BRIEF DESCRIPTION SEVERAL VIEWS OF THE DRAWING
The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein:
FIG. 1 is an end view of one exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 2 is a sectional view, not to scale, of the exemplary burner taken along line 2-2 of FIG. 1;
FIG. 3A is a sectional view, similar to FIG. 2, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 3B is a sectional view, similar to FIG. 3A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 3C is a sectional view, similar to FIG. 3A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 4A is a sectional view, similar to FIG. 2, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 4B is a sectional view, similar to FIG. 4A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 4C is a sectional view, similar to FIG. 4A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 5A is a sectional view, similar to FIG. 2, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 5B is a sectional view, similar to FIG. 5A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 5C is a sectional view, similar to FIG. 5A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 6A is a sectional view, similar to FIG. 2, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 6B is a sectional view, similar to FIG. 6A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 6C is a sectional view, similar to FIG. 6A, of another exemplary embodiment of a burner constructed in accordance with the subject invention;
FIG. 7 is a sectional view, similar to FIG. 2, but showing still other exemplary embodiments of a burner constructed in accordance with the subject invention;
FIGS. 8A-8E are schematic diagrams of the arrangement and shape of several different exemplary orifices of some exemplary burners of the subject invention; and
FIGS. 9A-9I are enlarged end views of various shaped orifices that can be used with the burners of the subject invention;
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1 wherein like reference characters refer to like parts there is shown at 20 one exemplary embodiment of a staged fuel burner constructed in accordance with this invention. That burner exhibits good plug flow characteristics and low NOx emissions and is what is commonly referred to as a staged burner. To that end, the burner 20 includes a central nozzle 22 that is surrounded by a plurality of staging or staged nozzles 24. In the exemplary embodiment of FIG. 1 ten such staged nozzles 24-1 to 24-10 are provided. That arrangement is exemplary of a multitude of burners that can be constructed in accordance with this invention. In particular, burners constructed in accordance with this invention can include any number of staged nozzles surrounding the central nozzle. Each nozzle may include a single orifice or plural orifices. Moreover, the orifices may be of any shape and size, as will be seen later with reference to FIGS. 8A-8D and 9A-9I. In the exemplary embodiment shown in FIGS. 1 and 2 each nozzle includes a single, circular shaped orifice 26. Each orifice 26 is arranged to produce a stream or jet of a fluid along a longitudinal axis from the exit plane 28 of the orifice (i.e., the plane at the downstream end of the orifice). Thus, the orifice 26 of the central nozzle produces a jet of air and, if desired some fuel and/or combustion products, along the central longitudinal axis of the burner. The air, fuel and/or combustion products are provided to the central nozzle from means (not shown). The direction of this “central jet” is shown by the arrow designated as Vc in FIG. 2. It should be pointed out at this juncture that the direction of the central jet need not be parallel to the central longitudinal axis of the burner, such as shown in FIG. 2, but rather may extend at an angle thereto as shown in FIGS. 6A-6C (to be described later).
Each of the orifices 26 of each of the staged nozzles of burners constructed in accordance with this invention produces a jet of fluid (a “staged jet”), which includes fuel and may, if desired include some air and/or combustion products, along the longitudinal axis of the orifice from its respective exit plane. The fuel, air and/or combustion products are provided to the staged nozzles from means (not shown). The staged jets can all be directed in the same direction (e.g., parallel to the central longitudinal axis, at a converging angle to the central longitudinal axis or at a diverging angle to the central longitudinal axis) or can be directed in different directions to one another. For example, in the exemplary embodiment of FIGS. 1 and 2, four of the nozzles, namely, 24-1, 24-4, 24-6 and 24-9 are each directed at an inwardly converging angle to an axis 30 that is parallel to the longitudinal axis 32 of the central nozzle 22, while the other six nozzles 24-2, 24-3, 24-5, 24-7, 24-8 and 24-10 are each directed parallel to the longitudinal axis 32 of the central nozzle 22. In FIG. 2 the jet produced by the orifice of the nozzle 24-1 is shown by the arrow designated as V1, and it extends at an angle θ1 to the axis 30, while the jet produced by the orifice of the nozzle 24-7 is shown by the arrow designated as V7 and extends parallel to the longitudinal central axis.
