Patent Application
20210080101
The present invention relates to burner apparatuses and methods for reducing NOx emissions from heaters, boilers, incinerators, other fired heating systems, and other combustion systems of the type used in refineries, power plants, and chemical plants, and in other industrial services and facilities.
A continuing need exists for burners and burner combustion methods which will significantly reduce NOx emissions from fired heaters, boilers, incinerators, and other combustion systems used in industrial processes. The improved burners will also preferably provide flame lengths, turndown ratios, and stability levels which are at least as good as or better than those provided by the current burner designs.
For burners which are used in industrial applications, if the burner fuel is thoroughly mixed with air and combustion occurs under ideal conditions, the resulting combustion products are primarily carbon dioxide and water vapor. However, when the fuel is burned under less than ideal conditions, e.g., at a high flame temperature, nitrogen present in the combustion air reacts with oxygen to produce nitrogen oxides (NOx). Other conditions being equal, NOx production increases as the temperature of the combustion process increases. NOx emissions are generally considered to contribute to ozone depletion, acid rain, smog, and other environmental problems.
For gaseous fuels with no fuel bound nitrogen, thermal NOx is the primary mechanism for NOx production. Thermal NOx is produced when the flame reaches a high enough temperature to break the covalent N2 bond so that the resulting “free” nitrogen atoms bond with oxygen to form NOx.
Typically, the temperature of combustion is not great enough to break all of the N2 bonds. Rather, most of the nitrogen in the air stream passes through the combustion process and remains as diatomic nitrogen (N2) in the combustion products. However, some of the N2 will typically reach a high enough temperature in the high intensity regions of the flame to break the N2 bond and form “free” nitrogen. Once the covalent nitrogen bond is broken, the “free” nitrogen is available to bond with other atoms. Fortunately, the free nitrogen will most likely react with other free nitrogen atoms to form N2. However, if another free nitrogen atom is not available, the free nitrogen will react with oxygen to form NOx.
As the temperature of the burner flame increases, the stability of the N2 covalent bond decreases, causing increasing production of free nitrogen and thus also increasing the production of thermal NOx emissions. Consequently, in an ongoing effort to reduce NOx emissions, various types of burner designs and theories have been developed with the objective of reducing the peak flame temperature.
The varied requirements of refining, power generation, petrochemical processes, and other processes necessitate the use of numerous different types and configurations of burners. The approaches used to lower NOx emissions can differ from application to application. However, thermal NOx reduction is generally achieved by slowing the rate of combustion. Since the combustion process is a reaction between oxygen and the burner fuel, the objective of delayed combustion is typically to reduce the rate at which the fuel and oxygen mix together and burn. The faster the oxygen and the fuel mix together, the faster the rate of combustion and the higher the peak flame temperature.
Examples of different types of burner design approaches used for reducing NOx emissions have included:
The present invention provides a low NOx burner apparatus and method which satisfy the needs and alleviate the problems discussed above. The inventive burner apparatus and method provide a significantly increased amount internal flue gas recirculation (IFGR) while maintaining or improving the stability of the burner. The inventive burner and method will typically provide from about 16 to about 24 pounds of IFGR per pound of burner fuel and will provide significantly reduced NOx emissions levels in the range of from 12 ppmv to 5 ppmv or less. In addition, the inventive burner apparatus and method can be used in most types of fired heaters, boilers, incinerators, and other combustion systems used in industrial processes.
