Theoretical Study On Dynamic Deposition Of Fine Particles On Fiber

Bag filter has high efficiency of fine particle removal and plays an important role in industrial dust emission control.Its fiber filtration process is essentially a gas-solid flows problem.In this paper,the mechanical characteristics of gas-solid flows,filtration mechanism and classification filtration efficiency in the filtration process of bag filter are calculated and analyzed.And the dynamic deposition process,filtration efficiency and porosity of fine particles on single fiber and multi-fibers are numerically simulated respectively,based on computational fluid dynamics and discrete element theory.Firstly,the forces of fine particles in gas-solid flows is theoretically calculated and analyzed,and the dominant force that dust particle movement and deposition in the filtration stage of bag filter is determined.The main filtration mechanisms(inertia,interception,diffusion)of bag filter are elaborated in detail,and the grading filtration efficiency of bag filter for fine particles is theoretically calculated,the penetrable particle size of fine particles is determined.Then,based on computational fluid dynamics and discrete element model,the numerical model of the dynamic deposition process of fine particles on the surface of single fiber in multiphase flows is established,and a numerical simulation is carried out.The evolution of particle deposition morphology,mean coordination number,porosity and other parameters,the relevant parameters in the simulation is predicted theoretically.Based on the above theoretical results,the relevant parameters in the simulation were further calibrated.The results show that the time consumption of simulation calculation is effectively shortened by reducing the Young’s modulus,and the reasonable Young’s modulus can be set to the order of 108,and the corresponding surface energy is about 1 mJ;reducing the coefficient of restitution increases the particle collection efficiency,and the reasonable coefficient can be set to 0.1;the simulation result is not sensitive to the change of the coefficient of static friction,and the coefficient can be set as 0.5;the simulation result is sensitive to the change of the coefficient of rolling friction,and the reasonable coefficient can be set as 1.5.After that,the numerical model for the dynamic deposition of fine particles in multiphase flow on multi-fibers surface was established,and has carried on the simulation.The results reproduce the dynamic deposition process of the fine particles on multi-fibers:as the number of captured particles increase,the particle chains between the fibers will bend,contact and bridge,and eventually form a dust cake.The transient collection efficiency curve is S-shaped,which can be fitted to a logistic equation.The dynamic filtration with dust-loaded fibers can be classified into three stages:the quasi-clean filtration,the particle chain bridging,and the dust cake compaction.Finally,the effects of intercept coefficient,particle density and fiber array on multi-fibers dust filtration process were simulated and studied.The results show that:the higher the intercept coefficient R,the smaller the number of particles and the shorter the time required to establish the dust cake,and the higher the filtration efficiency.For common particles,the effect of particle density on fiber dynamic filtration is notsignificant,but when the particle density is more than 4000 kg/m3,the filtration efficiency of simulation calculation will decrease.The filtration performance of horizontal staggered multi-fibers was the best,followed by parallel multi-fibers,and vertical staggered multi-fibers was the worst.