Composition and structure evolution characteristics of product from segmenting pyrolysis of Xinjiang Hefeng coal

The pyrolysis technology for cascade utilization of low rank coal have been attracted much attention in recent years. Xinjiang is one of the important coal-chemical industrial base in China. But the fundamental research on pyroly- sis of Xinjiang coal is relatively few. In this paper,the single stage ( without iso-thermal stage,defined as process 1) and multi stage ( with iso-thermal stage at 350 ℃ and defined as process 2,with iso-thermal stages at 350 ℃ and 450 ℃ and defined as process 3) pyrolysis characteristics of a typical Xinjiang coal (Hefeng coal) were first investi- gated by using a thermogravimetric analyzer(TGA) and a fixed bed reactor. The results showed that the weight loss of coal samples during the single stage and multi stage pyrolysis in TGA exhibited a little difference. The multi stage py- rolysis led to the increase of gas yield and decrease of tar yield,especially for process 3,in which the tar yield further decreased to 11. 35% ,about 15. 42% decrement compared with that in process 2. The H2 yield was only 1. 94 mL / g when temperature was lower than 450 ℃ . Further increase temperature from 450 ℃ to 600 ℃ ,no tar was formed, while gas yield accounted for 60. 87% of total gas amount,especially for H2 which accounted for 95. 02% of total H2 yield. It indicates that gaseous products was mainly collected in this temperature range. FTIR analysis showed that only slight difference of the functional groups between the char obtained at 350 ℃ pyrolysis and raw coal was observed. While these functional groups nearly disappeared in char obtained at 450 ℃ . The simulating distillation and NMR a- nalysis results showed that holding stage in coal pyrolysis was favorable to upgrade the tar quality,which was embodied by the decrease of pitch content and the aromatic carbon ratio,especially for the two stage holding pyrolysis. Based on that,a theoretical basis for staged thermal conversion of low rank coal was supplied.