As best seen in FIG. 2, all of the staged nozzles 24-1 to 24-10 of the burner 20 are disposed equidistantly from one another about the central nozzle 22. Moreover, the exit plane of the orifices of the staged nozzles 24-1 to 24-10 is located rearward of the exit plane 28 of the orifice 26 making up the central nozzle 22. This arrangement is also merely exemplary of many arrangements of the position of the nozzles of burners constructed in accordance with this invention. Thus, the staged nozzles 24 need not be equidistantly spaced from one another. Moreover, the relative position of the exit plane of the orifice of the central nozzle to the orifices of the staged nozzles need not be like shown in FIG. 2. For example, as shown in FIGS. 4A-4C the exit planes of the orifices 26 of all of the burner's nozzles can be in the same plane. Alternatively, as shown in FIGS. 5A-5C the exit planes of the orifices 26 making up the staged nozzles can be located forward of the exit plane of the orifice of the central nozzle. In fact, it is contemplated that different orifices have different exit planes than other orifices. Further still, the number of staged nozzles used in any given burner is also matter of design choice, depending upon the application for the burner. Thus, burners constructed in accordance with this invention may include any number of plural staged nozzles extending about the central nozzle. Further yet, the radial distance of each staged nozzle from the central longitudinal axis of the burner need not be the same. Accordingly, one or more staged nozzles 24 can be at a greater or lesser radial distance from the central longitudinal axis 32 than another staged nozzle.
Irrespective of the arrangement, number, size and direction of the nozzles/orifices, there exists a critical burner design parameter which causes a drastic change in the overall furnace flow pattern, much like laminar-to-turbulent transitions. This design parameter is the momentum ratio (hereinafter sometimes referred to as “MR”) of the staged jets 24 to the central jet 22. In particular, it has been found that when a burner 20 is constructed so that the sum of the momentums of the staged jets is nearly equal to momentum of the central jet, an even or plug-like flow profile is observed. Most preferably this ratio is 0.8 (i.e., the sum of the momentums of the staged jets is 80% of the momentum of the central jet). However, it has been determined that plug-type flow can be achieved if the ratio is within the range 0.5 to 1.5 (i.e., 50% to 150%).
Turning again to FIG. 2, the momentum of the central jet produced by the nozzle 22 of the burner 20 is designated by {dot over (m)}c, while the momentum of each of the surrounding staged jets produced by the nozzles 24-1 to 24-10 is designated by {dot over (m)}s,i where s designates that the momentum is of a staged jet and i represents the particular staging jet, e.g., in the embodiment shown in FIG. 2 i=“7” since the staging jet is that produced by the orifice making up the nozzle 24-7.
As mentioned above, the staged jets need not be all directed along axes parallel to the longitudinal axis of the central jet. In fact, in the exemplary preferred embodiment, shown in FIGS. 1 and 2 some staged jets, namely, the jets produced from the nozzles 24-1, 24-4, 24- 6 and 24-9, extend at an inwardly converging angle to the longitudinal axis of the central jet. The other of the staged jets, namely, the jets produced by nozzles 24-2, 24-3, 24-5, 24-7, 24-8 and 24-10, extend parallel to the longitudinal central axis of the central jet. Thus, the momentum ratio exhibited by burners constructed in accordance with this invention takes into account angularly directed jets. In particular, the momentum ratio produced by burners of this invention is the ratio of the combined momentums of the components of the staging jets that are directed parallel to the longitudinal axis of the central jet to the momentum of the central jet. As is well known, momentum is the product of mass flow and jet velocity and is a vector in the direction of the velocity. Here the jet velocity is the mean or average velocity based on the actual stream thermodynamic state (as defined by temperature, pressure, composition, etc.) at the point of exit from the orifice producing the jet and the area of the orifice through which the jet will pass, e.g., the area of the exit plane 28 of the jet's orifice 26. For staged fuel jets, this velocity can be readily determined, e.g., calculated based on the orifice area and the pressure at design rate measured during testing or in operation. For the central jet, the velocity is based on the area of the orifice and the combustion air temperature, or the burner opening into the furnace and the adiabatic flame temperature of the combustion air and the primary fuel, whichever is higher. Numerically, MR is defined by the following formula:
where {dot over (m)} is mass flow rate of the identified jet, V is velocity of the identified jet at the exit plane of the orifice from which the jet projects, θ is the included angle between the central longitudinal axis and the longitudinal axes of the staged nozzles, and the subscripts s, c, i represent staged, central and i-th number of staged nozzles, because the burner includes multiple staged jets whose orifices have longitudinal axes which may extend at different angles to the central longitudinal axis of the central nozzle.
