The Behavior In Reaction Of Volatiles Generated From Low-rank Coal Pyrolysis

Coal pyrolysis is an important step in the process of coal conversion.High calorific value gas and high added value tar can be obtained from coal by pyrolysis.The volatiles generated from coal pyrolysis are heated by the rising hot gas quickly to a higher temperature.The temperature increases and residence time cause reactions of volatiles and directly affect the composition and yeild of tar.However,the tar from reactions of volatiles has poor quality and plugging of the volatile products lines.In this paper,fixed-bed pyrolysis devices were built to simulate the behavior of volatiles reaction in industrial reactors,temperature increases and residence times were correlated with tar composition and yeild of Shengli(SL),Naomaohu(NMH)and Shenhua(SH).The results showed that reactions of volatiles differed greatly in temperature increases than residence time.The tar yield follow a trend that decreases with an increase in temperature increase in volatiles.When the heating rate of SL and SH was 70?/min and reaction temperature of volatiles was 900 ?,the tar yield decreased from 13.7% to 8.3% for SL and from 13.0% to 6.6% for SH,respectively.For NMH,the tar yield decreased with an increase in temperature while the gas and coke yield increased.The tar yield at 850 ? decreased from 62.1% to 17.2% when the residence time was 0s and from 62.1% to 17.6% when the residence time was 10 s.The voaltiles generated from different rank coals pyrolysis had different composition,which affected the tar yield.The yield of light tar(HS)decreased by 63.8% for SL and 40.5% for SH,at reaction temperature of 900 ? with residence time of 14 s.The yield of heavy tar(THFs)decreased by 43.8% for SL and 75.0% for SH,respectively.For NMH,the yield of HS and THFs decreased with an increase in temperature,and reached minimum at 850 ?.The yield of HS was 5.7% and the yield of THFs was 7.8%.According to GC-MS analysis,it was found that the compenonts tend to form a more stable structure.Because of the damage of aliphatics side chain,the types of aliphtic compounds decreased.The chain of aliphatics was decreased from C7-C21 to C7-C8.In a high temperature environment,in the part of volatiles,the content of benzene compounds increased exponentially.During the reaction process,the content of the phenolic compounds decreased drastically,this may be the dehydration reaction in volatiles.At the reaction temperature of 900 ?,the content of phenolic compounds decreased from 14.3% to 0.03% for SL and from 14.1% to 1.2% for SH.For NMH,the content of aliphatic compounds and aromatic compounds reached a minimum at 550 ?,was 14.2% and 8.9%,respectively.The content of phenols increased at low temperature and reached maximum(42.5%)at 550 ?.The FT-IR analysis results of THFs showed that the THFs contained a large amount of aliphatic and oxygen-containing functional groups.The long chain hydrocarbons were broken,and the chain length was shortening.The carbonyl content of unit aromatic ring increased in THFs of SL while it was decreased in THFs of SH.For NMH,the contents of aliphatic hydrocarbons,carbonyl and ether bond increased with the decrease of residence time,however,the content of the aromatic hydrocarbons decreased in THFs of tar at different temperatures.