Alternate combustion type regenerative radiant tube burner apparatus

Abstract

The present invention relates to an alternate combustion type regenerative radiant tube burner apparatus which comprises a circular plate positioned between a burner unit and a main combustion chamber, so that preheated secondary combustion air is fed through an opening of the circular plate to the main combustion chamber. The burner apparatus has the circular plate ( 10 ), an annular air throat ( 2 ), a cylindrical peripheral cover ( 30 ) and a heat-transfer tube ( 11,16 ). A front end portion of the peripheral cover is integrally connected with a peripheral edge portion of the circular plate so as to prevent the secondary combustion air of the air throat from leaking on a periphery of the circular plate to the air diluting chamber ( 3 ). According to the present invention, the concentration of nitrogen oxides in the combustion exhaust gas can be definitely prevented from increasing, without being affected by the installation condition or thermal deformation of the radiant tube burner apparatus.

1 . An alternate combustion type regenerative radiant tube burner apparatus, which has a radiant tube ( 14 ) defining a main combustion chamber ( 4 ) and burner units ( 15 ) provided on both end portions of the radiant tube, the burner unit being provided with a regenerator ( 13 ) and fluid passages ( 17 ,  18 ) for primary combustion air and fuel, the regenerator being alternately in heat-transfer contact with secondary combustion air or combustion exhaust gas, and the fluid passages extending through the regenerator, comprising: 
 a circular plate ( 10 ) positioned between said burner unit ( 15 ) and said main combustion chamber ( 4 ); an annular air throat ( 2 ) provided between the circular plate and the regenerator, into which the secondary combustion air flows after passing through said regenerator; a cylindrical peripheral cover ( 30 ) extending from a peripheral edge portion of said circular plate to a peripheral edge portion of said regenerator; and a heat-transfer tube ( 16 ) protruding forward of said circular plate and opening to said main combustion chamber;    wherein a fuel injection port ( 17   a ) and a primary combustion air delivery port ( 18   a,    18   b ) open in said heat-transfer tube, an inner area of the heat-transfer tube constitutes a primary combustion chamber ( 1 ) for mixing the primary combustion air and the fuel, an air diluting chamber ( 3 ) in an annular form opening to said main combustion chamber is formed around a distal end portion of the heat-transfer tube, and said circular plate has an opening ( 12 ) for communication between said air throat and said air diluting chamber; and    wherein a front end portion of said peripheral cover is integrally connected with the peripheral edge portion of said circular plate so as to prevent the secondary combustion air of said air throat from leaking at a periphery of said circular plate to said air diluting chamber.    
   
   
       2 . The apparatus as defined in  claim 1 , wherein said peripheral cover is contained in the radiant tube in such a condition that thermal deformation of the cover in its axial direction is not restrained by the radiant tube and the regenerator.  
   
   
       3 . The apparatus as defined in  claim 1 , wherein a center (PC) of the opening ( 12 ) is positioned in a zone radially outside of a circle (R) centered on a center line (C) of said circular plate, the circle (R) having a predetermined radius S and the radius S equals (an inner diameter Dt of the radiant tube+ an outer diameter Dr of the heat-transfer tube)/4].  
   
   
       4 . The apparatus as defined in  claim 1 , wherein said opening ( 12 ) of the circular plate is positioned in a range of a central angle of the circular plate (γ) equal to or less than 250 (γ≦250°).  
   
   
       5 . The apparatus as defined in  claim 1 , wherein a velocity of airflow at the opening ( 12 ) of said circular plate is set to be equal to or lower than 30 m/s.  
   
   
       6 . The apparatus as defined in  claim 1 , wherein said fuel injection port ( 17   a ) and said primary combustion air delivery port ( 18   a,    18   b ) are positioned on a plane of said circular plate or in front thereof.  
   
   
       7 . The apparatus as defined in  claim 1 , wherein a flame stabilizing tube ( 41 ) is located in said heat-transfer tube so as to surround said fuel injection port ( 17   a ) and said primary combustion air delivery port ( 18   a,    18   b ), and a pilot fuel injection port ( 40 ) opens in the flame stabilizing tube.  
   
