Roads to improve the performance of hybrid thermosolar gas turbine power plants: Working fluids and multi-stage configurations

Abstract

[EN]This paper presents a general thermodynamic model for hybrid Brayton central tower thermosolar plants. These plants have been proved to be technically feasible but R+D e orts need to be done in order to improve its commercial interest. From the thermodynamic viewpoint it is necessary to increase its performance to get larger power production with reduced fuel consumption, and so reduced emissions. We develop a model for multi-step compression and expansion stages with that aim. The model is exible and allows to simulate recuperative or non-recuperative plants, with an arbitrary number of stages and working with di erent subcritical uids. The results for multi-step con gurations are compared with those obtained for a plant with one turbine and one compressor. Di erent working uids are analyzed, including air, nitrogen, carbon dioxide, and helium. Several plant layouts and the corresponding optimal pressure ratios are analyzed. It is concluded that con gurations with two-stages compression with intercooling combined with one or two expansion stages can signi cantly improve overall plant ef- ciency and lower fuel consumption. Power block e ciencies can reach 0.50 and overall plant e ciency can attain values about 0.40 working with air or CO2. For instance, comparing with a single stage plant running with air, a plant with subcritical CO2, two compression stages with intercooling and single step expansion can reach an overall e ciency about 19% larger and a fuel conversion rate around 23% larger. For such con guration, the speci c fuel consumption is predicted to be about 108 kg/(MW h) at design point conditions.