Numerical simulation and response surface optimization of micro-vortex flocculation process for high turbidity water treatment
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摘要: 针对微涡流絮凝工艺处理高浊水开展连续性工艺优化研究,采用计算流体力学(CFD)数值模拟软件,探究不同流量(流速)下絮凝区液流状态变化,确定最佳絮凝时间;应用响应面Box-Behnken设计方法,研究流量、混凝剂投加量与回流比及其交互作用对微涡流絮凝工艺处理高浊水效果的影响。结果表明:随着流量(流速)增大,絮凝区内湍动能、有效能耗、速度梯度及其变化率逐渐增大,但流速过大会导致絮凝时间不足,最佳流量为4.2~7.0 m3/h(最佳流速为0.41~0.67 m/s);回流比是微涡流絮凝工艺的极显著影响因素,其次是混凝剂投加量,最后是流量,三者间具有协同作用;微涡流絮凝工艺处理高浊水的最佳工艺参数,流量为5.9 m3/h,混凝剂投加量为34.8 mg/L,回流比为0.8,浊度、UV254、CODMn去除率分别可达99.23%、95.03%、71.42%。优化后的微涡流絮凝工艺为高浊水处理提供了新途径,具有一定的应用前景。Abstract: The optimization of continuous process was conducted for the treatment of high turbidity water by micro-vortex flocculation process. The computational fluid dynamics (CFD) numerical simulation software was applied to explore the changes of liquid flow state in the flocculation area under different flow rate (flow velocity) so as to determine the optimal flocculation time. By using response surface Box-Behnken design method, the effects of flow rate, coagulant dosing and reflux ratio and their interactions on the treatment effectiveness of high turbidity water by micro-vortex flocculation process were studied. The research showed that as the flow rate (flow velocity) increased, the turbulent kinetic energy, effective energy consumption, G-value and its rate of change in the flocculation zone gradually increased, but too excessive flow velocity could lead to insufficient flocculation time, and thus the optimal flow rate range was 4.2-7.0 m3/h. or the optimal flow velocity was 0.41-0.67 m/s. The reflux ratio was a highly significant factor affecting the micro-vortex flocculation process, followed by the coagulant dosage and flow rate, with a synergistic effect between the three. The best process parameters of micro-vortex flocculation process for treating high turbidity water were: flow rate 5.9 m3/h, coagulant dosage 34.8 mg/L, and reflux ratio 0.8; the removal rates of turbidity, UV254 and CODMn were 99.23%, 95.03%, and 71.42%, respectively. The optimized micro-vortex flocculation process could provide a new way for high turbidity water treatment technology with certain application prospects.
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表 1 配水水质
Table 1. Distributed water quality
水温/℃ pH 浊度/NTU CODMn/(mg/L) UV254/cm−1 15.3~21.8 6.2~7.5 195~213 7.8~12.5 0.256~0.282 表 2 Fluent数值模拟工况的进口参数
Table 2. Inlet parameters of Fluent numerical simulation conditions
流量/(m3/h) 絮凝时间/min 进口流速/(m/s) 雷诺数 湍流强度/% 4 25.4 0.39 7 765.64 1.87 6 17 0.59 11 648.46 1.97 8 12.7 0.79 15 531.29 2.04 表 3 评价指标
Table 3. Result evaluation indicators
雷诺数
湍流强度/% 湍动能/
(m2/s2)有效能耗/
(m2/s3)涡旋速度
梯度/s−1${\rm{R} }{ {\text{e} }_{{\rm{DH}}} } = \dfrac{ {\rho \nu d} }{\mu } = \dfrac{ {\nu d} }{\upsilon }$ $I = 0.16{{ { {\rm{Re} } } _{ {\rm{DH} } } }^{ - \frac{1}{8} } }$ $k = \dfrac{3}{2}{({\mu _{{\rm{avg}}} }I)^2}$ $\varepsilon = {C\mu }^{^{\frac{3}{4} } }\dfrac{ { {k^{\frac{3}{2} } } }}{l}$ $G = \sqrt {\dfrac{ {\rho \varepsilon } }{\mu } }$ 表 4 边界条件和求解方法
Table 4. Boundary conditions and algorithm
类别 结构参数求解设置 进口边界 流速进口(velocity inlet)、湍流强度、
水力直径出口边界 自由出流(outflow) 壁面边界 标准壁面函数 自由面边界 对称边界、刚盖定律 求解方法 SIMPLE格式求解,收敛初始值设置为10−5,
标准k-ε湍流模型表 5 高浊水中试试验响应面分析因素与水平
Table 5. Response surface analysis factors and levels for high turbidity water pilot test
水平 流量/(m3/h) 混凝剂投加量/(mg/L) 回流比 −1 4 15 0.5 0 6 30 1.0 1 8 45 1.5 表 6 优化试验设计及结果
Table 6. Optimization of experimental design and analysis of results
序号 X1/(m3/h) X2/(mg/L) X3 Y1/% Y2/% Y3/% 1 8 20 1.0 92.26 75.17 42.44 2 6 25 1.0 97.55 89.44 65.55 3 8 30 1.0 98.85 93.72 68.41 4 6 20 1.5 89.81 70.03 38.12 5 6 30 0.5 90.56 73.48 41.98 6 4 20 1.0 93.09 76.30 50.34 7 8 25 0.5 99.32 93.86 68.95 8 6 25 1.0 94.77 84.94 61.18 9 6 20 0.5 98.59 93.63 67.20 10 6 25 1.0 95.03 86.78 62.10 11 6 25 1.0 90.94 74.25 41.98 12 4 25 0.5 93.62 83.68 51.15 13 4 25 1.5 99.44 94.84 69.26 14 6 25 1.0 99.82 96.12 69.36 15 4 30 1.0 95.50 86.93 63.71 16 6 30 1.5 97.88 89.74 66.10 17 8 25 1.5 94.77 86.39 61.31 表 7 浊度、CODMn和UV254去除率回归方程显著性检验
Table 7. Significance test of regression equation of turbidity, CODMn and UV254 removal rate
模型 均值 变异
系数相关系
数(R2)信噪比 校正后相关
系数( $R_{{\rm{adj}}}^2$)失拟项 显著性 Y1 0.95 1.14 0.953 3 11.849 0.893 2 0.017 显著 Y2 0.85 2.94 0.961 7 12.492 0.912 5 0.11 显著 Y3 0.58 7.17 0.939 6 9.783 0.861 9 0.19 显著 -
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