Effects of reaction temperature and pressure on the distribution of lignite pyrolysis products in Santanghu Basin
The gasification reaction efficiency of coal in the gasification channel is a key issue affecting the gas composition and calorific value of underground coal gasification.To reveal the effects of reaction temperature and pressure on the gasification behavior and product distribution characteristics of lignite in water vapor using the coal deposited in the Santanghu Basin,pyrolysis experiments were carried out using lignite collected from the Xishanyao Formation of the Santanghu Basin based on a fixed-bed pyrolysis furnace under different reaction temperatures and pressures.With the increase of reaction temperature(300-900 ℃),the gas mass fraction increased from 3.84％to 24.29％,and the mass fractions of water and tar increased first and then decreased.The volume of H2 and CH4 increased significantly with the increase of reaction temperature,with the maximum volume of 100.89 and 106.09 mL/g at 900 ℃,respectively.The total mass of pol-lutants decreases,and the mass is relatively small at 900 ℃,17.72 mg/g.Increasing the reaction pressure(1.5-3.0 MPa)is beneficial to improve the conversion of semi-coke and increase the gas mass fraction.The increase of reaction pressure aggravates the secondary reac-tion,which is conducive to the occurrence of hydrogasification reaction and methanation reaction,resulting in a significant increase in the volume of CH4.At 700℃,the volume of CH4 increases by up to 26.89 mL/g.However at 700 ℃,the free radical hydrogenation satura-tion reaction is promoted,resulting in an increase in the total mass of pollutants.It is suggested that in the actual production,the reaction temperature and pressure should be increased by controlling the moving speed of steam injection,and the temperature of gasification reac-tion zone should be controlled away from 700 ℃,which is beneficial to the formation of H2 and CH4,so as to improve the efficiency and clean development of underground coal gasification process.The research results can provide guidance for the underground coal gasifi-cation process of lignite in Xishanyao Formation of the Santanghu Basin.
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