Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C7/00—Combustion apparatus characterised by arrangements for air supply
  • F23C7/02—Disposition of air supply not passing through burner
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C5/00—Disposition of burners with respect to the combustion chamber or to one another; Mounting of burners in combustion apparatus
  • F23C5/08—Disposition of burners
  • F23C5/32—Disposition of burners to obtain rotating flames, i.e. flames moving helically or spirally
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
  • F23L9/00—Passages or apertures for delivering secondary air for completing combustion of fuel 
  • F23L9/02—Passages or apertures for delivering secondary air for completing combustion of fuel  by discharging the air above the fire

Definitions

• TANGENTIAL FIRING SYSTEM filed in the names of Todd D. Hellewell, John Grusha and Michael S. McCartney.
• This invention relates to tangentially fired, fossil fuel furnaces, and more specifically, to overfire air systems for reducing the NO emissions from tangentially fired, pulverized coal furnaces.
• Pulverized coal has been successfully burned in suspension in furnaces by tangential firing methods for a long time.
• the tangential firing technique involves introducing the fuel and air into a furnace from the four corners thereof so that the fuel and air are directed tangent to an imaginary circle in the center of the furnace.
• This type of firing has many advantages, among them being good mixing of the fuel and the air, stable flame conditions, and long residence time of the combustion gases in the furnaces.
• thermal NO A oxides of nitrogen are created during fossil fuel combustion by two separate mechanisms which have been identified to be thermal NO A and fuel NOA.
• Thermal NOA results from the thermal fixation of molecular nitrogen and oxygen in the combustion air.
• the rate of formation of thermal NO is extremely sensitive to local flame temperature and somewhat less so to local concentration of oxygen.
• Virtually all thermal NO is formed at the region of the flame which is at the highest temperature.
• the thermal NO concentration is subsequently "frozen” at the level prevailing in the high temperature region by the thermal quenching of the combustion gases.
• the flue gas thermal NO concentrations are, therefore, between the equilibrium level characteristic of the peak flame temperature and the equilibrium level at the flue gas temperature.
• fuel NO derives from the oxidation of organically bound nitrogen in certain fossil fuels such as coal and heavy oil.
• the formation rate of fuel NO is strongly affected by the rate of mixing of the fuel and air stream in general, and by the local oxygen concentration in particular.
• the flue gas NO concentration due to fuel nitrogen is typically only a fraction, e.g., 20 to 60 percent, of the level which would result from complete oxidation of all nitrogen in the fuel. From the preceding it should thus now be readily apparent that overall NO formation is a function both of local oxygen levels and of peak flame temperatures.
• a furnace is provided in which pulverized coal is burned in suspension with good mixing of the coal and air, as in the case of the now abandoned U. S. patent application, which has been the subject of discussion hereinabove.
• all of the advantages previously associated with tangentially fired furnaces are obtained, by having a swirling, rotating fireball in the furnace. The walls are protected by a blanket of air, reducing slagging thereof.
• auxiliary air is directed at a circle of larger diameter than that of the fuel, thus forming a layer of air adjacent the walls.
• overfire air consisting essentially of all of the excess air supplied to the furnace, is introduced into the furnace at a level considerably above all of the primary and auxiliary air introduction levels, with the overfire air being directed tangentially to an imaginary circle, and in a direction opposite to that of the auxiliary air.
• Yet another such change resulted in the arrangement for firing pulverized coal as a fuel with low NO emissions that forms the subject matter of U.
• the gaseous mixtures of primary air and pulverized fuel injected by the first and second pulverized fuel injection compartments of the apparatus are mixed in such proportions as to reduce the NO production.
• the primary air-pulverized fuel mixture from the second pulverized fuel injection compartment which alone can hardly be ignited stably, is allowed to coexist with the flame of the readily ignitible mixture from the first pulverized fuel injection compartment to ensure adequate ignition and combustion.
• An apparatus is thus allegedly provided for firing pulverized fuel with stable ignition and low NO production.
• the apparatus in accordance with the teachings of U. S. Patent Number 4,669,398 is characterized in that additional compartments for issuing an inert fluid are disposed, one for each, in spaces provided between the three compartments.
• the gaseous mixtures of primary air and pulverized fuel are thus kept from interfering with each other by a curtain of the inert fluid from one of the inert fluid injection compartments, and the production of NO ⁇ from the gaseous mixtures that are discharged from the first and second pulverized fuel injection compartments allegedly can be minimized.
• a furnace is fired with pulverized coal in a manner that reduces the peak temperature in the furnace while still maintaining good flame stability and complete combustion of the fuel.
• the manner in which this is accomplished is as follows. Pulverized coal is conveyed in an air stream towards the furnace. In the course of being so conveyed, the stream is separated into two portions, with one portion being a fuel rich portion and the other portion being a fuel lean portion. The fuel rich portion is introduced into the furnace in a first zone. Air is also introduced into the first zone in a quantity insufficient to support complete combustion of all of the fuel in the fuel rich portion.
