Power Plant Β· Flow
Feedwater Heater β Extraction Steam Flow
Extraction steam flow of a closed feedwater heater from an exact energy balance with IAPWS-IF97 enthalpies, including a cascaded drain from the next higher heater and a casing heat-loss factor β or the feedwater flow from a measured extraction flow.
Verified against published standard
Feedwater side
Shell side
Ignored if dryness x is entered.
Only for saturated/wet extraction steam.
100 β casing/radiation loss. Typical 99β100 %.
Cascaded drain from the higher-pressure heater (optional)
Enter the inputs and press Calculate.
About This Calculation
The extraction steam flow of a closed feedwater heater follows from an energy balance: heat released by the condensing and sub-cooling extraction steam (plus any cascaded drain) equals heat absorbed by the feedwater. Using exact IF97 enthalpies avoids the errors of a constant specific heat at 200 bar and 200 Β°C.
Frequently Asked Questions
Why use compressed-liquid enthalpy at feedwater pressure?
Liquid enthalpy at 200 bar differs by several kJ/kg from saturated-liquid values at the same temperature, which changes the duty by a visible fraction of a percent.
What if the drain is cascaded?
Enter the cascade flow and state from the higher-pressure heater; it supplies part of the duty and is subtracted from the required extraction.
Why does the drain temperature matter for the extraction flow?
The condensed steam leaves at the drain temperature, so the enthalpy it carries away sets how much energy is released to the feedwater. A drain cooler that sub-cools the condensate releases more energy per kilogram, so less extraction steam is needed for the same duty.
What heat-transfer effectiveness should I use?
Closed heaters are well insulated, and 99β100 % is typical. Use the lower end if the casing is known to lose heat. The value has only a small effect on the result compared with the feedwater flow and temperature measurements.