Process optimization of syngas production from gasification of waste plastic using a small-scale infrared reactor

Abstract

Due to the negative impact of fossil fuel on the environment and its finite potential, the quest for renewable energy sources, climate protection, energy sustainability, and conservation of humankind's natural habitat has become a contemporary civilization's greatest challenge. To achieve such a goal, governments, scientists, and engineers have to design ways to meet the world’s energy security while addressing climate change and reducing the environmental pollution. Currently, South Africa faces two major challenges, (i) energy security and (ii) environmental pollution, particularly the one caused by waste plastic. Despite the country's effort to mitigate these two serious challenges, it is clear in regard to the country’s current energy crisis and environmental pollution that there is a need for a more drastic approach in solving these challenges. This work focuses on the optimization of syngas production from gasification of waste plastic using a small-scale IR reactor. The work is based on a modeling and simulation approach using Aspen plus®, and on experimental analysis of a pilot gasification plant. A model was simulated on Aspen plus® and the kinetic free equilibrium model was used to investigate the optimization of waste plastic gasification. The gasification plant is a small laboratory scale plant that aims to generate gaseous products as fuel for further processing in a separate process outside the scope of this study. The gasification plant not only constitutes an infrared reactor, which is responsible for the gasification of the feedstock, but also of a catalytic water gas shift (WGS) system that is responsible for enhancing the hydrogen production via the concentration of syngas thermal energy. It was evident from this simulation study that the temperature at which syngas production was optimum was in the range 750–800°C. At this interval, the model revealed syngas content of 39% H2, 32% CO, 17% CO2, and 10% CH4. Pertaining to the flow rate parameters, the water flow rate appears to generate more syngas when alternated in comparison to the airflow rate. The experimental studies did not agree with the simulation and modeling results. However, they were in agreement with the literature. At a temperature of 653°C, syngas produced was composed of 21.3% H2, 5.7% CO, 15.2% CO2 and 0.2% CH4. The results obtained in this work particularly the hydrogen and carbon monoxide content are highly desirable for the Fischer-Tropsch synthesis.