Multiphase Flow And Separation Of Hydrate Slurry Spiral Tubes

There are huge amount of Natural Gas Hydrate(NGH)deposits stored beneath the ocean floor.Zhou Shouwei,Academician of Chinese Academy of Engineering,proposed a new approach of solid fluidizing mining technology for marine non-diagenetic NGH in shallow surface.In this regard,the separation of sediments from the mixed slurry of marine NGH must be resolved after crushing.As the mixed slurry is usually composed of minerals(mainly sediments),NGH,and sea water,it is a separation problem of liquid-solid-solid multiphase flowing.To reduce the energy consumption of the mixed NGH slurry during transport,it is necessary to carry out pre-separation of the sediments.This will also minimize the risks of pipeline clogging due to sediment deposition.In particular,the spiral branch pipe is a structure suitable for the separation of marine multiphase flowing.In this paper,based on the multiphase flow dynamics and discrete element method,as well as CFD-DEM coupling simulation,studies on the proposed separating structure that had been simplified and featured curved branch pipe with a sediment trap were conducted as follows:(1)To have a grasp of the current status and progress of researches on marine multiphase flow separation,through review of Chinese and international study reports.(2)ECFD-DEM coupling interface program development and verification.To explore the mechanical behaviors of solid particles in fluid,based on the basic theories,including multiphase flow dynamics and discrete element method.Given the effect of fluids on the rotational moment of the particles,an interface program for FLUENT-EDEM coupling simulation was developed and verified through experiments.(3)Numerical simulation of the flow characteristics of the spiral pipe.The movement patterns of the hydrates or sediment particles inside the spiral pipe were simulated with the verified interface program.After the equation for a single particle's movement trajectory on the section of the spiral pipe was established,the movement pattern of the hydrate slurry was further simulated.(4)Efficiency study on the separation of the curved branch pipe with a sediment trap.According to the distribution of the hydrate slurry's flow filed in the spiral pipe,a separating structure of spiral branch pipe was proposed and simplified into a curved structure.The separation efficiency of two types of structures,i.e.,curved branch pipes with or without a sediment trap,was compared by using the coupling simulation program.(5)Parameter optimization for the separation of the curved branch pipe with a sediment trap.Key structural and operating parameters were properly selected,to determine an orthogonal test scheme with 6 factors and 5 levels that affect the separation efficiency of the curved branch pipe with a sediment trap.Through optimization of the orthogonal test,the optimal combination of the structural and operating parameters was obtained,resulting in a higher separation efficiency.In summary,the distribution of the solid particles when the hydrate slurry was flowing in the spiral pipe was identified,and a curved branch pipe with a sediment trap was proposed to separate the hydrate slurry.Through optimization of the orthogonal test,the optimal combination of the structural and operating parameters was obtained,achieving an overall separation efficiency of 91.5%with the curved branch pipe with a sediment trap,and a hydrate particle content of 99.25%at its Outlet 2.This study provides a valuable reference for the separation of marine NGH slurry.