The air preheater uses the hot feed water to preheat the combustion air and obtain a cool water flow in the return. This cold flow can now be used in an additional economiser bundle to further reduce the flue gas temperature. This increases efficiency by 2% points, or flue gas temperatures that are roughly 40K lower.
As the air preheating utilises the combustion air as internal heat sink, the increased efficiency is fully reflected in the reduction in annual fuel costs.
Info on Air preheater
The Bosch air preheating system consists of:
Bosch air preheating system
Flue gas heat exchanger stage 1
Heat exchanger, combustion air
Flue gas heat exchanger stage 2