The Analysis Of Flow Regime And Affecting Factors Of Reaction Tank With Hyperboloid Stirrer

As the constitution of A2/O process, the running state of anaerobic and anoxic tank is essential to the effect of nitrogen and phosphorus. By setting the stirrer in anaerobic and anoxic tank, the rotation of the impeller to drive mixed liquid in a state of suspension and mixture, and to complete the mixing and reaction process of activated sludge and pollutants. As a new stirring equipment, hyperboloid stirrer has the characteristics of low energy consumption and good mixing effect, and it’s widely used in anaerobic and anoxic tank. But the design, selection and flow regime of the hyperboloid stirrer tank is not very clear, mainly relies on the experience of engineers, leads to stirrers and tanks don’t match, so as to make the most of the stirring tank has not been able to in the optimal working condition. With the development of computational fluid dynamics(CFD) technology, the numerical simulation method can be very convenient to obtain the mixing flow regime in the tank. This paper takes the running three kinds of anoxic tank in NO.4 Wastewater Treatment Plant of Xi’an City, to determine the actual velocity distribution and analysis of mixed state, on the basis, using the computational fluid dynamics software- FLUENT, the method of multiple reference frame(MRF) and a standard k?? model for numerical simulation of flow field, and investigated the stirring tank size, stirrer structure, installation height and stirring power on the effects of the mixed to provide basis for the design, selection and optimization of hyperboloid mixer. The main research results are as follows:(1)Due to the special results, hyperboloid mixer through drive the fluid into the bottom, so as to form a stable circulation in the tank, the velocity has the uneven distribution, at the bottom of tank is high, the upper central second, the central lowest, and has the features of low energy consumption and good mixing effect.(2)The flow field of numerical simulation of a single rectangle hyperboloid stirring tank are compared with the measured results, both relatively close, indicates that the method is feasible. The maximum velocity anoxic tank emerged on 200 mm from the bottom; distance from the wall 1.0 ~ 1.5 m is lowest place; stirring impeller focus in the area of 200 ~ 400 mm from the bottom, shows that the working principle of hyperboloid mixer for the use of a small circulation flow in a fluid to drive the whole tank.(3)The stirring tank size, stirrer structure, installation height and the factors of the stirring power are researched, The results shows that the stirrer diameter to the side of stirring tank ratio(D/L) is 0.188 ~ 0.250, impeller diameter to impeller height ratio(D/B) is 2.5, installation height is 500 mm from the bottom, and stirring power is 2~4W/m3, the mixing effect is best.(4)In the corridor type aerobic tank install more than one hyperboloid mixer turn them into without partition anoxic tank method is feasible. According to simulation results, further modification and optimization of corridor type anoxic tank in the NO.4 Wastewater Treatment Plant of Xi’an City are proposed, the existing 5 impeller diameter of 2500 mm, the power of 5.5 kW of stirrer to ten of the impeller diameter of 2000 mm, the power of 2.0 kW of stirrer, without any increase in power consumption under the premise of stirring bottom of maximum flow rate can be increased from 0.093 m/s to 0.241 m/s, not only can obtain a better mixing effect, but also can effectively prevent the sludge at the bottom of mud and show form scum.