Simulation Study Of Spray Desulfurization Process Based On Fluent Software

The improvement of living standards has made people pay more and more attention to the quality of life.However,due to the environmental and social economic hazards caused by sulfur dioxide,the public has been terrifying.The industrial production processes such as steel and coking are the main emission sources for sulfur dioxide.In recent years,with the official implementation of the most stringent environmental protection law,the application of desulfurization technology is becoming increasingly important for industrial demand.Moreover,design and optimization of desulfurization process based on computational simulation has attracted a great attentions from researchers in recent years.In this thesis,the operating parameters during rotary spray semi-dry desulfurization process were collected and analyzed,then simulated by CFD technology via fluent simulation software,taking spray drying tower as the research object.On the basis of certain hypothesis simplification,the physical model is established by Designmodeler software and the research object is divided into unstructured tetrahedral meshes by meshing software.Owing to the flow field of desulfurization tower is composed of continuous phase in flue gas and discrete phase in droplet,turbulence model（k-εmodel）and discrete phase model（DPM model）are selected as the theoretical basis,and the finite volume method,Simple algorithm and explicit difference scheme are adopted.Taking inlet velocity and pressure as initial conditions and using UDF function,the program of mass transfer process of SO₂ in gas and liquid is embedded in fluent software,and then the physical fields such as velocity,pressure and discrete phase distribution in desulfurization spray tower are simulated and analyzed.Ⅰ.The influence of process parameters on the desulfurization efficiency during actual production were investigated.To determine the content and types of active components for sulfur dioxide adsorption,the compositions of intermediate products obtained in different sections were analyzed by ion chromatography.It is shown that the desulfurization ash solid is composed by sodium carbonate,sodium sulfate and sodium sulfite,the ash and sprayed slurry mainly consists of sodium carbonate and sodium sulfate.During the scope of ordinary operating conditions,moderate molar ratio of Na₂CO₃ to SO₂ and large liquid-gas ratio,which can reduce mass transfer resistance and prolong the drying time of slurry droplet,is beneficial to enhance the desulfurization efficiency.Ⅱ.The effects of different physical models,flue gas velocity,inlet pressure on the velocity field and pressure field in the desulfurization tower were analyzed by ANSYS fluent software.The internal flow field distribution of the original model is not uniform,which can seriously affects the gas-liquid mass transfer process,resulting in the low desulfurization efficiency.The increasing or decreasing the inlet flow rate can not alter the distribution pattern of internal flow field to improve mass transfer,whereas blindly increasing the flow rate will increase the pressure drop and lead to higher operating costs.When the entrance shape is changed from circular to rectangular,the area of the low-speed region increases in the middle lower parts of the tower,while the turbulence intensity decreases slightly in the same part,demonstrating that the circular entrance shape is more favorable for the flow field distribution in the tower.With the increase of the entrance angle,the flow field distribution becomes worse under the double entrance type,therefore,the small entrance angle under the double entrance can significantly enhance the flow field distribution uniformity and improve the gas-liquid mass transfer.Ⅲ.Under the condition that the parameters of continuous phase were the same,the parameters of discrete phase were changed and nine operating conditions were designed under three operating conditions.The distribution of discrete phase and its effect on desulfurization efficiency were studied under different droplet temperature,injection speed and injection angle.In this part,the discrete phase model suitable for granular phase is selected and the gas-liquid two-phase flow field was simulated by commercial software ANSYS fluent.It is shown that in condition A,droplet temperature at 50℃was chosen as the optimum operating condition and the desulfurization efficiency can reach 94.8%;In condition B,the optimum injection speed was 15m/s and the desulfurization efficiency can reach 88.2%;In condition C,the optimum operating injection angle was 60degree and the desulfurization efficiency can reach 89.8%;The desulfurization efficiency can meet the requirement with the change of above operating conditions under the corresponding working conditions.