Experiment And Model Study Of Pyrolysis Reaction Kinetics Of Low-rank Coal

Coal pyrolysis is the first step in coal thermal processing and utilization.The kinetic model of coal pyrolysis is helpful to understand the interaction of various chemical components,element migration and volatile matter removal during coal pyrolysis.Various pyrolysis kinetic models have been reported in the current literature to evaluate their adaptability to different coal pyrolysis processes,and to clarify the differences of model parameters,which will provide reference for reactor design.At the same time,further study on the interaction mechanism between molecules in pyrolysis process is of great significance to improve the theory and dynamics model of pyrolysis reaction.In this paper,the devolatilization kinetics of three kinds of coal samples under TG experiment was analyzed by the isoconversion method and the distributed activation energy model.It was found that the FWO model can better describe the TGA data among the isoconversion models.In order to solve the arbitrariness of pre-exponential factor selection in the previous distributed activation energy model,the pre-exponential factor values of different coal types were determined by the pre-exponential factor distribution function obtained from the isoconversion method.Considering the reaction order,the reaction temperature index,the number of reaction stages and the type of activation energy distribution function,it is found that the double-Gaussian activation energy n-stage reaction model has the best fitting of the TG curves of the three coal samples.The basic composition of the chemical structure in the straight chain model of coal macromolecules was determined by pyridine extraction experiments,elemental analysis,industrial analysis and ¹³C-NMR solid nuclear magnetic experiments of three coal samples.In addition,competition and coordination reaction mechanisms between the bridge scission and condensation was proposed to solve the asynchronism of noncondensable gas and tar release at high temperature.It can better predict the weight loss of Tichi coal in PY experiment and reveal the reaction mechanism of different chemical structures with temperature change.In the actual industry,char is one of the main products of pyrolysis,and the pyrolysis process has an important influence on the apparent morphology change of char.In this paper,the fluidized bed pyrolysis device was designed and the char particles were successfully prepared.Compared with the char prepared in PY experiment,the pores of the char prepared by fluidized bed are more abundant.With the increase of pyrolysis temperature,the char particle size decreases first and then increases slightly under the PY cracking condition,while the char particle size prepared in fluidized bed decreases.Compared with the raw coal,the two-dimensional sphericity of the char shows a decreasing trend under the two pyrolysis conditions.