Means and method for controlling excess air inflow

Claim 2

A control system for operating apparatus including a combustion zone and an exhaust flue and operable to derive variable amounts of heat energy from an off-gas fuel having a first heating value and an auxiliary fuel having a second heating value substantially greater than said first heating value, comprising: sensor means disposed in flow relation with the exhaust flue for identifying the percentage of molecular oxygen in the system exhaust gases and outputting a flue oxygen signal; first flow rate sensing means disposed in flow relationship with the fuels flowing to the combustion zone for developing signals representing the flow rate of said fuels; second flow rate sensing means disposed in flow relationship with air flowing to the combustion zone for developing signals representing the flow rate of the air; analyzing means in flow relationship with said off-gas fuel for outputting signals representing the relative percentages of the constituents of the fuels including the inert constituents of said off-gas fuel; supervisory control means coupled to said flow rate sensing means and to said analyzing means and responsive to signals representing said flow rates and fuel constituents for outputting a target signal representing the proportion of molecular oxygen in the system exhaust gases which corresponds to the presence of a predetermined proportion of excess air in the combustion zone; controller means responsive to said sensor means and said supervisory control means for developing a setpoint signal; and a ratio station for controllably varying the relative amounts of fuel and air flowing to the combustion zone in response to the setpoint signal.

Claim 3

A control system according to claim 1, wherein said supervisory control means includes means for deriving the total flow of inert materials into the combustion zone including the inert portion of atmospheric air.

Claim 4

A control system for operating apparatus including a combustion zone and an exhaust flue and operable to derive variable amounts of heat energy from an off-gas fuel having a first heating value and an auxiliary fuel having a second heating value substantially greater than said first heating value, comprising: an oxygen sensor disposed in flow relation to the exhaust flue for identifying the percentage of molecular oxygen in the system exhaust gases and outputting a flue oxygen signal; first flow rate sensing means disposed in flow relationship with fuels flowing to the combustion zone for developing signals representing the flow rates of said off-gas and auxiliary fuels; second flow rate sensing means disposed in flow relationship with air flowing to the combustion zone for developing signals representing the flow rate of the air; a supervisory control coupled to said flow rate sensing means for receiving signals representing said flow rates and developing a signal representing the molar flow rate of the oxygen required for complete combustion of said fuels, the total products of combustion, and the inert materials flowing from the combustion zone; a target stage coupled to said supervisory control for receiving said last-named signals and responsive thereto for outputting a target signal representing the proportion of molecular oxygen in the system exhaust gases which corresponds to the presence of a predetermined proportion of excess air in the combustion zone; controller means coupled to said oxygen sensor for outputting a setpoint signal reflecting the values of said flue oxygen signal and said target signal; and a ratio station responsive to said setpoint signal for controllably varying the relative amounts of fuel and air flowing to the combustion zone.

Claim 5

A control system for operating apparatus including a combustion zone and an exhaust flue and operable to derive variable amounts of heat energy from an off-gas fuel having a first heating value and an auxiliary fuel having a second heating value substantially greater than said first heating value, comprising: an oxygen sensor disposed in flow relation to the exhaust flue for identifying the percentage of molecular oxygen in the system exhaust gases and outputting a flue oxygen signal; first flow rate sensing means disposed in flow relationship with fuels flowing to the combustion zone for developing signals representing the flow rates of said off-gas and auxiliary fuels; second flow rate sensing means disposed in flow relationship with air flowing to the combustion zone for developing signals representing the flow rate of the air; a supervisory control coupled to said flow rate sensing means for receiving signals representing said flow rates and developing a signal representing the molar flow rate of the oxygen required for complete combustion of said fuels, the total products of combustion, and the inert materials flowing from the combustion zone; a target stage coupled to said supervisory control for receiving said last-named signals and responsive thereto for outputting a target signal representing the proportion of molecular oxygen in the system exhaust gases which corresponds to the presence of a predetermined proportion of excess air in the combustion zone; controller means coupled to said oxygen sensor for outputting a setpoint signal reflecting the values of said flue oxygen signal and said target signal; and a ratio station responsive to said setpoint signal for controllably varying the relative amounts of fuel and air flowing to the combustion zone.

Claim 6

A control system according to claim 3, further including means coupling said target stage to said ratio station for transmitting said setpoint signal to said ratio station.

Claim 7

A control system according to claim 4, wherein said flow rate sensing means develops signals representing the mass flow rates of said fuels.

Claim 8

A control system according to claim 5, wherein said flow rate sensing means develops signals representing the mass flow rates of at least some constituents of said fuels.

Claim 9

A control system according to claim 6, wherein said means coupling said target stage to said ratio station is the controller means, said controller means being operative to compare a signal from said oxygen sensor means with said target signal to obtain a setpoint signal.

Claim 10

A control system according to claim 7, wherein said ratio station is responsive to said setpoint signal to change the ratio of air to fuel in said combustion zone in a manner which lessens said setpoint signal.

Claim 11

A control system for operating apparatus including a combustion zone and an exhaust flue and operable to derive variable amounts of heat energy from an off-gas fuel having a first heating value and at least one auxiliary fuel having a second heating value substantially greater than said first heating value, comprising: sensor means disposed in flow relation to the exhaust flue for identifying the percentage of molecular oxygen in the system exhaust gases; a ratio station for controllably varying the relative amounts of fuel and air flowing to the combustion zone in response to a setpoint signal; first flow rate sensing means disposed in flow relationship with fuels flowing to the combustion zone for developing signals representing the flow rates of said fuels; second flow rate means disposed in flow relationship with air flowing to the combustion zone for developing signals representing the flow rate of the air; supervisory control means coupled to said flow rate sensing means for receiving signals representing said flow rates and developing a signal representing the molar flow rates of the oxygen required for complete combustion of said fuels, the total products of combustion, and the inert materials flowing from the combustion zone; a target stage coupled to said supervisory control means for receiving said last-named signals and responsive thereto for outputting a target signal representing the proportion of molecular oxygen in the system exhaust gases which corresponds to the presence of a predetermined proportion of excess air in the combustion zone; and means responsive to said target stage and to said sensor means for applying a setpoint signal to said ratio station for determining the fuel/air ratio to be maintained thereby.

