Thermodynamic analysis on a novel bypass steam recovery system for parabolic trough concentrated solar power plants during start-up processes

Most concentrated solar power plants undergo daily start-up and shut-down processes, which consume much energy. If the start-up energy losses can be recovered, the power plant efficiency may be enhanced. The energy loss of bypass steam is one of the major start-up energy losses, but the method to recover bypass steam is absent. Therefore, we proposed a novel system to recover bypass steam by integrating a steam accumulator, and the recovered bypass steam was used to replace the extraction steam of regenerative heaters. The dynamic models of the bypass steam recovery system were developed, and the design parameters and discharging strategy of the steam accumulator were optimized. Results show that simultaneously increasing the initial pressure and volume of the steam accumulator can increase recovered exergy, and switching the regenerative heater received steam during the steam accumulator discharging process can improve electricity production. The optimal initial pressure and volume of the steam accumulator are 2.6 MPa and 246.4 m3, respectively, by balancing the tradeoff between the annual electricity production and the steam accumulator volume. Integrating the steam accumulator with optimal design parameters can improve the annual electricity production by 1.1 GWh (0.55%) for a 50 MW parabolic trough concentrated solar power.