Abstract:
A compound spin vane (CSV) for use in an air passage of a fossil fuel-fired burner. In one embodiment, the CSV is a multi-piece construction of platelike outer and inner vane elements connected to an intermediate platelike rail element. In another embodiment, the CSV includes at least two and possibly three vane portions, rigidly interconnected in spaced lateral relationship with respect to each other. If desired, the vane portions may be simple, curved planar surfaces, and may be arranged with trailing edges arranged at angles with respect to each other. The invention may be employed as a replacement for flat spin vanes found in secondary air passages of known single and dual register burners. When used in such manner in a single register burner, the invention changes secondary air flow characteristics so as to mimic those commonly found in a dual register burner.

Description:
The present invention relates in general to furnace burners, and in particular to a new and useful spin vane for fossil fuel-fired burners. It is a divisional application of U.S. Ser. No.  09/178,855 Oct.  26, 1998 (now U.S. Patent No. 6,146,130), which is itself a divisional application of U.S. Ser. No. 08/584,785 filed Jan. 11, 1996 (now U.S. Patent No. 5,827,054). 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to furnace burners, and in particular to a new and useful spin vane for fossil fuel-fired burners. 
     2. Description of the Related Art 
     Among the key physical features of burners used in industrial and utility boilers are the spin vanes which typically are located in at least one annular secondary air flow passage that surrounds the burner fuel nozzle. These spin vanes function to change the flow direction of incoming secondary (combustion) air and to impart a swirl velocity on the air as it exits the burner and mixes with the burning fuel. The imparted swirl velocity changes the air-fuel mixing characteristics of the burner and by so doing affects the emission production level and unburnt carbon losses of the combustion process. The spin vanes usually are fabricated from flat sheet metal, and they may be situated in the annular air flow passage(s) so that they are either stationary or movable in relation to the incoming air. Where the spin vanes are movable, they often may be adjusted from a completely closed position to a fully opened position. Movable spin vanes can be useful in instances where field tuning a burner is needed to meet certain performance requirements specified by a burner user. 
     Spin vanes may be used in both single and dual register burners. FIG. 1 illustrates a known single register burner  10  of The Babcock &amp; Wilcox Company (B&amp;W) with spin vanes  11  located in annular secondary air flow passage  12  which surrounds burner nozzle  13 . Pulverized coal and primary air, which serves principally as a coal transport medium, are supplied to burner  10  at inlet  14 . Secondary air is delivered to annular secondary air flow passage  12  from windbox  15  which is positioned concentrically about passage  12 . Secondary air flow from windbox  15  to passage  12  can be controlled by sliding air damper  16 . Burner nozzle  13  and passage  12  respectively deliver the pulverized coal/primary air mixture and the secondary air to the interior of furnace  17  through opening  18  in furnace wall  19 . As indicated in FIG. 1, spin vanes  11  induce a swirled air flow pattern which is directed into a burner flame. 
     FIG. 2 depicts a known dual register burner  20 , also of B&amp;W. Like the single register burner  10 , the dual register burner  20  has a burner nozzle  13 , a pulverized coal/primary air inlet  14  and a sliding damper  16 . Dual register burner  20  is distinguishable from single register burner  10  by inner secondary air zone  22  and outer secondary air zone  24 , both of which air zones encircle burner nozzle  13  and thereby serve as passages through which secondary air is delivered to the interior of furnace  17 . Secondary air zones  22  and  24  are separated from one another by air separation plate  25  which is positioned concentrically about burner nozzle  13 . Inner secondary air zone  22  and outer secondary air zone  24  have movable spin vanes  26 . Outer secondary air zone  24  also has stationary spin vanes  28  located upstream of movable vanes  26  situated in the outer air zone. As indicated in FIG. 2, inner and outer secondary air mixing patterns respectively exit from inner secondary air zone  22  and outer secondary air zone  24  and are directed into a burner flame. 
