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Basic design of an ORC demonstrator system for implementation in an Iron & Steel plant through the DECAGONE projectWindfeldt, Magnus; Deng, Han; Andresen, Trond; Schifflechner, ChristopherWaste heat recovery (WHR) technologies offer great opportunities for improving energy efficiency and reducing CO2 emissions for energy intensive industrial processes. The DECAGONE project is developing an innovative ORC-based WHR system to be demonstrated in an iron & steel plant located in the Czech Republic. The design of the ORC system considers the practical site-specific conditions and limitations, such as variations in heat source conditions, heat sink availability, and size and space limitations for the ORC components. Various cycle configurations are compared with a thermodynamic optimization model for maximizing the net power output subject to the process constraints, including (1) recuperative vs. non-recuperative designs, (2) air vs. water as heat sink and (3) direct vs. indirect evaporation. The recuperative cycle with indirect evaporation and direct air condensation is deemed the most suitable solution for the project site conditions. The results provide recommendations for performance improvement and indications for performance subject to practical plant operating conditions, such as large range of temperature and flow rate of waste heat source. Analyses in this work provide the basis for detailed component design and decision processes towards finalizing the design of the demonstrator.- Potential for surplus-heat-to-power conversion in current and future aluminium production process with off-gas recyclingBueie, Jonas; Windfeldt, Magnus; Andresen, TrondIncreased 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.
