Pilot verification of a two-stage fluidized bed gasifier with a downer pyrolyzer using oxygen-rich air

Abstract A novel two-stage fluidized bed gasification system coupling a downer pyrolyzer and a riser gasifier was proposed, and a pilot facility of 15 kg/h of feedstock was further built and tested, by which the resulting technology gains its advantages of realizing the two-stage gasification principle in fluidized beds and having the large tolerance to biomass quality and size. Gasification of pine chips was in turn investigated at various equivalent ratios of air by changing the O2 concentration of gasifying agent composed of nitrogen and oxygen. The pilot facility was successfully operated at an ER value of 0.15, which generated 1.33 Nm3 product gas per kilogram of feedstock and containing 26.5% CO, 13.6% CO2, 8.89% H2, 12.6% CH4 and 0.63% CnHm. The LHV of the obtained fuel gas was as high as 9.35 MJ/Nm3 with a reasonably low tar content at 8.08 g/Nm3. By increasing the ER from 0.15 to 0.3, the temperatures of the pyrolyzer and gasifier were increased from 790 to 823 °C and from 881 to 925 °C, respectively. The gas yield was decreased to 1.1 Nm3/kg to have a reduced cold gas efficiency of 65.5% and a lower tar content of 4.35 g/Nm3 in the gas. These thus verified the technical feasibility of the proposed two-stage gasifier consisting of a downer and a riser.