     For further clarity, FIG. 3 shows an enlarged profile view of the known spin vanes  11  and  26  which have been pointed out respectively in FIG.  1  and FIG. 2, above. As shown in FIG. 3, the plate-like spin vane is defined by base edge  31 , leading edge  32  which intersects one end of base edge  31  at obtuse angle A, trailing edge  33  which intersects the other end of base edge  31 , also at obtuse angle A, and curved outer edge  34  which intercepts the ends of leading and trailing edges  32  and  33 , which are farthest from base edge  31 . 
     U.S. Pat. No. 1,620,180 discloses angled vanes with a projecting flange. The flange, however, is not placed in a flow path and is fixed to the vane for support purposes, and not for air flow direction. 
     U.S. Pat. No. 2,647,568 discloses vanes or ribs which are inclined relative to the burner&#39;s axis. While the vanes or ribs have flared and contoured surfaces, they do not have any extension perpendicular to part of the length. 
     U.S. Pat. No. 2,515,813 is a further example of angled vanes without an extension. 
     U.S. Pat. No. 3,049,055 discusses optimum vane angularity. 
     SUMMARY OF THE INVENTION 
     The present invention relates to various embodiments of a novel spin vane of the type used in fossil fuel-fired burners. More particularly, in a first embodiment three separate and distinct flat sheet metal elements are assembled and oriented relative to one another so as to provide a multi-piece spin vane which may be called a compound burner vane (CBV) or compound spin vane (CSV). The sheet metal elements are an outer vane element, an inner vane element and a rail element. Both outer and inner vane elements are aligned perpendicularly with respect to outer and inner faces of the rail element and are positioned so that the outer vane is attached to the outer face of the rail and the inner vane is attached to the inner face of the rail. While the outer and inner vane elements may be aligned relative to one another so that they divert the secondary air flow in the same direction both outside and inside of the rail element, the vane elements may be angled in relation to one another, preferably at an angle ranging from ten (10) to forty (40) degrees, so that they will divert the air flow in differing directions. Additionally, the profiles of either or both of the vane elements may be altered to create converging or diverging air flow patterns. A ratio of outer vane element height to inner vane element height (h o /h i ) also may be established to provide an air flow pattern that is optimized for specific burner requirements. The structure of the invention has been found to change the secondary air flow characteristics of the known single register burner so  5 . as to mimic those of the known dual register burner. Previous measurements suggest that certain combustion-generated pollutants are lower for the dual register burners than for their single register counterparts. Thus, the invention, when applied to a known single register burner that has already been put into service, allows the burner to be quickly and inexpensively modified so that the level of its emissions are reduced to a point which is comparable to that of the known dual register burner and so that the flame produced by the modified single register burner is shorter than that of the known dual register burner. The invention also may be used in the known dual register burner in the event that a need should arise to achieve emission standards more stringent than those currently encountered by users of the known dual register burner. 
     Accordingly, one aspect of the present invention is drawn to a multi-piece spin vane which may be used in an air passage of either a single register or a dual register fossil fuel-fired burner, and this vane is comprised of: 
     A plate-like, rectangular-shaped rail element oriented in the air passage such that an outer face of the rail element is directed toward an outer wall of the air passage and an inner face of the rail element is directed toward an inner wall of the air passage; 
     A plate-like outer vane element which has a base edge, leading and trailing edges and an outer edge, and which is fastened at the base edge to the outer face of the rail element so that the outer vane element and the outer face of rail element are perpendicularly aligned; and 
     A plate-like inner vane element which also has a base edge, leading and trailing edges and an outer edge, and which is fastened to the inner face of the rail element so that the inner vane element and the inner face of the rail element are perpendicularly aligned. 
     Another aspect of the present invention is drawn to a fossil-fueled burner apparatus having means for providing a fossil fuel to an outlet end of the burner apparatus for combustion, a single annular air flow passage partially defined between an inner wall and an outer wall of the burner apparatus, and an arrangement of multi-piece spin vanes of the aforementioned construction installed and positioned within the annular air flow passage for imparting a spin to combustion air flowing through the annular air flow passage. 