• the fuel lean portion is introduced into the furnace in a second zone. Also, air is introduced into the second zone in a quantity such that there is excess air over that required for combustion of all of the fuel within the furnace. Lastly, lime is introduced into the furnace simultaneously with the fuel so as to minimize the peak temperature within the furnace and so as to also minimize the formation of NO and SOx., in the combustion g 3 ases,
• overfire air The theory of NO emissions reduction by overfire air is as follows. Operation with overfire air inhibits the rate of NO formation by both atmospheric nitrogen fixation (thermal N0 ⁇ ) and fuel nitrogen oxidation (fuel NO ).
• thermal N0 ⁇ atmospheric nitrogen fixation
• fuel NO fuel nitrogen oxidation
• overfire air reduces the total oxygen available in the primary flame zone.
• fuel nitrogen undergoes a recombination reaction to form molecular nitrogen, N 2 , rather than nitrogen oxide, simply due to insufficient oxygen in this zone and the intense competition with carbon species for the available oxygen.
• overfire air is through one or two closely grouped ports at a single fixed elevation at the top of the windbox, referred to as close-coupled overfire air, or at a higher elevation, referred to as separated overfire air.
• close-coupled overfire air or at a higher elevation
• separated overfire air Typical application of overfire air is through one or two closely grouped ports at a single fixed elevation at the top of the windbox, referred to as close-coupled overfire air, or at a higher elevation, referred to as separated overfire air.
• Experimental testing has shown a significant reduction in NO with fossil fuel firing when, for a fixed total quantity of overfire air, the overfire air is introduced partly through close-couple overfire air ports and partly through separated overfire air ports.
• experimental testing has shown that there exists a most favorable distribution of overfire air between the close coupled overfire air ports and the separated overfire air ports.
• this most favorable distribution has 1/3 of the overfire air flowing through the close coupled overfire air ports and 2/3 of the overfire air flowing through the separated overfire air ports.
• the manner in which overfire air is introduced into a furnace such that the air mixes with furnace gases in a controlled and thorough manner is also critical to maximizing overfire air effectiveness.
• Test data has shown that improvements in NO emissions are attainable when the overfire air is injected from each furnace corner through two, three or more compartments with each compartment introducing a portion of the total overfire air flow at different firing angles such as to achieve a horizontal "spray” or “fan” distribution of air over the furnace plan area as compared to when other injection patterns are utilized for purposes of injecting the overfire air into the furnace.
• furnace outlet conditions are also improved inasmuch as a more uniform flame pattern is created at the vertical outlet plane of the furnace. All tangentially fired, fossil fuel furnaces have a nonunifor flow pattern in the convective pass due to the tangential lower furnace flow pattern.
• overfire air mixing with the furnace gases can be had by introducing the overfire air at high momentum.
• the overfire air is introduced at velocities significantly above those typically employed in prior art firing systems, e.g., 200 to 300 ft./sec. versus 100 to 150 ft./sec.
• a boost fan may be needed to attain these higher overfire air velocities.
• an object of the present invention to provide a new and improved advanced overfire air system for NO control which is designed for use in a firing system of the type that is employed in fossil fuel-fired furnaces.
• Another object of the present invention is to provide such an advanced overfire air system for NO A control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces characterized in that the advanced overfire air system involves the use of multi-elevations of overfire air compartments consisting of close coupled overfire air compartments and separated overfire air compartments.
• a still another object of the present invention is to provide such a multi-elevation advanced overfire air system for NO A control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that there is a predetermined most favorable distribution of overfire air between the close coupled overfire air compartments and the separated overfire air compartments.
• a further object of the present invention is to provide such an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system involves the use of a multi-angle injection pattern.
• a still further object of the present invention is to provide such an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that in accordance with the multi-angle injection pattern thereof a portion of the total overfire air flow is introduced at different firing angles such as to achieve a horizontal "spray” or "fan” distribution of overfire air over the plan area of the furnace.
• an object of the present invention is to provide such an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system involves the injection of overfire air into the furnace at velocities significantly higher than those utilized heretofore in prior art firing systems.
• Yet a further object of the present invention is to provide such an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces such that through the use thereof no additions, catalysts or added premium fuel costs are needed for the operation thereof.
• Yet another object of the present invention is to provide such an advanced overfire air system for NO A control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system is totally compatible with other emission reduction-type systems such as limestone injection systems, reburn systems and selective catalytic reduction (SCR) systems that one might seek to employ in order to accomplish additional emission reduction.
• emission reduction-type systems such as limestone injection systems, reburn systems and selective catalytic reduction (SCR) systems that one might seek to employ in order to accomplish additional emission reduction.
• Yet still another object of the present invention is to provide such an advanced overfire air system for N0 ⁇ control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system is equally well suited for use either in new applications or in retrofit applications.
• an advanced overfire air system for NO control which is designed for use in a firing system of the type that is particularly suited for employment in fossil fuel-fired furnaces embodying a burner region.
• the subject advanced overfire air system includes multi-elevations of overfire air compartments. These multi- elevations of overfire air compartments consist of a plurality of close coupled overfire air compartments and a plurality of separated overfire air compartments.
