Method and Apparatus for Firetube Boiler and Ultra Low NOx Burner

Abstract

The current invention disclose a method and apparatus for production of hot water or steam in a firetube boiler and burner, said method comprising the steps of producing a first flue gas in a first stage of a burner associated with the firetube boiler, passing at least a portion of said first flue gas through a first pass and a second pass of the boiler, wherein each of said first and second passes comprises at least one firetube; routing said portion of said first flue gas to a second stage of said burner to reduce the flame temperature and NOx emissions of said second stage of said burner; producing a second flue gas in said second stage of said burner; passing said second flue gas through a third pass of the boiler, wherein said third pass comprises at least one firetube.

What is claimed is: 
     
         1 . A method of producing hot water or steam, comprising the steps of,
 producing a first flue gas in a first stage of a burner associated with a firetube boiler,   passing at least a portion of said first flue gas through a first pass and a second pass of the boiler, wherein each of said first and second passes comprises at least one firetube;   routing said portion of said first flue gas to a second stage of said burner to reduce the flame temperature and NOx emissions of said second stage of said burner;   producing a second flue gas in said second stage of said burner;   passing said second flue gas through a third pass of the boiler, wherein said third pass comprises at least one firetube.   
     
     
         2 . The method as described in  claim 1  further comprises a step of passing said second flue gas through a fourth pass of the boiler, wherein said fourth pass comprises a plurality of firetubes. 
     
     
         3 . The method as described in  claim 2  further comprises a step of passing said second flue gas through a fifth pass of the boiler, wherein said fifth pass comprises a plurality of firetubes. 
     
     
         4 . The method as described in  claim 3  further comprises a step of passing said second flue gas through a sixth pass of the boiler, wherein said sixth pass comprises a plurality of firetubes. 
     
     
         5 . The method as described in  claim 1  wherein the first stage and the second stage of the burner are supplied with combustion air from a single blower. 
     
     
         6 . An apparatus for producing hot water or steam, said apparatus comprising
 a firetube boiler comprising
 a shell substantially cylindrical in shape, the shell having a front end, a back end, and a water entry port; 
 a plurality of firetubes disposed in the shell and substantially extending the length of the shell between the front end and the back end, said firetubes form a first pass, a second pass and a third pass in the boiler, wherein said first pass comprises at least one of said firetubes and allows flue gas to flow in the direction from the front end to the back end; said second pass comprises at least one of said firetubes and allows flue gas to flow in the direction from the back end to the front end; said third pass comprises at least one of said firetubes and allows flue gas to flow in the direction from the front end to the back end; and 
   A burner affixed to the front end of said firetube boiler comprising
 a first stage that produces a first flue gas; 
 a second stage that produce a second flue gas; 
 wherein at least a portion of said first flue gas goes through said first and second passes of said boiler, and is routed to the second stage of the burner to reduce the flame temperature and NOx emissions of said second stage; said second flue gas goes through said third pass of said boiler. 
   
     
     
         7 . The apparatus as described in  claim 6  wherein said firetube boiler further comprises a fourth pass that comprises a plurality of firetubes and allows flue gas to flow in the direction from the back end to the front end. 
     
     
         8 . The apparatus as described in  claim 7  wherein said firetube boiler further comprises a fifth pass that comprises a plurality of firetubes and allows flue gas to flow in the direction from the front end to the back end. 
     
     
         9 . The apparatus as described in  claim 8  wherein said firetube boiler further comprises a sixth pass that comprises a plurality of firetubes and allows flue gas to flow in the direction from the back end to the front end. 
     
     
         10 . The apparatus as described in  claim 6  wherein the first stage and second stage of the burner are supplied with combustion air from a single blower. 
     
     
         11 . The apparatus as described in  claim 6  wherein the first stage and second stage of the burner use non-premix type combustion. 
     
     
         12 . The apparatus as described in  claim 6  wherein the first stage and second stage of the burner use premix type combustion. 
     
     
         13 . The apparatus as described in  claim 6  wherein the firetube boiler is a Scotch Marine dry back design. 
     
     
         14 . The apparatus as described in  claim 6  wherein the firetube boiler is a Scotch Marine wet back design. 
     
     
         15 . The apparatus as described in  claim 6  wherein the first pass comprises one firetube, the second pass comprises one firetube disposed at the center of a circle, and the third pass comprises multiple firetubes disposed on said circle, wherein the first flue gas exiting the second pass is distributed evenly to the third pass. 
     
     
         16 . The apparatus as described in  claim 10  wherein the first stage accounts for 10%-35% of the heat release of the burner, and the second stage accounts for 65-90% of the heat release of the burner, when both stages are in operation. 
     
     
         17 . The apparatus as described in  claim 10  wherein the first stage and second stage of the burner use non-premix type combustion. 
     
     
         18 . The apparatus as described in  claim 10  wherein the first stage and second stage of the burner use premix type combustion. 
     
     
         19 . The apparatus as described in  claim 16  wherein the first stage and second stage of the burner use non-premix type combustion. 
     
     
         20 . The apparatus as described in  claim 16  wherein the first stage and second stage of the burner use premix type combustion. 
     
     
         21 . The apparatus as described in  claim 20  wherein the first stage of the burner is run at a higher oxygen level in the flue gas than the second stage. 
     
     
         22 . The apparatus as described in  claim 21  wherein the first stage of the burner is run at 7-10% oxygen level in the first flue gas dry volume based, and the second stage is run at 1-6% oxygen level in the second flue gas dry volume based. 
     
     
         23 . The apparatus as described in  claim 22  wherein the second stage is run at 1-3% oxygen level in the second flue gas dry volume based.