Abstract:
A bulk material feeder is disclosed for improving material flow as the material makes the generally ninety degree (90°) transition from the downcomer to the generally horizontal conveyor. The downcomer presents an innermost divergent surface that extends upwardly from the discharge opening of the downcomer. The divergent surface may be defined by an inlet wall that is fit within the outer casing wall of the downcomer, or by the outer casing wall itself. The present invention also concerns the method of retrofitting an existing feeder with a divergent inlet.

Description:
RELATED APPLICATIONS 
     Not Applicable 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to bulk material feeders and, more particularly, to a divergent inlet that improves material flow from the supply downcomer to the horizontal conveyor of the feeder. 
     2. Discussion of Prior Art 
     Those ordinarily skilled in the art will appreciate that numerous processes involve conveying a mass or masses of solid particulate material (alternatively referred to as bulk material) along a path from one location to another. Moreover, the material flow path will often involve a transition from generally downward flow to substantially horizontal flow. For example, bulk material will commonly pass through a downcomer to a substantially horizontal conveyor, whereby the material is directed downwardly through the downcomer to the conveyor and then carried horizontally away from the downcomer by the conveyor. Such an arrangement is often designed to move the material along the path or, in some instances, control the volume-rate or mass-rate of flow of material along the path. In addition, the downcomer and horizontal conveyor are often collectively referred to as a bulk material feeder. 
     In any case, there are often problems associated with material flow through a bulk material feeder. For example, the material is often not transferred to the conveyor at a uniform rate, even though there is a consistent rate of material being supplied to the downcomer. This problem has been particularly identified with respect to a certain type of bulk material feeder known as a gravimetric feeder. The gravimetric feeder includes a variable speed conveyor which may be designed to change speed in response to the amount of material being carried by the conveyor. In this respect, the conveyor speed may be increased or decreased to ensure that the desired amount of material is being moved by the conveyor. Manifestly, if the material is being unevenly transferred from the downcomer to the conveyor, the conveyor speed will necessarily have to adjust to accommodate for such fluctuations. The virtually continuous increase and decrease in conveyor speed presents numerous additional problems, including undue wear on the feeder components. 
     Those ordinarily skilled in the art will further appreciate that the downcomer on a gravimetric feeder traditionally includes a downstream discharge opening through which material is permitted to pass as it is moved along the path by the conveyor. In addition, the structure defining the discharge opening is designed to control the amount of material being transferred by the conveyor so as to facilitate relatively even and consistent volumetric transfer of material from the downcomer to the conveyor. This design, of course, assumes that sufficient material is being continuously deposited on the conveyor to cause the material that is moved out of the downcomer by the conveyor to be leveled off as it passes through the discharge opening. However, as will be set forth in further detail below, it has been determined that the traditional downcomer design simply does not permit the discharge opening to operate in the desired manner. 
     Another type of feeder that is susceptible to some of the aforementioned problems is a volumetric feeder. Such a feeder relies heavily on uniform and accurate volumetric flow and, contrary to a gravimetric feeder, includes no means for adjusting the belt speed in response to fluctuations in the volumetric flow rate. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Responsive to these and other problems, an important object of the present invention is to improve material flow through bulk feeders. In this respect, it is also an important object of the present invention to provide a bulk material feeder having uniform material flow from the downcomer to the conveyor. Another important object of the present invention to improve upon the construction of conventional volumetric and gravimetric feeder designs. Particularly, it is an object of the present invention to provide a feeder that does not suffer from undesirable conveyor speed fluctuations caused by uneven material flow. 
     In accordance with these and other objects evident from the following description of the preferred embodiments, the present invention concerns a bulk material feeder having a conveyor that is operable to convey material along a substantially horizontal path. Of course, if the principles of the present invention are being used on a gravimetric feeder, the conveyor speed may be adjustable responsive to the amount of material being carried by the conveyor. The feeder further includes a downcomer presenting a lower edge adjacent the conveyor, with the downcomer being configured to deliver the material onto the conveyor in an upright column. Moreover, the downcomer includes an innermost downwardly divergent surface which is believed to significantly improve material flow through the downcomer and onto the conveyor. The present invention also concerns a feeder inlet design that presents the divergent surface and is configured to be installed within an existing downcomer for improving material flow within the feeder without requiring extensive modification to the feeder. In addition, the present invention concerns the method of retrofitting an existing feeder with the inlet design. 
