Characteristics and evolution of products under moderate and high temperature coal pyrolysis in drop tube furnace

Abstract Drop tube furnace is a high-efficiency pyrolysis reactor, which is helpful for fundamental research of coal base poly-generation technology. In this paper, the characteristics of coal pyrolysis product at various temperature using drop tube furnace were investigated. A typical Chinese lignite Pingzhuang coal was used in current research, pyrolysis temperature ranged from 600 to 1000 °C with a step of 100 °C. The compositions of pyrolysis gas, coal tar and char were characterized and discussed in detail. Results showed that volatiles and moisture content decreased after pyrolysis, hydrophilic functional groups like carboxyl and hydroxyl also decreased, pyrolysis was a dehydration upgrading process for lignite. Specific surface area and total pore volume increased from 1.65 m2/g and 11.57 mm3/g in raw coal to 199.10 m2/g and 191.95 mm3/g in 1000 °C char, respectively. As for pyrolysis gas, when temperature increased, H2 and CO increased obviously, other compositions like CO2, CH4 and C2∼C3 hydrocarbons decreased, consequently, the gross heating value of pyrolysis gas decreased from 22.5 MJ/m3 at 600 °C to 13.1 MJ/m3 at 1000 °C. High temperature pyrolysis had a high content of syngas (H2+CO), which can be utilized as raw material in synthetic chemical industry. There were high content of toluene in low temperature coal tar. There were more polycyclic aromatic hydrocarbons and less aliphatic chain hydrocarbons in high temperature coal tar.