Techno-economic assessment of waste heat harnessing in the primary aluminum industry through a dual-stage organic Rankine cycle integration

The primary aluminum industry dissipates more than 50 % of its energy as waste heat. This study delves into an innovative application of the Double-Pressure Organic Rankine Cycle (DPORC) to recover waste heat from flue gases and smelter sidewalls, employing both high-temperature (HT) topping and low-temperature (LT) bottoming cycles. The research aims to assess its technical and economic viability. The study investigates operational considerations, such as intermediate pressure and working fluid type, with economic factors to evaluate both the thermodynamic and economic performance of the system. The findings reveal notable improvements in power output and exergetic efficiency by leveraging two distinct heat sources within the DPORC framework. Integrating an LT bottoming cycle yields a notable 33 % increase in thermal efficiency. Economic analysis underscores substantial efficiency gains and financial returns compared to conventional ORC setups, with the DPORC achieving a maximum net output power increase of 2844 kW, varying between 7200 kW and 7310 kW across various scenarios. Moreover, by assessing the temperature range of both heat sources and introducing a pre-heater, further performance enhancements were noted. Furthermore, the DPORC system demonstrates a considerably shortened payback period of 0.44–0.5 years, enhancing its economic appeal. This research underscores the potential of the DPORC for efficient energy recovery and economic viability in industrial waste heat applications, paving the way for future advancements in two-stage ORC systems.