Multi-stage combustion using nitrogen-enriched air

Abstract

Multi-stage combustion technology combined with nitrogen-enriched air technology for controlling the combustion temperature and products to extend the maintenance and lifetime cycles of materials in contact with combustion products and to reduce pollutants while maintaining relatively high combustion and thermal cycle efficiencies. The first stage of combustion operates fuel rich where most of the heat of combustion is released by burning it with nitrogen-enriched air. Part of the energy in the combustion gases is used to perform work or to provide heat. The cooled combustion gases are reheated by additional stages of combustion until the last stage is at or near stoichiometric conditions. Additional energy is extracted from each stage to result in relatively high thermal cycle efficiency. The air is enriched with nitrogen using air separation technologies such as diffusion, permeable membrane, absorption, and cryogenics. The combustion method is applicable to many types of combustion equipment, including: boilers, burners, turbines, internal combustion engines, and many types of fuel including hydrogen and carbon-based fuels including methane and coal.

1 . A method for burning fuel in a combustion system, comprising: 
 producing combustion of fuel in at least two combustion stages, and    directing a nitrogen-enriched air as an oxidant into at least the first of the combustion stages.    
     
     
         2 . The method of  claim 1 , wherein combustion occurs in each combustion stage for producing energy and additionally including extracting energy produced by the combustion between the combustion stages to perform work or provide heat.  
     
     
         3 . The method of  claim 1 , wherein the first stage of combustion is fuel rich (phi>1) and the final stage of combustion is at or nearly stoichiometric.  
     
     
         4 . The method of  claim 1 , wherein the first stage of combustion uses the nitrogen-enriched air for combustion and subsequent stages of combustion use the nitrogen-enriched air or air for combustion.  
     
     
         5 . The method of  claim 1 , additionally including controlling the combustion temperature and products in the first combustion stage by combining fuel rich combustion of Φ=1.1-1.5 with nitrogen enriched air of 79.5%-90% to obtain high operation-temperature for the combustion, low corrosive and oxidative products, and low NO x .  
     
     
         6 . The method of  claim 1 , additionally including controlling production of NO x  in the first combustion stage by burning fuel rich, controlling production of NO x  in subsequent combustion stages by burning slightly fuel rich with Φ=0.90-1.10 and/or by maintaining the temperature in the subsequent combustion stages less than that in the first combustion stage and with the final combustion stage having the lowest combustion temperature and operating at or near stoichiometric conditions of Φ=0.90-1.10, to obtain low corrosive and oxidative products and low NO x  production, low CO production, and low hydrocarbon emissions.  
     
     
         7 . The method of  claim 1 , additionally including obtaining a desired operational temperature by the use of nitrogen enriched air which permits burning less fuel rich.  
     
     
         8 . The method of  claim 1 , additionally including obtaining a desired operational temperature by the use of burning fuel rich permits using low amounts and concentrations of nitrogen enriched air.  
     
     
         9 . The method of  claim 1 , additionally including fuel injection in stages beyond the first stage to ensure that combustion occurs in stages subsequent to the first stage.  
     
     
         10 . The method of  claim 1 , additionally including providing a fuel for the combustion system selected from the group consisting of any combustible matter, fossil fuels, inorganic fuels, and organic fuels.  
     
     
         11 . The method of  claim 10 , wherein the fossil fuels are selected from the group consisting of oil natural gas, and coal; wherein the inorganic fuels are selected from the group consisting of ammonia, hydrazine, and calcium; and wherein the organic fuels are selected from the group consisting of alcohols, ethers, and wood.  
     
     
         12 . The method of  claim 1 , additionally including providing a fuel for the combustion system selected from the group consisting of methane and low-sulfur coal.  
     
     
         13 . The method of  claim 1 , additionally including providing the combustion system from the group consisting of any system where combustion takes place to perform work or provide heat, furnaces, and engines.  
     
     
         14 . The method of  claim 13 , wherein the furnaces are selected from the group consisting of burners, boilers, and smelters; and wherein the engines are selected from the group consisting of Otto, diesel, and turbine.  
     
     
         15 . The method of  claim 1 , additionally including providing the combustion system from the group consisting of boilers and furnaces having multi-state combustors, and multi-stage turbines.  
     
     
         16 . The method of  claim 1 , additionally including producing the nitrogen-enriched air using air separation technologies selected from the group consisting of cryogenics, absorption, diffusion, and permeation.  
     
     
         17 . The method in  claim 16  using separation technologies to produce nitrogen enriched air also produces at the same time oxygen enriched air that can be used locally to enhance the local combustion process, although the overall combustion process would still be nitrogen enriched.  
     
     
         18 . The permeation method in  claim 16  uses a permeable membrane that is designed for nitrogen enrichment of air in the range of 79.5-85% to achieve low pressure drop for the nitrogen enriched flow.