Fluidized bed two-stage gasification of coal with steam/O2 for production of low-tar syngas

The fluidized bed two-stage gasification (FBTSG) decouples the reaction process into fuel pyrolysis in a downer and char gasification in a riser or transport bed. By sending all pyrolysis products into the bottom section of the gasifier, the tars containing in the pyrolysis volatile can be thermally and catalytically cracked in the gasifier via its high-temperature circumstance and catalysis of conveyed char, respectively. Thus, low-tar producer gas is possible for the FBTSG. Taking Yulin bituminous coal as raw material and using steam-oxygen as gasification reagent, the FBTSG was tested in a laboratory facility treating about 10 kg/h fuel to produce low-tar syngas under varied excessive oxygen ratio ER, steam to carbon ratio S/C, and temperature of pyrolysis and/or gasification reaction. The results showed that the continuous steady operation of FBTSG is fully feasible, and for a continuous test lasting for more than 3 h at ER = 0.36 and S/C = 0.15, its characteristic temperatures of pyrolysis and gasifier were stable at 735℃ and 877℃, respectively. The produced syngas contained 14.33% CO, 10.07% CO2, 18.39% H2, 9.89% CH4, 1.82% CnHm and 45.50% N2, giving an LHV of 8.99 MJ/m3. The gas yield was 1.8 m3/kg, and tar content in the gas reached its lower value of 0.437 g/m3, showing the technical characteristics of preparing low-tar syngas. For practical long-term continuous operation, higher gasification temperature will result in better low-tar characteristics of two-stage fluidized bed gasification. © 2022 Chemical Industry Press. All rights reserved.