   
       8 . An alternate combustion type regenerative radiant tube burner apparatus, which has a radiant tube ( 14 ) defining a main combustion chamber ( 4 ) and burner units ( 15 ) provided on both end portions of the radiant tube, the burner unit being provided with a regenerator ( 13 ) and fluid passages ( 17 ,  18 ) for primary combustion air and fuel, the regenerator being alternately in heat-transfer contact with secondary combustion air or combustion exhaust gas, and the fluid passages extending through the regenerator, comprising: 
 a circular plate ( 10 ) positioned between said burner unit ( 15 ) and said main combustion chamber ( 4 ); an annular air throat ( 2 ) formed between the circular plate and the regenerator, into which the secondary combustion air flows after passing through said regenerator; a cylindrical peripheral cover ( 30 ) extending from a peripheral edge portion of said circular plate to a peripheral edge portion of said regenerator; and a heat-transfer tube ( 16 ) protruding forward of said circular plate and opening to said main combustion chamber;    wherein a fuel injection port ( 17   a ) and a primary combustion air delivery port ( 18   a,    18   b ) open in said heat-transfer tube, an inner area of the heat-transfer tube constitutes a primary combustion chamber ( 1 ) for mixing the primary combustion air and the fuel, an air diluting chamber ( 3 ) in an annular form opening to said main combustion chamber is formed around a distal end portion of the heat-transfer tube, and said circular plate has an opening ( 12 ) for communication between said air throat and said air diluting chamber; and    wherein a distance (L 4 ) between said regenerator and said circular plate is set in such a manner that a ratio (L 4 /Dt) of the distance (L 4 ) to an inner diameter (Dt) of the radiant tube is equal to or less than 1.0.    
   
   
       9 . The apparatus as defined in  claim 8 , wherein said peripheral cover and said regenerator are connected with each other displaceably in an axial direction.  
   
   
       10 . The apparatus as defined in  claim 8 , wherein a velocity of airflow at said opening ( 12 ) of the circular plate is set to be equal to or less than 30 m/s, and a velocity of the exhaust gas at the opening is set to be equal to or less than 35 m/s.  
   
   
       11 . The apparatus as defined in  claim 8 , wherein a thickness (T) of said peripheral cover is set to be equal to or less than 8 mm.  
   
   
       12 . The apparatus as defined in  claim 8 , wherein said peripheral cover is constituted from a heat-resistant metal alloy plate shaped by bending.  
   
   
       13 . A combustion method in an alternate combustion type regenerative radiant tube burner apparatus; wherein a circular plate ( 10 ) is positioned between a main combustion chamber ( 4 ) in a radiant tube ( 14 ) and a regenerator ( 13 ) alternately in heat-transfer contact with secondary combustion air or combustion exhaust gas, primary combustion air and fuel are fed to the main combustion chamber through a heat-transfer tube ( 11 ,  16 ) extending through the circular plate; and wherein an air diluting chamber ( 3 ) in an annular form opening to the main combustion chamber is formed around a distal end portion of the heat-transfer tube so that the secondary combustion air (A) heated up to a high temperature by heat-transfer contact with the regenerator enters the air diluting chamber, and said fuel and said primary combustion air are mixed with said secondary combustion air in the main combustion chamber while an ejected flow of the secondary combustion air induces the combustion gas of the main combustion chamber, comprising: 
 blocking fluid communication between areas on both sides of said circular plate, at a periphery of the circular plate, so that the fluid communication between these areas are limited to an opening ( 12 ) disposed in a range of central angle of said circular plate (γ) equal to or less than 250 (γ≦250), a center (PC) of the opening being positioned in a zone radially outside of a circle (R) with a predetermined radius S about a center line (C) of the circular plate, and the radius S being equal to (an inner diameter Dt of the radiant tube+an outer diameter Dr of the heat-transfer tube)/4; and    injecting said secondary combustion air to said air diluting chamber at a velocity equal to or less than 30 n/s by said opening ( 12 ), and directing an ejected flow of the combustion exhaust gas of said main combustion chamber toward said regenerator at a velocity equal to or less than 35 m/s by the opening ( 12 ).    
   
   
       14 . The method as defined in  claim 13 , wherein a quantity of supply of said primary combustion air is set to be 10˜20% of a theoretical amount of air required for complete combustion of the fuel.  
   
   
       15 . The method as defined in  claim 13 , wherein said primary combustion air and said fuel are fed to said primary combustion chamber through a flame stabilizing section ( 41 ) and a pilot fuel of 2˜8% of supply of said fuel is fed to the flame stabilizing section.