Self-condensing transcritical CO2 cogeneration system with extraction turbine and ejector refrigeration cycle: A techno-economic assessment study

Abstract

This paper attempts to provide guidance for practical applications in utilizing low-grade heat sources by designing a novel combined cooling and power system. This system is integrated with a self-condensing transcritical CO2 Rankine cycle, an extraction turbine and a transcritical CO2 ejector refrigeration cycle. A mathematical model is established to analyze the thermodynamic performance and the model is validated through comparing results with data in open literature. System sensitivity analysis under various conditions is carried out to assess the relationships between key functioning variables and the system performance with regard to both thermal and economic perspectives. Results demonstrate that a favorable adaptability for balancing the cooling and power outputs is achieved by this combined system, and the user demand and plenty of net power can be remained. Besides, decreasing the turbine back pressure can maximally increase the refrigeration capacity of the system. The refrigeration capacity is greatly improved by 866.14% with a decrease in turbine back pressure from 10.4 MPa to 9 MPa at the cost of reducing net power by 50.11%. It is favorable and reasonable to increase liquefaction pressure and decrease cooling temperature to achieve goals of improving system energy and exergy efficiency and simultaneously reducing the product unit cost.