Dynamic performance and control strategy comparison of a solar-aided coal-fired power plant based on energy and exergy analyses

Abstract

Solar-aided coal-fired power generation is a hybrid technique to generate power with the coal and solar energy. The performance of solar-aided coal-fired power plant (SACFPP) with solar irradiance fluctuations received little attention in previous studies. Dynamic and exergy analysis models of SACFPP are developed to evaluate the SACFPP performance in transient processes caused by solar irradiance disturbances and the consequent system regulation. An SACFPP integrating the trough collector system (TCS) in parallel with HP2 and HP3 heaters of a 660 MW coal-fired power plant is simulated. Influences of solar irradiance and feedwater ratio to TCS disturbances on SACFPP performance are analyzed, including step cases and typical solar days. The solar-to-power exergy efficiency fluctuates sharply in the dynamic process. It increases from 32.62% to 57.25% and decreases to 28.1% when solar irradiance step decreases from 700 to 400 W m−2. Accumulations of additional power and exergy destruction are the highest in Autumn Equinox. Then, control strategies of feedwater flow to TCS are proposed and compared to obtain maximal solar-to-power exergy efficiency during transients. Results indicate that the feedwater flow to TCS should follow the solar irradiance decrease with a dynamic period of less than 200 s; otherwise, extra exergy destruction occurs.