• the plurality of close coupled overfire air compartments are suitably supported at a first elevation within the burner region of the furnace.
• a close coupled overfire air nozzle is supported in mounted relation within each of the plurality of close coupled overfire air compartments.
• the plurality of separated overfire air compartments are suitably supported at a second elevation within the burner region of the furnace so as to be spaced from but aligned with the plurality of close coupled overfire air compartments.
• a plurality of separated overfire air nozzles are supported in mounted relation within the plurality of separated overfire air compartments such that the plurality of separated overfire air nozzles extend at different angles relative to each other whereby the overfire air exiting therefrom establishes a horizontal "spray” or "fan” distribution of overfire air over the plan area of the burner region of the furnace.
• An overfire air supply means is operatively connected to both the close coupled overfire air nozzles and to the separated overfire air nozzles for supplying overfire air thereto in accordance with a predetermined most favorable distribution of overfire air therebetween and for supplying overfire air through the separated overfire air nozzles into the burner region of the furnace at velocities significantly higher than the velocities employed heretodate in prior art firing systems to inject overfire air into a furnace.
• a method of operating an advanced overfire air system for NO control which is designed for use in a firing system of the type that is particularly suited for employment in fossil fuel-fired furnaces embodying a burner region.
• the subject method of operating an advanced overfire air system for NO control includes the steps of injecting close coupled overfire air into the burner region of the furnace at a first elevation thereof and of injecting separated overfire air into the burner region of the furnace at a second elevation thereof in accordance with a predetermined most favorable distribution of overfire air between the first elevation and the second elevation, and such that the overfire air being injected into the burner region of the furnace at the second elevation thereof establishes a horizontal "spray” or "fan” distribution of overfire air over the plan area of the burner region of the furnace and such that the overfire air being injected into the burner region of the furnace at the second elevation thereof is injected into the burner region of the furnace at velocities significantly higher than the velocities employed heretodate in prior art firing systems to inject overfire air into a furnace.
• Figure 1 is a diagrammatic representation in the nature of a vertical sectional view of a fossil fuel-fired furnace embodying an advanced overfire air system for NO control constructed in accordance with the present invention
• Figure 2 is a diagrammatic representation in the nature of a vertical sectional view of a firing system of the type employed in tangentially fired, fossil-fuel furnaces illustrating the embodiment therein of an advanced overfire air system for NO control constructed in accordance with the present invention
• Figure 3 is a graphical depiction of the effect on N0 ⁇ when using an advanced overfire air system constructed in accordance with the present invention wherein there is a predetermined apportionment of the overfire air between close coupled overfire air and separated overfire air;
• Figure 4 is a plan view of the horizontal "spray” or “fan” distribution pattern for the overfire air which is employed in an advanced overfire air system constructed in accordance with the present invention
• Figure 5 is a graphical depiction of the effect on N0 ⁇ of using an advanced overfire air system constructed in accordance with the present invention wherein the overfire air is distributed in accordance with the horizontal "spray” or “fan” distribution pattern illustrated in Figure 4;
• Figure 6 is a graphical depiction of the effect on NO of using an advanced overfire air system constructed in accordance with the present invention wherein the overfire air is injected into the furnace at high velocities.
• a firing system generally designated by the reference numeral 12 in Figure 1 of the drawing
• an advanced overfire air system generally designated by the reference numeral 14 in Figure 1 of the drawing, constructed in accordance with the present invention such that in accordance with the present invention the advanced overfire air system 14 is capable of being installed in the furnace 10 as part of the firing system 12 and when so installed therein is operative for reducing the N0 ⁇ emissions from the fossil fuel-fired furnace 10, it is deemed to be sufficient that there be presented herein merely a description of the nature of the components of the fossil fuel-fired furnace 10 with which the aforesaid firing system 12 and the aforesaid advanced overfire air system 14 cooperate.
• the fossil fuel-fired furnace 10 as illustrated therein includes a burner region, generally designated by the reference numeral 16.
• Both the horizontal pass 18 and the rear gas pass 20 commonly contain other heat exchanger surface (not shown) for generating and super heating steam, in a manner well-known to those skilled in this art.
• the steam commonly is made to flow to a turbine (not shown), which forms one component of a turbine/generator set (not shown), such that the steam provides the motive power to drive the turbine (not shown) and thereby also the generator (not shown), which in known fashion is cooperatively associated with the turbine (not shown), such that electricity is thus produced from the generator (not shown).
• the advanced overfire air system 14 is designed to be utilized in a firing system, such as the firing system 12, so that when the firing system 12 in turn is utilized in a furnace, such as the fossil fuel-fired furnace 10 of Figure 2 of the drawing, the advanced overfire air system 14 is operative to reduce the NO emissions from the fossil fuel-fired furnace 10.
• the firing system 12 includes a housing preferably in the form of a windbox denoted by the reference numeral 22 in Figures 1 and 2 of the drawing.
• the windbox 22 in a manner well-known to those skilled in this art is supported by conventional support means (not shown) in the burner region 16 of the fossil fuel-fired furnace 10 such that the longitudinal axis of the windbox 22 extends substantially in parallel relation to the longitudinal axis of the fossil fuel-fired furnace 10.
