| In recent years,the catering industry has been developing rapidly in China.While promoting economic growth,it has caused many environmental problems as well,and one of the focus is how to efficiently separate oil from oily sewage in catering industry.Vegetable oil is widely used in catering industry in China.Owing to the density of vegetable oil is similar to that of water,it is difficult to apply the static hydrocyclone separation technology in treatment of oily sewage from catering industry.Therefore,this paper proposed a method to treat vegetable oil sewage by dynamic hydrocyclone separation technology.Although there are some achievements in the research of dynamic hydrocyclone separation technology during recent years,its improvement awaits forther study in theoretical analysis,numerical simulation and technical equipment due to the fact that structures of dynamic hydrocyclone is more complex than static hydrocyclone.In this paper,the above problems were investigated,and the main contents and results are as follows:(1)Analyzed the separation mechanism of oil-water two-phase flow in dynamic hydrocyclone.Firstly,according to the working principle of the dynamic hydrocyclone,the flow law of oil-water two-phase in separation process was investigated,and it is known that the internal vortex of the dynamic hydrocyclone is a combination of quasi-forced vortex and quasi-free vortex.In fact,the separation process of oil-water two-phase is that the flow pattern turns from oil droplet dispersion to water-based annular flow.Secondly,through the force analysis of oil droplets in the dynamic hydrocyclone,it is known that oil droplets mainly converge to the axis of the dynamic hydrocyclone by centripetal buoyancy.Finally,two main causes of oil droplet breakage are vortex flow and turbulent flow in the dynamic hydrocyclone obtained by analyzing the mechanism of oil droplet breakage.(2)Designed a dynamic hydrocyclone oil-water separation system according to the processing capacity and rotational speed,which mainly includes separation process design,mechanical structure design and electrical control design.Firstly,according to the working principle of the dynamic hydrocyclone,the process that can realize the oil-water mixture recycling separation was designed.Secondly,based on the process of the system,the structures of the oil-water separation system,such as the rotating drum,the rotating guide vanes and the outlet,were designed.Finally,through the analysis of system function requirements,electrical system of the oil-water separation system was designed,and the operation parameters such as inlet flow rate,rotational speed and split ratio can be monitored in the upper computer system.(3)Investigated the effects of structure parameter and operation parameters on oil water separation efficiency of dynamic hydrocyclone by the method of numerical simulation.Firstly,the influences of structure parameter(the ratio of length to diameter)and operation parameters(inlet flow rate,rotational speed and split ratio)on oil water separation efficiency of dynamic hydrocyclone was studied by two-factor analysis method,and obtained that the optimum ratio of length to diameter is 18.Secondly,the effects of operation parameters such as inlet flow rate,rotational speed and split ratio on oil water separation efficiency of dynamic hydrocyclone was considered by response surface methodology.The optimum parameters were obtained:inlet flow rate is 1.8 m~3/h,rotational speed is 756 r/min,split ratio is 49%,and oil-water separation efficiency is 90%under the optimal conditions.(4)Studied the internal flow field characteristics of dynamic hydrocyclone by use of numerical simulation.Firstly,based on the results of separation efficiency simulation,the distribution characteristics of oil water velocity field,pressure field,turbulent flow field and concentration field in the dynamic hydrocyclone under the optimal conditions were evaluated.It is known that tangential velocity and static pressure have great influence on the separation performance of the dynamic hydrocyclone;the turbulence intensity near the rotating guide vanes and the wall of the rotating drum is higher;and the”oil core”with high oil concentration is formed at the axis of the dynamic hydrocyclone.Secondly,based on the results of flow field analysis in the dynamic hydrocyclone under the optimal conditions,the effects of inlet flow rate,rotational speed and split ratio on the velocity field,pressure field and turbulent flow field inside the dynamic hydrocyclone were observed.The results show that inlet flow rate mainly affects the axial velocity distribution inside the dynamic hydrocyclone,and rotational speed primarily impacts the tangential velocity and static pressure distribution inside the dynamic hydrocyclone.In this paper,a dynamic hydrocyclone oil-water separation system was designed.Based on the oil-water separation mechanism of dynamic hydrocyclone and numerical simulation method,the factors affecting oil-water separation performance of dynamic hydrocyclone were optimized,such as its structure parameter and operation parameters.And the flow laws of oil-water two-phase flow in the dynamic hydrocyclone were further explored through the flow field analysis.The research results are of great significance to the technology development and engineering application of dynamic hydrocyclone. |
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