Numerical Study On Multiphase Flow In The Spiral Tubular Reactor

Hydrate technology has wide application prospects.In this paper,the phase equilibrium conditions for hydrate formation in various application scenarios are discussed,and the multiphase flow is numerically simulated in a spiral tube hydrate reactor.A thermodynamic model is established by combining Chen-Guo model,SRK equation of state and Pitzer activity coefficient model,and the phase equilibrium conditions of gas hydrate formation in pure water and salt system are predicted respectively.The reliability of the model is verified by comparing with the experimental data reported in the literature.The results show that although the model has low prediction accuracy for some components,it is sufficient to meet the engineering requirements and is widely applicable.Subsequently,this model is used to predict the phase equilibrium conditions and equilibrium composition of hydrate formation of flue gas,coalbed methane and biogas.The results indicate that the CO₂content of the hydrate phase can reach about 90%after the flue gas through two levels of hydration;for coalbed methane hydrate,the CH₄content in the hydrate phase can reach more than 96%;salt is added to lower the freezing point of water to ensure sub-zero hydrate production without affecting storage efficiency;hydrate technology can be used to store and transport the biogas after purification.Numerical simulation method is used to investigate the hydrate slurry flow process in the spiral tubular reactor.The results show that,compared with smooth tubes,the presence of spiral grooves will cause periodic disturbances to the fluid near the wall,resulting in secondary flow and centrifugal force on the cross section.The secondary flow continuously scour the pipe wall to prevent the formation of hydrate from attaching and affecting the heat transfer,which plays the role of wall renewal;the different densities of gas-liquid-solid three phase leads to different centrifugal force,which makes three phase separation,the gas is aggregated to the center of the tube,the liquid is aggregated to the wall of the tube,and the hydrate is aggregated to the area between the center of the tube and the wall.In this process,the gas-liquid interface is constantly updated,which strengthens the mass transfer.The influence of pitch（26.8 mm,30.0 mm and 33.2 mm）and groove depth（1.2mm,1.4 mm and 1.6 mm）on the performance of spiral groove tube was investigated.The results indicate that the above process can be further strengthened by using smaller pitch and larger groove depth.