT  In order to improve the spoutability for fine particles, a new type of spout-fluid bed with an enlarged column section was proposed. Comparison of flow regime maps for the new design with a conventional spout-fluid bed showed that the range of stable spouting regime was extended when an enlarged column section was employed.   Key Words: Spout-fluid bed, Enlarged column, Flow regime map, Stable spouting  INTRODUCTION  Spouted beds possess certain structural and flow characteristics that are very desirable for fast, highly exothermic and endothermic catalytic reactions (1, 2, 3, 4). However, the use of spouted beds as chemical reactors may suffer from less catalyst interfacial area due to relatively larger particles, especially for fast catalytic reactions which are limited by mass transfer and only the external catalyst surface is effective. Therefore, it may be more favorable to operate spouted beds with relatively finer particles when applying as catalytic reactors (1).   For spouting of fine particles, stable spouting and regular circulation of solids are obtained only for a narrow gas velocity (5, 6, 7). Moreover, in order to fulfill the criteria for stable spouting, relatively smaller nozzle is required, which gives rise to the formation of dead zone in the bed bottom and serious particle attrition (5). By introducing auxiliary fluid through a porous or perforated distributor surrounding the central orifice, the spout-fluid bed technique increases the fluid-solid contact in the annulus and alleviates the likelihood of dead zones (8).   In the present paper, a novel design of spout-fluid beds, i.e. a conical-cylindrical structure with an enlarged column section was proposed in order to improve the spout stability for fine particles.   EXPERIMENTAL  Three spout-fluid beds were build, one is the conventional conical-cylindrical configuration (Configure A) with an inside diameter D1 of 0.15 m and height of 2.0 m equipped with a 60° conical based perforated distributor (See Fig. 1(a)). There were 48 orifices, each 2 mm in diameter, evenly spaced over the conical surface. The other two spout-fluid beds have the same size and configuration of conical section                                                  * Corresponding author. Email: baoxj@cup.edu.cn. Fax: (8610)89734979. 1Xu et al.: HYDRODYNAMICS OF A SPOUT-FLUID BED WITH AN ENLARGED COLUMN FOR FIPublished by ECI Digital Archives, 2010as Configure A, but with an enlarged column section, whose inside diameters D2 are 0.17 m (Configure B) and 0.18 m (Configure C), respectively, as shown in Fig. 1(b). Spouting gas and fluidizing gas, both provided by an air compressor, were controlled and measured separately by pressure regulators and rotameters. Two narrow size-distributed alumina particles were used as bed materials. Their properties are listed in Table 1.  Differential pressures at 10 axial locations with a vertical interval of 30 mm were measured simultaneously using rapid-response pressure transducers (Omega, PX164-010D5V). Measurements were all taken from the wall. The bed voidage was measured by an optical fiber system, which deduced the solids volume information from the reflection of emitted light. Pre-tests were carried for each kind of particles to obtain a correlation between light attenuation and bed voidage by linear fitting. For each voidage measurement, the time interval and the number of data sampled were 0.005 s and 3000, respectively, and their averages were then adopted as experimental data.  Spouting GasFluidizing GasD1=150mmSpouting GasFluidizing GasD2D1=150mm(a) (b)  Fig. 1. Schematic of experimental setup  Table 1. Properties of bed materials Material dp (mm) ρb (kg/m3) ρp (kg/m3) Alumina #1 0.461 1076 1811 Alumina #2 0.253 1103 1206  2The 13th International Conference on Fluidization - New Paradigm in Fluidization Engineering, Art. 88 [2010]http://dc.engconfintl.org/fluidization_xiii/88RESULTS AND DISCUSSION  The flow regime maps for the three spout-fluid bed configurations were determined on the basis of visual observations, for a given bed height, by changing the spout gas velocity while keeping the fluidizing gas velocity constant or by adjusting the fluidizing gas velocity while maintaining the spouting gas velocity. For the combination of gas, solids, and vessel configuration employed in the present study, five flow regimes were visually observed:  z Fixed bed regime: The particles were loosely packed and immobile. z Stable spouting regime: Stable fountain and regular particle circulation were formed. z Unstable spouting regime: This regime was characterized by swirling and pulsation of the spout with time. z Bubbling regime: In this regime, the momentum of the spout jet was not strong enough to penetrate through the bed. Bubbles formed instead in the central region when the fluidizing flow rate was low. When the fluidizing flow rate was high, bubbles also formed in the annular region. z Slugging regimes. Bubbling was evolved to slugging when the fluidizing gas velocity or spouting gas velocity was further increased.  