Abstract: A method supplies reactants, including fuel gas, to burners that discharge the reactants into a furnace process chamber. In a stable flame mode of operation, stable flames are projected from the burners into the furnace process chamber. At a time when the furnace process chamber has a temperature at or above an autoignition temperature of the fuel gas, a diffuse combustion mode is initiated by supplying a selected burner with additional reactants, including reactants diverted from another burner, to blow off the stable flame at the selected burner.

Abstract: A low NOx combustion method includes steps of injecting reactants into a combustion chamber. A primary reactant stream, including fuel and combustion air premix, is injected from a premix burner port into the combustion chamber. A staged fuel stream is injected into the combustion chamber from a staged fuel injector port adjacent to the premix burner port. A stream of recirculated flue gas is injected into the combustion chamber from a flue gas injector port that is adjacent to the premix burner port and adjacent to the staged fuel injector port. In this manner, the stream of recirculated flue gas is injected into the combustion chamber unmixed with the primary reactant stream and unmixed with the staged fuel stream.

Abstract: A method supplies reactants, including fuel gas, to burners that discharge the reactants into a furnace process chamber. In a stable flame mode of operation, stable flames are projected from the burners into the furnace process chamber. At a time when the furnace process chamber has a temperature at or above an autoignition temperature of the fuel gas, a diffuse combustion mode is initiated by supplying a selected burner with additional reactants, including reactants diverted from another burner, to blow off the stable flame at the selected burner.

Abstract: A grate-kiln pelletizing furnace includes a grate that conveys pelletized material to a rotary kiln, a cooler that cools pelletized material from the rotary kiln, and a gas flow apparatus that directs a stream of gas from the cooler to the rotary kiln to provide preheated process air for pelletized material in the rotary kiln. The gas flow apparatus also directs a stream of gas from the grate to the rotary kiln to vitiate the preheated process air.

Abstract: A primary reactant stream is injected from a burner port into a combustion chamber along an axis. Staged reactant streams are injected into the combustion chamber adjacent to the primary reactant stream in differing configurations. The differences between the configurations of the staged reactant streams include differences in radial distance from the burner port, axial distance from the burner port, and direction relative to the axis. The reactant streams are shifted between differing modes, with differences between the modes including the presence or absence of a flame at the burner port, differences in fuel flow rates, and differences in combustion air flow rates. A heat release profile developed by combustion of the primary reactant stream, or the length of a flame developed by combustion of the primary reactant stream, can be controlled by shifting between the differing modes with reference to the heat release profile or the length of the flame.

Abstract: A low NOx combustion method includes steps of injecting reactants into a combustion chamber. A primary reactant stream, including fuel and combustion air premix, is injected from a premix burner port into the combustion chamber. A staged fuel stream is injected into the combustion chamber from a staged fuel injector port adjacent to the premix burner port. A stream of recirculated flue gas is injected into the combustion chamber from a flue gas injector port that is adjacent to the premix burner port and adjacent to the staged fuel injector port. In this manner, the stream of recirculated flue gas is injected into the combustion chamber unmixed with the primary reactant stream and unmixed with the staged fuel stream.

Abstract: A NOx suppression apparatus is configured for use with a burner that injects fuel into a stream of process air flowing into and through a rotary kiln. The apparatus comprises a premix injection system that forms a premix of fuel gas and air, and injects the premix into the stream of process air upstream of the burner port. This enables premix products of combustion to suppress the production of NOx by vitiating a combustion air portion of the process air before the combustion air portion combusts with fuel injected from the burner port.

Abstract: A method delivers fuel gas to a furnace combustion chamber from a premix burner having a reaction zone with an outlet to the furnace combustion chamber. This includes the steps of injecting a premix of primary fuel gas and combustion air into the reaction zone, and combusting the premix to provide combustion products including vitiated combustion air in the reaction zone. Further steps include injecting staged fuel gas into the reaction zone separately from the premix, discharging the staged fuel gas and vitiated combustion air from the reaction zone through the outlet to the furnace combustion chamber, and combusting the staged fuel gas and vitiated combustion air in the furnace combustion chamber. This enables low NOx combustion in the furnace combustion chamber to be achieved as a result of interacting the staged fuel gas with the vitiated combustion air in the reaction zone.

Abstract: A flow of air is provided from a hot air main into a combustion chamber at a time when a burner is firing into the combustion chamber to heat a bed of regenerative media. The flow of air into the combustion chamber helps to keep products of combustion from flowing into the hot air main. In preferred embodiments, sensors sense pressure in the combustion chamber and the hot air main. A controller shifts a valve back and forth within a range of open conditions to regulate the flow of air in response to the sensed pressures.