• a first air compartment denoted generally by the reference numeral 24 in Figure 2 of the drawing, is provided at the lower end of the windbox 22.
• An air nozzle denoted by the reference numeral 26, is supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the air compartment 24.
• An air supply means which is illustrated schematically in Figure 1 of the drawing wherein the air supply means is denoted generally by the reference numeral 28, is operatively connected in a manner to be more fully described hereinafter to the air nozzle 26 whereby the air supply means 28 supplies air to the air nozzle 26 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10.
• the air supply means 28 includes a fan seen at 30 in Figure 1 of the drawing, and the air ducts denoted by the reference numeral 32 which are connected in fluid flow relation to the fan 30 on the one hand and on the other hand, as seen schematically at 34 in Figure 1 of the drawing, to the air nozzle 26 through separate valves and controls (not shown).
• a first fuel compartment denoted generally by the reference numeral 36 in Figure 2 of the drawing, is provided in the windbox 22 within the lower portion thereof such as to be located substantially in juxtaposed relation to the air compartment 24.
• a first fuel nozzle denoted by the reference numeral 38 in Figure 2 of the drawing, is supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the fuel compartment 36.
• a fuel supply means which is illustrated schematically in Figure 1 of the drawing wherein the fuel supply means is denoted generally by the reference numeral 40, is operatively connected in a manner to be more fully described hereinafter to the fuel nozzle 38 whereby the fuel supply means 40 supplies fuel to the fuel nozzle 38 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10.
• the fuel supply means 40 includes a pulverizer, seen at 42 in Figure 1 of the drawing, wherein the fossil fuel that is to be burned in the fossil fuel-fired furnace 10 undergoes pulverization in a manner well-known to those skilled in this art, and the fuel ducts, denoted by the reference numeral 44, which are connected in fluid flow relation to the pulverizer 42 on the one hand and on the other hand, as seen schematically at 46 in Figure 1 of the drawing, to the fuel nozzle 38 through separate valves and controls (not shown).
• the pulverizer 42 is operatively connected to the fan 30 such that air is also supplied from the fan 30 to the pulverizer 42 whereby the fuel supplied from the pulverizer 42 to the fuel nozzle 38 is transported through the fuel ducts 44 in an air stream in a manner which is well-known to those skilled in this art.
• the windbox 22 is also provided with a second air compartment, denoted generally by the reference numeral 48 in Figure 2 of the drawing.
• the air compartment 48 as best understood with reference to Figure 2 of the drawing, is provided in the windbox 22 such as to be located substantially in juxtaposed relation to the fuel compartment 36.
• the air nozzle 50 is operatively connected to the air supply means 28, the latter having been described herein previously, through the air ducts 32, which as best understood with reference to Figure 1 of the drawing are connected in fluid flow relation to the fan 30 on the one hand and on the other hand, as seen schematically at 52 in Figure 1 of the drawing, to the air nozzle 50 through separate valves and controls (not shown) whereby the air supply means 28 supplies air to the air nozzle 50 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10 in the same manner as that which has been described herein previously in connection with the discussion hereinbefore of the air nozzle 26.
• a second fuel compartment denoted generally by the reference numeral 54 in Figure 2 of the drawing, is provided in the windbox 22 such as to be located substantially in juxtaposed relation to the air compartment 48.
• a second fuel nozzle denoted generally by the reference numeral 56 in Figure 2 of the drawing, is supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the fuel compartment 54.
• the fuel nozzle 56 is operatively connected to the fuel supply means 40, the latter having been described previously herein, through the fuel ducts 44, which as best understood with reference to Figure 1 of the drawing, are connected in fluid flow relation on the one hand to the pulverizer 42 wherein the fossil fuel that is to be burned in the fossil fuel-fi ed furnace 10 undergoes pulverization in a manner well-known to those skilled in the art, and on the other hand, as seen schematically at 58 in Figure 1 of the drawing, to the fuel nozzle 56 through separate valves and controls (not shown) whereby the fuel supply means 40 supplies fuel to the fuel nozzle 56 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10 in the same manner as that which has been described herein previously in connection with the discussion hereinbefore of the fuel nozzle 38.
• the pulverizer 42 is operatively connected to the fan 30 such that air is also supplied from the fan 30 to the pulverizer 42 whereby the fuel supplied from the pulverizer 42 to the fuel compartment 54 is transported through the fuel ducts 44 in an air stream in a manner which is well-known to those skilled in the art.
• a third air compartment denoted generally by the reference numeral 60 in Figure 2 of the drawing.
• the air compartment 60 as best understood with reference to Figure 2 of the drawing, is provided in the windbox 22 such as to be located substantially in juxtaposed relation to the fuel compartment 54.
• An air nozzle denoted by the reference numeral 62 in Figure 2 of the drawing, is supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the air compartment 60.
