Metering grain unloader for tower dryer

A metering unloader (29) of the present invention is for use in a tower grain dryer (T). The tower dryer has a grain drying path (11) and the latter has a grain outlet (27) at the lower end thereof, and the tower has at least one discharge outlet (15) in the lower portion thereof. The metering unloader is rotatably mounted within the lower portion (23) of the tower for rotation about a vertical axis (39) and the unloader is powered by a motor (41) for rotatably driving the metering unloader about the vertical axis. The metering unloader is in communication with the grain outlet of the grain drying path and it substantially uniformly removes dried grain from all regions of the lower portion of the dryer upon each revolution of the metering unloader and delivers the dried grain to the discharge outlet for the tower dryer. A method for metering the unloading of grain from the dryer is also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to an unloader for a tower grain dryer or the like, 
and more particularly to such an unloader which meters or positively 
unloads the dried grain from such a dryer in such manner that dried grain 
is substantially uniformly removed from all regions of the dryer outlet 
section. 
Tower grain dryers are well known. Generally, they comprise a vertical 
tower of cylindrical or other shape. The tower has a plenum located within 
the tower and spaced from the inner surfaces of the outer walls of the 
tower. Typically, the walls of the tower and of the plenum are of porous 
construction such that air from within the plenum may be forced through 
the walls. Grain to be dried is conveyed to the upper reaches of the tower 
and fills the space between the outer tower wall and the plenum so as to 
form a drying path for the grain to be dried. As dried grain is 
continuously discharged from the lower end of the grain drying path, 
additional grain to be dried is loaded into the upper end of the drying 
path. 
The plenum is supplied with heated air by means of one or more 
burner/blower assemblies. The heated air is forced from within the plenum 
through the porous or perforated walls of the plenum, through the grain in 
the drying path, and is forced through the porous outer wall of the tower 
carrying away moisture from the grain. 
Reference may be made to the following U.S. Patents which describe tower or 
other similar types of grain dryers of the type discussed above: U.S. Pat. 
Nos. 3,710,449, 3,766,664, 3,864,845, 3,896,562, 3,955,288, 4,398,356, 
4,423,557, 4,914,834, 5,129,164, and 5,136,791. 
In certain of these prior art tower grain dryers, the lower portion of the 
drying path converges inwardly of the tower in a generally conical shape 
and is divided into a number of separate converging channels. The lower 
ends of the channels discharge the dried grain into the bottom of the 
tower to be unloaded. Unloading can be accomplished in a variety of ways. 
Of course, grain being a fluent material may flow by gravity out through 
gravity outlets. Alternatively, the grain may be swept from the base of 
the tower by a sweep auger or the like and conveyed by the sweep auger to 
a discharge outlet, as described in the above-noted U.S. Pat. No. 
3,896,562. Still further, discharge augers may be located directly below 
the grain drying paths, as shown in U.S. Pat. No. 3,864,845, to unload the 
dried grain. 
However, it has been found that with tower dryers in which the grain drying 
path converges inwardly at the bottom of the tower and in which the grain 
drying path is divided into a number of converging channels, dried grain 
is oftentimes not uniformly removed from all of the channels. It has been 
found that grain will be removed at faster rates from some of the channels 
than from others. Because the speed at which the grain moves through the 
drying path (and hence the amount of time the grain is exposed to the 
drying air) varies in direct relation to the rate at which the dried grain 
is removed from the outlets of the channels, prior grain unloaders which 
did not uniformly remove dried grain from all of the grain channels caused 
some of the grain to move too fast through the dryer such that this faster 
moving grain might not be sufficiently dried, while other grain in the 
drying path might move too slowly such that this slower moving grain might 
become over dried. Of course, under dried grain is not desirable because 
it could lead to spoilage of the grain, and over dried grain is not 
desirable because it might become damaged from excessive exposure to the 
heated air which would waste energy and may damage the grain. 
