The fire monitor operates with a rotary air heater (1) that has a cylinder (2) rotating about a vertical axis and has axial (4) and circumferential (5) supports. A large- section duct (6) delivers flue gas vertically through one half of the cylinder, heating the cylinder. As the cylinder rotates the heated part moves beneath an air duct (10) and transfers heat to the air. There are two or more optical radiation pyrometers (12,13) mounted in the mouth of the air duct and positioned to monitor two wide regions across the air duct. USE/ADVANTAGE - Reliable detection of fires starting in the rotary drum of a flue gas heat recuperator.
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