• the air nozzle 62 is operatively connected to the air supply means 28, the latter having been described herein previously, through the air ducts 32, which as best understood with reference to Figure 1 of the drawing are connected in fluid flow relation to the fan 30 on the one hand and. on the other hand, as seen schematically at 64 in Figure 1 of the drawing, to the air nozzle 62 through separate valves and controls (not shown) whereby the air supply means 28 supplies air to the air nozzle 62 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10 in the same manner as that which has been described herein previously in connection with the discussion hereinbefore of the air nozzles 26 and 50.
• the firing system 12 in accordance with the embodiment thereof illustrated in Figures 1 and 2 of the drawing, further includes a third fuel compartment, denoted generally by the reference numeral 66 in Figure 2 of the drawing.
• the fuel compartment 66 is provided in the windbox 22 such as to be located substantially in juxtaposed relation to the air compartment 60.
• a third fuel nozzle, denoted by the reference numeral 68 in Figure 2 of the drawing, is supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the fuel compartment 66.
• the fuel nozzle 68 is operatively connected to the fuel supply means 40, the latter having been described previously herein, through the fuel ducts 44, which as best understood with reference to Figure 1 of the drawing are connected in fluid flow relation on the one hand to the pulverizer 42 wherein the fossil fuel that is to be burned in the fossil fuel-fired furnace 10 undergoes pulverization in a manner well-known to those skilled in the art, and on the other hand as seen schematically at 70 in Figure 1 of the drawing to the fuel nozzle 68 through separate valves and controls (not shown) whereby the fuel supply means 40 supplies fuel to the fuel nozzle 68 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10 in the same manner as that which has been described herein previously in connection with the discussion hereinbefore of the fuel nozzles 38 and 56.
• the pulverizer 42 as can be seen with reference to Figure 1 of the drawing is operatively connected to the fan 30 such that air is also supplied from the fan 30 to the pulverizer 42 whereby the fuel supplied from the pulverizer 42 to the fuel compartment 66 is transported through the fuel ducts 44 in an air stream in a manner well-known to those skilled in the art.
• a fourth air compartment denoted generally by the reference numeral 72 in Figure 2 of the drawing.
• the fourth air compartment 72 is provided in the windbox 22 such as to be located substantially in juxtaposed relation to the fuel compartment 66.
• a fourth air nozzle denoted by the reference numeral 74 in Figure 2 of the drawing, is supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the air compartment 72.
• the air nozzle 74 is operatively connected to the air supply means 28, the latter having been described herein previously, through the air ducts 32, which as best understood with reference to Figure 1 of the drawing are connected in fluid flow relation to the fan 30 on the one hand and on the other hand, as seen schematically at 76 in Figure 1 of the drawing, to the air nozzle 74 through separate valves and controls (not shown) whereby the air supply means 28 supplies air to the air nozzle 74 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10 in the same manner as that which has been described herein previously in connection with the discussion hereinbefore of the air nozzles 26,50 and 62.
• a fourth fuel compartment denoted generally by the reference numeral 78 in Figure 2 of the drawing, is provided in the windbox 22 such as to be located substantially in juxtaposed relation to the air compartment 72.
• a fourth fuel nozzle denoted by the reference numeral 80 in Figure 2 of the drawing, is supported in mounted rel tion, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the fuel compartment 78.
• the fuel nozzle 80 is operatively connected to the fuel supply means 40, the latter having been described previously herein, through the fuel ducts 44, which as best understood with reference to Figure 1 of the drawing are connected in fluid flow relation on the one hand to the pulverizer 42 wherein the fossil fuel that is to be burned in the fossil fuel-fired furnace 10 undergoes pulverization in a manner well-known to those skilled in the art, and on the other hand as seen schematically at 82 in Figure 1 of the drawing to the fuel nozzle 80 through separate valves and controls (not shown) whereby the fuel supply means 40 supplies fuel to the fuel nozzle 80 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10 in the same manner as that which has been described herein previously in connection with the discussion hereinbefore of the fuel nozzles 38,56 and 68.
• the pulverizer 42 is operatively connected to the fan 30 such that air is also supplied from the fan 30 to the pulverizer 42 whereby the fuel supplied from the pulverizer 42 to the fuel compartment 78 is transported through the fuel ducts 44 in an air stream in a manner well-known to those skilled in the art.
• the advanced overfire air system 14 in accordance with the present invention includes a pair of close coupled overfire air compartments, denoted generally by the reference numerals 84 and 86, respectively, in Figure 2 of the drawing.
• the close coupled overfire air compartments 84 and 86 are provided in the windbox 22 of the firing system 12 within the upper portion of the windbox 22 such as to be located substantially in juxtaposed relation to the air compartment 78, the latter having been the subject of discussion hereinbefore.
• a pair of close coupled overfire air nozzles denoted by the reference numerals 88 and 90, respectively, in Figure 2 of the drawing, are supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the pair of close coupled overfire air compartments such that the close coupled overfire air nozzle 88 is mounted in the close coupled overfire air compartment 84 and the close coupled overfire air nozzle 90 is mounted in the close coupled overfire air compartment 86.
