Low NOx combustion method and apparatus

An apparatus for injecting fuel and preheated oxidant into a combustion zone at target rates, said apparatus comprising:

• a device which is operative to sense the temperature of the preheated oxidant;
• a controller which is operative in response to said device to identify an oxidant-to-fuel ratio at which combustion of the fuel with the preheated oxidant can occur at a predetermined adiabatic flame temperature;
• and
• a reactant supply system which is operative in response to said controller to inject primary fuel and the preheated oxidant into the combustion zone at the identified ratio to produce a flame with the predetermined adiabatic flame temperature, with the preheated oxidant being injected at the target rate of oxidant injection and the fuel being injected at a first reduced rate which is less than the target rate of fuel injection;
• said reactant supply system being further operative in response to said controller to simultaneously inject secondary fuel into the combustion zone separately from the flame at a second reduced rate equal to the difference between the first reduced rate and the target rate of fuel injection.