     Again, it has been determined that the divergent surface ensures that material flow is uniform from the downcomer to the conveyor. Particularly, it is believed that the divergent surface prevents the material from clogging within the downcomer as it flows downwardly toward the conveyor. It is also believed that the innermost divergent surface ensures that the discharge opening operates in its intended manner; that is, the structure defining the discharge opening serves to control the amount of material being moved away from the material column by the conveyor. As previously indicated, this leveling action facilitates uniform volumetrically efficient material transfer by the conveyor. In addition, it is believed that uniform material transfer by the conveyor is further facilitated by the fact that the divergent innermost surface provides essentially only lateral support to the material within the downcomer, such that virtually the entire material column confined by the divergent surface is supported on the conveyor. It is particularly believed that this relatively significant, downwardly directed pressure within the downcomer further decreases material flow fluctuations within the feeder and ensures that the material conveyed by the conveyor has uniform density. 
     Those ordinarily skilled in the art will appreciate that conventional bulk material feeders simply do not provide the advantages afforded by the present invention. It has been determined that this is primarily attributable to the traditional downcomer construction. Particularly, the downcomer wall is traditionally straight (i.e., generally parallel to the longitudinal axis of the downcomer), and it is believed that this straight-walled construction is not conducive to solid particulate material being fed to the conveyor by gravity and then through the discharge opening by the conveyor. It has further been determined that the material tends to bridge across the interior of the straight-walled downcomer and thereby create stoppages of material flow or, at the very least, uneven material flow. This phenomenon referred to herein as “bridging” is a result of the cohesive force of the material and the adhesive force between the material and the downcomer walls overcoming the gravitational influence on the material. Furthermore, it has been determined that material flow to the conveyor is typically uneven enough and insufficient in quantity to permit the discharge opening from operating in its intended manner. These problems become even more troublesome when dealing with a “sticky” material or material that becomes more cohesive as its moisture content increases (e.g., coal). 
     Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     Preferred embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein: 
     FIG. 1 is a side elevational view of a gravimetric-type bulk material feeder having a divergent inlet constructed in accordance with the principles of the present invention, with portions of the feeder being broken away to reveal internal details of construction; 
     FIG. 2 is an enlarged, fragmentary side elevational view of the feeder shown in FIG. 1, particularly illustrating the inlet portion of the downcomer and its relationship to the conveyor; 
     FIG. 3 is a fragmentary vertical sectional view of the feeder taken along line  3 — 3  of FIG. 2; and 
     FIG. 4 is a fragmentary side elevational view of an alternative embodiment of the present invention, wherein the innermost downwardly divergent surface of the downcomer is defined by the pipe wall. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning first to the embodiment shown in FIGS. 1-3, the bulk material feeder  10  selected for illustration is provided along a material flow line that is vertical both upstream and downstream from the feeder  10 . The illustrated feeder  10  comprises a traditional gravimetric feeder that serves to control the rate of material flow along the path, although it will be appreciated that the principles of the present invention are equally applicable to various other feeders. With the foregoing caveat in mind, it will be appreciated that the gravimetric feeder  10  includes a material supply downcomer  12  for connecting to the supply line  14  and a downwardly directed discharge spout  16  for connecting to the discharge line  18 , in the usual manner. Except for the inventive features identified herein, it is entirely within the ambit of the present invention to variously construct both the downcomer  12  and the discharge spout  16 . It is noted that the illustrated gravimetric feeder  10  is particularly well suited for use in a coal-fired power plant. In this respect, the supply line  14  traditionally extends upstream from the downcomer  12  immediately to a coal hopper (not shown), while the discharge line  18  will typically connect directly to a material processing station, such as a mill (also not shown) for pulverizing the coal into a fine highly, combustible powder. 
     In the usual manner, extending between the downcomer  12  and the discharge spout  18  is a variable speed conveyor  20  for conveying material therebetween. The illustrated conveyor  20  comprises an endless belt  22  that wraps around a pair of horizontally spaced pulleys  24  and  26 , one or both of which may be powered to drive the belt  22 . The belt  22  presents a substantially horizontal upper conveying stretch  22   a  (also referred to as an upper strand) that moves leftwardly, when viewing FIG. 1, to convey material from the downcomer  12  to the discharge spout  16 , and a lower return stretch  22   b  (also referred to as a lower strand) that moves in the opposite direction. However, it will be appreciated that the principles of the present invention are equally applicable to various other conveyor designs. For example, it is entirely within the ambit of the present invention to provide a conveyor having a noncontinuous conveyor bed, with a plurality of beater bars being located below the bed to facilitate downstream movement of the material along the bed. It is also possible to provide a conveyor with a conveying stretch that slopes slightly downwardly toward the discharge end to promote movement of the material. 
