Two-fluid Model Simulation Investigation On Particle Flow Behaviors And Emissions Control In A Gas-solid Fludizied Bed

Fluidized beds are widely applied in the industrial processing,and attract more interests from researches for guiding industrial reactor design because of the characteristics of fuel flexibility,high combustion efficiency and low pollution emissions.With the increasing requirement of environmental protection,how to reduce the emission of pollutants in fluidized bed is worthy of further study.Therefore,the combustion and emission control in a fluidized bed riser will be numerically simulated in this work using Two-Fluid Model.In the simulation,it is crucial to establish the correct mathematical model in this work.The Lattice Boltzmann Model?LBM?and Discrete Particle model?DPM?can accurately describe particle movement.However,in this work,the computation efficiency is too low to use these two methods,because the particles in fluidized bed has a huge amount.In this work the application of Two-Fluid Model based on the theory of the particles move can accurately describe the particle flow and combustion reaction.In Two-fluid model,drag model influence the particle flows a lot,in this work,we compare Huilin-Gidaspow drag model with the EMMS drag model during the numerical simulation of particle flow state.The result of EMMS drag model fit experimental data of Zhou et al better,therefore,we select EMMS drag model in this work.According to Zhou et al.'s experiment,a two-dimensional riser simulation study was carried out,and a three-dimensional riser simulation was carried out for 240t/h circulating fluidized bed.In the simulation,different Ca/S ratio and excess air coefficient are applied.Coal pyrolysis,char and volatile combustion reactions mainly occur near the coal inlet.In each simulation condition,as the height rises,the temperature first rises near the coal inlet,then falls cause of the cold secondary wind,then rises again due to the combustion temperature of some volatiles,and drops again near the outlet due to the exhaustion of volatiles and oxygen.With the increase of excess air coefficient,the temperature of the riser decreases,and with the increase of the ratio of calcium to sulfur,the temperature of the riser decreases.W with the increase of excess air coefficient,NO emission from the export pollutant increases,and the emission of SO₂ from the export pollutant decreases.With the increase of the calcium-sulfur ratio,NO emission increases and SO₂ emission decreases.