A single particle of hydrated lime suspended in an acoustic levitator will reveal how sulphur dioxide gets absorbed from industrial exhaust gases. This matters because the UK’s 2030 emission regulations require far better cleaning of flue gas from Energy-from-Waste plants, but current semi-dry desulphurisation systems rely on trial-and-error rather than a solid understanding of the underlying physics. The researchers will build that understanding from the micro scale—how temperature, humidity, and particle size affect a single particle’s ability to capture SO₂—up to the macro scale of full reactor behaviour. They will also develop an online monitoring system that tracks particle distribution and SO₂ removal simultaneously. If successful, the work could allow a single-stage flue gas cleaning system to meet emission standards, cutting capital costs for EfW plants and making the technology more affordable for developing countries. Reduced reagent consumption would lower production and transport emissions, while less residue means fewer plant shutdowns for cleaning. The project is fundamentally about understanding complex particle–droplet–gas interactions, but that understanding has a direct route to cleaner air and cheaper waste-to-energy operations.
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Effective flue gas cleaning to remove sulphur dioxide (SO2) emissions from industrial sources, including Energy-from-Waste (EfW) plants, is crucial for mitigating environmental damage, protecting public health, and meeting stringent regulatory standards. Current technologies must be significantly upgraded to comply with the 2030 National Emission Ceilings Regulations and support the UK’s circular economy goals. The UK government’s comprehensive resource and waste strategy, which aims to eliminate all avoidable waste by 2050, underscores the importance of EfW solutions with efficient flue gas cleaning systems. These solutions reduce the volume of waste sent to landfills, cut emissions, generate energy, and facilitate material recovery, thereby contributing to a closed-loop circular economy. Semi-dry flue gas desulphurisation employs chemical reagents like hydrated lime to absorb SO2 from flue gases. Given stricter emission regulations, it is essential to significantly enhance this process without disproportionately increasing operational costs. Enhanced SO2 removal can facilitate compliance with emission standards through a single-stage flue gas treatment system, significantly lowering capital expenditure for EfW plants and making the technology more accessible, especially for developing countries. Efficient SO2 removal with reduced reagent consumption will decrease production and delivery costs of hydrated lime, thus reducing transportation carbon emissions and making the overall operation more economical and sustainable. Moreover, it will minimise the production of residues that need treatment or landfill disposal. Minimising residue production also lowers the fouling risks and the need for plant shutdowns for manual cleaning, thereby increasing plant availability and potentially saving costs. Achieving SO2 removal enhancements requires moving beyond trial-and-error methods and developing a robust theoretical foundation for process design and optimisation. A prerequisite for further improvements is a fundamental understanding of the underlying physics of two common semi-dry technologies: Particle-Powder Spouted Beds and Circulating Fluidised Bed Reactors. Both technologies involve interactions between solid particles (e.g., hydrated lime), liquid droplets (e.g., water or slurry), and gas phases (flue gas). Factors such as temperature, humidity, particle size, and particle spatial distribution significantly influence these interactions, making numerical modelling and accurate SO2 removal predictions challenging. Furthermore, physical models characterising the interfacial transport and chemical processes require further experimentally informed development. Fulfilling this modelling gap is the main aim of the present proposal. We will take a micro-to-macro scale approach to comprehend the SO2 removal process in semi-dry desulphurisation, which involves (i) understanding the effects of operating conditions, (ii) exploring the effects of complex particle interactions, and (iii) developing online monitoring techniques to characterise inter-particle dynamics and quantitative SO2 removal rate simultaneously. Non-uniform temperature and velocity distributions in large-scale desulphurisation reactors cause particles to experience different localised conditions based on their position. To address this, we will develop a parametric regime map for micro-scale transport phenomena by conducting single-particle experiments in an acoustic levitator under high temperature and humidity conditions. The complex interactions between solid particles and liquid droplets in semi-dry desulphurisation reactors introduce significant hydrodynamic challenges. We will investigate inter-particle interactions in an innovative vertical wind tunnel with a diverging cross-section to develop experimentally informed models. Furthermore, the impact of inter-particle behaviour on overall bed performance and SO2 removal is not well understood. We will adapt and utilise the experimental methodology of the Depth-from-Defocus to evaluate particle spatial distribution and inter-particle distances and combine it with quantitative SO2 measurements using Planar Laser-Induced Fluorescence to create an online monitoring system.
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