Downhole Hydrocyclone For Fluidized Mining Of Marine Natural Gas Hydrate

With the increasingly prominent energy and environmental issues,the exploration of clean and renewable energy has become a research hotspot.Natural gas hydrate is the most promising alternative energy source in the future due to its high calorific value,high energy density,clean combustion and abundant reserves.About 99%of the natural gas hydrates on the earth are stored in the seafloor formations.In 2014,China first proposed solid-state fluidized mining technology for marine natural gas hydrates,one of its key technologies is to realize real-time separation of hydrate and sand mixed slurry,and backfill the sand to the seabed.Therefore,a novel liquid-solid hydrocyclone suitable for subsea gas hydrate extraction is proposed in this paper.It can realize real-time sand removal and backfilling of hydrate mixed slurry,reduce the sand content of produced fluid,protect the submarine stratum structure,and reduce the energy consumption of pipeline transportation.Experimental and simulated research methods were used to investigate the separation performance of an axial flow hydrocyclone with a nominal diameter of 100 mm.The main conclusions are as follows:As the flow rate increases,the residence time of the particles in the hydrocyclone greatly decreases,and the separation efficiency shows a trend of first increasing and then decreasing.There is an optimal flow range for particle separation,but an increase in flow will bring a continuous increase in pressure drop.For large particle sizes larger than 60 ?m,7 m3/h is the optimal operating flow rate,but for particles with smaller particle sizes,a larger separation flow rate is required due to the more complex loading conditions of the particles.Reducing the height of the sand outlet X/D will lead to the reduction of the separation blind area,the residence time of the particles in the entire separation process is greatly reduced,the difficulty of escape and the difficulty of capture are reduced.Therefore,reducing the height of the sand outlet X/D can effectively improve the separation efficiency of the hydrocyclone,while reducing the pressure drop.When the L/D is small,the turbulence intensity at the water outlet inlet and the sand outlet is strong.The turbulent flow carries particles into the water outlet which causes lower separation efficiency.The residence time of the particles in the hydrocyclone is very short.With the increase of L/D,the lzvv is more regular and stable,the turbulence intensity in the separation annulus is lower.But the increase in the flow path of the fluid causes the residence time of the escaped particles to increase.Increased resistance loss along the flow causes increased pressure drop.The purpose of this study is to achieve real-time sand removal and backfilling sand slurry and to guide industrial design.