An air preheater is a general term to describe any device designed to heat air before it is used in another process, for example, combustion in a boiler. The primary objective of air preheating is to increase the overall thermal efficiency of the process. In this example, the purpose of the air preheater is to recover the heat from the boiler flue gas. This increases the thermal efficiency of the boiler by reducing the useful heat which is lost in the flue gas that is stack-vented to atmosphere. Air preheaters may also be used as process gas heat exchangers which recover waste heat from one gas stream and use it to heat or preheat another. Air preheaters and gas to gas heat exchangers function similarly.
There are many types and designs of air preheaters, however, MECS offers either non-welded or fully welded construction and specializes in dimpled heat transfer plate design. MECS air preheaters are constructed of stacked, parallel plates that provide a smooth, continuous path for the least pressure drop or flow resistance. The combination of raised and depressed conical dimples provides uniform plate pitch and an improved heat transfer coefficient. In the MECS design, the flow path for the heated gas is commonly Z-shaped and countercurrent to the cold gas resulting in longer residence time and maximum heat transfer - MECS-ThermoZ Welded and OCAP Non-Welded Plate Air Preheaters, Monplex II Gas to Gas Heat Exchangers.