Pilot verification of a low-tar two-stage coal gasification process with a fluidized bed pyrolyzer and fixed bed gasifier

A 50 kg/h autothermal two-stage gasifier, consisting of a fluidized bed (FB) pyrolyzer and a downdraft fixed-bed gasifier, has been designed and built according to our previous laboratory researches. In the experiments, lignite gasification was performed in this innovative two-stage gasifier to demonstrate the process feasibility for clean fuel gas production. The results showed that when keeping the reaction temperatures of the FB pyrolyzer and downdraft fixed bed gasifier respectively at about 860 °C and 1100 °C, the tar content in the produced fuel gas from the two-stage gasifier was effectively lowered to 84 mg/Nm3 and the heating value of fuel gas was close to 4.186 MJ/Nm3. Compared with the tar produced in the FB pyrolyzer, the tar from the downdraft fixed bed gasifier had obviously higher content of light oil components and lower content of heavy components, showing essentially an effective catalytic reforming of tar components by the hot char bed of the downdraft fixed bed gasifier.