Analytical Modeling of DSG in Parabolic Trough Solar Collectors
Abstract
Currently concentrated solar plants with parabolic trough collectors use a thermal fluid to transfer the energy delivered by the solar field to a Rankine cycle turbine via a heat exchanger. The thermal fluid used has a temperature limit, usually around 400 oC, which establishes the maximum cycle efficiency. Direct steam generation (DSG) in the absorber pipes of parabolic trough collectors is a promising alternative to the use of thermal oil since it enables higher cycle temperatures and efficiencies, reducing the cost of the system. This paper presents an analytical model of DSG process in parabolic trough collectors. A collector row was divided in three sections and for each section a system of differential equations was obtained. The model was implemented and simulations were performed using a configuration and parameters similar to works published in the technical literature. Results have shown good agreement with them and allow obtaining many important parameters of the DSG process along the collector row: external and internal absorber temperature, fluid flow and temperature, vapor title and useful energy. A linear relationship between useful energy and collected irradiance has been obtained. Using the utilizability method, this result enables to make long term predictions about the system’s performance.