ABSTRACT
The air heaters can be direct …red or indirect …red designs. A direct …red unit mixes the †ue gases from the burner directly into the stream to be heated. An indirect …red system heats air or, more typically, a recycled †ue gas, to provide the hot-side †ue gas for a gas-to-gas heat exchanger, in which the cold side is the gas (air, nitrogen, etc.) to be heated.
