| Currently, the flow pattern in the peripheral-feed and peripheral effluent secondary clarifier of General Water of China (Xiangtan) Sewerage Company is not good. This phenomenon will lead to sedimentation effect and the efficiency of precipitation fell. It's necessary and meaningful to do research about the flow field and the distribution of suspended solid concentration in peripheral-feed and peripheral effluent secondary clarifier, and then the best reflux ratio could be determined more accurately. It would provide useful references for the operation management of peripheral-feed and peripheral effluent secondary clarifier.Firstly, based on the present research all over the world,a two-dimensional two-phase mixture model is built. The solid phase is treated as pseudo fluid in the model,which is coupled with improved RNG k ?εtwo-equation model. Fluent 6.3, a CFD software, was used to simulate the flow field distribution and the distribution of suspended solid concentration in peripheral-feed and peripheral effluent secondary clarifier with different reflux ratios. The comparison between simulation results and production dada of wastewater treatment plant. The simulate results show that: (1) The flow pattern is not the same to the design flow pattern; (2) the bottom of the sludge is a compressional zone with high sludge concentration and the thickness is no more than 0.11m; (3) it has the best sedimentation efficiency when reflux ratio is 0.6, half of the present reflux ratio 1.2. It means that this change could increase the sedimentation efficiency and reduce the energy consumption, achieve the purpose of energy saving and emission reduction.After the simulation of the peripheral-feed and peripheral effluent secondary clarifier with different constructions and reflux ratios. The simulate results show that when the grade is 0.1 and the reflux ratio is 0.2, it has the best sedimentation efficiency and the least energy consumption. |
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