| With the approaching of the dual carbon target,natural gas hydrate,a clean energy with large reserves,wide distribution,low pollution and high calorific value,has been paid more and more attention.At present,there are many kinds of natural gas hydrate mining methods in the world.In the geological environment of argillaceous siltstone in Shenhu sea area of South China Sea,the most suitable method is solid fluidization mining.There is a serious problem of sand production in the mining process.Downhole gas hydrate cyclone separator can effectively solve this problem.The downhole natural gas hydrate cyclone separator has the characteristics of simple design,no internal moving parts and suitable for narrow bottom hole space,and the failure rate is low.Its working principle is to generate swirl through spiral blades,and guide the mixture of seawater,natural gas hydrate and sediment to rotate around the central column of the downhole natural gas hydrate cyclone separator.Using the centrifugal separation principle of liquid-solid and solid-solid immiscible,under the action of centrifugal force,the sediment particles with large density are thrown into the inner wall of the inner tube of the downhole natural gas hydrate cyclone separator,so that they are discharged along the bottom sediment outlet,so as to achieve the purpose of separating sediment from natural gas hydrate and backfilling sediment in situ.The separation efficiency of traditional downhole gas hydrate cyclone separator is low,so ’ high efficiency and low resistance ’ has become the most important research direction of downhole gas hydrate cyclone separator.In this paper,the spiral blades of downhole natural gas hydrate cyclone separator are analyzed.The main factors affecting the separation efficiency and pressure drop are determined by single factor analysis.The structural dimensions of different pitches of variable pitch spiral blades are optimized by response surface optimization design method.In order to improve the separation efficiency of downhole natural gas hydrate cyclone separator to sediment in the mixture,and ensure that the energy loss is minimized,that is,the pressure drop.The main research contents and conclusions of this paper are as follows :(1)Based on the actual working conditions of the offshore drilling platform,the boundary conditions are set up,and the grid independence verification is carried out to select the appropriate number of grids and grid structures.The numerical simulation results are compared with the experimental results to verify the accuracy of the numerical simulation method.(2)The numerical simulation of the traditional fixed pitch downhole cyclone separator is carried out,and the single factor method is used to analyze the structural parameters.The results show that the number of spiral blades and their pitch have a great influence on the separation efficiency and pressure drop of the downhole cyclone separator.(3)RSM-CCD experimental design was carried out on the two-stage variable pitch cyclone separator.The optimized two-stage pitches were 200 mm and 135 mm,respectively.The separation efficiency was 80.15 %,and the pressure drop was 91.10 KPa.Compared with the structure before optimization,the separation efficiency was improved while reducing the pressure drop.Compared with the traditional fixed pitch downhole cyclone separator,the separation efficiency was significantly improved without greatly increasing the pressure drop.(4)RSM-BBD experimental design was carried out on the three-stage variable pitch cyclone separator.The optimized three-stage pitches were 187.97 mm,150 mm,and 77.174 mm,respectively.The separation efficiency was 85.55 %,and the pressure drop value was 167.0 KPa.Compared with the structure before optimization,the separation efficiency was improved while the pressure drop value was unchanged.Compared with the two-stage variable pitch cyclone separator,although the pressure drop value was increased,the separation efficiency was significantly improved. |
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