Techno-economic Assessment of Liquid Desiccant Recovery, Transport and Use of Regenerative Thermal Oxidiser Heat

Regenerative thermal oxidisers (RTOs) are widely used for volatile organic compounds (VOCs) abatement in automotive paint shops. They produce significant heat with variable exhaust temperatures, complicating the conversion of this energy source into a stable and usable service. This study assesses whether using liquid desiccant solutions to recover RTO stack heat, store it thermochemically through changes in solution concentration and supply temperature and humidity control is techno-economically viable. An annual performance model coupled with a techno-economic assessment was developed for two utilisation strategies in a paint shop: on-site for flash-off drying and off-site for climate control in a nearby gym via pipeline transport. The analysis considers aqueous lithium chloride (LiCl) and calcium chloride (CaCl2), outdoor air conditions, RTO exhaust temperature variability and operational adjustments, including regenerator exhaust air recirculation and auxiliary heat, to balance dehumidification and regeneration year-round. Results show that coupling RTO heat recovery with liquid desiccant regeneration is technically feasible and that on-site flash-off drying offers the strongest economic case, with payback periods of 5.3 years (NPV £134.4k, IRR 18.1%) and 10.9 years (NPV £22.9k, IRR 6.6%) for aqueous CaCl2 and LiCl, respectively. The off-site gym application is less favourable for the investigated distance and end-user demand. Sensitivity analysis confirms that viability is strongly dependent on energy prices, pipeline distance and working fluid. The results indicate that on-site utilisation should always be prioritised, while off-site applications require larger end-user demand and/or shorter distances, together with more favourable operating conditions.