It has been observed that a smaller MR ratio means lower staged fuel fraction and the burner resembles more closely a single central jet. The flame is dominated by the center air jet, and a narrow flame ensues. When such burners are used in a typical furnace, the space between the flame produced thereby and the process tubes or the wall of the furnace will be filled by recirculating flue gas. A slight perturbation can cause the flame to touch the process tubes. In the limit, the burner is represented by a single point source. Because the point source has a high velocity, but the neighboring firing wall has zero velocity, the velocity differential and the resultant pressure difference create recirculation zones next to the jet, which become the origin of a large scale recirculation zone in the furnace.
As the MR ratio increases, more fuel is staged, and the burner gets farther away from a single central jet. When the MR ratio gets to approximately unity, the fuel (staged) jets and air (central) jet have similar momentums. The combined fuel and air jets from the burner have the best opportunity to develop a plug-type flow pattern and maintain the forward direction down the burner axis. If the MR is too large, the flame resembles a hollow jet and will collapse inward to the center and become short and bushy. Such flames tend to overheat the process tubes near the burners.
A desired flame must balance the forward projecting power of a large air jet at the center and the heat release capacity of the fuel (staged) jets surrounding it. As was mentioned earlier, this balance manifests in this form as a momentum ratio close to one, with a ratio of 0.8 being optimum. Near the optimal MR ratio, the combined central air jet and staging jets attain pressure balance and produce a flame, which when used in a furnace proceeds in a straight line along the firing axis. While the flow will tend to change direction and cross the process tubes, at some point (e.g., due to the flue gas extraction system) such action occurs at a sufficient distance from the burner so that the furnace gas temperature at the point where it crosses the process tubes is sufficiently low that overheating of the process tubes does not present a hazard. The plug flow in the combustion zone prevents flame impingement on the process tubes and discourages the formation of a large scale high temperature recirculation zone. As long as the combustion is complete, the combustion gases can go wherever they prefer without causing process tube overheating. The plug flow enables higher heat release intensity per cubic foot of combustion space without tube overheating. The elimination of the high temperature recirculation zone also reduces NOx emissions, since the formation of NOx is proportional to both temperature and retention time. The lower temperature also increases tube and catalyst life, and reduces soot formation in the process tubes.
In FIG. 3A there is shown an alternative burner constructed in accordance with this invention. This embodiment is similar to the embodiment of FIG. 2, except that all of the staged nozzles are directed so that their orifices 26 create staged jets extending parallel to the longitudinal axis 32 of the central nozzle 22. Thus, in the interest of brevity the common components of the embodiments of FIGS. 2 and 3 will be given the same reference designations. As can be seen the burner of FIG. 3 has a central nozzle 22 that produces a central jet whose direction of flow is shown by the arrow designated as Vc while the two staged nozzles 24-1 and 24-2 shown produce respective staged jets shown by the arrows designated as V1 and V2. In FIG. 3B there is shown another alternative burner constructed in accordance with this invention. That burner is similar in construction to the burner shown in FIG. 3A except that its staged nozzles are directed so that the orifice of each creates a staged jet extending at an inwardly converging angle θ to an axis 30 that is parallel to the longitudinal axis 32 of the central nozzle 22. The direction of the jets from the orifices of the staged nozzles in FIG. 3B are shown by the arrows designated as V1 and V2. The other details of the construction of the burner of FIG. 3B are similar to the details of the burner of FIG. 3A and hence are given the same reference designations and will not be reiterated herein. In FIG. 3C there is shown another alternative burner constructed in accordance with this invention. That burner is similar in construction to the burner shown in FIG. 3A except that its staged nozzles are directed so that the orifice of each creates a staged jet extending at an outwardly diverging angle θ to an axis 30 that is parallel to the longitudinal axis of the central nozzle 22. The direction of the jets from the orifices of the staged nozzles in FIG. 3C are shown by the arrows designated as V1 and V2. The other details of the construction of the burner of FIG. 3C are similar to the details of the burner of FIG. 3A and hence are given the same reference designations and will not be reiterated herein.
FIGS. 4A-4C show further embodiments of burners constructed in accordance with this invention. The embodiments of FIGS. 4A-4C are similar to the embodiments of FIGS. 3A-3C, respectively, except that the exit planes of the orifices of all of the nozzles are coplanar. Thus, in the interest of brevity the common components of the embodiments of FIGS. 4A, 4B and 4C and FIGS. 3A, 3B and 3C, respectively, will be given the same reference designations and no further discussion of the details of the construction of the burners will be given.
