流化床半焦燃烧的DEM三维数值模拟
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摘要
气相场基于欧拉法,颗粒相采用离散单元法(DEM),同时考虑气固流动、传热传质以及化学反应,构建了基于CFD-DEM法的稠密气固系统热转化过程的并行数值模拟方法及平台,并对实验室规模的流化床半焦燃烧过程进行了研究。通过准三维流化床中单颗粒燃烧模拟对所建立的模型进行了验证,其后考察了不同过量空气系数下的三维流化床半焦燃烧,获得了颗粒流型、空隙率、温度、组分浓度等分布,结果表明高气量增加了反应初始阶段半焦燃烧速率,加速了半焦温度的升高。
The gas phase is modelled by Eulerian method and the solid phase by discrete element method(DEM). The gas-solid flow, heat and mass transfer, and chemical reaction are simultaneously considered. A parallel numerical method and platform for heat conversion process of dense gas-solid system is established, which is applied to the simulation of char combustion in a lab-scale fluidized bed. Based on the validation by the single particle combustion in a quasi-three dimensional(3 D)fluidized bed, the combustion processes in a 3 D fluidized bed under different air ratios are studied.The gas-solid flow pattern, profiles of voidage, temperature, and gas composition are obtained. The results show that char combustion rate of initial reaction stage increases with the increasing air ratio,accelerating the rise of char temperature.
The gas phase is modelled by Eulerian method and the solid phase by discrete element method(DEM). The gas-solid flow, heat and mass transfer, and chemical reaction are simultaneously considered. A parallel numerical method and platform for heat conversion process of dense gas-solid system is established, which is applied to the simulation of char combustion in a lab-scale fluidized bed. Based on the validation by the single particle combustion in a quasi-three dimensional(3 D)fluidized bed, the combustion processes in a 3 D fluidized bed under different air ratios are studied.The gas-solid flow pattern, profiles of voidage, temperature, and gas composition are obtained. The results show that char combustion rate of initial reaction stage increases with the increasing air ratio,accelerating the rise of char temperature.
引文
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[6] Geng Y M, Che D F. An Extended DEM-CFD Model for Char Combustion in a Bubbling Fluidized Bed Combustor of Inert Sand[J]. Chemical Engineering Science, 2011,66(2):207-219
[7] Ku X, Li T, Lovas T. CFD-DEM Simulation of Biomass Gasification with Steam in a Fluidized Bed Reactor[J].Chemical Engineering Science, 2015, 122:270-283
[8] Zhong W Q, Yu A B, Zhou G W, et al. CFD Simulation of Dense Particulate Reaction System:Approaches, Recent Advances and Applications[J]. Chemical Engineering Science, 2016, 140:16-43
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[10] Tsuji Y, Kawaguchi T, Tanaka T. Discrete Particle Simulation of Two-Dimensional Fluidized Bed[J]. Powder Technology, 1993, 77(1):79-87
[11] Oevermann M, Gerber S, Behrendt F. Euler-Lagrange/DEM Simulation of Wood Gasification in a Bubbling Fluidized Bed Reactor[J]. Particuology, 2009, 7(4):307-316
[12] Hayhurst A N, Parmar M S. Measurement of the Mass Transfer Coefficient and Sherwood Number for Carbon Spheres Burning in a Bubbling Fluidized Bed[J]. Combustion and Flame, 2002, 130(4):361-375
[13] Burcat A, Ruscic B. Third Millenium Ideal Gas and Condensed Phase Thermochemical Database for Combustion with Updates From Active Thermochemical Tables[M].Illinois:Argonne National Laboratory Argonne, 2005:27-387
[14] Topal H, Atimtay A T, Durmaz A. Olive Cake Combustion in a Circulating Fluidized Bed[J]. Fuel, 2003, 82(9):1049-1056
[2] Zhou W, Zhao C, Duan L, et al. Two-Dimensional Computational Fluid Dynamics Simulation of Coal Combustion in a Circulating Fluidized Bed Combustor[J]. Chemical Engineering Journal, 2011, 166(1):306-314
[3] Xie J, Zhong W Q, Jin B S, et al. Three-DimensionalEulerian-Eulerian Modeling of Gaseous Pollutant Emissions from Circulating Fluidized-Bed Combustors[J]. Energy&Fuels, 2014, 28(8):5523-5533
[4] Zhou H, Flamant G, Gauthier D. DEM-LES Simulation of Coal Combustion in a Bubbling Fluidized Bed Part II:Coal Combustion at the Particle Level[J]. Chemical Engineering Science, 2004, 59(20):4205-4215
[5] Liu D Y, Chen X P, Zhou W, et al. Simulation of Char and Propane Combustion in a Fluidized Bed by Extending DEM-CFD Approach[J]. Proceedings of the Combustion Institute, 2011, 33:2701-2708
[6] Geng Y M, Che D F. An Extended DEM-CFD Model for Char Combustion in a Bubbling Fluidized Bed Combustor of Inert Sand[J]. Chemical Engineering Science, 2011,66(2):207-219
[7] Ku X, Li T, Lovas T. CFD-DEM Simulation of Biomass Gasification with Steam in a Fluidized Bed Reactor[J].Chemical Engineering Science, 2015, 122:270-283
[8] Zhong W Q, Yu A B, Zhou G W, et al. CFD Simulation of Dense Particulate Reaction System:Approaches, Recent Advances and Applications[J]. Chemical Engineering Science, 2016, 140:16-43
[9] Cundall P A, Strack O D. A Discrete Numerical Model for Granular Assemblies[J]. Geotechnique, 1979, 29(1):47-65
[10] Tsuji Y, Kawaguchi T, Tanaka T. Discrete Particle Simulation of Two-Dimensional Fluidized Bed[J]. Powder Technology, 1993, 77(1):79-87
[11] Oevermann M, Gerber S, Behrendt F. Euler-Lagrange/DEM Simulation of Wood Gasification in a Bubbling Fluidized Bed Reactor[J]. Particuology, 2009, 7(4):307-316
[12] Hayhurst A N, Parmar M S. Measurement of the Mass Transfer Coefficient and Sherwood Number for Carbon Spheres Burning in a Bubbling Fluidized Bed[J]. Combustion and Flame, 2002, 130(4):361-375
[13] Burcat A, Ruscic B. Third Millenium Ideal Gas and Condensed Phase Thermochemical Database for Combustion with Updates From Active Thermochemical Tables[M].Illinois:Argonne National Laboratory Argonne, 2005:27-387
[14] Topal H, Atimtay A T, Durmaz A. Olive Cake Combustion in a Circulating Fluidized Bed[J]. Fuel, 2003, 82(9):1049-1056