Flexibility enhancement versus thermal efficiency of coal-fired power units during the condensate throttling processes

The improvement in operational flexibility of thermal power plants plays an essential role in the stable and safe operation of large-scale power grids. Condensate throttling is an effective method for enhancing the operational flexibility of thermal power plants, but it inevitably influences their thermal efficiency. In fact, the entire condensate throttling process consists of two stages: the condensate throttling process and the recovery process of the deaerator water level. To evaluate exergy efficiency during the entire condensate throttling process, dynamic models of a condensate throttling system were developed and exergy analysis was performed. Results indicate that additional exergy losses occur during the condensate throttling process. The cold end system is the component that exhibits the highest additional exergy loss (64.89%), followed by the deaerator (40.49%), heaters (4.82%), and turbines (−10.20%). Operational flexibility is in contrast with thermal efficiency during the condensate throttling process. The cycling and total exergy losses of the system increase with an increase in the condensate throttled ratio. Cycling loss can be decreased by a maximum of 51.46% by selecting an appropriate condensate water adjustment strategy during the entire condensate throttling process.