In one aspect, there is provided a burner apparatus for discharging a burner flame in a heating system having gaseous products of combustion therein. The burner apparatus preferably comprises at least: (i) a burner wall having a forward longitudinal end and an exterior, (ii) a flow passageway for air or other oxygen source which extends through and is at least mostly surrounded by the burner wall, the flow passageway having a discharge at the forward longitudinal end of the burner wall; (iii) a combustion zone of the burner apparatus which has a beginning end located substantially at the forward longitudinal end of the burner wall; (iv) a series of primary fuel ejection structures which are positioned outside of and which at least partially surround the flow passageway, the primary fuel ejection structures being located rearwardly of and radially outward from the forward longitudinal end of the burner wall and each of the primary fuel ejection structures being oriented to eject a primary fuel stream along a primary fuel flow path outside of the burner wall toward the combustion zone; (v) at least one primary radial impact structure which is provided on the exterior of the burner wall and is positioned in the primary fuel flow paths for contacting by at least a portion of the primary fuel stream ejected by each of the primary fuel ejection structures; (vi) a series of secondary fuel ejection structures which are positioned outside of and which at least partially surround the flow passageway, the secondary fuel ejection structures being located rearwardly of and radially outward from the primary fuel ejection structures and each of the secondary fuel ejection structures being oriented to eject a secondary fuel stream along a secondary fuel flow path outside of the burner wall toward the combustion zone; and (vii) at least one secondary radial impact structure which is provided on the exterior of the burner wall and is positioned rearwardly of the at least one primary radial impact structure, in the secondary fuel flow paths, for contacting by at least a portion of the secondary fuel stream ejected by each of the secondary fuel ejection structures.
In another aspect, the at least one primary radial impact structure on the exterior of the burner wall can optionally also be positioned in the secondary fuel flow paths for contacting by at least a portion of the secondary fuel steam ejected by each of the secondary fuel ejection structures.
In another aspect, the combustion zone of the inventive burner apparatus can optionally be a single stage combustion zone having only one combustion stage for combusting both the primary fuel streams ejected from the primary fuel ejection structures and the secondary fuel streams ejected from the secondary fuel ejection structures.
In another aspect, the inventive burner apparatus can optionally further include: (a) a series of tertiary fuel ejection structures which are positioned outside of and which at least partially surround the flow passageway, the tertiary fuel ejection structures being located rearwardly of and radially outward from the secondary fuel ejection structures and each of the tertiary fuel ejection structures being oriented to eject a tertiary fuel stream along a tertiary fuel flow path outside of the burner wall toward the combustion zone and (b) at least one tertiary radial impact structure which is provided on the exterior of the burner wall and is positioned rearwardly of the at least one secondary radial impact structure, in the tertiary fuel flow paths, for contacting by at least a portion of the tertiary fuel stream ejected by each of the tertiary fuel ejection structures.
In another aspect, there is provided a method of reducing NOx emissions from a burner apparatus. The method preferably comprises the steps of: (a) discharging air or other oxygen source into a combustion zone from a discharge opening of a flow passage which is at least partially surrounded by a burner wall, the discharge opening of the flow passage being located at a forward end of a burner wall, the burner wall having an exterior, and the combustion zone having a beginning end which is located substantially at the forward end of the burner wall; (b) ejecting primary fuel streams outside of the burner wall toward the combustion zone from a plurality of primary fuel ejection structures, wherein at least a portion of each of the primary fuel streams contacts at least one primary radial impact structure which is provided on the exterior of the burner wall; and (c) ejecting secondary fuel streams outside of the burner wall toward the combustion zone from a plurality of secondary fuel ejection structures, wherein the secondary fuel ejection structures are located rearwardly of and radially outward from the primary fuel ejection structures, at least a portion of each of the secondary fuel streams contacts at least one secondary radial impact structure which is provided on the exterior of the burner wall, and the at least one secondary radial impact structure is positioned rearwardly of the at least one primary radial impact structure.
In another aspect, at least a portion of each of the secondary fuel streams ejected in step (c) of the inventive method can optionally also contact the at least one primary radial impact structure.
In another aspect, the inventive method can also optionally include both (i) at least a portion of each of the primary fuel streams being delivered to and combusted at the beginning end of the combustion zone and (ii) at least a portion of each of the secondary fuel streams being delivered to and combusted at the beginning end of the combustion zone.