Abstract: An indurating furnace has a heating station and an air passage leading to the heating station. A draft of preheated recirculation air is driven through the passage toward the heating station, and is mixed with fuel gas to form a combustible mixture of preheated recirculation air and fuel gas that ignites in the passage. This is accomplished by injecting the fuel gas into the passage in a stream that does not form a combustible mixture with the preheated recirculation air before entering the passage.

Abstract: An indurating furnace has a heating station and an air passage leading to the heating station. A draft of preheated recirculation air is driven through the passage toward the heating station, and is mixed with fuel gas to form a combustible mixture of preheated recirculation air and fuel gas that ignites in the passage. This is accomplished by injecting the fuel gas into the passage in a stream that does not form a combustible mixture with the preheated recirculation air before entering the passage.

Abstract: A method of combusting non-gaseous fuel to heat a load in a process chamber includes the steps of injecting reactant streams into a combustion chamber. The combustion chamber does not contain a load to be heated, but communicates with the process chamber through a burner port. A first reactant stream includes the non-gaseous fuel, and is injected into the combustion chamber to cause the non-gaseous fuel to volatilize in the combustion chamber. A second reactant stream, which includes a premix of gaseous fuel and primary oxidant, also is injected into the combustion chamber. The first and second reactant streams then combust together to yield products of combustion that flow through the burner port from the combustion chamber to the process chamber. Importantly, the second reactant stream is injected into the combustion chamber adjacent to the first reactant stream.

Abstract: A grate-kiln pelletizing furnace includes a grate that conveys pelletized material to a rotary kiln, a cooler that cools pelletized material from the rotary kiln, and a gas flow apparatus that directs a stream of gas from the cooler to the rotary kiln to provide preheated process air for pelletized material in the rotary kiln. The gas flow apparatus also directs a stream of gas from the grate to the rotary kiln to vitiate the preheated process air.

Abstract: An indurating furnace has a heating station and an air passage leading to the heating station. A draft of preheated recirculation air is driven through the passage toward the heating station, and is mixed with fuel gas to form a combustible mixture of preheated recirculation air and fuel gas that ignites in the passage. This is accomplished by injecting the fuel gas into the passage in a stream that does not form a combustible mixture with the preheated recirculation air before entering the passage.

Abstract: A NOx suppression apparatus is configured for use with a burner that injects fuel into a stream of process air flowing into and through a rotary kiln. The apparatus comprises a premix injection system that forms a premix of fuel gas and air, and injects the premix into the stream of process air upstream of the burner port. This enables premix products of combustion to suppress the production of NOx by vitiating a combustion air portion of the process air before the combustion air portion combusts with fuel injected from the burner port.

Abstract: Techniques for suppressing NOx in an indurating furnace include the use of a premix burner, the use of a staged fuel injector structure to enhance fuel lean conditions in the downdraft, and the use of a Venturi mixture structure in the downcomer.

Abstract: A baffle for a regenerative burner has a primary reactant port, secondary reactant ports, and internal flow paths. The primary port is centered on an axis. The secondary ports are arranged in an array that is asymmetrical relative to a plane containing the axis. The internal air flow paths convey secondary air streams from the regenerative bed to the secondary ports. A reactant delivery structure for use with the baffle includes a pilot burner, a main fuel conduit, and a primary air conduit. The pilot burner projects a pilot flame toward the primary port. The main fuel conduit has an annular outlet that directs a main fuel stream over the pilot flame and outward from the primary port. The primary air conduit has an annular outlet that directs a primary air stream outward from the primary port over the main fuel stream.

Abstract: A reactant supply and control system supplies a regenerative burner assembly with streams of pilot fuel and pilot air. The system can maintain a pilot flame throughout regenerative cycles in which a main flame is turned on and off, and supplies either or both of the pilot streams with an increased flow rate for shifting from a regenerative exhaust condition to a regenerative firing condition.

Abstract: An apparatus includes a furnace structure defining a reaction zone. A burner structure communicates with the reaction zone through a burner port. The burner port is centered on a burner axis and has a radius. A fuel inlet structure communicates with the reaction zone through a fuel port. The fuel port is centered on a fuel port axis that is spaced radially from the burner axis a distance within a range from about twice the radius to about six times the radius. The fuel port axis is skewed relative to the burner axis to direct the fuel emerging from the fuel port to flow into the reaction zone along a spiral flow path.

Abstract: A method includes the step of extinguishing a flame fired from a burner in a reaction zone upon determining that a sensed combustion chamber temperature is at or above the auto-ignition temperature of a fuel. A subsequent step is performed before the sensed combustion chamber temperature drops below the auto-ignition temperature. The subsequent step provides a flow of the fuel through the burner and into the combustion chamber through a reaction zone outlet. This initiates diffuse combustion of the fuel by auto-ignition in the combustion chamber in the absence of a flame fired from the burner in the reaction zone.