• the close coupled overfire air nozzles 88 and 90 are each operatively connected to the air supply means 28, the latter having been described herein previously, through the air ducts 32, which as best understood with reference to Figure 1 of the drawing are connected in fluid flow relation to the fan 30 on the one hand and on the other hand as seen schematically at 92 in Figure 1 of the drawing to each of the close coupled overfire air nozzles 88 and 90 through separate valves and controls (not shown) whereby the air supply means 28 supplies air to each of the close coupled overfire air nozzles 88 and 90 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10.
• the advanced overfire air system 14 further includes a plurality of separated overfire air compartments, which are suitably supported, through the use of any conventional form of support means (not shown) suitable for use for such a purpose, within the burner region 16 of the furnace 10 so as to be spaced from the close coupled overfire air compartments 84 and 86, and so as to be substantially aligned with the longitudinal axis of the windbox 22.
• the aforementioned plurality of separated overfire air compartments in accordance with the preferred embodiment of the invention, comprises in number three such compartments, which are denoted generally in Figure 2 of the drawing by the reference numerals 94,96 and 98, respectively.
• a plurality of separated overfire air nozzles are supported in mounted relation, through the use of any conventional form of mounting means (not shown) suitable for use for such a purpose, within the plurality of separated overfire air compartments 94,96 and 98 such that the separated overfire air nozzle 100 is mounted for both the vertical (tilting) and horizontal (yaw) movement in the separated overfire air compartment 94, the separated overfire air nozzle 102 is mounted for both vertical (tilting) and horizontal (yaw) movement in the separated overfire air compartment 96, and the separated overfire air nozzle 104 is mounted for both vertical (tilting) and horizontal (yaw) movement in the separated overfire air compartment 98.
• the plurality of separated overfire air nozzles 100,102 and 104 are each operatively connected to the air supply means 28, the latter having been described herein previously, through the air ducts 32, which as best understood with reference to Figure 1 of the drawing are connected in fluid flow relation to the fan 30 on the one hand and on the other hand as seen schematically at 106 in Figure 1 of the drawing to each of the separated overfire air nozzles 100,102 and 104 through separate valves and controls (not shown) whereby the air supply means 28 supplies air to each of the separated overfire air nozzles 100,102 and 104 and therethrough into the burner region 16 of the fossil fuel-fired furnace 10.
• air is introduced into the burner region 16 of the fossil fuel-fired furnace 10 through the air compartments 24,48,60 and 72
• fossil fuel is introduced into the burner region 16 of the fossil fuel-fired furnace 10 through the fossil fuel compartments 36,54,66 and 78.
• combustion of the fossil fuel that is introduced thereinto through the fossil fuel compartments 36,54,66 and 78 and of the air that is introduced thereinto through the air compartments 24,48,60 and 72 is initiated in the burner region 16 of the fossil fuel-fired furnace 10 combustion of the fossil fuel that is introduced thereinto through the fossil fuel compartments 36,54,66 and 78 and of the air that is introduced thereinto through the air compartments 24,48,60 and 72.
• the hot gases give up heat in a manner well-known to those skilled in this art to the fluid flowing through the tubes (not shown) that in conventional fashion line all four of the walls of the fossil fuel-fired furnace 10.
• these hot gases exit the fossil fuel-fired furnace 10 through the horizontal pass 18 of the fossil fuel-fired furnace 10, which in turn leads to the rear gas pass 20 of the fossil fuel-fired furnace 10.
• the horizontal pass 18 and the rear gas pass 20 commonly each contain other heat exchanger surface (not shown) for generating and super heating steam, in a manner well- known to those skilled in this art. Thereafter, this steam commonly is made to flow to a turbine (not shown), which forms one component of a turbine/generator set (not shown), such that the steam provides the motive power to drive the turbine (not shown) and thereby also the generator (not shown), which in known fashion is cooperatively associated with the turbine (not shown), such that electricity is thus produced from the generator (not shown).
• the objective sought to be achieved through the use thereof is that of inhibiting the rate of NO formation by both atmospheric nitrogen fixation (thermal NO ) and fuel nitrogen (fuel NO ). This is accomplished by reducing the total oxygen that is available in the primary flame zone.
• overfire air is introduced through one or two closely grouped compartments at a single fixed elevation of the burner region 16 of the fossil fuel-fired furnace 10 at the top of the windbox 22, and through one or more additional compartments located at a higher elevation.
• the closely grouped compartments are seen at 84 and 86 in Figure 2 of the drawing, and the compartments located at the higher elevation, commonly referred to in the industry as separated overfire air compartments, are seen at 94,96 and 98 in Figure 2 of the drawing.
• One of the characteristics which the advanced overfire air system 14 embodies in accordance with the present invention is that the overfire air is introduced into the burner region 16 of the fossil fuel-fired furnace 10 partly through the close coupled overfire air compartments 84 and 86 and partly through the separated overfire air compartments 94,96 and 98 such that there exists a predetermined most favorable distribution of the overfire air between close coupled overfire air and separated overfire air.
• Figure 3 is a graphical depiction of the effect on N0 ⁇ when using an advanced overfire air system constructed in accordance with the present invention wherein there is a predetermined apportionment of the overfire air between close coupled overfire air and separated overfire air.
