Gas separation: processes – Filtering – With cleaning of filter
Reexamination Certificate
2001-09-10
2003-09-09
Smith, Duane (Department: 1724)
Gas separation: processes
Filtering
With cleaning of filter
C055S300000, C055S337000, C055S459100, C055S518000, C095S278000, C210S321630
Reexamination Certificate
active
06616734
ABSTRACT:
FIELD OF INVENTION
The present invention provides a method and related apparatus for separating or classifying ultra-fine or nanometer-sized powder particles. The method and apparatus are effective in separating and classifying various nano-sized powders, which can be used in industrial or consumer products such as abrasives, chemical catalysts, agricultural chemicals, animal feeds, carbon & graphite, cement, ceramics, clay, coal & coke, construction materials, cosmetics, detergents, fertilizers, fillers, frits, enamels & glazes, food products & colorings, herbs & spices, industrial & specialty chemicals, insecticides & pesticides, marine feeds, metallic minerals & ores, metallic powders, oxides & compounds, minerals (non-metallic), paints, pigments & dye stuffs, pharmaceuticals, pulverized fuel ash, rare earth metals & compounds, refractory materials, resins & waxes, slags, surface coatings, and toners.
BACKGROUND OF INVENTION
Particle separators or classifiers for ultra-fine solid powders have a tremendous utility value. This is due to the unusually wide range of applications that ultra-fine powders, including nanometer-sized powders, have enjoyed. Nano-sized powders are essential ingredients in a broad array of both industrial and consumer products, listed above. In most of these applications, particles of well-defined sizes and/or a narrow size distribution are highly desirable for improved product performance.
Additionally, nano-sized metal powders are being considered for use as primers, propellants, and high explosive energetic materials. The particle size uniformity and homogeneity of particle mixing are two critical factors that hold the promise of further improving the performance of these metal powders. However, no method currently exists to guarantee the particle size uniformity in the desired range of nanometer sizes. Conventional mechanical methods of separation (e.g. metal screen sieves) are not feasible for separating particles at the nanometer scale. Current electrostatic charge and air-current methods are not capable of providing classification of nanometer-sized particles of an ultra-narrow size distribution as may be required of highly efficient and reliable energetic materials. An urgent need exists for an innovative method and equipment that are capable of precisely classifying nanometer-sized particles into groups of very narrow size ranges at a good production rate.
The following patents are believed to represent the state of the art of powder classifiers:
1. H. Morimoto, et al., “Air Current Classifying Separator,” U.S. Pat. No. 6,269,955, Aug. 7, 2001.
2. S. Akiyama, “Powder Classifier,” U.S. Pat. No. 5,931,305, Aug. 3, 1999.
3. W. A. Howell, “Dust-free Powder Substance Delivery and Filter System,” U.S. Pat. No. 5,518,343, May 21, 1996.
4. H. Kanda, “Gas Current Classifying Separator,” U.S. Pat. No. 5,165,549, Nov. 24, 1992.
5. M. Kato, et al., “Air Current Classifier, Process for Preparing Toner, and Apparatus for Preparing Toner,” U.S. Pat. No. 5,016,823, May 21, 1991.
6. Y. Yamada, et al., “Powder Classifier,” U.S. Pat. No. 4,604,192, Aug. 5, 1986 and U.S. Pat. No. 4,560,471, Dec. 24, 1985.
7. N. Nakayama, “Air Classifier,” U.S. Pat. No. 4,221,655, Sep. 9, 1980.
8. Y. Sogo, “Cyclone Separator,” U.S. Pat. No. 4,149,861, Apr. 17, 1979.
9. J. Drew, et al., “Centrifugal Separator Apparatus,” U.S. Pat. No. 3,753,336, Aug. 21, 1973.
10. B. G. E. Mansson, “Apparatus for Separating Solids in a Whirling Gaseous Stream,” U.S. Pat. No. 3,643,800, Feb. 22, 1972.
11. B. N. Hoffstrom, “Rotary Flow Classifier,” U.S. Pat. No. 3,334,741, Aug. 8, 1967.
12. J. D. Miller, E. E. Koslow, K. W. Williamson, U.S. Pat. No. 4,676,807, Jun. 30, 1987 and U.S. Pat. No. 4,759,782, Jul. 26, 1988.
