A steam generator system employing a fired burner with a flue gas recirculation system with low NOx emission is disclosed. A method to retrofit fired burners for low NOx emission is also disclosed. In the system, the flue gas recirculation system is configured to include a pre-mixer, and the recirculated flue gas (RFG) is routed to the stage of the pre-mixer for mixing with a portion of the fuel stream, forming a secondary RFG fuel mixture. The secondary RFG fuel mixture is routed to the secondary stage of the burner via a plurality of injector ports. The injection of the second RFG fuel mixture results in a reduction of temperature for the NOx emission to be less than 5 ppm at 3% O2, dry basis.