CFD simulation of chemical conditioning unit of municipal sludge

doi:10.11949/j.issn.0438-1157.20150319

Abstract

Abstract:

Chemical conditioning is commonly used before the mechanically dewatering process for sewage sludge. The flow field distribution of conditioning tank has a significant effect on conditioning when paddles are operating. Moving reference frame-volume of fluid model was used for simulating flow field distribution of a sludge conditioning tank with the inner diameter of 40 cm by CFD (computational fluid dynamics) technology, and the gas-liquid two-phase distribution was verified. The results showed that in the single straight blade paddle conditioning tank, the optimium ratio of paddle diameter to tank diameter was 1:1.75 and the optimum ratio of baffle width to tank diameter was 1:20. Under these optimum conditions, the fluid swirl could be effectively eliminated and the turbulent action could be enhanced. Furthermore, the flow field distribution simulation was conducted for pilot-scale conditioning tank with the inner diameter of 110 cm and the simulation results were compared with test results. Moving reference frame-volume of fluid model used in this study can provide references for design and optimization of similar sludge conditioning tank.

Key words: chemical conditioning, gas-liquid flow, computational fluid dynamics (CFD), moving reference frame, volume of fluid (VOF), stirred vessel

摘要：

市政污泥机械脱水前多采用化学调理,调理装置搅拌过程中的流场分布直接影响调理效果。采用多重参考系-流体体积模型对实验室污泥调理罐(内径为40 cm)的流场特性进行计算流体力学(computational fluid dynamics,CFD)模拟研究,验证了实验室调理罐模型气液两相分布情况。实验室调理罐的模拟结果表明:单层直桨叶调理罐的搅拌桨直径与调理罐内径比优化值为1:1.75,挡流板宽度与调理罐内径比优化值为1:20,可有效消除流体旋涡,增强湍动作用。在此基础上,对中试调理罐(内径为110 cm)的流场特性进行模拟并与实际测量值校验。该研究采用的多重参考系-流体体积模型可为同类污泥调理罐设计与优化提供参考。

关键词: 化学调理, 气液两相流, 计算流体力学, 多重参考系方法, 流体体积模型, 搅拌容器

CLC Number:

X705

XU Qi, DENG Chao, SHI Yafei, XU Xinyu, YU Wenbo, LI Chao, CHEN Ye, LIANG Sha, HU Jingping, HE Shu, WANG Rong, YANG Changzhu, YANG Jiakuan. CFD simulation of chemical conditioning unit of municipal sludge[J]. CIESC Journal, 2015, 66(10): 4145-4154.

许琪, 邓超, 时亚飞, 徐新宇, 虞文波, 郦超, 陈烨, 梁莎, 胡敬平, 何姝, 王荣, 杨昌柱, 杨家宽. 市政污泥化学调理装置CFD模拟[J]. 化工学报, 2015, 66(10): 4145-4154.

