CA1086052A - Method and apparatus for controlling the drying and cooling of field harvested seeds in storage - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Process and apparatus are provided for conditioning and preserv-ing living seeds. The grain drying apparatus is of the type having a plenum chamber formed in the lower part thereof and a gas-pervious floor forming the top of the plenum chamber. The improvement includes means for introducing atmospheric air in the plenum chamber; heating means for adding heat energy to the air in the plenum chamber, means for sensing the tempera-ture of air in the plenum chamber; means for sensing the temperature of the air in the top of the grain bin, the air being air exhausting from the grain bin; and differential temperature control means operating in response to the difference in temperature between the air in the plenum chamber and the air in the top of the grain bin for controlling the heating means by acti-vating the heating means when the result of the temperature in the plenum chamber minus the temperature in the top of the grain bin is a predeter-mined amount or less, and for deactivating the heating means when the tem-perature in the plenum chamber minus the temperature in the top of the grain bin is greater than the predetermined amount. The process involves placing the seeds in a closed environment; adding atmospheric air to one point in the closed environment; allowing air to exit from another point in the close environment; determining the temperature of air at the point of entry into the closed environment; determining the temperature of air at the point of exit from the closed environment; adding heat to air within the closed en-vironment only when the temperature difference between the entering air and the exiting air is greater than a predetermined amount; and controlling the amount of such heat always to maintaining the temperature of the exiting air cooler than the temperature of the entering air. The differential set-ting is selectively controllable to accomodate the hydroscopic properties of differing seeds and variations of seasonal temperatures and humidities.

Description

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~ This invention relates to a grain drying bin for controlling the drying and cooling of field-harvested seeds in storage.
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- The technique of early harvesting includlng field shelling and subsequent conditioning of corn and other cereal grains in storage is becomang increasingly popular. The present methods of conditioning or drying these cereal grains range from simply storing the seeds and letting them dry in the atmosphere, to placing them in drying bins and passing heated air through the grain seeds. In more recent years, complicated mechanical devices for agitating the stored grain or for removing the bottom-most layer of stored grain have increased equipment and operational expenses and severely damaged both the physical and food properties of the - grains and not infrequently the storage structure itself.
Grain exposed by storing in atmospheric air frequently is inadequately dried. In most cases, the drying process is so slow that problems of mold and biochemical changes result in serious losses to the stored grain. Also, drying of this type is interrupted by undesirable weather conditions, e.g., high humidity or prolonged wet and rainy periods~
both of which result in accelerated degradation of the stored grain.
Wet grain that is artificially dried by flow of heated air in a drying bin is frequently damaged due to the fact that commercial drying techniques often use drying air temperatures from 100F. to 140F., and sometimes even as high as 200F., with resultant destruction of enzymes and - amino acid proteins and other volatile ingredients.
The early harvesting techniques used in producing corn today frequently involve field shelling of the corn when it is at a moisture content of 27%. At this moisture level, grain deteriorates rapidaly and becomes mold infested. Corn approaches physiological maturity when its moisture content is 20%. The maturing process involves~not only the re-moval of moisture, but also chemical stabilization. Because mature corn .
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is more stable, it may be stored safely over long periods under proper con-ditions while storlng of corn with excegsive moisture inhibits or even pre-vents the natural occurrence of biOlogicalmaturity. Maturing involves the chemical stabilization o~ starch and protein which constitutes 85% of the corn kernel. In the maturing procegg, sugar moleculeg bond together to form starch molecules which are more complex carbohydrateg and are more stable chemically. Similar processes are involved with protein6 and amino acids.
In these processes water is eliminated, and thus drying or the elimination of water i9 an essential aspect of maturing of grain. Temperature and moisture are both factors in grain stabilization; however, above certain moisture levels, chilling of grain does not prevent deterioration of the seed. The following table shows germination loss in stored, refrigerated corn.
GE~MINATION LOSS IN STORED, REFRIGERATED CORN
GERMINATION EMERGENCE*
MOISTURE AFTER 6 MOS. AFTER 18 MOS. AFTER-6 MOS. AFTER 18 MOS.
Above 24% 17% 0% 0% 0%
18 - 24% 42% 13% 33% 53%

16 - 18% 74% 71% 59% 8~%
20 14 - 16% 70% 73% 56% 86%

12 - 14% 75% 75% 47% 93%
10 - 12% 65% 69% 70% 91%
Under 10% 74% 73% 75% 84%
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AVER~GE 56.5% 82,5 Storage temperature approximately 35F.

*Percentage Emergence within five day~ of planting ;

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It i~ not uncommon for the drying air used in conventional pro-cesses to be at a tempcrature of 110F. to ~0F., and occasionally even higher~ e.g., up to 200F. It would seem that such temperatures would speed dryinga but because o~ the sharp contrast with ambient ~emperatures as the air approaches the surface, resulting in moisture condensation and blockage to alr flow, the drying proces~ is slowed. When the grain is stirred, con-densation in bin walls is intensified because of contrasting temperatures, resulting in rusted wall and rotted grain. Destruction of pro~ein, loss of corn oils and other heat-suscepible ingredients can result in as much as five pounds per bushel loss of weight when high heat drying is utili~ed.
Commonly, hydrocarbon fuels~ e.g., propane, are used as a heat source. The combustion of these fuels is associated with the production of water. The BTU per hour output of heaters commonly employed range from 500,000 to 3,000,000 so that the per day production of water as a product of combustion can range from 75 to 500 gallons. This vapour is in tha air that goes through thc grain.
The seriousness of this problem is attested to by the fact that nearly every drying bin has crusted and sprouting surface grain, overdried bottom grain, rusting of bin wal~s and rotting of grain.
Present principles and practic~s of drying stored grain rest on the assumption that obtaining saturated, exhaust air is desirable. In the prior art, specific zones in the grain bulk are referred to, i.e., the dry zone, the drying æone and the wet zone.
Weight losses of 1~ of the dry matter have been found to correlate to a 20% loss of germination, and in today's economy, such deterioration can amount to as much as 20~ per bushel loss in value. Since loss of germina-tion mcans 1089 of value, it is desirable to maintain maximum germination.
Therefore, maximum control provides maximum germination, and the induction of dormancy from the earliest time follo~ing the harvest of .. . . . . .
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the grain by exposing the harvested graln to controlled air flow and mois-ture removal is desirable. Dormancy is a state of retarded respiration;
accelerated respiration increases kernel food consumption and weight loss.
Respiration is the conversion of oxygen to carbon dioxide (the carbon being derived from the consumed sugar) and is exothermic, i.e., heat is generated.
Thus, when high-moisture corn is exposed to warm saturated air, the rapid development of mold and heating of grain is intensified by the exothermic process of respiration as well as by the external addition of heat.
In ~he case of excessive differen~ial, overdried grain will re-sult; if saturated air is obtained, deteriorative conditions are established. The process of this invention proposes to maximize utiliza-tion of natural air, and to maximize preservation of seed quality and mar-ket weight and value. The equilibrium corn moisture obtained during venti-lation is shown in the following table.
Similar moisture equilibrium charts can be prepared for other grains.