In another aspect, the inventive method can further include the step of ejecting tertiary fuel streams outside of the burner wall toward the combustion zone from a plurality of tertiary fuel ejection structures, wherein the tertiary fuel ejection structures are located rearwardly of and radially outward from the secondary fuel ejection structures, at least a portion of each of the tertiary fuel streams contacts at least one tertiary radial impact structure which is provided on the exterior of the burner wall, and the at least one tertiary radial impact structure is positioned rearwardly of the at least one secondary radial impact structure.
Further aspects, features, and advantages of the present invention will be apparent to those in the art upon examining the accompanying drawings and upon reading the following Detailed Description of the Preferred Embodiments.
Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the preferred embodiments and steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein are for purposes of description and not of limitation.
Also, unless otherwise specified, the inventive features, structures, and steps discussed herein can be advantageously employed using any number or type of fuel ejection tips or other structures. In addition, the inventive burners described herein can be single stage burners or burners using staged fuel and/or staged air designs.
An embodiment 2 of the burner apparatus provided by the present invention is illustrated in
The inventive burner 2 is shown as installed through the wall 34 of a combustion chamber 36. The inventive burner apparatus 2 can be used to heat the combustion chamber 36 of generally any type of fired heating system. The combustion chamber 36 is filled with the gaseous inert products of combustion (i.e., flue gas) 38 produced in the combustion chamber 36 by the burner combustion process. In addition, although the inventive burner apparatus 2 is illustrated in
The combustion air stream or other oxygen source 6 is received in the housing 4 of the inventive burner 2 and is directed into the rearward longitudinal end 28 of burner flow passageway 8. The quantity of combustion air or other oxygen source entering the housing 4 can be regulated, for example, by an air inlet damper 40. The oxygen source stream 6 can be provided to housing 4 as necessary by forced circulation, natural draft, a combination thereof, or in any other manner employed in the art. The oxygen source stream 6 will preferably be air which is delivered to the inventive burner assembly 2 by forced circulation, natural draft, a combination thereof.
As used herein and in the claims, unless otherwise stated, it will also be understood that the oxygen source stream 6 which travels through the flow passageway 8 of the inventive burner 2 can be, for example, 100% air or can be a mixture of combustion air and/or other oxygen source with one or more other components such as, but not limited to, (i) one or more externally recirculated inert (i.e., non-flammable) components such as flue gas, (ii) steam, (iii) CO2, and/or (iv) N2. However, the air or other oxygen source stream 6 preferably will not contain any fuel gas or other fuel material. In addition, except for one or more burner pilot assemblies 42a, 42b, 42c for initiating and maintaining combustion in the combustion zone 24 which projects from the forward end 30 of the burner wall 10, no fuel tips or other fuel ejection structures will preferably be located in or extend through the flow passageway 8 for the oxygen source stream 6.
Although other structures and materials of construction can alternatively be used, the burner wall 10 is preferably constructed of a high temperature refractory burner tile material.
As mentioned above, the inventive burner apparatus 2 includes two, three, four, or more series of surrounding fuel ejection structures wherein the fuel ejection structures in each series (a) are positioned outside of and radially surround, or at least partially surround, the flow passageway 8 for the oxygen source stream 6 and (b) eject gas or liquid fuel streams, preferably gas fuel streams, toward the combustion zone 24 which projects from the forward end 30 of the burner wall 10. Proceeding rearwardly from the forward end 30 of the burner wall 10, each succeeding series of surrounding fuel injection structures will preferably be located rearwardly of and radially outward from the preceding series of surrounding fuel injection structures.
By way of example, but not by way of limitation, the multiple series of fuel ejection structures used in the embodiment 2 of the inventive burner apparatus illustrated in
Each of the fuel ejection structures 12, 14, and 16 can have one or more ejection ports of any desired shape. Each fuel ejection structure 12, 14, and 16 will preferably have only a single ejection port, which will also preferably be circular in shape.
