Flow Distribution And Relevant Synergy In Chemical Process Equipments

Environment protection is the main theme at present,and the removal of exhausted gas is the key problem in environmental chemical engineering.Larger size and higher efficiency are the current tendency for absorption apparatuses of desulfurization and denitration,so the problem of flow uniformity in process intensification is of high importance.Problem of flow uniformity is ubiquitous in chemical apparatuses.Considered as a general problem in chemical engineering,its background,significance,progress of research,state of art,research techniques are summarized.Take the ammonia oxidation reactor and the Wet Flue Gas Desulphurization(WFGD)spray column as examples of single and multiphase flow respectively,the problem of flow uniformity and some relevant problems are researched.The present study is mainly conducted by computational fluid dynamics(CFD)and assisted by theoretical analysis and experimental observation and measurement.The new research method——flow control and synergistic idea are employed to get the mechanism of flow uniformity,technology and the intensification scheme for the relevant problems.Flow homogenization is a process of flow control in essence.Compared with drag distributed mechanism in macroscale,a mechanism based on flow control theory is put forward to research the flow uniformity.Flow field is controlled by geometries of apparatus and operating conditions,so seeking the relationship between flow structure and geometries,operating conditions is the key to control the flow field efficiently and accurately.Flow structure is the chain to link the geometries,operating conditions with the performance of the apparatus.In the research of desulfurization spray column,the mechanism of flow uniformity——self-adjustment effect is firstly obtained,then based on the mechanism and the synergy analysis,the performance of the column is optimized in three aspect:flow uniformity,enlargement of interfacial area and the intensification of gas-droplet interaction.The main conclusions include:(1)Self-adjustment effect has a prerequisite of countercurrent state of gas-droplet flow,but this requirement is in contradiction with the enlargement of interfacial area in the selection of droplet diameter.In a single layer column,the rod bank internal can be introduced to assist the self-adjustment effect come into effect so as to enlarge the interfacial area;in a multi-layer column,synergistic effect between different layers can be used to optimize the problem--accomplish the flow uniformity in the bottom layer and enlarge the flow uniformity in rest layers.(2)Besides the assistance for flow uniformity,the rod bank internal can adjust the flow structure in the column,enhancing the local liquid hold-up and vorticity.To match the area with high liquid hold-up and high vorticity can achieve the field synergy effect and intensify the gas-droplet interaction and mass transfer.In the three modes under different geometries and operating conditions,rising-falling mode is the proper one to achieve the match.In the research of flow uniformity in single phase flow,on the background of ammonia-oxidation reactor,the mechanism,process,energy consumption of flow homogenization are researched.The new structure of distributor as well as its design scheme are proposed.The main conclusions are shown below:(1)In single phase flow,mechanism of flow homogenization is the radial flow distributed mechanism.Based on the mechanism,the process can be divided into four steps:generation of radial flow;allocation of radial flow;conversion of radial flow;momentum transfer of axial flow downstream.According to four steps,the new structure of distributor is put forward by the optimization of traditional perforated plate in different areas.Taking the flow uniformity and energy consumption into consideration simultaneously,new structure of distributor is the combination of a small perforated plate in the centre and the surrounding vertical baffles.(2)Combined with theoretical analysis and numerical simulation,a CFD based scheme——flow field analysis scheme is put forward.According to the flow field in numerical simulation,structure of distributor can be optimized by the relationship between geometries and flow structure in theoretical analysis.