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, said method comprising the steps of producing a first flue gas using a first stage of a burner in a first pass of a firetube boiler; passing at least a portion of said first flue gas through a second pass of said boiler, wherein said second pass comprises a plurality of firetubes; routing said portion of said first flue gas to a second stage of said burner to reduce NOx emissions from said second stage of said burner; producing a second flue gas from said second stage of said burner in a third pass of said boiler; passing said second flue gas through a fourth pass of said boiler, wherein said fourth pass comprises a plurality of firetubes.

What is claimed is: 
     
         1 . An apparatus for producing hot water or steam, said apparatus comprising
 1) a firetube boiler comprising
 1a) a shell substantially cylindrical in shape, having a front end and a back end; 
 1b) a front tube sheet and at least one back tube sheet; 
 1c) two furnace tubes and a plurality of firetubes positioned inside the shell and substantially extending the length of the shell from the front end to the back end, said furnace tubes form a first pass and a third pass, said firetubes form a second pass and a fourth pass in the boiler, wherein said first pass comprises a furnace tube and allows a first flue gas to be produced and flow in the direction from the front end to the back end; said second pass comprises a plurality of firetubes and allows said first flue gas to flow in the direction from the back end to the front end; said third pass comprises a furnace tube and allows a second flue gas to be produced and flow in the direction from the front end to the back end; and said fourth pass comprises a plurality of firetubes and allows said second flue gas to flow in the direction from the back end to the front end. 
   2) a burner affixed to the front end of said firetube boiler comprising
 2a) a first stage that produces said first flue gas; 
 2b) a second stage that produces said second flue gas; 
 wherein at least a portion of said first flue gas goes through said second pass of said boiler, and is routed to the second stage of the burner to reduce NOx emissions from said second flue gas; said second flue gas goes through said fourth pass of said boiler. 
   
     
     
         2 . The apparatus as described in  claim 1  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. 
     
     
         3 . The apparatus as described in  claim 2  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. 
     
     
         4 . The apparatus as described in  claim 1  wherein the first stage and second stage of the burner are supplied with combustion air from a single blower. 
     
     
         5 . The apparatus as described in  claim 1  wherein the first stage of the burner use premix type combustion. 
     
     
         6 . The apparatus as described in  claim 1  wherein the firetube boiler is a dry back design. 
     
     
         7 . The apparatus as described in  claim 1  wherein the firetube boiler is a wet back design. 
     
     
         8 . The apparatus as described in  claim 1  wherein the first stage accounts for 10%-33% of the heat input of the burner, and the second stage accounts for the rest of the heat input of the burner. 
     
     
         9 . The apparatus as described in  claim 8  wherein the first stage of the burner is run at a higher oxygen level in the first flue gas than the second flue gas from the second stage of the burner. 
     
     
         10 . The apparatus as described in  claim 9  wherein the first stage of the burner is run at 5-11% oxygen level in the first flue gas, and the second stage is run at 1-5% oxygen level in the second flue gas. 
     
     
         11 . The apparatus as described in  claim 9  wherein the second stage is run at 1-3% oxygen level in the second flue gas dry volume based.