Oxy-steam fluidized bed co-gasification of plastic wastes and biomass: experimental study and CFD simulation

Plastic waste management remains a challenge due to low recycling rates and slow degradation. Gasification offers a solution by converting plastic waste into syngas, which can be used as fuel or for hydrogen production. While fluidized bed co-gasification of plastics at high temperatures has been widely studied, research on low-temperature oxy-steam co-gasification of biomass and plastics is limited. This study aims to fill this research gap by investigating the co-gasification process at low-temperature (715-745 °C) using pine residue and plastics like polyethylene terephthalate, high-density polyethylene, low-density polyethylene, polypropylene, and polystyrene. Furthermore, numerous gasification models have been oversimplified by considering only a small subset of gasification reactions, often overlooking important reactions like tar cracking that significantly influence gasification performance. To address this, a Eulerian-Eulerian computational fluid dynamics model is combined with a detailed 1D chemical reaction model. This model includes thirteen chemical reactions (six oxidation reactions, five reduction reactions, and two tar-cracking reactions) to simulate the oxy-steam fluidized bed gasification of plastic wastes. The carbon conversion efficiencies (conversion of feedstock carbon into gas) of the co-gasification process ranged from 57.98 % for polystyrene-biomass (50/50) to 78.20 % for pure biomass. The model effectively predicted syngas compositions from the gasification of various plastics, achieving average root mean squared errors of less than 5 % for C₂-C₃, CH₄, CO, H₂, and CO₂ gases. The experimental data and kinetic models developed in this study will aid in the preliminary scale up and design for the industrial-scale low-temperature oxy-steam fluidized co-gasification of various plastic wastes and biomass.