湿颗粒流化床流动特性的实验研究
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摘要
基于可视化湿颗粒流化床实验系统,研究了多种Geldart-D类颗粒在不同含液量时的流动特性变化规律,包含流型、床层压降、最小流化速度。实验结果表明:1)在湿流化床内,颗粒出现聚团结块行为,气泡呈现不规则形状;湿颗粒流化过程的稳定性较干颗粒床明显下降,床内近壁面区域易出现局部沟流。2)固定床阶段,由于空隙率的增加,相同气速条件下,湿颗粒床层压降低于干颗粒;基于厄贡公式,得出了湿颗粒固定床床层压降的计算方法。3)湿颗粒的最小流化速度U_(mf)高于干颗粒,且随粒径d_p的增加而增加;导出了预测D类湿颗粒最小流化速度的半经验公式,Re_(mf)=0.279.Ar~(0.5),该式计算结果与实验测量结果偏差小于15%。
In the present work,a visual wet granular fluidized bed setup is established.Fluidization characteristics of various Geldart-D particles with different liquid contents are investigated in this experimental system,containing flow pattern,pressure drop and minimum fluidization velocity.Some notable conclusions can be obtained from the experimental results.1) In the wet fluidized bed,agglomeration behavior for wet particles and bubbles with irregular shapes can be observed apparently.Meanwhile,the stability of wet granular flow process is lower than that of dry granular bed.In the region near the wall,local channeling is easy to happen.2) At the stage of fixed bed,bed pressure drop for wet particles is smaller than that for dry particles due to the increases of voidage.Based on the Ergun formula,the calculating method of pressure drop for wet granules fixed bed is proposed.3) The minimum fluidization velocity U_(mf) for wet granular is higher than that for dry particles.The U_(mf) for wet particle increases with the increase of particle size d_p.A semi-empirical correlation,Re_(mf) = 0.279·Ar~(0.5),is developed to predict the U_(mf) of the wet particles.The predictions calculated by this correlation agree well with the present experimental results with the error of less than 15%.
In the present work,a visual wet granular fluidized bed setup is established.Fluidization characteristics of various Geldart-D particles with different liquid contents are investigated in this experimental system,containing flow pattern,pressure drop and minimum fluidization velocity.Some notable conclusions can be obtained from the experimental results.1) In the wet fluidized bed,agglomeration behavior for wet particles and bubbles with irregular shapes can be observed apparently.Meanwhile,the stability of wet granular flow process is lower than that of dry granular bed.In the region near the wall,local channeling is easy to happen.2) At the stage of fixed bed,bed pressure drop for wet particles is smaller than that for dry particles due to the increases of voidage.Based on the Ergun formula,the calculating method of pressure drop for wet granules fixed bed is proposed.3) The minimum fluidization velocity U_(mf) for wet granular is higher than that for dry particles.The U_(mf) for wet particle increases with the increase of particle size d_p.A semi-empirical correlation,Re_(mf) = 0.279·Ar~(0.5),is developed to predict the U_(mf) of the wet particles.The predictions calculated by this correlation agree well with the present experimental results with the error of less than 15%.
引文
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[15]Anand A,Curtis J S,Wassgren C R,et al.Experimental Study of Wet Cohesive Particles Discharging From a Rectangular Hopper[J].Industrial&Engineering Chemistry Research,2015,54(16):4545-4551
[2]Bacelos M S,Passos M L,Freire J T.Effect of Interparticle Forces on the Conical Spouted Bed Behavior of Wet Particles with Size Distribution[J].Powder Technology,2007,174(3):114-126
[3]McLaughlin L J,Rhodes M J.Prediction of Fluidized Bed Behaviour in the Presence of Liquid Bridges[J].Powder Technology,2001,114(1):213-223
[4]Zhou Y,Shi Q,Huang Z,et al.Effects of Liquid Action Mechanisms on Hydrodynamics in Liquid-Containing Gas-Solid Fluidized Bed Reactor[J].Chemical Engineering Journal,2016,285:121-127
[5]Sutkar V S,Deen N G,Patil A V,et al.Experimental Study of Hydrodynamics and Thermal Behavior of a Pseudo-2D Spout-Fluidized Bed with Liquid Injection[J].AIChE Journal,2015,61(4):1146-1159
[6]Mikami T,Kamiya H,Horio M.Numerical Simulation of Cohesive Powder Behavior in a Fluidized Bed[J].Chemical Engineering Science,1998,53(10):1927-1940
[7]Lim C,Wee E,Tan H,et al.Mixing Behaviors of Wet Granular Materials in Gas Fluidized Bed Systems[J].AIChE Journal,2013,59(11):4058-4067
[8]Wang T,He Y,Tang T,et al.Experimental and Numerical Study on a Bubbling Fluidized Bed with Wet Particles[J].AIChE Journal,2016,62:1970—1985
[9]Jia D,Cathary O,Peng J,et al.Fluidization and Drying of Biomass Particles in a Vibrating Fluidized Bed with Pulsed Gas Flow[J].Fuel Processing Technology,2015,138:471-482
[10]Ergun S.Fluid Flow Through Packed Columns[J].Chemical Engineering Progress,1952,48:89-94
[11]Feng C L,Yu A B.Quantification of the Relationship Between Porosity and Interparticle Forces for the Packing of Wet Uniform Spheres[J].Journal of Colloid and Interface Science,2000,231(1):136-142
[12]Gidaspow D.Multiphase Flow and Fluidization:Continuum and Kinetic Theory Descriptions[M],Academic Press,1994:98-103
[13]Molerus O.Interpretation of Geldart's Type A,B,C and D Powders by Taking Into Account Interparticle Cohesion Forces[J].Powder Technology,1982,33(1):81-87
[14]Schneider T,Bridgwater J.The Stability of wet Spouted Beds[J].Drying Technology,1993,11(2):277-301
[15]Anand A,Curtis J S,Wassgren C R,et al.Experimental Study of Wet Cohesive Particles Discharging From a Rectangular Hopper[J].Industrial&Engineering Chemistry Research,2015,54(16):4545-4551