Method for low NOx fire tube boiler

A method for operating a low oxides of nitrogen (NOx) fire tube boiler, comprising:

• providing a boiler shell including at least one combustion pipe disposed at least partially inside the shell and a plurality of fire tubes disposed inside the shell, the plurality of fire tubes being configured to receive combustion products from the combustion pipe, the combustion pipe being characterized by a length and an inside diameter, the boiler shell being structured to hold boiler water, the combustion pipe surrounding a combustion volume and forming a continuous volume with the plurality of fire tubes, and the combustion pipe and fire tubes being configured to collectively hold the boiler water out of the combustion volume;
• providing a perforated flame holder including a body that defines a plurality of void volumes operable to convey the fuel and air and to hold a combustion reaction;
• supporting the perforated flame holder in the combustion pipe;
• outputting fuel and combustion air into the combustion volume in a direction aligned to deliver mixed fuel and combustion air to the perforated flame holder;
• holding a combustion reaction supported by the fuel and combustion air with the perforated flame holder;
• delivering hot combustion products to the fire tubes;
• transferring heat from the fire tubes to the boiler water;
• outputting hot water or steam from the boiler;
• and
• outputting combustion products including less than 10 parts per million NOx at 3% excess oxygen.