A system for controlling the injection of an inert gas into the air supplied a burner to inhibit the formation of no{11

Claim 2

In a combustion control system for a vapor generator having a furnace to which fuel and air supplied through a burner and wherein flue gas discharged from the vapor generator is injected into the air supplied the burner to depress the flame temperature and the formation of NOx, in combination, means establishing a first control signal corresponding to the rate of flow of flue gas into the air supply and means under the control of said first control signal maintaining a constant rate of flow of flue gas into the air supply.

Claim 3

A control system in accordance with claim 1 including means measuring the rate of air flow to the burner, means responsive to said last named means establishing a second control signal corresponding to the rate of air flow to the burner and means establishing the constant rate of flow maintained by said first control signal responsive to said second control signal whereby the rate of flow of flue gas injected into the air supply is maintained in functional relationship with the rate of air flow to the burner.

Claim 4

A control system in accordance with claim 2 wherein the vapor generator is provided with a first duct and fan means in said duct for recirculating flue gas discharged from the vapor generator into the furnace to alter the heat absorption pattern within the vapor generator, a second duct connected to said first duct on the discharge side of said fan for injecting flue gas into the air supply, and wherein the means under the control of said first signal is a first damper-drive unit located in said second duct.

Claim 5

A control system in accordance with claim 3 wherein the vapor generator is provided with a third duct and a fan connected to said duct for supplying air to the burners and wherein the means for measuring rate of air flow comprises an air foil located in said duct and means for measuring the differential pressure produced by the air foil.

Claim 6

A control system in accordance with claim 4 wherein the air foil extends from side to side of the air duct, the flue gas is injected into the air supply from the interior of the air foil through a plurality of ports located in the recovery section of the air foil and said means for measuring the rate of flue gas injection into the air supply comprises means for measuring the differential across said ports.

Claim 7

A control system according to claim 5 wherein the vapor generator is provided with a reheater and a second damper-drive unit is located in said first duct ahead of said fan means, means measuring the temperature of the vapor leaving the reheater, and means responsive to said measuring means generating a third control signal corresponding to the temperature of the vapor controlling the positioning of said second damper-drive unit as required to maintain the reheated vapor at a predetermined temperature.

Claim 8

A control system according to claim 6 further comprising means measuring the rate of flow of recirculated gas, means responsive to said last named means generating a feed back signal corresponding to the rate of flow of recirculated gas, a difference unit responsive to said third control signal and said feed back signal producing an error signal proportional to the difference between said third signal and said feed back signal, and a proportional plus integral unit responsive to said error signal generating a fourth control signal controlling the positioning of said second damper-drive unit.

Claim 9

A control system according to claim 7 further comprising a high signal selector responsive to said first and third control signals transferring the control of said second damper-drive unit from said third to said first control signal whenever said first control signal is greater than said third control signal. 9. A control system according to claim 3 further including a third damper-drive unit in said first duct between said furnace and the connection to said second duct, and wherein said first control signal first operates said first damper-drive unit to an open position as the requirement for flue gas injection into the air supply increases and thereafter operates said third damper-drive unit to a closed position upon further increases in the requirement for flue gas injection.

Claim 10

A control system according to claim 8 further including supplemental means for regulating reheat temperature responsive to said third control signal when said first control signal is greater than said third control signal.