Co-Gasification of Plastics and Biomass in a Downdraft Gasifier

The sharp rise in plastic consumerism and abundance of palm oil biomass waste, particularly the oil palm fronds, has brought about the challenges to treat waste sustainably. Co-gasification has the potential to become an effective technology for developing a long-term waste management system that reduces landfill emissions while optimizing energy recovery. However, there has been limited work on co-gasification of plastic with oil palm fronds, and this gap becomes a hindrance for the industry to take up the technology. This study aims to explore the potential of co-gasification as a sustainable waste management and energy recovery solution by examining the thermochemical behavior of plastic-biomass blends. Specifically, the objective is to investigate the impact of co-gasifying different plastics (high-density polyethylene, polypropylene, and polystyrene) with oil palm fronds (OPF). Experiments were performed in a downdraft gasifier with reaction temperatures between 750°C and 950°C as well as plastic proportions of between 0 wt.% and 30 wt.%. Increasing the plastic content in the feedstock blend led to a higher methane (CH₄) yield, while reducing the yield of other gases. Similarly, increasing the temperature to 950°C during co-gasification of polystyrene with OPF enhanced the production of synthetic gas (syngas) components such as hydrogen (H₂) and carbon monoxide (CO) while reducing the yield of CH₄. This is attributed to the increased cracking and reforming of volatile compounds at higher temperatures, converting them into permanent gases like H₂ and CO. Co-gasification with polypropylene resulted in the highest higher heating value (HHVgas) as the temperature and plastic content rose. Syngas composition was influenced by both plastic type and blending ratio with OPF. Polystyrene had the greatest yield concentrations of H₂ and CO gases, while polypropylene showed the highest HHVgas among other blends.