The primary fuel ejection structures 12 are configured and oriented to eject primary fuel streams 18 in free jet flow outside of the burner wall 10 along primary fuel flow paths 48 toward the combustion zone 24. The secondary fuel ejection structures 14 are configured and oriented to eject secondary fuel streams 20 in free jet flow outside of the burner wall 10 along secondary fuel flow paths 52 toward the combustion zone 24. The tertiary fuel ejection structures 16 are configured and oriented to eject tertiary fuel streams 22 in free jet flow outside of the burner wall 10 along tertiary fuel flow paths 56 toward the combustion zone 24.
As will be understood by those skilled in the art, the term “free jet,” as used herein and in the claims, refers to a jet flow issuing from a fuel tip, nozzle or other ejection structure into a fluid which, compared to the jet flow, is more at rest. In this case, the fluid substantially at rest is the flue gas 38 which is present within the combustion chamber 36. The free jet flow of the primary, secondary, and tertiary fuel streams 18, 20, and 22 operates to entrain flue gas 38 and to thoroughly mix the flue gas 38 with each fuel stream 18, 20, and 22 as it travels to the combustion zone 24 at the outlet end of the burner wall 10.
The combustion zone 24 of the inventive burner 2 can be a multistage combustion zone or can be a single stage combustion zone having only a single combustion stage 58. The combustion zone 24 is preferably a single stage combustion zone wherein all of the primary fuel streams 18, secondary fuel streams 20, and tertiary fuel streams 22 are delivered to, and combusted in, the same combustion stage 58. Most preferably, at least a portion of each primary, secondary, and tertiary fuel stream 18, 20, and 22 is delivered to and combusted at the beginning end 60 of the combustion zone 24. The beginning 60 of the combustion zone 24 is preferably located substantially at (i.e. either at or within 8 (Normally 0.5) inches rearwardly or 0 to 60 (Normally 0) inches forwardly of) the forward end 30 of the burner wall 10.
In the inventive burner 2, each fuel ejection structure 12, 14, and 16 is depicted as being a fuel ejection tip which is secured on the end of a riser or other fuel conduit 62, 64, or 66 which is connected to a fuel supply manifold 68 located outside of the wall 34 of the combustion chamber 36. Each fuel riser 62, 64 and 66 extends through the wall 34 of the combustion chamber 36 and then longitudinally through a surrounding outer skirt portion 68 of the burner wall 10.
As the ejected primary, secondary, and tertiary fuel streams 18, 20, and 22 flow outside of the burner wall 10 within the combustion chamber 36, flue gas 38 from the combustion chamber 36 is entrained in each of the ejected fuel streams 18, 20, and 22 and is mixed therewith. In addition, in order to stabilize and increase the amount of flue gas 38 which mixes with each of the primary, secondary, and tertiary fuel streams 18, 20, and 22, and to stabilize the combustion zone 24 and the combustion flame, each of the primary, secondary, and tertiary flow streams 18, 20, and 22 is oriented and directed to contact at least one radial impact structure which is formed or other otherwise provided on and around, or at least partially around, the exterior 70 of the outer skirt 68 of the burner wall 10.
Each such impact structure can generally be any type of obstruction which will decrease the flow momentum and/or increase the turbulence of the fuel streams 18, 20, or 22 sufficiently to promote flue gas entrainment and mixing while allowing the resulting mixture to flow on to combustion zone 24. Proceeding rearwardly from the forward end 30 of the burner wall 10, each succeeding radial impact structure is preferably broader in diameter or width than, and is located longitudinally rearward of and laterally outward from, the previous impact structure.
In the embodiment 2 of the inventive burner apparatus illustrated in
In addition, in order to provide an even greater amount of IFGR and mixing in the secondary and tertiary fuel streams 20 and 22, the forward and rearward primary radial impact structures 72 and 74 are preferably also positioned in the secondary and tertiary fuel flow paths 52 and 56 so that at least a portion of each secondary fuel stream 20 and at least a portion of each tertiary fuel stream 22 also contacts the primary radial impact structures 20 and 22. Moreover, a further amount of IFGR and mixing are also provided by positioning the forward and rearward secondary radial impact structures 76 and 78 in the tertiary fuel flow paths 56 so that at least a portion of each tertiary fuel stream 22 also contacts the forward and rearward secondary radial impact structures 76 and 78.
