AU700295B2

AU700295B2 - Attrition mill III

Info

Publication number: AU700295B2
Application number: AU40326/95A
Authority: AU
Inventors: Udo Enderle; Peter Woodall
Original assignee: Mount Isa Mines Ltd; Erich Netzsch GmbH and Co Holding KG
Current assignee: Mount Isa Mines Ltd; Erich Netzsch GmbH and Co Holding KG
Priority date: 1994-12-20
Filing date: 1995-12-08
Publication date: 1998-12-24
Anticipated expiration: 2015-12-08
Also published as: AU4032695A

Description

-i -1-

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Names of Applicants: MOUNT ISA MINES LIMITED A.C.N. 009 661 447 and ERICH NETZSCH GmbH CO HOLDING KG Actual Inventors: Peter WOODALL and Udo ENDERLE 0 SAddress of Service: SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000 Invention Title: "ATTRITION MILL Im" SDetails of Associated Provisional Application No. PN0168 dated 20th December, 1994 The following statement is a full description of this invention, including the best method of performing it known to us:- __11IMMM i I I M lj IO)~l~ l -2- This invention relates to an attrition mill and more particularly to feed arrangements for such a mill.

The term "attrition mill" is herein used to include mills used for fine and ultrafine grinding for example, stirred mills in any configuration such as bead mills, peg mills, and wet mills such as colloid mills, fluid energy mills, ultrasonic mills, petit pulverisers, and the like grinders.

The invention is particularly applicable to a mill having a throughput of greater than 20 cubic metres/hour and more particularly in excess of 75 cubic metres/hour.

A material to be ground ("feedstock") in such a mill is usually admitted as a slurry of the material with water. Such mills are also provided with a grinding medium which may consist of spheres, beads, cylinders, rods, polygonal or irregulally shaped grinding materials, which may be of steel, zircon, silica, slag, glass or other suitable material.

Prior art mills generally have a capacity of less than 20 cubic metres per hour when grinding minerals or the like from a size range of 20 90 microns down to fines of 0.5 25 microns. More usually the throughput is less than 10 cubic metres/hour.

The mills comprise a grinding chamber, an axial impeller driven by a drive train, an inlet for feedstock to be ground, often a separate inlet for make-up grinding media, an outlet and a water cooling jacket or the like for cooling the chamber.

S 20 In use, the grinding media wears and approaches an equilibrium average particle size. Losses are replenished by addition of media via the main or a separate port at 12 or 24 hourly intervals.

In more sophisticated systems it has been practiced to add media semia continuously to the feedstock slurry at a point between the slurry pump and the chamber inlet by calculating the average consumption of media and adding a precalculated quantity of media to the slurry at more frequent intervals of fixed duration.

In operating an attrition mill scaled up to provide a throughput of ore in excess of 75 tonnes/hour solid in which the solid is reduced in size from a P80 r_ 4 4e *o 4 4 aa o 44 4 44 a aY a 44r~* I _I -3passing size) of 50-90 microns down to a P80 of 15-20 microns, it was found that the variation of product size and/or variation in throughput was unacceptably high.

It is an object of the present invention to provide an improved attrition mill and method of operation which avoids or ameliorates at least one of the above disadvantages of the prior art.

According to a first aspect the invention consists in a method of operating an attrition mill devoid of cooling comprising the steps of: combining in an aqueous slurry a feedstock to be ground and a grinding medium; (ii) feeding the slurry to the mill at a predetermined volumetric flow rate; 10 (iii) monitoring the power consumption of the mill; and (iv) adjusting the rate of addition of the grinding medium to the slurry so as to maintain the power consumption of the mill at or close t a predetermined value.

In preferred embodiments of the first aspect of the invention the media is added to the slurry upstream of the slurry pump amnd the proportion of grinding media to feedstock in the slurry is substantially continuously adjusted to maintain the predetermined power consumption value.

