Structural Analysis Of Residue Carbon Formed By Gasification Of Different Coal Macerals

Coal gasification technology is widely used in modern coal chemical industry due to the advantages of wide range of raw material,high carbon conversion and large processing capacity of single furnace.Gasification fine slag contains a high content of carbon,which causes waste of resources and environmental hazards.In essence,fine slag is a comprehensive reflection of the separate gasification of various macerals in coal.In this study,different macerals concentrates were firstly prepared from Yangchangwan(YCW)and Meihuajing coal(MHJ).The pyrolysis and gasification of different types of coal macerals concentrates were then carried out under the same conditions.A thermogravimetric analyzer was chosen as the experimental equipment for pyrolysis,and the reaction conditions were 1000℃,Ar atmosphere and heating rate of 10 k/min.The gasification was carried out in situ high-temperature heating stage coupled with optical microscope,thermogravimetric analyzer and Joule heating device,respectively.The detailed structural characteristics of the gasification residue carbon prepared by the different gasification devices were analyzed separately,and the main conclusions were obtained as follows:(1)The aromatic degree of inertinite concentrates of the two coals is greater than that of vitrinite,with larger Lc and larger aromatic cluster size;the vitrinite contained more aliphatic group and aromatic ring side chains.During the active pyrolysis stage(200-600℃),the weight loss rate of vitrinite is higher than that of inertinite,and the sample weight loss rate reaches the maximum at about 445℃.The maximum thermal weight loss rate of YCW and MHJ vitrinite is 1.57 and 1.38 times higher than that of inertinite.(2)During the HTSOM gasification,the surface of coal char samples in the inertinite was rougher and richer in porous structures during the gasification process,and the stronger crushing and shrinking ability of the inertinite might lead to the formation of a larger comparative area and the exposure of more active sites,which provides a site for the reaction,resulting in a larger final gasification carbon conversion level in the inertinite than in the vitrinite.The consumption rate of active site in vitrinite pyrolysis char is very different from inertinite.In the early stage of the reaction,the vitrinite fresh char presented a relatively high reaction rate due to the high active site content and low structural order,but the reaction activity gradually decreased with the rapid consumption of active sites.For the inertinite fresh char,although its initial active site content is low,as it is easily broken and contracted at high temperature,new active sites and specific surface area are released constantly.Therefore,the inertinite could maintain high reactivity in gasification process.(3)The variation of char yield in the gasification process under rapid heating conditions shows a tendency to change drastically and then level off.The vitrinite reacted 70%of the total reactions in the 30 s of gasification reaction,while the two coal inertinite reacted 52%and 84%of the total reactions in the 30 s of gasification,respectively.During the gasification under the rapid heating condition,the atomicity of the inertinite gasification residue carbon of YCW and MHJ coals was always greater than that of the vitrinite,indicating that the aromatic carbon content of the residue carbon in the vitrinite was more and the reaction degree of the inertinite was higher.The change of active sites of the residue carbon showed a trend of increasing firstly and then decreasing,and the number of active sites of the vitrinite was always larger than that of the inertinite.The change of the orderliness of the residue carbon showed a trend of decreasing firstly and then increasing,and finally the orderliness of the gasification residue carbon of the inertinite was higher than that of the vitrinite.