Thermochemical processing of complex multi-phase and non-recyclable waste streams

By EU waste policy, an irreversible treatment of non-recyclable waste through thermal processing (i.e., incineration or gasification) is mandatory to keep intended cycles of materials in the Circular Economy clean and safe. This way, the energetic content of the waste can be largely recovered in the form of electricity, steam/heat, energy carriers (syngas) and/or valuable organic compounds, whilst toxic organic compounds are destroyed. It also creates opportunities for advanced recovery of inorganic materials and compounds of high interest from the ashes generated. However, when waste is exposed to high-temperature environments in thermal processes, the inorganics present in the waste exhibit a complex behavior by which they are distributed over solid, gas and liquid outputs. In state-of-the-art thermal processing plants for non-recyclable waste, the behavior of inorganics is still highly uncontrolled, which provokes significant operational problems. It also poses challenges in view of increasing yields of energy and materials from the waste treated, reducing chemicals for treatment of flue gasses and residues generated, and implementing carbon capture technologies downstream. The objective of this PhD project is to develop an in-depth understanding of the complex multiphase behaviour of inorganic compounds present in (selected) wastes when gasified/incinerated. The project comprises both experimental work and Fluent CFD simulations, and aims at unravelling the influence of physical process conditions imposed (in terms of temperature, pressure, flow, and induced heat and mass transfer) on chemical effects observed. For the experimental part, a thermal waste reactor at the pilot-scale, equipped with advanced analytical equipment, is used to research different types of waste under industrially representative process conditions and temperatures up to 1250°C. Examples include: tyre rubbers (containing Zn and Mg), brominated flame retardant plastics (Br and Sb), anti-microbial packaging materials and textiles (Ag and Cu), pruning wood from vineyards (Cu and S), CCA-treated wood (Cu, Cr and As) and sewage sludge from municipal waste water treatment (P). The PhD is partially funded by leading companies in the European Waste-to-Energy industry. The work is executed in interaction with universities from Lubljana and Budapest, which opens up the possibility for a stay abroad.