Flight for Asphalt Rotary Dryer

Abstract

An improved geometry for flights used in rotary drums of aggregate dryers in the manufacture of asphalt causes the aggregate to shower in an even veil across the full width of the drum under all loading conditions. An opening in the flight having a narrow bottom and wider top allows more aggregate to shower early, especially when flights are lightly loaded, on the uplift side of the drum to complete the aggregate veil and prevent hot gases from bypassing. The opening is oriented with its narrow bottom nearest the inner surface of the drum and its wider top farthest therefrom. The opening does not extend through the full height of the flight, which would form an undesired gap allowing an excessive volume of aggregate to flood out of fully loaded flights on the uplift side of rotation. Such flooding discharge causes a similar imbalance of drying to that caused by too little discharge from light loaded flights. The size and shape of the opening can be varied to adjust the amount of aggregate discharged from each flight to form the veil and to adjust the shape of the veil.

Claims

1. A dryer configured for use in an asphalt plant, the dryer comprising: a drum having an interior with an inner wall; and a flight disposed within the interior of the drum, the flight comprising: a proximal edge attached to the inner wall of the drum; a distal edge that is spaced apart from the proximal edge; and an opening having a shape defined by a plurality of isosceles trapezoids that each comprise a plurality of line segments connected end-to-end, the plurality of isosceles trapezoids comprising at least: a first isosceles trapezoid comprising: an upper line segment spaced apart from the distal edge of the flight, the upper line segment having a first end and a second end; a pair of first middle line segments disposed between the upper line segment and the proximal edge of the flight, the pair of first middle line segments comprising:  a first left middle line segment connected to the first end of the upper line segment, wherein the first left middle line segment and the upper line segment intersect at an angle; and  a first right middle line segment connected to the second end of the upper line segment, wherein the first right middle line segment and the upper line segment intersect at an angle; and a middle line disposed below and parallel to the upper line segment, the middle line having a first end connected to the first left middle line segment and a second end connected to the first right middle line segment; and a second isosceles trapezoid comprising: the middle line; a pair of second middle line segments disposed between the middle line and the proximal edge of the flight, the pair of second middle line segments comprising:  a second left middle line segment connected to the first end of the middle line, wherein the second left middle line segment and the middle line intersect at an angle; and  a second right middle line segment connected to the second end of the middle line, wherein the second right middle line segment and the middle line intersect at an angle; and a lower line segment disposed below and parallel to the middle line, the lower line segment having a first end connected to the second left middle line segment and a second end connected to the second right middle line segment.

2. The dryer of claim 1 wherein the opening is centrally located between left and right edges of the flight.

3. The dryer of claim 1 wherein a width of the opening measured between the first and second ends of the upper line segment is between 40% and 60% of a length of the flight measured between right and left edges of the flight.

4. The dryer of claim 1 wherein the upper line segment is parallel to the distal edge of the flight.

5. The dryer of claim 1 wherein the first left middle line segment and the first right middle line segment are of equal length, and the second left middle line segment and the second right middle line segment are of equal length.

6. The dryer of claim 1 wherein one or more of the plurality of line segments that comprise the first and second isosceles trapezoids are straight line segments.

7. The dryer of claim 1 wherein the flight has a first shape profile that is scoop-shaped, such that the flight is operable to sequentially contain, lift, and discharge aggregate materials within the interior of the drum as the drum rotates.

8. The dryer of claim 1 wherein the flight comprises separable left and right plates that are symmetrically opposed on either side of a centerline of the flight that divides the opening into two symmetrically opposed halves, and wherein the left and right plates of the flight are operable to be joined together along the centerline to form the flight and the central opening.