In the embodiment 2 of the inventive burner apparatus illustrated in
During the operation of the inventive burner 2, the contacting flow and momentum of the primary, secondary, and tertiary fuel streams 18, 20 and 22, and the flow and the momentum of the air or other oxygen source stream 6 flowing from forward discharge opening 32 at the forward end 30 of the burner wall 10, results in the creation of reduced pressure areas on the forward faces 84, 86, 88, 90, 92, and 94 of the ledges or other radial impact structures 72, 74, 76, 78, 80, and 82 provided on the exterior 70 of the burner wall 10. These reduced pressure areas operate to increase the amount of flue gas which is entrained in the fuel streams, improve the mixing of the fuel, flue gas and oxygen source, stabilize the primary, secondary, and tertiary fuel streams 18, 20 and 22, and stabilize the burner combustion zone 24 and the burner flame.
In the inventive burner apparatus 2, the risers 62 for the primary fuel ejection structures 12 preferably extend forwardly through the surrounding outer skirt 68 of the burner wall 10 such that (a) the primary fuel ejection structures 12 are positioned in or at least partially forward of openings 96 provided in the forward face 88 of the forward secondary radial impact ledge 76 and (b) the secondary fuel ejection structures 14 are located in or at least partially forward of openings 98 provided in the forward face 92 of the forward tertiary radial impact ledge 80. Consequently, the primary fuel ejection structures 12 preferably eject the primary fuel streams 18 forwardly toward the combustion zone 24 from, or substantially from, the forward face 88 of the forward secondary radial impact ledge 76. Similarly, the secondary fuel ejection structures 14 preferably eject the secondary fuel streams 20 forwardly toward the combustion zone 24 from, or substantially from, the forward face 92 of the forward tertiary radial impact ledge 80.
As illustrated in
In order to prevent the secondary fuel streams 20 from interfering with the ejection and free jet flow of the primary fuel streams 18, the secondary fuel ejection structures 14 are preferably off-set from the primary fuel ejection structures 12 such that the secondary fuel streams 20 are ejected into or over the gap areas 100 provided between the primary fuel ejection structures 12. Similarly, in order to prevent the tertiary fuel streams 22 from interfering with the ejection and free jet flow of the secondary fuel streams 20, the tertiary fuel ejection structures 16 are preferably off-set from the secondary fuel ejection structures 14 such that the tertiary fuel streams 22 are ejected into or over the gap areas 102 provided between the secondary fuel ejection structures 14.
As indicated above, the lateral cross-sectional shape of the burner wall body 10 of inventive burner 2 can be circular, square, rectangular, oval or generally any other desired shape. In addition, although in most embodiments and applications of the inventive burner 2 the burner wall 10 and the two or more series of fuel ejection structures 12, 14, and 16 employed in the inventive burner 2 will entirely surround the flow passageway 8 for the oxygen source stream 6, in some applications this will not be the case. For example, the burner wall 10 and/or the fuel ejection structures 12, 14, and 16 may not completely surround the flow passageway 8 in certain applications where the inventive burner apparatus 2 is used in a furnace sidewall location or must be specially configured to provide a particular desired flame shape.
Although three series of surrounding fuel ejection structures 12, 14, and 16 are used in the embodiment 2 of the inventive burner illustrated in
Also, for each such additional succeeding series of fuel ejection structures, one or more (preferably two) additional radial impact structures, for contacting by the fuel streams ejected by the added series of ejection structures, would preferably be added to the exterior 70 of the burner wall 10 between the added series of ejection structures and the preceding series of ejection structures. Proceeding rearwardly, the lateral diameter or width of each added radial impact structure would preferably be greater than the diameter or width of the preceding impact structure.
