Effect Of Particle Size On The Pyrolysis Characteristics And Char Structure For Low Rank Coal

The difference in raw coal particle size will lead to different heat and mass transfer conditions in the pyrolysis furnace,which will affect the pyrolysis characteristics of coal,char structure and performance.This effect is not only reflected in the overall performance of char obtained by pyrolysis of raw coals of different particle sizes,but also in the structure and performance of char particles in the radial direction.Therefore,it is important to study the pyrolysis characteristics and char structural characteristics of raw coals with different particle sizes and establish their corresponding relationships.It is of great theoretical significance and use value to better meet the needs of downstream users such as blast furnace injection.In this study,the N₂ adsorption method,Raman,XRD and FTIR were used to analyze the overall structure changes of char prepared from raw coal of different particle sizes and the structural changes of samples at different positions（edges,centers）in the radial direction of char with different particle sizes.By setting different external mass transfer resistance conditions in the coal pyrolysis process,the mass transfer phenomenon in the pyrolysis process of raw coal with different particle sizes was studied by using a thermogravimetric mass spectrometry（TG-MS）.Finally,the small particle raw coal used in the small-sized pyrolysis furnace of enterprise and the char produced by it were used for the permeability test.The permeability index was used to characterize the permeability of the charge and explore the reasonable pyrolysis parameters and mass transfer conditions.The research show that:（1）With the increase of pyrolysis temperature（500℃～700℃）,the specific surface area of char first increases and then decreases,reaching the maximum value at 650℃;the char prepared at this temperature,with the raw coal particle size as the specific surface area and pore volume of char increase,the degree of ordering increases;for char prepared from raw coals with two sizes of 30mm and 40mm,the specific surface area of sample from particle surface is larger than that of sample from particle center.The pyrolysis of the edge sample is more complete,and the degree of ordering is low.（2）The coal pyrolysis process is mainly affected by the external diffusion resistance during the mass transfer process.The larger the raw coal particle size,the faster the weight loss rate in the pyrolysis process and the greater the weight loss rate.The effect of increased external diffusion resistance on the pyrolysis process is more significant,after the increase of external diffusion resistance,the precipitation temperature of the main pyrolysis gas is pushed back,and the maximum precipitation rate decreases.（3）The small particle size raw material has a great influence on the gas permeability in the material layer.According to the raw material conditions,the n value fitted by the Voice formula,and then the fitted n value is brought into the Voice formula,the permeability index of the raw material can be measured.Based on this,the gas permeability and pressure difference of the low-temperature coal pyrolysis industrial device of small particle size coal were analyzed.When the particle size distribution of raw materials is roughly the same,the char has better permeability than raw coal.As the blending amount of pulverized coal（0-5mm）is increased from 0%to 25%,the pressure difference in industrial pyrolysis furnace is increased from 674pa to 2398.66pa,and the influence of 0-5mm pulverized coal on the permeability of the charge is very significant.In conclusion,to study the pyrolysis characteristics and structural differences of raw coals with different particle sizes,the quality,performance and yield of char can be adjusted by changing the pyrolysis conditions of raw coals.Through the measurement of the gas permeability index of a specific charge,the pressure difference and permeability of the charge in the industrial furnace on an industrial scale are predicted,with a view to efficiently producing char,which laid basis.