     Yet another aspect of the present invention is drawn to a another form of a compound spin vane for imparting a spin to combustion air flowing through an annular air flow passage of a fossil-fueled burner apparatus, the passage being partially defined between an inner wall and an outer wall. This form of the compound spin vane comprises a first vane portion having a leading edge exposed to the oncoming flow of air, and a trailing edge located downstream thereof with respect to the flow of air as it passes by the first vane portion. The first vane portion also has an inner edge, and an outer edge located proximate to the outer wall of the annular air passage. The first vane portion also has opposite, lateral sides. A second vane portion having a leading edge exposed to the oncoming flow of air, a trailing edge downstream thereof with respect to the flow of air as it passes by the second vane portion, is also provided. The second vane portion also has an inner edge located proximate to the inner wall of the annular air passage, an outer edge, and opposite, lateral sides. Finally, means are provided for rigidly connecting a first lateral side of the second vane portion to one side of the first vane portion in spaced lateral relationship with respect to the first vane portion so that both the first and second vane portions move together as a unit when the compound spin vane is installed and positioned in the annular air flow passage of the burner apparatus. 
     Yet still another aspect of the present invention is drawn to a fossil-fueled burner apparatus having means for providing a fossil fuel to an outlet end of the burner apparatus for combustion, a single annular air flow passage partially defined between an inner wall and an outer wall of the burner apparatus, and an arrangement of compound spin vanes installed and positioned within the annular air flow passage for imparting a spin to combustion air flowing through the annular air flow passage, wherein some of the compound spin vanes comprise the foregoing construction. 
     Another aspect of the invention is to provide a compound burner vane (CBV) which is simple in design and is more economical to manufacture than single-piece vanes having complex shapes. As suggested from the foregoing summary, the invention also provides a user of existing single register burners with a low cost alternative to replacing such burners with higher cost dual register burners in order to reduce boiler emissions. By replacing existing single register burner vanes with the invention, a burner user also may significantly reduce the amount of boiler down time that otherwise would be required for total burner replacement. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a side elevational view of a known B&amp;W single register fossil fuel-fired burner which uses spin vanes of conventional design; 
     FIG. 2 is a side elevational view of a known B&amp;W dual register fossil fuel-fired burner which uses spin vanes of conventional design; 
     FIG. 3 is a side elevational view of a known spin vane; 
     FIG.  4 ( a ) is a perspective view of one embodiment of a spin vane constructed according to the invention; 
     FIG.  4 ( b ) provides a side elevational view of an outer vane element and an inner vane element, as well as a top plan view of a rail element of the spin vane shown in FIG.  4 ( a ); 
     FIG.  5 ( a ) is a perspective of another embodiment of a spin vane constructed according to the invention; 
     FIG.  5 ( b ) provides a side elevational view of an outer vane element and an inner vane element, as well as a top plan view of a rail element of the spin vane shown in FIG.  5 ( a ); 
     FIG. 6 is an end view of a single register burner, taken from the furnace side, employing another embodiment of the compound spin vane of the present invention; 
     FIG. 7 is a schematic representation of the compound spin vane of FIG. 6 when viewed from the outer circumference of the annular passageway, the outer wall being removed for clarity; 
     FIGS. 8-9 are schematic representations of side and end views, respectively, of the compound spin vane of FIGS. 6 and 7; 
     FIG. 10 is an end view of a single register burner, taken from the furnace side, employing another embodiment of the compound spin vane of the present invention; 
     FIG. 11 is a schematic representation of the compound spin vane of FIG. 10 when viewed from the outer circumference of the annular passageway, the outer wall being removed for clarity; 
