Gasification characteristics of waste plastics (SRF) in a bubbling fluidized bed: Use of activated carbon and olivine for tar removal and the effect of steam/carbon ratio

This study investigates the gasification characteristics of waste plastic (SRF; solid refuse fuel) and tar removal properties of activated carbon (AC) and olivine using 1 kg/h lab scale bubbling fluidized bed gasifier. The steam gasification was conducted at steam/carbon (S/C) ratio from 1.0 to 2.0 to increase the product gas quality. AC bed gas velocity is 0.12 m/s and temperature is varied from 600 to 800 degrees C. AC triggers the cracking and reforming of heavier compounds, reducing the tar content by 64% at 800.C and increases H-2 and CO content. Increasing AC bed temperature causes reduction of C-2-C-3 hydrocarbons, thus decreasing carbon conversion efficiency (CCE), cold gas efficiency (CGE), and lower heating value (LHV) of product gas. Using olivine as the bed material increases contents of H-2, CO, CH4 and reduces content of CO2 in the product gas, therefore improving CCE and CGE. Olivine reduces the tar content up to 32% due to the steam-iron process and increases light aromatics but reduces naphthalene content in tar. Steam gasification significantly increases H-2 and CO content of the product gas compared to air gasification. Increasing S/C ratio further increases the H-2 and CO content, and the CO2, CH4, and C-2-C-3 hydrocarbons decreases due to intensification of water-gas shift, steam reforming, and water-gas reactions. Exceeding S/C ratio above 1.5 decreases the H-2 and CO content, but increases CCE, CGE, and LHV of the gas due to higher C-2-C-3 hydrocarbons content in the product gas. Increasing S/C ratio above 1.5 also increases condensable tar content of the product gas, increases consumption of AC bed thus reducing its catalytic effect.