Experimental Study On Coal-gas Catalytic Co-pyrolysis Enhanced By Microwave

“Rich coal,less oil,less gas”energy distribution pattern determines coal resources will still dominate the energy structure for a long time in our country.Coal accounts for over 70%of the total primary energy consumption in China,and low rank coal resources accounts for 48%of all proven reserves of coal resources.The pyrolysis of low rank coal to produce blue-coke,coal tar and gas is considered to be one of the best ways to utilize.Domestic existing mainstream pyrolysis technology with traditional heating methods of mixed combustion of coal gas and air is closely related to the following intractable prominently problems,lower utilization of pulverized coal,longer production cycle,lower yield of tar,poorer quality of gas and much serious environmental pollution,etc.Therefore,how to realize more efficient clean conversion utilization of low rank coal is still the current research focus in the coal chemical industry field.In recent years,Microwave pyrolysis technology as a new approach to realize clean efficient conversion and comprehensive utilization of low rank coal have showed obvious technical advantages with fast pyrolysis,higher yield and quality of tar,higher content of valuable components in the gas such as hydrogen,methane and carbon monoxide,etc.Combined fully with microwave pyrolysis and catalytic hydrogenation pyrolysis of coal technical advantages,A pyrolysis technology study on realizing coal-gas microwave enhanced catalytic co-pyrolysis through low rank pulverized coal as raw material mechanically mixed with catalysts powder in circulation gas atmosphere from microwave pyrolysis system was put forward in this paper.The mechanism of the catalysts in the microwave field was discussed preliminarily by comparison with conventional pyrolysis experimental study;Microwave pyrolysis experiment of low rank coal added with transition metal compounds molybdenum disulfide and cheap pyrite as representative catalysts were carried out,and effects of added amount of catalysts,molding pressure,circulating coal gas flow rate and added amount of elemental sulfur on yield and component of pyrolysis products were explored.The main conclusions were as follows:(1)Compared with conventional pyrolysis,microwave pyrolysis process of coal heated up faster.Coal-gas conventional pyrolysis,coal-gas microwave pyrolysis,coal-gas-MoS₂conventional pyrolysis and coal-gas-MoS₂ microwave pyrolysis four dfferent kinds of pyrolysis processes were studied.It showed that the liquid products yield was the highest,light oil components content in coal tar was higher leading to its better stability in coal-gas-MoS₂ microwave pyrolysis technology.And valuable components(CH₄+CO+H₂)content in pyrolysis gas was the highest,while H₂ content was relatively lower.It indicated that microwave environment and the participation of MoS₂ catalyst were to improve hydrogen utilization,gas quality and the yield and quality of tar in coal-gas pyrolysis process.(2)Considering and evaluating comprehensively yield of liquid products and quality of coal tar from the perspective of high to low,four kinds of pyrolysis processes are to choose the order priority as follows:coal-gas-MoS₂ microwave pyrolysis>coal-gas-MoS₂conventional pyrolysis>coal-gas microwave pyrolysis>coal-gas conventional pyrolysis.(3)Function of MoS₂ as catalyst in coal-gas microwave pyrolysis process reflected in:MoS₂,as a kind of capable of absorbing wicrowave substance called“sensitizer”in microwave field,thus making microwave energy was transformed into heat energy and metallic active sites with hydrogenation ability became stronger,are to promote catalytic hydropyrolysis ability of low rank coal and improve effectively coal conversion rate and yield of liquid products.(4)The yield of liquid products obtained from microwave pyrolysis of low rank coal was highest up to 28.4%,the yields of blue-coke and gas reached 64.0%and7.6%,respectively.And valuable components(CH₄+CO+H₂)content in pyrolysis gas was highest up to 79.04%,gas heat value was up to 15.14MJ/m³,and content of light oil component in coal tar was as high as 67.55%when the optimal pyrolysis process conditions with MoS₂ related pulverized coal addition ratio 8.3%,coal molding pressure 7Mpa,circulating coal gas flow rate 0.6L/min and elemental sulfur addition ratio 0.25%were selected.(5)The yield of liquid products obtained from microwave pyrolysis of low rank coal was highest up to 27.2%,the yields of blue-coke and gas reached 64.1%and8.7%,respectively.And valuable components(CH₄+CO+H₂)content in pyrolysis gas was highest up to 75.65%,gas heat value was up to 13.05MJ/m³,and content of light oil component in coal tar was as high as 48.17%when the optimal pyrolysis process conditions with Fe S₂ related pulverized coal addition ratio 12.0%,coal molding pressure 7Mpa,circulating coal gas flow rate 0.6L/min and elemental sulfur addition ratio 0.25%were selected.(6)Addition of a small amount of S in coal-gas microwave catalytic co-pyrolysis process could effectively improve the yield of liquid products and increase the content of light oil component.However,the excess of S could cause the catalyst active site to be poisoned by the excess H₂S,which leads to a worse thermal decomposition effect.(7)The catalytic effect of MoS₂ is better than that of Fe S₂ in coal-gas microwave catalytic co-pyrolysis,the yield of liquid products was generally higher,and the content of light oil in tar is also higher.