Perforated flame holder with integrated sub-quench distance layer

Abstract

A flame holder assembly includes a flame holder element and a flame shield element. The flame holder element has a first plurality of apertures extending through the flame holder element. The flame shield element has a second plurality of apertures extending through the flame shield element. Each of the second plurality of apertures has a lateral dimension that is no greater than a flame quenching distance. The flame shield element is positioned facing the flame holder element, and the flame holder assembly is configured such that fuel is supplied to the flame holder element via the second plurality of apertures of the flame shield element.

What is claimed is: 
     
         1 . A flame holder assembly, comprising:
 a flame holder element, including a first face and a second face lying opposite each other, and a first plurality of apertures extending through the flame holder element between the first and second faces, each of the first plurality of apertures having lateral dimensions that are greater than a flame quenching distance, the flame holder element having a void fraction greater than 0.50; and   a flame shield element including a third face and a fourth face lying opposite each other, and a second plurality of apertures extending through the flame shield element between the third and fourth faces, each of the second plurality of apertures having at least one lateral dimension that is no greater than the flame quenching distance, the flame shield element being positioned with the third face facing the second face of the flame holder element.   
     
     
         2 . The flame holder assembly of  claim 1 , wherein the flame holder element is configured to hold a combustion reaction substantially within the first plurality of apertures and between the first and second faces. 
     
     
         3 . The flame holder assembly of  claim 2 , wherein each of the first plurality of apertures extends substantially unobstructed between the first and second faces. 
     
     
         4 . The flame holder assembly of  claim 1 , comprising an assembly support element configured to hold the flame holder element and the flame shield element in a spaced-apart relationship. 
     
     
         5 . The flame holder assembly of  claim 4 , wherein the assembly support element extends around an entire lateral perimeter of the flame holder assembly, enclosing a space between the flame holder element and the flame shield element. 
     
     
         6 . The flame holder assembly of  claim 1 , wherein the flame holder element and flame shield element are positioned with the third face of the flame shield element in direct contact with the second face of the flame holder element. 
     
     
         7 . The flame holder assembly of  claim 1 , wherein each of the second plurality of apertures has a slot shape, extending laterally in the flame shield element a distance at least equal to a distance between two adjacent ones of the first plurality of apertures. 
     
     
         8 . The flame holder assembly of  claim 1 , wherein the flame holder element has a void fraction of greater than 0.50. 
     
     
         9 . The flame holder assembly of  claim 8 , wherein the flame holder element has a void fraction of greater than 0.60. 
     
     
         10 . The flame holder assembly of  claim 8 , wherein the flame holder element has a void fraction of about 0.70. 
     
     
         11 . The flame holder assembly of  claim 1 , wherein a length of each of the first plurality of apertures is greater than a transverse dimension of the respective one of the first plurality of apertures by a factor of at least 4. 
     
     
         12 . The flame holder assembly of  claim 11 , wherein the length of each of the first plurality of apertures is greater than a transverse dimension of the respective one of the first plurality of apertures by a factor of at least 12. 
     
     
         13 . The flame holder assembly of  claim 12 , wherein the length of each of the first plurality of apertures is greater than a transverse dimension of the respective one of the first plurality of apertures by a factor of at least 16. 
     
     
         14 . The flame holder assembly of  claim 13 , wherein the length of each of the first plurality of apertures is greater than a transverse dimension of the respective one of the first plurality of apertures by a factor of at least 24. 
     
     
         15 . The flame holder assembly of  claim 14 , wherein the length of each of the first plurality of apertures is greater than a transverse dimension of the respective one of the first plurality of apertures by a factor of at least 48. 
     
     
         16 . The flame holder assembly of  claim 1 , comprising a preheat structure configured to apply thermal energy to the flame holder element, when activated. 
     
     
         17 . The flame holder assembly of  claim 16 , wherein the preheat structure includes an electrical heating element positioned adjacent to the flame holder element. 
     
     
         18 . A method, comprising:
 introducing a fuel stream to a perforated flame holder having a void fraction of at least 0.50, via a plurality of passages formed in a shield element positioned between the perforated flame holder and a source of the fuel stream, each of the passages having transverse dimensions that are no greater than a quenching distance for a fuel component of the fuel stream; and   combusting a majority of the fuel within a plurality of apertures extending between first and second faces of the perforated flame holder.   
     
     
         19 . The method of  claim 18 , wherein the introducing a fuel stream to a perforated flame holder having a void fraction of at least 0.50 comprises introducing a fuel stream to a perforated flame holder having a void fraction of at least 0.60. 
     
     
         20 . The method of  claim 18 , wherein the introducing a fuel stream to a perforated flame holder having a void fraction of at least 0.50 comprises introducing a fuel stream to a perforated flame holder having a void fraction of about 0.70. 
     
     
         21 . The method of  claim 18 , wherein the introducing a fuel stream to a perforated flame holder comprises introducing a fuel stream having an average fuel-to-oxidant ratio that is below a lower combustion limit of the fuel component of the fuel stream. 
     
     
         22 . The method of  claim 18 , comprising premixing the fuel stream, including adding a fuel component to an oxidant component. 
     
     
         23 . The method of  claim 18 , wherein the combusting a majority of the fuel within a plurality of apertures extending between first and second faces of the perforated flame holder comprises combusting a majority of the fuel stream within a plurality of apertures that extend without obstruction between the first and second faces of the perforated flame holder. 
     
     
         24 . The method of  claim 23 , comprising combusting a quantity of fuel sufficient to produce at least 1.5 MBTUH/ft 2  of thermal energy. 
     
     
         25 . The method of  claim 24 , wherein the combusting a quantity of fuel sufficient to produce at least 1.5 MBTUH/ft 2  of thermal energy comprises combusting a quantity of fuel sufficient to produce at least 3 MBTUH/ft 2  of thermal energy. 
     
     
         26 . The method of  claim 25 , wherein the combusting a quantity of fuel sufficient to produce at least 3 MBTUH/ft 2  of thermal energy comprises combusting a quantity of fuel sufficient to produce at least 5 MBTUH/ft 2  of thermal energy. 
     
     
         27 . The method of  claim 23 , comprising preheating at least a portion of the perforated flame holder to a start-up temperature during a start-up procedure. 
     
     
         28 . The method of  claim 27 , wherein the preheating at least a portion of the perforated flame holder comprises applying an electrical current to an electrically resistive element positioned adjacent to the perforated flame holder. 
     
     
         29 . A method, comprising:
 introducing a fuel stream to a perforated flame holder via a plurality of passages formed in a shield element positioned between the perforated flame holder and a source of the fuel stream, each of the passages having a transverse dimension that is no greater than a quenching distance for a fuel component of the fuel stream; and   combusting a majority of the fuel within a plurality of apertures extending between first and second faces of the perforated flame holder, including combusting a quantity of fuel sufficient to produce at least 1.5 MBTUH/ft 2 .   
     
     
         30 . The method of  claim 29 , wherein the combusting a quantity of fuel sufficient to produce at least 1.5 MBTUH/ft 2  comprises combusting a quantity of fuel sufficient to produce at least 3 MBTUH/ft 2 . 
     
     
         31 . The method of  claim 30 , wherein the combusting a quantity of fuel sufficient to produce at least 3 MBTUH/ft 2  comprises combusting a quantity of fuel sufficient to produce at least 5 MBTUH/ft 2 .