AU669453B2

AU669453B2 - Plant for comminuting the carbonaceous waste and refuse of an aluminium smelter

Info

Publication number: AU669453B2
Application number: AU74265/94A
Authority: AU
Inventors: Francis Desrumaux
Original assignee: FCB
Current assignee: FCB
Priority date: 1993-09-28
Filing date: 1994-09-28
Publication date: 1996-06-06
Anticipated expiration: 2014-09-28
Also published as: CA2133044A1; AU7426594A; NZ264567A; FR2710557A1; FR2710557B1

Description

I _I 669453

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION 1100 /011 PR'qu1 atio 3f FOR A STANDARD PATENT

ORIGINAL

I

r TO BE COMIPLETED BY APPLICANT Name of Applicant: FCB Actual Inventor: Francis Desrumaux Address for Service: CALLINAN LAWNRIE, 278 High Street, Kew, 3101, Victoria, Australia Invention Title: "PLANT FOR COMMINUTING THE CARBONACEOUS WASTE AND REFUSE OF AN ALUMINIUM SMELTER" The following statement is a full description of this invention, including the best method of performing it known to me:- 9!28i94GS7915,F10.1 In electrolylic aluminium production plants, the spent-anode butts and the refused whole anodes must be comminuted with a view to recycling the carbonaceous products to the ar,ode making shop.

This comminution consists in reducing either refused whole anodes approximately 0.6 m 3 in volume and 900 kg in weight, or recirculatable waste measuring approximately 0.6 x 1.45 x 0.25 m as a maximum and weighing about 300 kg into pieces the dimensions of which are smaller than 30 mm.

These products contain cast iron, steel and aluminium fragments.

On the other hand, the electrolytic pot lining, which is made of carbonaceous products and constitutes the cathode, wears out and deteriorates as it is used and it is necessary to remove them periodically, by carrying out an operation called pot unlining, and to replace it by a new lining.

Unlining is carried out by means of pneumatic tools and gives large-size lumps which may ontain inclusions of metals such as iron and aluminium.

Next, these lumps are reduced, by different means, to a size allowing them to go through a more or less 400 mm square-mesh grate.

Old potlinings are said to be dangerous because they are impregnated with noxious products, fluorides and cyanides in particular, and it is necessary to treat them to neutralize these products, The presently known treatments, especially those which include a calcining operation, are applicable only to products with a size in the order of 2,5-3 mm. Therefore, it is necessary to grind the old potlinings to reduce them to this size.

Up to now, there has been no plant for grinding old potlinings since the latter have always been sent to rubbish tips ;this solution is now prohibited by the new regulations about pollution and environmental protection.

Plants used to reduce the size of anode butts consist usually of 3 crushing stages, 1 screen, 3 magnetic separators to eliminate the scrap iron upstream of each crushing stage, and handling units which convey the products between the various crushing stages and between the last crushing stage and the screen.

l.- One of the aims of the present invention is to perform this size reduction in two stages only so as to reduce the investment, operating and maintenance costs.

Another aim of the invention is to make it possible to use the same plant to grind old potlinings provided that minor and quickly feasible modifications are made.

According to the invention there is provided a plant for comminuting recirculatable carbonaceous products and refuse of an aluminium smelter, said plant including a crusher and an autogenous or semi-autogenous mill provided with a central opening, with peripheral openings equipped with calibrated opening grates, and with means for closing the said peripheral openings, and wherein the mill is air swept and the fine fraction of the ground products is discharged by the air stream through the peripheral openings of the mill and/or through the central opening.

If recirculatable carbonaceous products are to be processed, the major part of the comminuted products are discharged through peripheral openings provided with calibrated-opening grates.

i. If old potlinings are to be processed, the mill peripheral openings are closed and the whole flow of ground products is discharged pneumatically by the mill-sweeping air, through the central opening in the bottom of the mill. A separating unit, e.g. a cyclone, permits to separate the ground products from the airstream. A classification unit, e.g. a screen, may be used to separate the too coarse grains with a view to recyling them.

To prevent the comminuted products to pollute each other, and to make it possible to change quickly from a production to the other, witlhout any restricting cleaning, the autogenous or semi-autogenous mill is associated with two independent filters, one of which is used exclusively for recirculatable carbonaceous products and the other for old potlinings only.

Ungrindable bodies the size of which is bigger than the dimension of the mill outlet openings remain in the mill and constitute a grinding charge which adds, if any, to the ball charge; they can be eliminated periodically by means of a semi-automatic discharge system specific to this type of mill.

1. 4 IXl.1'791 SI'T,2 Preferably, the angle formed by the crusher jaws should be smaller than that of a conventional jaw crusher and below 200 such a reduced angle improves the ability to grip a product said to be soapy as anodes are.

A magnetic separator can be arranged downstream of the mill to eliminate the iron scraps which may have gone through the outlet openings.

An eddy-current metal separator also can be placed downstream of the mill to eliminate the other metal scraps.

Other features of the invention will be brought to the fore by the following description which refers to the drawings appended thereto which show, as a non-limiting example, an embodiment of the invention and in which: Figure 1 is a diagram of a plant in conformity with the invention for comminuting anode butts and refused anodes and for grinding old potlinings Figure 2 is a partial sectional view of the autogenous mill showing an 11o outlet opening equipped with a grate ;and S. 15 Figure 3 is a view similar to figure 2 and showing the opening closed by an obturator.

•e The plant shown in figure 1 consists basically of a jaw crusher 10, an autogenous mill 12, a screen 14, a separating cyclone 16, two dust collecting filters 18 and 20, conveyors 22 and 24 and an elevator 26.

