Waste heat recovery in the air-cooling stage of foundry and steel forging: A thermo-fluid and economic analysis

The iron and steel industry is recognised as one with high thermal waste, which provides a significant opportunity for recovery. This research presents a method of recovering waste heat during the air-cooling process of a steel billet, specifically during the heat treatment and forging stages of manufacture, with temperature ranges between ℃ 800 − 1200 ℃ . The work also develops a transient computational fluid dynamics model through the use of thermal boundary conditions and the surface-to-surface radiation model to determine the waste heat recovered through an enthalpy change within the chosen heat transfer fluid, Therminol-66. Simulations were expanded with additional validation in the form of a sensitivity analysis, which was processed by reduced-order model development and systematic sensitivity analysis to determine the individual impact of each considered input parameter towards the overall heat recovery ability of the system, with the purpose of parameter optimisation. A numerical approach for calculating overall waste heat recovery potential, alongside Carnot potential, is being validated by literature with results which lie within the range of ∼ 45 to ∼ 51 % , suggesting a significant contribution towards industry decarbonisation. It is also proposed that, with the use of an organic Rankine cycle (ORC) system, the system is capable of power generation that can be used to offset electrical expenditure, for which a UK based foundry, Castings plc was used as a case study for economic analysis, which resulted in both financial and environmental benefits, with median €2.87/tonne and 3.48 kgCO2/tonne savings. Financial KPI analysis of net present value, internal rate of return, and payback period has also shown system performance to be above the benchmarks found in the literature when considering electricity prices for the EU27+UK.