Co-gasification of waste PET, PP and biomass for energy recovery: A thermodynamic model to assess the produced syngas quality

Abstract

Co-gasification of plastics with biomass is an attractive energy-recovery option to handle the plastic waste generated by society and requires further study. This work presents a simulation-based analysis of the air co-gasification of polypropylene (PP), polyethylene terephthalate (PET) and biomass (straw) using different combinations (PP/PET, PP/biomass, PET/biomass and PP/PET/biomass) and proportions, temperatures (650–850 °C), and equivalence ratios (0.25–0.45). A thermodynamic equilibrium model based on the Cantera chemistry toolbox and Python scripting was used in the simulations. Results indicate that increasing the proportion of plastics in the gasification feedstock increases the gas heating value (to a maximum of 5.78 MJ/Nm3) and tar contents (to a maximum of 72.89 g/Nm3). Additionally, it was found that PET is the plastic that adds the least value to the gas because of its lower heating value and tendency to form tar. Moreover, when gasifying a mixture of PP/PET/biomass, the gas H2/CO ratio decreases with temperature (from 1.91 at 650 °C to 1.14 at 750 °C and an equivalence ratio of 0.25), an aspect of particular importance for the end-use of the syngas. From the simulation results, a surrogate model was computed, and a series of response surface and polynomials were produced.