     As perhaps best shown in FIG. 2, the illustrated conveyor  20  includes a series of support rollers  28 ,  30 ,  32 ,  34 ,  36 ,  38  located along the underside of the conveying stretch  22   a  generally below the downcomer  12 . The support rollers  28 - 38  provide support to the belt  22  at the point where the weight of the material is greatest, as will subsequently be described. The rollers  28 - 38  are similarly constructed, and it therefore shall be sufficient to explain that the downstream roller  28  includes a central cylindrical bar  40  and a pair of stub shafts  42  and  44  projecting from opposite ends of the bar  40  (see FIG.  3 ). The shafts  42  and  44  are journaled for rotational movement on adjacent support walls  46  and  48  by respective bearing assemblies  50  and  52 . 
     Downstream from the series of support rollers  28 - 38  are a pair of similarly constructed rollers  54  and  56  that are spaced along the length of the conveying stretch  22   a  to define a weigh span therebetween. In the usual manner, a weigh roller  58  is precisely centered along the weigh span and is shiftably supported by a pair of load cells  60  (only one of the load cells being shown in the drawing figures), with the load cells  60  generating an electric signal that is proportional to the weight of material supported on the weigh span. The load cells  60  are connected to the power mechanism (not shown) for the conveyor  20  so that driving power supplied to one or both of the pulleys  24  and  26  may be varied depending upon the weight of the material supported on the weight span. In this respect, the conveyor speed may be adjusted to control the amount of material being moved along the path. 
     In the illustrated embodiment, the conveyor  20  is contained within a housing  62  that is substantially cylindrical in shape to present a top surface  64 , a bottom surface  66 , a pair of side surfaces  68  and  70  extending between the top and bottom surfaces  64  and  66 , and a pair of end surfaces  72  and  74  sealing off the opposite ends of the housing  62 . Those ordinarily skilled in the art will appreciate that when the feeder  10  is used to convey combustible materials the housing  62  is traditionally constructed to standardized explosion pressure ratings. For example, the walls  64 ,  66 ,  68 ,  70 ,  72 ,  74  may be designed to withstand an internal housing pressure of up to one-hundred pounds per square inch. It is noted that each of the end surfaces  72  and  74  has an access opening (not shown) for providing access to the interior of the housing  62 , with a pair of doors  76  and  78  being swingably supported on the respective end surfaces  72  and  74  for selectively covering the access openings. 
     The material deposited on the conveying stretch  22   a  by the downcomer  12  is moved toward the discharge pulley  24  and will ultimately drop off the discharge end of the conveyor  20 . The material then falls by gravity into the discharge spout  16  and is thereby directed to the discharge line  18 . It is noted that the discharge spout  16  has a hopper-type configuration for converting the material flow back into a stream that has a generally circular cross-sectional shape. That is to say, the discharge spout  16  causes the material falling from the conveyor  20  to converge downwardly into the cylindrical discharge line  18 . Similar to the housing  62 , the discharge spout  16  is preferably designed to withstand a predetermined internal pressure. 
     As noted above, except for the inventive features described below, the illustrated downcomer  12  is generally conventional in construction. Thus, it shall be sufficient to explain that the downcomer  12  includes an inlet valve  80  connected to the supply line  14  and a vertical pipe  82  extending downwardly from the valve  80  to the conveyor  20 . The pipe  82  is cylindrical in shape and divided into three sections  82   a ,  82   b ,  82   c , although the shape and sectioning of the pipe may vary as desired. The valve  80  and upper pipe section  82   a  are fastened to one another in the usual manner by flanges  84  and  86 . The adjacent ends of the upper pipe section  82   a  and intermediate pipe section  82   b  are similarly interconnected by flanges  88  and  90 . The lower pipe section  82   c  is preferably fixed to the top surface  64  of the housing  62 , with the upper end of the lower pipe section  82   c  being spaced from the lower end of the intermediate pipe section  82   b . An expansion joint  92  serves to interconnect these two sections of the pipe  82 . In the usual manner, the expansion joint includes a pair of vertically spaced rings  94 ,  96 , a sleeve  98  interposed in the space between the rings  94  and  96 , a plurality of long nut and bolt assemblies  100  spaced circumferentially about the rings  94  and  96 , and a gasket (not shown) located between the sleeve  98  and the pipe sections  82   b  and  82   c  (see FIG.  2 ). Thus, when the assemblies  100  are tightened, the expansion joint  92  securely seals around the adjacent ends of the intermediate and lower pipe sections  82   b  and  82   c , yet permits limited relative movement therebetween. 