     FIGS. 12-13 are a schematic representations of side and end views, respectively, of the compound spin vane of FIGS. 10 and 11; 
     FIG. 14 is an end view of a single register burner, taken from the furnace side, employing another embodiment of the compound spin vane of the present invention; 
     FIG. 15 is a schematic representation of the compound spin vane of FIG. 14 when viewed from the outer circumference of the annular passageway, the outer wall being removed for clarity; 
     FIGS. 16-17 are schematic representations of side and end views, respectively, of the compound spin vane of FIGS. 14 and 15; 
     FIG. 18 is an end view of a single register burner, taken from the furnace side, employing another embodiment of the compound spin vane of the present invention; 
     FIG. 19 is a schematic representation of the compound spin vane of FIG. 18 when viewed from the outer circumference of the annular passageway, the outer wall being removed for clarity; 
     FIGS. 20-21 are schematic representations of side and end views, respectively, of the compound spin vane of FIGS. 18 and 19; 
     FIG. 22 is an end view of a single register burner, taken from the furnace side, employing another embodiment of the compound spin vane of the present invention; 
     FIGS. 23-24 are schematic perspective views of the compound spin vane of FIG. 22; 
     FIG. 25 is an end view of a single register burner, taken from the furnace side, employing another embodiment of the compound spin vane of the present invention; and 
     FIGS. 26-27 are schematic perspective views of the compound spin vane of FIG.  25 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following discussion, like numerals represent the same or functionally similar elements throughout the several drawings. A first embodiment of the present invention, as shown in FIG.  4 ( a ), involves a multi-piece spin vane  40  having three flat sheet metal elements: a rail element  41 , an outer vane element  42  and an inner vane element  43 . As shown in FIG.  4 ( b ), rail element  41 , when viewed from the top, has a rectangular shape. Rail element  41  will be oriented in a secondary air passage of a burner such that the outer vane element  42  will be directed toward an outer wall of the air passage and the inner vane element  43  will be directed toward an inner wall of the air passage. 
     Outer vane element  42 , as also shown in FIG.  4 ( b ), is defined by base edge  42 A, leading edge  42 B, trailing edge  42 C and curved outer edge  42 D. Base edge  42 A is equal in length to rail element  41  and is intersected at one of its ends by leading edge  42 B and at the other of its ends by trailing edge  42 C. Equal obtuse angles, designated by α in FIG.  4 ( b ), are formed by leading edge  42 B and trailing edge  42 C where they intersect base edge  42 A. Curved outer edge  42 D intercepts the ends of leading and trailing edges  42 B and  42 C, which are located farthest from base edge  42 A. Preferably, the amount of curvature exhibited by curved outer edge  42 D will correspond to the inside wall curvature of the air passage in which spin vane  40  is situated. 
     As also indicated in FIG.  4 ( b ), inner vane element  43  has a profile which resembles an inverted isosceles trapezoid defined by base edge  43 A, leading edge  43 B, trailing edge  43 C and outer edge  43 D. The length of base edge  43 A approximates that of the diagonal of rail element  41 . Leading edge  43 B and trailing edge  43 C are of equal lengths and intersect opposite ends of base edge  43 A to form equal acute angles designated β in FIG.  4 ( b ). Outer edge  43 D is parallel to base edge  43 A and intercepts the ends of leading edge  43 B and trailing edge  43 C, which are located farthest from base edge  43 A. 
     Rail element  41 , outer vane element  42  and inner vane element  43 , when assembled, appear as depicted generally in FIG.  4 ( a ). Outer vane element  42  is attached at base edge  42 A to the outer face of rail element  41  so that base edge  42 A runs parallel to and is positioned midway between the longer sides of rail element  41 . Inner vane element  43  is secured at base edge  43 A to the inner face of rail element  41  so that base edge  43 A runs diagonally across rail element  41 . The preferred method of affixing vane elements  42  and  43  to rail element  41  is to weld the elements to one another; however, any other suitable fastening method may be employed. Vane elements  42  and  43  are joined to rail element  41  so that they both are aligned perpendicularly with respect to the faces of rail element  41 . 
