CFD-DEM simulations of a gas-solid-liquid fluidization system: Effects on the flow field and particle behavior of semi-dry desulfurization fluidized bed

Gas-solid-liquid multiphase flow systems have been widely applied in energy engineering, petrochemical industries, biochemical industries and food industries, etc., which usually involve multi-physical processes and multi-reaction stages. As a typical gas-solid-liquid multiphase flow system, the semi-dry flue gas desulfurization fluidized bed has been widely applied by small and medium-scale thermal power plants for its advantages of excellent mixing effect, relatively high efficiency and low cost. This study focused on the fluid hydrodynamics, wet particle motions and the transfer efficiency (SO2 removal efficiency) in a fluidized bed via two-way coupled CFD-DEM numerical simulations with the implementation of different semi-dry desulfurization stages ("constant-rate" absorption stage, "falling-rate" absorption stage and solid absorption stage) as well as the liquid bridge force. To avoid the fast evaporation of small droplets, simulations based on larger particles (Geldart group D) were also conducted to clarify the influence of varying liquid volume contents. Results revealed that the existence of liquid layers would partly enhance the desulfurization efficiency, while in this case the bed exhibits poor fluidization characteristics. Adding humification water in the solid absorption stage would transform the reaction stage from solid absorption stage to "constant-rate" absorption stage, which improves the desulfurization efficiency significantly. It could also be summarized that the increase of Ca/S molar ratio would enhance the desulfurization efficiency partly, but the improvement would not be obvious when the Ca/S molar ratio is greater than a certain range.