AU2379101A - Method and equipment for feeding a counter jet mill - Google Patents

Description

WO 01/45848 PCT/FIOO/01122 1 Method and equipment for feeding a counter jet mill. This invention refers to a method for feeding a counter jet mill with material to be ground, wherein the material 5 to be ground is pressurized intermittently and after being pressurized the pressurized material batch is drop ped into an equalizing tank, wherefrom it through a flui dization is led as a continuous stream of a gas solids suspension through acceleration nozzles of the counter 10 jet mill to a grinding chamber, wherein solid particles are ground on colliding against each other. The invention also concerns a device for feeding a coun ter jet mill with material to be ground comprising a ver 15 tical pressurizing chamber for a material batch to be ground, said chamber being separated by two closing val ves, which pressurizing chamber communicates through a lower closing valve with a pressurized equalizing tank, having a conveyor axially transporting material to be 20 ground to a fluidizing portion, in which fluidizing por tion there is a tangentially terminating charge pipe for fluidizing gas, and a grinding chamber for disintegrating solid particles, which communicates with the fluidizing portion through at least two acceleration nozzles direc 25 ted substantially against each other. In previously known methods and devices of this type the material batch to be ground is pressurized to a pressure maintained in the equlizing tank, after which the lower 30 valve of the pressurizing chamber is opened in order to drop the pressurized material batch into the equalizing tank. Such a procedure will succeed well when the volume weight of the material to be ground is high enough, whereby the material batch falls easily down into the 35 equalizing tank as soon as the lower valve has been opened. The pressure in the equalizing tank will then WO 01/45848 PCT/FI00/01 122 2 remain constant, so that the feed of the gas-solids suspension will occur evenly. If, however, the volume weight of the material to be ground is very low, the material to be ground will not fall down into the 5 equalizing chamber, but a major part of the material batch will remain in the pressurizing chamber. The feed of material into the grinding chamber will then become uneven and incomplete, which will harmfully affect the whole grinding result. 10 A presupposition for a good grinding result is that the pressure of the equalizing tank and the gas-solids ratio of the gas-solids suspension formed in the fluidizing portion are kept as constant as possibly. The realizing 15 of this requires constantly presence of enough material to be ground in the equalizing tank. The object of the present invention is to achieve a feeding method securing feeding of material to be groung 20 and maintaining constant grinding conditions. This is achieved by a method, characterized in that intermittent pressurizing is carried out to a considerably higher pressure than the fluidizing pressure in order to secure proceeding of the the pressurized material, and that 25 feeding pressure of the fluidizing gas is adjusted to keep the pressure in the equalizing tank constant also when a new pressurized material batch is charged therein. The object of the invention is also to achieve such a 30 feeding device, in which the method according to the invention can be carried out. This object is achieved by a device, which is characterized in that a separate compressor unit is provided to achieve a superpressure in the pressurizing chamber, which compressor unit during 35 the pressurizing stage will be brought into contact with the pressurizing chamber, and that feeding pipe for the WO 01/45848 PCT/FI00/01 122 3 fluidizing gas is provided with an automatically opera ting pressure adjusting valve, for keeping the pressure in the equalizing tank constant also when a new material batch is received. 5 Further features of the invention will appear from the enclosed dependent claims. Below the invention will be disclosed in more detail with 10 reference to the enclosed drawing showing a schematical side view of one embodoment of a device according to the invention. The feeding device according to the invention comprises a 15 vertical pressurizing chamber 3, the top and bottom end of which is provided with cooperating closure valves 1, 2. The pressurizing chamber 3 communicates through the lower closure valve 2 with a pressurized equalizing tank 4. The equalizing tank is substantially shaped as a hori 20 zontal cylinder having a fluidizing portion 5 at one end. In order to transfer material to be ground to the fluidi zing portion 5, the equalizing tank 4 is provided with an axial conveyor 6 extending through its whole length. The fluidizing portion 5 is provided with a tangentially 25 ending feed pipe 7 for fluidizing gas. The fluidizing portion 5 communicates through at least two opposed acceleration nozzles 8 with a grinding chamber 9, wherein solid particles are ground on colliding against one another at a high speed. The feeding device is provided 30 with a separate compressor unit 10, which through closure valves 14 and 17 can be brought into contact with the pressurizing chamber 3, in order to achieve a super pressure in the pressurizing chamber 3 during each pressurizing stage. The device is provided with a main 35 compressor 13 in order to generate a working gas and the fluidizing gas. The feed pipe 7 for fluidizing gas is WO 01/45848 PCT/FIOO/01122 4 provided with an automatically operating pressure adjusting valve 11, which is programmed to maintain the pressure of the equalizing tank 4 constant also when a new material batch is received. 5 The main compressor 13 can be brought into contact with the pressurizing chamber 3 through a closure valve 12 at the beginning of the pressurizing stage. 10 The pressurizing chamber 3 can be brought into contact with a gas-solids separator 16 through a pressure dis charge pipe 15 provided with a closure valve. According to a prefered embodoment the pressure discharge 15 pipe 15 ends tangentially in a conical bottom portion of the gas-solids separator 16, a top portion of said sepa rator comprising a pair of electrodes generating a high voltage electric field, said pair being formed by a cylindrical inner mantle and a central rod provided with 20 emitting edges, which pair of electrodes due to a corona phenomenon separates possible solid particles from the discharging gas flow, which particles can be removed through the bottom opening of the separator 16 and retur ned to the pressurizing chamber 3 together with a next 25 batch of material to be ground. In order to feed the counter jet mill, material to be ground is fed batchwise to the pressurizing chamber 3 through the upper closure valve 1. When the material 30 batch has been fed to the pressurizing chamber 3 the upper closure valve 1 is closed, after which closure valve 12 is opened so that the pressurizing chamber will communicate with the main compressor 13, which will increase the pressure in the pressure chamber 3 to the 35 working pressure, e.g. to a level of about 3 bar, after which the closure valve 12 is closed and the pressurizing WO 01/45848 PCT/FI00/01 122 5 chamber 3 is brought into contact with the separate com pressor unit 10 by opening the closure valves 17 and 14, in order to further increase the pressure in the pressu rizing chamber about 1 to 3 bar, after which the closure 5 valve 17 is closed and the lower closure valve 2 is opened, whereby the pressurized material batch due to the super pressure falls down into the equalizing tank 4, wherein the above mentioned working pressure is maintai ned. In order to avoid a pressure peak in the equalizing 10 tank 4 due to the super pressure in the pressurizing chamber 3, the feed pipe 7 for fluidizing gas is provided with a pressure adjusting valve 11 operating to prevent the pressure in the equalizing tank from increasing. Material to be ground is fed continuously by means of the 15 screw conveyor 6 to the fluidizing portion, wherein mate rial to be ground is fluidized by means of the fluidizing gas to a gas-solids suspension, which is fed as a cons tant flow to the grinding chamber 9 through two substan tially opposed acceleration nozzles 8. The position of 20 the acceleration nozzles 8 will appear from the more detailed section view in the drawing showing the grinding chamber 9 from the right as a vertcal section. When the material batch has fallen into the equalizing 25 tank 4, the lower closure valve 2 is closed again and the closure valve in the pressure discharge pipe 15 is opened, whereby the pressure prevailing in the pressu rizing chamber 3 is discharged through the gas-solids separator 16 to the outer atmosphere or to any kind of a 30 pressure accumulator, as shown by the upper arrow. Solid partricles possibly following the gas flow from the pressurizing chamber 3 are separated effectively from the gas by means of the corona phenomenon in the gas-solids separator 16. The solid particles are returned to the 35 pressurizing chamber 3 as shown by the downward arrow, together with a next material batch. After the pressure WO 01/45848 PCT/FIOO/01 122 6 discharge the closure valve 14 is closed and the upper closure valve 1 of the pressurizing chamber 3 is opened for a new material batch. 5 With the method and the device according to the invention the grinding result is increased remarkably due to a more secure and effective feeding.

