Study On The Effect Of Coal Quality On The Magnetization Roasting Process Of Limonite

China is a big consumer of the iron and steel,but it has a poor self-sufficiency of the iron ore.Magnetization roasting-magnetic separation technology is effective in improving iron ore supply and demand structure of our country by using low-magnetic iron ore.Kiln-ringing which has a great limitation on the development and promotion of the magnetization roasting is closely linked with the reducing coal.This thesis is devoted to studying influences of different coal on magnetization roasting process,improving magnetization roasting process,strengthening theories regarding the roasting process,and exploring the impact of reducing coal on the kiln-ringing.These subjects are greatly beneficial to the use of the low-magnetic iron ore and the sustainable development of the national iron and steel industry.In the thesis,three typical reductants which have great differences in physical and chemical performances-brown coal,soft coal,anthracite,were selected to figure out influences and laws and principles of the temperature and concentration of the reducing atmosphere on magnetization roasting process of coal and mixed limonite ore.In addition,mechanism of isothermal kinetics was used to study the kinetics of different coal on the magnetization roasting process of the mixed limonite so as to provide the theoretical basis and technical support for optimizing the magnetization roasting technology and reducing the kiln-ringing.The main findings are as follows:(1)Thermodynamic analysis of coal-based magnetization roasting of the iron oxideThe volatiles in the coal which are dissociated to produce H₂and C only at a high temperature have little reducing action in the roasting.The reductant used in roasting of the iron ore is mainly produced through the Boudouard of the residual carbon generated from the volatiles of the coal.Magnetizing roast of limonite coincides with the Boudouard of carbon,and the gasification of carbon improves the rate of the roast.When generating the magnetic iron by roasting of the iron oxide in the temperature of 923?1123K,CO and H₂as the reductants were found a lower concentration of reducing gas and easy occurrence of iron oxide magnetization and roasting in balanced reaction;area with T<1019K is the stable area of the magnetite;(2)Laws of coal's effect on magnetization roastingThe higher the carbon content of the coal is,the lower the coal blending;all three kinds of coal are able to bring good roasting under the appropriate conditions with over 90%magnetic susceptibility;high volatiles are corresponding to great carbon residue porosity,better reactivity,fast gasification reaction rate of coal and CO₂,and favorable brown iron magnetization and roasting.(3)Mechanism of the coal's influence on kiln-ringingBy using X-ray diffraction and scanning electron microscopy,it was found that large garnet agglomeration appeared in the calcined ore of the three kinds of coal as the reducing agents under the temperature of 1173K.The garnet agglomeration connection of three kinds of coal is as follows:soft coal>brown coal>anthracite,the following conclusion reached based on the ring mechanism of the rotary kiln:contents of Ca O and Si O₂in coal ash have a great influence on the generation of the ring.(4)Kinetic study of coal-based magnetization roasting of the iron oxideThe comparison shows that lignite is magnetization roasting of limonite ore with brown coal takes place easily.Fitting results of three gas-solid control kinetic model show that magnetization roasting with the three kinds of coal is consistent with the unreacted core model controlled by gas-solid chemical reaction.The apparent activation energy of magnetization roasting of limonite ore with brown coal is43.790KJ/mol.Brown coal has better reactivity;(5)Effect of the coal on the rate of magnetization roastingCoal with strong reactivity has fast gasification reaction rate,high concentration of reducing atmosphere,and rapid magnetization.At the same roasting temperature,coal with a strong reactivity brings a fast roasting reaction;the reactivity of coal increases as temperature rises,so increase in temperature of magnetization roasting will speed up the magnetization roasting.