Research On Particle Movement In Hydrate Slurry Of Hydrocyclone

At present,with the large-scale exploitation of traditional fossil energy sources,energy shortages have caused people to constantly search for new energy sources.The huge reserve of marine natural gas hydrate is considered as a new type of clean energy that can replace traditional fossil energy in the future.In the technology of the solid fluidization development of non-diagenetic natural gas hydrate stored in seafloor surface,in order to reduce the energy consumption during transport of natural gas hydrate from seabed to offshore platforms.As natural gas hydrate slurry is mainly composed of hydrate particles,sediment particles and seawater,it is a solid-solid-liquid multiphase separation problem.Taking into account the pre-separation in the seabed,combined with the advantages of the hydrocyclone itself,it was determined that a hydrocyclone is used to separate natural gas hydrate slurry.When using hydrocyclone to separate natural gas hydrate slurry,studying the trajectory of hydrate particles is a key scientific issue.Therefore,in this paper,the DEM-CFD coupling simulation method is used to carry out,studies the particle movement of natural gas hydrate slurry in hydrocyclone as follows:(1)By consulting the literatures at home and abroad,the research status of hydrocyclone,especially the research results of particle movement in hydrocyclone.(2)The development of DEM-CFD coupling program.Based on the basic theories of multiphase fluid and discrete element methods,the forces of particle in fluid is studies.The DEM-CFD coupling simulation program is developed and the reliability is verified.(3)Study on the flow of hydrate slurry in a hydrocyclone and the motion of solid particles.The multiphase flow of natural gas hydrate slurry in a hydrocyclone is studied by using the validated coupling program.Firstly,the flow field of liquid-phase seawater in the hydrocyclone is analyzed,and the movement law of seawater is obtained.Then the movement of hydrate particle and sediment particle in hydrocyclone is studied.Due to the light specific gravity of hydrate particle,it would move spirally upwards in the inner swirl and eventually be discharged from the overflow port.Due to the heavy specific gravity of sediment,it would spiral downward along the outer swirling flow and eventually be discharged from the bottom flow mouth.As the main purpose of separation is to obtain more hydrate particles,the movement of hydrate particles in the hydrocyclone has been studied intensively.(4)Study on the movement characteristics of single hydrate particle in different inlet regions.By using the validated multiphase flow simulation program,the motion characteristics of single hydrate particle in different inlet regions.According to the simulation results,the position,velocity and force data of hydrate particles in the representative five locations of inlet region are extracted,and the separation trajectories of the hydrate particles,the movement velocity and the force of the hydrate particles are analyzed.(5)Study on influence of entrance area and particle size on hydrate particle motion laws.In order to study thoroughly the influence of hydrate particles on the trajectory of the hydrate from different regions of the entrance,the inlet region is discretized and is divided into smaller regions.The hydrate particles of different inlet regions were studied in the hydrodynamic swirling field.The closer hydrate particles are located to the upside and the inside of inlet,the easier particles can be discharged from the overflow port.It is form efficient separation zone.The closer hydrate particles are generated to the downside and outsides of inlet,the easier particles can be discharged from the bottom flow port.It is form inefficient separation zone.When changing the particle size of hydrates,new changes will occur in the movement law.With the particle size of hydrate particle decreases,the upper part of the high-efficiency separation zone in the inlet zone gradually decreases toward the inner side of the inlet,the lower part of the separation high-efficiency zone gradually decreases toward the upper side of the inlet.The upper part of the separation-inefficient zone gradually expands to the inner side of the inlet.The lower part of the separation inefficiency gradually expands toward the upper side of the entrance.Through the above studies,the flow law of hydrate slurry in the hydrocyclone was mastered.Through the theoretical analysis and numerical simulation,the trajectory characteristics of the hydrate particles and sediment particles in the hydrocyclone were obtained.It is found that there is an efficient separation zone and an inefficient separation zone in the inlet zone.These results have a direct reference value for designing hydrocyclone with high efficiency for separating hydrate slurry,especially for design of a highly efficient hydrocyclone,providing a new analytical means and methods.