Boiler Air Heaters are fitted for main reasons below:
- To increase efficiency by recovery of heat from flue gases ( except where bled steam heaters are in use, these increase overall plant efficiency but by a different method)
- Accelerate rate of combustion
- Avoid effect of cold air impinging on boiler surface
Air heaters also form a convenient way to warm up a standby boiler before initial firing. However, the effects of dew point corrosion and fouling in smoke tube air heaters should be taken into account when designing the heat absorption limit. The amount of heat to be removed from the flue gas should have a limit. For water tube boilers gas air heaters are only considered where the temperature at the inlet to economizer is greater than 200oC. Due to greater heat transfer efficiency between gas/water economizers are preferred to gas/air exchangers. At low loads, gas/air heaters should be bypassed to keep uptake temperatures as high as possible
