Study On The Behavior Of Volatiles' Reaction During The Pyrolysis Of Low-rank And Subbituminous Coal

The reaction of volatiles generated from coal pyrolysis determines the yield and quality of products.To understand this reaction in detail particularly on the condensation reaction that forms coke,this paper studies the reaction of volatiles generated from a lignite and a subbituminous coal using a two-stage fix-bed reactor,with the first stage for coal pyrolysis and the second stage for reaction of volatiles.The yields of tar,gas and coke formed on the wall and presented in tar at a second-stage temperature range of 440-700 ? and a residence time range of 1.5-6.9 s are quantified.The concentration,g value and linewidth of radicals in tars,mainly in coke presented in tars,are measured by electron spin resonance(ESR)and discussed to explore the transformation of coke in structure.The effects of second stage temperature range from 440 ? to 700? and second stage residence time range from 1.5 s to 6.9 s on the tars' composition distribution,especially the contents and evolution priciples of aromatic components that were easily to be further processed,were focused.This article also emphasized on the distribution of mixture of pitch and oil which were divided into different temperature range according to their B.P.It is found that the reactions of volatiles generated from the lignite and the subbituminous coal are different in the temperature range studied but the structure of coke formed in these two volatiles differs mainly at temperatures lower than 600 ?.The proportion of coke formed on the reactor wall is small at 440 ?,but large at 650 and 700 ?,close to 50%in 4.2 s.The increase in concentration and decreases in g value and linewidth of radicals with increasing temperature over time suggest that the coke undergoes condensation,leading to loss in oxygen and increase in aromaticity.Besides,it was found that The volatiles' reactions of bituminous coal show stronger influence on the tars' components than that of lignite,notably at temperatures higher than 600 ? and the main components in tars derived from the volatiles' reactions were oil,with the oil in lignite tar at around 83 wt.%,higher than that of bituminous oil at about 60 wt.%.During the high temperature process,the medium molecule fractions in tars condensed or cracked into lighter volatiles' fragments and larger molecule cluster after the volatiles' reactions.i.e.the difference component transformed into aromatic compounds and the heavier pitch.It was suggested that the working temperature should better be controlled under 600 ? to ensure it was adaptable to both the young and old coals duo to that the over-reactions of lignite volatiles have negative effects on the tars' composition since the high temperature and long residence time increased the large molecule fractions in volatiles,such as pitch and coke,but the temperature increase was beneficial to the process procedure of tar at temperatures higher than 600 ?.This discovery has a good guiding significance for the industrial regulation of operating temperature.