Supercritical Carbon Dioxide Brayton Cycle for Power Generation : Utilizing Waste Heat in EU Industries

Abstract: The industrial sector accounts for approximately 30% of the global total energy consumption and up to 50% of it is lost as waste heat. Recovering that waste heat from industries and utilizing it as an energy source is a sustainable way of generating electricity. Supercritical CO2 (sCO2) cycles can be integrated with various heat sources including waste heat. Current literature primarily focuses on the cycle’s performance without investigating the economics of the system. This is mainly due to the lack of reliable cost estimates for the cycle components. Recently developed cost scaling models have enabled performing more accurate techno-economic studies on these systems. This enables a shift in focus from plant efficiency to economics as a driver for commercialization of sCO2 technology. This work aims to develop a techno-economic model for these waste-heat-to-power systems. Based on the literature, waste heat from different industries is calculated, showing that the four industries with the greatest potential for waste heat recovery are cement, iron and steel, aluminum and gas compressor stations. Six different sCO2 cycle configurations were developed and simulated for these four industries. The techno-economic model optimizes for the highest Net Present Value (NPV) using an Artificial Bee Colony algorithm. The optimization variables are the pressure levels, split ratios, recuperators effectiveness, condenser temperature and the turbine inlet temperature limited by the heat source. The results show a vast potential for industries to cut down costs using this system. Out of the four industries modeled, a waste heat recovery system in an iron and steel factory yielded the highest NPV. Results show that the integration of sCO2 cycle in the cement industry could help reduce their waste heat by 60%, whilst simultaneously enabling them to cover up to 56% of their electricity demand. The payback period for the four industries varies between 6 to 9 years. Furthermore, simple recuperated sCO2 cycles with preheating are more economical than recompression cycles. Even though recompression cycles have higher thermal efficiency, they are limited by the temperature glide in the waste heat exchanger. This analysis could help investors and engineers take more informed decisions to increase the efficiency and economic return on investment for sCO2 cycles and heat recovery at industrial sites. To encourage adoption of supercritical CO2 cycles, a demo is needed along with more research for higher temperature applications with special attention to mechanical integrity.