Claims (9)

1. Method for feeding a counter jet mill with material to be ground, wherein the material to be ground is pressu 5 rized intermittently and after being pressurized the pressurized material batch is dropped into an equalizing tank, wherefrom it through a fluidization is led as a continuous stream of a gas-solids suspension through acceleration nozzles of the counter jet mill to a 10 grinding chamber, wherein solid particles are ground on colliding against each other, characterized in that the intermittent pressurizing is carried out to a conside rably higher pressure than the fluidizing pressure in order to secure proceeding of the the pressurized mate 15 rial, and that feeding pressure of the fluidizing gas is adjusted to keep the pressure in the equalizing tank constant also when a new pressurized material batch is charged therein. 20

2. Method according to claim 1, characterized in that a feeding pipe for the fluidizing gas is provided with a pressure equalizing valve.

3. Method according to claim 1, characterized in that 25 pressure difference between pressurizing stage and the fluidizing pressure is in the range of 1 to 3 bar.

4. Method according to claim 1, characterized in that in order to reduce the pressure in the pressurizing chamber 30 to a pressure of the surrounding atmosphere for receiving a new material batch, pressurized gas discharge is led through a gas-solids separator.

5. Method according to claim 4, characterized in that the 35 pressurized gas discharge is led tangentially into bottom WO 01/45848 PCTFIOO/01 122 portion of the gas-solids separator, possible solids being separated from the gas flow in the top portion of said separator by means of a high voltage electric field. 5

6. Device for feeding a counter jet mill with material to be ground comprising a vertical pressurizing chamber (3) for a material batch to be ground, said chamber being separated by two closing valves (1, 2), which pressuri zing chamber communicates through a lower closing valve 10 (2) with a pressurized equalizing tank (4), having a conveyor (4) axially transporting material to be ground to a fluidizing portion (5; , in which fluidizing portion there is a tangentially terminating charge pipe (7) for fluidizing gas, and a grinding chamber (9) for disinte 15 grating solid particles, which communicates with the fluidizing portion (5) through at least two acceleration nozzles (8) directed substantially against each other, characterized in that a separate compressor unit (10) is provided to achieve a super pressure in the pressurizing 20 chamber (3), which compressor unit during the pressuri zing stage will be brought into contact with the pressu rizing chamber (3), and that feeding pipe (7) for the fluidizing gas is provided with an automatically opera ting pressure adjusting valve (11), for keeping the 25 pressure in the equalizing tank constant also when a new material batch is received.

7. Device according to claim 6, characterized in that the pressurizing chamber (3) in the beginning of the pressu 30 rizing stage can be brought into contact with a main compressor (13) through a closure valve (12).

8. Device according to claim 7, characterized in that the pressurizing chamber can be brought into contact with a WO 01/45848 PCT/FIOO/01 122 9 gas-solids separator (16) through a pressure discharging pipe (15) provided with a closure valve.

9. Device according to claim 8, characterized in that the 5 pressure discharging pipe (15) ends tangentially into the conical bottom portion of the gas-solids separator, the top portion of said separator comprising a pair of electrodes generating a high voltage electric field formed by a cylindrical inner mantle and a central rod 10 provided with emitting edges, which pair of electrodes is arranged to separate possible solid particles from the discharging gas flow by means of a corona phenomenon.