Damper control system for process heaters

Claim 1

APPARATUS FOR CONTROL OF A FUEL-BURNING HEATER COMPRISING DAMPER MEANS ADAPTED TO BE LOCATED IN THE COMBUSTION AIR SUPPLY FOR A HEATER, MEANS FOR ADJUSTABLY POSITIONING SAID DAMPER MEANS TO CONTROL THE HEATER COMBUSTION AIR SUPPLY, MEANS CONTROLLED BY SAID POSITIONING MEANS FOR PRODUCING A FIRST OUTPUT PROPORTIONAL TO THE OPENING PROVIDED BY SAID DAMPER MEANS, MEANS CONTROLLED BY THE FLOW OF FUEL INTO A HEATER FOR PRODUCING A SECOND OUTPUT PROPORTIONAL TO THE FUEL FLOW RATE, MEANS RESPONSIVE TO CHANGES IN SAID SECOND OUTPUT FOR OPERATING SAID DAMPER POSITIONING MEANS TO RETURN THE FUEL-AIR RATIO IN A HEATER APPROXIMATELY TO THAT EXISTING BEFORE SUCH A CHANGE, AN OXYGEN ANALYZER ADAPTED TO BE RECEPTIVE OF PRODUCTS OF COMBUSTION FROM A HEATER AND OPERATING TO PRODUCE A THIRD OUTPUT PROPORTIONAL TO THE OXYGEN CONTENT OF SAID COMBUSTION PRODUCTS, MEANS ESTABLISHING A SET POINT FOR OXYGEN CONTENT OF SAID COMBUSTION PRODUCTS, MEANS RESPONSIVE TO SAID THIRD OUTPUT AND TO SAID ESTABLISHING MEANS FOR EFFECTING A CONTROL OF SAID FIRST OUTPUT, THEREBY OPERATING SAID POSITIONING MEANS TO MAINTAIN THE OXYGEN CONTENT OF SAID COMBUSTION PRODUCTS NORMALLY APPROXIMATELY AT SAID SET POINT, TEMPERATURE-RESPONSIVE MEANS ADAPTED TO BE PLACED IN A HEATER, AND MEANS CONTROLLED BY SAID TEMPERATURE-RESPONSIVE MEANS FOR CAUSING OPERATION OF SAID POSITIONING MEANS TO INCREASE THE OPENING PROVIDED BY SAID DAMPER MEANS WHEN THE TEMPERATURE EXCEEDS A PREDETERMINED VALUE.