Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
  • B02C23/08—Separating or sorting of material, associated with crushing or disintegrating
  • B02C23/10—Separating or sorting of material, associated with crushing or disintegrating with separator arranged in discharge path of crushing or disintegrating zone
  • B02C23/12—Separating or sorting of material, associated with crushing or disintegrating with separator arranged in discharge path of crushing or disintegrating zone with return of oversize material to crushing or disintegrating zone
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C19/00—Other disintegrating devices or methods
  • B02C19/06—Jet mills
  • B02C19/065—Jet mills of the opposed-jet type

Definitions

• the present invention concerns a method and an equipment for processing of particularly finely divided material, wherein the material is fed by means of a mechanical feeder device into a pressurized equalization tank, out of the equalization tank the material is fed by means of a screw conveyor as a uniform flow into a fluidization chamber, wherein process gas is fed to among the material particles to produce a gas-solids suspension, and the gas-solids suspension produced is accelerated, by means of the positive pressure prevailing in the fluidization chamber, through a bifurcation device and through accelera ⁇ tion nozzles of a counter-jet grinder, connected to the branch pipes of said bifurcation device, into the grinding chamber in the counter-jet grinder so as to grind the solid particles, and the ground gas-solids suspension produced in the grinding chamber is passed, by the effect of the after-pressure of the grinding chamber, through a connecting pipe into a centrifugal classifier, from which the fine fraction is removed, being carried by the gas employed in the process, through a substantially axial opening for the removal of the fine fraction.
• the solids content in the gas-solids suspension is relatively high.
• attempts have been made to introduce additional air into the classification chamber e.g., through tangentially directed additional-air nozzles.
• these additional-air jets cause flow phenomena that disturb the process of classification, so that, with the prior-art equipments it has proved extremely difficult to obtain a satisfactory result of classification in respect of ultra- fine material.
• Coarse fraction is very often removed from classifiers as a continuous gas-solids suspension flow, whereby a con ⁇ siderable amount of fine material is also removed from the classifier along with the coarse fraction.
• the fine fraction that follows along with the coarse fraction must then be separated from the coarse fraction, e.g., in a separate cyclone or returned with the coarse fraction into the feeder of the jet grinder, which operations restrict the operation and the capacity of the whole equipment unnecessarily.
• the object of the present invention is to eliminate the above drawbacks, which is accomplished by means of a method which is characterized in that additional air of low pressure is passed into the connecting pipe so as to lower the solids content in the gas-solids suspension, and the coarse fraction is removed from the centrifugal classifier through a removal opening placed in the periph- eral face of the classifier into a pocket placed outside the peripheral face, and the coarse fraction gathered in the pocket is removed batchwise to normal atmospheric pressure through a closing device placed in the bottom of the pocket.
• FIG. 1 is a schematical illustration of an exemplifying embodiment of a processing equipment in accordance with the invention
• Figure 2 shows a second exemplifying embodiment of the classifier part in an equipment in accordance with the invention
• Figure 3 is a sectional view taken along the line A-A in Fig. 2, and
• Figure 4 is an axial sectional view of an alternative embodiment of the classifier.
• the equipment in accordance with the invention comprises a mechanical feeder device provided with a feed funnel 1, such as a dual-valve feeder 2, a pressurized equalization tank 4, which is provided with a screw conveyor 3 and which is jointly operative with the feeder 2, an advantageously cylindrical fluidization chamber 5 mounted at the outlet end of the screw feeder, into which chamber process gas is fed through a tangential inlet pipe 6, a bifurcation device 17 connected to the outlet opening of the fluidization chamber 5, and accelera ⁇ tion nozzles 20, which are connected to the branch pipes 18 of the bifurcation device and which terminate in the grinding chamber of a counter-jet grinder 19, as well as a substantially cylindrical classifier 8, which is con ⁇ nected to the outlet opening of the counter-jet grinder 19 by the intermediate of a connecting pipe 7, said connecting pipe 7 terminating in said classifier 8 tangen- tially, and said classifier 8 being provided with a substantially axial opening 9 for the removal of the fine fraction.
• a feed funnel 1 such as a dual-valve feeder 2
• the inlet pipe 11 for additional air is con ⁇ nected to the connecting pipe 7 at a sharp angle, and in the peripheral face of the narrow centrifugal classifier 8 there is an opening 10 for the removal of the coarse fraction, said opening passing into a pocket 12 placed outside the peripheral face, a closing member 13 being placed in the bottom of said pocket.
• Fresh material is fed into the feed funnel 1 of the equipment by means of a screw feeder 21.
• the material to be processed falls into the tank of the dual-valve feeder 2 when the upper valve 2a is open and when the lower valve 2b is closed.
• the upper valve 2a is closed automatically, and the tank of the feeder is pressurized to the desired level by means of process gas.
• the supply of gas is switched off and the lower valve 2b in the feeder is opened, whereby the batch contained in the tank of the feeder 2 falls down into the equalization tank 4, wherein a substantially equally high invariable pressure is maintained.
• valve 2b is closed and the pressure in the feeder 2 tank is lowered to the normal pressure, whereupon the upper valve 2a is opened for a new batch.