     As perhaps best shown in FIGS. 2 and 3, the lower pipe section  82   c  defines the lower edge  102  of the downcomer  12 , with the edge  102  presenting a generally horizontal section  102   a  that is spaced just above the conveying stretch  22   a  and a downstream section  102   b  that is progressively spaced from the conveying stretch  22   a  in the downstream direction. The downstream section  102   b  consequently defines a discharge opening  104  through which material is permitted to pass laterally from the downcomer  12 . As noted above, the downstream section  102   b  of the lower edge  102  is designed to limit or control the amount of material moved out of the downcomer  12  by the conveyor  20 . In the illustrated embodiment, the downstream section  102   b  is defined along a plane that projects obliquely upward in the downstream direction relative to the conveying stretch  22   a , such that the discharge opening has a so-called “ungular” shape, although the downstream section  102   b  may be variously arranged. It is also noted that the lower pipe section  82   c  includes an upstream panel  106  that projects upwardly from the lower edge  102  in an upstream direction. However, it is entirely within the ambit of the present invention to eliminate the upstream panel  106  so that the entire lower pipe section  82   c  has a circular cross-sectional shape, if desired. 
     It will be appreciated that the pipe sections  82   a , 82   b , 82   c  cooperatively present a casing wall that is substantially parallel to the longitudinal axis of the pipe  82 . As previously indicated, it has been determined that this straight-walled construction causes problems with material flow through the feeder. If desired, the pipe sections and the expansion joint  92  may have an explosion resistant construction similar to the discharge spout  16  and housing  62 . 
     In this respect, the illustrated downcomer  12  has been provided with a divergent inlet  108  that is believed to significantly improve material flow through the feeder  10 . In the present embodiment, the inlet  108  comprises a tube  110  that is configured to fit lengthwise within the pipe  82 . As perhaps best shown in FIG. 2, the tube  110  presents opposite wall sections  110   a  and  110   b  that diverge outwardly from a central throat  110   c . With the inlet  108  installed in the downcomer  12 , the upper wall section  110   a  converges downwardly toward the throat  110   c , while the lower wall section  110   b  diverges downwardly toward the conveyor  20 . The lower divergent wall section  110   b  is significantly longer than the upper convergent wall section  110   a , and the lower divergent wall section  110   b  preferably has a length that is approximately at least two times greater than the diameter of the pipe  82 . However, it is entirely within the ambit of the present invention to vary the length of either or both wall sections (e.g., the upper convergent wall section  110   a  could have the same length as the lower divergent wall section  110   b ). 
     In any case, it will be appreciated that the upper convergent wall section  110   a  serves to converge material flow within the downcomer  12  so that it may subsequently diverge as it moves toward the conveyor  20 . Although it would be possible to provide a divergent inlet without the upper convergent wall section (e.g., an inlet having a radially inwardly extending flat wall that interconnects the inner surface of the pipe  82  and the throat of the inlet), such an arrangement is more likely to obstruct material flow. Thus, the inlet  108  preferably includes the upper convergent wall section  110   a  so that the risk of plugging at the throat  110   c  is reduced. It will be appreciated that the inlet  108  must have a section that is of reduced diameter relative to the straight-walled pipe  82 , such as the throat  110   c , because the divergent wall section  110   b  is located within the pipe  82 . The upper convergent wall section  110   a  is preferably disposed at an angle between approximately thirteen and fourteen degrees relative to the pipe  82 . This angle will be referred herein to as the angle of convergence, and is approximately 13.75 degrees in the illustrated embodiment (note, the illustrated pipe  82  has a diameter of approximately twenty-four inches). It has been determined that the illustrated convergent wall section  110   a  does not noticeably affect or impede material flow within the downcomer  12 . However, other materials and even other coals may require a different angle of convergence. The angle of convergence may also need to be increased if the downward force of the material above  110   a  is insufficient to push the material through the restriction formed by central throat  110   c . For most coals, the stated angle of convergence is sufficient. 
