Drying and gas or vapor contact with solids – Apparatus – With waste gas heat and/or power conservers
Reexamination Certificate
1999-12-07
2001-04-03
Gravini, Stephen (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
With waste gas heat and/or power conservers
C034S093000, C034S167000, C034S168000
Reexamination Certificate
active
06209223
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION(S)
This application claims the priority benefits of foreign patent application number S19981023, Vietnam, filed Dec. 8, 1998.
FIELD OF THE INVENTION
The present invention relates generally to a grain drying system, and particularly to a rice drying system comprising a hot air generating source, such as a high-efficiency dehumidifier or a fuel burner, and a modular drying bin which can be easily disassembled and reassembled for ease of transportation.
BACKGROUND OF THE INVENTION
Drying of freshly harvested paddy rice is essential to insure its conservation. Typically, paddy rice is harvested between 20% and 30% moisture content and good conservation requires less than 14%. Paddy rice is traditionally dried under the sun. This method, although low in cost, has many deficiencies. Sun drying is difficult to control, drying is not even between the top layer and the bottom layer, and rain can ruin exposed grains. Birds, rodents and insects can also substantially damage a harvest. Drying paddy rice in humid climates is especially difficult during the rainy season because the ambient air is already wet, and the rice will not dry unless heated to high temperatures which can damage the quality of the rice as well as reduce the whole grain yield.
The need for better quality finished rice has called for better methods of drying. The International Rice Research Institute (IRRI) and other institutions have studied methods of drying paddy rice based on hot air and given recommendations for optimum conditions of temperature, humidity, flow rates, and time of drying. In short, these conditions can be summarized as follows: lower temperatures are generally better, and the temperature should be kept below 45-50 degrees C.; relative humidity of the drying air should be low enough to insure efficient drying; the air flow rate must be high enough to insure drying throughout the whole mass of the grains; and drying rates of about 2% to 3% moisture reduction per hour are best because faster drying could make the grain brittle.
Until now, the majority of rice dryers relied on the heating of ambient air, with heat sources such as an oil or a coal burner, and the blowing of the hot air into a drying bin containing the paddy rice. This principle is quite appropriate in dry climates, but deficient in humid climates because the ambient air contains high levels of moisture and can only provide marginal drying capacity. Therefore, high temperatures (as high as 60 degrees C.) are used to the detriment of rice quality, and long hours of drying result in high energy costs.
Several types of drying bins are now used. Two of them are quite common in Asia: flat bed dryers and tower dryers. Flat bed dryers are made of a large surface chamber with a perforated floor located about half way up in the chamber, creating a bottom air plenum and a grain storage chamber on top. Hot air is blown into the bottom chamber and admitted into the grain storage chamber through the perforated floor. Although very simple, the flat bed dryers do not provide even drying; the bottom layer dries faster than the top layer. Even drying requires labor intensive and health-hazardous manual turning over, a task which exposes workers to hot, humid air as well as harsh, silicon-rich grain dust.
Another system is the tower dryer, consisting of a tall tower in which grain is fed at the top and allowed to fall to the bottom, while hot air is blown upwards in a counter flow fashion. In a tower dryer, grain does not dry in one pass, but must be recirculated several times, requiring mechanical devices such as a bucket elevator. Because of their complexity, the tower dryers are more expensive and can only be economical in larger capacities. Both of the above dryer systems are very difficult to move, because they are fairly large and require a prepared fixed surface. The flat bed system dries grains in thin layers (typically less than 25 cm) and therefore requires a large surface. The tower dryer, as the name indicates, is usually very tall (on the order of 10 meters) and includes complicated grain conveying devices such as bucket elevators.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a grain drying system which can overcome the above mentioned drawbacks. While the system may be used with any grain, bean, seed, kernel, or similar product, the preferred embodiment is specially designed for use with rice. This invention is a new, energy efficient, environmentally clean grain drying system which consists of two main parts: a hot drying air generator and a modular, portable drying bin. The hot drying air generator is capable of providing drying air at relatively high air pressure and volume. The drying air can be produced by direct heating, indirect heating or by the use of a heat pump or a dehumidifier. Such a hot air generator can use, for example, fossil fuels, biomass, electricity, or solar energy as a power source.
One novel aspect of the air generator is the introduction of a heat pipe design which enhances the efficiency of a dehumidifier heat pump, making its use economically feasible, especially for humid climates. Another novel aspect is the use of advanced burners incorporating antipollution devices. The hot air generator can operate on many sources of energy such as electricity; gasoline; diesel; biomass such as wood, charcoal, or rice husks; or even solar energy.
The rice drying system of the present invention includes a modular bin made of several modules which can be disassembled for ease of transportation and reassembled at the site of use together without tools. The bin design also creates a very low air pressure drop, allowing substantial savings on blower energy.
The complete system, comprising a drying air generator and a modular bin, will offer great benefits for developing countries that are producers of rice, especially for those with humid climates. With this advanced dryer system, the small producers of rice located far from means of transportation can preserve their harvest and offer higher quality products at a lower production cost.
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Letter from Bureau of Postharvest Research & Extension re: experimental testing during 1999 peak harvest season.
Advanced Dryer Systems, Inc.
Gravini Stephen
Kinney & Lange , P.A.
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