In the method of the present invention, the stream of air or other oxygen source 6 is discharged into the combustion zone 24 of the inventive burner apparatus 2 from the discharge opening 32 of the burner flow passaged 8 at the forward longitudinal end 30 of the burner wall 10. At the same time, the primary fuel streams 18, the secondary fuel streams 20, and the tertiary fuel streams 22 are also discharged outside of the burner wall 10 toward the combustion zone 24 from the series of primary fuel ejection structures 12, the series of secondary fuel ejection structures 14, and the series of tertiary fuel ejection structures 16.
As the primary fuel streams 18 travel outside of the burner wall 10 along the primary fuel flow paths 48, at least a portion of the each of the primary fuel streams 18 contacts the rearward primary radial impact ledge 74 on the exterior of the 70 of the burner wall 10. Then, as the primary fuel streams 18 continue along the primary fuel flow paths 48, at least a portion of each of the primary fuel streams 18 also contacts the forward primary radial impact ledge 72 (i.e., the forward end 30) of the burner wall 10.
The reduced pressure area created by the momentum of the primary fuel streams 18 on the forward face 86 of the rearward primary impact ledge 74, and the increased turbulence created by the contact of the primary fuel streams 18 with the rearward primary ledge 74, operate to enhance the entrainment and mixing of the gaseous products of combustion 38 in the combustion chamber 36 with the primary fuel streams 18. As the primary fuel streams 18 then continue to flow to the combustion zone 24, the reduced pressure area created by the momentum of the primary fuel streams 18 and the flow momentum of the oxygen source stream 6 on the forward face 84 of the forward end 30 of the burner wall 10, and the turbulence created by the contact of the primary fuel steams 18 with the forward end 30 of the burner wall 10, not only enhance the entrainment and mixing of an additional amount of flue gas 38 with the primary fuel streams 18, but also operate to enhance the mixing of the oxygen source 6 with the primary fuel streams 18 at the beginning end 60 of the combustion zone 24 and to stabilize the combustion zone 24 and the burner flame at the forward end 30 of the burner wall 10.
As the secondary fuel streams 20 travel outside of the burner wall 10 along the secondary fuel flow paths 50, at least a portion of the each of the secondary fuel streams 20 contacts the rearward secondary radial impact ledge 78 on the exterior of the 70 of the burner wall 10. Then, as the secondary fuel streams 20 continue along the secondary fuel flow paths 50, at least a portion of each of the secondary fuel streams 20 also contacts the forward secondary radial impact ledge 76.
The reduced pressure areas created by the momentum of the secondary fuel streams 20 on the forward faces 90 and 88 of the rearward and forward secondary impact ledges 78 and 76, and the increased turbulence created by the contact of the secondary fuel streams 20 with the rearward and forward secondary ledges 78 and 76, operate to enhance the entrainment and mixing of the gaseous products of combustion 38 with the secondary fuel streams 20.
As the tertiary fuel streams 22 travel outside of the burner wall body 10 along the tertiary fuel flow paths 52, at least a portion of each of the tertiary fuel streams 22 contacts the rearward tertiary radial impact ledge 82 on the exterior of the 70 of the burner wall 10. Then, as the tertiary fuel streams 22 continue along the tertiary fuel flow paths 52, at least a portion of each of the tertiary fuel streams 22 also contacts the forward tertiary radial impact ledge 80.
The reduced pressure area created by the momentum of the tertiary fuel streams 22 on the forward faces 94 and 92 of the rearward and forward tertiary impact ledges 82 and 80, and the increased turbulence created by the contact of the tertiary fuel streams 22 with the rearward and forward tertiary ledges 82 and 80, operate to enhance the entrainment and mixing of the gaseous products of combustion 38 with the tertiary fuel streams 22.
