Influence of thermal pretreatment on pyrolysis of lignite

The effects of thermal pretreatment on pyrolysis behavior of Shengli lignite were investigated in a fixed bed reactor. In comparison with raw coal, the thermally pretreated coal has lower content of hydroxyl group and lower ratio of aromatic-H to aliphatic-H. The yield of pyrolysis water is lowered after thermal pretreatment in N2, N2+O2 and CO2 atmospheres. The pretreatment also causes a higher CO2 content in pyrolysis gas, which thus lowers the heating value of the gas. Pretreating the coal in superheated steam raises the tar yield by 3–4 weight percentage points, and the composition of tar varies with the atmosphere and temperature of the pretreatment. The light fraction (with boiling points below 360°C) increased by 27 weight percentage points by pretreatment in 200°C -steam. The pretreatments at 200°C and 250°C in the mixture of steam and simulated flue gas elevate the light oil and phenol oil fractions in tar by 60 and 42 weight percentage points, respectively.