NZ264567A

NZ264567A - Aluminium smelter comminuting plant for anode butts and old pot linings

Info

Publication number: NZ264567A
Application number: NZ26456794A
Authority: NZ
Inventors: Francis Desrumaux
Original assignee: Fcb
Priority date: 1993-09-28
Filing date: 1994-09-28
Publication date: 1996-02-27
Also published as: AU669453B2; FR2710557A1; AU7426594A; FR2710557B1; CA2133044A1

Description

264 56 ' Priority Date(s):.. ...as.tale.3 ; Complete Specification Filed: i Class: (3) .^P3.fes/.QQ-.r.g><?3c.nJ03 Publication Date: 7 Fl-jj r:.0. Journal No: JMtfr?. j.

Patents Form No 5 THE PATENTS ACT 1953 COMPLETE SPECIFICATION PLANT FOR COMMINUTING THE CARBONACEOUS WASTE AND REFUSE OF AN ALUMINIUM SMELTER WE, FCBa company organised and existing under the laws of France, of 38 rue de la Republique, 93100 Montreuil, France, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la) 26 4 56 7 In electrolytic 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 anode making shop.

This comminution consists in reducing either refused whole anodes approximately 0.6 m3 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 contain 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 cru^f1'" Jy^ * ;stage and the screen. r. <*, -1 a- 264567 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 5 same plant to grind old potlinings provided that minor and quickly feasible modifications are made.

The invention provides a plant for comminuting recirculatable carbonaceous products and refuse of an aluminium smelter comprising a crusher and an autogenous or semi-autogenous mill provided with 10 peripheral openings equipped with removable calibrated-opening grates and a central opening, wherein means are provided to optionally close the said peripheral openings and, that 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. 15 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.

If old potlinings are to be processed, the mill peripheral openings are closed and the whole flow of ground products is discharged 20 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 recycling them.

To prevent the comminuted products to pollute each other, and to make it possible to change quickly from a production to the other, without 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 30 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 discharg^system specific to 35 this type of mill. /'v i i ■ I z 26 4 5 6 Preferably, the angle formed by the crusher jaws should be smaller than that of a conventional jaw crusher and below 20° ; 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 outlet opening equipped with a grate ; and Figure 3 is a view similar to figure 2 and showing the opening closed by an obturator.

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 22°), 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 through opening 30 provided in the wall, close to the other head which has also a central 26 4 5 6 7 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 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 20.

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 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 allo^ 26 4 5 6 7 products 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 the 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 50.

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 device 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 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 within the scope of the invention.

Claims

2.6 *5^;10;15;® 20;WHAT WE CLAIM IS IS;1. A plant for comminuting recirculatable carbonaceous products and refuse of an aluminium smelter comprising a crusher and an autogenous or semi-autogenous mill provided with peripheral openings equipped with removable calibrated-opening grates and a central opening, wherein means are provided to optionally close the said peripheral openings and, that 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.;2. The plant according to claim 1, wherein the crusher is a jaw crusher, the jaws of which have a jaw angle smaller than 20° and preferably equal to 16°.;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 filters connected to the outlet of the central opening, and means allowing any one of these filters to be selected for use.;5. The plant according to claim 4 wherein the two filters are also connected to the outlet of the peripheral openings.;6. A plant for comminuting recirculatable carbonaceous products and refuse of an aluminium smelter substantially as herein described with reference to the accompanying drawings.;FCB;By Their Authorised Attorneys JOHN A REMMINGTON & ASSOCIATES*