Novel parabolic trough power system integrating direct steam generation and molten salt systems: Preliminary thermodynamic study

A novel hybrid parabolic trough power system that integrates direct steam generation and molten salt systems is proposed in this study to stably and efficiently operate solar power plants. The feedwater from the power block is preheated and evaporated in a low temperature direct steam generation solar field. A high-temperature solar field using molten salt as heat transfer fluid is employed to superheat and reheat the steam to 540 degrees C. The heat transfer model based on energy conversion and balance is applied to numerically investigate the overall performance of various power plants. This paper presents a comparative study of the effects of different locations, steam turbines, and system configurations on the outputs of the power plants. The hybrid systems exhibit favorable system stability and reliability and an excellent overall performance. The molten salt loop percentages of hybrid systems with and without reheat section are only 45.1% and 37.4%, which lead to low energy loss in the operation period and low molten salt freezing protection energy. The annual thermal energy productions of the hybrid systems with and without the reheat section in Tonopah are 685.1 and 691.7 GWh, and the percentages of energy required for freezing protection of those systems are 3.2% and 2.7%, respectively. The hybrid systems with reheat section exhibit optimal electricity production and economic performances compared with those of other configurations. The electricity production increments of novel systems in Tonopah and Lhasa are 14.0% and 14.8%, respectively, compared with those of molten salt systems.