According to a second aspect the invention consists in an attrition mill having a throughput capacity in excess of 10 cubic metres/hour, said mill comprising: a slurry reservoir containing a sluny of feedstock and in communication with the mill; (ii) means for controlling the volumetric flow rate of slurry to the mill; (iii) means for monitoring the power consumption of the mill; and

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-r -3a- (iv) means for addition of grinding media to the slurry so as to maintain a substantially constant mill power consumption.

In preferred embodiments of the invention the volumetric flow rate of slurry into the mill is maintained at a constant rate by a slurry pump under the feedback control of a flow meter.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

9 of "including, but not limited to".

*9a.

e .9 -4- Power consumption of the mill is measured by electronic monitoring of the mill motor to provide a signal indicative of mill power consumption to a computer. Media from a storage bin is combined with the slurry by a hopper valve under control of the computer to add media to the feedstock slurry in an amount which varies according to the discrepancy between actual and a target power consumption.

In a highly preferred embodiment of the invention the mill does not have a water jacket and the chamber is devoid of external cooling. Instead temperature of the flow at the mill outlet is monitored. If the outlet temperature rises above a predetermined temperature additional water is added to the feed sump, the mill temperature being controlled by the rate of throughput. If desired the added water may be chilled so that the mill chamber is cooled endogenously by the feedstock.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings wherein: Figure 1 is a schematic flow chart illustrating the invention.

An ore to be ground, for example pyrite, arsenopyrite, galena, or other ore is first ground in a semi-autogenous grinding (SAG) Mill 1. The siliceous product from SAG Mill 1 is classified by screens 2, 3, the first screen having, for example, 3 mm orifices and the second screen 3 having, for example, 1 mm orifices. A cut passing "the first screen 2 and retained by the second 3 is conveyed at 4 to a media storage bin 5 for use as grinding media.

Particles of ground feedstock material (80% passing of 50-90 microns) from a source 16 not illustrated in Figure 1 are combined with media from bin 5 in a feed :sump 6, the amount of grinding media combined with the feedstock being controllable n by means of a hopper valve or variable screw feeder 7, or the like. Water is added to 25 sump 6 from a supply via line 16. Optionally chilled water may be added to sump 6.

Slurry containing feedstock and media is conveyed by a variable speed pump 8 a centrifugal pump) from sump 6 to inlet port 9 of mill 10. A flow meter 11 (for example a magnetic flow meter) provides a feedback signal 12 which is used by controller 13 to control variable speed pump 8 so that the volumetric flow rate into and through the mill is controlled to a preset value.

i- Mill motor 14 is supplied with power via a control circuit 15 which may be preset to target a predetermined power consumption rate. Control circuit 15 monitors the difference between the power consumption of motor 14 at any time and a preset target power consumption rate and produces a difference signal 17 which in turn generates a control signal 18 to adjust the amount of media added to the feedstock by valve or feeder 7. The amount of media added to the feedstock is increased or decreased as the power consumption departs from or approaches the target power consumption so as to maintain a substantially constant mill power. In preferred embodiments the increase or decrease in media addition rate does not vary linearly with changes in power consumption but rather is varied in accordance with a time proportioning algorithm stored in a control circuit 15 memory, for example in ROM or RAM, and which increases or decreases the valve opening time according to the difference between actual power consumption and a target power consumption value, Mill feed density is monitored by a densitometer on the mill inlet. Automatic particle size or density measurement device 22 at the output 20 is used to adjust the preset target power consumption valve so as to avoid excessive or inadequate grinding.

Temperature is monitored adjacent outlet 20 by sensor 21 and a rise in temperature 1 beyond predetermined limits causes water to be added to the infed slurry via a control u circuit 23 and control valve 24 on water line 16 with adjustment to the flow rate preset value. Temperature at the outlet is maintained below o It has been found that by these means the mill may be operated automatically at a high throughput (in excess of 100 m 3 /hr) and with a uniform product.

