Model-based determination of optimal operating parameters for different solid waste gasification

Abstract

In this study a 2D visualization technique is presented that is suitable for determining the optimal operational parameters of solid waste gasification depending on the intended use of the product. Steam gasification of different wastes (wheat straw, wood, municipal solid waste (MSW), polyethylene (PE), green waste) was modelled in Aspen Plus simulation software, validated with literature data and a MATLAB – Aspen Plus inter software connection was also created to minimize the possibility of errors when the raw material composition and other parameters are changed. Correlation was found between the simulation and literature data; therefore, the model was also suitable for evaluating the effects of process parameters (T = 650–1100 °C, steam rate = 0–1.5 kg/h) on gas composition, lower heating value and H₂/CO ratio. The model was also extended to a wide range of domestic waste types, making it possible to determine the optimal process parameters without performing a high number of time- and energy-intensive gasification experiments. Regarding the process parameters it was established that the temperature has a significant effect on the gasification reactions and shifts the chemical reactions towards hydrogen and carbon monoxide formation, but above 800 °C it has a limited effect on the gas composition, lower heating value and H₂/CO ratio. The increasing steam rate also facilitated the hydrogen and carbon monoxide formation, but above a certain ratio its effect was opposite due to the water-gas shift reaction and the shorter residence times. The obtained gases can be used for energy purposes or as raw material for Low-Temperature Fischer-Tropsch synthesis, or production of aldehyde, higher alcohol, acetic acid or even polycarbonate for which the optimal temperatures and steam rates were also determined.