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Accordingly, it is an object of a broad aspect of this invention to provide a grain drying bin for conditioning grain ~o controlled dormancy and moisture, and to maximi~e weight and market value for specific markets while maintalning optimum seed conditions.
It is an object of a further aspect of this invention to provide a grain drying bin for "cool-drying" grain by reference to the temperature differential between dry-air and wet-air in which the dry-air temperature is automatically regulated and the source of heating ~he drying air can be inactivated when the difference between the wet-air temperature (exhaust) and the dry-air temperature (plenum) ls greater than the preset tolerance, allowing for fluctuations of the plenum-air temperature that occur season-ally.
An object of a further aspect of this invention is to provide a process for drying, preserving, curing or drying seeds.
By one aspect of this invention, an improvement is provided in a grain drying bin of the type having a plenum chamber formed in the lower part thereof, and a gas-pervious ~loor forming the top of the plenum chamber, the improvement comprising: means for introducing atmospheric air in the plenum chamber; heating means for adding heat energy to the air in the plenum cham-i 20 ber; means for sensing the temperature of air in the plenum chamber; means Por sensing the temperature of the air in the top of the grain bin, the air being air exhausting from the grain bin; and differential temperature control means operating in response to tha difference in temperature between the air in the plenum chamber and the air in the top of the grain bin ~or controlling the heating means by activating the heating means when the result of the tempcrature in the plenum chamber minus the temperature in the top of the grain bin i9 a predetermined amo~lnt or less~ and for deactivating the heat-ing means when the temperature in the plenum chamber minus the temperature in the top of the grain bin is greater than the predetermined amount.

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. ' By another aspect of this invention, an improvement is provided in a grain drying bin of the type having a plenum chamber formed in the lower part thereof and a gas-pervious floor forming the top of the plenum - chamber, the improvement comprising: means for introducing atmospheric air into the plenum chamber, heating means for ad~ing heat energy to the air in the plenum chamber; means for sensing the temperature of air in the plen-um chamber; means far sensing the temperature of air exhausting from the grain bin; thermostat means for controlling the operation of the heating means; and differential temperature control means adapted to override the thermostat means controlling the heating means and thereby to inactivate the heating means when the temperature difference between the drying air in the plenum chamber and the air exhausting the grain bin is greater than a predetermined amount, while not inactivating the heating means when the temperature difference between the drying air in the plenum chamber and the air exhausting the grain bin is less than the predetermined amount.
By one variant thereof, the bin includes: means for indicating the temperature of the air in the plenum chamber; and means for indicating the temperature of the air exhausting from the grain drying bin.
By another variant, the means for introducing atmospheric air operates at approximately 1.5 to 9.0 cubic feet per minute per bushel of grain at moistures between 18 and 30 percent moisture.
By still another variant, the bin includes: a control panel;
means mounted on the control panel for continuously indicating the tempera-ture of the air in the plenum chamber; means mounted on the control panel for continuously indicating the temperature of the alr exhausting from the grain drying bin; adjustable means mounted on the control panel for con-trolling the thermostat means; and ad~ustable means mounted on the control panel for controlling the temperature control means.
By yet another variant, the temperature differen~ial is deter-mined by subtracting the temperature of the air exhausting from the grain .7 .. . . . . . .. . . ..

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bin from the higher temperature of the inlet air in the plenum chamber.
By a further aspect of this invention, an improvement is provided in a grain drying bin of the type having a first chamber formed in the lower part thereof, a gas-pervious floor forming the top of the first chamber and a second chamber formed in the top of the grain bin, one of the chambers being a plenum chamber and the other of the chambers being an exhaust cham-ber, the improvement comprising: means for introducing atmospheric air into the plenum chamber; heating means for adding heat energy to the air in the plenum chamber; means for sensing the temperature of the air in the plenum chamber; means for sensing the temperature of the air in the exhaust cham-ber; and differential temperature control means operating in response to the difference in temperature between the air in the plenum chamber and the air in the exhaust chamber for activating the heating means when the result of the temperature in the plenum chamber minus the eemperature in the exhaust chamber is a predetermined amount or less, and for deactivating the heating means when the result of the temperature in the plenum chamber minus the temperature in the exhaust chamber is greater than the prede-termined amount.
By still another aspect of this inventlon an improvement is pro-vided in a grain drying bin of the type having a first chamber formed inthe lower part thereof, a gas-pervious floor forming the top of the first chamber, and a second chamber formed between the grain and the top of the grain bin, one of the chambers being an exhaust chamber, the improvement comprising: means for introducing atmospheric air into the plenum chamber;
heflting means for adding heat energy to the air in the plenum chamber; means or sensLng the temperature of air in the plenum chamber; means for sensing the temperature of air in the exhaust chamber; thermostat means operating in response to the temperature of air in the plenum chamber for controlling the operation of the heating means by activating the heating means when the .; . . . .

sz temperature of the air in the plenum chamber is below a predetermined tem-perature, and for inactivating the heating means when the temperature of the air in the plenum chamber is above the predetermined temperature; and differential temperature control means operating in response to the differ-ence in temperature between the air in the plenum chamber and the air in the exhaust chamber for overriding the activation of the heating means by the thermostat means when the difference in temperature exceeds a predeter-mined temperature amount, thereby to inactivate the heating means only while tha difference in temperature exceeds the predetermined temperature, the differential control temperature means having no overriding effect on ; the thermostat means ~hen the difference in temperature does not exceed the predetermined temperature.
By a variant thereof, the bin includes means for indicating the temperature of the air in the plenum chamber; and means for indicating the temperature of the air in the exhaust chamber.
By another variant, the temperature differential is determined by subtracting the temperature of the air exhausting from the exhaust chamber from the higher temperature of the inlet air in the plenum chamber.
, By still a further aspect of this invention, an improvement is provided in a grain drying bin of the type having a first chamber formed in the lower part thereof, a gas-pervious floor forming the top of the first chamber, and a second chamber formed between the grain and the top of the grain bin, one of the chambers being a plenum chamber and the other of the chambers being an exhaust chamber, the improvement comprising: means for in-troducing atmospheric air into the plenum chamber; heating means for adding heat energy to the air in the plenum chamber; means for sensing the tem-perature of air in the plenum chamber; electric circuit means for control-l:Lng the heat:Lng means; means for sensing the temperature of air in the ex-haust chamber; thermostat means for opening or for closing the circuit means in response to the temperature of air in the plenum chamber, whereby to ~ - 8 a -,..... `. .:

asz activate the heating means so long as the air in the plenum chamber is be-low a predetermined temperature; and difEerential temperature control means set at a predetermined temperature differential between the temperature of the air in the plenum chamber and the temperature of the air in the exhaust chamber for automatically opening the circuit means of the heating means when the predetermined temperature differential is exceeded, and for closing the circuit means when the differential temperature is less than the prede-termined temperature differential setting.
By a variant thereof, the bin includes: means for indicating the temperature of the air in the plenum chamber; and means for indicating the temperature of the air in the exhaust chamber.
By another variant, the temperature differential is determined by subtracting the temperature of the air exhausting from the exhaust cham-ber from the temperature of the inlet air in the plenum chamber.
By yet another aspect of this invention, an improvement is pro-vided in a grain drying bin of the type having a first chamber formed in the lower part thereof, a gas-pervious floor forming the top of the first chamber, and a second chamber formed between the grain and the top of the grain bin, one of the chambers being a plenum chamber and the other of the chambers being an exhaust chamber, the improvement comprising: means for in-troducing atmospheric air into the plenum chamber; heating means for adding heat energy to the air in the plenum chamber;.means for sensing the tempera-ture of air in the plenum chamber; means for sensing the temperature of air in the exhaust chamber; first thermostat means operating in response to the temperature of air in the plenum chamber for activating the heating means so long as the air in the plenum chamber is below a predetermined temperature; and second thermostat means operating in response to tlle tem-perature of air in the exhaust chamber for further controlling the heating means by automatically overriding the first thermostat means by preventing the operation of the heating means when the temperature of the air in the y~
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exhaust chamber is below a predetermined temperature, the predetermined temperature of the first thermostat means being higher than the predeter-mined temperature of the second thermostat means.
By one variant thereof, the heating means is an electrical heat-ing means.
By a variation thereof, the electrical heating means has a total wattage of 10 to 40 watts per one hundred bushels of grain capacity.
By another variation9 the electrical heating means comprises at least one heat lamp.
By a further variation, the electrical heating means comprises a plurality of heating lamps.
By still another variation, the means for introducing atmospheric air into the plenum ~chamber comprises a plurality of fans spaced about the plenum chamber.
By a further aspect of this invention, a process is provided for drying and preserving, or curing, or drying, uncurred seeds, which process comprises: placing the seeds in a closed environment; adding atmospheric alr to one point in the closed environment; allowing air to exit from ano-ther point in the close environment; determining the temperature of air at the point of entry into the closed environment; determining the tempera-ture of air at the point of exit from ~he closed environment; adding heat to air within the closed environment only when the temperature difference between the entering air and the exiting air is greater than a predeter-mined amount; and controlling the amount of such heat always to maintaining the temperature of the exiting air cooler than the temperature of the en-~ering air.

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By another aspect of this invention, a process is provided by curing seeds comprising: placlng uncured seeds in a closed environment; ad--ding atmospheric air to one point of the closed environment; allowing air . to exhaust at another point in the closed environment; maintaining the . addition of atmospheric air witllin specified quantities; measuring the tem-;~ .perature of the air at the point of entry of the atmospheric air; measuring the temperature of the air at the point of exhaust from the closed environ-ment; adding heat to the entering atmospheric air only when the temperature difference between the entering air minus the exhaust air is less than a predetermined amount; controlling the amount of such heat being add, thereby always to maintain the temperature of the exhaust air cooler than the tem-perature of the entering atmospheric air; and continuing the addition of atmospheric air and controlling the addition of heat to the atmospheric air until a desired equilibrium moisture has been achi.eved in the stored seeds.
By a variant thereof, the desired equilibrium moisture is at 18 percent and the temperature of the seeds is at 40F.
By yet another aspect of this invention a process is provided for drying uncurad seeds in a closed environment; adding atmospheric air to one point of the closed environment; allowing air to exhaust from another point in the closed environment; determining the temperature of the air at the point of entry into the seeds; determining the temperature of the air at the point of exhaust from the seeds; adding heat to the entering atmos-pheric air only when the difference between the temperatures of the enter-ing air minus the exhaust air ls less than a predetermined amount required to ach:Leve a desired equilibrium moisture in the stored seeds; and control-.l:Lng the amount oE such heat being added, thereby always to maintain the temperature of the exhaust alr cooler than the temperature of the entering atmospheric air.

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By yet a further aspect of this invention a process is provided for drying uncured seeds comprising the steps of: placing uncured seeds in a closed environment; constantly adding 1.5 to 9.0 cubic feet per minute of atmospheric air per bushel of uncured seeds to one point of the closed en-vironment; allowing the added air to traverse the seeds and to exit as exiting air at another point of the closed environment; adding heat to the added atmospheric air at a rate of no more than 1.36 sTU per hour per bushel, the heat being added only when the determined temperature difference between the added air and the exiting air is greater than a predetermined amount and is controlled so as always to maintain the temperature of the exiting air cooler than the temperature of the added air; and continually using the pro-cess until the seeds are cured.
By a still further aspect of this invention a process is provided for drying uncured seeds comprising the steps of: placing uncured seeds in a closed environment; constantly adding 1.5 to 9.0 cubic feet per minute of atmospheric air per bushel of uncured seeds to one point of the closed en-vironment; allowing the added air to traverse the seeds and to exit as exit-ing air at another point of the closed environment; adding heat to the at-mospheric air at a rate of no more than 0.4 watts per bushel beEore the added air is introduced into the seeds, the heating being added only when the determined temperature-difference between the added air and the exiting air is greater than a predetermined amount and is controlled so as always to maintain the temperature of the exiting air cooler than the temperature of the added air; and continually using the process until the seeds are cured.
By a variant thereof, the additional heat is supplied in the form of infrared rays rom a heat lamp.
By yet another aspect of this invention a process is provided for drying and preserving seeds, the seeds being in a bin having heating means for forcing air into a plenum chamber in the lower part of the bin, the - - 8 e -.

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; -heating means being disposed in the plenum chamber, the plenum chamber being ` covered by a floor pervious to gas flow, the process comprising the steps of:
introducing atmospheric air into the plenum chamber; determining the tempera-ture within the plenum chamber; determining the temperature of exhaust air leaving the bin; inactivating the heating means w~en the temperature~of the air in the plenum chamber minus the temperature of the exhaust air is grea-ter than a preselected amount; and controlling the amount of heat from the heating means always to maintain the exhaust air temperature cooler than the inlet air temperature while the 8rain is curing.
According to one embodiment of this invention, grain to be con-ditioned or dried is placed in a storage bin, generally of the type having a means for blowing drying air into a plenum chamber below the body of grain to be dried. The roof of the plenum chamber, which is also the floor of the storage bin, is pervious to gas flow and allows the drying air to percolate up through the body of grain to be dried. Bins of this type are quite common in the prior art, but they usually include a blower furnace as the means for supplying drying air to the bin.
In the present invention in one of its embodiments, the drying which is effected much more closely approximates what can be termed "natural - 20 drying". Specifically, it utili~es a flow of air and a heat source which is more controllable and less destructive to the grain than prior art techniques.
Strictly natural air dyring is not fully adequate to reduce grains to mois-ture levesl safe for long-term storage, due to humidity and temperature con-d:ltions that exist in fall and early winter, as noted in the following ~ble.

