Pyrolysis Behavior Of Coals And Their Macerals

Medium and low temperature coal pyrolysis is one of the important technologies to achieve clean and efficient coal conversion.The composition of coal macerals is one of the important factors affecting the pyrolysis behavior.Because of the different sources of coals,the composition of macerals and pyrolysis behavior are quite different.In this paper,Daliuta?DLT?coal and Hongshaquan?HSQ?coal,with a relatively high proportion of inertinite and Zichang?ZC?coal,with a relatively high proportion of vitrinite were used to study the pyrolysis behavior of macerals.Besides,the effect of CO₂ reforming of methane?CRM?atmosphere on pyrolysis behavior of macerals was investigated.The main findings are as follows:The pyrolysis behaviors of DLT raw coal,HSQ raw coal and ZC raw coal and their macerals under N₂ atmosphere were studied in a fixed-bed reactor,and the coal pyrolysis products were correlated with the structure of coal samples.The results showed that ZC raw coal contains more aliphatic structure,and has tar yield as high as 17.26 wt.%,which is significantly higher than the other two raw coals.The volatile content and tar yield of vitrinite are obviously higher than those of inertinite from the same coal.That ZC raw coal has lower tar yield than its macerals is due to the raw coal contains more minerals such as Fe and Ca,which has a certain cracking effect on coal tar.GC-MS analysis of tar showed that the coal structure affects the composition of tar to some extent.The relative content of aliphatics in the ZC inertinite pyrolysis tar is as high as 47%,which is contributed to the abundant aliphatic carbon in the coal.The content of phenols in tar from HSQ coal is significantly higher than those from other two coals.In pyrolysis of three coals,the tar yield and composition from DLT vitrinite?DLT-V?and DLT inertinite?DLT-I?has the largest difference.In order to understand the interaction between DLT-V and DLT-I,this two samples were mechanically mixed and subjected pyrolysis experiments in a fixed-bed reactor.The results showed that the interaction between vitrinite and inertinite mainly reduces the tar yield,and gives an increase in content of dihydroxybenzene and a slightly reduction in content of benzenes.Besides,the minerals in the coal have a cracking effect on the pyrolysis tar.The effect of temperature and the atmosphere of CO₂ reforming of methane on pyrolysis process of DLT macerals were investigated.Temperature and atmosphere have different effects on different macerals during the pyrolysis process.The vitrinite is less condensed than the raw coal and inertinite,and achieves the highest tar yield?19.58 wt.%?at 600°C,while the highest tar yield is obtained for raw coal and inertinite at 650°C.The tar yield of DLT raw coal and its macerals are significantly improved in integrated process of coal pyrolysis with CO₂ reforming of methane?CP-CRM?.The free radicals generated from CRM process stabilize the volatile fragments generated from coal pyrolysis and result in an increase in the tar yield during the CP-CRM,and the inertinite with higher condensation degree has the most obvious increase in tar yield,which is increased by 16%compared with that under N₂ atmosphere.Analyses of tar composition showed that CP-CRM process also contributes to the increase in light tar fractions,and the content of 3-ring and 4-ring polycyclic aromatic hydrocarbons in the inertinite pyrolysis tar obviously decrease.The vitrinite pyrolysis tar produces longer aliphatic side chains and this part of the side chain combines with the free radicals generated by the CRM process.Therefore,the relative content of light tar from the vitrinite is significantly improved in CP-CRM process.