Dynamic exergy analysis of feed water heater in nuclear power plant during start-up process

In order to study the thermal economy of the feed water heater (FWH) start-up process (SUP), a dynamic mechanism model has been established, and the dynamic exergy analysis was conducted using this model. The effects of step and continuous changes in extraction steam flow on the exergy characteristics of the SUP were investigated. For the step change study, the step amplitude of extraction steam flow increased from 12.5 % to 100 % and the effects on the exergy characteristics were analyzed. To study the effects of the continuous change in extraction steam flow, the exergy was characterized and analyzed with three types changes: the quick opening, the linear and the equal percentage. The dynamic characteristics of the exergy parameters during the SUP of the FWH were then clearly defined. The highest steady-state exergy efficiency (95.72 %) was achieved for the FWH when the step amplitude was at 50 %. The more optimal start-up method should have the equal percentage extraction steam flow change characteristics with the highest process average exergy efficiency (94.07 %) and the lowest accumulated exergy destruction (21.339 GJ). This study could provide important guiding significance for the SUP of the FWH.