SUMMARY OF THE INVENTION 
Among the several object of the present invention may be noted the 
provision of a metering unloader installed in the lower reaches of a tower 
grain dryer for substantially uniformly unloading dried grain from all 
regions of the outlet portion of the dryer; 
The provision of such an unloader in which the drying path of the tower 
dryer terminates in a number of side-by-side converging channels and in 
which the dried grain discharged from these channels is substantially 
uniformly unloaded from all of the channels; 
The provision of an unloader which insures that the rate in which the speed 
of the grain moving through the drying flow path is substantially uniform; 
The provision of such i an unloader which positively meters the grain from 
each region of the grain drying path so as to insure that all of the grain 
moving through all regions of the grain drying path moves at substantially 
the same speed and thus is uniformly dried; 
The provision of such an unloader in which the rate at which grain may be 
unloader from the dryer can be regulated by speeding up or slowing down 
the operation of the unloader; 
The provision of such an unloader which is free of jams, is of simple and 
rugged construction, and which is of economical construction. 
Other objects and features of this invention will be in part apparent and 
in part pointed out hereinafter. 
Briefly stated, a metering unloader of the present invention is intended 
for use in a tower grain dryer. The later comprises a vertical tower 
having a plenum therein. The plenum has a plenum wall. The tower has an 
outer wall surrounding the plenum wall with the tower outer wall being 
spaced outwardly from the plenum for forming a grain drying path between 
the tower outer Wall and the plenum wall. The grain to be dried is 
conveyed through the grain drying path generally from the top to the 
bottom of the dryer. The outer wall of the tower and the plenum wall are 
porous to permit air to flow therethrough The tower dryer has means for 
moving air into the plenum, through the plenum wall, through the grain in 
the grain drying path thereby to dry the grain, and through the tower wall 
to exhaust the air to the atmosphere on the exterior of the outer tower 
wall. The grain drying path has a grain outlet at the lower end thereof. 
The tower has at least one discharge outlet in the lower portion thereof. 
The metering unloader is rotatably mounted within the lower portion of the 
Tower for rotation about a vertical axis. Means is provided for rotatably 
driving the metering unloader about the vertical axis. The metering 
unloader is in communication with the grain outlet of the grain drying 
path for substantially uniformly removing dried grain from all regions of 
the lower portion of the tower upon each revolution of the metering 
unloader and for the delivery of such dried grain to the at least one 
discharge outlet. 
The method of the present invention relates to substantially uniformly 
unloading dried grain from a tower grain dryer. The tower dryer has a 
plenum therewithin with the walls of the plenum being porous, an outer 
tower wall surrounding the plenum and defining a grain drying path 
therebetween. The outer tower wall is porous. Means is provided for 
forcing heated air into the plenum, through the plenum walls, through the 
grain in the drying path, and through the outer tower wall. The drying 
path has an outlet end for the discharge of the dried grain into the lower 
portion of the tower. The lower portion of the tower has a discharge 
outlet through which the dried grain may be unloaded from the tower dryer. 
Specifically, the method of this invention comprises the steps of 
providing a metering unloader in the lower portion of the tower. The 
unloader has a grain inlet in communication with the dried grain 
discharged from the outlet end of the drying path, a discharge end in 
register with the discharge opening, and a path between the grain inlet 
and the discharge end. The unloader is rotated about a vertical axis. The 
dried grain is substantially uniformly scooped from all regions of the 
outlet end of the drying path as the unloader rotates and is conveyed 
through the path within the unloader to the discharge outlet.

Corresponding reference characters represent corresponding parts throughout 
the various views of the drawings. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings, and more particularly to FIG. 1, a tower 
dryer T is shown in partial cross section More specifically, tower dryer T 
comprises a vertical grain drying tower 1 which may, for example, be fifty 
feet or more in height. The tower has a base 3 of suitable structural 
steel members mounted in a suitable foundation (not shown). A plenum 5 is 
disposed within the grain dryer. The plenum is defined by a generally 
cylindrical porous plenum wall 7. Tower 1 has an outer cylindrical tower 
wall 9 of porous construction surrounding plenum wall 7 and spaced 
outwardly therefrom so as to define a vertical, annular grain drying path 
11. Grain may be supplied to grain drying path 11 by means of a grain 
inlet 13 at the top of tower 1 and dried grain may be discharged from the 
tower dryer by means of a grain discharge outlet 15 at the lower end of 
the dryer. 
