Flighting for horizontal dryers

An improved flighting for dryers is the subject of the present invention. An elongated drying drum is disposed for rotation about its longitudinal axis. The inner surface of the drum is provided with a plurality of material distributing vanes in circumferentially spaced relationship. The vanes are characterized by first surface extending generally transverse to a tangent to set body at the point of attachment and a second wedge-shaped surface intersecting the first surface. The wedge-shaped surface may also be provided with a lip extending circumferentially therefrom. A plurality of interference structures are disposed from a central longitudinal support and provide means for distributing material gravitating from the outer peripheral vanes. A plurality of return flighting members are disposed along the inner surface of the drum between the afore described material distributing vanes. These flighting members are disposed at an angle and conform generally to the curvature of the inner surface. A method of drying a product includes passing the product through a dryer, rotating the dryer, and comminuting the product while it is being dried.

This invention relates generally to hot air dryers and, more particularly, 
to a dryer having improved flighting for handling bulk solid material. 
Various types of flighting arrangements for dehydrators are shown in my 
prior U.S. Pat. Nos. 3,717,937; 3,798,789; and 3,861,055. In each of the 
prior patents, peripheral vanes are disposed around the circumference of a 
rotating drum so as to distribute material throughout the cross-sectional 
area as the drum rotates. In the case of the latter two patents, so-called 
"return flighting" is employed radially spaced from the peripheral vanes 
so as to help direct material back toward the drum inlet against the flow 
of air through the drum. While this technique and equipment have been 
found to be highly effective and represent a significant advance in the 
art, further improved results are possible with the equipment of the 
present invention. 
With the construction shown in the prior patents referenced above, material 
being dried is picked up by the peripheral vanes, moved partially around 
the circumference of the drum, and is then dropped off under gravitational 
forces. A study of the cross-sectional area of a dehydrating drum as 
material is being dried has revealed that the material gravitating from 
the peripheral vanes tends to drop in "globs" or "bunches" leaving voids 
where little or no material is present in the cross-sectional area. Thus, 
the heat which is present at the location of these voids is not being 
effectively utilized and the relatively large masses of material which are 
present in other areas are unable to use the heat within their vicinity in 
the most efficient manner. 
It is, therefore, a primary object of the present invention to increase the 
quantity of material being dried that is present in any given 
cross-sectional area of a rotary drum dryer thereby utilizing such area to 
the maximum possible extent. 
As a corollary to the above object, it is an important objective to more 
evenly distribute material throughout any given cross-sectional area of a 
rotary dryer thereby reducing "voids" while also reducing large masses of 
material. 
Another important objective of this invention is to provide apparatus which 
will achieve more efficient drying in a rotary drying drum by distributing 
the material being dried in a physical form throughout the drum that is 
congruous with the most medium employed. 
An important one of the aims of my invention is to provide a rotary drying 
drum where the holding time of the material being dried is increased for a 
given length of dryer, thereby, increasing the drying efficiency and 
allowing the drum to be shortened, or alternatively, a greater volume of 
material to be passed through a drum of given length. 
It is also a very important objective of this invention to provide a rotary 
horizontal drying drum which incorporates the advantages of flash dryers 
and fluidized beds through utilization of a novel flighting arrangement 
while still maintaining the lower energy requirements, convenience, and 
other advantages of a rotary dryer. 
Another one of the aims of this invention is to provide a rotary horizontal 
dryer having return flighting on the perimeter of the drum along the inner 
surface. 
Another object of the invention is to provide a method and apparatus for 
drying a product wherein the product is comminuted while it passed through 
the dryer.

Referring initially to FIG. 1 of the drawing, a dryer according to the 
present invention is designated generally by the numeral 10 and comprises 
an elongated cylindrical drum 12 having a material inlet 14 and a material 
outlet 16. The drum is disposed horizontally relative to its longitudinal 
axis and is rotated on trunnion wheels 18. The inlet 14 of the dryer is 
coupled with an inlet cone indicated schematically by the numeral 20 and a 
forced air fan indicated schematically at 22. In some instances it may be 
desirable to have a draft fan coupled with the dryer at the opposite end 
from fan 22. The dryer 10 may be designed to operate completely on waste 
heat, or on a direct or indirect fired heat source (not shown) or a 
combination of the foregoing. Recycled gases may also be employed to 
enhance the efficiency of the primary heat source. At the outlet end 16, a 
settling chamber (or elbow) indicated schematically at 24 is provided. An 
outfeed screw (not shown) will normally be coupled with this chamber to 
remove dried material from the area. 