9. A dryer flight configured for attachment to an inner wall of a drum of a dryer, wherein as the drum rotates, the dryer flight scoops, carries, and showers aggregate materials used in making asphalt pavements, the dryer flight comprising: a proximal edge configured for attachment to the inner wall of the drum; a distal edge that is spaced apart from the proximal edge; and an opening having a shape defined by a plurality of isosceles trapezoids that each comprise a plurality of line segments connected end-to-end, the plurality of isosceles trapezoids comprising at least: a first isosceles trapezoid comprising: an upper line segment spaced apart from the distal edge of the flight, the upper line segment having a first end and a second end; a pair of first middle line segments disposed between the upper line segment and the proximal edge of the flight, the pair of first middle line segments comprising: a first left middle line segment connected to the first end of the upper line segment, wherein the first left middle line segment and the upper line segment intersect at an angle; and a first right middle line segment connected to the second end of the upper line segment, wherein the first right middle line segment and the upper line segment intersect at an angle; and a middle line disposed below and parallel to the upper line segment, the middle line having a first end connected to the first left middle line segment and a second end connected to the first right middle line segment; and a second isosceles trapezoid comprising: the middle line; a pair of second middle line segments disposed between the middle line and the proximal edge of the flight, the pair of second middle line segments comprising: a second left middle line segment connected to the first end of the middle line, wherein the second left middle line segment and the middle line intersect at an angle; and a second right middle line segment connected to the second end of the middle line, wherein the second right middle line segment and the middle line intersect at an angle; and a lower line segment disposed below and parallel to the middle line, the lower line segment having a first end connected to the second left middle line segment and a second end connected to the second right middle line segment.

10. The dryer flight of claim 9 wherein the opening is centrally located between left and right edges of the dryer flight.

11. The dryer flight of claim 9 wherein a width of the opening measured between the first and second ends of the upper line segment is between 40% and 60% of a length of the flight measured between right and left edges of the dryer flight.

12. The dryer flight of claim 9 wherein the upper line segment is parallel to the distal edge of the dryer flight.

13. The dryer of claim 9 wherein the first left middle line segment and the first right middle line segment are of equal length, and wherein second left middle line segment and the second right middle line segment are of equal length.

14. The dryer of claim 9 wherein one or more of the plurality of line segments that comprise the first and second isosceles trapezoids are straight line segments.

15. The dryer of claim 9 wherein a first shape profile of the flight is scoop-shaped, such that the flight is operable to sequentially contain, lift, and discharge aggregate materials within the interior of the drum as the drum rotates.

16. The dryer of claim 9 wherein the flight comprises separable left and right plates that are symmetrically opposed on either side of a centerline of the flight that divides the opening into two symmetrically opposed halves, and wherein the left and right plates of the flight are operable to be joined together along the centerline to form the flight and the central opening.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other embodiments of the invention will become apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:

[0025] FIG. 1 depicts a perspective view of a flight for an asphalt dryer according to an embodiment of the invention;

[0026] FIG. 2 depicts a front elevation view of the flight of FIG. 1;

[0027] FIGS. 3A and 3B depict an end elevation view of the flight of FIG. 1;

[0028] FIG. 4 depicts the interior of an asphalt dryer drum according to an embodiment of the invention; and

[0029] FIGS. 5 and 6 depict the profile of an opening in the flight of FIG. 1.

DETAILED DESCRIPTION

[0030] FIG. 4 depicts a rotary dryer 100 for use in an asphalt plant. The dryer 100 includes an elongate cylindrical drum 110 set at an incline and through which flows heated air or combustion gases from a burner. Aggregate material 102 to be dried is introduced at an entrance to the drum 110, and as the material travels through the drum under the force of gravity, it comes into contact with the heated air. Attached to the interior peripheral walls of the drum 110 are multiple radially-spaced fin-like structures referred to as flights 10. The flights 10 aid in circulating the aggregate material 102 while increasing the amount of time the aggregate material 102 remains exposed to the heated air and/or combustion gases inside the drum 110. In this manner, the flights 10 improve the efficiency of the dryer 100 by increasing the heat transfer between the heated air and the aggregate material. With continued reference to FIG. 4, as the drum 100 rotates in direction “R,” the flights 10 retain and raise portions of the aggregate material 102 toward the top of the drum 110. As it nears the top of the drum 110, the aggregate material 102 showers downward from the flights 10 and falls through the flow of heated air, creating a curtain 108 of aggregate material 102 across the width of the drum 110.

[0031] A proper geometry of the flights 10 is critical in producing an evenly distributed curtain 108 of aggregate material 102 across the diameter of the drum for various operating conditions, which may be affected by differences in the mix of aggregate material and differences the processing rates and volumes. FIGS. 1, 2, 3A-3B and 5 depict a preferred embodiment of a flight 10 having a geometry optimized for this purpose.