As generally indicated at 17, a heater/blower assembly is provided within 
the grain dryer for drawing ambient air through the grain path 11 in the 
lower reaches of the tower and, if demanded, for heating the air, and for 
discharging the heated air under pressure into plenum 5. In this manner, 
the air discharged from heater/blower 17 is distributed substantially 
uniformly within the plenum and is forced to flow through the porous 
plenum wall 7, through the grain in grain drying path 11, so as to be 
exhausted through the porous outer walls tower 9 to the atmosphere thereby 
carrying moisture from the grain to the atmosphere. Whole heater/blower 17 
is shown in FIG. 1 to be located within tower 1, it will be understood 
that within the broader aspects of this invention that the heater/blower 
may be located outside the tower in close proximity thereto and air from 
the heater/blower may be ducted into plenum 5. 
Typically, fuel for heater/blower assembly 17 is supplied by gas fuel 
supply lines 19 and operation of the heater/blower assembly and overall 
operation of tower dryer T is controlled by a computer control housed in a 
control panel 21. Computer control is preferably of the type disclosed in 
the co-assigned U.S. patent application Ser. No. 08/193,710 filed Feb. 9, 
1994 which is incorporated by reference herein, but reprogrammed to 
operate with tower dryer T rather than with the continuos flow of grain 
dryers disclosed in the above noted patent application. 
As shown in FIG. 1, tower 1 has a converging conical hopper bottom 23. As 
shown in FIG. 2, hopper bottom 23 receives grain from grain drying path 11 
and the portion of drying path in hopper bottom 23 is divided into a 
plurality of converging grain flow channels 25 leading downwardly at the 
slope of the hopper bottom from the lower cylindrical reaches of the 
drying path in tower 1. Each of the converging grain channels 25 has a 
respective grain outlet opening 27 at its lower end for the discharge of 
dried grain from the drying path 11. 
As generally indicated at 29, a metering grain unloader of the present 
invention is provided in the lower reaches of hopper bottom 23 for 
receiving grain discharged from grain outlet openings 27 for positive, 
metered unloading of the dried grain from each of the outlet openings 27, 
and for conveying this dried grain to grain discharge outlet 15 such that 
dried grain is substantially uniformly unloaded from all of the grain 
channels 25. Metering grain unloader 29 is somewhat smaller in diameter 
than the diameter of the lower end of hopper bottom 23 at the height of 
grain outlet openings 27 so as to form an annular grain channel 31 
interposed between the grain outlet openings 27 and the body of metering 
grain unloader 29. The lower end of hopper bottom 23 is closed off by a 
generally horizontal bottom wall 33. As shown in FIG. 3., bottom wall 33 
has grain discharge opening 15 at the center thereof. The bottom wall is 
provided with a plurality of attachment tabs 35 which allow the bottom 
wall to be bolted to the inner surface of the conical hopper bottom 23. 
In accordance with this invention, metering grain unloader 29 is mounted 
within hopper bottom 23 for rotation about a vertical axis for positively 
gathering grain from within annular grain channel 31 and for positively 
discharging the dried grain through grain discharge opening 15 in bottom 
wall 33. More specifically, metering grain unloader 29 comprises an 
unloader body 37 secured to a vertical shaft 39. Shaft 39 is rotated by a 
variable speed drive motor 41 having a speed gear reducer 43. The motor 
and speed reducer are mounted on a motor frame 45 secured to the inner 
walls of hopper bottom 23 above unloader body 37. The lower end of 
vertical shaft 39 is journalled in a lower bearing 47 located below 
opening 15 in bottom wall 33. 
