TRANSIENT ANALYSIS OF TWO-PHASE FLOWS IN A CSP PLANT WITH DIRECT STEAM GENERATION

Resumo

Parabolic trough solar concentrators for electric power generation plants are currently being designed all over the world. Concentrating solar power plants generally use synthetic oil as the collector working fluid. The vapor generation is carried out by a heat exchanger. The vapor can be directly generated inside the concentrator by substituting oil with water to avoid the need for a huge quantity of oil. Nevertheless, controlling the convective boiling of the water inside the concentrator represents a considerable challenge due to the strong increase in the heat transfer coefficient and the instability of the flow during steam production. In this study, a theoretical transient model to simulate direct steam generation in a solar concentrator is presented. This model computes the quantity and quality of steam produced, its energy (pressure, temperature), the thermal loss and the efficiency of the collector. A parametrical study is described herein and the results show that optimal operation conditions can be found and used as a strategy for the sizing of real installations. Depending of the length of the collector and the solar irradiation, an ideal mass flow is found that minimizes the heat loss and optimizes the evaporation of the fluid. Also, in this case, cloud shading simulation is done to see the transient comportment of the vapor quality.