For the 0.461 mm diameter alumina particles with a bed height of 300 mm, the flow regime maps of the three spout-fluid beds are shown in Figs. 2-4, with the fluidizing gas velocity plotted on the ordinate axis and the spouting gas velocity plotted on the abscissa. Fig.5 compares the stable spouting regimes observed at the same bed height for the three spout-fluid bed configurations as shown in Figs 2-4. Clear expansion of the stable spouting region can be found for the spout-fluid beds with enlarged column, comparing with the conventional structure. It also can be seen from Fig. 5 that, as the diameter of the enlarged section increased from D2=170 mm to 180 mm, the region of stable spouting regime expanded. Fig.6 compares the stable spouting regimes observed at bed height of 350 mm for the three configurations, similar results were obtained.  0.00 0.02 0.04 0.06 0.08 0.10 0.120.000.020.040.060.080.100.12SluggingBubblingUnstablespoutingStablespoutingFixedBed  Uf, m/sUs, m/s  0.00 0.03 0.06 0.09 0.12 0.15 0.180.000.020.040.060.080.100.12  Uf, m/sUs, m/sFixedBedStableSpoutingUnstableSpoutingBubblingSlugging Fig. 2 Flow regime map for the conventional spout-fluid bed (Configure A) at H=300 mm, dp=0.461 mm, D1=150 mm Fig. 3 Flow regime map for  the spout-fluid bed with enlarged column (Configure B) at H=300 mm, dp=0.461 mm, D1=150 mm, D2=170 mm 3Xu et al.: HYDRODYNAMICS OF A SPOUT-FLUID BED WITH AN ENLARGED COLUMN FOR FIPublished by ECI Digital Archives, 20100.02 0.04 0.06 0.08 0.10 0.12 0.140.000.020.040.060.080.10  Uf, m/sUs, m/sFixedBedStableSpoutingUnstableSpoutingBubblingSlugging 0.05 0.06 0.07 0.08 0.09 0.10 0.110.000.010.020.030.040.050.060.07   Configure A Configure B Configure CUf, m/sUs, m/sFig. 4 Flow regime map for  the spout-fluid bed with enlarged column (Configure C) at H=300 mm, dp=0.461 mm, D1=150 mm, D2=180 mm Fig. 5 Comparison of stable spouting regimes for  the three spout-fluid bed configurations at H=300 mm, dp=0.461 mm   0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.130.000.010.020.030.040.050.060.07 Uf, m/sUs, m/s Configure A Configure B Configure C Fig. 6 Comparison of stable spouting regimes for  the three spout-fluid bed configurations at H=350 mm, dp=0.461 mm  The effect of the diameter expansion in the cylindrical section on the spout ability of the spout-fluid beds was investigated by a rough estimation of the axial distribution of gas flow rate in the annular region. For a short bed height L, the pressure drop ΔP was measured by pressure transducer as described in the experimental section. The gas velocity in the annular region Ua can be calculated according to Ergun equation (9):  ( )3 3 22 2 3 31 1.75 1150 ga ap p p pP U UL d dε ρ εμϕ ε ϕ ε− −Δ = +  (1)  Where ε is taken as average bed voidage of the annular region for the bed height of L, which was measured by the optical fiber system. The gas flow rate in the annular region Qa can then be determined by:  ( )2 24a a c sQ U D Dπ= × −  (2)  4The 13th International Conference on Fluidization - New Paradigm in Fluidization Engineering, Art. 88 [2010]http://dc.engconfintl.org/fluidization_xiii/88Where Dc is the bed diameter, Ds is the average spout diameter for bed height L which was determined by measuring the radial bed voidage profile.  The calculated axial distribution of the gas flow rate in the annular region for the three spout-fluid bed configurations were shown in Figs. 7-9, respectively. It can be seen that the expansion of the bed diameter results in a decrease in annular gas flow rate, which means that more gas was penetrated from the annular region into the spout region. The increase in spout gas flow rate increases the spout jet momentum flow rate, which leads to an increase of penetration ability of the spout jet (10, 11). This may explain why the range of stable spouting regime is extended for the new design with an enlarged column.  