More specifically, unloader body 37 has an outer cylindrical body wall 49 
defining the inner surface of annular grain channel 31. This vertical 
cylindrical wall 49 extends upwardly from bottom wall 33. Cylindrical wall 
49 has a grain inlet opening 51 therein. Unloader body 37 further has a 
spiral wall 53 mounted within cylindrical body wall 49 extending up from 
bottom wall 33 and defining a spiral shaped grain unloading path 55 (see 
FIG. 5) within the unloader body. Spiral wall 53 has a leading edge 57 
which also constitutes the trailing edge of grain inlet opening 51. In 
this manner, as metering grain unloader 29 is rotated in clockwise 
direction (when viewed from above) with vertical shaft 39, grain inlet 
opening 51 rotates around the inner surface of annular grain channel 31 
thereby to uniformly pick up grain discharged from each grain outlet 
opening 27 from each of the tapered grain channels 25. Rotary motion of 
the metering grain unloader causes the grain to flow within grain 
unloading path 55 from grain inlet opening 51 to a grain discharge opening 
15 in bottom wall 33 and thence to be discharged from tower dryer T in to 
a suitable grain unloading auger or the like (not shown). 
Metering unloader body 37 further comprises a cover plate 59 secured to the 
upper surface of cylindrical wall 49. A hub 61 is carried on the upper 
surface of cover plate 59. A hub cover plate 63 is secured to the upper 
face of hub 61. The hub cover plate in turn in secured to vertical shaft 
39. In this manner, metering unloader body 37 is secured to vertical shaft 
39 so as to be rotatable therewith. As noted above, the bottom end of 
shaft 39 is received in bearing 47 such that the weight of the metering 
body is supported by the drive shaft which in turn is supported by frame 
45 and bearing 47. Unloader body 37 is adjusted such that the lower edge 
of cylinder wall 49 is just clear of floor 33 such that as the metering 
unloader body is rotated with drive shaft 39, the weight of the metering 
unloader body does not bear on floor 33. Hub webs 65 stiffen cover plate 
59 and help support the cover plate relative to hub 61. An inner cylinder 
67 is secured to the bottom of cover plate 59 and the lower rim of the 
inner cylinder 67 is secured to the upper, inner margins of spiral wall 53 
thereby to rigidly support the spiral wall at its center and to securely 
hold the spiral all in place relative to unloader body 37 and to thus 
accurately maintain the spiral or involute shape of grain unloading path 
55 as the grain unloader 29 rotates with shaft 39. 
In operation, grain to be dried is loaded within tower dryer T via grain 
inlet 11 at the top of the tower. The grain flows down over the conical 
cap of plenum 5 and is uniformly distributed into the vertical, annular 
grain drying path 11 and fills the grain drying path from top to bottom. 
It will be understood that as the grain fills the drying tower it will be 
initially discharged from outlet openings 27 from grain channels 25 so as 
to substantially fill annular space 31 and to surround metering unloader 
body 37. Once the annular space 31 becomes filled with grain to a level 
somewhat above the tops of grain outlet openings 27, the grain will back 
up within grain chutes 25. Continued loading of grain into tower 2 will 
fill the vertical grain drying path 11 with grain. 
Once the grain drying path 11 has been filled with grain, as above 
described, heater/blowers 17 are operated such that heated air is 
discharged under pressure into plenum 5. The heated air is distributed 
uniformly within the plenum and is forced through the porous plenum wall 7 
into the grain in the grain drying path 11, through the grain to pick up 
moisture therefrom, and is discharged to the atmosphere via the porous 
outer tower wall 9 forming the outer surface of the grain drying path. 