     The lower divergent wall section  110   b  of the inlet  108  projects generally from the lower end of the upper convergent wall section  110   a  such that the adjacent ends of the upper and lower sections  110   a  and  110   b  cooperatively define the throat  110   c , although the throat may be lengthened to extend along the pipe  82  if desired. In any case, the divergent wall section  110   b  presents an innermost surface of the downcomer  12 , along which the material flows as it moves downwardly toward the conveyor  20 . The illustrated divergent wall section  110   b  preferably terminates at the uppermost boundary of the discharge opening  104  and projects upwardly therefrom generally to the top of the intermediate pipe section  82   b . The divergent wall section  110   b  is preferably disposed at a one degree to two degrees angle relative to the straight wall of the pipe  82 . This angle will be referred to herein as the angle of divergence, and the illustrated angle of divergence is 1.25 degrees. Although the angle of divergence may vary, it is important that the divergent wall section  110   b  extends sufficiently along the length of the pipe  82 . Particularly, the angle of divergence must be large enough to prevent bridging of material within the wall section  110   b  but small enough to ensure that the material is delivered onto the conveyor  20  in the manner described hereinbelow. 
     It is believed that the lower divergent wall section  110   b  of the inlet  108  significantly improves material flow through the downcomer  12  and to the conveyor  20 . That is to say, the inlet  108  has provided the unexpected result of virtually eliminating interruptions and/or fluctuations in material flow through the downcomer  12  and on the conveyor  20 . It has been determined that this is primarily attributable to the fact that the divergent wall section  110   b  simply serves to confine the material in an upright column and provides virtually no other support thereto. In other words, the risk of bridging of the material across the interior of the divergent wall section  110   b  , which is believed to be caused by the cohesiveness of the material overcoming the influence of gravity, is significantly reduced. Therefore, the material confined within the wall section  110   b  is continuously presented to the conveyor  20 . As perhaps best shown in FIG. 1, the divergent wall section  110   b  causes a material column M to be deposited directly onto the conveying stretch  22   a  above the series of support rollers  28 - 38 . Because the divergent wall section  110   b  provides only lateral support to the material column M, the entire column exerts a pressure downwardly against the conveying stretch  22   a . This downwardly directed pressure causes the material at the base of the column to be rather compacted and have a generally uniform density. Those ordinarily skilled in the art will appreciate that these conditions are often desirable when conveying solid particulate material. In addition, such conditions reduce variances in the amount of material being transferred by the conveyor  20 , thereby further reducing the risk of undesirable conveyor speed fluctuations. It is also noted that the downstream section  102   b  of the lower edge  102  functions in the desired manner by limiting the amount of material transferred out of the downcomer  12  by the conveyor  20 . As shown in FIG. 1, the lower edge  102  cooperates with the conveying stretch  22   a  to cause a generally steady, level stream of material to be moved along the flow path. 
     It is noted that the tube  110  preferably has a circular cross-sectional shape to conform to the shape of the pipe  82 . In this respect, the shape of the tube  110  may be varied similar to the pipe  82 , although it is preferred that the tube  110  and pipe  82  have generally the same shape. As perhaps best shown in FIG. 2, the wall thickness of the tube  110  is preferably less than the wall thickness of the pipe  82 . It will be appreciated that the tube  110  need only be constructed to confine the material therein and be of sufficient thickness to account for wear, while the pipe  82  is preferably designed to certain explosion pressure ratings. That is to say, the tube  110  need not be designed to withstand high internal pressure, as the pipe  82  is already designed to accommodate for such situations. One suitable downcomer construction involves a tube  110  having a wall thickness of approximately 0.125 inch and a pipe having a wall thickness of approximately 0.375 inch. Of course, the wall thickness of the tube  110  may alternatively be greater than the pipe  82 . For example, the upper convergent and lower divergent wall sections may have sufficient thickness to entirely consume the space between the inner surface of the pipe  82  and the inner surface of the tube  110 . These alternative wall sections will consequently have odd shapes and will likely require such an alternative tube to be molded from a synthetic resin material. 
