Pyrolysis of low-rank coal with heat-carrying particles in a downer reactor

A novel co-current downer pyrolyzer was developed that can feed heat-carrying particles (silica sand, particle size, dp,sand=0.116mm) preheated in a fluidized bed separately with coal from the top of the reactor. This allows the high-temperature particles to directly contact coal particles. The influence of the pre-heated heat-carrying particles on the pyrolysis of dried Loy Yang coal particles (particle size, dp,coal=0.350–0.500mm) in a quartz glass downer reactor (1.0m in length and 20mm in inner diameter) was investigated at 1173K in the absence and presence of the steam (up to 30vol%) under different silica/coal ratios. Increase in sand feed rate increased the amount of carbon surface deposits and the yields of CO2 and CO. TOF-MS and FT-IR spectra of the produced heavy tar and deposited carbon on silica sand indicated that the heavy tar very rapidly deposited on the surfaces of sand and forms cokes by polymerization. No significant influence of the steam on pyrolysis reaction was observed within the estimated residence time of coal particles (~0.54–0.61s) in this pyrolyzer. •A novel downer pyrolyzer that feeds coal and sand particles separately is developed.•Influence of pre-heated sand particles on the pyrolysis of Loy Yang coal was studied.•Almost all the heavy tar is deposited on surfaces of the sand in 0.54–0.61s.•Polymerization of the heavy tar on surfaces of sand by coking also takes place.•Negligible influence of steam was observed on the pyrolysis in the residence time.