ION PARTICLE CLASSIFIER AND CLASSIFYING METHOD

Abstract: The invention refers to an ion particle classifier and a method for classifying coarse solid particles from an air suspension of micronized particles, said ion particle classifier comprising a housing surrounding an electrically conductive, cylindrical inner layer, acting as a first electrode, and a centrally positioned rod with a number of radially directed tips, acting as a second electrode, said electrodes being electrically insulated from said housing and coupled to a high voltage current source, an inlet pipe for said air suspension of micronized particles to be classified terminates at a one end of said first electrode and an outlet pipe for an air suspension of classified fine particles is mounted close to the opposed end of said first electrode, one end of said is provided with discharge means for a fraction of classified coarse particles of said air suspension, said classifier further being provided with a rinsing air input entering said classifier at one of its ends.

Description: Ion Particle Classifier and Classifying Method BACKGROUND OF THE INVENTION This invention refers to an ion particle classifier and a method for classifying coarse solid particles from an air suspension of micronized particles All industrial fields from medical industry to mine- and building material industry use as raw materials a continuously increasing amount of different types of micronized powder like dry products. The micronizmg of these products is nowadays generally carried out m jet mills, in which highly pressurized air or overheated water vapor is generally used as grinding energy. Depending on the final product and the fineness thereof the energy consumption of these grinding and classifying processes is about 100 to 3000 kWh/ton. At this moment a micronizmg technique operating according to the opposed jet mill principle is considered to be the most effective and the most economic micronizmg method. However, a wider utilization and application of the developed opposed j et mill technique has been considerably disturbed by the lack of effective auxiliary techniques applicable in connection with the opposed jet mill technique and/or their low efficiency and high energy costs. Previously known micronizmg devices and methods are especially affected with the below presented basic problems and shortcomings, which undoubtedly will cause a lot of unnecessary energy consumption and will limit the quality of the final products. Said shortcomings will also considerably limit an effective realization of the basic idea of opposed jet grinding. In microniz g a high-energy power gas, most oftenly pressurized air, is used as grinding energy. The micronizmg devices will need industrial compressor effects ranging from 100 k to 1000 kW depending upon application. Classifying of a product micronized n an opposed jet mill as well as the methods and the devices previously used to separate power gas and solids from each other, are affected by big technical shortcomings. In the separation of solids and power gas from each other, methods and devices using different kinds of filter fabrics have been utilized, which are affected by often appearing obstruction and efflux problems, as well as of an energy consumption caused by pressure differences and, without no exception, a centrifugal fan has to be used in all applications of the separation stage m order to develop pressure differences sufficient for the operation of the device. The finer final product is to be produced, the more expensive and more difficult to control will the classifying and the separation processes turn to be. In previously used grinding processes, wherein the size of particles to be treated was more than 5 μm, such a problem did not appear. The classifying has been based on centrifugal forces arising as a result of flow rate of a power gas and solids suspension and possibly of rate of rotation of a rotor mounted in a conventional classifying device. Control of a classifying process has been carried out by regulating the rate of rotation of sa d rotor as well as of the flow rate of the suspension of power gas and solids through the classifier during an initial stage of the classifying procedure, but no continuous regulation has been carried out. It is therefore, an object of the present invention to eliminate the above drawbacks by providing a new and improved ion particle classifier. It is another object of the present invention to provide a new and improved classifying method for separating coarse particles from an air suspension of micronized particles. SUMMARY OF THE INVENTION In accordance with the present invention there is provided an ion particle classifier comprising a housing surrounding an electrically conductive, cylindrical inner layer, acting as a first electrode, and a centrally positioned electrically conductive rod with a number of radially directed tips, acting as a second electrode, said electrodes being electrically insulated from said housing and coupled to a high voltage current source, an inlet pipe for said air suspension of micronized particles to be classified terminates at one end of said first electrode and an outlet pipe for an air suspension of classified fine particles is mounted close to the opposed end of said first electrode, one end of said housing is provided with discharge means for a fraction of classified coarse particles of said air suspension, said classifier further being provided with a rinsing air input entering said classifier at either end of said first electrode. The classifier can be vertical or horizontal . By means of such an ion particle classifier a very sharp and effective classifying effect s achieved when flowing an air suspension of micronized particles to be classified at a low speed through a high voltage electrical field maintained said classifier. The ion particle classifier according to this invention