References 22

[1]	Zhang Weijun, Xiao Ping, Liu Yuanyuan, Xu Shiwei, Xiao Feng, Wang Dongsheng, Christopher W K Chow. Understanding the impact of chemical conditioning with inorganic polymer flocculants on soluble extracellular polymeric substances in relation to the sludge dewaterability [J]. Separation and Purification Technology, 2014, 132: 430-437.
[2]	Wu Xuefeng (吴雪峰), Li Qingqing (李青青), Li Xiaoping (李小平). Management system of municipal sludge treatment and disposal [J]. Environmental Science & Technology (环境科学与技术), 2010, 33 (4): 186-195.
[3]	Liu Huan (刘欢), Yang Jiakuan (杨家宽), Shi Yafei (时亚飞), Li Ye (李野), He Shu (何姝). Relationship of evaluation indexes of sludge dewatering performance under different conditioning programs [J]. Environmental Science (环境科学), 2011, 32 (11): 3394-3399.
[4]	Wang Hongna, Jia Xiaoqiang, Wang Xue, Zhou Zhengxi, Wen Jianping, Zhang Jinli. CFD modeling of hydrodynamic characteristics of a gas-liquid two-phase stirred tank [J]. Applied Mathematical Modelling, 2014, 38 (1): 63-92.
[5]	Tamburini A, Cipollina A, Micale G, Brucato A, Ciofalo M. CFD simulations of dense solid-liquid suspensions in baffled stirred tanks: Prediction of solid particle distribution [J]. Chemical Engineering Journal, 2013, 223: 875-890.
[6]	Jahoda M, Tomášková L, Moštěk M. CFD prediction of liquid homogenisation in a gas-liquid stirred tank [J]. Chemical Engineering Research and Design, 2009, 87 (4): 460-467.
[7]	Wang Leqin (王乐勤), Du Hongxia (杜红霞), Wu Dazhuan (吴大转), Dai Weiping (戴维平). Numerical simulation of mixing process in stirred tank with multiple impellers [J]. Journal of Engineering Thermophysics (工程热物理学报), 2007, 28 (3): 418-420.
[8]	Zhou Guozhong (周国忠), Wang Yingchen (王英琛), Shi Litian (施力田). CFD study of mixing process in stirred tank [J]. Journal of Chemical Industry and Engineering (China) (化工学报), 2003, 54 (7): 886-890.
[9]	Ranade V V, Bourne J R, Joshi J B. Fluid mechanics and blending in agitated tanks [J]. Chemical Engineering Science, 1991, 46 (8): 1883-1893.
[10]	Ma Qingshan (马青山), Nie Yiqiang (聂毅强), Bao Yuyun (包雨云), Wang Yingchen (王英琛), Shi Litian (施力田). Numerical simulation of hydrodynamics in stirred tank [J]. Journal of Chemical Industry and Engineering (China) (化工学报), 2003, 54 (5): 612-618.
[11]	Ma Qingshan (马青山), Wang Yingchen (王英琛), Shi Litian (施力田), Wang Jiajun (王嘉骏). Measurement and numerical simulation of flow field in stirred tank with multiple impellers [J]. Journal of Chemical Industry and Engineering (China) (化工学报), 2003, 54 (12): 1661-1666.
[12]	Hou Shuandi (侯拴弟), Zhang Zheng (张政), Wang Yingchen (王英琛), Shi Litian (施力田). Numerical simulation of turbulent flow in stirred tank agitated by axial impeller [J]. Journal of Chemical Industry and Engineering (China) (化工学报), 2000, 51 (1): 70-76.
[13]	Sun Hui (孙会), Pan Jiazhen (潘家祯). Numerical investigation of flow fields in stirred vessels with novel combined inner and outer agitators [J]. Journal of Chemical Industry and Engineering (China) (化工学报), 2006, 57 (1): 13-20.
[14]	Liu Baoqing (刘宝庆), Zhang Yikun (张义堃), Liu Jingliang (刘景亮), Qin Fulei (秦福磊), Lin Xinghua (林兴华), Jin Zhijiang (金志江). Numerical simulation of power consumption and mixing characteristic in stirred vessel with novel coaxial mixer [J]. CIESC Journal (化工学报), 2013, 64 (4): 1135-1144.
[15]	Pan Zhongyong (潘中永), Li Shuai (李帅), Zhang Hua (张华), Shi Weidong (施卫东). Numerical simulation of pulp suspension flow in stirred pot [J]. Journal of Drainage and Irrigation Machinery Engineering (排灌机械工程学报), 2011, 29 (3): 204-208.
[16]	Joëlle Aubin, Catherine Xuereb. Design of multiple impeller stirred tanks for the mixing of highly viscous fluids using CFD [J]. Chemical Engineering Science, 2006, 61 (9): 2913-2920.
[17]	Kelly W, Gigas B. Using CFD to predict the behavior of power law fluids near axial-flow impellers operating in the transitional flow regime [J]. Chemical Engineering Science, 2003, 58 (10): 2141-2152.
[18]	Chen Jia (陈佳), Xiao Wende (肖文德). Gas-liquid flow dynamics simulation in side-entering stirred tank [J]. CIESC Journal (化工学报), 2013, 64 (7): 2344-2352.
[19]	Li Liangchao (李良超), Wang Jiajun (王嘉骏), Gu Xueping (顾雪萍), Feng Lianfang (冯连芳), Li Bogeng (李伯耿). Computational fluid dynamics simulation of bubble size and local gas holdup in stirred vessel [J]. Journal of Zhejiang University:Engineering Science (浙江大学学报: 工学版), 2010, 44 (12): 2396-2400.
[20]	Cláudio P Fonte, Bruno S Pinho, Vania Santos-Moreau, José Carlos B Lopes. Prediction of the induced gas flow rate from a self-inducing impeller with CFD [J]. Chemical Engineering Technology, 2014, 37 (4): 571-579.
[21]	Zhou Guozhong (周国忠), Shi Litian (施力田), Wang Yingchen (王英琛). Computational fluid dynamics progress in stirred tank reactors [J]. Chemical Engineering (China) (化学工程), 2004, 32 (3): 28-32.
[22]	Lao Liyun (劳力云), Zheng Zhichu (郑之初), Wu Yingxiang (吴应湘), Li Donghui (李东晖). On the gas-liquid two-phase flow regimes and their recognition methods [J]. Advances in Mechanics (力学进展), 2002, 32 (2): 235-249.