A steam air heater is a simple radiator. The steam air heater consists of rows of finned tubes housed in an insulated metal case. The heat load is calculated from the quantity and specific heat of the air. Figure 4-1 shows a steam air heater such as those used to heat a warehouse. This simple example demonstrates many of the characteristics of steam air heaters of all sizes and applications. steam air heater enters the heater at the top. As the moving air draws away the heat, the steam air heater condenses. The condensate flows down the tubes, through the steam trap, and into the condensate drain header. It is the one essential part of any steam air heater and will receive further attention later. Bypass control on a steam air heater is similar to bypass control on any other type of heat exchanger. The fan blows off air to the steam air heater where the heated air is then mixed with steam and blown into the top and bottom of the shredder. Also, a portion of the air heated with the steam air heateris blown into the entrance and exit and the dust collection line. The flow of steam air is automatically adjusted by opening and closing the control valve depending on the internal temperature of the shredder. When leaving the heater, the air is divided into three systems: primary air to the pulverizer, secondary air to the burners and cooling air to the test steam air heater. The steam air heater supply valve is fully open and the exhaust fan is running at low speed. During summer operation the unit heater is inoperative. Duct identifies a piece of equipment or component that has air passing through it, duct from the forced draft fan to steam coil air heater. An ID fan will draw the flue gas out of the boiler through the steam air heater and air pollution equipment and then exiting up through the stack. They move air temperatures ranging from ambient to 200 degrees Fahrenheit, depending on where the steam air heater is located. Most often, the FD fan is located before the steam coil air pre-heater and will not require any thermal insulation for personnel protection, but may require acoustical sound and noise protection. The fibrous lucerne material is dried in an air steam heated by geothermal hot water which is passed through finned tubular-type heat exchanger units. The internal filter of the steam air heater must be cleaned periodically due to ash and rust left by the flue gas that accumulates in the steam heater, reducing the heat exchange efficiency. The circulation flush pump for the steam air heater and gas-gas heater must have sufficient pumping capability to suction and pump slurry liquid. Furthermore, the pump material must be highly corrosion resistant since the liquid used to clean the gas-gas heater contains strong acids. The gas exiting the steam air heater is called the flue gas and is still hot (usually more than 120°C) to prevent the condensation of any acids in the flue gas and to provide buoyancy to the gas when it is discharged from the stack. Finish drying by means of heated air requires not only an steam air heater but also a vacuum pump of comparatively great capacity to process the rather great quantities of air needed for the desired quick finish drying.
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