Biomass Combustion

Abstract

A splitter divides a flow of low heating value biomass into a central stream and an annular stream. A stable flame may be achieved by combusting the central stream with oxygen. This avoids the use of costly fossil fuels or biomass (that have higher heating values than the biomass fuel) as an auxiliary fuel for achieving a stable flame.

What is claimed is: 
     
         1 . A biomass burner, comprising:
 a burner block having an injector passage extending between rear and front faces;   a fuel conduit having inlet and outlet ends and being concentrically disposed within said bore at said front face, an annular combustion air flow space being defined between an inner surface of said outer conduit and an outer surface of said fuel conduit;   an oxygen injector having inlet and outlet ends and being concentrically disposed within said outer conduit at said front face; and   a tubular fuel flow splitter concentrically disposed within said fuel conduit at said front face, said splitter having an inlet end disposed upstream of said fuel conduit inlet end and also having an outlet end, wherein said oxygen injector has:   an annular cross-sectional shape and is adjacent to and surrounds said splitter; or   a cylindrical cross-sectional shape and is concentrically disposed within said splitter.   
     
     
         2 . The biomass burner of  claim 1 , wherein the outlet ends of the fuel conduit, oxygen injector, and splitter are flush with said front face. 
     
     
         3 . The biomass burner of  claim 1 , wherein the outlet ends of said oxygen injector and splitter are recessed back from said fuel conduit outlet end. 
     
     
         4 . The biomass burner of  claim 1 , wherein said oxygen injector has an annular cross-sectional shape and is adjacent to and surrounds said splitter. 
     
     
         5 . The biomass burner of  claim 4 , wherein said oxygen injector outlet end is configured as a closed face with a plurality of radially distributed injection holes. 
     
     
         6 . The biomass burner of  claim 4 , wherein said oxygen injector outlet end is configured as an open face. 
     
     
         7 . The biomass burner of  claim 1 , wherein said oxygen injector has a cylindrical cross-sectional shape and is concentrically disposed within said splitter. 
     
     
         8 . The biomass burner of  claim 7 , wherein said oxygen injector outlet end is configured as a closed face with a plurality of radially distributed injection holes. 
     
     
         9 . The biomass burner of  claim 7 , wherein said oxygen injector outlet end is configured as an open tube. 
     
     
         10 . The biomass burner of  claim 1 , further comprising an outer conduit concentrically disposed within said bore having an inlet end disposed downstream of said burner block rear face and also having an outlet end, said annular combustion air flow space being split into a secondary combustion air flow space and a tertiary combustion flow space by said outer conduit, the secondary combustion air flow space being defined by an outer surface of said fuel conduit and an inner surface of said outer conduit, the tertiary combustion air flow space being defined by an outer surface of said outer conduit and an inner surface of said bore. 
     
     
         11 . The biomass burner of  claim 1 , further comprising:
 a secondary combustion air swirler disposed within said secondary combustion air flow space upstream of said burner block front face; and   a tertiary combustion air swirler disposed along an inner surface of said bore adjacent to said burner block front face.   
     
     
         12 . The biomass burner of  claim 1 , wherein said splitter further comprises a main section extending between said splitter inlet and outlet ends, the splitter inlet end having a diameter D 1 , the main body having a diameter D 2 , wherein D 1 <D 2 . 
     
     
         13 . The biomass burner of  claim 1 , wherein said fuel conduit has a diameter D 4 , said splitter inlet end has a diameter D 1  and 0.05 D 4 ≦D 1 ≦0.25 D 4 . 
     
     
         14 . A biomass combustion system, comprising the biomass burner of  claim 1 , a biomass hopper, a biomass fuel feeder, a source of oxygen, and one or more blowers, wherein:
 said biomass fuel feeder is operatively associated with said hopper and at least one of said one or more blowers to receive particulate biomass from said hopper, convey the particulate biomass with a flow of combustion air from said at least one blower to provide a flow of biomass fuel, and direct the flow of biomass fuel to said fuel conduit inlet end;   at least one of said one or more blowers is in fluid communication with said combustion air flow space; and   said source of oxygen is in fluid communication with said oxygen injector inlet end.   
     
     
         15 . The biomass combustion system of  claim 14 , wherein said source of oxygen is selected from group consisting of a vacuum swing adsorption system, an oxygen pipeline, a cryogenic air separation unit, and a vaporizer connected to a tank of liquid oxygen. 
     
     
         16 . A biomass-fired boiler installation, comprising:
 a plurality of the biomass burner of  claim 1 ;   one or more blowers;   at least one biomass hopper;   at least one biomass fuel feeder;   a source of oxygen; and   a boiler, wherein
 said at least one biomass fuel feeder is operatively associated with said at least one hopper and at least one of said one or more blowers to receive particulate biomass from said at least one hopper, convey the particulate biomass with a flow of air from said at least one blower to provide a flow of biomass fuel, and direct the flow of biomass fuel to said fuel conduit inlet ends; 
 at least one of said at least one blower is in fluid communication with said combustion air flow spaces; 
 said source of oxygen is in fluid communication with said oxygen injector inlet ends; and 
 said plurality of burners are mounted on walls of said boiler. 
   
     
     
         17 . The biomass-fired boiler installation of  claim 15 , wherein said source of oxygen is selected from group consisting of a vacuum swing adsorption system, an oxygen pipeline, a cryogenic air separation unit, and a vaporizer connected to a tank of liquid oxygen. 
     
     
         18 . A method of combusting biomass, comprising the steps of:
 injecting a flow of particulate biomass conveyed with air from a fuel conduit of a biomass burner into a combustion space, the fuel conduit having a tubular splitter concentrically disposed therein, the flow of biomass being split by the splitter into a central flow on the inside of the splitter and an annular flow on the outside of the splitter;   injecting a flow of oxygen into the flow of injected biomass from an oxygen injector concentrically disposed within said fuel conduit;   combusting the injected central flow of biomass with the oxygen in the combustion space;   injecting an annular flow of combustion air from the burner around the annular flow of biomass; and   combusting the injected annular flow of biomass with the combustion air in the combustion space.   
     
     
         19 . The method of  claim 18 , wherein the central biomass flow has a velocity V 1 , the annular biomass flow has a velocity V 2 , and the flow of oxygen has a velocity V 3 , where (V 3 −V 2 )<(V 3 −V 1 ). 
     
     
         20 . The method of  claim 19 , wherein no fuel other than the particulate biomass is combusted. 
     
     
         21 . The method of  claim 19 , wherein the oxygen and the central flow of biomass begin to mix at a point upstream of said fuel conduit outlet end. 
     
     
         22 . The method of  claim 19 , wherein said oxygen is injected in a center of the central flow of biomass. 
     
     
         23 . The method of  claim 19 , wherein said oxygen is injected in an annulus surrounding said splitter. 
     
     
         24 . The method of  claim 19 , wherein the oxygen is swirled. 
     
     
         25 . The method of  claim 19 , wherein the oxygen has a concentration of >95%. 
     
     
         26 . The method of  claim 19 , wherein the combustion air is injected in two annular flows, a first of which is secondary combustion air adjacent the annular flow of biomass and a second of which is tertiary combustion air adjacent the secondary combustion air. 
     
     
         27 . The method of  claim 19 , wherein an overall oxygen enrichment of the combined biomass fuel, injected oxygen and combustion air achieved by injection of the oxygen is between 21% and 25%.