CFD-DEM simulation of the supercritical water-solid flow in cyclone

With the increasingly growing energy demand and serious environmental pollution, the utilization of hydrogen energy is obtaining attention because it has high calorific value and its combustion products are environmentally friendly. It is found that hydrogen can be attained from coal gasification efficiently by using a new method of supercritical water (SCW) circulating fluidized bed reactor. To separate the incomplete combustion of coal powder particles from SCW for ensuring the whole system is safe and stable, cyclone has always been employed. The traditional gas-solid cyclones are widely studied, while it is still limited for revealing the mechanism of particle behavior in cyclone under SCW environment because of the extreme conditions and complex solid-fluids interactions. In this study, the combined discrete element method (DEM) and computational fluid dynamics (CFD) model is employed for investigating the SCW-solid flow in the cyclone. The effect of inlet velocity is investigated and analyzed in terms of flow fields, and the interaction forces between particle-fluid, particle-particle and particle-wall. The simulation results indicate that particles have a great impact on the distributions of the flow fields and the value of interaction forces between particle and wall are much smaller than that between particle and particle. It takes about 2.4 s for the flow to reach macroscopically steady-state condition and particles first appear in the outlet tube at approximately 0.72 s. The results should be helpful to understand the mechanism of SCW-cyclone and can be used to optimize the cyclone for better performance.