Fractal Solution Of Comprehensive Permeability Of Dust-Covered Filter Bag And Its Impacts On Operation Characteristics Of Bag Filter

In the CFD,CSD simulation study of bag filter,the permeability of filter bag is one of the important boundary conditions,which is determined the simulation results are credibility whether or not.Filter cake is formed in the filtration process of bag filter,while the influence of filter cake is not considered in the study of the bag filter simulation,and the relative research on permeability of filter cake is also rare.In order to accurately obtain the composite porous media permeability of filter bag and filter cake in the flow field numerical simulation of dust-covered filter bag,the characteristics of composite porous media permeability is described by the comprehensive permeability of the dust-covered filter bag.A method based on fractal theory is proposed to calculate the comprehensive permeability,and the comprehensive permeability is used to simulation in filtration process and injection process,then the influence of filter cake on simulation results was explored.The main contents and conclusions in this paper are as follows:(1)The filter cake was sampled by the bag filter of the integrated physical experiment platform of Tianjin cement Design Institute and the SEM image of filter cake surface was obtained by scanning electron microscope(SEM).The SEM images obtained by different processing methods of filter cake are also very different.It is concluded that the pore structure of filter cake has self-similarity characteristics by using image processing technology.(2)Based on the fractal theory and the improved capillary model,the fractal expression of filter cake permeability is established,and the comprehensive permeability of dust-covered filter bag is calculated by Darcy's law.The comprehensive permeability of dust-covered filter bag is between 1.615?m~2 and 4.784?m~2 under different resistance conditions.When the filter cake is considered in the simulation,the comprehensive permeability of the dust-coated filter bag will be more accordingly with the actual working conditions.(3)In order to explore the influence of filter cake on the filtration process and injection process of bag filter,the comprehensive permeability parameters obtained by this method are used to simulate and analyze the evaluation indexes of filtration process and injection process.The simulation results between clean filter bag and dust-covered filter bag are quite different.For the filtration process,the comprehensive permeability of dust-covered filter bag under different resistance conditions is used to simulate and analyze the filtration process.The simulated pressure difference between the inside and outside of the filter bag is in good agreement with the experimental measurement value,which shows the accuracy of the method for calculating the comprehensive permeability in this paper.Dust-covered filter bag has little effect on the rising velocity of air flow at the bottom of the bag,but has a certain effect on the rising velocity and filtration speed of the air flow between the bags,and the filtration uniformity of the dust bag is better.For the injection process,the dust-covered filter bag has a great influence on the peak pressure and the maximum reverse acceleration.Under the certain injection pressure,the thicker the filter cake,the greater the peak pressure and the maximum reverse acceleration during the injection,indicating that the lower pressure required by the bag filter under the higher running resistance is smaller.