     Another embodiment of the present invention is illustrated by FIGS.  5 ( a ) and  5 ( b ). Multi-piece spin vane  50  is comprised of rail element  51 , outer vane element  52  and inner vane element  53 . As in the case of spin vane  40 , all elements of spin vane  50  are fabricated from flat sheet metal. Rail element  51 , when viewed from the top, has a rectangular shape. 
     Outer vane element  52 , is defined by base edge  52 A, leading edge  52 B, trailing edge  52 C and curved outer edge  52 D. Base edge  52 A is equal in length to the diagonal of rail element  51  and is intersected at one of its ends by leading edge  52 B and at the other of its ends by trailing edge  52 C. Unequal obtuse angles, designated by α 1  and α 2 , in FIG.  5 ( b ), are formed respectively by leading edge  52 B and trailing edge  52 C where they intersect base edge  52 A. Curved outer edge  52 D intercepts the ends of leading and trailing edges  52 B and  52 C, which are located farthest from base edge  52 A. 
     Inner vane element  53  has a trapezium-like profile which is defined by base edge  53 A, leading edge  53 B, trailing edge  53 C and outer edge  53 D. The length of base edge  53 A is equal to the diagonal of rail element  51 . Leading edge  53 B and trailing edge  53 C are of unequal lengths and intersect opposite ends of base edge  53 A to form unequal acute angles respectively designated β 1  and β 2  in FIG.  5 ( b ). Outer edge  53 D intercepts the ends of leading edge  53 B and trailing edge  53 C, which are located farthest from base edge  53 A. 
     FIG.  5 ( a ) illustrates how rail element  51 , outer vane element  52  and inner vane element  53  appear when assembled to form spin vane  50 . Outer vane element  52  is attached at base edge  52 A to the outer face of rail element  51  so that base edge  52 A runs diagonally across rail element  51 . Inner vane element  53  is secured at base edge  53 A to the inner face of rail element  51  so that base edge  53 A also runs diagonally across rail element  51 , but between corners of rail element  51  which are opposite to those spanned by base edge  52 A of outer van element  52 . The preferred method of affixing vane elements  52  and  53  to rail element  51  is the same as that described for spin vane  40 , above, i.e., welding, and like vane elements  42  and  43  of spin vane  40 , vane elements  52  and  53  of spin vane  50  are joined to rail element  51  so that they both are aligned perpendicularly with respect to the faces of rail element. 
     FIGS.  4 ( b ) and  5 ( b ) further show that outer vane elements  42  and  52  and inner vane elements  43  and  53  respectively will have an outer vane element height, h o , and an inner vane element height, h i . Vane element heights h o  and h i  are measured between the base edge and the outer edge of the vane elements. The ratio of outer vane element height to inner vane element height (h o /h i ) may vary so as to provide for air flow volumes above and below rail elements  41  and  51 , which will help to optimize burner combustion performance. As also shown in FIGS.  4 ( b ) and  5 ( b ), outer and inner vane elements  42  and  43  of spin vane  40  and outer and inner vane elements  52  and  53  of spin vane  50  will be oriented relative to one another so as to form an angle δ. The preferred magnitude of angle δ may range anywhere from 10 to 40 degrees, with a specific value within that range being selected so as to produce air flow patterns above and below rail elements  41  and  51 , that will further help to achieve optimum burner performance. 
     Use of spin vane  50  may be preferred over spin vane  40  where a need exists to create air flow patterns which either converge or diverge after they leave the burner. The straight edges of outer and inner vane elements  52  and  53  can be cut at angles that will cause the air flows above and below rail element  51  to take paths that either converge or diverge by the time the flows pass the trailing edges of vane elements  52  and  53 . 
     Because each of the embodiments of the present invention create multiple air flow paths in a secondary air flow passage, the invention makes it is possible to change the aerodynamic characteristics of a known single register burner, like burner  10  shown in FIG. 1, to mimic those of a known dual register burner, like burner  20  illustrated in FIG.  2 . The change may be accomplished through a simple replacement of the known single-piece spin vanes  11  with the invention. Such replacement is believed to be a low cost, time-efficient alternative to completely removing an already installed single register burner and replacing it with a higher cost dual register burner. 