is very effective and requires considerably less energy in classifying micronized solids although having very small particle size than has been possible previously known classifying devices. In accordance w th the invention there is also provided a classifying method for separating coarse particles from an air suspension of micronized solid particles, comprising the steps of flowing said air suspension of micronized particles at a low speed up through a high voltage electric field in a classifier, between a first outer cylindrical electrode and a concentrically therewith positioned second inner rod shaped electrode having a number of radially directed tips, whereby coarse particles are attracted to the inner wall of said first electrode, fall down due to force of gravity and are removed by means of discharge means, the classification being regulated by adjusting the rate of the air suspension, the voltage of the electric field as well as by adjusting solid content of the air suspension flowing through the electric field by adding r smg air. By means of this invention the energy economy and the efficiency of the micronizmg and classifying process can be considerably improved, the environmental load can be decreased, and special products with a higher fineness than earlier can be produced, e.g. a product having a fineness of even a nano level. Further features of the invention will appear from the attached depending claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematical vertical sectional view of a classifier according to the present invention; FIG. 2 is a schematical vertical sectional view of a micronizmg equipment including three somewhat different ion particle classifiers according to this invention coupled m series to each others; FIG. 3 is a schematical vertical sectional view of another embodiment of the ion particle classifier according to the invention; FIG. 4 is section B-B of Fig. 3. DESCRIPTION OF A PRE ERED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 1 thereof, there is shown an example of an ion particle classifier 1 comprising a housing 2 surrounding a vertical, electrically conduc- tive, cylindrical inner layer 3, acting as a first electrode , and a centrally positioned electrically conductive rod 4 with a number of radially directed tips 4a, acting as a second electrode. Between sa d housing 2 and said electrodes 3, 4 there are electrical insulation means 5, 6. Said electrodes 3 and 4 are connected to a high voltage current source 7 in order to achieve a high voltage electric field between said electrodes 3, 4. An inlet pipe 8 for an air suspension of micronized particles to be classified enters the housing 2 at its bottom portion 2a and terminates coaxially towards said second electrode 4. An outlet pipe 9 for an air suspension of classified fine particles is mounted in the upper end of said housing 1, starting close to the upper end of the first electrode 3. The bottom portion 2a of said housing 2 is conically tapered and provided with discharge means 10 for a fraction of classified coarse particles of said air suspension. To improve the controllability of the classifying process the classifier 1 is further provided with a r smg air input 11 entering said classifier 1 at the bottom portion 2a of the housing 2, and terminates at the lower end of said first electrode 3 coaxially towards said second electrode 4. In some cases the rmsmg air can be fed into the classifier through the opposite end of the classifier. The r smg air input 11 is preferably mounted concentrically with the inlet pipe 8 for the air suspension of micronized particles to be classified, and thus having an annular cross section. Air suspension of micronized solid particles to be classified is fed through the inlet pipe 8 into the classifier 1. The diameter of the first electrode 3 has such a lengths that the flowing rate of the air suspension through the classifier is about 0.5 to 1 m/s. Due to the high voltage electric field coarse between the first 3 and the tips 4a of the second 4 electrode solid particles of the air suspension are attracted to the inner wall of the first electrode 3. Due to force of gravity said coarse particles will fall down to the bottom portion 2a of the classifier 1, wherefrom they are removed by means of discharge means 10. The discharged fraction of coarse solid particles will be recycled to a micronizmg step. The air suspension of classified fine particles are removed from the classifier through the outlet pipe 9 and are led to the next treatment, such as another classifier for recovering the a further fraction of or all fine particles present in the air suspension. The classifying process is regulated by adjusting the flow rate of the air suspension through the classifier 1 and the voltage of the electric field as well as by adjusting the solid content in said air suspension by adding rmsmg air. The flow rate is regulated to be about 0.5 m/s up to about 1 m/s, which interval has proved to be most advantageous. By regulating the high voltage in the interval between about 1 kV and about 100 kV, preferably between about 5 kV and about 70 kV, the particle size of the particles m the coarse fraction, which is to be removed from the air suspension, can be varied very easily. In order to receive an optimal content of solid particles m the air suspension fed to the classifier and to regulate the flow rate, an adjustable amount of rmsmg air is fed to the classifier 1 together with the air suspension of particles to be classified. By feeding the rmsmg air into the classifier 1 through an annular inlet pipe 11 , surrounding the inlet pipe 8 for the air suspension of micronized particles to be classified, a most advantageous mixture of the rmsmg air and the air suspension is received. Referring to FIG 3 and FIG. 4, there is shown another embodiment of the ion particle classifier according to the invention. The inlet pipe 8 for an