1.0 1.2 1.4 1.6 1.8 2.0 2.20.30.40.50.60.70.80.91.0Qa/QtDimensionless bed height, Z/Dc Qf/Qmf=0.13 Qf/Qmf=0.18 Qf/Qmf=0.24 Qf/Qmf=0.26 Qf/Qmf=0.291.0 1.2 1.4 1.6 1.8 2.0 2.20.00.20.40.60.81.0D1=150 mmQa/QtDimensionless bed height, Z/Dc Qf/Qmf=0.24 Qf/Qmf=0.29 Qf/Qmf=0.34 Qf/Qmf=0.37D2=170 mmFig. 7 Axial distribution of gas flow rate in the annular region in the conventional spout-fluid bed (Configure A) at H=350 mm, dp=0.461 mm, Qs=4.8 m3/h Fig. 8 Axial distribution of gas flow rate in the annular region in the spout-fluid bed with enlarged column (Configure B) at H=350 mm, dp=0.461 mm, D1=150 mm, D2=170 mm, Qs=4.6 m3/h   1.0 1.2 1.4 1.6 1.8 2.0 2.20.00.20.40.60.81.0D1=150 mmQa/QtDimensionless bed height, Z/Dc Qf/Qmf=0.24 Qf/Qmf=0.29 Qf/Qmf=0.40 Qf/Qmf=0.50D2=180 mm Fig. 9 Axial distribution of gas flow rate in the annular region in the spout-fluid bed with enlarged column (Configure C) at H=350 mm, dp=0.461 mm, D1=150 mm, D2=180 mm, Qs=5.0 m3/h  CONCLUSION  5Xu et al.: HYDRODYNAMICS OF A SPOUT-FLUID BED WITH AN ENLARGED COLUMN FOR FIPublished by ECI Digital Archives, 2010In order to improve the spoutability for fine particles, a novel configuration of spout-fluid beds, i.e. a conical-cylindrical structure with an enlarged column section was proposed. Three spout-fluid beds were build, one is the traditional conical-cylindrical configuration (Configure A) with an inside diameter of 0.15 m. The other two spout-fluid beds have the same size and configuration of conical section with Configure A, but have an enlarged column section, whose inside diameters are 0.17 m and 0.18m, respectively. The flow regime maps of the three beds obtained by means of visual observation showed that the range of stable spouting regime of the new design was extended, indicating improved spoutability.   The axial distribution of the gas flow rate in the annular region for the three spout-fluid bed configurations was calculated. It can be seen that the expansion of the bed diameter results in an increases in the spout jet momentum flow rate, which leads to an increase of penetration ability of the spout jet. This may explain why the range of stable spouting regime is extended for the new design with an enlarged column.  ACKNOWLEDGEMENT  Financial support from Major State Basic Research Development Program of China (973 Program, 2005CB221205), and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of the People’s Republic of China.  NOTATION  D1 Normal bed diameter, mm D2 Enlarged bed diameter, mm Dc Bed diameter, mm dp Particle diameter, mm Ds Spout diameter, mm H Bed height, m Uf Fluidizing gas velocity, m/s Us Spouting gas velocity, m/s Qa Gas flow rate in annular region, m3/h Qf Fluidizing gas flow rate, m3/h Qmf Minimum fluidizing gas flow rate, m3/h Qt Total gas flow rate, m3/h μ Gas viscosity, Pa s ρg Gas density, kg/m3 ρp Particle density, kg/m3 ϕp Particle sphericity  REFERENCE  1. Marnasidou, K., S. Voutetakis, G. Tjatjopoulos, and I. Vasalos, (1999), "Catalytic partial oxidation of methane to synthesis gas in a pilot-plant-scale spouted-bed reactor". Chem. Eng. 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Bao, (2006), "Computational fluid dynamics(CFD) modeling of fine particle spouting". Int. J. Chem. Reactor Eng. 4:  A27. 7. Epstein, N. and P. Chandnani, (1987), "Gas spouting characteristics of fine particles". Chem. Eng. Sci. 42(12):  2977-2981. 8. Pianarosa, D.L., L.A.P. Freitas, C.J. Lim, J.R. Grace, and O.M. Dogan, (2000), "Voidage and particle velocity profiles in a spout-fluid bed". Can. J. Chem. Eng. 78(1):  132-142. 9. Ergun, S., (1952), "Fluid flow through packed columns". Chem. Eng. Prog. 48(2):  89-94. 10. Zhong, W. and M. Zhang, (2005), "Pressure fluctuation frequency characteristics in a spout-fluid bed by modern ARM power spectrum analysis". Powder Technol. 152(1-3):  52-61. 11. Zhong, W., R. Xiao, and M. Zhang, (2006), "Experimental study of gas mixing in a spout-fluid bed". AIChE J. 52(3):  924-930.   7Xu et al.: HYDRODYNAMICS OF A SPOUT-FLUID BED WITH AN ENLARGED COLUMN FOR FIPublished by ECI Digital Archives, 2010

HYDRODYNAMICS OF A SPOUT-FLUID BED WITH AN ENLARGED COLUMN FOR FINE PARTICLES

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HYDRODYNAMICS OF A SPOUT-FLUID BED WITH AN ENLARGED COLUMN FOR FINE PARTICLES

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