Experimental Study On The Pyrolysis Characteristics Of Zhundong Coals Blended With Other Coals

Coal pyrolysis is an effective way for efficient and clean utilization of coal.In recent years,many scholars have studied coal pyrolysis and achieved a lot of results.In this paper,the pyrolysis characteristics of Zhundong coal,Shenhua bituminous coal and Mengdong lignite were studied by utilizing thermogravimetric analyzer(TGA)and pyrolyzer-gas chromatography-mass spectrometer(Py-GC-MS)devices.The distribution of multi-step rapid pyrolysis products at different temperatures for single coal was analyzed.And the pyrolysis characteristics of blended coal for Zhundong coal mixed with different rank of Shenhua bituminous coal and Mengdong lignite at500?C with and without acid washing were investigated.Results from thermogravimetric experiments showed that the main pyrolysis stage of coal occurred at 400 ? C ~ 700 ? C,and the activation energy of pyrolysis reaction of different coal types was obviously different.The initial pyrolysis reaction temperature and the activation energy increased as the degree of coal metamorphism increased.The experimental data of Py-GC-MS showed that the products of rapid pyrolysis of all coal samples at temperatures below 300?C were mainly esters in the multi-step rapid pyrolysis experiment.The main pyrolysis stage occurred in the temperature range of 400?C ~ 600?C.The products in this stage were mostly aromatic hydrocarbons and phenols.There were also some aliphatic hydrocarbons released in this stage.The maximum total product yield and the most kinds of products were observed at 500 ? C.Above the temperature of 600? C,the total yield and types of product gradually decreased,and the main products were aromatic hydrocarbon substances.When the temperature was above 900?C,there was a few product detected.Different coals had different characteristics during the rapid pyrolysis process,and the Mengdong lignite coal had more total yield of pyrolysis products than other types of coal when the temperature was above 700?C.There was a great difference in the products of different coal under single-step rapid pyrolysis at 500 ? C.The content of aliphatic hydrocarbon products from Shenhua bituminous coal was the highest,accounting for 22.51% of the total amount of products.The aromatic hydrocarbons in the pyrolysis products of Zhundong coal were higher than that from Shenhua bituminous coal,with an relative yield of 30%.The phenolic product was also one of the main pyrolysis products.The yield of phenolic products from Mengdong brown coal was the highest,accounting for30.57% of the total products.The single-step rapid pyrolysis experiment of blended coal at 500 ? C showed that the regularity of pyrolysis products was not a simple superposition of single coal,but nonlinear relationships.Different blending ratios have different pyrolysis characteristics.The yield of aliphatic hydrocarbons products released from Zhundong coal blended with less than 50% of Shenhua bituminous coal,especially long-chain aliphatic hydrocarbons,were higher than that of Zhundong coal.Blending with 20% Shenhua bituminous coal reduced the total content of aromatic hydrocarbons in the pyrolysis process of Wucaiwan coal and Jiangjun coal.The content of aliphatic hydrocarbons and phenolic products increased significantly when Zhundong coals were mixed with Mengdong brown coal.After the acid washing,the relative areas of small molecule products decreased,while that of the macro molecular products increased.The total amount of pyrolysis products increased,which indicated that the removal of minerals after the acid washing increased the yield of volatile tar products.The content of phenolic products in different coals after acid washing were improved,especially in the Shaerhu coal with a lot of metallic minerals,the relative content of phenolic products released from which increased from 29.32% to 33.09%.After acid washing,the activation energy of the pyrolysis reaction of Zhundong blended coal(blending ratio is 1:1)increased.When mixed with Shenhua bituminous coal,the activation energy increased from38.12 kJ/mol to 58.90 kJ/mol.While for lignite,the activation energy increased from38.71 kJ/mol to 57.54 kJ/mol.After acid washing,the distribution of rapid pyrolysis products of blended coal tends to be the weighted average calculation value,which indicated that acid washing reduced the synergistic effects in the coal pyrolysis process.