13. J. G. Billingsley, et al. “Cyclone Separator,” U.S. Pat. No. 5,236,479, Aug. 17, 1993.
14. A. Matsui, “Dust Collector Adapted for Use in a Hopper Dryer,” U.S. Pat. No. 4,848,990, Jul. 18, 1989.
15. C. Davis, “Low Pressure HEPA Filtration System for Particulate Matter,” U.S. Pat. No. 4,490,162, Dec. 25, 1984.
16. H. J. Obermeier, “Dual Cyclone Dust Separator for Exhaust Gases,” U.S. Pat. No. 4,406,677, Sep. 27, 1983.
17. H. J. Lader, “System for Controlling and Utilizing Finer Powder Particles in a Powder Coating Operation,” U.S. Pat. No. 5,454,872, Oct. 3, 1995.
18. S. Masuda, “Electric Dust Collector Apparatus,” U.S. Pat. No. 3,985,524, Oct. 12, 1976.
19. S. Nishikiori, et al. “Cyclone Type Dust Collector,” U.S. Pat. No. 6,042,628, Mar. 28, 2000.
20. S. Minakawa, “Cyclone Dust Collector,” U.S. Pat. No. 5,948,127, Sep. 7, 1999.
21. B. G. Jung, “Dust Collector Using Purse-Type Filter Cloth,” U.S. Pat. 5,683,477, Nov. 4, 1997.
As indicated in the-above-cited patents, various techniques for separating and classifying powders have been proposed. One of such conventional techniques, known as powder classifier, provides a rotor for classifying powders by using the rotation of the rotor and airflow. The rotor spins at a high speed inside a casing with the rotor being equipped with a plurality of powder classifying vanes swirling around, while ventilating the rotor from the periphery to the center. The airflow and the centrifugal force caused by the rotation act on the powder flow to classify the powder particles in accordance with the boundary defined by a desired particle size.
More specifically, an air introduction path is formed to be directed toward the inside of the rotor from the position where the powder classifying vanes are provided, and a powder introduction port or powder intake is formed above the classification rotor along the circumference thereof from which powder particles fall onto the powder classifying vanes. A powder supply port is provided on the upper center of a casing for supplying the powder as a raw material. The powder supplied is fed from the powder intake to the powder classifying vanes within the rotor, i.e., fed into a classification chamber while being scattered on the upper surface of the rotor. In the classification chamber, the centrifugal force of the powder classifying vanes and the air flowing into the center of the rotor act on the powder. In other words, fine powder particles with a small diameter that is very susceptible to air viscous resistance are carried by the airflow to the central portion and taken out from a fine powder outlet, while coarse powder particles having a large diameter that is very susceptible to the centrifugal force are scattered to the outer edge of the classification rotor by the centrifugal force and collected to a coarse powder outlet provided on the outer peripheral of the rotor. The powder is thus classified in accordance with the boundary defined by a desired particle size.
Such a conventional powder classifier is also provided with a balance rotor, unitarily with the classification rotor, so that the air passing through the classification rotor is introduced through the balance rotor from the center of the classification rotor into the fine powder outlet provided in the outer edge of the classification rotor. The balance rotor is provided with a view to regulating the flow of air passing through the classification rotor or a vent cavity or ventilating the vent cavity smoothly so that the powder can be classified in accordance with the desired value.
Since in the conventional classifier the balance rotor is coupled to the lower portion of the classification rotor, the flow can be balanced in the vertical direction. Such a balance rotor, however, makes the entire mechanism of the powder classifier complicated and the rotor large scale to increase the weight. The heavy rotor causes an increase in output of a drive mechanism for driving the rotor to rotate. Further, since in the powder classifier the vent path from the classification rotor to the balance rotor is bent substantially at 180 degree and the sectional area of the path is increased from the center to the circumference, the ventilating speed is reduced and hence the classified powder particles could be accumulated or adhere to the inner surface of the vent path. T
Nanotek Instruments, Inc.
Pham Minh-Chau T.
Smith Duane
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