Dual parallel turbines configuration of medium and large scale CSP steam power plants. Case study of a 30-MW medium scale CSP-ORC power plant

Abstract

This research focuses on investigating of a different and new design at the power block level for Concentrated solar power technology. Concentration solar power plants designs could profit from the maturity of power conversion cycle in particular Rankine and Organic Rankine cycles and previous developments on these cycles in terms or reliability and efficiency. It is however important to note that such cycles have generally been developed and built for fossil fuel power plants and/or biomass, waste heat and, in general, with heat sources of high stability and continuity. Solar irradiation presents the particularity of being highly variable during a single day and also throughout an entire year. The consequence of this is a lower average efficiency of the power cycle due to long time operation at partial load, and much more frequent turbine start-up and shut down particularly during unstable weather which may consume useful time, reduce production duration and affect systems durability. Hence, a solution could be the use of multiple small power units in parallel instead of a single larger one and profit from full or close to full load operation of a small power cycle avoiding the functioning at very low load or even below minimum operation load for larger cycles. The objective of the present work is then to identify the most efficient configurations of multiple power blocks for the case of a 1 MWe CSP-ORC plant and assess their impact on plant performance versus a single cycle configuration. This purpose of this project is to investigate the potential application of a new configuration featuring two turbines instead of one on the same power block for medium to large scale commercial power plants, aims at investigating possible improvements in the design of the plant which could be applied, if proven, to future projects in the CSP industry. For this purpose, a power plant of the order of 30-MW was developed using the software Ebsilon®professional in three different configurations: the first one has been designed in the conventional design with only one turbine rated 30 MW, the second design features two turbines in the same block respectively of 20-MW and 10-MW with a ratio of 2/3, and 1/3 of the total production of the plant. Finally, a configuration featuring two turbines of the same power rating as the second design with a 3-hours of indirect thermal energy storage using Molten Salts. The two different designs will be programmed though Ebsilon’s scripting Pascal language to have a specific control of the mass flow of the fluid that carries the heat, in order to be channeled and controlled in the most optimal way. This control comes after studying the changes and fluctuations of the weather, mainly the direct normal irradiance and the ambient temperature as they are the parameters that highly affect the harnessing of solar energy from CSP technology. A simulation of the weather data and the power production over hourly values of a full year in the green city of Benguerir is performed, in order to see the behavior of the three different designs over the different times of the year. The results of the simulation show a higher advantage of the design featuring two turbines with the thermal energy storage especially during days in the winter where the DNI values fluctuate during a single day as the smaller turbines are close to full load power production in the new design.