Air Preheater

Air Preheater (external heat source type):   Air preheaters that utilize low temperature heat from an external source (e.g. low pressure steam) to improve heater or boiler efficiency.

Air Preheater (direct exchange type):   Air preheaters that exchange heat directly between flue gas and air.  These air preheaters often require an external heat source air preheater to increase the air inlet temperature to prevent cold end corrosion.

Air Preheater (indirect exchange type):   Air preheaters that use water or hot oil to cool the flue gas.  The heated water is used to heat up the air.  Cold end corrosion is prevented by keeping the water or hot oil is kept above the dewpoint temperature. 
 

Common terms used in Boilers and Heaters

         heat pipe:   A compact heat exchanger consisting of a pressure vessel and a bundle of heat pipes. The heat pipes extract heat from a hot fluid and transport it into a pressure vessel where steam is generated.

header box:   The internally insulated structural compartment, separated from the flue gas stream, which is used to enclose a number of headers or manifolds. Access is afforded by means of hinged doors or removable panels.

header or return bend:   The common term for a 180-degree cast or wrought fitting that connects two or more tubes.

hot face layer:   The refractory layer exposed to the highest temperatures in a multilayer or multicomponent lining.