Modelling and Control of a Solar-Thermal Parabolic Trough DSG Superheater With Several Parallel Rows and Central Steam Separation

In this paper, a solar-thermal parabolic trough power plant with direct steam generation (DSG) is investigated with respect to the controllability of the superheating section in a commercial-scale facility with several parallel collector rows. The plant is operated in recirculation mode which has been proven to provide a good live steam quality under changing operating conditions in single-row systems. In a multiple-row collector field, the separation of the remaining water at the end of the evaporator can be achieved by using one central or several distributed separators. Central separation, which will be investigated in this work, appears to be the superior concept. The article proposes a decentralized adaptive proportional-integral (PI) control approach together with a static output mapping for the control valves at the end of the superheating section. The section is fed by a single saturated steam mass flow which has to be distributed on the parallel superheater rows. Together with the individually controlled injection coolers in each row, the distribution control enables the solar field to provide the power block with a reliable steam temperature in the presence of significant local irradiance and input mass flow transients induced by varying solar intensity during the day and passing clouds.