The Air And Particle Concentration Distribution Research Of Bag Filter In Dust Removal Space

In recent years, coal consumption was increasing year by year; coal is still occupied the main position in China energy structure in near future.There was much smoke dust left to be removed after coal. At the same time as the National Environmental Protection Act is increasing strict, technology requirements on Dust removal is becoming more and more sophisticated. dust emission concentration of the new coal-fired plant and the old coal-fired plant before 2010 should be below 30～50mg/m3. With the increasing capacity of the plant, the mounting volume of smoke dust need the bag filter to become bigger and bigger in volume..However, a large bag filter on the requirements of system stability and service life is getting higher and higher, meanwhile ways of airflow into the bag filter and particle concentration distribution are two key factors in bag filter operational condition,this paper is aiming at three ways of bag filter airflow organization and dust space's particle concentration distribution research. by the combination of theoretical analysis and CFD simulation respectivelyThe issue began with the research of particle concentration distribution around the filterbag by theoretical analysis, the mathematical model of particle concentration distribution around the filterbag was established through momentum conservation equation after the bag filter's ash cleaning. For lower inlet style bag filter that the dusty flow inlet was situated on the lower part of the bag-house, this model was applied to calculate the particle dispersion by changing the size of particle,updraft speed and bag spacing with time varying. The calculation results show that the fine particles are floating under the pocket about 0.5m to 2.5m (8.3%-41.7%of bag length), on the other hand the coarse particles are suspended in the lower part of filterbag spacing; The smaller bag spacing, the higher the filtration concentration as well as the filtration speed; the higher updraft speed, the closer to the top of filterbag with particle suspended in filtration spacing, and the lower average concentrations.In addition, this modle could calculate the particle dispersion of every items of inlet style bag filter by changing the boundary condition.Aiming at a ESP transform into the bag filter project for disposing with gas flow about 4620000m3/h, the author designed three different forms of bag fiters, such as airflow came into the bag filter through end side of the bag-house which was a tradional bag filter called end side inlet style bag filter, side inlet style and lower inlet style bag filter and had a CFD simulation to that three style of bag filter. The CFD simulation analysis results show that the lower inlet style bag filter deals with the most uniform gas flow in every boxes of dust space; the face velocity of end side inlet bag filter is higher than others,which can reach 3.0-6.0m/s,what's more, it can exceed 8.0m/s below some the bottom of some filterbags, on the other hand, the face velocity is less than 3.0m/s in the inlet style and side inlet style bag fiter.Through the analysis of the streamline chart and eddy velocity in the ash container which in three ways of airflow coming into the filter bag,we can see that the eddy velocity is highest, and the next are side inlet style and end inlet style bag filter, however the first ash container's eddy velocity is very larger in the end inlet style bag filter; analyzing the updraft speed in the different position of the bag filter, the side inlet style and the end inlet style bag filter have the same trend taking on the both ends being higher than the center,but the another one have a gradually deceasing trend from the bottom to the top of the filterbag, meanwhile the updraft speed of lower inlet style is higher in the entire dust removal space.By the application early established mathematical model, we can calculating the particle concentration distribution, and find that compared to side inlet style and end side inlet style bag filter, the average concentration of particles is higer than 18% and 18.6% in the lower inlet style bag filter. With the example of the project, the paper compares two different ways of airflow coming into the bag filter in the bag filter reconstruction. the author has analyzed the problem of the bag filter in a state of high resistance,frequent ash cleaning and some filterbags dilapidation which was section of crushing and screening industrial milling in the third dry cooling coke system through CFD simulation analysis.there are two reasons for this problem:one is the eddy velocity can reach 7.0～8.0m/s in the ash container,and the velocity is about 2.0m/s under the bottom of filter bag,All that cause the dust floating from the containers below again; the other is that the velocity can reach about 3.0-5.0m/s,which can cause the dusty gas flows washing the filter bag. According to the reasons, this article gives a design of bag filter which the dusty gas comes into the bag filter in the side of the bag filter, and it also analyzes the updraft speed for dusty gas which comes into the bag filter in two ways, Finally analysis results show that the new designed bag filter is better than the primary bag filter in updraft speed.