CFD Simulation And Process Optimization Of Ammonia Absorption In Absorption Tower

One of the most traditional ammonia recovery processes involves using water as an absorbent to extract ammonia from ammonia-containing waste gas.While this process is simple and low in energy consumption,it still has a high water consumption.In order to make the process greener and more economical,a small absorption tower was selected as a preliminary research device in this study.CFD techniques were used to simulate the process of ammonia absorption by water in the tower,to visualize the flow field distribution,and to explore the operating conditions that promote ammonia absorption with controlled spray water flow.Initially,a simplified physical model of the absorber tower was constructed using Spaceclaim software.The model was then structured and meshed by ICEM CFD software.Using Fluent software,the standard k-ε turbulence model was employed to simulate the gas-liquid 3D flow distribution,while the porous media model was used to simulate the packing.The flow field with different inlet velocity,inlet volume fraction,and porosity of porous media was solved by Mixture multiphase flow model.From the simulation results,it was observed that the spraying range is concentrated in the middle of the absorption tower,resulting in the mixed gas easily gathering in the side of the tower.As a result,the gas-liquid contact situation is not good,necessitating the selection of suitable packing and its reasonable layering to promote mass transfer.When the spray water flow rate is fixed,the closer the ammonia gas velocity is to the liquid flood gas velocity,the more conducive it is to gas-liquid mixing and the higher the mass transfer efficiency.A small increase in the volume fraction of ammonia effectively enhances the absorption rate of ammonia.However,if the volume fraction increases too much,the increase in absorption rate will gradually be smaller than the increase in ammonia concentration,preventing mass transfer from occurring.Furthermore,if the porosity of the porous medium,which is regarded as a whole,increases due to the change of the bulk packing stacking method,the excessive increase of the liquid holding capacity of the packing will cause the flow of ammonia to be blocked and it is difficult to contact with water fully.Without replacing the filler,the stacking density should be as large as possible to ensure that the average porosity of the filler layer is closer to the porosity of the individual filler,which is more conducive to absorption.