• the line denoted by the reference numeral 108 in Figure 3 represents a baseline plot of the N0 ⁇ ppm levels from a furnace, such as the fossil fuel-fired furnace 10, when operating with a firing system, such as the firing system 12.
• the line denoted by the reference numeral 110 in Figure 3 represents a plot of the NO ppm levels from a furnace, such as the fossil fuel-fired furnace 10, when operating with a firing system, such as the firing system 12, and with 0% overfire air.
• the line denoted therein by the reference numeral 112 represents a plot of the NO ppm levels from a furnace, such as the fossil fuel- fired furnace 10, when operating with 20% overfire air and wherein all 20% of the overfire air is introduced into the furnace as close coupled overfire.
• the line denoted in Figure 3 by the reference numeral 114 represents a plot of the NO ppm levels from a furnace, such as the fossil fuel-fired furnace 10, when operating with 20% overfire air and wherein all 20% of the overfire air is introduced into the furnace as separated overfire air.
• the point denoted therein by the reference numeral 116 is a plot of the NO ppm level from a furnace, such as the fossil fuel-fired furnace 10, when operating with a firing system 12 with which an advanced overfire air system 14 constructed in accordance with the present invention is cooperatively associated and with 20% overfire air, and wherein of the 20% overfire air in accordance with a most favorable distribution thereof 9% of this overfire air is introduced as close coupled overfire air and 11% of the overfire air is introduced as separated overfire air.
• a second characteristic which the advanced overfire air system 14 embodies in accordance with the present invention is that the separated overfire air is injected into the burner region 16 of the fossil fuel-fired furnace 10 from each of the four corners thereof through a plurality, e.g., two, three or more compartments with each compartment introducing a portion of the total separated overfire air flow at different firing angles, which angles are established by moving the separated overfire air nozzles 94,96 and 98 vertically (tilting) and/or horizontally (yawing), such as to achieve a horizontal "spray” or "fan” distribution of separated overfire air over the furnace plan area.
• the four corners 10a,10b,10c and lOd of the fossil fuel-fired furnace 10 are each provided with separated overfire air compartments 94,96 and 98.
• the separated overfire air that is injected into the burner region 16 of the fossil fuel-fired furnace 10 from each of the four corners 10a,10b,10c and lOd thereof through the separated overfire air compartments 94,96 and 98 located thereat is injected at a different firing angle, the latter being denoted in Figure 4 by means of the reference numerals 118,120 and 122, respectively, and wherein for ease of reference the same numerals are utilized in connection with each of the four corners 10a,10b,10c and lOd of the fossil fuel-fired furnace 10.
• the injection into the burner region 16 of the fossil fuel-fired furnace 10 at the different firing angles denoted by the reference numerals 118,120 and 122 in Figure 4 has the effect of producing a horizontal "spray” or "fan” distribution of the separated overfire air over the furnace plan area.
• the separated overfire air that is injected into the burner region 16 of the fossil fuel-fired furnace 10 at each of the different firing angles 118,120 and 122 follows the path denoted by the reference numerals 124,126 and 128, respectively.
• Figure 5 is a graphical depiction of the effect on NO of using an advanced overfire air system constructed in accordance with the present invention wherein the overfire air is distributed in accordance with the horizontal "spray" or "fan” distribution pattern illustrated in Figure 4.
• the point denoted therein by the reference numeral 130 is a plot of the N0 ⁇ ppm level from a furnace, such as the fossil fuel-fired furnace 10, when operating with a firing system, such as the firing system 12, and wherein all of the separated overfire air that is injected through the separated overfire air compartments is injected into the burner region 16 of the fossil fuel-fired furnace 10 at the same firing angle, i.e., at an angle of +15° such that the separated overfire air is injected so as to be co-rotational with the fuel and air that is being injected into the burner region 16 of the fossil fuel-fired furnace 10 through the fuel compartments 38,54,66 and 78 and the air compartments 24,48,60 and 72, respectively.
• the point denoted in Figure 5 by the reference numeral 132 is a plot of the NO ppm level from a furnace, such as the fossil fuel-fired furnace 10, when operating with a firing system, such as the firing system 12, and wherein all of the separated overfire air that is injected through the separated overfire air compartment is injected into the burner region 16 of the fossil fuel-fired furnace 10 at the same firing angle, i.e, at an angle of -15" such that the separated overfire air is injected so as to be counter rotational with the fuel and air that is being injected into the burner region 16 of the fossil fuel-fired furnace 10 through the fuel compartments 38,54,66 and 78 and the air compartments 24,48,60 and 72, respectively.
• the point denoted therein by the reference numeral 134 is a plot of the N0 ⁇ ppm level from a furnace, such as the fossil fuel-fired furnace 10, when operating with a firing system 12 with which an advanced overfire air system 14 constructed in accordance with the present invention is cooperatively associated and wherein all of the separated overfire air is injected through each of the separated overfire air compartments 94,96 and 98 at a different firing angle such that the horizontal "spray” or "fan” distribution of separated overfire air that is depicted in Figure 4 of the drawing is achieved over the furnace plan area.
