Process synthesis and experimental analysis of waste tire thermochemical conversion processes

The thermochemical conversion of waste tires for chemicals and power production is investigated using process synthesis techniques and experimental analysis. Pyrolysis and gasification technologies were evaluated in terms of the fundamental thermodynamic metrics of carbon efficiency, atom economy, e-factor and chemical potential efficiency, thermal efficiency and their market-related revenue potential. The synergetic effect of co-gasification and co-pyrolysis of waste tires with alternative waste materials is also evaluated experimentally. The thermodynamic analysis found that pyrolysis pathways perform better in terms of thermodynamic efficiency and carbon footprint than gasification processes, which lose about 45% of the carbon feed to carbon dioxide. However, the gasification routes offer higher potential revenue, yielding as much as $625 per ton of waste tire as compared to $205 from the pyrolysis route. It was also found that waste tire integrated gasification combined cycle (IGCC) net-work output is 10.5 GJ/ton of tire much higher than that of conventional coal IGCC at 9.6 GJ/ton of coal. The results of the techno-economic analysis showed the feasibility and sustainability of operating a 550-tonne-per-day plant producing methanol or electricity requires a minimum government subsidy of 0.115 $/kg to make the process economical and cost competitive to fossil-fuelled plants. With the levy, the minimum selling price for electricity would be $ 0.098/kWh and that of methanol at $420/ton. The results reported here clearly demonstrate the synergistic capabilities for integrating waste materials such as gypsum and spent fluid catalytic cracking (FCC) catalyst in tire recovery facilities to recover valuable products and reduce the carbon footprint via catalytic CO2-assisted gasification. The findings of this dissertation indicate that, from an environmental aspect, converting waste tires to transportation fuels is more desirable than landfilling them, and that gasification technologies may offer better long-term prospects than pyrolysis, despite their higher emissions. Globally, fossil fuels are currently being burned, and it has been demonstrated that waste tires potentially perform as well as or better than existing fossil fuel processes; therefore, there is still a strong environmental justification for the usage of waste tires.

Civil and Chemical Engineering

D. Phil. (Science, Engineering & Technology)