Potential for surplus-heat-to-power conversion in current and future aluminium production process with off-gas recycling
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Date
2024Metadata
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- Publikasjoner fra CRIStin - SINTEF Energi [1707]
- SINTEF Energi [1843]
Original version
Proceedings of the 7th International Seminar on ORC Power Systems - ORC2023Abstract
Increased utilization of industrial surplus heat can make significant contributions towards reaching energy efficiency and emissions reduction goals. The off-gas from metal production smelters can contain large amounts of thermal energy, and conversion to electric power often appears an enticing prospect. However, the practical potential for exploitation can be significantly reduced from plant processes that are designed considering surplus heat as a waste product to get rid of. This typically makes the heat accessible only at reduced temperatures. The HighEFF research centre for industrial energy efficiency has studied technologies, applications, and cases for surplus heat utilization since its start in 2016. Heat-to-power conversion has been explored in several cases provided by the partner industries from – among others – Norwegian aluminium manufacturers. Centre research activities also include novel production processes and modifications, which has side effects providing very different conditions and constraints for energy recovery. One such process modification is off-gas recirculation, mainly developed to increase concentration of CO2 in the off-gas to improve conditions for CO2 capture in the future, but which also will alter off-gas temperature and recoverable heat as a side effect. This could improve the potential for energy recovery. In this work, the potential for energy recovery is evaluated and compared in four cases – one representing a current aluminium process, and three future process scenarios with flue gas recycling. The simulated heat-to-power conversion is done by applying an organic Rankine cycle (ORC) optimization model to each case. The results indicate significant benefits to energy recovery in the recycling cases. In the case with the highest recycling rate and flue gas temperature, the potential for electric power production increases by 270 % compared to the present-day case. In addition, the reduced work of the main exhaust fans in the recycling cases brings further energy savings on the system level equivalent to 25–50 % of the ORC power output, further increasing overall energy efficiency. From this, some potential synergies between process design, heat-to-power, and thermal integration of other technologies such as CO2-capture are discussed Potential for surplus-heat-to-power conversion in current and future aluminium production process with off-gas recycling