Boiler heat recovery
Recovering heat from flue gas and hot water around boilers.
Recovery and reuse · Heat to heat · No. 122
- Recovery and reuse
- Heat grade: Medium and low
Cool a boiler's flue gas by just 22 C and it gets one point more efficient, using heat already paid for.
Chart: Illustration: Boiler heat recovery
Where it comes from
Chart: Map of where it comes from
Boilers leak heat three ways: hot flue gas at 230 to 480 C, hot blowdown water and hot condensate. All can warm the cold feedwater arriving at 10 to 15 C right next door.
Three things to know
- Cooling flue gas from about 230 C to 41 C can lift a boiler from 80% to 95% efficiency, by condensing its water vapour.
- Below about 121 C, natural gas flue gas starts dripping acid, so condensing units need stainless steel.
- Returned condensate still holds more than 10% of the steam's energy, plus water already treated.
The journey
- 1 Boiler leaksHot flue gas, blowdown and condensate
- 2 EconomiserFlue gas warms incoming feedwater
- 3 CondenserRecovers latent heat from water vapour
- 4 Water loopCondensate and blowdown heat returned
- 5 Less fuelSame steam from a smaller flame