Numerical Simulations On Hydrodynamic Characteristic Of Multi-component Particles In A Liquid-solid Fluidized Bed With A Jet

Liquid-solid fluidization has advantages of stable bed structure, good quality, high efficiency of mass and heat transfer. This conversion unit is widely used in various industry area with its simple structure, low cost, automatic control and management. Due to process requirements, fluidized bed is shown in different styles. In order to improve the mixing property of liquid and solid in processing of oil removal in the sewage, we make up a new idea to combine the technology of inverse fluidized bed and jetting fluidized bed. However the theoretical investigation on inverse liquid-solid fluidized bed with a jet is comparatively less. Furthermore, characteristics of liquid-solid system are complicated and indeterminate. Therefore, numerical simulation will be used to research the mechanism and flow structure in this kind of fluidized bed.Flow behaviors of particles and liquid are modeled with the combination of the discrete element method(DEM) and computational fluid dynamics(CFD) in a two-dimensional inverse liquid-solid fluidized bed with a jet. Liquid turbulence is modeled by k-ε model, and DEM is used to model the collision of particles. Gidaspow model is adopted to calculate drag force between liquid and solid. The simulated results of one-component particles show that the flow process is divided into three stages: particles carried by the drag force flow down, buoyancy force carry particles flow up, interaction between all kinds of forces achieve dynamic balance. Particles dispersed as convex as well as accumulated near the wall. Fluidized quality could be improved by increasing jet speed, fluid viscosity or particle restitution coefficient and homogenizing particle size. Particle temperature and rotational particle temperature are also bring in to calculate particle fluctuations.The simulated results of two-components particles show the same flow behavior as one-component except that the accumulation near the wall is the big one. Solid volume fraction along bed height increase firstly then decrease. The position of the maximum particle concentration is decreased with the increasing liquid viscosity. Appropriate increase of velocity could improve the quality of fluidization. But if it is larger than particle terminal velocity, particle agglomeration will be intensified. Fluidized quality could also be improved by increasing coarse particles density or decreasing size difference of coarse particle and fine particle. It also reveals that particle density has greater influence on mixing degree than particle size. Simulation results has a better conformity with Rowe. It indicates the reliability of this simulation method and lays a foundation for further study in fluidized bed.