Characterization and pilot scale test of a fluidized bed two-stage gasification process for the production of clean industrial fuel gas from low-rank coal

To utilize low rank coal efficiently, a fluidized bed two-stage (FBTS) gasification process, mainly consisting of a FB pyrolyzer and a transport FB (TFB) gasifier, has been proposed for the production of clean fuel gas. To verify the feasibility and technical features of this novel gasification technology, a pilot autothermal platform, with a treating capacity of 100 kg/h for coal, was designed and built up. By adopting a kind of lignite from Inner Mongolia, the running state and fuel gas quality were compared systematically under typical operational conditions. The results show that by keeping the reaction temperatures of pyrolyzer and gasifier at around 840 °C and 1000 °C, respectively, the corresponding tar content in fuel gas at the outlets of pyrolyzer and gasifier were 1127 mg/Nm3 and 365 mg/Nm3, reaching a high tar removal efficiency. Under the stable operation state, the volume fractions of CO, H2, CH4 and CO2 in fuel gas were 14.4%, 8.3%, 3.4% and 11.3%, respectively, and the corresponding higher heating value of fuel gas was about 1100 kcal/Nm3. Compared with the tar from pyrolyzer, the heavy oil fraction in tar from gasifier reduced significantly, while the light oil components increased sharply simultaneously, showing significant effect of catalytic reforming by hot char bed on tar removal. Keywords: Coal, Clean conversion, Tar, Two-stage gasification, Fluidized bed, Decouplin