Two-stage air gasification of mixed plastic waste: Olivine as the bed material and effects of various additives and a nickel-plated distributor on the tar removal

Air gasification of mixed plastic waste was conducted in a two-stage gasifier. The effects of the combination of olivine as the fluidized bed material and activated carbon with or without other additives for tar cracking, as well as a Ni-plated distributor, the use of steam as a gasifying agent, and the calcination of olivine on the producer gas compositions and tar production, were also investigated. The maximum H2 concentration (27.3 vol%) was obtained with 900 g of activated carbon in the tar-cracking zone, and through the use of calcined olivine as the bed material. In the experiments, the maximum tar removal efficiency calculated using a base case reached 98.2%. The LHVs of the producer gases were in the range of 6.1-9.0 MJ/Nm3. The increase in the activated carbon amount led to an enhanced H2 production, as well as a decrease in tar production. The Ni-plated distributor was found to be effective for tar removal. In the application of dolomite in the tar-cracking zone and the use of steam as a fluidizing medium resulted in a high rate of HCl removal. The minimum HCl concentration in the producer gases was under 1 ppm.