Analysis of direct steam generation in parabolic trough solar collectors under hot climate

Abstract

• We present in the following, all the main contributions of this article. • Modeling and simulation of parabolic trough collectors for direct steam generation. • Numerical investigation of the direct steam generation thermohydraulic behavior. • A parametric analysis using various operating conditions is performed. • The optimal working conditions are proposed for the adopted installation. • Direct steam generation feasibility under climatic condition of Ouarzazate region. Direct steam generation in parabolic trough solar collectors is a promising technology for improving the performance of solar power plants. However, it remains a challenge because it induces liquid-vapor flows in the solar field. This process requires adequate control to avoid the deterioration risk of the receiver tube walls. In the present paper, a detailed numerical model of the system has been presented and validated. The proposed model is based on the conservation laws of the liquid-vapor mixture coupled with the energy balances of the receiver tube and the cover. An accurate parametric analysis is carried out to predict the appropriate operating conditions of the adopted installation. Indeed, the effects of the inlet conditions (mass flow, pressure, and fluid temperature) on the thermohydraulic behavior are investigated. From the obtained results, it emerges that for a good operation of the system, it is suitable to choose a mass flow rate higher than 0.4 kg/s to avoid the stratification phenomenon. Moderate pressure is appropriate to have a compromise between pressure drops and stratification of the mixture flow. The numerical simulation of the system operating under the meteorological conditions of the Ouarzazate region (Morocco) shows that regulation of the inlet flow rate according to the solar flux (0.5-0.75 kg/s for December 17 and 0.5-1.2 kg/s during June 20) and the combination of once-through and recirculation operating mode can ensure a steam production with sufficiently high qualities and durations.