| In the past few years,the gray haze days happened frequently in China,and the environmental problems were becoming more and more prominent.As one of the important emission sources of particulate matter,iron and steel plant has attracted wide attention from the public.The main problem is that the dust removal equipment used in iron and steel plant has very limited classification removal efficiency of fine particles,even the removal efficiency of coarse particles is very high.Therefore,it has significant value to develop an applicable fine particle removal method and technology for emission reduction based on re-examine the characteristics of the particles emitted from iron and steel plant.The main purpose of this paper is to the recognize magnetic properties of particles from iron and steel plant,ulteriorly to explore the influence factors of particle removal efficiency with magnetic agglomeration and to improve the numerical simulation method of magnetic agglomeration behavior.The particle samples were collected in sintering,ironmaking and steelmaking process from a typical iron and steel plant in China.The magnetic characteristics such as saturation magnetization,coercivity and magnetic susceptibility were test in detail.Meanwhile,the particle size distribution,morphology and chemical composition were also tested to indicate the influence factors of magnetic characteristics.On this basis,an experiment platform of magnetic agglomeration combined with a bag filter was design and set up independently.The effect of key parameters,such as magnetic field intensity and filtration velocity,on particle removal efficiency were investigated experimentally.Finally,based on the boundary conditions obtained from the experiments,the magnetic agglomeration process of particles was studied in silico modeling by programming CFD coupled with DEM method.Meanwhile,the magnetic agglomeration efficiency and the number of particle collision were also calculated.The creative results are shown as below.(1)An innovative method was put forward that combine magnetic agglomeration process with cloth bag dust removal technology to enrich the R&D method of both magnetic agglomeration technology and dust removal technology.To cover the shortage of agglomeration efficiency,dust removal efficiency was used to illustrate the agglomeration result.At the same time of experiment research,a CFD-DEM numerical method was established to simulate the agglomerate process of particles that using the experimental data of magnetic field and air velocity as boundary conditions.(2)The differences of saturated magnetization intensity,coercivity,magnetization rate and other magnetic parameters of particles from different working processes in iron and steel plant were revealed.The particles can be divided into three categories according to the magnetic parameters:1)the high-magnetization particles include the particles emitted from the casting house and the pretreatment of hot metal;2)the middle-magnetization particles include the paritlces in flue gas of the converter,the sintering machine head,the sintering machine tail and the ore channel of blast furnace;3)the low-magnetization particles include the paritlces in secondary flue gas of the converter and the blast furnace gas.The particle emitted form iron and steel plant are ferromagnetic polydomain particle with coercive force below 10 mT.Furthermore,Fe content is the main factor that affects the saturation magnetization and residual magnetization of particles.(3)The effects of magnetic field intensity and airflow velocity on the magnetic agglomeration and the efficiency of bag filter were revealed.Reducing the airflow velocity and increasing the external magnetic field is beneficial to increase the magnetic agglomeration efficiency of 0.3 and 0.5 ?m particles and improve the classification removal efficiency and total removal efficiency.The external magnetic field has a significant promotion on the dust removal efficiency of the high-magnetization particle,especially the particle from the casting house,which can reach to 35%under certain conditions.The promotion on dust removal efficiency of the middle-magnetization particle and low-magnetization particle about is 15%and 10%respectively.Therefore,magnetic agglomeration method is suitable for particles with high and medium magnetization,but not for particles with low magnetization.(4)Based on the real magnetic susceptibility of particles,the in house CFD-DEM coupling calculation program reveals the particles in the magnetic field moving along the direction of magnetic field lines to form chain-like aggregates and running along the flow direction.A large amount of aggregates can be formed in 0.2 ms without flow field and in 10 ms with flow field.In addition,the particle collision efficiency in the gradient magnetic field is higher than that in the uniform magnetic field. |
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