The combustion air preheater is definitely one of heat exchanger applications. Based on Figure 1 below, flue gas simply leaves steam boiler and passes via air preheater. The combustion air is passed through this equipment too to increase its temperature before being combined with boiler fuel.
Because the temperature of combustion air is lower than the temperature of flue gas, combustion air receive heat transfer from flue gas through combustion air preheater in the process of convection heat transfer. The heat transfer make temperature of flue gas lower and consequently minimizes its heat loss and also decreases the air temperature to stack.
There are a number of considerations to factor when determining the best boiler for your steam generation needs like operating pressure, steam pounds/hour output, demand fluctuation, general application requirments and total cost of ownership, etc.
Two primary boiler types, the firetube boiler and the watertube boiler, are essentially opposite in design. The firetube boiler passes combustion gas inside a series of tubes surrounded by water in a vessel to produce steam, while a watertube instead sends water through a series of tubes surrounded by combustion gas used to transfer heat energy and produce steam.
