Morphology of char particles from coal pyrolysis in a pressurized entrained flow reactor: Effects of pressure and atmosphere

A pressurized drop tube furnace was used to study the pyrolysis behavior of bituminous and lignite coal at elevated pressure. Experiments were conducted at the pressure range from 1 to 10 atm in 100% N₂ or 100% CO₂ atmosphere. The volatile yields, char morphology, swelling ratio, and pore structure were discussed in detail. The results show that the pressure, atmosphere and coal rank could effect on the volatile releasing and char evolution significantly. In N₂ atmosphere, the total volatile yields of YL and NM coal decrease as the pressure elevated, while in CO₂ atmosphere, the mass release of NM coal increases at high pressure contributed by the reaction of CO₂ with organic macromolecule inside the particles; different with bituminous coal, no significant swelling behavior is found with the increase of pressure; the BET surface area of YL char decreases as the pressure increases, while for lignite coal, in N₂ atmosphere and at high pressure, less macro pores are formed, which could contribute to the BET surface area. While in CO₂ atmosphere, the CO₂-macromocular organic reaction would promote the volatile releasing, and the BET surface area decreases significantly at high pressure.