Integrated Process Of Coal Pyrolysis With Coal Gas Reforming For Improving Tar Yield

Coal pyrolysis is one of the most important technologies to achieve the clean,efficient and comprehensive use of coal.However,owing to low molar ratio of H/C in coal,the tar yield and quality obtained by direct pyrolysis is low and poor.Although hydropyrolysis is one of the important ways to improve the yield and quality of tar,high hydrogen production costs constrain its industrial application.It is reported the quantily and quality of tar can be further improved by the developed process of coal pyrolysis with low-carbon alkane conversion.Considering that coal pyrolysis gas itself contains a large amount of hydrogen-rich gases such as H₂ and CH₄,and its energy efficiency is low for combustion heating.Therefore,in this study,the integrated process?CP-RSCG?of coal pyrolysis?CP?with catalytic reforming of simulated coal gas?RSCG?was investigated,the effect of process parameters such as atmospheres on the distribution of pyrolysis products was studied and the related mechanisms were explained.In this study,Yulin?YL?sub-bituminous coal was selected as the coal sample to study the effects of different temperature,each active gas in simulated coal gas?SCG?and their mixture gases on the distribution of coal pyrolysis products.The tesults showed that the best pyrolysis temperature of YL coal is 650 ^oC,and the pyrolysis atmosphere with different gases composition remarkably influence the products distribution.The tar yield at this temperature is approximately in the order of SCG>tri-component>bi-component>mono-component>N₂,the tar yield of coal pyrolysis in simulated coal gas?CP-SCG?is 12.4%higher than that of N₂.In addition,H₂ can significantly reduce the char yield.When the atmosphere contains both H₂ and CO₂,the water yield is increased by the reaction of reverse water gas shift.The analysis of tar showed that the atmospheres in SCG not only change the tar yield but also effect the tar composition.The addition of CH₄ increases the content of benzenes and phenols,the introduction of H₂ mainly increases naphthalenes content,while the introduction of CO inhibits the formation of phenols.Eventually,the content of pitch is reduced,aromatic hydrogen and aliphatic carbon are enhanced,and the quality of tar in the CP-SCG process is improved.In order to further activate the reaction atmosphere,the Ni-based catalysts were used to catalytic reforming of SCG,and the product distribution of the integrated process was studied.The results showed that the CP-RSCG process can improve the tar yield and quality further,but the tar yield increase is insignificant compared with the CP-SCG process because the CH₄reforming was suppressed due to the presence of H₂ and CO in SCG.In order to further improve the tar yield of the CP-RSCG process,the RSCG process was strengthened by means of optimizing the gas compositions in SCG,introducing steam into SCG and using the catalyst with high catalytic performance.Under optimized conditions,pyrolysis gases were used as SCG for circulatory pyrolysis,the results showed that,the tar yield gradually increased with the number of cycles,and the products tend to be stable and reach equilibrium at the fourth time.Isotope tracing experiments of the CP-RSCG process were performed with D₂,CD₄ and¹³CH₄ as tracers.The MS analysis showed that isotope D and ¹³C were present in the coal tar,indicating that the SCG participats in the coal pyrolysis reaction after reforming.The reason for the improvement in tar yield and quality of CP-RSCG process is ascribed to the active·H and·CH_x radicals produced by catalytic reforming of hydrogen-rich gases?H₂ and CH₄?in SCG.These small molecular radicals stabilize some radicals fom the coal pyrolysis,retarding the polymerization reaction among large radicals,and realizing the migration of pyrolysis products from solid char to liquid tar.