Fluidized Bed Two-Stage Gasification Process for Clean Fuel Gas Production from Herb Residue: Fundamentals and Demonstration

A new two-stage gasification process, decoupling complex biomass gasification from biomass pyrolysis and char gasification, has been proposed for the production of clean industrial fuel gas. In this work, Chinese herb residues will be used as raw material, and the fundamental studies and demonstration of this process were conducted on an externally heated laboratory two-stage gasification setup and an industrial demonstration plant, respectively. The fundamental studies found that the appropriate operation of the upstream fluidized bed (FB) pyrolyzer occurred at 700 degrees C and the suitable conditions for effective tar removal in the downstream gasifier were as follows: 850 degrees C, an equivalent ratio of air (ER) at 0.04, and a retention time of tar containing fuel gas above 0.9 s. On the basis of these fundamental data, an autothermal demonstration plant treating 600 kg of herb residue per hour was built and successfully commissioned for its continuous running to verify the technology feasibility. The running data showed that the tar content in the gasified gas was as low as 400 mg/Nm(3) at temperatures of 700 degrees C for the FB pyrolyzer and 850 degrees C for the transport fluidized bed gasifier. The produced fuel gas had a heating value of similar to 5.0 MJ/Nm(3). All of these displayed well-the technical characteristics and demonstrated the process feasibility for this newly developed gasification technology.