Particle size at the outlet may employ light scatter, ultrasonic or other measurement means.

25 Various safety features are also incorporated. If power consumption rises above a predetermined level the mill content is dumped via a port in the chamber provided for that purpose.

A suitable transducer monitors levels in the sump and automatically provides water to sump 6 if the sump level falls below a predetermined level.

-6- The mill may be started when full or empty.- If empty the start up sequence loads the mill with process water and a predetermined media charge, returning the water to a spillage sump. The dump valves are first closed. The feed sump process water is then put under level control. Flow control is then set to normal rate. After starting the discharge pump, the mill motor may be started and then the mill feed pump, and subsequently the media feed pump. The media is then fed on continuous control from mill power.

Those skilled in the art will understand from the teaching hereof that the invention may be implemented using any of a variety of pumps, feed control valves, lo and electronic control circuits without departing from the invention herein disclosed.

Claims

1. A method of operating an attrition mill devoid of cooling comprising the steps of: combining in an aqueous slurry a feedstock to be ground and a grinding medium; (ii) feeding the slurry to the mill at a predetermined volumetric flow rate; (iii) monitoring the power consumption of the mill; and (iv) adjusting the rate of addition of the grinding medium to the slurry so as to maintain the power consumption of the mill at or close to a predetermined value. 10

2. A method as claimed in claim wherein the media is added to the slurry upstream of the slurry pump and the proportion of grinding media to feedstock in the slurry is substantially continuously adjusted to maintain said predetermined power consumption value.

3. A method as claimed in claims 1 or 2, wherein the attrition mill has a throughput 15 capacity in excess of 10 cubic metres/hour.

4. An attrition. mill having a throughput capacity in excess of 10 cubic m-fetres/hour, said mill including: a slurry reservoir containing a slurry of feedstock and in communication with the mill; (ii) means for controlling the volumetric flow rate of slurry to the mill; (iii) means for monitoring the power consumption. of the mill; and (iv) means for addition of grinding media to the slurry so as to maintain a substantially constant mill power consumption.

A mill as claimed in claim 4, wherein the volumetric flow rate of slurry into the mill is maintained at a constant rate by a slurry pump under the feedback control of a flow meter.

6. A mill as claimed in claim 4 or claim 5, wherein power consumption of the mill is measured by electronic monitoring of the inill motor to provide a. signal indicative of mill power consumption to a computer.

7. A mill as claimed in claim 6, wherein media from a storage bin is combined with the slurry by a hopper valve under control of the computer to add media to the feedstock -8- slurry in an amount which varies according to the discrepancy between actual and a target power consumption.

8. A mill as claimed in any one of claims 4 to 7, wherein the mill does not have a water jacket and the chamber is devoid of external cooling.

9. A mill as claimed in any one of claims 4 to 8, wherein the temperature of the flow at the mill outlet is monitored.

A rrill as claimed in claim 9, wherein if the outlet temperature rises above a predetermined temperature additional water is added to the feed sump, the mill temperature being controlled by the rate of throughput. o: 10

11. A mill as claimed in claim 10, wherein the added water is chilled so that the mill chamber is cooled endogenously by the feedstock.

12. A method of operating an attrition mill substantially as hereinbefore described with reference to the accompanying drawings.

13. An attrition mill substantially as hereinbefore described with reference to the 15 accompanying drawings. DATED this 9th day of November 1998 ERICH NETZSCH GmbH CO. HOLDING KG S0, Attorney: RUTH M. CLARKSON Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS I- ABSTRACT A method of operating an attrition mill devoid of cooling comprising the steps of: combining in an aqueous slurry a feedstock to be ground and a grinding medium; (ii) feeding the slurry to the mill at a predetermined volumetric flow rate; (iii) monitoring the power consumption of the mill; and (iv) adjusting the rate of addition of the grinding medium to the slurry so as to maintain the, power consumption of the mill at or close to a predetermined value. a