• the firing angles that are employed for this purpose for the separated overfire air compartments 94,96 and 98 are +15°, 0' and -15°.
• a third characteristic which the advanced overfire air system 14 embodies in accordance with the present invention is that the separated overfire air is injected into the burner region 16 of the fossil fuel-fired furnace 10 at velocities significantly higher than those utilized heretofore in prior art firing systems, e.g., 200 to 300 ft./sec. versus 100 to 150 ft./sec.
• the advantages that accrue from the injection of the separated overfire air at such increased velocities are best understood with reference to Figure 6 of the drawing.
• Figure 6 is a graphical depiction of the effect on NO of using an advanced overfire air system constructed in accordance with the present invention wherein the overfire air is injected into the furnace at high velocities.
• the line denoted by the reference numeral 136 in Figure 6 represents a plot of the NO ppm levels from a furnace, such as the fossil fuel- fired furnace 10, when operating with a firing system, such as the firing system 12 and wherein the overfire air is injected at low velocities, i.e., at the velocities commonly utilized heretofore in prior art firing systems.
• the line denoted by the reference numeral 138 in Figure 6 represents a plot of the NO ppm levels from a furnace, such as the fossil fuel-fired furnace 10, when operating with a firing system 12 with which an advanced overfire air system 14 constructed in accordance with the present invention is cooperatively associated and wherein the separated overfire air injected into the burner region 16 of the fossil fuel-fired furnace 10 through the separated overfire air compartments 94,96 and 98 is injected at velocities significantly higher than those utilized heretofore in prior art firing systems, e.g., 200 to 300 ft./sec. versus 100 to 150 ft./sec.
• a new and improved advanced overfire air system for NO control which is designed for use in a firing system of the type that is employed in fossil fuel-fired furnaces.
• an advanced overfire air system for NO control that is designed for use in a firing system of the type that is employed in tangentially fired, fossil fuel furnaces.
• an advanced overfire air system for N0 ⁇ control for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces such that through the use thereof N0 ⁇ emissions are capable of being reduced to levels that are at least equivalent to, if not better than, that which is currently being contemplated as the standard for the United States in the legislation being proposed.
• an advanced overfire air system for NO A control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces characterized in that the advanced overfire air system involves the use of multi-elevations of overfire air compartments consisting of close coupled overfire air compartments and separated overfire air compartments.
• an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that there is a predetermined most favorable distribution of overfire air between the close coupled overfire air compartments and the separated overfire air compartments.
• an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system involves the use of a multi-angle injection pattern.
• an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that in accordance with the multi-angle injection pattern thereof a portion of the total overfire air flow is introduced at different angles such as to achieve a horizontal "spray” or “fan” distribution of overfire air over the plan area of the furnace.
• an advanced overfire air system for NO A control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system involves the injection of overfire air into the furnace at velocities significantly higher than those utilized heretofore in prior art firing systems.
• an advanced overfire air system for NO ⁇ control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces such that through the use thereof no additions, catalysts or added premium fuel costs are needed for the operation thereof.
• an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system is totally compatible with other emission reduction-type systems such as limestone injection systems, reburn systems and selective catalytic reduction (SCR) systems that one might seek to employ in order to accomplish additional emission reduction.
• an advanced overfire air system for NO control that is designed for use in a firing system of the type employed in tangentially fired, fossil fuel furnaces and which is characterized in that the advanced overfire air system is equally well suited for use either in new applications or in retrofit applications.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Exhaust Gas After Treatment (AREA)
• Control Of The Air-Fuel Ratio Of Carburetors (AREA)
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• 1991
  • 1991-06-24 BR BR919107060A patent/BR9107060A/pt active Search and Examination
  • 1991-06-24 EP EP91912984A patent/EP0554254B1/en not_active Expired - Lifetime
  • 1991-06-24 ES ES91912984T patent/ES2092573T3/es not_active Expired - Lifetime
  • 1991-06-24 DE DE69121579T patent/DE69121579D1/de not_active Expired - Lifetime
  • 1991-06-24 HU HU9300808A patent/HUT65491A/hu unknown
  • 1991-06-24 WO PCT/US1991/004440 patent/WO1992008078A1/en active IP Right Grant
  • 1991-06-24 JP JP3512292A patent/JP2731794B2/ja not_active Expired - Fee Related
  • 1991-06-24 AU AU81086/91A patent/AU646677B2/en not_active Ceased
  • 1991-06-24 CA CA002091341A patent/CA2091341C/en not_active Expired - Lifetime
  • 1991-07-15 ZA ZA915500A patent/ZA915500B/xx unknown
  • 1991-08-06 MX MX9100537A patent/MX9100537A/es not_active IP Right Cessation
  • 1991-08-16 YU YU141991A patent/YU141991A/sh unknown
  • 1991-10-29 CS CS913277A patent/CS327791A3/cs unknown
• 1993
  • 1993-04-28 KR KR93701252A patent/KR970009483B1/ko not_active IP Right Cessation
  • 1993-04-29 FI FI931941A patent/FI931941A/fi not_active Application Discontinuation

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