Direct Steam Generation in Parabolic Trough Collectors

AbstractExisting commercial parabolic trough power plants use thermal oil as a heat transfer fluid, with working temperatures in the region of 400°C. In order to achieve more efficient generating systems, a second generation of parabolic troughs that operate at temperatures higher than 400°C is being developed.One possibility, Abengoa Solar is assessing, it is the use of direct steam generation (DSG) inside parabolic troughs in order to achieve higher temperatures; the first stage heating up to 450°C and the second stage heating up to 550°C. There is, however, a certain degree of complexity in the use of DSG technology that has resulted in it not yet being utilized in commercial plant designs. Due to the presence of saturated steam inside the parallel loops the required control system is more complex, particularly during transitory periods of radiation. Also the higher operating pressures and temperatures in the solar field mean that the receiver tubes and interconnections between collectors are very critical components. For this reason, typical systems utilize an intermediate fluid for energy transfer.In order to overcome these challenges, Abengoa Solar has built a demonstration plant of 8 MWht. The plant is composed of an evaporator field with three parallel loops and a superheater field with two loops in order to work at 85bar and 450°C. The demonstration plant has been operated and evaluated for one year.During this test period, the following have been evaluated and validated:•An innovative control strategy system that guarantees the stability of the plant even under transient conditions.•Receiver tube design able to achieve 450°C, analyzing the mechanical behavior, optical performance, and heat losses.•Different configurations of interconnections between collectors with ball joints and flexible rotation joints.A theoretical model has been developed for commercial scale DSG plants and validated with experimental data obtained from the demonstration plant