Pyrolysis behavior of a typical Chinese sub-bituminous Zhundong coal from moderate to high temperatures

Abstract

The pyrolysis mechanism of Zhundong sub-bituminous coal (ZD) was investigated by tube furnace, gas chromatography and GC/MS. Coal samples were pyrolyzed in a tube furnace at any of six temperatures (from 500 to 1000°C in 100°C increments) and the pyrolysis products were analyzed. The volatile release characteristics were investigated by gas chromatography and the tars generated during pyrolysis were analyzed by GC/MS. Additionally, relevant physicochemical properties of the obtained char were discussed by FTIR and BET. Results suggested that increasing pyrolysis temperature could improve the volatile release volume and rate as well as the calorific value of the resultant gas due to the substantial increase of H2 and an incremental increase of CH4. Pyrolysis also effectively increased the coal rank and reduced the O/C ratio of char. FTIR spectra indicated that during pyrolysis, functional groups on the organic macromolecule decomposed and released to form the gas volume. The average pore diameter of ZD char decreased with pyrolysis temperature to a minimum value at about 700°C after which the average pore diameter gradually increased. The trends of specific surface area and pore volume with pyrolysis temperature were opposite the trend for average pore diameter. As for the tar components, the aliphatic hydrocarbons decreased and aromatic hydrocarbons increased while the polar organics first increased to a high value and then decreased. Finally, the mass balance demonstrated the pyrolysis gas yield increased with the temperature while the char showed the opposite trend. Besides, the tar yield achieved its maximum value at about 600°C.