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Optimization of the Part-Load Operation Strategy of SCO2 Power Plants

Supercritical CO2 cycles for power generation are gaining a large interest from industry, institutions and academia as demonstrated by the large amount of investments, founded projects and research papers. This attention is motivated by the potential of sCO2 technology for replacing conventional steam plants in a number of applications and likely to play a relevant role in the future energy scenario.

Climate Change and Environment

The H2020 sCO2-Flex project is studying the application of sCO2 cycles in coal-fired power plants in order to enhance their flexibility and ease the integration with non-dispatchable renewable energy sources such as wind and solar. The sCO2-Flex project has also the aim of investigating the replicability of the concept with other heat sources such as CSP, biomass and WHR. Main advantages of sCO2 power plants with respect to USC technology are: (i) potential higher efficiency, (ii) compactness of the turbomachinery, (iii) no need of water treatment, deaerator, vacuum pump, etc., (iv) fast transients and (v) high performance at part-load. This study focuses on the last topic with the aim of investigating a different part-load operation strategy for a waste heat recovery power plant based on a sCO2 cycle exploiting a stream of 50 kg/s of flue gases at 550°C. The selected sCO2 cycle is a recuperative recompressed cycle with high temperature recuperator bypass, whose maximum/minimum pressure and maximum temperature are optimized in design condition obtaining an overall recovery efficiency of 22.65%. Different operating strategies at part-load are investigated considering the combinations of component features such as rotational speed and variable geometry at the inlet of turbomachinery, fan speed on the heat rejection unit, and variation of the fluid inventory. The best operating strategy energy-wise is finally proposed, providing a numerical estimation of the off-design overall plant performance, highlighting the impact on the compressor operating points and on the fluid inventory variation within the cycle.