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NA~U~AL AIR GRAIN DRYNESS* ~Y T~E MONT~ (IOWA) AVG. CORN W~T-BULB** AVG~ CORN WET-BULB**
MOISTURE: DEPRESSION MOISTUR13 DEPRESS_ON
Jan. 20% 1 - 2~ July 111/2X 7 - 10 Feb. l9X 1 3 Augo 12X 7o _ 9o March17X 2 - 5 Sept.13Z 6 - 8 April16X 50 7o Oct. 14X 5o _ 7o ~lay13 1/2X 7 - 8 Nov. 16X 3 _ 5 June13 1/2X 7 - 8 Dec. 19X 1 - 3 *Varies With Different Grains; also with yarietal and sea-sonal differences.
* Average Mean Wet-~ulb Depressions ~rom U S. ~eather Bureau Data. - - ¦

The grain drying bin of aspects of this invention departs funda-mentally from this generally accepted assumption and employs a controlled balance of volume of air flow to grain volume and of air dryness to grain dry-ness while substantially avoiding the clash of warm grain air temperatures 'I with cool or cold ambient temperatures. The effect is to maintain a relat-Lve humidity in the exhaust air below saturation so that some drying can occur within the entire bulk of grain and thus substantially eliminate the "wet zone"
of high-moisture perishable grain exposed to saturated air. Accelerated rates of respiration (in the grain itself and in molds and other micro-organisms exposed to warm, humid conditions3 that intensify losses of weight and food value are likewise substantially prevented.
The grain drying bin of aspects of this invention utllizes the fact that, as water evaporates from a surface, the surface becomes cool. Therefore, as dry air Ls passed through the body of moist grain, evaporation takes place ~nd cools the grain air a certain amount; the amount of cooling is dependent upon a number of factors, e.g., the par~icular grain being dried, the tem-perature of the drying air, the moisture content of the grain, and the rela-tive - 9 a .' - . .' ' . ' ', . , , , . `

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humidity of the drying air. The effect of evaporative cooling is to render the kernel and micro-organism dormant and thus to stabilize the kernels and nicro-organisms. It is a feature of an aspect of this invention that the - drying alr is not heated to such an extent that the grain can be damaged thereby or overdriedO It is desired to approximate as closely as practica-ble the conditions of natural air drying, and accordingly, the drying air is preferably conditioned only to control its dryness or relative humidity without greatly raising it above ambient temperatures.
The temperature of the plenum air is controlled, e.g., by a thermostat or other similar modulating or cycling device. According to one aspect of the invention the temperature differential between plenum air and exhaust air is monitored, and the heating means is inactivated when the differential exceeds a preselected value.
Specifically, according to an aspect of this invention a controlled flow of ideal, natural "harvest air" is maintained within the stored grain with an apparatus for measuring and controlling natural air dryness or relative humidity so as to control grain dryness and dormancy. The addltion of dry energy (heat) to the drying air is selectively controllable so as to determine the extent of drying that can occur within the grain. This is accomplished by obtaining a measure of the "dry-bulk" temperature and the "wet-bulb" temperature depression that occurs within the grain with the addition of heat only when the wet-bulb depression is less than the pre-determined tolerance.
Since only a small rise in temperature of the drying air i8 re-quired in tha use of the grain drying bin of an aspect of thls invention electrical heating means are ideally suited, and because oi their extraor-dinary safety, convenience ' , ~ ` . ~

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and serviceability , heat lamps are preferred as a means for heating the drylng air. The facet o~ the present application i5 further disclosed and claimed in a divisional application.
Heat lamps distributed about the plenum chamber uniformly warm metal floor and floor supports, giving good distribution of the added heat. The ex-ceptional economies of light energy as a heat source are well known.
Additionally, radiant heat energy from electrical sources is totally dry energy and does not aggravate problems of moisture condensation as does the combustion of hydrocarbon fuels.
In summary, the grain drying bin of aspects of this invention pro-vides that, because of the sensitive nature of seeds and other products with similar sensitivities, the application of heat as used in conventional drying of non-living products is excessive and intolerably damaging, and that preservation of weight and food value is grain is accomplished only in preserving the biological integrity of the seed.
Further, even wnen drying is accomplished with low levels of heat, these can be excessive because of the adverse environment created by the heat in increasing seed respiration and in causing stratification of mois-ture within the grain whlch allow for mold infestation.
Because of high costs of energy and limitations of energy re- -sources, their wise management, especially in drying grains, is obviously urgent because of the vast expenditure of energy resulting from the growing practice of drying food grains.
More specifically9 this invention in another of its aspects in-cludes a grain drying bin operated in such a way that the biological inte-~ity or livlng character of biological products, espec~ally food grains, is preserved by drying, chilling and conditioning in a controlled storage environment. Such control of storage environment is by ventilation, which maintains a balanced ratio of air-volume to grain-volume, and which sub-stantially prevents - .: ' :: ' ~: : . . :
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stagnatlon of, and accumulation oE, moisture in the interstitial grain-air. Throughout the conditioning process of aspects of this invention, the temperature of the product in storage remains colder than ambient tempera-- tures and that when the product has achieved the desired equilibrium rnois-ture, it is at the same temperature as the ambient air.
Furthermore, monitoring means indicate the extent of heat expen-diture or evaporative cooling during ventilation, i.e., the differential temperature observed from the tine the air enters the grain to the time it exhausts, thereby providing direct indication of equilibrium moisture being achieved within the grain at any time. Control means are provided which automatically activate or deactivate heat sources in response to evaporative cooling and make possible the selective control of moisture content in the grain by selective control of differential temperatures.
In the accompanying drawings, Figure 1 is a side elevation view, partially cut away, showing a grain bin equipped according to one aspect of this invention;
Figure 2 is an exploded view showing the details of heat lamp mountings according to one aspect of the invention;
Figure 3 is a front elevation ViRW showing a control panel for use in accordance with one aspect of this invention;
Figure 4 shows a schematic operational circuit diagram for the operation of the grain bin of one embodiment of the invention;
Figure 5 shows a schematic operational circuit diagram for the operation of the grain bin of another embodiment of the invention; and Figure 6 is a partial perspective view of the interior bottom of the grain bin equipped with a multiple fan arrangement according to one aspect of this invention, with certain portions removed for clarity.
According to one embodiment of this invention? a grain drying bin is now provided which has ` ~ - 12 -. .
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the ability to produce grain having precisely controlled levels of moisture and also provides that these levels are obtained in a manner which results in minimum germination loss of the grain with resultant maximum quality for ultimate use. Some processing techniques require specific moisture levels, and the ability to supply grain with these specific levels will produce com-petitive advantages in certain cases.
A feature of one aspect of this invention is that the ultimate grain moisture can be obtained by selected settings of the controls. These controls include a thermometer mounted so as to measure plenum-air tempera-ture, and a temperature cycling control, e.g., a thermogtat~ that activates or deactivates heat sources in response to the plenum-air temperature. A
second thermometer, sensing the temperature of the exhaust air, provides a differential reading of temperature from the plenum-air so as to provide an indication of grain moisture and extent of drying taking place. The differ-ential reading, when greater than a preset level, càuses the heat sources to be-inactivated regardless of the thermostat setting.
Incorporated in aspects of this invention is eIectrical apparatus including a heating means which provide indirect and direct conditioning of the air.
By means of electrically powered fans, a controlled volume of air i9 kept flowing through the grain according to grain moisture content as has been described in the aforementioned United States Patent No. 3,408,747, according to the following chart. Because of chilled-air temperatures, the process of aspects of this invention allows for reduced volumes of air (by ~0~) over previously cited recommendations.