[0032] The flight 10 preferably comprises scoop-shaped right and left plates 12 and 14 that are joined together by an angle bracket 16. The plates 12 and 14 are secured to the bracket 16 by bolts 18. As shown in the profile views of FIGS. 3A and 3B, the plates 12 and 14 are bent at three locations to form the scoop-shaped profile. Although only plate 12 is depicted in FIGS. 3A and 3B, it will be appreciated that plate 14 is bent in the same manner. In a preferred embodiment, each plate 12 and 14 includes four plate sections—such as plate sections 12a, 12b, 12c and 12d in plate 12—defined by the three bends. It will be appreciated that other embodiments may include fewer or more plate sections defined by fewer or more bends.

[0033] As shown in FIGS. 1 and 2, the plates 12 and 14 each have a cutout on their inside edges, such that when the inside edges are joined, the cutouts form a symmetrical opening 20 shaped as a series of adjacent isosceles trapezoids in the center of the flight 10. The opening 20 is oriented with its straight top parallel to the length of the flight 10, thereby allowing the aggregate material 102 to drop through the opening 20 and shower into the hot air/gas stream from the burner of the dryer 100 as the drum 110 rotates the flight 10 upward. This action promotes the early showering of the aggregate material 102, especially when the drum 110 is lightly loaded. Such a showering characteristic is particularly advantageous when making asphalt paving mixtures having high content of recycled asphalt pavement, as well as certain other mixes that tend to reduce the capacity of the dryer 100.

[0034] In preferred embodiments, the overall length L.sub.S0 of the opening 20 is parallel to the length of the flight, and is about 40% to 60% of the total length L.sub.F of the flight 10. In the embodiment depicted in FIGS. 2 and 5, L.sub.S0 is 30 inches and L.sub.F is 48 inches, such that L.sub.S0 is about 63% of L.sub.F. In preferred embodiments, the height H.sub.O of the opening 20 is about 50% to 80% of the height H.sub.F of the flight 10, as measured in a radial direction from the inner surface of the drum 110. In the embodiment depicted in FIGS. 2 and 5, the height H.sub.O is approximately 10 inches and the height H.sub.F is 14.56 inches, such that H.sub.O is about 70% of H.sub.F.

[0035] In the preferred embodiment, the opening 20 is centered within the length of a single flight 10. However, in alternative embodiments, two flights—each containing half of the opening 20—may be positioned end to end in such a manner as to form the full opening 20.

[0036] As depicted in FIG. 5, a preferred embodiment of the opening 20 is defined by a pair of isosceles trapezoids IT1 and IT2 that each comprise multiple line segments connected end-to-end. The line segments include an upper line segment S0, four middle line segments S1-S4, and a lower line segment S5. The first isosceles trapezoid IT1 includes the upper line segment S0, the two middle line segments S1 and S2, and the middle line ML. The second isosceles trapezoid IT2 includes the middle line ML, the two middle line segments S3 and S4, and the lower line segment S5.

[0037] In the embodiment depicted in FIG. 5, the upper line segment S0 of the opening 20 has a length L.sub.S0 of 30 inches, the two middle line segments S1 and S2 have lengths L.sub.S1 and L.sub.S2 of 8.48 inches, the two middle line segments S3 and S4 have lengths L.sub.S3 and L.sub.S4 of 9.84 inches, and the lower line segment S5 has a length L.sub.S5 of 6.00 inches.

[0038] In some embodiments, the shape of the opening 20 is approximately pear shaped, with the line segments S1-S5 being fit to a pear-shaped curve. It will be appreciated that more lower segments could be included to more closely fit a continuous curve, such as the dashed-line curve shown in FIG. 5. For example, in the embodiment of FIG. 6, there are seven lower line segments S1-S7 that form three isosceles trapezoids. As the term is used herein, “fitting” a curve means forming a piecewise linear approximation of a curve using multiple line segments connected end-to-end, although this does not require any of the lines or endpoints of the line segments to coincide exactly with any particular curve. Also, the curve of the opening 20 may exactly follow a continuous curve in some embodiments.

[0039] The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.