Modelling and simulation of autothermal downdraft co-gasification of biomass and plastic wastes using Aspen Plus

In this study, the autothermal downdraft co-gasification of biomass and plastic wastes has been investigated. Thus, a restricted equilibrium model employing approach temperature and Gibbs free energy minimisation was developed and validated with data from the literature. A detailed sensitivity analysis reveals an increase in equivalence ratio from 0.1 to 0.5 augments gasification temperature from 751 ℃ to 1305 ℃. The equivalence ratio of 0.3 is found to be optimum, with the lower heating value and cold gas efficiency at 5.3 MJ/Nm³ and 66 %, respectively. The co-feeding of plastics with biomass exhibits possible synergy evident from the syngas lower heating value and cold gas efficiency improvement from 4 MJ/Nm³ to 5.8 MJ/Nm³ and 60.6 % to 68.8 %, respectively, as feed plastic content is increased from 0 to 30 %. An increase in oxygen enrichment in the air from 21 % to 100 % improves gasification temperature and H₂ content from 858 ℃ to 1017 ℃ and 14.3 % to 40.9 %, respectively. A statistical analysis using Analysis of Variance (ANOVA) and Response Surface Methodology (RSM) was also performed using Minitab software to find the comparative influence of each process parameter on the performance and the correlation equation. In addition, the multi-objective optimisation revealed optimum process parameters to be 0.25, 30 %, 8 % and 50 %, respectively, for equivalence ratio, plastic content in the feed, biomass moisture content and oxygen content in enriched air with their performance at 903 ℃, 8.65 MJ/Nm3 and 71.04 % for gasification temperature, syngas lower heating value and cold gas efficiency.