Claim 12

A control system for operating apparatus including a combustion zone and an exhaust flue and operable to derive variable amounts of heat energy from an off-gas fuel having a first heating value and at least one auxiliary fuel having a second heating value substantially greater than said first heating value, comprising: sensor means disposed in flow relation to the exhaust flue for identifying the percentage of molecular oxygen in the system exhaust gases; a ratio station for controllably varying the relative amounts of fuel and air flowing to the combustion zone in response to a setpoint signal; first flow rate sensing means disposed in flow relationship with fuels flowing to the combustion zone for developing signals representing the flow rates of said fuels; second flow rate means disposed in flow relationship with air flowing to the combustion zone for developing signals representing the flow rate of the air; supervisory control means coupled to said flow rate sensing means for receiving signals representing said flow rates and developing a signal representing the molar flow rates of the oxygen required for complete combustion of said fuels, the total products of combustion, and the inert materials flowing from the combustion zone; a target stage coupled to said supervisory control means for receiving said last-named signals and responsive thereto for outputting a target signal representing the proportion of molecular oxygen in the system exhaust gases which corresponds to the presence of a predetermined proportion of excess air in the combustion zone; and means responsive to said target stage and to said sensor means for applying a setpoint signal to said ratio station for determining the fuel/air ratio to be maintained thereby.

Claim 13

A machine process of operating an off-gas combustion system fueled by an off-gas product fuel having a first heating value and at least one auxiliary fuel having a second heating value to maintain a fixed value of excess air input, comprising the steps of: measuring the flow rate for each fuel and producing signals representative thereof; measuring the rate of flow of combustion air; multiplying said signals by selected values to derive a first representation of the total theoretical oxygen required for complete combustion of each fuel; manipulating said signals to derive a second representation of the total combustion products of the fuels; manipulating said signals to derive a third representation of the inert components of at least the off-gas product fuel; associating said representations with a signal which reflects a predetermined percentage of excess air to obtain a setpoint signal representing the proportion of molecular oxygen which occurs in the system exhaust gases when the fuels are burned in the presence of said percentage of excess air; and adjusting the air inflow to the combustion system to achieve said proportion of excess oxygen in the system exhaust gases.

Claim 14

A machine process of operating an off-gas combustion system fueled by an off-gas product fuel having a first heating value and at least one auxiliary fuel having a second heating value to maintain a fixed value of excess air input, comprising the steps of: measuring the flow rate for each fuel and producing signals representative thereof; measuring the rate of flow of combustion air; multiplying said signals by selected values to derive a first representation of the total theoretical oxygen required for complete combustion of each fuel; manipulating said signals to derive a second representation of the total combustion products of the fuels; manipulating said signals to derive a third representation of the inert components of at least the off-gas product fuel; associating said representations with a signal which reflects a predetermined percentage of excess air to obtain a setpoint signal representing the proportion of molecular oxygen which occurs in the system exhaust gases when the fuels are burned in the presence of said percentage of excess air; and adjusting the air inflow to the combustion system to achieve said proportion of excess oxygen in the system exhaust gases.

Claim 15

A machine-implemented method for operating an off-gas combustion system fueled by an off-gas fuel having a first heating value and at least one auxiliary fuel having a second heating value substantially higher than said first heating value, and comprising the steps of: measuring the mass flow rate of each fuel; measuring the rate of flow of combustion air; determining the mass-mol rate of flow of the combustible constituents of each fuel; determining the proportion of oxygen required for complete combustion of each fuel; determining the mass-mol rates of flow for both the inert constituents of at least said off-gas and the oxygen required for combustion; deriving the proportion of oxygen in the resulting combustion products; selecting a desired value of excess air to be introduced into the combustion system; determining the proportion of molecular oxygen which will arise in the exhaust from the combustion system for the selected value of excess air; sensing the proportion of molecular oxygen actually occurring in the exhaust from the combustion system; and adjusting the flow of air to the combustion system to cause the sensed proportion of molecular oxygen to correspond to the proportion which will arise for the selected value of excess air.

Claim 16

A machine-implemented method for operating an off-gas combustion system fueled by an off-gas fuel having a first heating value and at least one auxiliary fuel having a second heating value substantially higher than said first heating value, and comprising the steps of: measuring the mass flow rate of each fuel; measuring the rate of flow of combustion air; determining the mass-mol rate of flow of the combustible constituents of each fuel; determining the proportion of oxygen required for complete combustion of each fuel; determining the mass-mol rates of flow for both the inert constituents of at least said off-gas and the oxygen required for combustion; deriving the proportion of oxygen in the resulting combustion products; selecting a desired value of excess air to be introduced into the combustion system; determining the proportion of molecular oxygen which will arise in the exhaust from the combustion system for the selected value of excess air; sensing the proportion of molecular oxygen actually occurring in the exhaust from the combustion system; and adjusting the flow of air to the combustion system to cause the sensed proportion of molecular oxygen to correspond to the proportion which will arise for the selected value of excess air.