     The present invention may also be employed to replace known spin vanes  26  of dual register burner  20  and to thereby modify the burner&#39;s aerodynamic attributes. Such a replacement may prove desirable in a situation where it is necessary for the burner to achieve emission standards which are more stringent than those currently imposed upon dual register burner users. 
     Referring to FIGS. 6-9, there is shown another embodiment of the present invention. It will be noted at the outset that in all of FIGS. 6-27, the preferred vane configuration is curved, but straight vanes could be applied in certain instances. FIG. 6 is an end view of a fossil-fueled burner apparatus, such as a single register burner  10 , taken from the furnace side, employing a plurality of compound spin vanes  70  for imparting a spin to combustion air  72  flowing through an annular air flow passage  74 . The passage  74  is partially defined between an inner wall  76  and an outer wall  78 . 
     Compound spin vane  70  advantageously comprises a first vane portion  80  having a leading edge  82  exposed to the oncoming flow of air  72 , a trailing edge  84  located downstream thereof with respect to the flow of air  72  as it passes by the first vane portion  80 , and a length L 1  defined therebetween. The first vane portion  80  also has an inner edge  86 , an outer edge  88 , preferably curved to match the inside curvature of outer wall  78  but to allow clearance when the compound spin vane is moved, located proximate to the outer wall  78  of the annular air passage  74 , and a height H 1  defined therebetween. The first vane portion  80  also has opposite, lateral sides  90  and  92 . 
     A second vane portion  100  is also provided, having a leading edge  102  exposed to the oncoming flow of air  72 , a trailing edge  104  downstream thereof with respect to the flow of air  72  as it passes by the second vane portion  100 , and a length L 2  defined therebetween. Again, the second vane portion  100  also has an inner edge  106  located proximate to the inner wall  76  of the annular air passage  74 , an outer edge  108 , and a height H 2  defined therebetween. Just as was the case with the first vane portion  80 , the second vane portion  100  also has opposite, lateral sides  110 ,  112 . 
     Means  114 , advantageously rigid links, are provided for rigidly connecting a first lateral side  110  of the second vane portion  100  to a first lateral side  90  of the first vane portion  80  in spaced lateral relationship with respect thereto. In this way, both the first and second vane portions  80 ,  100  can move together as a unit when the compound spin vane  70  is installed and positioned in the annular air flow passage  74  of the burner apparatus  10 . 
     In certain circumstances, the compound spin vane  70  may also be provided with a third vane portion  120  substantially identical in configuration to the second vane portion  100 . Again, means  114  would be provided for rigidly connecting a first lateral side  110  of the third vane portion  120  to a second, opposite lateral side  92  of the first vane portion  80  in spaced lateral relationship with respect to the first vane portion so that the first, second, and third vane portions  80 ,  100 ,  120  move together as a unit when the compound spin vane  70  is installed and positioned in the annular air flow passage  74  of the fossil-fueled burner apparatus  10 . 
     FIGS. 10-13 are substantially identical to FIGS. 6-9, the main difference being that the means for rigidly connecting the second  100  and third  120  vane portions in spaced lateral relationship with respect to the first vane portion  80  comprises first rigid plate means  122  connected inbetween the one lateral side  90  of the first vane portion  80  and the first lateral side of the second vane portion, and second rigid plate means  124  connected inbetween the opposite lateral side  92  of the first vane portion  80  and the first lateral side  110  of the third vane portion  120 . 
     Each of the first, second and third vane portions  80 ,  100 ,  120  is preferably formed as a simple, curved planar surface, and the same simple, curved planar surface would be applied to all vanes. Advantageously, the simple, curved planar surface configuration has a vane profile defined as a portion of a wall of a cylinder. 
