| According to total emissions of air pollutants and the status of air pollution in China of2012, SO2and dust caused by the fossil fuel-fired boilers are still the main pollutants of theatmosphere. But, the demands of air quality are continuously improving and the emissionstandards of air pollutants are increasingly stringent. It results in the updating ortransformation of desulphurization equipment being imperative. Therefore, this paper presentsa study of the structural optimization for the PCF wet desulfurization and dusting precipitatorwhich is widely used in engineering practice. It is significant to further improve thedesulfurization and dusting efficiency and save the cost of renovation project. The mainresearch contents and results of this study are as follows:The structure of physical model is established according to the size of experimentalapparatus and three grid sizes are tested for the independent of the characteristics of grid.Meanwhile, the good agreements between the simulation results and the correspondingexperimental datum validate the accuracy of mathematical model. Basing on the original PCFentrance structure, three different optimization entrance structures are designed. Four kinds ofdifferent entrance structure model are calculated by choosing the right turbulence model andsetting the correct boundary conditions. Comparative analyses of the gas flow field, thedistributions of liquid and solid particles between these devices are presented. In addition,different angles (30°,45°and54°) of right tangential entrance were investigated for thelow-speed area. The results show that tangential entrances unify the velocity distribution ofthe gas flow, strengthen the turbulence intensity in the preliminary treating chambers andoptimize the velocity components in the tangential direction. The tangential entrance of45°isbetter than30°and54°, which is conformed to requirement of the practical application inengineering.According to the simulation results of the structure optimization for the entrance, theeffect of first layer deflector is discussed to further promote the uniform distribution of theliquid phase under the consideration of gas-liquid heat transfer and droplet evaporation. Theresults show that the flue gas distribution and velocity distribution of device C-2and D-2remain the competitive advantage as device C-1and D-1. The first deflector layer has afunction to promote the uniform distribution of the flue gas in the original apparatus. Afterremoving the first layer deflector, the distribution of liquid-phase concentrating in the nearwall region is greatly improved. Greater tangential velocities in device C-2and D-2do not make the distributions of liquid-phase become more uneven in the optimized devices, and thefirst layer deflector is the main reason for uneven distribution. Combining the advantages ofgas-and liquid-phase distributions, the temperature and relative humidity distribution becomemore uniform and conducive for the desulfurization in device C-2. Besides, the heat transferbetween gas-and liquid-phase is very fast and takes place at the upper part of the preliminary treatingchamber, which is related to the temperature gap between the gas-and liquid-phase. Thus, afterremoval of the first deflector layer, not only keep the advantages of device C-1and D-1, butalso further improve the distribution of the liquid phase in device C-2and D-2.The forces of liquid-and solid-phase particles are studied during them keeps moving in thepreliminary treating chamber using the Newton’s Second Law. The results show that the tangential speed isthe major component of velocity in the tangential entrance structures. The dusting efficiency of device C-2and D-2is more superior than the original structure due to the optimization of velocity and tangential speeddistributions. The increase of tangential speed does not make the distribution of liquid-phase become moreuneven under the size of this test device and the main reason for uneven distribution of liquid-phase is thefirst layer deflector. This conclusion is consistent with the simulation results, which illustrates therationality of the structural model and numerical models again.Basing on the analyses of gas flow field, liquid-phase distribution, solid-phase distribution,temperature distribution and the pressure drop, this paper presents a study of structure optimization for thePCF device. The uniform distributions of gas-, liquid-and solid-phase are came true in the final optimizedstructure, which is significant to provide guidance for the research of equipment design and the update ofinstalled PCF device. |
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