Flexibility assessment of a modified double-reheat Rankine cycle integrating a regenerative turbine during recuperative heater shutdown processes

Highlights: • The dynamic model of a Rankine cycle with a regenerative turbine is developed. • The flexibility of the Rankine cycle declines with a regenerative turbine. • The power output performance could be improved with control strategies. • The deaerator pressure could be limited to the normal value with control strategies. Integrating a regenerative turbine (RT) is a significant modification to improve the Rankine cycle efficiency by reducing the superheat degree of extraction steam. This work evaluates the short-term operational flexibility of the modified cycle, emphasizing the evaluation of recuperative heater shutdown as a method to rapidly increase the power generation. A number of scenarios were modeled that included a shutdown of recuperative heaters, and the power change was observed. Results indicate that the utilization of an RT decreases the operational flexibility of the power plant with the high-pressure recuperative heater (HPH) shutdown. It shows that the adjusting time of total power generation increases by 492.9–550.6 s and the maximal output power increment reduces by 6.0–28.1 MW compared to that of the conventional Rankine cycle (CRC). Control strategies are proposed and evaluated to improve response performance and limit the deaerator (DTR) pressure. The results reveal that the adjusting time of the total power and maximum negative overshoot value could be reduced by 342.8 s and 7.79 MW, respectively, with a normal DTR pressure under the condition of No.3 and No.4 HPH shutdowns.