Thermodynamic modelling and techno-economic assessment of mechanical vapour recompression for decarbonising low-temperature alumina refining

Industrial process heat is a major source of energy use and emissions in alumina refining. Low-temperature alumina refineries have recoverable heat and vapour streams that can potentially be upgraded to useful steam conditions using mechanical vapour recompression (MVR). This study presents a thermodynamic and techno-economic assessment of open-cycle MVR for low-temperature alumina refining and compares it with direct electric boilers. The model evaluates how waste-heat temperature, required steam temperature and plant capacity affect compression requirements, coefficient of performance (COP), capital expenditure (CAPEX), operating expenditure (OPEX), levelised cost of heat (LCOH) and operational emissions. The results show that temperature lift is the main driver of MVR performance. Feasible MVR cases achieve COP values of approximately 2–7, corresponding to 62–70% of the Carnot limit. Warmer waste-heat sources reduce compression work and can reduce the number of required compression stages. The economic results show that MVR becomes more competitive at larger plant capacities because specific CAPEX decreases and the energy-saving benefit of higher COP becomes more important. Median MVR–DEB cost parity occurs near the MW scale under favourable temperature-lift conditions. The emissions analysis shows that MVR can reduce operational emissions relative to gas-fired steam generation when electricity carbon intensity is sufficiently low. The results identify the source-temperature, steam-temperature and capacity conditions under which MVR can provide a competitive alternative to direct electric steam generation for low-temperature alumina refining.