Simulation of Solid-Liquid Cascade Filtration Based on CFD-DEM
-
摘要: 采用计算流体力学(CFD)和离散单元法(DEM)耦合的方法,在不同滤层结构的三维随机堆积颗粒层过滤器内进行固液分级过滤的数值模拟研究。实验结果表明,过滤效率的模拟计算值与实验值吻合良好,压降值的偏差在Ergun方程允许误差范围内。过滤器的容垢能力由模型计算的颗粒沉积均匀度表示,并拟合得到沉积均匀度的关联式。颗粒沉积分布的模拟结果显示:单层细滤料过滤器的颗粒沉积主要发生在近入口处,容垢能力较低;分级过滤器的细滤料层保证了高过滤效率,粗滤料层则提供了较大的容垢能力。Abstract: A three-dimensional model for a random packed bed filter was established by coupling computational fluid dynamics (CFD) and discrete element method (DEM). To ensure more accurate simulation results can be obtained, the interactions of liquid-solid, particle-granule and particle-particle were taken into consideration. The filtration performance including filtration efficiency, pressure drop and impurity holding capacity were carefully analyzed, and particle deposition distribution and morphology were also numerically investigated. The simulation results of filtration efficiency have a good agreement with the experimental results. The deviation of the pressure drop is within the allowable error range of the Ergun equation. The impurity holding capacity is represented by the deposition uniformity obtained by simulation results, which increases with the superficial velocity. Correlation of deposition uniformity for granular bed filters is presented and it has good prediction accuracy. The results show that cascade filtration has both a high filtration efficiency and a low pressure drop by combining deep bed filtration and surface filtration. The quality factor of the cascade filter is greater than that of a single-layer filter. The simulation analysis of particle deposition morphology and distribution shows that particles mainly deposit on the surface of single-layer filter packed with fine granules, resulting in its small holding capacity. As for the cascade filter, the fine granular layer ensures high filtration efficiency while coarse granular layer provides large impurity holding capacity.
-
表 1 模拟物性参数
Table 1. Physical parameters in the simulation
Item Density/
(kg·m−3)Poisson’s ratio Shear modulus/Pa Restitution coefficient Static friction coefficient Rolling friction coefficient Particle (granule) 3200 0.25 1.0×108 0.5 0.154 0.05 Wall 1500 0.25 1.1×109 0.3 0.154 0.01 -
[1] ALTMANN J, REHFELD D, TRAEDER K, et al. Combination of granular activated carbon adsorption and deep-bed filtration as a single advanced wastewater treatment step for organic micropollutant and phosphorus removal[J]. Water Research, 2016, 92: 131-139. doi: 10.1016/j.watres.2016.01.051 [2] ANDREASEN R R, PUGLIESE L, POULSEN T G. Water flow exchange characteristics in coarse granular filter media[J]. Chemical Engineering Journal, 2013, 221: 292-299. doi: 10.1016/j.cej.2013.02.002 [3] STANGHELLE D, SLUNGAARD T, SONJU O K. Granular bed filtration of high temperature biomass gasification gas[J]. Journal of Hazardous Materials, 2007, 144(3): 668-672. doi: 10.1016/j.jhazmat.2007.01.092 [4] XIAO G, WANG X H, ZHANG J P, et al. Granular bed filter: a promising technology for hot gas clean-up[J]. Powder Technology, 2013, 244: 93-99. doi: 10.1016/j.powtec.2013.04.003 [5] VEERAPANENI S, WIESNER M R. Role of suspension polydispersivity in granular media filtration[J]. Journal of Environmental Engineering, 1993, 119(1): 172-190. doi: 10.1061/(ASCE)0733-9372(1993)119:1(172) [6] SCHMIDT E W, GIESEKE J A, GELFAND P, et al. Filtration theory for granular beds[J]. Journal of the Air Pollution Control Association, 1978, 28(2): 143-146. doi: 10.1080/00022470.1978.10470582 [7] ZAMANI A, MAINI B. Flow of dispersed particles through porous media: Deep bed filtration[J]. Journal of Petroleum Science & Engineering, 2009, 69(1/2): 71-88. [8] QIAN F P, HUANG N J, LU J L, et al. CFD-DEM simulation of the filtration performance for fibrous media based on the mimic structure[J]. Computers & Chemical Engineering, 2014, 71: 478-488. [9] YUE C, ZHANG Q, ZHAI Z. Numerical simulation of the filtration process in fibrous filters using CFD-DEM method[J]. Journal of Aerosol Science, 2016, 101: 174-187. doi: 10.1016/j.jaerosci.2016.08.004 [10] 肖桐, 王千红, 沈盈莺, 等. 颗粒床内固液过滤的三维CFD-DEM模拟[J]. 华东理工大学学报(自然科学版), 2020, 46(2): 164-172. [11] WANG F L, HE Y L, TANG S Z, et al. Real-time particle filtration of granular filters for hot gas clean-up[J]. Fuel, 2019, 237: 308-319. doi: 10.1016/j.fuel.2018.09.138 [12] YANG G H, ZHOU J H. Experimental study on a new dual-layer granular bed filter for removing particulates[J]. Journal of China University of Mining & Technology, 2007, 17(2): 201-204. [13] SHI K Y, YANG G H, HANG S, et al. Study on filtering characteristics of aerosol particulates in a powder-grain dual-layer granular bed[J]. Powder Technology, 2015, 272: 54-63. doi: 10.1016/j.powtec.2014.11.034 [14] TIEN C. Principles of Filtration[M]. Holand: Elsevier, 2012. [15] 景有海. 均质滤料过滤过程的水头损失计算模型[J]. 中国给水排水, 2000, 16(2): 9-12. doi: 10.3321/j.issn:1000-4602.2000.02.003 [16] MENTER F R. Two-equation eddy-viscosity turbulence models for engineering applications[J]. AIAA Journal, 1994, 32(8): 1598-1605. doi: 10.2514/3.12149 [17] MENTER F R, KUNTZ M, LANGTRY R B. Ten years of industrial experience with the SST turbulence model[J]. Turbulence Heat Mass Transfer, 2003, 4: 625-632. [18] MINDLIN R D. Compliance of elastic bodies in contact[J]. Journal of Applied Mechanics, 1949, 16: 259-268. doi: 10.1115/1.4009973 [19] MARSHALL J S. Discrete-element modeling of particulate aerosol flows[J]. Journal of Computational Physics, 2009, 228(5): 1541-1561. doi: 10.1016/j.jcp.2008.10.035 [20] ERGUN S. Fluid flow through packed columns[J]. Journal of Chemical Engineering Progress, 1952, 48(2): 89-94. [21] KUO Y M, HUANG S H, LIN W Y, et al. Filtration and loading characteristics of granular bed filters[J]. Journal of Aerosol Science, 2010, 41(2): 223-229. doi: 10.1016/j.jaerosci.2009.09.011 [22] IVES K J. Rapid filtration[J]. Water Research, 1970, 4(3): 201-223. doi: 10.1016/0043-1354(70)90068-0 -