The characteristics and mechanism for the formation of tars from low temperature pyrolysis of lignite

In this paper, the effect of pyrolysis conditions on low-temperature formation of tars characteristics and viscosity of lignite was investigated in a self-researched fixed bed reactor. The relationship between tar quality parameters and its formation and viscosity characteristics was investigated by multiple linear regression. The composition characteristics of low temperature tar were also investigated. The results showed that the yield and viscosity of tar increased with the increase of heating rate and pyrolysis temperature. Low temperature tar started to escape at 350 degrees C and reaches a maximum at 600 degrees C. The maximum tar yield was obtained at 550 degrees C-600 degrees C, 0.31%/min. The tar viscosity increased significantly after 550 degrees C, and the tar yield of isothermal pyrolysis was higher than that of non-isothermal pyrolysis after 500 degrees C. The tar yield under hydrogen atmosphere was higher than that under nitrogen, carbon dioxide, methane and carbon monoxide atmosphere. The tar yield increased gradually with the increasing of H-2 flow rate, until it reached the maximum at the flow rate of 720 ml/min, which was 12.58%. The mathematical models of tar formation and viscosity characteristics of Yunnan lignite during low temperature pyrolysis were Yield(tar) (%) = 12.14 H/C + 48.35 O/C - 12.54 f(a) + 0.29 A(d) and Viscosity(tar)(mPa.s ) = 14.99 H/C + 62.53 O/C - 0.39 f(a), respectively. The content of aliphatic and aromatic components in tar increased with the increase of pyrolysis temperature, while the content of polar substances decreased gradually. The content of aliphatic and aromatic components was more than 53%, and the polar compounds content dropped to about 41.7% at 600 degrees C.