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

Abstract

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 efforts 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 flexible and allows to simulate recuperative or non-recuperative plants, with an arbitrary number of stages and working with different subcritical fluids. The results for multi-step configurations are compared with those obtained for a plant with one turbine and one compressor. Different working fluids are analyzed, including air, nitrogen, carbon dioxide, and helium. Several plant layouts and the corresponding optimal pressure ratios are analyzed. It is concluded that configurations with two-stages compression with intercooling combined with one or two expansion stages can significantly improve overall plant efficiency and lower fuel consumption. Power block efficiencies can reach 0.50 and overall plant efficiency can attain values about 0.40 working with air or CO 2. For instance, comparing with a single stage plant running with air, a plant with subcritical CO 2 , two compression stages with intercooling and single step expansion can reach an overall efficiency about 19% larger and a fuel conversion rate around 23% larger. For such configuration, the specific fuel consumption is predicted to be about 108 kg/(MW h) at design point conditions.

Thermodynamic and Cost Analysis of a Solar Dish Power Plant in Spain Hybridized with a Micro-Gas Turbine

“…All heat transfers and losses included in the model are schematically represented. Details on all definitions, calculations, and equations can be found in previous works [21,22]. The overall plant thermal efficiency, η, is defined as the ratio between the net power output and the total energy input per unit time:…”

“…Explicit calculations to obtain this equation can be found in [21,22]. In the case of a purely solar operation, f = 1 and η = η s η h ε HS , and for pure combustion, f = 0 and…”

“…The energy delivered from the receiver to the working fluid depends not only on the optical losses, but also on the undesired heat transfer from the receiver to the surroundings. The latter are calculated as in [22,25], including convective, conductive, and radiation losses. Thus, the whole efficiency of the solar subsystem, η s , is:…”

“…After an analysis of the optical subsystem and the regime conditions for the thermodynamic model based on previous developments [21,22], off-design simulations are performed for an annual evaluation in different locations. The purpose of this assessment is to analyze the subsystems' efficiencies, the global efficiency, the annual energy production, the average solar share, or the specific CO 2 emissions from combustion.…”

Exergy Cost Analysis of New Method for Efficiency Improvement in Small Gas Turbines Using LNG Cold Exergy

“…Genetic algorithm and TOPSIS method implemented to find the optimal operating point. Santos and et al [14] modeled Brayton hybrid thermo-solar plants and considered Multi-stage recuperative configurations and different working fluids. Results show the good improvement over a reference plant.…”