Oxygen enhanced combustion of biomass

Abstract

The energy output of a power plant combustion chamber that combusts fuel comprising biomass as all or part of the fuel can be increased by feeding oxygen into the combustion chamber so that said fuel is in contact with gaseous oxidant whose oxygen content exceeds that of air by up to 5 vol. % above that of air.

What is claimed is: 
     
         1 . A method of combustion, comprising
 (A) providing apparatus that includes a combustion chamber in which fuel having a given moisture content and a given specific energy content fed into the combustion chamber at a given mass feed rate can be combusted in air to produce heat energy at a given rate,   (B) feeding into said combustion chamber fuel that contains biomass and that has a specific energy content lower than said given specific energy content, so that combustion in air of said fuel fed at said given mass fed rate in said combustion chamber in air produces heat energy at a rate lower than said given rate, while feeding oxygen into said combustion chamber so that said fuel is in contact with gaseous oxidant whose oxygen content exceeds that of air by up to 5 vol. % above that of air, and   (C) combusting the fuel with said gaseous oxidant in said combustion chamber.   
     
     
         2 . The method of  claim 1  wherein the fuel has an energy content of less than 7500 BTU/lb. 
     
     
         3 . The method of  claim 1  wherein in step (B) oxygen is fed into said combustion chamber so that said fuel is in contact with gaseous oxidant whose oxygen content exceeds that of air by up to 1 vol. % above that of air. 
     
     
         4 . A method of increasing fuel combustion rate in a combustion chamber with a convective heat transfer zone in which fuel that contains biomass is combusted with combustion air in said combustion chamber to produce flue gas containing a specific oxygen concentration between 3 vol. % and 8 vol. % at a given maximum fuel feed rate limited by the capacity of an FD fan if present for feeding said combustion air, the capacity of an ID fan if present to evacuate flue gas from said combustion chamber, the flue gas velocity in said convective heat transfer zone, or the carbon monoxide concentration in said flue gas, feeding into said combustion chamber additional fuel containing biomass and additional oxidant containing at least 50 vol. % O 2 , reducing said combustion air flow rate by the amount that reduces said oxygen concentration in said flue gas by 0.1 to 5.0 vol. % and combusting said additional fuel without exceeding said FD fan capacity, said ID fan capacity, said flue gas velocity, nor said carbon monoxide concentration. 
     
     
         5 . The method of  claim 4  wherein said oxygen concentration in said flue gas is reduced by 0.1 to 1.0 vol. %. 
     
     
         6 . The method of  claim 4  wherein said additional oxidant contains at least 90% vol. O 2 . 
     
     
         7 . The method of  claim 4  wherein the ratio of the oxygen contained in said additional oxidant to said additional fuel is less than 2,000 SCF/MMBtu. 
     
     
         8 . The method of  claim 4  wherein the ratio of the oxygen contained in said additional oxidant to said additional fuel is less than 1,500 SCF/MMBtu. 
     
     
         9 . The method of  claim 4  wherein said fuel combustion rate in said combustion chamber is increased by 3% to 30% in Btu content. 
     
     
         10 . The method of  claim 4  wherein said additional oxidant is injected to one or more oxygen deficient areas in said combustion chamber. 
     
     
         11 . The method of  claim 4  wherein said additional oxidant contains at least 90% vol. O2. 
     
     
         12 . A method of increasing fuel combustion rate in a combustion chamber with a grate for combustion of fuel with a convective heat transfer zone in which fuel that contains biomass is combusted with combustion air in said combustion chamber to produce flue gas containing a specific oxygen concentration between 3 vol. % and 8 vol. % at a given maximum fuel feed rate limited by the carbon monoxide concentration in said flue gas, feeding into said combustion chamber additional fuel containing biomass and additional oxidant containing at least 50 vol. % O 2  to one or more oxygen deficient areas on said grate to maintain or reduce said carbon monoxide concentration. 
     
     
         13 . The method of  claim 12  wherein said oxygen concentration in said flue gas is reduced by 0.2 to 1.0 vol. %. 
     
     
         14 . The method of  claim 12  wherein said additional oxidant contains at least 90% vol. O2. 
     
     
         15 . The method of  claim 12  wherein said additional oxidant is injected from above said grate, from below said grate, or from both above and below said grate.