Drum 12 is of circular vertical cross section and has a smooth continuous 
inside surface 26. A central tubular support 28 is mounted concentric with 
the longitudinal axis of drum 12 by a plurality of hanger supports (not 
shown) extending from the tubular member outwardly to surface 26. Mounted 
in equal spaced relationship around support 28 and extending radially 
therefrom is a plurality of interference structures 30. These interference 
structures are all substantially identical although in moving from one end 
of the drum to the other the structures 30 are alternately disposed in 
first one direction and then the other. Referring to FIG. 4, each 
interference structure comprises a stem plate 32 which extends radially 
from and is rigid with tubular support 28 and a cross plate 34 attached to 
plate 32 at the top thereof and intersecting the plane of plate 32. Cross 
plate 34 intersects the plane of plate 32 at an acute angle on one side 
and a supplemental angle on the opposite side. Projecting from the plane 
of cross plate 34 are return flights 36. Another return flight 38 is 
angularly disposed on the side of plate 32 opposite the side visible in 
FIG. 4. 
Disposed in circumferentially spaced relationship around inside surface 26 
are a plurality of bars 39 which extend substantially the length of drum 
12 and are rigid with the inside surface. These bars mount a plurality of 
relatively short material distributing vanes designated generally by the 
numeral 40. One of the vanes 40 is shown in FIG. 5. Each vane 40 is from 
about one half foot to eight feed in length and extends less than one 
fourth of the distance from the inside surface to the center of the drum. 
Each vane includes a first planar surface 42 that extends generally 
perpendicular to a tangent to the drum body at a point opposite the point 
of attachment of the vane. This first surface merges into a second 
wedge-shaped surface 44 that extends from the plane of the first surface 
at an angle of between about 90.degree. to 150.degree.. Surface 44 
intersects the plane of surface 42 at a point spaced from the edge of the 
latter surface. Projecting upwardly from wedge-shaped surface 44 is a 
wedge-shaped lip 46. Manifestly, lip 46 tapers off toward the narrow end 
of surface 44. 
Vanes 40 are rigidly secured to bars 39 and surface 44 is thereby disposed 
at an angle of less than 60.degree. relative to the longitudinal axis of 
drum 12 (see FIG. 4). It will also be noted from viewing FIG. 3 that the 
leading edge of surface 44, from which lip 46 extends, is disposed at an 
acute angle relative to a vertical longitudinal section line passing 
through surface 42. 
Referring now to FIG. 2, vanes 40 and interference structures 30 have been 
omitted in order to better illustrate the arrangement of flighting members 
45. Disposed between adjacent bars 39 are a plurality of flighting members 
45. Flighting members 46 project from inside surface 26 and generally 
conform to the curvature of this surface. Each flighting member 45 is 
disposed at an angle relative to an imaginary vertical cross-sectional 
plane through the drum body, which angle is between about 
30.degree.-75.degree. and preferably about 45.degree.. 
In operation, the dryer of the present invention may be utilized for drying 
virtually any solid material. The material is fed into the dryer and will 
be picked up by vanes 40 as drum 12 rotates. The material falling onto 
surfaces 44 will gravitate from these surfaces with the material located 
at the narrow end of the surface 44 falling ahead of material at the 
opposite end of the same surface. This enhances the "dribbling" effect of 
the these vanes and results in a more even flow of material throughout any 
given cross-sectional volume of the drum. The material will gravitate onto 
interference structures 30 where it is further held and dried before being 
dropped back onto subsequent vanes 40. Any material falling between vanes 
40 will be acted upon by return flighting members 46 which will tend to 
cause the material to move back toward the direction of inlet 14. This of 
course increases the retention time of the material in the dryer improving 
drying efficiency. It has been found that return flights 45 disposed 
between vanes 40 cooperate well with the latter vanes to provide greatly 
enhanced efficiency of the overall drying operation. 
