Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Utility Patent
1999-05-17
2001-01-02
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S475000, C034S493000, C034S168000
Utility Patent
active
06167638
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of drying materials. It is particularly applicable to grain such as wheat, and other crops. It involves passing through a bed of the grain, crops or other materials a stream of very dry air which is dried preferably while cooled and under pressure so that when it is warmed again its relative humidity is very low. Preferred techniques for drying and circulating the air are disclosed.
BACKGROUND OF THE INVENTION
It is desirable to dry grain and other crops not only to reduce spoilage, but also to save on shipping charges based on weight, which otherwise would be calculated to include shipping the entire original moisture content of the grain or other agricultural product. Drying is also used to achieve a more or less standard or target moisture content, representing a regulatory or commercially desired maximum or optimum. Apart from any quality effects, it is undesirable to sell grain (and other products worth more than water) having a moisture content substantially less than such a maximum. Thus, it is common not only to reduce the moisture content of grain, but not to reduce it substantially below an acceptable maximum. This means the drying method must not only be efficient but readily controlled to achieve a target moisture content.
A rather basic method commonly used is simply to employ a large blower to force a stream of untreated atmospheric air through a silo or other container of grain. This method is subject to the vicissitudes and vagaries of weather conditions, particularly the temperature and relative humidity, and may actually add moisture to the grain rather than remove it. It is not efficient when the relative humidity is high, and generally cannot be used at night or at other times when temperatures are cool; therefore the operator may not be able to completely dry the grain in time to meet scheduled rail cars or other transportation. Also, the blowers must be quite large and will consume large quantities of power over time when relative humidity is high or when the back pressure is significant.
To increase the efficiency of atmospheric blowers, heaters for the air have been added, although simply heating does not remove moisture from the air but merely lowers the relative humidity. Some dryers using heated air also employ mechanical movers or manipulators of one type or another for the grain, so that the air need not pass through an entire bed of grain at once. If this is not done, the warm air has a tendency to deposit the moisture picked up from the lower (or upstream) part of a bed, into the upper (or downstream) part of the bed, as it is cooler than the warm air not carrying significant amounts of moisture. This means the warm air must do its job of picking up moisture more than once, an obviously inefficient result. To overcome this, the operator may increase the temperature further, which may tend to toast or at least over-dry the lower parts of the grain bed, reducing the value of the grain in more ways than one. And, the area in the presence of a flame to heat the air requires safety precautions because of the danger of explosions from grain dust. Fire hazards in such installations greatly increase insurance costs as well if insurance is available at all. Of course costs are increased by the additional equipment required for heating the air.
An early U.S. patent to Cushing, U.S. Pat. No. 1,390,341, describes an air-tight silo having radial pipes with perforations used for the distribution of compressed air; the compressed air is said to be dry, and may be heated. Typically, the silo is first decompressed to create a vacuum, and the compressed air is then released into the silo, followed by the removal of moisture. The silo remains closed, however, and the compressed air is not passed through a bed of material but simply fills the silo. No means for drying the compressed air are shown. Compressed air is also used in a drying system by Clement in U.S. Pat. No. 2,494,644.
In U.S. Pat. No. 4,189,848, inventors Ko, Grodzka, and McCormick note that the conventional heated air techniques used for drying grain waste considerable energy, as the energy used to heat the air is released to the atmosphere after the process. Their answer is to circulate the air through a desiccant to aid in removing the moisture and they provide for the conservation of heat energy partly by recirculating the desiccant, which means dehydrating it for reuse. Desiccant is circulated also by Shoeld in U.S. Pat. No. 2,376,095.
Woodard, in U.S. Pat. No. 5,632,805, describes the assisted dehydration of compressed air through the use of various dehydrating devices, including a semipermeable membrane, interposed between compression stages in the compressor. No mention is made of using the air for drying grain or other agricultural products, nor is it suggested that the delivered air be heated for that purpose.
SUMMARY OF THE INVENTION
Our process involves the compression, cooling, dehydration and warming of air prior to passing it through a bed of grain or other agricultural product to be dried; mechanical energy released on decompression is used to transport the air through the grain or other bed. The process takes advantage of the fact that the dehydration of compressed, cooled air is very efficient when conducted particularly in drying vessels designed for the purpose and with good desiccants or otherwise with known techniques. Air prepared by our process and warmed to a temperature of 80° F. to 120° F., having a relative humidity of less than two percent (2%), will quickly and reliably dry virtually any agricultural product or other bed or particulates it contacts.
REFERENCES:
patent: 1390341 (1921-09-01), Cushing
patent: 2376095 (1945-05-01), Shoeld
patent: 2465162 (1949-03-01), Lockwood
patent: 2494644 (1950-01-01), Clement
patent: 2535902 (1950-12-01), Dailey, Jr.
patent: 2799947 (1957-07-01), Elwess
patent: 3266165 (1966-08-01), Apostle et al.
patent: 3621585 (1971-11-01), Robertson
patent: 4094075 (1978-06-01), Caruso
patent: 4189848 (1980-02-01), Ko et al.
patent: 4209911 (1980-07-01), Weber
patent: 4257169 (1981-03-01), Pierce
patent: 4974337 (1990-12-01), Tavakoli et al.
patent: 5632805 (1997-05-01), Woodard
patent: 5915816 (1999-06-01), Graeff
Mueller Wayne
Vavro Matthew E.
Clearwater, Inc.
Krayer William L.
Mattera Michelle A.
Wilson Pamela
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