Direct Steam Generation in parabolic troughs at 500°C - first results of the REAL-DISS project

Abstract

Parabolic trough solar thermal power plants have the highest maturity of all concentrated solar power systems. Current R&D activities are focusing on further cost reduction of these systems by reducing component costs or by increasing efficiency. One approach to increase efficiency of these systems is to increase the process temperature of the power block. So far the maximum operation temperature is limited to approx. 380°C by the thermal stability of the synthetic oil used in the collector field. Several alternative heat transfer fluids (HTF) are conceivable. At present the most promising candidates are molten salts, compressed gases or water-steam. In case of water-steam as the HTF, the process is called direct steam generation (DSG). The main challenges of the direct steam generation are: 1. the development of components such as receiver tubes or flexible tube connections applicable to process temperatures of up to 500°C and pressures of more than 120 bars, 2. the development of a cost effective storage system and 3. the process management of the direct steam generation in a distributed collector field with numerous parallel rows. To develop and demonstrate receiver tubes and flexible tube connections applicable to the mentioned process parameters under real conditions, a joint German-Spanish R&D project was initiated. This paper will present the test set-up and the first experimental results of the project. The development and investigation of the storage system is not subject of this paper. This issue will be presented in a different paper.