In order to unload grain from tower dryer T, drive motor 41 is energized so 
as to rotate vertical shaft 39 and to thus cause unloader body 37 to 
rotate with the shaft. As noted, annular grain channel 31 surrounding body 
wall 49 of the unloader body is filled with dried grain discharged from 
grain outlet openings 27 in grain channels 25 within hopper section 23 of 
the tower dryer. As the unloader body 37 rotates with vertical shaft 39, 
the leading edge 57 of grain inlet opening 51 rotates through the grain 
within annular grain space 31 and positively scoops up grain from the 
annular grain space and directs the dried grain into grain unloading path 
55. Continued turning of unloader body 37 causes the grain within grain 
unloading path 55 to be conveyed within the grain unloading path from 
grain inlet 51 to the inner end of the grain unloading path for discharge 
from the tower dryer via grain discharge outlet 15 located within the 
bottom wall 33. As noted, a suitable grain discharge auger unloader or the 
like (not shown) may be provided to convey the dried grain from the tower 
dryer. 
As indicated by the arrows in FIG. 1, ambient air is drawn into tower T 
through the lower reaches of the outer porous tower wall 9, through the 
grain which has been heated and dried in the upper reaches of the tower 
and thence through the porous inner plenum wall 7 for intake into the 
heater/blower 17. This cooler, ambient air passing through the heated, 
dried grain tends to cool the grain and to recover heat from the grain so 
that at least some of the heat is regenerated and is again utilized in the 
drying process. It will also be appreciated that the heated grain in the 
lower portion of the grain drying path 11 is substantially free of excess 
moisture such that the inflow of air to the heater/blower 17 does not 
carry excessive moisture. 
It will be particularly understood that the unloader 29 of the present 
invention is a metering unloader. That is, upon each revolution of 
unloader body 37, a given amount of dried grain is picked up by the grain 
inlet 51 on each revolution of the unloader body in turn from each of the 
outlets 27 of the grain channels 25. In this manner, it is insured that 
grain from each of the grain channels 25 will be uniformly unloaded. This 
overcomes a problem with prior art grain dryers utilizing gravity 
discharge outlets where grain would be unevenly unloaded from certain of 
the discharge chutes but would not be as readily unloaded from adjacent 
chutes. This non-uniform unloading resulted in grain flowing through the 
drying path 11 at non-uniform rates which resulted in some of the grain 
possibly becoming overheated and over dried, while other grain that moved 
through the drying path at a faster rate was under dried. 
As noted, motor 41 is a variable speed motor preferably under 
microprocessor control of control panel 21. By varying the speed at which 
motor 41 is operated, the rotational speed of unloader body 31 may also be 
varied thus increasing or decreasing the rate at which grain is unloaded. 
Of course, as grain is unloaded more quickly, the grain flowing downwardly 
through the grain drying path 11 will move faster thus increasing the 
through put and drying capacity of tower dryer T. Those skilled in the art 
will recognize that by controlling the rate at which unloader body 37 is 
rotated controls the rate at which grain may be continuously dried by 
tower T. 
By way of example, drive motor 41 may be operated between a very slow speed 
mode of operation and its normal maximum operating speed such that the 
motor driving unloader 29 through speed reducer 43 will rotate from a 
speed slightly more that 0 rpms (revolutions per minute) up to about 30 
rpms. However, it has been found that under most operating conditions, the 
unloader will be rotated between about 10 and 15 rpms. It will be 
appreciated that with unloader 29 operating between about 10 and 15 rpm, 
the grain inlet opening 51 in the unloader will move past each of the 
grain outlets 27 once every 4-6 seconds and remove grain from grain 
channel 31 thus allowing more grain to flow down each of the grain 
channels 25 to replace the grain scooped up by the unloader and conveyed 
from the tower dryer via grain unloading channel 55 in the unloader. This 
in turn allows the grain in grain drying path 15 to move downwardly at a 
substantially uniform rate around all regions of the drying path. This 
insure uniform drying of the grain. Further, by speeding or slowing the 
rate at which the unloader is rotated, the rate at which the grain moves 
downwardly (and thus the length of time that the grain in the drying path 
is exposed to drying air) may be regulated and controlled. 
It can be seen that the detailed description of the preferred forms and 
embodiments of the invention fulfill the objects and advantages set forth 
above. Inasmuch as numerous modifications may be made to the preferred 
embodiments without departing from the spirit and scope of the invention, 
the scope of the invention is to be determined by the scope of the 
following claims.