| Ozone is an excellent disinfectant and is able to effectively decompose organic pollutant, inactivate pathogenic microorganisms, and especially inactivate Cryptosporidiumparvum and Giardia. This causes ozone-active carbon process, the mainstream craft of tap water advanced treatment, to obtain a more widespread application both at home and abroad. However, due to design deficiency, short circuiting and backflow were severe in most current ozone contactors which result in low T10 , the indicator of hydraulic efficiency. According to the disinfection dynamics, the deactivation efficiency is determined by the CT value (ozone concentration C and the disinfection time T). When the effluent CT10 remain unchanged, by increasing the T10 value, we can reduce the C value, that is, ozone dosage, and thus reduce the amount of bromate generated. It can come to the conclusion that increasing T10 through ozone contactor optimizing is one of main bromate controlling methods. This thesis is to aim at optimizating ozone contactor to improve its hydraulic efficiency.As the development of computer technology, computational fluid dynamics (CFD) has become a important tool for modeling and optimizing hydraulic efficiency. This thesis takes the computational fluid dynamics (CFD) as the research tool to simulate and optimize ozone contactor.Two kinds of tank (tankâ… and tankâ…¡) were chosen for research object based on the existing typical structure of the ozone contact tank . The VOF model is applied in the simulation with T10/HRT as the optimization index while the aeration effect on flow state was not taken into consideration. The tank with higher hydraulic efficiency was got and then optimized by increasing baffles in proper point(there are three programs for increasing baffles, program 1, program 2 and program 3, respectively). Considering the huge simulation calculated amount of ozone contactor, a bubble column which own the same liquid and gaseous mass transfer was taken as research object. Ozone concentration distribution of the column was obtained through modeling with the Eulerian model.Then the model, after which was validated by experiment, was applied to ozone contactor and to acquire the ozone concentration distribution of the aeration chambers of ozone contactor. At last, the overall ozone concentration distribution and CT distribution of the optimized ozone contactor was obtained by using species transport model.The following conclusions can be obtained by the research: the first, severe short circuiting and backflow were exists in the two typical tanks which result in low hydraulic efficiency; the second, hydraulic efficiency of tankâ… with T10/HRT as 0.246, is superior to the of that of tankâ…¡,whose T10/HRT was 0.126. However, tankâ… 's hydraulic efficiency was not satisfying at all. The third, after optimization, the T10/HRT of the three programs were 0.346, 0.388 and 0.406 respectively, making the hydraulic efficiency of tankâ… increased by 48%, 58% and 65%. Apparently, program 3 was the best. The fourth, except the vicinity area of the aerator where large simulation error occurred, above 0.8m of the tall bubble column, simulation result approximately consistent with the experimental results. The last, species transport model calculation result showed that the aveage CT value before and after optimization by program 3 is 3.79g/lmin and 5.17mg/lmin respectively. The CT value increase 36.4% after optimization. |
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