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  Oxygen to expand burner combustion capabilityUSPTO Application #: 20070298357Title: Oxygen to expand burner combustion capability Abstract: A burner at which fuel cannot be combusted with air as the only source of oxygen for combustion in a stable flame at the burner when the feed rate of the fuel is too low, when the fuel is fed at too high an air-to-fuel mass ratio, when the fuel contains too high an amount of inert matter, or when the specific energy content of the fuel is too low, is modified by supplying oxidant containing more than 21 vol. % oxygen into the base of a flame at the burner, whereupon such fuels can be combusted at the burner. (end of abstract) Agent: Praxair, Inc. Law Department - M1 557 - Danbury, CT, US Inventor: Stefan E.F. Laux USPTO Applicaton #: 20070298357 - Class: 431 10 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070298357. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001]The present invention relates to combustion of carbonaceous fuel in a combustion device such as a coal-fired utility boiler. BACKGROUND OF THE INVENTION [0002]Combustion systems are usually designed to burn fuel that is characterized in that one or more properties of the fuel relevant to combustion of the fuel lies within a range of values. The combustion system generally performs at its highest efficiency when the fuel characteristics fall within the ranges for which the system is designed. Attempts to combust fuel having one or more characteristics outside the range for that characteristic might encounter equipment limitations that prevent the system from reaching design capacity or might lead to negative side effects resulting in operational problems, higher emissions and increased maintenance. Features that may be affected by attempts to combust fuels having one or more characteristics outside of the ranges for which the system is designed include stability of the combustion process, flame heat release pattern, combustion efficiency, NOx emissions, and air and flue gas fan capacity. [0003]One example of a characteristic for which a combustion system is often designed is the mass flow rate of fuel into the combustion chamber of the system. Most solid fuel fired combustion systems (for example, systems that combust coal in a boiler) use air-swept pulverizers to dry and pulverize the fuel, which is then carried into the combustion chamber and ignited. Since the transport medium for the pulverized fuel is air, the pulverizers and the fuel piping are designed to achieve at least a minimum air velocity to avoid settling of fuel particles in the flowing stream of transport air. This design condition then requires operating the pulverizer with at least a minimum air flow rate, even under conditions of low fuel mass flow rates. Maintaining this minimum air flow rate thus dilutes the air/fuel mixture, under conditions of low fuel mass flow rates, to a degree that stable combustion can not be attained and the burner flame gradually extinguishes. This is typically the case at loads below 30% of the full load capacity of the pulverizer. Practitioners have found it necessary to use auxiliary fuel (such as natural gas or oil) to maintain flame and combustion stability when the fuel is being fed at such low rates. [0004]A combustion method that permits combustion to be maintained with a stable flame, even at fuel mass flow rates below those for which the system is designed, would thus be useful. [0005]Other examples of characteristics for which a combustion system is often designed are the content of inert (i.e. not combustible) matter (whether solid, such as ash and minerals, or liquid, typically water), and the specific energy value of the fuel, i.e. the amount of energy obtainable upon combustion of the combustible matter present per unit mass of combustible matter. Fuels that contain more inert matter than the range of inert matter for which the combustion system is designed, and fuels that have a specific energy value below the range of specific energy values for which the system is designed, when fed into the combustion system, cause many of the problems such as inability to maintain combustion with a stable flame. [0006]Fuels that may lead to such operational problems may nonetheless have an economical advantage over fuels that conform to the design specifications of the system. Thus, a combustion method that permits combustion to be maintained with a stable flame, even with fuel that contains too high a proportion of inert matter or too low a specific energy value for the system, would thus be useful. BRIEF SUMMARY OF THE INVENTION [0007]One aspect of the present invention is a method of modifying operation of a burner, comprising [0008](A) providing a burner through which a stream of air mixed with particulate solid carbonaceous fuel, and one or more streams of air other than the air mixed with said fuel, can be fed and combusted in a stable flame at said burner, but wherein maintaining said stable flame at said burner when air provided in said streams is the only source of oxygen for said combustion requires that the fuel satisfy one or more conditions in that one or more of (1) the mass flow rate of the fuel through said burner, (2) the fuel-to-air ratio of the stream of air mixed with fuel that is fed through the burner, (3) the content of combustible (i.e. non-inert) matter in the fuel, and (4) the specific energy value of the fuel, must be at least sufficient for said stable flame to be maintained at said burner, [0009](B) inserting through said burner a lance the outlet end of which is positioned to eject gas into the base of a flame at said burner, [0010](C) feeding through said burner a stream of air mixed with particulate solid fuel which does not satisfy at least one of said conditions and therefore cannot be combusted in a stable flame at said burner in air as the only source of oxygen for combustion, and feeding through said burner said one or more streams of air other than the air mixed with said fuel, [0011](D) feeding gaseous oxidant comprising more than 21 vol. % oxygen through the outlet end of said lance, and [0012](E) combusting said fuel and air fed in step (C) with said oxidant fed in step (D) in a stable flame at said burner, wherein said oxidant is fed into the base of said flame at a mass flow rate that maintains said stable flame. [0013]Another aspect of the present invention is a method of operating a burner, comprising [0014](A) providing a burner through which a stream of air mixed with particulate solid carbonaceous fuel, and one or more streams of air other than the air mixed with said fuel, can be fed and combusted in a stable flame at said burner, but wherein maintaining said stable flame at said burner when air provided in said streams is the only source of oxygen for said combustion requires that the fuel satisfy one or more conditions in that one or more of (1) the mass flow rate of the fuel through said burner, (2) the fuel-to-air ratio of the stream of air mixed with fuel that is fed through the burner, (3) the content of combustible matter in the fuel, and (4) the specific energy value of the fuel, must be at least sufficient for said stable flame to be maintained at said burner, [0015](B) feeding through said burner a stream of air mixed with particulate solid fuel which does not satisfy at least one of said conditions and therefore cannot be combusted in a stable flame at said burner in air as the only source of oxygen for combustion, and feeding through said burner said one or more streams of air other than the air mixed with said fuel, and [0016](C) combusting said fuel and air fed in step (B) in a stable flame at said burner while also feeding a stream of gaseous oxidant comprising more than 21 vol. % oxygen into the base of said flame at said burner, wherein said oxidant combusts with said fuel and air, wherein said oxidant is fed into the base of said flame at a mass flow rate that maintains said stable flame. [0017]In both of the aforementioned aspects of the present invention, the stream of gaseous oxidant comprising more than 21 vol. % oxygen is in addition to the fuel-air stream and the one or more streams of air other than the air mixed with the fuel in the fuel-air stream. [0018]In both of the aforementioned aspects of the present invention, the combustion that is made possible by feeding the gaseous oxidant is advantageously carried out without feeding supplemental fuel in gaseous, liquid or solid form such as natural gas or methane, fuel oil or liquid hydrocarbons, or solids which contain a higher content of volatilizable matter than is contained in the particulate solid fuel that is fed and combusted in the practice of this invention. [0019]As used herein, that a flame is "stable" means that, once it is established under a given set of combustion conditions, it continues to burn indefinitely under those combustion conditions. BRIEF DESCRIPTION OF THE DRAWING [0020]FIG. 1 is a cross-sectional view of one embodiment of apparatus with which the present invention can be practiced. Continue reading... Full patent description for Oxygen to expand burner combustion capability Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Oxygen to expand burner combustion capability patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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