     In addition to the novel compound spin vane configurations disclosed herein, an important aspect of the present invention is drawn to a fossil-fueled burner apparatus employing these constructions. In the single annular air flow passage partially defined between an inner wall and an outer wall of the burner apparatus, an arrangement of compound spin vanes is installed and positioned within the annular air flow passage for imparting a spin to combustion air flowing through the annular air flow passage. Some of the compound spin vanes comprise just the aforementioned first and second vane portions  80 ,  100 . Of course, the fossil-fueled burner apparatus would be provided with means for field adjusting the position of the compound spin vanes to vary the amount of spin imparted to the combustion air flow flowing through the annular air flow passage and past the arrangement of compound spin vanes. In addition, some of the compound spin vanes are further comprised of the third vane portion  120  which, as mentioned earlier, is substantially identical in configuration to the second vane portion  100 . Rigid connecting means, such as the links or plates, would be used as required to locate the vane portions in spaced lateral relationship with respect to each other so that the first, second, and third vane portions move together as a unit when the compound spin vane is installed and positioned in the annular air flow passage of the burner apparatus. Again, each of the first, second and third vane portions is formed as a simple, curved planar surface configuration (advantageously a section of a cylindrical surface) and each vane portion has substantially the same simple, curved planar surface configuration. 
     As shown in the drawings, another way to characterize the various compound spin vane configurations is to identify a ratio of the numbers of different types of vane portions provided in the burner annular air passage  74 . In general, a plurality of first, second, and third vane, portions are positioned and installed in the burner apparatus. As shown in FIGS. 7,  11 ,  22  and  25 , a ratio of (the total number of second and third vane portions) to (the total number of first vane portions) is preferably equal to 2. Alternatively, other spin vane arrangements are possible, such as those shown in FIGS. 15 and 19, wherein a plurality of first, second, and third vane portions are positioned and installed in the burner apparatus, and a ratio of (the total number of second and third vane portions) to (the total number of first vane portions) is equal to 4:3. Of course, it is possible for all of the compound spin vanes to be comprised of first, second and third vane portions. 
     Yet another way to characterize the various compound spin vane configurations is to identify a repeating pattern of compound vane types, such as shown in FIGS. 14 and 18. There, the arrangement of compound spin vanes  70  comprises, in order, a repeating pattern of: compound spin vanes having first and second vane portions, compound spin vanes having first, second and third vane portions, and compound spin vanes having first and third vane portions, installed and positioned around an entire circumference of the annular air flow passage  74 . 
     Referring to FIGS. 22-27, there is shown another embodiment of the compound spin vanes  70  of the present invention, the fundamental difference being the particular means by which the vane portions are rigidly connected to one another. Again, these vane configurations are particularly suited to use in a fossil-fueled burner apparatus. In the case of FIGS. 22-24, the rigid plate means comprises a single plate  126  connected to the inner edge  86  of the first vane portion  80  and to the outer edges  108  of the second and third vane portions  100 ,  120  for rigidly connecting the second and third vane portions  100 ,  120  in spaced lateral relationship with respect to each other, so that the first, second, and third vane portions  80 ,  100 ,  120  move together as a unit when the compound spin vane  70  is installed and positioned in the annular air flow passage  74  of the burner apparatus  10 . In FIGS. 25-27, only a single second vane portion  100  is provided. In either case, each of the first, second and third vane portions  80 ,  100 ,  120  is formed as a simple, curved planar surface configuration and each vane portion has substantially the same simple, curved planar surface configuration. However, for these embodiments, the rigid plate means  126  connects the first, second and third vane portions in a fixed relationship with respect to one another such that the trailing edge of the first vane portion is at an angle theta θ with respect to the trailing edges  84  of the second and third vane portions having a value lying within a range of 0 degrees to approximately 20 degrees. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. For example, the present invention may be applied in new construction involving existing single register burner apparatus, or to the replacement, repair or improvement of existing burner apparatus. As discussed in connection with the various forms of the CBV having the first, second and third vane portions, in some embodiments of the invention, certain features of the invention may sometimes be used to advantage without a corresponding use of the other features. Accordingly, all such changes and embodiments properly fall within the scope of the following claims.