Flue gas condensing heat recovery
Condensing heat recovery from boiler flue gases is individualized to suit each instance:
- flue gases often have a high content of humidity, resulting in a large heat recovery potential in proportion to the boiler effect. The diagram illustrates the potential heat recovery from flue gases of a biomass burning boiler as a percentage of the boiler thermal output; in this example one can see the heat recovery under favourable circumstances is 50% of the boiler output.
- in district heating or related burning plants, provided there are low temperature incoming water flows, the heat recovered can be transferred and utilized in the production of heat.
- when there is also a requirement to clean boiler flue gases, heat is recovered with a wet scrubber, and flue gases are cleaned in the same unit.
The requirements for successful condensing heat recovery from boiler flue gases are a low temperature and sufficient thermal capacity of the heat receiving flow, like district heating return or steam boiler feed water flows. In some cases condensing heat recovery can be enhanced by humidifying the combustion air using the flue gas low temperature energy, which, at the low end of the cooling temperature range, would otherwise remain unexploited.