Hydrodynamic Simulation Of The Circulating Fluidized Bed Reactor For Swage Treatment And Optimized Structure Design

Circulating fluidized bed is a new-type sewage treatment equipment.It has effective mixing of the air-liquid-solid three phases,and excellent performance in the flow circulation.The scope of its application is becoming wider and wider.Research methods of the circulating fluidized bed are mainly focused on experiment and numerical simulation based on computational fluid dynamics,besides traditional theoretical analysis.Throughout recent decades,with the rapid development of computing technology,the method of numerical simulation has bigger advantage than before,for it can reduce the cost of time and material resources.According to demand of a sewage plant,flow field of circulating fluidized bed has been studied by using numerical simulation in this paper.And optimized structures have been designed.The model for aerated circulating fluidized bed used in sewage disposal was built in three-dimensional structure.Eulerian-Eulerian three-phase model and transient model were adopted to calculate the flow field.The pattern how process parameters,such as gas inlet velocity,and scale effect impact the flow field has been studied.The results indicate:As gas inlet velocity increases,distribution of air narrows down in the flow field.Velocity of loop flow trends to increase along with gas inlet velocity in certain range.The closer the density of biologic particles and water are,the better fluidization quality is.Effect from variation of the fluidized bed scale also have been studied.As the scale grows,gas inlet velocity needs to be amplified,to provide sufficient energy impelling the flow field a whole loop.To improve the fluidization quality,and avoid the particles gathering,two kind of optimized structures for aerated circulating fluidized bed have been designed.One of them,a top diversion structure,can significantly reduce the kinetic energy loss in the top flow field and increase the velocity of loop flow as the numerical simulation results indicate.It also can improve mixing of the solid particles.The cross division structure of draft tube improves the distribution of air in the rising zone.A simulation model was built for catalytic fluidized bed in the tertiary sewage treating process.It was built in actual size with fluid-solid two-phase flow.Influence to fluidization quality of factors,including density,diameter,initial piling height of particles,have been studied based on numerical calculation.The results show:Decrease of the particle's density improves catalysis.While the density is too low,particles may runout through the water outlet.Decrease of particle size improves fluidization quality of catalyzer.The max height of particles increases with the initial piling height in a certain range.Main process parameters have been decided,based on the numerical results.The parameters have been used in sewage treating process of a paper enterprises.And expected effect has been achieved.