SMALL SCALE ENERGY CONVERSION OF PLASTIC WASTE : Identification of gasification process parameters through modelling in Aspen Plus

The present work investigates further development of a small-scale fixed bed batch operating gasification pilot system intended to be used as a waste-to-energy process to reduce littering of PET-bottles on Pemba Island in Tanzania. By developing a simplified gasification model and identifying the most important parameters to obtain a syngas with a lower heating value suitable for combustion and maximizing the overall efficiency and cold gas efficiency. By a literature study the most important parameters were identified along with how the methodology for developing the model and selection of modelling software. The model was developed as an equilibrium-based model in Aspen Plus representing the pilot system, the most important parameters was identified as equivalence ratio and temperature. Multiple scenarios, regarding sensitivity analysis of these parameters was conducted to determine how the outcome of the process was affected. The model was validated against a reference study and was proven to be accurate with small variations. High content of methane and carbon monoxide promoted the highest lower heating value which was at an equivalence ratio of 0.25 and a temperature of 450°C, which also indicated the highest overall efficiency. Increasing the temperature favoured the carbon monoxide content and the cold gas efficiency but indicated a decrease in lower heating value and overall efficiency. It was concluded that the optimal operational conditions were at an equivalence ratio at 0.25 and a temperature at 450°C. At these conditions, the formation of by-products from the gasification is higher than at higher equivalence ratios and temperature which needs to be further investigated through experimental work. It was also concluded that the system could benefit to operate in a semi- batch configuration with a higher equivalence ratio to utilize the excess heat from the process