air suspension of micronized solid particles to be classified enters the bottom portion 2a of the classifier 1 tangentially and the rmsmg air input 11 enters the classifier at a lower level and terminates coaxially or tangentially with the second electrode 4 as in the previous embodiment. By this embodiment the lower end of the classifier will act as a cyclone separating the coarsest particles from the air suspension before it reaches the high voltage electric field between the electrodes 3 and 4. Referring now to FIG. 2, there is shown a preferred embodiment of a micronizmg equipment comprising ion particle classifiers according to the invention. Material to be micronized is fed, as illustrated by arrow 12, to a supply hopper 13 at the top of a double valve feeder 14 operating as a feeder device of an equalizing tank 15 of an opposed jet mill. From the supply hopper the material is fed by means of the double valve feeder 14 in portions to the equalizing tank 15, wherein a static pressure required for the micronizmg is maintained. By means of a screw feeder or a rotor the material is transposed from the equalizing tank 15 into a flowing, high-energy power gas, preferably air, as illustrated by arrow 16 in order to form an air suspension of the solid particles. The air suspension of the solid particles is led through a dividing device 17 and at least two substantially opposedly directed acceleration nozzles into a small grinding chamber 18, wherein the particles to be ground collide against one another and are crushed/micronized almost autogenically. The grinding chamber 18 is preferably of a type as described in our copending U.S. patent application. The discharge opening of the grinding chamber 18 is connected to a first ion particle classifier 1 through an inlet pipe 8 for an air suspension of micronized solid particles to be micronized. This first ion particle classifier 1 is similar to that shown in FIG. 1, and acts as described above. In the ion particle classifier 3 the micronized material is classified by means of the high voltage electric field into a fine fraction and a coarse fraction. The coarse fraction is removed through a discharge device 10 mounted at a bottom end of said classifier 1. In the shown embodiment the coarse fraction is recycled to the hopper 13 of the opposed jet mill, as indicated by arrow 19 for regrmding, but in some cases the coarse fraction can be recovered as a separate final product. The fine fraction is discharged as an air suspension of these classified fine particles through the outlet pipe 9 mounted at the top of the classifier 1. The air suspension of fine particles is led through the outlet pipe 9 into a second ion particle classifier 1' . In said second classifier 1' , a first final product s separating from the air suspension of classified fine particles by means of a high voltage electric field achieved by a high voltage current source 7' between the electrodes 3' and 4' in said second classifier 1'. If necessary rinsing air is fed to the second classifier 1' through input 11' . The first final product is discharged from the bottom of said second classifier 1', as indicated with arrow 20. The remaining air suspension or the classified finest solid particles is led through a second outlet pipe 9' to a final ion particle classifier 1", wherein all remaining solid particles are separated from the air by means of a third high voltage electric field between electrodes 3" , and 4" achieved by a third high voltage current source 7" , and are recovered as a second, extremely fine final product, as indicated by arrow 21. Often a very valuable solid material, having a nano level fineness, can be recovered from the final classifier 1" . The purified air is removed from the final classifier 1" through outlet pipe 9" . This purified air can be fed directly to the atmosphere or be recycled to a compressor to pressurize power gas for the micronizmg process. By using a micronizmg equipment according to this invention there will be no environmental load. By means of the present invention ultra fine powders can be produced considerably more effectively and economically than before from different dry and moist raw materials, when the final products have a D98 particle size of 0, 3μm to 150μm, and an average or D50 particle The developed equipment and method can very well be used in separating, enriching and dry enriching of different types of e.g. minerals, metals and organic materials as well as in the production of crystal seed used by different industrial areas. The method will also make it possible to produce final products having a finer particle size than previously, i.e. at the nano level from solid raw materials . According to a preferred embodiment the micronizmg equipment is used in recovering carbon from used car tires. The used car tires are pyrolized, the steel is separated from the pyrolized carbon using a magnet separator. The pyrolized substantially steel free carbon is fed to the supply hopper 13 of the micronizmg equipment. The coarse fraction, separated from the air suspension in the first classifier is discharged from the first classifier by means of the discharge means 10 provided with a branch pipe 22 having a magnetic separator 23 influencing possibly present steel particles in the coarse fraction to deviate into said branch pipe in order to be recovered, as indicated with arrow 24. The coarse carbon fraction is recycled to the micronizmg device, as indicated with arrow 19. From the second ion particle classifier 1', and first final product of micronized carbon will be recovered by means of a discharge means, such as a lock feeder or a double valve feeder. Said first final produce can be used as raw material in oroducmg new car tires. Tne extremely fine solid fraction recovered from the final ion particle classifier, as indicated by arrow 21 can be used as pigment for instance in producing black plastic foils.

