Method of improving fire tube burner efficiency by controlling combustion air flow and an air damper for a fire tube

Abstract

A method of improving natural draft fire tube burner efficiency by controlling combustion air flow. The method involves positioning in a fire tube an air damper body comprising a fixed plate having a plurality of air flow openings and a rotatable plate having a plurality of air flow openings. Air flow through the air damper body is controlled by adjusting the relative rotational position of the fixed plate and the rotatable plate. The air damper body has an air inlet face, an air outlet face, and an outer circumference. The method involves establishing and maintaining a relationship between an air damper open area, firing rate and excess air to maintain stack oxygen below 3% in accordance with a formula A2+A3<DR×FR×A1.

What is claimed is: 
     
         1 . An air damper for a natural draft fire tube, comprising:
 an air damper body comprising a fixed plate having a plurality of air flow openings and a rotatable plate having a plurality of air flow openings, with air flow through the air damper body being controlled by adjusting the relative rotational position of the fixed plate and the rotatable plate, the air damper body having an air inlet face, an air outlet face, and an outer circumference; and   a relationship is maintained between an air damper open area, firing rate and excess air in accordance with a formula A2+A3<DF×FR×A1, in which:
 A1=total area of air flow openings in the air damper body created by a relative positioning of the air flow openings of the fixed plate and the air flow openings of the rotatable plate at a given closing position for a given firing rate; 
 A2=total area of other openings in the air damper body through which air can bypass the air flow openings; 
 A3=total area between an outer diameter (OD) of the air damper body and an inner diameter (ID) of the fire tube through which air can bypass the air flow openings, and 
 FR=firing rate in % of maximum rate for a particular firetube-burner combination; 
 DF=diameter factor, where D=fire tube inner diameter and the factor is a relationship of 0.12D̂2−6.29D+92. 
   
     
     
         2 . The air damper of  claim 1 , wherein a central burner passage through the air damper body, the central burner passage being adapted to receive a burner body. 
     
     
         3 . The air damper of  claim 1 , wherein a deformable circumferential seal around the outer circumference of the air damper body, the circumferential seal being adapted to engage an inner circumference of a fire tube solely by friction. 
     
     
         4 . The air damper of  claim 1 , wherein the rotatable plate is positioned at the inlet face of the air damper body and the fixed plate is positioned at the outlet face of the air damper body. 
     
     
         5 . The air damper of  claim 4 , wherein the outlet face of the air damper body has outwardly projecting air deflectors overlying the air flow openings of the fixed plate. 
     
     
         6 . The air damper of  claim 4 , wherein a handle is provided on the rotatable plate, whereby a manual force is exerted via the handle to rotate the rotatable plate thereby adjusting the position of the air flow openings of the rotatable plate relative to the air flow openings of the fixed plate. 
     
     
         7 . The air damper of  claim 2 , wherein an ignitor passage extends through the air damper body in parallel spaced relation to the central burner passage, wherein an ignitor can be inserted and removed, a seal being provided to prevent airflow through the ignitor passage bypassing the air damper. 
     
     
         8 . The air damper of  claim 2 , in combination with a burner body, the burner body being positioned within the central burner passage of the air damper body, the burner body having a nozzle end protruding passed the air outlet face of the air damper body and a fuel gas source attachment end protruding passed the air inlet face of the air damper body. 
     
     
         9 . The air damper of  claim 8 , in combination with a fire tube. 
     
     
         10 . An air damper for a natural draft fire tube having an inner circumference and a burner body disposed therein, the air damper comprising:
 an air damper body comprising:
 a burner passage adapted to receive the burner body; 
 a peripheral seal adapted to engage the inner circumference of the fire tube; and 
 a plurality of air flow openings disposed about the central burner passage with the size of the air flow openings adjustable; 
   wherein, in use, air flow between the central burner passage and the burner body is impeded, air flow between the peripheral seal and the inner circumference of the fire tube is impeded, and air flow through the air flow openings is user adjustable with a relationship maintained between an air damper open area, firing rate and excess air in accordance with a formula A2+A3<DF×FR×A1, in which:
 A1=total area of air flow openings in the air damper body created by a relative positioning of the air flow openings of the fixed plate and the air flow openings of the rotatable plate at a given closing position for a given firing rate; 
 A2=total area of other openings in the air damper body through which air can bypass the air flow openings; 
 A3=total area between an outer diameter (OD) of the air damper body and an inner diameter (ID) of the fire tube through which air can bypass the air flow openings, and 
 FR=firing rate in % of maximum rate for a particular firetube-burner combination; 
 DF=diameter factor, where D=fire tube inner diameter and the factor is a relationship of 0.12D̂2−6.29D+92. 
   
     
     
         11 . A method of improving natural draft fire tube burner efficiency by controlling combustion air flow, comprising:
 positioning in a fire tube an air damper body comprising a fixed plate having a plurality of air flow openings and a rotatable plate having a plurality of air flow openings, with air flow through the air damper body being controlled by adjusting the relative rotational position of the fixed plate and the rotatable plate, the air damper body having an air inlet face, an air outlet face, and an outer circumference; and   establishing and maintaining a relationship between an air damper open area, firing rate and excess air to maintain excess air below 3% in accordance with a formula A2+A3<DF×FR×A1, in which:
 A 1 =total area of air flow openings in the air damper body created by a relative positioning of the air flow openings of the fixed plate and the air flow openings of the rotatable plate at a given closing position for a given firing rate; 
 A2=total area of other openings in the air damper body through which air can bypass the air flow openings; 
 A3=total area between an outer diameter (OD) of the air damper body and an inner diameter (ID) of the fire tube through which air can bypass the air flow openings, and 
 FR=firing rate in % of maximum rate for a particular firetube-burner combination; 
 DF=diameter factor, where D=fire tube inner diameter and the factor is a relationship of 0.12D̂2−6.29D+92. 
   
     
     
         12 . An air damper for a natural draft fire tube, comprising:
 an air damper body comprising a fixed plate having a plurality of air flow openings and a rotatable plate having a plurality of air flow openings, with air flow through the air damper body being controlled by adjusting the relative rotational position of the fixed plate and the rotatable plate, the air damper body having an air inlet face, an air outlet face, and an outer circumference; and   a deformable circumferential seal around the outer circumference of the air damper body, the circumferential seal being adapted to engage an inner circumference of a fire tube solely by friction.   
     
     
         13 . The air damper of  claim 12 , wherein an ignitor passage extends through the air damper body, wherein an ignitor can be inserted and removed, a seal being provided to prevent airflow through the ignitor passage bypassing the air damper.