FIGS. 5A-5C show further embodiments of burners constructed in accordance with this invention. The embodiments of FIGS. 5A-5C are similar to the embodiments of FIGS. 3A-3C, respectively, except that the exit planes of the orifices of the staged nozzles are coplanar and located forward of the exit plane of the orifice of the central nozzle. Thus, in the interest of brevity the common components of the embodiments of FIGS. 5A, 5B and 5C and FIGS. 3A, 3B and 3C, respectively, will be given the same reference designations and no further discussion of the details of the construction of the burners will be given.
FIGS. 6A-6C show further embodiments of burners constructed in accordance with this invention. The embodiments of FIGS. 6A-6C are similar to the embodiments of FIGS. 4A-4C, respectively, except that the central nozzle and its orifice extend at an angle to the central longitudinal axis 32 of the burner so that the central jet extends at that angle as shown by the arrow designated Vc. Thus, in the interest of brevity the common components of the embodiments of FIGS. 5A, 5B and 5C and FIGS. 4A, 4B and 4C, respectively, will be given the same reference designations and no further discussion of the details of the construction of the burners will be given.
FIG. 7 shows still a further exemplary embodiment of a burner constructed in accordance with this invention. FIG. 7 is similar to FIGS. 4B and 4C, except that its staged nozzles extend at different angles to each other. In particular, one staged nozzle 24-1 extends at an inwardly converging angle θ1 to an axis 30 that is parallel to the longitudinal axis of the central nozzle 22, while another staged nozzle 24-2 extends at an outwardly converging angle θ2 to an axis 30 that is parallel to the longitudinal axis of the central nozzle 22.
As mentioned earlier the orifice(s) making up the central nozzle and/or any of the staged nozzles can be of any shape or size. For example, as shown in FIG. 8A the central nozzle 22 can have a single orifice 26 of circular cross section and be surrounded by four staged nozzles 24-1, 24-2, 24-3 and 24-4. Each of the staged nozzles has a single circular shaped orifice 26, whose diameter is substantially smaller than the diameter of the central orifice. Moreover, the orifices 24-1, 24-2, 24-3 and 24-4 are equidistantly spaced from each other and equidistantly spaced from the central orifice. In FIG. 8B there is shown another nozzle arrangement. This arrangement is similar to the arrangement of FIG. 8A, except that the central nozzle includes a square shaped orifice 26. In FIG. 8C there is shown another nozzle arrangement. This arrangement is similar to the arrangement of FIG. 8A, except that the central nozzle includes a hexagonal shaped orifice 26. FIG. 8D shows another nozzle arrangement. This arrangement is similar to the arrangement of FIG. 8A, except that the central nozzle includes a rectangular shaped orifice 26. FIGS. 9A-9H show various other shapes for orifices that can be used in burners of this invention, such as the circular orifice of FIG. 9A, the square orifice of FIG. 9B, the hexagonal orifice of FIG. 9C, the rectangular orifice of FIG. 9D, the multi-cross slotted orifice of FIG. 9E, the cruciform orifice of FIG. 9F, and the two cross slotted orifice of FIG. 9G. FIG. 9H shows a nozzle which can be the central nozzle 22 or any or all of the staged nozzles 24, where the nozzle has three circular shaped orifices 26 arranged in a triangular array in the lower half of the nozzle. FIG. 9I shows a nozzle which can be the central nozzle 22 or any or all of the staged nozzles 24, where the nozzle has two circular shaped orifices 26 arranged in a linear array in the lower half of the nozzle. It must be pointed out at this juncture that the orifices and nozzles shown herein are merely a few examples of a myriad of shapes and sizes that can be used in burners constructed in accordance with this invention.
As should be appreciated by those skilled in the art the burners of the subject invention has particular utility for use in furnaces. However, its use is not limited to such applications. When used in furnaces the burners of the subject invention will eliminate the high temperature recirculation zone by creating a plug flow like flow pattern. With the high temperature recirculation zone eliminated, a higher firing rate can be maintained. Furthermore, the process tubes of a furnace making use of burners constructed in accordance with the subject invention will have an extended life due to the lower and even surrounding temperature. The lower temperature will also decrease the soot formation and increase catalyst life. Finally, since NOx formation is proportional to temperature, eliminating hot spots will decrease NOx emissions.
While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
Patent Application
20080096146