The peculiarity of jaw crusher 10 as compared with conventional jaw crushers consists in its reduced jaw angle a (for example, 16' instead of 220), which improves the ability to grip the anodes, which are said to be soapy.

Crusher 10 reduces the products to be comminuted into lumps the maximum size of which is not in excess of 400 mm. These lumps are moved by conveyor 22 to the inlet of mill 12.

Mill 12 is an autogenous or semi-autogenous mill consisting of a horizontal axis drum the diameter of which is significantly larger than the length. One of its heads is provided with a central opening into which a feed duct 28 opens. The ground products are discharged throuh opening provided in the wall, close to the other head which has also a central opening -3- 31. Openings 30 can be provided with grates 52 the size of whose openings determines the maximum size of the ground products (figure 2) or closed by obturators 54 (figure 3).

Openings 30 are surrounded with a closed ring-shaped casing 32 the base of which is provided with a lock chamber for the discharge of the ground products.

Casing 32 and central outlet opening 31 are connected to the inlet of a fan 36 through cyclone 16 and filters 18 and 20. Thus, it is possible to create a negative pressure in the mill and to removed the fine fraction of the ground product which is recovered in the cyclone and the filters.

Mill 12 is rotated by a gearmotor 38 the low speed pinion of which engages with a girthgear fixed to the body of the mill.

A semi-automatic draining device 40 permits to eliminate periodically the unground material. This system consists basically of a spoon which is 15 introduced in the mill, through the feed central opening, after stopping the feed and discharging the whole of the grindable material.

A valve 46 permits to put selectively into operation filter 18 or filter When the plant is used to comminute anode butts and refused anodes, openings 30 are equipped with grates 52 and the products which go out of mill 12 through these grates are removed by conveyor 24 and elevator 26 up to storage silos 42 and 44. By choosing the grates adequately, it will be possible, for example, to get a ground product nearly all pieces of which will be smaller than 30 mm, from 400 mm feed lumps. The fine fraction of the ground .i products is discharged by the sweeping air through grates 52 and central opening 31 connected to the inlet of fan 36, It is separated from the air stream in cyclone 16 and in the filter selected for this operation, e.g. filter 20, and sent to a storage silo.

When the plant is used for grinding old potlinings, openings 30 are closed by obturators 54, dust collecting filter 18 is put into operation, by means of valve 46, and the working conditions of fan 36 are so set as to allow all the -4products ground to the required grain size to be pneumatically discharged through central opening 31. These products are recovered at the spigot of cyclone 16 and in filter 18, and sent onto screen 14. Those grains 1he size of which exceeds the dimensions of the screen mesh -about 3mm- are recirculated into mill 12. The finished product is stored in a silo In order to prevent the products from mixing with each other, when changing from one operation to the other, one shall proceed as follows: one stops the feed and leaves the plant running without load for a certain time, sweeping the inside of mill 12 with air so as to clean it, discharges the remaining unground material, by means of dev,ue 40, closes openings 30 or provides them with grates, depending on the selected type of operation, selects the appropriate filter and set the sweeping air flow rate at the required value.

For the two operations, i.e. comminution of anodes and grinding of old 15 potlinings, mill 12 can be run as a semi-autogenous mill by adding a small charge of balls or other grinding media.

Of course it is understood that any modifications which may be made in the above described embodiment by substituting equivalent technical means fall witnin the scope of the invention.

i iJ

Claims

1. A plant for comminuting recirculatable carbonaceous products and refuse of an aluminium smelter, said plant including a crusher and an autogenous or semi-autogenous mill provided with a central opening, with peripheral openings equipped with calibrated opening grates, and with means for clos' the said peripheral openings, and wherein the mill is air swept and the fine lidction of the ground products is discharged by the air stream through the peripheral openings of the mill and/or through the central opening.

2. The plant according to claim 1, wherein the crusher is a jaw crusher the jaws of which form together an angle smaller than 200.

3. The plant according to claim 1 or 2, wherein an emptying device is associated with the mill in order to periodically remove the ungrindable material.

4. The plant according to claim 1, 2 or 3, further including two ,15 filters and means for selectively connecting the central opening of the mill to I: any one of the filters.

The plant according to claim 1, 2 or 3, further including two filters and means for selectively connecting the peripheral openings of the mill to any one of the filters.

6. The plant according to claim 2, wherein said angel is 16°.

7. The plant for comminuting recirculatable carbonaceous products and refuse of an aluminium smelter substantially as herein described and with reference to the accompanying drawings DATED this 15th day of April, 1996. FCB By their Patent Attorneys: CALLINAN LAWRIE I VWI.I IXd7 SIL9 ABSTRACT OF THE TECHNICAL CONTENT OF THE INVENTION PLANT FOR COMMINUTING THE CARBONACEOUS WASTE AND REFUSE OF AN ALUMINIUM SMELTER FOB The invention relates to aluminium smelters in which the spent anode butts and the refused whole anodes must be comminuted with a view to recycling the carbonaceous products to the anode making shop, and in which the treatment of spent potlinings (carbonaceous products resulting from the- demolition of the lining of the walls and bottom of the electrolytic pots) requires a prior size reduction of the potlinings into pieces not bigger than a few millimeters in size. The invention is aimed at making it possible to use the same plant to comminute the anode butts and the refused anodes, on the one hand, and the spent potlinings, on the other hand, subject to minor and quickly feasible modifications to the equipment. The plant forming the subject of the invention is characterized in that it consists basically of a jaw crusher (10) and an autogenous or serni- autogenous grinding mill (12) including peripheral openings (30) fitted with calibrated-opening grates and a central opening (31) allowing the fine fraction of the ground products to be pneumatically removed, and in that means are provided for closing the peripheral openings of the mill.