. .
' ' ~ . . ' ' . ' REQUIRE~D C . F.M. /BU.
Percent moisture: c.f.m./bu.
30 . . . . . . . . . . . 9.0 28 . . . . . . . . . . . 7.0 25 . . . . . . . . . . . 5.0 22 . . . . . . . . . . . 3.5 20 . . . . . . . . . . . 2.5 18 . . . . . . . . . . . 1.5 Indirect electrical heating is obtained by fan blade friction and by the heat given off by electric motors powering the fans. Also, the pres-sure in the plenum would be above atmospheric, and the higher pressure gives greater drying capacity to the air as is well known. The combination of fan blade friction, electric motor heat and pressurized air may in some cases raise the temperature as much as from 2 to 5F. This temperature increment together with ideal weather conditions can, in some cases, provide adequate capacity for accomplishing the desired degree of grain dryness. However, during most seasons the supplemental addition of some heat energy will be required. Electrical sources are ideally suited for this additional heat.
Advantages obtained by electrical heating include greater safety, in that the fire hazard is reduced compared to that when conventional blower fur-naces are used or when propane burners are used. Service requirements are at a minimum and only require changing a light or heat element in most case~. Additionally, the well-known sanitizing advantage of infrared ren-ders certain bacteria and mold spores inactive upon expcsure, which effect i9 o great value in stabilizing a safe-keeping environment for food gra:Ln.
The present invèntion in one of its aspects minimizes problems resulting Erom conventional high heat drying including uneven drying, overdrying, con-densation cf moisture within the grain causing accelerated biochemical activity, and moisture condensation on the bin walls. Conventional high-,, ~: ;

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,, heat drying generally includes introducing the products of combustion into the drying bins, and as a result, large amounts of water are introduced into the grain.
Referring now to Figure 1 of the drawings, a grain storage bin 11 i9 shown having side walls 12, a conically shaped roof 13, and an opening 14 in the top of the roof. The bin has a foundation 15 and floor supports 16 supporting a floor 17 which is pervious to gas flow. A body of grain to be conditioned is indicated at 18, and fan 19 and duct 20 leading from the fan for introducing air into the plenum chamber are shown. A group of heat lamps 21 mounted in frames 40 are located around the outer wall of the plen- -` um chamber formed between the bin foundation 15 and the bin floor 17, and control panel 22 is located on the side wall 12 of the bin. According to one simple aspect of this invention the heat lamps 21 distributed about the lower part of the grain bin side walls 12 are simply turned on and left on during the entire drying procedure, which may take several weeks. In some cases, the heat lamps 21 may be thermostatically controlled to main-tain a desired temperature level in the plenum chamber. The kilowatt imput accomplished with lamps is generally within a range from 1/4 to 3/4 watt per bushel of bin capacity.
According to a variant of the invention also shown in Figure 1, a temperature sensing means 37 is shown in the top of the body of grain 18 and is located preferably near the center of the bin to minimize the effects of heat loss through the bin wall. Plenum air thermostat 33 (see Figure 3) with differential sensor 36 closes the circuit supplying power to cable 47 within the range of preset tolerances, i.e., if the exhaust air drops below the preset tolerance of cooling, the circuit is opened, or if the plenum-alr temperature rises above the thermostat setting the circuit is broken.
As the alternative to the use of fan 19 and duct 20 as shown in -. . .-, :. -, - ,~
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Figure 1, a plurallty of small fans 2~ could be spaced about the bin directly on the lower bin wall, (which is also seen in Figure 1). These smaller fans wold preferably be individually operable bo guard again6t a surge of electri-cal load if all the fans were turned on together, and would include suitable closure means on each fan (not shown) substantially to prevent pressuri~ed air from the plenum chamber from exiting through a fan that is not running.
A preferred embodiment of the heating means to be utilized in an aspect of this invention is illustrated in Figure 2. As shown therein, a window frame 40 which may be round, square, or rectangular, attaches to the ~0 bin wall 12 by means of bolts 41 or other suitable means through holes in bin wall 12. Heat la~p 42 is carried by receptacle 43 carried on transpar-ent window 44. Window 44 can be removed for changing a burned out lamp or for providing access to the plenum chamber for cleaning or inspection sim-ply by removing bolts 45. Some of the advantages provided by this embodiment include ease of maintenance, access to plenum for inspection or cleaning, illumination of both plenum and grounds outside the bin, and substantial prevention of mildew. This embodiment also reduces fire`hazards which are present when flame heaters are used, and substantially eliminates the pol-lution resulting from flame heaters or glowing resistance elements.
Figure 3 shows a grain dryness control panel 22 suitable for mounting on the lower side wall of the bin below the floor 17.
The control panel includes: a thermostat 32 with a remote sensor 37 that measures the exhaust air temperature; a thermostate 31 that meas-ures the plenum air temperature; a cycling (thermostat humidstat) and/or moldulating mcans 33 with remote sensor 36 and differential (humidity/
tcmperature) selector 34; a light 38 indicating when the circuit is open or closed; a power cord 47 supplying power to the heat sources; and a mano-met~r 35 that indicates air flow.

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In Figure 4 the power cord 47 is connected to a power source (not - shown) and forms a circuit having a heat lamp 42, a thermostat 33, and a differential temperature controller 34 all connected in series. The ther-mostat 33 responds to warming through sensor 46. Thermometer 31 indicates the temperature in the plenum at sensor 46, and this temperature reading is also carried to thermostat 33 and differential controller 34 by lines 33' and 34', respectively. The temperature of the exhaust chamber of the grain bin is measured by sensor 36, which temperature reading is indicated on thermometer 32 and is also input into differential controller 34.
In Figure 5, the power cord is likewise connected to a power source (not shown) and has oonnected, in series therewith, a thermostat 53, and a heat lamp 42. Thermostat 33 operates exactly as described in the Figure 4 embodiment, i.e., it responds to warming. Thermostat 33 closes the contact when the temperature at sensor 46 is below the setting thereon, and the contact is opened when the temperature at sensor 46 rises to the temperature set on the setting, or above the setting. Thermostat 53 works in an opposite fashion in that it responds to chilling, i.e. 9 when the tem-perature sensed by sensor 46 is lower than the setting thereon, the ther-mostat 53 contact is open and when the temperature sensed by sensor 36 is at the setting or above, the circuit is closed. It will be understood that the heat lamp 42 operates only when the contacts of both thermostats 33 and 53 are closed. This arrangement, li~e that of the embodiment of Figure 4, is fully automatic.
Figure 6 shows a view of the base of the grain drying bin, includ-ing the side walls 12 resting on the foundation 15 and floor supports 16 whlch support a floor 17 which is pervious to gas flow. The group of heat lamps 21 are shown disposed around the perimeter of the floor supports 16, and the fana 19 and ducts 20 leading therefrom for introducing air into the plenum chamber are shown to be spaced around the perimeter of ... . . .. .~. , , , ~ , .

