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 °C. AC triggers the cracking and reforming of heavier compounds, reducing the tar content by 64% at 800 °C and increases H₂ and CO content. Increasing AC bed temperature causes reduction of C₂-C₃ 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 H₂, 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 H₂ and CO content of the product gas compared to air gasification. Increasing S/C ratio further increases the H₂ and CO content, and the CO₂, CH₄, and C₂-C₃ hydrocarbons decreases due to intensification of water–gas shift, steam reforming, and water–gas reactions. Exceeding S/C ratio above 1.5 decreases the H₂ and CO content, but increases CCE, CGE, and LHV of the gas due to higher C₂ –C₃ 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.