Method and apparatus for low NOX combustion of gaseous fuels

In combination, apparatus for limiting NOX content in flue gas emission from a combustor in a compact boiler comprising:

• a combustion chamber further comprising:
• an essentially cylindrical chamber wall formed by coiled tubing, said tubing carrying boiler feed water for extracting heat from said combustor flue gas, said chamber having inlet and outlet ends;
• means circulating said boiler feed water through said tubing for transferring heat and reducing said flue gas temperatures thereby;
• and,
• an exhaust stack abutting said chamber outlet end;
• combustor means abutting said chamber inlet end for generating flue gas, further comprising:
• a burner in said combustor;
• gaseous fuel and combustion air inlet means in said burner;
• and,
• valve means in said air inlet intermediate said air inlet and ambient air, for controlling combustion air flow therethrough;
• means supplying combustion air to said combustion air inlet;
• a duct projecting into said exhaust stack;
• an enlarged end on said stack projection for capturing flowing stack flue gas;
• valve means in said burner combustion air inlet for admitting said captured stack flue gas;
• means measuring the NOX level in said flue gases, said means generating signals indicative of gaseous NOX levels;
• and,
• means operating said combustion air inlet valve in accordance with measured NOX levels for controlling concentration of recirculated flue gas.

Apparatus for limiting NOX emission in a compact boiler comprising:

• a compact boiler having a combustion chamber, said chamber having a combustor end and a distal heat exchange end;
• an exhaust stack in said heat exchange end;
• and,
• combustion means in said combustor end for generating flue gas,
• further comprising:
• a gaseous fuel inlet;
• a combustion air inlet;
• valve means in said air inlet intermediate said air inlet and ambient air, for controlling flow therethrough;
• means supplying combustion air to said combustion means;
• means in said stack for collecting flue gas;
• comprising:
• a duct projecting into said stack;
• a bell mouthed end on said stack projection for capturing flowing stack flue gas,
• means measuring NOX level in said gases, said means generating signals indicative of gas NOX level;
• and,
• means operating said valve in accordance with said NOX levels for controlling flue gas recirculation.

Apparatus for limiting the NOX content in flue gas emission from a compact boiler comprising:

• a combustion chamber, further comprising:
• an essentially cylindrical chamber wall of coiled tubing, said tubing carrying boiler feed water for extracting heat from said combustor flue gas, said chamber having inlet and outlet ends;
• means circulating boiler feed water through said wall, thereby limiting combustor flue gas temperatures;
• and,
• an exhaust stack abutting said chamber outlet end;
• and,
• combustion means abutting said chamber inlet end for generating flue gas further comprising;
• a burner;
• a cylindrical refractory shell having a discharge end and an inlet end, said shell discharge end partially and movable extending into said combustion chamber inlet end;
• means movably mounting said burner in said shell;
• gaseous fuel and combustion air inlet means in said burner;
• means supplying gaseous fuel and combustion air to said burner and shell fuel air inlets at said shell inlet end;
• a combustion air inlet port defined by said shell extension into said chamber for admitting combustion air to said chamber, said combustion air having a flow pattern peripheral to the external surface of said shell;
• means supplying combustion air to said combustion air inlet port;
• means mixing said burner fuel and air internal of said shell for delivering completed and partially completed combustion products from said shell outlet end and into said chamber;
• whereby combustion is completed in said combustion chamber after exiting said shell;
• and,
• ambient air inlet means;
• valve means in said air inlet means intermediate said burner combustion air inlet for controlling flow of combustion air therethrough;
• means in said exhaust stack for collecting predetermined amounts of flue gas flowing therethrough;
• means in said combustion air inlet admitting said collected flue gas;
• means measuring NOX levels in said flue gases, said means generating signals indicative of gas NOX levels;
• and,
• means operating said valve for controlling flue gas recirculation in accordance with predetermined NOX levels.

A method for reducing NOX content in flue gas exhaust of a compact boiler of the type having a burner using pressurized combustion air, recirculated flue gas and ambient air, comprising the steps of:

• incorporating air and flue gas pressurization means;
• incorporating a water wall combustion chamber;
• mounting said burner in said water wall combustion chamber;
• supplying ambient air to said pressurization means;
• capturing a portion of said boiler flue gas;
• supplying said captured flue gas to said pressurization means;
• measuring NOX content of said boiler flue gas;
• controlling said ambient air supplying means to maintain a predetermined NOX level in said boiler flue gas.

In an automatic self-operating compact boiler of the type having a sequentially staged start-up system including a pre-ignition purge cycle of the combustion chamber, said boiler employing flue gas recirculation, the improvement comprising:

• an essentially cylindrical refractory combustion chamber in said boiler having conoidal ends and oppositely positioned heat exchange and combustion ports in said ends;
• a boiler stack for exhausting said flue gas;
• a burner abutting said combustion port having means admitting fuel and atmospheric combustion air said burner injecting combusting fuel and air into said chamber for generating flue gases therein;
• heat exchange means intermediate said heat exchange port and stack;
• first valve means in said combustion air admitting means for controlling flow therethrough;
• duct means in said stack for capturing flue gas;
• means combining said captured flue gas and burner combustion air;
• and
• second valve means in said capturing means, operable by said start-up system during said purge for preventing admission of flue gas during the purge cycle;
• and
• means measuring NOX level in said flue gases, said means generating signals indicative of gas NOX level;
• and
• means operating said first valve means in accordance with NOX levels for controlling flue gas recirculation.

In a low NOX burner for a forced circulation compact boiler utilizing combustion products captured in the boiler stack and recirculated through combustion air supplied to the burner, the improvement comprising:

• a combustion chamber, having oppositely positioned heat exchange and combustion means;
• a stack on said heat exchange end for exhausting combustion products;
• a burner in said combustion end for generating combustion products;
• means supplying atmospheric combustion air to said burner;
• duct means, fluid communicating said stack and combustion air means, said duct means including a bell mouthed end in said stack oriented to capture flowing stack gas.

In an automatic self-operating compact boiler of the type having a sequentially staged start-up system including a pre-ignition purge cycle of the combustion chamber, said boiler employing flue gas recirculation, the improvement comprising:

• combustion chamber in said boiler having oppositely positioned heat exchange and combustion ends for generating high temperature flue gas comprising:
• an essentially cylindrical coiled tubing chamber wall, said tubing carrying boiler feed water for extracting heat from ongoing combustion processes therein;
• and,
• a boiler stack abutting said heat exchange end for exhausting said flue gas;
• a burner in said chamber combustion end having means admitting fuel and atmospheric combustion air;
• first valve means in said combustion air admitting means for controlling flow therethrough;
• duct means in said stack for capturing flue gas;
• means combining said captured flue gas and burner combustion air;
• and
• second valve means in said capturing means, operable by said start-up system during said purge for preventing admission of flue gas during the purge cycle;
• and
• means measuring NOX level in said gases, said means generating signals indicative of gas NOX level;
• and
• means operating said first valve means in accordance with NOX levels for controlling flue gas recirculation.