Study On The Efficiency Improvement And Resistance Reduction Of Bag Filter Based On CFD Numerical Simulation

As national standards for control of air pollution are raised,bag-type dust removal technologies are faced with challenges such as high resistance to transform,insufficient space on site and unacceptable emissions.Therefore,this paper addressed the problems of high resistance and insufficient space in bag filter.After the analysis,an idea that we can assemble filter bags and cartridges together was proposed.The distribution of filter bags and cartridges and their position in the bag filter and the uniformity of the internal air flow were investigated by experiments and numerical simulation.And three transformation methods were proposed.Meanwhile numerical simulation analysis was performed.Practical engineering cases were analyzed at the end of this study.Conclusions were as follow:The results of electron microscopy and the test of dynamic filter filtration performance showed that the surface filter media had dense fiber surface,small pores and a gradient structure which can prevent the dust from entering the filter media.The filtration efficiency of the surface filter media was significantly higher than that of the deep filtration media.At the same time,the pleated cartridge of the selected filter material is 50%more accurate than the filter bag.Therefore,the experiment used spunlace filter(surface filtration),of which the material was PPS(polyphenylene sulfide).The resistance of the bag filter increased with the increase of the wind speed.After0.8 m/min,the increase rate of the resistance increased significantly and the resistance increased at a high rate.Long-term experiments also further verified this phenomenon.Therefore,the wind speed of the filter in the bag filter should not be higher than0.8m/min in the hybrid filtration scheme.The Ki value of one-cycle was used to evaluate the blowing effect.The results showed that the injection tube type D=12 mm with a blowing nozzle demonstrated the best effect.The effects of different mixing ratios and position distributions on the resistance of the filter were studied.The lowest drag ratio in each mixing ratio is 4 cylinders 2bags(out),3 cylinders 3 bags(2 in 1),2 cylinders(medium)4 bags,1 cylinders(in)5bags(The position of the filter element is indicated in parentheses,the first two mixing ratios are expressed as the position of the filter bag,and the last two are indicated as pleated cartridge positions),compared with the full bag filter and full pleated cartridge,the mixed transformation interval between 2:1~1:2.Using the numerical simulation method,the distribution of the favorable flow field at the outlet of the further pleated cartridge in the mixed simulation was analyzed.In the mixing ratio of 1:5 in the pleated cartridge relative to the number of less,the pleated cartridge has little effect on the resistance of the overall filter and the distribution of the flow field.Simulation analysis of the three transformation arrangements by CFD(Computational Fluid Dynamics)numerical simulation shows that the distribution uniformity of the Plan2 flow field is better,and the internal flow field of the pleated cartridges is more evenly spaced,and the pleated cartridge should not be too close to filter bags.By changing the number and position distribution of the filter bags and the pleated cartridges and optimizing the Plan2,the uniformity of the flow rate and the flow distribution coefficient are improved,that is,the distribution of the flow field inside the filter is more uniform and the resistance is further reduced.Replacing part of filter bags with pleated cartridges not only increased the efficiency of dust removal and reduced the effect of resistance,but also extended the service life of filter elements and shortened the replacement cycle.Through comprehensive analysis,the transformation program can bring economic benefits.In the case of actual engineering transformation,the transformation of a low-pressure pulse-type bag filter for a CFB coal-fired boiler in a thermal power plant was carried out.After the transformation,the dust emission from the bag filter was less than15 mg/Nm~3,which was far below the national environmental protection standard(30mg/Nm~3).And the dust removal efficiency surpassed 99.9%.The running resistance of the bag filter was reduced by about 20%after transformation,indicating that replacing the pleated cartridges with filter bags and distributing the different filter elements can effectively reduce the resistance and improve the distribution of the airflow inside the precipitator,so that the energy consumption of the equipment operation can be reduced.