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the floor support and between the heat lamps 21. The ducts 20 are provided with air controlling registers 54.
The operation of the control panel shown in Figure 3 is based upon the following considerations:
When corn moisture is above 26%, sufficient water is present so that evaporation and evaporative cooling approximates that of water from a f~ee surface. Therefore, the temperature depression measured in the ex-haust air when compared with that of the plenum air provides the wet-bulb temperature reading. This being so, the previously cited moisture equili-brium chart (TABLE 1) provides a meaningful guide (based on psychometricwet-bulb depression) as to how dry the grain is becoming.
To obtain 13% moisture corn, the wet-bulb depression to be main-tained should be 7F. approximately.
As the grain dries, its hydroscopic property (i.e., internal seed forces holding water) increasin~Ly resists evaporation, and as evaporation decreases evaporative cooling also decreases. When grain moisture reaches equilibrium with air moisture, the plenum air and exhaust air temperatures will be the same and no drying will take place.
Therefore, the comparison of these two temperatures provides positive indication as to when drying does or does not take place and as to how dry tbe grain is becoming; heretofore, the farmer could only guess about these situations. More complex charts can be supplied as a valuable aid to the producer in controlling drying, e.g., the chart shown in Table I.
The ultimate dryness of the grain is determined by the ultimate dryness of the air. It can be observed from a psychrometric chart that a 5F. wet-bulb depression at 70F. represents 74% relative humidity (14.0%
corn moisture); while a 10F. ~et-bulb depression at 70F. represents a 55%
relative humid:Lty and 11.4~ corn moisture; while a 20F. wet-bulb depres-sion represents a 36% relative h~midity and corn moisture under 9%. Simi-larly, relative humidities and equilibrium corn moisture can be found . . : :. . .
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6~52 for all other normally occurring temperatures. The actual wet-bulb depres-sion observed in the surface grain may be somewhat less than the real wet-bulb depression as the grain dries, and increasingly so the closer grain moisture approaches equilibrium moisture with the atmosphere, so that actual grain dryness being achieved would, in fact, be lower than that suggested by the observed temperature differential. The corn equilibrium chart contained in the aforesaid United States Patent No. 3,408,747 gives corn moisture levels below those cited on the chart contained in this invention and represents an accommodation to the changing hydroscopic characteristics of grain as it dries, and may therefore more accurately represent grain moisture being achieved.

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~860S;Z~ -The measure of wet-bulb depresslon is a measure of relative humidity; it is obvious, therefore, that controlling wet-bulb depression - controls relative humidity.
.~ When the setting on thermostat 33 is below the temperature observed on thermometer 31, the contacts of the thermostat are open and light 38 will be on.
~ en drying begins, thermostat 33 is set as desired (e.g., 6F.
above ambient) by turning the knob of 33 in the direction of "increase"
indicated by the arrow.
l~hen the thermostat 33 setting is above the plenum temperature, the contacts close to activate the heat source and light 38 goes out.

When the temperature of the plenum is the same as the thermostat setting, the heat sources are deactivated. It can happen that because of low relatlve humidity in the natural air, overdrying can occur even though the temperature of the plenum air would never reach the thermostat setting.
Undesirable overdrying would result if the heat source were not deactivated.
Such conditions are indicated if the exhaust air temperature drops excessive-ly below the plenum temperature, e.g., 10F. An adjustable temperature differential control means 34 is provided in conjunction with the thermo-stat 33. Differential control means 34 is adapted to determine the differ-ential between plenum air and exhaust air, and automatica:Lly to open thethermostat circuit, thereby deactivating the heat source, when the differ-ential exceeds the value preset on control means 34.
The manometer 35 measures static pressure (inches water) and indi-cates the volume of air being delivered by the fan(s~.
The required ratio of air-voLume to grain-volume varies with the grain moisture. By knowing the actual and the required ratios, the opera-tor knows how fast the bin can safely be filled. The required ratios (cfm/Bu.) for heated air drying are defined in the aforesaid United States Patent No. 3,408,747, but because of chilled air temperatures are less than , . . . . .
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. : ,, . , , .~ ~ , :,, ':: ' , ' : . .. :: ' : - -6~;i2 those required in the above identified patent, as has been observed pre-viously. Filling of the bin can tontinue as long as ratios are maintained.
By fixing the depth of grain (8 - 14l), a prescribed horsepower requirement can be defined to maintain a certain level of air.
By maintaining horse power application of 1/2 to 1-1/2 h.p. per lOOO bushels of corn, an air-to-grain ratio of 3 cfm/~u. can be maintained and substantially complete filling of the structure allowed. For example, a 10 H.P. is recommended for 10,000 bushels of corn; a 33' diameter bin is required to obtain 10,000 bushels in a 12 - 14'depth. As grain depth in-creases, pressure increases apd air flow decreases, thus decreasing thesafe fill rate~ Air volume has to be maintained according to grain moisture content as previously cited, which principle is basically applicable to all grains.
Ileretofore it has been customary to use single fans. The appli-cation of multiple fans offers distinct advantages: control of air flow according to grains need lower electrical requirements; increased air flow;
more uniform air flow, more easily serviced; more direct attachment to the bin by sizing fan housing to plenum depth; and a more flexible application of horsepower to fit a wide variation of systems.

2~ The fans 19 have flap closures around the plenum chamber which allow the respective fans to introduce air into the plenum chamber, but which substantially prevent àir from leaving the pleDum chamber when that same respective fan is not opera~ive. Further, it becomes practLcable to prefabricate an electrical harness that attaches in series to the previous Ean providing a simple "add on" approach to increase fan numbers in a given sys~em.
It is a feature of this invention that grain can be dried in a manner more closely approximating natural drying, and over-heating and over-drying of the grain can be avoided. Specifically, satisfactory drying rates may be obtained without using supplemental heat sources e.g. the heat : . ~ . :. ,, : . . . :; . : , ~ 5Z

lamps 21 so long as the dryness of the a:lr is consistent with the desiredequilibrium dryness that will be obtained in the grain. When the outside air temperature is too cold and/or when it has a high humidity, the supple-mental heat source can then be activated to provide the necessary dryness in the air to obtain proper drying rates.
The differential setting for the operation will vary with the particular grain being dried and the ultimate moisture content desired.
A setting of 7 - 10F~ may be best for corn, while a 5 - 8F. differen-tial may be best for rough rice and a 3 - 6F. differential for soybeans.
It must be emphasized that adequate air flow must be provided in any drying operation of this type. ~s has been said, a thorough dis-cussion of the importance of air volume to the drying operation appears in the aforesaid United States Patent No. 3,408,747.
Dryness of the air determines dryness of the grain, while the volume of air employed and the temperature determines how long it will take to complete drying.
Calculated averages for dryness, for time required, as well as probability of weight and germination losses (as described in the afore-said United States Patent No. 3,408,747) can be determined acoording to differing conditions of air flows.
For example, 26~ moisture corn harvested on November l, using l-l/2 cfm/Bù. generally requires 44 days to dry to 13-l/2% moisture with a 64~ probability of losing 0.5% o dry matter (approximately 10~ germina-tion); doubling the air volume (3 cfm/Bu.) reduces the probability of weight loss to zero and reduces drying time to 22 days.
~ he application of this gradual process of moisture removal does not limit harvest capacities since under certain moisture levels (25~) _ instant and total filling of the bin~is possible. Even now, structures up to 48' diameter are available with capacities in excess of 20,000 bushels.