In addition, it is further preferred that: (i) as the secondary fuel streams 20 travel along the secondary fuel flow paths 50, at least a portion of each of the secondary fuel steams 20 also contacts the rearward primary impact ledge 74 and at least a portion of each of the secondary fuel streams 20 further contacts the forward primary radial impact ledge 72 (i.e., the forward end 30) of the burner wall 10; (ii) as the tertiary fuel streams 22 travel along the tertiary fuel flow paths 52, at least a portion of each of the tertiary fuel steams 22 also contacts the rearward secondary impact ledge 78 and at least a portion of each of the tertiary fuel streams 22 further contacts the forward secondary radial impact ledge 76; and (ii) as the tertiary fuel streams 22 continue to travel along the tertiary fuel flow paths 52, at least a portion of each of the tertiary fuel steams 22 also contacts the rearward primary impact ledge 74 and at least a portion of each of the tertiary fuel streams 22 further contacts the forward primary radial impact ledge 72 (i.e., the forward end 30) of the burner wall 10.
The positioning of the secondary impact structures 78 and 76 in the flow paths 52 of the tertiary fuel streams 22 and the positioning of the primary impact structures 74 and 72 in the flow paths 50 and 52 of the secondary fuel streams 20 and the tertiary fuel streams 22 operates to further enhance both (a) the low pressure areas on the forward faces 90, 88, 86, and 84 of these impact structures and (b) the mixing of the gaseous products of combustion 38 with the tertiary and secondary fuel streams 22 and 20. In addition, the preferred positioning of the forward end 30 of the burner wall body 10 in the flow paths 48, 50, and 52 of all of the primary, secondary, and tertiary fuel streams 18, 20, and 22 provides a highly stable, single stage combustion zone 24 and flame at the forward end 30 of the burner wall 10 wherein at least a portion of each of the primary, secondary, and tertiary fuel streams 18, 20, and 22 is delivered to and combusted at the beginning end 60 of the combustion zone 24.
To prevent the secondary fuel steams 20 from interfering with the free jet flow and flue gas entrainment of the primary fuel streams 18, the secondary fuel streams 20 are preferably ejected toward the gap areas 100 between the primary fuel ejection structures 12 as illustrated in
Because of the increased travel distance outside of the burner wall 10 and the increasing number of impact structures on the exterior 70 of the burner wall 10 which are contacted, the total amount of flue gas 38 which is entrained in and mixes with the secondary fuel streams 20 is greater than the amount of flue gas 38 which mixes with the primary fuel streams 18. Moreover, for the same reasons, the total amount of flue gas 38 which is entrained in and mixes with the tertiary fuel streams 22 is greater than the amount of flue gas 38 which mixes with the secondary fuel streams 20.
The amount of flue gas 38 contained in the fully conditioned primary fuel streams 18 which are delivered to the combustion zone 24 will be in the range of from about 80% to about 90% by volume based upon the total final volume of the fully conditioned primary fuel streams 18. The amount of flue gas 38 contained in the fully conditioned secondary fuel streams 20 delivered to the combustion zone 24 will be in the range of from about 92% to about 94% by volume based upon the total final volume of the fully conditioned secondary fuel streams 20. The amount of flue gas 38 contained in the fully conditioned tertiary fuel streams 22 delivered to the combustion zone 24 will be in the range of from about 94% to about 96% by volume based upon the total final volume of the fully conditioned primary fuel streams 22.
In addition to significantly increasing the amount of the gaseous products of combustion 38 which are entrained in and mixed with the secondary and tertiary flow streams 20 and 22, the inventive burner apparatus 2 provides further enhanced internal flue gas recirculation (IFGR) by reducing the amount of fuel which must be used in the fuel rich primary fuel streams 18 in order to stabilize the burner combustion zone 24 and the burner flame. This is due to the fact that, unlike prior burners, the stability of the secondary and tertiary fuel streams is also greatly enhanced by placing ledges or other radial exterior impact structures 82, 80, 78, 76, and/or 74, as well the forward impact ledge 72 at the forward end 30 of the burner wall 10, in the flow paths 52 and 54 of these fuel streams.
Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments and steps have been described for purposes of this disclosure, the invention is not limited in its application to the details of the preferred embodiments and steps. Numerous changes and modifications will be apparent to those in the art. Such changes and modifications are encompassed within this invention as defined by the claims. In addition, unless expressly stated, the phraseology and terminology employed herein are for the purpose of description and not of limitation.