Alternative embodiments of vanes 40 are illustrated in FIGS. 6 and 7 and 
designated respectively by the numerals 140 and 240. Vane 140 has a first 
surface 142 and a second surface 144 which intersects the first surface at 
an angle of approximately 120.degree. as compared with an angle of 
90.degree. which surface 44 presents with surface 42 in the preferred 
embodiment. Lip 146 extends from wedge-shaped surface 144. With vane 240 
shown in FIG. 7, wedge-shaped surface 244 extends along the entire leading 
edge of surface 242 and tapers somewhat more gradually than surface 44 of 
the preferred embodiment. Also, with vane 240 there is no lip projecting 
from the wedge-shaped surface 244. These alternative forms of the 
invention will find use with some types of materials which are to be 
dried. 
Another alternative construction of vanes 40, which is not shown, would be 
for surface 44 to be of a generally rectangular configuration rather than 
wedge shaped as illustrated in FIG. 5. The surface would still extend from 
surface 44 at an angle of 90.degree. and 150.degree.. 
Another alternative form of the invention is illustrated in FIG. 8. This 
figure shows interference structures 30 constructed of expanded metal and 
designated by the numeral 130. Expanded metal is a well known product and 
is defined by industry standards as being sheet metal which has been slit 
and expanded up to ten times its original width. The result is a product 
having a diamond shaped pattern as indicated in FIG. 10. The formation of 
the diamond shaped pattern adds to the strength and rigidity of the 
material but more importantly strands 130a provide sharp cutting surfaces 
which serve to comminute material gravitating onto the structures 130. 
Referring now to the structure 130 in greater detail, a stem plate 132 of 
expanded metal extends radially from and is rigid with tubular support 20 
and a crossplate 134 attached to plate 132 at the top thereof, intersects 
the plane of the stem plate. Preferably, the angle of intersection between 
plates 132 and 134 is at an acute angle on one side and a supplemental 
angle on the opposite side. Projecting from the plane of cross plate 134 
are return flights 36 as previously described in conjunction with 
interference structures 30. 
In some instances it may also be desirable to construct peripheral vanes 40 
of expanded metal and such a vane is illustrated in FIG. 9 and designated 
by the numeral 340. It is to be understood that any of the configuration 
for peripheral vanes as shown in FIGS. 5-7 and previously described can be 
employed with the vane 340 form of expanded metal. FIG. 11 illustrates the 
sharp cutting edges presented by expanded metal strands 130a in the 
construction of the embodiments of FIGS. 8 and 9. Referring to FIG. 10 of 
the drawing, the diamond pattern may be oriented so that its longest 
dimension is either parallel or perpendicular to the direction of flow of 
material. With any type of fibrous material this orientation should be 
perpendicular to the flow. 
When utilizing the vanes and interference structures of expanded metal as 
aforedescribed it will be appreciated that the invention contemplates a 
method of drying a product wherein the product is passed through the drum, 
the drum is rotated about its longitudinal axis, and the material is 
carried partially around the perimeter of the drum and is then allowed to 
gravitate from the perimeter onto the comminuting surface 134 of 
interference structures 130. If the peripheral vanes are also constructed 
of expanded metal further comminuting will occur as material drops back 
onto these vanes. 
By utilizing a dryer constructed according to the present invention, it has 
been found that solid materials can be placed in a geometrical form that 
is generally congruent with the gaseous media that is utilized to effect 
drying. Furthermore, the dryer of the present invention greatly 
facilitates even distribution of material throughout the cross-sectional 
area and maximizes the number of "particles" in any given area while 
greatly reducing the "voids." The result is greatly increased drying 
efficiency which can be utilized to reduce the overall length of the dryer 
or in the case of existing drums of a given length, increase the volume of 
material which can be placed through the drum in a given amount of time. 
The construction of a drying drum according to the present invention 
results in heavy foreign objects being held at the inlet end of the drying 
drum rather than passing through it. In many cases, the heavy foreign 
objects will actually bounce from the inlet as the drum rotates. In 
effect, the drying drum of the invention will classify the material 
between foreigns and what is desired to be dried so that the latter will 
pass through the drum while the former is either retained at the front end 
or is actually pushed back out the inlet as the drum rotates. 
It is believed that the present invention is the first time a comminuter 
has been specifically incorporated into a drying drum. The result is that 
any large particle materials which tend to "ball-up" can be ground into 
finer particles which will be dried much more effectively and efficiently. 
Another result is a greater concentration of "fines" in the dried product 
which burn more readily in a wider range of burners.