Multiscale Modelling of Non-Thermal Plasma Tar Cracking for Waste Gasification

Abstract

Gasification converts waste into syngas, producing fuel or material; yet tar by-products limit this by blocking reactors and catalysts. Tar cracking can be done by plasma – either thermal (TP) or non-thermal (NTP). The extreme conditions of TP gasification enable cleaner synthesis but require high energy. NTP tar cracking has been demonstrated on a lab scale with surrogate compounds, showing promising early results. However, there is a lack of model-based investigation in the field. This thesis aims to investigate the validity of NTP plasma tar cracking through a modelling perspective, exploring its reaction mechanisms, operational units, and potential environmental impact of TP and NTP waste gasification.

The modelling results of NTP tar cracking reaction kinetics show good agreement with experimental data, revealing the reaction mechanisms and showcasing the formation of radical species for ring opening reactions. The developed model is then combined with waste gasification process simulation. The waste gasification model was validated with experimental data and optimised for advanced syngas recovery. NTP tar cracking is represented through a reduced order correlation via multilinear regression. The produced syngas is compared for various scenarios, revealing the importance of high-energy recovery. Meanwhile, the co-production of material and energy was found to be unfavourable. Expanding the scope, TP gasification's environmental impact was systematically analysed, highlighting the environmental benefits of TP gasification, with advanced air pollution control and high energy recovery being key contributors. Lastly, the NTP waste gasification environmental impact is assessed. NTP gasification for material production shows the least environmental impact. Overall, the thesis's main contribution is a "proof-of-concept" for NTP waste gasification, substantiated via numerical validity from the modelling work.