Claims: CLAIMS 1. Ion particle classifier for classifying coarse solid particles from an air suspension of micronized particles, said ion particle classifier comprising a housing surrounding an electrically conductive, cylindrical inner layer, acting as a first electrode, and a centrally positioned rod with a number of radially directed tips, acting as a second electrode, said electrodes being electrically insulated from said housing and coupled to a high voltage current source, an mlet pipe for said air suspension of micronized particles to be classified terminates at one end of said first electrode and an outlet pipe for an air suspension of classified fine particles is mounted close to the opposed end of said first electrode, one end of said housing is provided with discharge means for a fraction of classified coarse particles of said air suspension, said classifier further being provided with a rmsmg air input entering said classifier at either end of said first electrode. 2. Ion particle classifier according to claim 1, wherein said inlet pipe for said air suspension of particles to be classified terminates coaxially with said second electrode. 3. Ion particle classifier according to claim 2, wherein said rinsing air inlet, having an annular cross section, terminates concentrically with said mlet pipe for the air suspension of particles to be classified. 4. Ion particle classifier according to claim 1, wherein the classifier is vertical having a conically tapered lower end, said inlet pipe for said air suspension of particles to be classified terminates tangentially into the bottom portion of the classifier. 5. Ion particle classifier according to claim 4, wherein the input of rmsmg air terminates at a lower level coaxially with said second electrode. 6. Ion particle classifier according to claim 1, wherein said discharge means for the fraction of classified coarse particles comprises a branch pipe provided with a magnetic separator for separating magnetic particles from said classified fraction of coarse particles leaving the classifier through said discharge means . 7. Ion particle classifier according to claim 1, wherein said classifier is connected as a classifier to a discharge pipe of an opposed jet mill. 8. Ion particle classifier according to claim 7, wherein the outlet pipe for the air suspension of classified fine particles terminates in a second ion particle classifier, charged with a higher voltage current . 9. Ion particle classifier according to claim 7, wherein said second ion particle classifier is connected in series to at least one further ion particle classifier, a final ion jet classifier being adjusted to separate all solid particles from the air suspension entering said classifier. 10. Classifying method for separating coarse particles from an air suspension of micronized solid particles comprising the steps of flowing said air suspension of micronized particles at a low speed up through a high voltage electric field in a classifier, between a first outer cylindrical electrode and a concentrically therewith positioned second inner rod shaped electrode having a number of radially directed tips, whereby coarse particles are attracted to the inner wall of said first electrode, fall down due to force of gravity and are removed by means of discharge means, the classification being regulated by adjusting the rate of said air suspension, the voltage of the electric field as well as adjusting the solid content of the air suspension flowing through said electric field, by adding rmsmg air. 11. Classifying method according to claim 10, wherein the air suspension of particles to be classified is fed coaxially towards said second electrode whereby coarse particles will be attracted to the first electrode and fall down to the bottom of the classifier, from which it will be discharged and fine particles will follow the air stream through the classifier and exit from the opposed end of the classifier as an air suspension of classified fine particles. 12. Classifying method according to claim 11, wherein rmsmg air is fed into the classifier concentrically with the air suspension of particles to be classified. 13. Classifying method according to claim 11, wherein rinsing air is fed into the classifier from the opposed end of the classifier flowing in the opposite direction to the air suspension of particles to be classified. 14. Classifying method according to claim 10, wherein the air suspension of particles to be classified is fed tangentially into the bottom portion of the vertical classifier. 15. Classifying method according to claim 10, wherein a voltage of about 1 kV to 100 kV, preferably 5 kV to 70 kV is connected between the electrodes. 16. Classifying method according to claim 10, wherein an air suspension of particles micronized in an opposed et mill is fed to the classifier and the fraction of classified coarse particles is recycled to said opposed jet mill. 17. Classifying method according to claim 16, wherein said particles are pyrolized and micronized carbon from used car tires. 18. Classifying method according to claim 16, wherein the air suspension of classified fine particles will be fed to a second classifier in order to recover a fraction of medium size micronized particles or to remove all particles from the air suspension. 19. Classifying method according to claim 16, wherein the air suspension of classified fine particles from the first classifier is fed in series to at least two further classifiers whereby the voltage and the speed of the air stream through the final classifier is regulated to remove all particles from the air suspension.

Inventors: ILMASTI VEIKKO, NIEMI JOUKO, SUOMINEN HANNU, ILMASTI, VEIKKO, NIEMI, JOUKO, SUOMINEN, HANNU
Applicants: BCDE GROUP WASTE MAN LTD OY, ILMASTI VEIKKO, MICROPULVA LTD OY, NIEMI JOUKO, SUOMINEN HANNU, BCDE GROUP WASTE MANAGEMENT LTD OY, ILMASTI, VEIKKO, NIEMI, JOUKO, SUOMINEN, HANNU
Application year: 2000
Main classification: B02C19
IPC codes: B03C3