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~8~1Ui52 The operatlon of one embodiment of ~he invention will now be illustrated by reference to Figures 1 and 3 of the drawings. A grain bin 11 is filled with grain to be conditioned, e.g., by filling through the opening 14 in the roof 13 of the bin. After the grain 18 is in the bin and has been levelled, tem-perature sensor 37 and sensor 36 for the differential temperature control are placed in the bed of grain near the surface thereof. Depending upon the ambient temperature and humidity conditions, a desired drying tempera-ture is set on the thermostat 33 and a setting selected for maxmimum tolerable differential. During fan 19 operation, air is forced into the plenum chamber and up through the floor 17 into the body of grain 18 and eventually out the opening 14. As the drying air passes through the body of grain, moisture will tend to be removed from the grain into the air, and the resultant evaporation will cause a lowering of the temperature of the air. The extent of the temperature lowering will be indicative of the rate of removal of water from the grain, and can be observed by the operator by reference to the thermometers 31 and 32. If the temperature differential indicated by thermometers 31 and 32 exceeds the differential setting of control 34, this indicates ~hat overdrying would occur, and the differential control 34 will function to inactivate the supplemental heating means. Drying will then continue utilizing air which has not had supplemen~al heat adcled thereto, other than the small amount resulting from the operation of the fan and motor. The differential temperature then will tend to work back toward the range set on the differential con-trol 34, and if the differential temperature becomes less than the amount set on control 34, the thermostat may again cause the heat lamps 21 to become activated, adding heat to the drying air.

: . . ~ : . : : . . . . . .

~ 366~5;2 Now with respect to the embodiment shown ln ~igure 4, in its operation, the heat lamp 42 will only operate when the contacts of both the ~hermostat and the differential controller 34 are closed. Consequently, in order for the heat lamp to operatç, the temperature sensed in the plenum by sensor 46 must be below the preset temperature of thermostat 33 in order to have the contact in thermostat 33 closed, and the differential tempera-ture between 36 and 46 (in the exhaust and plenum chambers, respectively) must be less than the differential setting on differential controller 34.

It will be understood that thermostat 33 and differential controller 34 respond automatically to close the contacts as wellas to open them to pro-vide a fully automated contro~

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,: . ; ., -

Claims (27)

The embodiments of the invention in which an exclusive prop-erty or privilege is claimed are defined as follows:

1. In a grain drying bin of the type having a plenum chamber formed in the lower part thereof, and a gas-pervious floor forming the top of the plenum chamber, the improvement comprising:
means for introducing atmospheric air in said plenum chamber, heating means for adding heat energy to the air in said plenum chamber;
means for sensing the temperature of air in said plenum chamber;
means for sensing the temperature of the air in the top of said grain bin, said air being air exhausting from said grain bin; and differential temperature control means operating in response to the difference in temperature between the air in said plenum chamber and the air in the top of said grain bin for controlling said heating means by activating said heating means when the result of the temperature in the plenum chamber minus the temperature in the top of said grain bin is a predetermined amount or less, and for deactivating the heating means when the temperature in the plenum chamber minus the temperature in the top of said grain bin is greater than said predetermined amount.

2. In a grain drying bin of the type having a plenum chamber formed in the lower part thereof and a gas-pervious floor forming the top of the plenum chamber, the improvement comprising:
means for introducing atmospheric air into said plenum chamber;
heating means for adding heat energy to the air in said plenum chamber;
means for sensing the temperature of air in said plenum chamber;
means for sensing the temperature of air exhausting from said grain bin;
thermostat means for controlling the operation of the heating means; and differential temperature control means adapted to override said thermostat means controlling the heating means and thereby to inacti-vate said heating means when the temperature difference between the drying air in said plenum chamber and the air exhausting said grain bin is greater than a predetermined amount, while not inactivating said heating means when the temperature difference between the drying air in said plenum chamber and the air exhausting said grain bin is less than said predeter-mined amount.

3. The grain drying bin as defined in claim 2 including: means for indicating the temperature of the air in said plenum chamber; and means for indicating the temperature of the air exhausting from said grain drying bin.

4. The grain drying bin as defined in claim 2 wherein said means for introducing atmospheric air operates at approximately 1.5 to 9.0 cubic feet per minute per bushel of grain at moistures between 18 and 30 percent moisture.

5. The grain drying bin as defined in claim 2 including:
a control panel;
means mounted on said control panel for continuously indica-ting the temperature of the air in said plenum chamber;
means mounted on said control panel for continuously indica-ting the temperature of the air exhausting from said grain drying bin;
adjustable means mounted on said control panel for controlling said thermostat means, and adjustable means mounted on said control panel for controlling said temperature control means.

6. The grain drying bin as defined in claim 2 whereby said temperature differential is determined by subtracting the temperature of the air exhausting from said grain bin from the higher temperature of the inlet air in said plenum chamber.

7. In a grain drying bin of the type having a first chamber formed in the lower part thereof, a gas-pervious floor forming the top of said first chamber, and a second chamber formed in the top of the grain bin, one of said chambers being a plenum chamber and the other of said chambers being an exhaust chamber, the improvement comprising:
means for introducing atmospheric air into said plenum chamber;
heating means for adding heat energy to the air in said plenum chamber;
means for sensing the temperature of the air in said plenum chamber;
means for sensing the temperature of the air in said exhaust chamber; and differential temperature control means operating in response to the difference in temperature between the air in said plenum chamber and the air in said exhaust chamber for activating said heating means when the result of the temperature in said plenum chamber minus the temperature in said exhaust chamber is a predetermined amount or less, and for deacti-vating said heating means when the result of the temperature in said plenum chamber minus the temperature in said exhaust chamber is greater than said predetermined amount.

8. In a grain drying bin of the type having a first chamber formed in the lower part thereof, a gas-pervious floor forming the top of said first chamber, and a second chamber formed between the grain and the top of the grain bin, one of said chambers being an exhaust chamber, the improvement comprising:
means for introducing atmospheric air into said plenum chamber;

heating means for adding heat energy to the air in said plenum chamber;
means for sensing the temperature of air in said plenum chamber;
means for sensing the temperature of air in said exhaust chamber;
thermostat means operating in response to the temperature of air in said plenum chamber for controlling the operation of said heating means by activating said heating means when the temperature of the air in said plenum chamber is below a predetermined temperature, and for inactiva-ting said heating means when the temperature of the air in said plenum chamber is above said predetermined temperature; and differential temperature control means operating in response to the difference in temperature between the air in said plenum chamber and the air in said exhaust chamber for overriding the activation of said heating means by said thermostat means when said difference in temperature exceeds a predetermined temperature amount, thereby to inactivate said heating means only while the difference in temperature exceeds said pre-determined temperature, said differential control temperature means having no overriding effect on said thermostat means when said difference in temperature does not exceed said predetermined temperature.

9. The grain drying bin as defined in claim 8 including: means for indicating the temperature of the air in said plenum chamber; and means for indicating the temperature of the air in said exhaust chamber.

10. The grain drying bin as defined in claim 8 whereby said temperature differential is determined by subtracting the temperature of the air exhausting from said exhaust chamber from the higher temperature of the inlet air in said plenum chamber.

