Effect Of The Thermal Field Temperature And Packing Medium On Reactions Of Volatiles From Pyrolysis Of Naomaohu Coal

The problem of pipeline blockage during coal rapid pyrolysis has not been solved,making it difficult to realize industrialization of many large-scale processes.It is believed that pipeline blockage is caused by many factors,such as the re-reaction behavior of volatiles,dust entrainment,condensation and accumulation of heavy tar.Therefore,improving the quality of tar and reducing the condensation of heavy components are effective methods to avoid the problem of pipeline blockage,which is of great significance to maintain the long-term stable operation of the process and optimize the technology of the post-treatment and reprocessing of tar.During the coal pyrolysis,the reaction of volatiles is affected by thermal field temperature,heating rate,residual time,steric hindering,packing medium,and so on,which leads to the change of tar quality,to some extent.In this article,a subbituminous coal with rich oil was selected for the separate pyrolysis and the coupling pyrolysis and gasification experiment with an integration device for the coupling pyrolysis and gasification.The effect of thermal field temperature?400–650 ^oC?,packing medium?activated carbon,?-Al₂O₃,quartz beads?and gasified gases on volatiles reaction were investigated,which will provide a theoretical support for improvement of the tar quality and reduction of the coke amount,and the directional regulation of volatiles reaction.The specific research conclusions of this paper are as follows:?1?When the volatiles flow through the zone C during pyrolysis of Naomaohu subbituminous coal,the yields and quality of pyrolysis products are significantly affected by temperature of zone C.With the increase of temperature of zone C,the amount of oil?HS?changes slightly,but asphaltenes?A?in tar are more likely to form heavy components,such as pre-asphaltenes and coke,by polycondensation,resulting in poor fluidity of tar and the increase of coke amount in tube?coke-D?.The temperature of 400–450 ^oC is of no significant effect on volatiles'reaction.When the temperature rises to 500 ^oC,the yield of pyrolysis water?based on 1 kg of dry coal?reaches the maximum,due to the decomposition of hydroxyl during volatiles'reaction.When temperature reaches 600–650 ^oC,the yield of tar decreases,while the yield of pre-asphaltene?PA?in tar increases,the quality of tar deteriorates.?2?The experiment of coupling pyrolysis and gasification was consistent with the above mentioned pyrolysis conditions.Compared with the separate pyrolysis experiment,the tar yield increases by 1–5%during coupling experiment,and the increase of tar yield is the largest with the temperature of zone C at 500–550 ^oC.The effect of gasified gases on the quality of tar components is different.When the temperature is higher than 500 ^oC,HS in tar increases,the condensation of PA to form coke is inhibited.When the temperature is below 500 ^oC,the amount of coke and PA decrease.The removal of O,N,S-heteroatomic compounds in tar is promoted by gasified gases containing steam.In addition,gasified gases promote the polycondensation of aromatic compounds in tar under higher temperatures in zone C.Under lower temperature,the gasified gases promote the generation of benzene compounds,aliphatic hydrocarbons,and phenolic compounds.?3?Adding packing medium in zone C can prolong the residence time of volatiles and enhance the extent of reaction,which makes the quality of tar and the amount of coke to change.Activated carbon as the packing medium will hinder the passage of high molecular weight components,such as A,since its microporous and mesoporous structures.And the disproportionation reaction of A in tar is promoted to form more light compounds and PA.In addition,the content of phenolic compounds in tar increases greatly.When?-Al₂O₃,with rich mesoporous structure,is used as the packing medium,the passage of macromolecular compounds?for example,precursor of PA in volatiles?is hindered,but its decomposition is promoted to form A,which is up to 89%.In addition,the amount of small molecular weight compounds such as HS reduce due to the condensation reaction.