Study on variation of anthracite pyrolysis products with temperature under in-situ conditions

To study the gas product yield characteristics during in-situ pyrolysis of deep buried anthracite for gas extraction, high-temperature and high-pressure triaxial tester and gas chromatography were used to obtain the pyrolysis gas yield and products of anthracite in the range of 100-600 ℃. The relationship between product and permeability was analyzed. The study showed that the variation of pyrolysis gas yield with temperature can be divided into four stages: the first stage（ｄｅｇａｓｓｉｎｇ ｓｔａｇｅ） from 100 ℃ to 200 °C, where the anthracite produces small amounts of gas and the precipitated gas is mainly N₂ and O₂. The second stage ａｙａyrolysis initiation stage） from 300 ℃ to 400 ℃, where the anthracite coal is further pyrolyzed and the gas yield further increases, and the gas is mainly composed of CH₄, CO₂, H₂ and C₂H₆ produced by coal pyrolysis. 400 ℃ is the first peak of pyrolysis gas production. The range of 400-500 ℃ is the third stage（ｐｙｒｏｌｙｓｉｓ ｓｔａｇｅ）, due to the thermal stability of organic substances in anthracite, resulting in lower gas production. The range of 500-600 ℃ is the fourth stage（ｃｒａｃｋｉｎｇ ｓｔａｇｅ）, and pyrolysis gas production once again continues to increase. The permeability is influenced by the gas yield and gas production during pyrolysis.