Steam Coil Air Pre Heaters

Steam Coil Air Pre Heater (SCAPH) is an extended surface type heat exchanger. This equipment is used to heat atmospheric air to the required process temperature by means of saturated steam. Steam flows inside the tube while air passes over the finned tubes .It is generally used for heating process air in Sugar Mills, Starch Mills, Chemical & allied Industries. SCAPH find extensive use with all types of High Capacity Boilers, Recovery Boilers, Dryers etc.

Steam coil air preheaters ( SCAPHS ) are used to heat air entering the air heater recuperative or regenerative type, in order to raise the average cold end temperature to prevent acid dew point corrosion. This type of equipment is normally incorporated into the design of a boiler unit for low load operation and startup operation particularly in those areas with low ambient air temperatures. They are desirable in that the main air heaters, recuperative or regenerative, have corrosion sections that are more readily maintained This type of air heater uses extended surface, normally referred to as fins, to reduce the overall size of this air preheater. It is generally located in the duct between the FD fan and the main air heater. iin those areas that have extremely low ambient air temperatures, it is  common to have this ahead of the FD fan that could preheat cold winter air up to about 40 degrees F.
Below sketch provide idea on the location of SCAPH in the process cycle of Boiler.