Drying and gas or vapor contact with solids – Apparatus – Gravity flow type
Reexamination Certificate
1999-12-13
2001-02-27
Ferensic, Denise L. (Department: 3744)
Drying and gas or vapor contact with solids
Apparatus
Gravity flow type
Reexamination Certificate
active
06192598
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
This invention relates in general to pest control using microwave energy, and in particular to the use of Super High Frequency (SHF) and Extremely High Frequency (EHF) band microwaves that kill insects in granular materials without the use of chemicals.
The principle of using microwaves as a pesticide in grain and granular materials has been known, but it has been determined that effective and consistent mortality rates are only possible when the grain in unpacked, mixed with air, and fairly uniform in density for effective microwave penetration.
The search for an operating frequency which would lead to enhanced selective heating of insects in the Extremely High Frequency (EHF) and Super High Frequency (SHF) ranges is motivated by the need to develop alternatives to certain important agricultural chemical pesticides for the treatment of stored products which are to be banned by the Clean Air Act by the year 2001. Operation at discrete frequencies in the microwave and millimeter wave ranges, including Industrial Scientific and Medical (ISM) frequencies specified in the U.S. Code of Federal Regulations (47 C.F.R., part 2), is attractive because of the availability of recently developed high-power oscillators with high continuous outputs and efficiencies at those frequencies. Unlike the relatively low-power microwave and lower frequency heaters, operating at frequencies less than or equal to 2.45 GHz, the EHF and SHF high-power sources offer the possibility of continuous processing of the treated product at high throughput rates while taking advantage of the electromagnetic shielding inherent in the waveguide-like piping or duct systems that arc common in transport systems at grain storage facilities.
There is a need for a consistently effective microwave granular treatment device and microwave range that effects high mortality rates while maintaining temperatures within acceptable limits.
SUMMARY OF THE INVENTION
In accordance with the present invention there is a microwave device for controlling insect infestation in stored products such as bulk grains, granular or milled materials at typical processing and storage facilities, or packaging materials and containers used in the packaging of processed products. The device includes at least one high-power coherent nonionizing electromagnetic radiation means, emitting energy in the SHF (3 GHz to 30 GHz) or EHF (30 GHz to 300 GHz) band of the spectrum where coupling to the free water in the insect is maximized, power supplies to energize the radiation means, a cooling system for both the power source and the treated stored product that includes a heat exchanger for removal of waste heat and regenerative heating of the product, an electromagnetic energy transmission system, a process control system including sensors to monitor and control the process variables, active control elements to initiate and terminate product flow, a facility protection system to shut the system down when safe operating margins are exceeded, an applicator or interaction chamber through which the dynamic (flowing) product is uniformly mixed with atmospheric air by means of an applicator and to which the energy is coupled, a means of controlling the atmosphere within the applicator to avoid combustible mixtures of air and fine dust, and a treated product collector.
This invention uses energy in that portion of the SHF and EHF spectrum common with the relaxation processes associated with free water and hemolymph, uniquely associated with insects (Weber. 1974. Grundriss der Insektenkunde, Gustav Fischer Verlag, Stuttgart. pp 640 & Seifert. 1995. Entomologisches Praktikum, Georg Thieme Verlag Stuttgart-New York: 76-81.), to selectively heat and destroy the insects in stored products. Halverson et al. “Microwave Radiation As An Alternative To Chemical Pesticides”, Paper No. 956129, ASAE Annual International Meeting, Chicago, Ill., Jul. 18-23, 1995; Halverson et al. “High-Power Microwave Radiation As An Alternative Insect Control Method For Stored-Products”, J. Econ. Entomol. 89(6) 1638-1648 (1996); Halverson et al. “Effects Of SHF And EHF Radiation On The Mortality Of
S. zeamais
In Soft White Wheat”, Paper No. 963013, ASAE Annual International Meeting, Phoenix, Ariz., Jul. 14-18, 1996; and in Plarre et al. 1997 disclosed testing of static infested samples of granular materials that maximum selective heating of insects occurs at exposers of discrete energy frequencies above 1 GHz.
Data taken with microwave network analyzers on samples of insects and white wheat and wheat flour, over frequency ranges from 50 MHz to 75 GHz, indicated that mortality of both
S. zeamais
and
Tribolium castaneum
(red flour beetle) is much greater at frequencies above about 24 GHz, confirming predictions obtained from analytical models (Halverson, et al. “SHF And EHF Microwave Radiation As A Pesticide Alternative For Stored Products”, Paper No. 55, 1996 Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions, Nov. 4-6, 1996). Subsequent dynamic high power tests were conducted at 28 GHz (Halverson et al. “Recent Advances In The Control Of Insects In Stored Products With Microwaves”, Paper No. 976098, ASAE Annual International Meeting, Aug. 10-14, 1997) which verified that mortality due to selective heating of insects was superior to that obtained at HF at lower product temperatures, that germination of the wheat was unaffected, and that dynamic treatment of the stored product in a continuous process at high mass flowrates was practicable. Static tests at 28 GHz have verified that the relationship between exposure time and mortality at constant energy input is solely energy dependent for product exposure times greater than 250 milliseconds.
In view of the foregoing physical relationships and test results, the present invention is also directed to systems for controlling insect infestation of a granular product by the transfer of energy from a source or sources of SHF or EHF electromagnetic radiation at high powers to kill the insect while keeping the product temperature at levels where the product quality is unaffected. In one embodiment of the invention, energy from one or more high-power SHF or EHF source is coupled to a continuously flowing granular product in an untuned, metal-walled resonator (an “applicator”) through a transmission system. The applicator, through which the infested product to be treated flows freely under the force of gravity, may be cylindrical, rectangular, ellipsoidal, conical, or spherical in form. The input power required is a function of the specified product throughput rate, the energy input per unit mass required to produce the desired level of insect mortality, and the coupling efficiency.
The applicator dimensions are large with respect to a wavelength at the frequency of operation. The applicator couples the electromagnetic energy and the product to achieve a relatively uniform energy density within the product. The applicator also accepts and regulates the flow of a product from an upstream pipe or conduit, and preferably is designed to control the fraction of the total applicator volume occupied by product flowing within the applicator to ensure penetration of the product by the microwave energy.
A process using the applicator is controlled by a system comprising an automatic or manual control station, a permission interlock system to prevent inadvertent operation and flow, temperature, pressure and system status sensors to monitor the process and provide the capability of shutting down the system in the event that the operational safety limits are exceeded. The flow sensors also provide control signals to outside systems which control the mass flow rate of the product.
Both the high-power microwave source and the applicator and the post treatment product will be cooled to remove waste heat through a heat exchanger. The rejected heat provides a means of preheating the product to improve overall operating efficiency.
These and other objects and advantages of the present inv
Bigelow Timothy S.
Halverson Steven L.
Drake Malik N.
Ferensic Denise L.
Lathrop & Clark LLP
Micro-Grain, Inc.
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