• the material to be processed which was fed into the equalization tank 4 is transferred in a loose state by means of the screw conveyor 3 as a uniform flow into the fluidization chamber 5, where the material is fluidized by means of the process gas supplied through the pipe 6.
• the process gas advantageously compressed air at a pressure of about 4 to 10 bars is used.
• the relatively dense gas-solids suspen ⁇ sion generated in the fluidization chamber 5 is divided in the bifurcation device 17 into two equivalent component flows, which rush out of the branch pipes 18 of the bifur ⁇ cation device 17 into the acceleration nozzles 20 of the counter-jet grinder 19, in which nozzles they are, by the effect of the high pressure prevailing in the fluidization chamber, accelerated to a supersonic velocity.
• the gas-solids suspen- sion ground in the grinding chamber rushes through the connecting pipe 7 tangentially into the centrifugal classifier 8.
• the classification of the gas-solids suspension rushing into the classifier 8 tangentially takes place by means of centrifugal force.
• the velocity of the finest particles is lowered almost immediately to the velocity of the gas circulating in the classifier 8, and said particles are removed along with the gas through the axial opening 9 for the removal of the fine fraction.
• the coarser particles retain their velocity to such an extent longer that they move along the peripheral face of the classifier 8 and rush out of the classifier 8 through the opening 10 for the removal of the coarse fraction, which is placed in the peripheral face of the classifier, being gathered in the pocket 12 placed outside the periph ⁇ eral face.
• the coarse fraction gathered in the pocket 12 is removed to the normal atmospheric pressure batchwise through the closing device 13 placed in the bottom of the pocket 12. Since the coarse fraction is not removed out of the pocket 12 as a continuous gas-solids flow, but as periodic solid batches, the finely divided particles do not attempt to escape out of the classifier 8 through the opening 10 for the removal of the coarse fraction.
• the closing device 13 consists of a dual-valve device.
• the valves 13a and 13b in this dual-valve device 13 are advantageously programmed so that they are alternatingly opened and closed at an adjustable frequency.
• First the upper valve 13a is opened and remains open for a while so that the tank in the dual-valve device 13 is filled up to a certain level, at which time the valve 13a is closed, and im ⁇ mediately thereupon the lower valve 13b is opened, whereby the batch of coarse fraction that was fed into the tank in the dual-valve device 13 rushes out, e.g., into a tank for coarse product or is returned into the feed funnel 1 of the equipment.
• valve 13a By the effect of the centrifugal force, a slight positive pressure is developed in the tank of the dual-valve device 13 every time when the valve 13a is open. This positive pressure promotes the removal of the batch of coarse fraction from the tank in the dual-valve device 13 upon opening of the valve 13b.
• the valve 13b After the tank in the dual-valve device 13 has been emptied, the valve 13b is closed again, and the valve 13a is opened for a new batch.
• the operations of the valves 13a and 13b in the dual-valve device 13 are preferably programmed so that they are opened and closed alternatingly at an adjustable frequency. The frequency is determined, e.g., in accordance with the material to be processed and with the capacity of the equipment.
• the closing device 13 consists of a compartment feeder, in which the speed of rotation of its compartment wheel 22 is adjusted in accordance with the material to be processed and with the capacity of the equipment.
• the costs of operation and acquisition of a compartment feeder 13 are considerably lower than those of a dual-valve device.
• the efficiency of the classifier can be improved further by forming the mantle face of the classifier 8 between the inlet opening 14 for the material-gas suspension and the opening 10 for the removal of the coarse fraction as an adjustable guide wing 15, by whose means the movement of circulation of the material-gas flow taking place in the classifier can be controlled and shaped as desired.
• the prevention of escaping of the fine fraction through the opening 10 for the removal of the coarse fraction can be intensified further by outside the guide wing 15 providing an expanding wedge-shaped acceleration passage 16 for low-pressure flushing air, said passage terminating at the level of the opening 10 for the removal of the coarse fraction, in order that a flow geometry favourable in view of the flushing could be obtained.
• the flushing air is supposed to flow through the removal opening 10 into the classifier 8 and, at the same time, to "flush" the particles of coarse fraction that are being removed through the removal opening 10, whereby any particles of fine fraction that may follow along with said coarse particles are passed, along with the flushing air, into the opening 9 for the removal of the fine fraction.
• the flushing air also contributes to the maintaining of the rapid movement of circulation, required by the centrifugal force, in the classifier 8.
• a rotor 24 operated by an electric motor 23, whose movement of rotation prevents the access of coarser particles into the opening 9 for the removal of the fine fraction effi ⁇ ciently.
• the optimal speed of rotation depends on the material that is processed.
• the rotor 24 extends in the axial direction substantially across the entire width of the classification chamber. Since the kinetic energy of the gas-solids flow rushing through the connecting pipe 7 tangentially into the classifier 8 can be utilized as drive energy of the rotor 24, which gives the rotor 24 a considerable initial speed, thus, a power source 23 of considerably lower output is adequate than in the prior- art rotor solutions.
• the additional air fed into the connecting pipe 7 and the flushing air fed into the classifier 8 through the opening 10 for the removal of the coarse fraction can be taken favourably out of a common source of low-pressure gas.
• the inlet pipe 11 for additional air and the inlet duct 16 for flushing air are provided with regulation valves 11a and 16a in order to achieve a correct quantitative ratio between these air supplies.