     In the illustrated embodiment, the inlet  108  includes a disk-shaped flange  112  that circumscribes the tube  110  and projects radially therefrom, although other suitable structure for mounting the tube  110  within the pipe  82  may be used. The illustrated flange  112  has a circular outermost boundary that corresponds with that of the flanges  88 , 90  of the adjacent pipe sections  82   a ,  82   b  (see FIG.  2 ). The inlet flange  112  includes a series of circumferentially spaced openings (not shown) for receiving the fasteners used to attach the pipe flanges  88  and  90  to one anther, whereby the inlet flange  112  is secured between the pipe flanges  88  and  90 . In the preferred embodiment, the flange  112  projects outwardly from the throat  110   c  and is consequently located at the junction of the upper wall section  110   a  and lower wall section  110   b  , although the location of the flange  112  along the length of the tube  110  may be varied as necessary. In addition, the flange  112  may alternatively be welded to one or both of the pipe flanges  88 ,  90 . 
     In this respect, it is possible to retrofit an existing downcomer with the inlet  108  simply by disassembling certain portions of the downcomer. For example, with respect to the illustrated downcomer  12 , the valve  80  and the pipe sections  82   a  and  82   b  are removed from the supply line  14  and lower pipe section  82   c  and detached from one another. The lower divergent wall section  110   b  is then inserted through the upper end of the removed intermediate pipe section  82   b  until the inlet flange  112  engages the pipe flange  90 . These components are then coupled to the lower pipe section  82   c  by inserting the lower end of the divergent wall section  110   b  into the lower pipe section  82   c . The upper pipe section  82   a  is then slid over the exposed convergent wall section  110   a , and the pipe flanges  88 ,  90  and inlet flange  112  may then be secured to one another. The inlet valve  80  is inserted between the supply line  14  and upper pipe section  82   a  so that the upper pipe section  82   a , intermediate pipe section  82   b , and inlet  108  are suspended from the valve  80 . Finally, the expansion joint  92  is secured about the pipe sections  82   b  and  82   c.    
     The operation of the feeder  10  shall be apparent from the foregoing description. Thus, it is sufficient to explain that bulk material is supplied by the line  14  to the downcomer  12 . This material flows smoothly and evenly down through the downcomer  12  to the conveyor  20 . Particularly, the material flow is first slightly converged by the upper section  110   a  of the inlet  108 , although such convergence does not noticeably impede material flow. Thereafter, the material passes through the divergent wall section  110   b , whereby bridging of the material across the interior of the downcomer  12  is prevented. The material is consequently confined in the upright column M which moves smoothly and uniformly to the lower open end of the pipe  82 . The conveying stretch  22   a  of the conveyor  20  urges material at the lower end of the column M leftwardly (when viewing FIGS.  1  and  2 ), with the downstream section  102   b  of the lower edge  102  serving to limit material flow from the downcomer  12 . 
     It is noted that the principles of the present invention are equally applicable to various other feeder constructions. Such an alternative is shown in FIG. 4, wherein the downcomer  200  is not provided with an inlet that serves to define the divergent innermost surface, but rather the pipe  202  is configured to define the divergent innermost surface. Similar to the embodiment shown in FIGS. 1-3, the pipe  202  includes an upper section  202   a , an intermediate section  202   b , and a lower section  202   c  fixed to the housing top surface  204 . Although the upper pipe section  202   a  presents a pipe wall that is straight and parallel to the longitudinal axis of the pipe  202 , the intermediate pipe section  202   b  and lower pipe section  202   c  cooperatively present a pipe wall that diverges downwardly. As indicated above, the angle of divergence presented by the pipe wall may vary, but is preferably 1.25 degrees. It will be appreciated that this design eliminates the need for a reduced diameter throat within the downcomer. The alternative feeder design includes a traditional support pan  206  below the downcomer  200 , with the pan  206  serving the same purpose as the support rollers  28 - 38  shown in FIGS. 1-3. It is noted that the lower pipe section  202   c  may alternatively have a straight-walled construction, as long as the lower pipe section is relatively short (e.g., less than twelve inches) and is at least as large in cross-sectional shape as the intermediate pipe section  202   b.    
     The preferred forms of the invention described above are to be used as illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. 
     The inventor hereby states his intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.