Low NOx Combustion Method and Apparatus

A method comprising:

• injecting a primary reactant stream, including fuel and combustion air premix, into a combustion chamber;
• injecting a staged fuel stream into the combustion chamber adjacent to the primary reactant stream at a first pressure;
• and
• injecting a stream of recirculated flue gas into the combustion chamber adjacent to the primary reactant stream at a second pressure less than the first pressure.

A method comprising:

• injecting a primary reactant stream, including fuel and combustion air premix, into a combustion chamber;
• injecting a staged fuel stream into the combustion chamber adjacent to the primary reactant stream at a first velocity;
• and
• injecting a stream of recirculated flue gas into the combustion chamber adjacent to the primary reactant stream at a second velocity less than the first velocity.

An apparatus comprising:

• a structure defining a combustion chamber;
• a premix burner having a port facing into the combustion chamber;
• a staged fuel injector having a port facing into the combustion chamber adjacent to the premix burner port;
• a flue gas injector having a port facing into the combustion chamber adjacent to the premix burner port and adjacent to the staged fuel injector port;
• sources of primary fuel, combustion air, and secondary fuel;
• a flue that draws products of combustion from the combustion chamber;
• and
• a reactant supply and control system including means for conveying primary fuel from the primary fuel source to the premix burner, means for conveying combustion air from the combustion air source to the premix burner, means for conveying staged fuel from the staged fuel source to the staged fuel injector, and means for conveying flue gas from the flue to the flue gas injector.

An apparatus comprising:

• means for injecting a primary reactant stream, including fuel and combustion air premix, into a combustion chamber;
• means for injecting a staged fuel stream into the combustion chamber adjacent to the primary reactant stream at a first pressure;
• and
• means for injecting a stream of recirculated flue gas into the combustion chamber adjacent to the primary reactant stream at a second pressure less than the first pressure.

An apparatus comprising:

• means for injecting a primary reactant stream, including fuel and combustion air premix, into a combustion chamber;
• means for injecting a staged fuel stream into the combustion chamber adjacent to the primary reactant stream at a first velocity;
• and
• means for injecting a stream of recirculated flue gas into the combustion chamber adjacent to the primary reactant stream at a second velocity less than the first velocity.