A Direct Fired Air Heater effectively heats air, as needed in a variety of heating processes. This equipment is most commonly employed in Fluidized Catalytic Cracker (FCC) units in petroleum refineries. The direct-fired air heater is primarily intended to be used during start-up operations and short feed outages to heat the catalyst bed in the regenerator section of the FCC unit (catalyst regeneration). During normal operation, the air heater is not fired and air flows directly to the regenerator through the air heater without being heated. The mass flow rate and operating pressure during the un-fired condition may vary from that used during the fired case.