Effect of Gaseous Admixtures on Cycles With Supercritical Carbon Dioxide

Supercritical carbon dioxide cycles are recently very perspective and they are researched all around the world. CO₂ is an interesting medium for applications in many technologies, from nuclear energy through geothermal, solar and waste heat recovery systems. However, S-CO₂ cycles have several issues which have to be researched, one of them being the presence of the so called pinch point in the heat exchangers design. Therefore, the Czech Technical University (CTU) conducts research on supercritical carbon dioxide cycles, which are focused on the effect of the gaseous admixtures in S-CO₂ on different cycle components. The research is primarily focused on the pinch point shift within heat exchangers caused by gaseous admixtures. Previous work has shown that the pinch point can be removed with the addition of small amounts of another gases. However, it is also important to describe the effect on the performance of the cycles. This is the main topic of this paper. One of the reasons for this research is the positive effects on components are possible. The first part of the study is focused on the development of computational code for calculation of the basic S-CO₂ cycles with mixtures. The second part of the study is focused on the calculation of basic cycles for binary mixtures. The calculation will be performed for pure CO₂ and some binary mixture. He, CO, O₂, N₂, Ar will be used for the calculation as the most common admixtures, furthermore H₂, CH₄ and H₂S will be used as well. The last part of the study will be focused on the optimization of individual cycles for different amount of admixtures in CO₂. The result of this study will define the optimum ratio of admixtures and description of their effect on cycle efficiency.