Numerical study on flow dynamics in the supercritical water circulating fluidized bed riser

Abstract

There are a few reports about supercritical water circulating fluidized beds (SCWCFBs), and simulations were conducted via a two-fluid model to investigate flow dynamics in a riser of SCWCFB across different flow velocities, solid circulation rates, pressures, and temperatures. The investigated characteristics include the void fraction distributions, fluid velocities, particle velocities, and drag forces. The results show that the flow characteristics in the SCWCFB riser are similar to those in the traditional gas–solid riser. In the supercritical water fluidized bed riser, the void fractions are mainly in the range of 0.85–0.95. They are low at the bottom but high at the top and low near the wall but high at the center. Particle velocities are mainly distributed between 0 and 1 m s−1. They are upward near the axis of the riser and downward near the walls, showing the annular-core flow structures. Fluid paths are tortuous at low fluid velocities but straight at high fluid velocities. Particle drag forces are mainly around 0.7–0.8 times particle weights. The effects of pressures on flow dynamics in the SCWCFB riser can be ascribed to the changes in density and viscosity of supercritical water, affecting the ability of fluid to carry particles.