11. In a grain drying bin of the type having a first chamber formed in the lower part thereof, a gas-pervious floor forming the top of said first chamber, and a second chamber formed between the grain and the top of the grain bin, one of said chambers being a plenum chamber and the other of said chambers being an exhaust chamber, the improvement comprising:
means for introducing atmospheric air into said plenum chamber;
heating means for adding heat energy to the air in said plenum chamber;
means for sensing the temperature of air in said plenum chamber;
electric circuit means for controlling said heating means;
means for sensing the temperature of air in said exhaust chamber;
thermostat means for opening or for closing the circuit means in response to the temperature of air in said plenum chamber, thereby to activate said heating means so long as the air in said plenum chamber is below a predetermined temperature; and differential temperature control means set at a predetermined temperature differential between the temperature of the air in said plenum chamber and the temperature of the air in said exhaust chamber for automa-tically opening said circuit means of said heating means when said pre-determined temperature diffierential is exceeded, and for closing said circuit means when said differential temperature is less than said prede-termined temperature differential setting.

12. The grain drying bin as defined in claim 11 including: means for indicating the temperature of the air in said plenum chamber; and means for indicating the temperature of the air in said exhaust chamber.

13. The grain drying bin as defined in claim 11, whereby said temperature differential is determined by subtracting the temperature of the air exhausting from said exhaust chamber from the temperature of the inlet air in said plenum chamber.

14. In a grain drying bin of the type having a first chamber formed in the lower part thereof, a gas-pervious floor forming the top of said first chamber, and a second chamber formed between the grain and the top of the grain bin, one of said chambers being a plenum chamber and the other of said chambers being an exhaust chamber, the improvement comprising:
means for introducing atmospheric air into said plenum chamber;
heating means for adding heat energy to the air in said plenum chamber;
means for sensing the temperature of air in said plenum chamber;
means for sensing the temperature of air in said exhaust chamber;
first thermostat means operating in response to the temperature of air in said plenum chamber for activating said heating means so long as the air in said plenum chamber is below a predetermined temperature; and second thermostat means operating in response to the tempera-ture of air in said exhaust chamber for further controlling said heating means by automatically overriding said first thermostat means by preventing the operation of said heating means when the temperature of the air in said exhaust chamber is below a predetermined temperature, said predeter-mined temperature of said first thermostat means being higher than said predetermined temperature of said second thermostat means.

15. The grain drying apparatus as defined in claim 14 wherein said heating means is an electrical heating means.

16. The grain drying apparatus as defined in claim 15 wherein said electrical heating means has a total wattage of 10 to 40 watts per one hundred bushels of grain capacity.

17. The grain drying apparatus as defined in claim 15 wherein said electrical heating means comprises at least one heat lamp.

18. The grain drying apparatus as defined in claim 15 wherein said electrical heating means comprises a plurality of heat lamps.

19. The grain drying apparatus as defined in claim 18 wherein said means for introducing atmospheric air into said plenum chamber com-prises a plurality of fans spaced about said plenum chamber.

20. A process for drying and preserving, or curing, or drying, uncured seeds, which process comprises:
placing said seeds in a closed environment;
adding atmospheric air to one point in said closed environ-ment;
allowing air to exit from another point in said close environ-ment;
determining the temperature of air at said point of entry into said closed environment;
determining the temperature of air at said point of exit from said closed environment;
adding heat to air within said closed environment only when the temperature difference between the entering air and the exiting air is greater than a predetermined amount; and controlling the amount of such heat always to maintain the temperature of the exiting air cooler than the temperature of the entering air.

21. A process for curing seeds comprising:
placing uncured seeds in a closed environment;
adding atmospheric air to one point of said closed environ-ment, allowing air to exhaust at another point in said closed environment;
maintaining the addition of atmospheric air within specified quantities;
measuring the temperature of the air at said point of entry of the atmospheric air;

measuring the temperature of the air at said point of exhaust from the closed environment;
adding heat to the entering atmospheric air only when the temperature difference between the entering air minus the exhaust air is less than a predetermined amount;
controlling the amount of such heat being add, thereby always to maintain the temperature of said exhaust air cooler than the tempera-ture of the entering atmospheric air; and continuing the addition of atmospheric air and controlling the addition of heat to said atmospheric air until a desired equilibrium moisture has been achieved in the stored seeds.

22. The process as defined in claim 21 wherein the desired equilibrium moisture is at 18 percent and the temperature of the seeds is at 40°F.

23. A process of drying uncured seeds comprising the steps of:
placing uncured seeds in a closed environment;
adding atmospheric air to one point of said closed environ-ment;
allowing air to exhaust from another point in said closed environment;
determining the temperature of the air at said point of entry into the seeds;
determining the temperature of the air at said point of exhaust from the seeds;
adding heat to said entering atmospheric air only when the difference between the temperatures of said entering air minus said exhaust air is less than a predetermined amount required to achieve a desired equilibrium moisture in the stored seeds; and controlling the amount of such heat being added, thereby always to maintain the temperature of said exhaust air cooler than the temperature of said entering atmospheric air.

24. A process of drying uncured seeds comprising the steps of:
placing uncured seeds in a closed environment;
constantly adding 1.5 to 9.0 cubic feet per minute of atmospheric air per bushel of uncured seeds to one point of said closed environment;
allowing said added air to traverse the seeds and to exit as exiting air at another point of said closed environment;
adding heat to said added atmospheric air at a rate of no more than 1.36 BTU per hour per bushel, said heat being added only when the determined temperature difference between the added air and the exit-ing air is greater than a predetermined amount and is controlled so as always to maintain the temperature of the exiting air cooler than the temperature of the added air; and continually using said process until the seeds are cured.

25. A process of drying uncured seeds comprising the steps of:
placing uncured seeds in a closed environment;
constantly adding 1.5 to 9.0 cubic feet per minute of atmospheric air per bushel of uncured seeds to one point of said closed environment;
allowing said added air to traverse the seeds and to exit as exiting air at another point of said closed environment;
adding heat to said atmospheric air at a rate of no more than 0.4 watts per bushel before said added air is introduced into the seeds, said heating being added only when the determined temperature difference between the added air and the exiting air is greater than a predetermined amount and is controlled so as always to maintain the tempera-ture of the exiting air cooler than the temperature of the added air; and continually using said process until the seeds are cured.

26. The process of claim 25 wherein said additional heat is supplied in the form of infrared rays from a heat lamp.

27. The process of drying and preserving seeds, said seeds being in a bin having heating means and means for forcing air into a plenum chamber in the lower part of the bin, said heating means being disposed in said plenum chamber, said plenum chamber being covered by a floor pervious to gas flow, said process comprising the steps of:
introducing atmospheric air into said plenum chamber;
determining the temperature within said plenum chamber;
determining the temperature of exhaust air leaving the bin;
inactivating said heating means when the temperature of the air in the plenum chamber minus the temperature of the exhaust air is greater than a preselected amount; and controlling the amount of heat from said heating means always to maintain the exhaust air temperature cooler than the inlet air tempera-ture while the grain is curing.