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. Pat. Nos. which describe tower or other similar types of grain dryers of the type discussed above: 746,410, 3,333,348, 3,710,449, 3,766,664, 3,864,845, 3,896,562, 3,955,288, 4,004,351, 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. In U.S. Pat. No. 3,333,348, a grain drying apparatus is disclosed having an inner wall and a spaced outer wall defining a grain flow path and having a pair of rotary agitator arms which extend out from the center of the dryer. In U.S. Pat. No. 4,004,351 uses rotary driven scoop arms to positively remove grain from the grain flow path.
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.
In the grain dryer described in the parent application of the present invention, now U.S. Pat. No. 5,566,470, dried grain is removed from the grain flow path by a rotary driven metering unloader body rotatably driven about a vertical axis and having a vertical wall for blocking the flow of grain from the grain flow path with the unloader wall having a grain inlet opening such that grain may enter the unloader body only by way of the grain inlet opening. Upon rotation of the unloader body, the grain within the unloader body is conveyed toward a center grain discharge outlet opening for removal from the dryer. While this unloader works well for its intended purpose, in order for it to vary the rate at which dried grain is unloaded, the rotary speed at which the unloader body is driven must be varied. This requires the use of a variable speed drive which is costly. In addition, the earlier metering unloader of this invention required a sweeping action to move the grain across the horizontal floor of the unloader to the grain discharge outlet. Therefore, there has been a need for a metering unloader body which does not require the use of variable speed drive and which does not require a sweeping action to discharge the grain.