A two-stage circulated fluidized bed process to minimize tar generation of biomass gasification for fuel gas production

[Display omitted] •Two-stage gasification process with a riser char gasifier and a downer fuel reactor is performed.•Its low-tar gasification capability in fuel gas from biomass is tested in a 15 kg/h pilot facility.•Using steam-oxygen as gasification reagent produces fuel gas containing tar below 100 mg/Nm3. This study tested a two-stage circulated fluidized bed process consisting of a downer for pyrolysis of biomass and a riser for char gasification and tar removal to produce fuel gas containing tar below 100 mg/Nm3 from pine chips using steam-oxygen (not N2-oxygen) as the agent. A pilot facility treating 15 kg/h biomass was run at different equivalent ratios (ERs) and steam-to-biomass ratios (S/Bs). Under the typical conditions of S/B = 0.15 and ER = 0.3, the produced fuel gas contained (in volume) 21.64% CO, 21.97% CO2, 15.34% H2, 18.59% CH4, 1.49% CnHm and 1.83 g/Nm3db tar. A long-tern running of the pilot pant realized a tar content low as 95.5 mg/Nm3db in the produced gas. These results thus well verified the technology feasibility for low-tar biomass fuel production via the two-stage circulated fluidized bed steam-oxygen gasification.