Effect of Mixtures on Compressor and Cooler in Supercritical Carbon Dioxide Cycles

With the increasing demand for electric power, the development of new power generation technologies is gaining increased attention. The supercritical carbon dioxide (S-CO₂) cycle is one such technology, which has relatively high efficiency, compactness, and potentially could provide complete carbon capture. The S-CO₂ cycle technology is adaptable for almost all of the existing heat sources such as solar, geothermal, fossil, nuclear power plants, and waste heat recovery systems. However, it is known that, optimal combinations of: operating conditions, equipment, working fluid, and cycle layout determine the maximum achievable efficiency of a cycle. Within an S-CO₂ cycle the compression device is of critical importance as it is operating near the critical point of CO₂. However, near the critical point, the thermo-physical properties of CO₂ are highly sensitive to changes of pressure and temperature. Therefore, the conditions of CO₂ at the compressor inlet are critical in the design of such cycles. Also, the impurity species diluted within the S-CO₂ will cause deviation from an ideal S-CO₂ cycle as these impurities will change the thermodynamic properties of the working fluid. Accordingly the current work examines the effects of different impurity compositions, considering binary mixtures of CO₂ and: He, CO, O₂, N₂, H₂, CH₄, or H₂S; on various S-CO₂ cycle components. The second part of the study focuses on the calculation of the basic cycles and component efficiencies. The results of this study will provide guidance and defines the optimal composition of mixtures for compressors and coolers.