Landscapes

• Engineering & Computer Science (AREA)
• Food Science & Technology (AREA)
• Combined Means For Separation Of Solids (AREA)
• Disintegrating Or Milling (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Prostheses (AREA)
• Control Of El Displays (AREA)
• Stringed Musical Instruments (AREA)
• Crushing And Grinding (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Heterocyclic Carbon Compounds Containing A Hetero Ring Having Nitrogen And Oxygen As The Only Ring Hetero Atoms (AREA)
• Heterocyclic Compounds That Contain Two Or More Ring Oxygen Atoms (AREA)

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Publications (1)

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Country Status (8)

Cited By (4)

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Citations (4)

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• 1988
  • 1988-11-28 FI FI885525A patent/FI84032C/fi not_active IP Right Cessation
• 1989
  • 1989-11-24 DE DE89912820T patent/DE68909613T2/de not_active Expired - Fee Related
  • 1989-11-24 EP EP89912820A patent/EP0445149B1/en not_active Expired - Lifetime
  • 1989-11-24 WO PCT/FI1989/000215 patent/WO1990006179A1/en active IP Right Grant
  • 1989-11-24 JP JP2500568A patent/JPH04501975A/ja active Pending
  • 1989-11-24 AU AU46214/89A patent/AU622742B2/en not_active Ceased
  • 1989-11-24 AT AT89912820T patent/ATE95081T1/de not_active IP Right Cessation
• 1991
  • 1991-05-23 US US07/689,852 patent/US5143303A/en not_active Expired - Fee Related
  • 1991-05-27 FI FI912551A patent/FI912551A0/fi not_active Application Discontinuation

Patent Citations (4)

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