Bubbling fluidized bed biomass gasification using a two-stage process at 600 °C: A way to avoid bed agglomeration

Air gasification of wood pellet was conducted using a two-stage gasifier consisting of a fluidized bed gasifier and a tar-cracking reactor filled with active carbon. The main aim of this study was to show that smooth gasification was possible at about 600 °C, where bed agglomeration could be avoided. Another important part of this study was to observe whether the low-temperature gasification could produce a producer gas with a similar gas quality to those obtained at high gasification temperatures. In the two-stage air gasification of wood pellet, active carbon showed an excellent performance in both removing tar and increasing H₂ production. The gas quality of the producer gas obtained at the fluidized bed gasifier temperature of about 600 °C proved to be similar to that obtained at about 800 °C. Further, the gas quality of the producer gas obtained without an electrostatic precipitator turned out to be comparable to that obtained with an electrostatic precipitator A long-term two-stage gasification (200 min) was conducted successfully without any operational problems, producing a H₂-rich (15 vol%) gas. The sole tar component of the producer gas from the long-term gasification was toluene, the content of which in the gas was only 8 mg/Nm³.