Study On Pulverization Mechanism Of East Inner Mongolia Lignite During Pyrolysis

China is rich in lignite resource.In order to realize the step ultilization of lignite,the oil and gas in the coal can be extracted by pyrolysis technology,and then the solid semi coke can be used for clean fuel or chemical raw material.However,the lignite pyrolysis is easy to produce dust due to the poor thermal stability of lignite,resulting in the entrainment of smoke,the blockage of pipeline and the difficulty of separation of oil and dust,which hinder the development of clean utilization of lignite.This paper takes two kinds of lignite(XM and BM)from the East Inner Mongolia as the study object,and conducts the experimental study on the pyrolytic pulverization of them by using the microscale fixed bed and the fluidized bed pyrolysis device.The effects of particle size,heating temperature,heating rate and solid residence time on the pyrolytic pulverization of lignite are investigated.In this study,the pyrolysis characteristics of both lignites are systematically studied from two aspects of experiment and theory,which mainly includes the following four parts:(1)Experimental study on pyrolytic pulverization of two East Inner Mongolian lignite under different loading of thermal and mechanical forces;(2)The relationship between the pulverization and the microstructure changes of particles;(3)The analysis of the main factors affecting the pulverization and the establishment of correlation model on particle size;(4)Process analysis and mechanism study on pyrolytic pulverization.The experimental results of the fixed bed under the action of heat alone show that,with the increase of particle size,heating temperature,heating rate or the extension of residence time,the pulverization degree of the two kinds of lignite is increased.From different loading tests of the thermal and mechanical force,it is known that the release of volatile matter under the thermalforce is the main reason for the change of particle size and the mechanical force is the main causes of the fine particles around the partical peeling off.It is found that the release of volatile matter is one of the main factors affecting the pulverization of coal particles by the TG analysis and proximate analysis of coal and semi coke;At the same time,the relationship between the change of particle pore structure and its pulverization was studied using mercury intrusion method and BET analysis.The results show that with the continuous release of volatile matter,the pores in the coal particles are gradually developed into large pores and cracks,meanwhile,new micropores and mesopores are produced.The thermal stress concentration in large pores and cracks is the direct cause of pulverization.The statistical analysis of the experimental data based on the grey correlation theory shows that,the heating rate is the main factors affecting the particle size change rate;the main factors affecting the pulverization rate are the heating rate,the particle size and the heating temperature,the fluidization number is also an important factors.The residence time had little effect on the particle pulverization,and the increase of the residence time could not significantly increase the degree of pulverization.According to the primary and secondary order of the factors,the correlation function model of the average particle size and the main factors is established,and it is verified that the applicability is good and can be used to predict the the change of particle size.The pyrolytic pulverization process of lignite is analyzed in this research.It is inferred that the large amount of volatile matter in the pyrolysis process of lignite can produce agglomeration pressure,which can promote the development of pore structure into large pores and cracks,forming a lot of broken cores,and the thermal stress is concentrated in the broken core to make the change of particle size and intensifies the degree of pulverization of particles.Based on the simulation of the spherical model,the pulverization mechanism of lignite pyrolysis was studied.First of all,the maximum stress of coal particles are only related to the elastic coefficient E of material,poisson ratio ?,expansion coefficient ?l and temperature difference AT,but not to the radius of coal particle r0 and thermal diffusivity ?;Secondly,the coal particles produces the maximum tensile stres,and the outermost layer produces the maximum compressive stress.The maximum tensile stress of sample BM is 8.96MPa and the maximum compressive stress is 23.22MPa in the pyrolysis process,which are greater than its material strength.Therefore,the tensile stress in the particles is the main reason of the change of particle size,and the amount of pulverization is mainly caused by the compressive stress.