Porous media burner for low calorific value fuel gases

Abstract

A method and burner for combusting fuels having a heating value of <80 BTU/scf (<2.98 MJ/Nm 3 ) in which the fuel premixed with air is injected into a porous inert media so that the fuel is combusted with the air. Oxygen may be optionally injected into the porous inert media separately from the premixed air/fuel.

What is claimed is: 
     
         1 . A burner for combusting fuels having a heating value of <80 BTU/scf (<2.98 MJ/Nm 3 ), comprising:
 an inner tube having open first and second ends;   an outer tube concentrically disposed around the inner tube and having a closed first end and a second end, the inner and outer tubes defining annular space between them for allowing a flow of premixed air/fuel therethrough, wherein:
 the annular space has a second end that is closed by a face that extends between the second ends of the tubes, 
 the face includes one or more openings for allowing a flow or flows of air and fuel, 
 the outer tube first end extends past the inner tube first end; and 
   a porous inert media comprising metal or ceramic and having first and second ends that is disposed within the inner tube adjacent the inner tube first end.   
     
     
         2 . The burner of  claim 1 , further comprising an oxygen lance having first and second ends and extending through a centrally disposed aperture formed in the closed first end of the outer tube so that the lance second end is disposed adjacent the first end of the media, wherein a space is defined by the outer tube first end, an outer surface of the lance, and an inner surface of the outer tube adjacent its first end. 
     
     
         3 . The burner of  claim 1 , further comprising a screening material disposed directly between the lance second end and the media first end. 
     
     
         4 . The burner of  claim 1 , wherein the lance second end abuts directly against the media first end. 
     
     
         5 . A method for combusting fuels having a heating value of <80 BTU/scf (<2.98 MJ/Nm 3 ), comprising the steps of:
 mixing air with a gaseous fuel having a heating value of <80 BTU/scf (<2.98 MJ/Nm 3 ) to provide a flow of premixed air/fuel;   directing the flow of premixed air/fuel through an annular space defined by inner and outer tubes of a burner;   injecting the flow of premixed air/fuel into a porous inert media disposed within the inner tube;   combusting the fuel with the air to produce a flow of combustion products within a downstream portion of the inner tube in a direction opposite that of the flow of premixed air/fuel; and   exchanging heat between the flows of combustion products and premixed air/fuel across the inner tube.   
     
     
         6 . The method of  claim 5 , further comprising the step of injecting a flow of oxygen into the porous inert media separate from the flow of premixed air/fuel for assisting the combustion of the fuel with the air. 
     
     
         7 . The method of  claim 6 , wherein the fuel is a reject stream from a landfill gas or digester gas purification process. 
     
     
         8 . The method of  claim 5 , wherein the fuel is a reject stream from a landfill gas or digester gas purification process. 
     
     
         9 . The method of  claim 5 , wherein the oxygen is at least 95% pure oxygen. 
     
     
         10 . The method of  claim 5 , wherein a flame resulting from combustion of the fuel with the air and oxygen is stabilized within the media. 
     
     
         11 . The method of  claim 5 , wherein a flame resulting from combustion of the fuel with the air and oxygen is stabilized at a downstream face of the media. 
     
     
         12 . The method of  claim 5 , wherein the fuel has a heating value of <50 BTU/Nft 3  (<1.86 MJ/Nm 3 ). 
     
     
         13 . The method of  claim 12 , wherein the fuel is a reject stream from a landfill gas or digester gas purification process.