Analysis of Once-Through Boiler Concepts in Parabolic Troughs

Abstract

Solar thermal power plants use collectors to concentrate the sunlight and heat up a fluid to high temperatures. This heat can be used to run a steam turbine and generate electricity. Such plants work similar to conventional steam power plants, with the only difference in replacing the fossil steam Generator by a solar one. The steam can directly be generated within the solar field. This direct steam generation (DSG) process is analyzed in detail for parabolic trough collectors. As in conventional power plants, there exist two main concepts, one with forced circulation during the evaporation phase and one in a once-through configuration. This work covers the complete range of solar once-through steam generators for the first time. Design criteria are derived, transient models are validated and robust control strategies for large-scale commercial plants are developed. Those are validated by experiments at a Commercial scale test facility at Plataforma Solar de Almería in Spain. Furthermore, a methodology for component life time estimation is proposed for such plants and the overall economic potential of the once-through configuration is compared to the state-of-the-art recirculation type. It is demonstrated for the first time that solar once-through steam generators are technically feasible and economically very promising.