WO2018002832A1

WO2018002832A1 - Element for use in non-ferrous smelting apparatus

Info

Publication number: WO2018002832A1
Application number: PCT/IB2017/053854
Authority: WO
Inventors: Brett John FRANCIS; Hugo Joubert; Martin Lluis Bakker; Stanko Nikolic; Stephen GWYNN-JONES
Original assignee: Tenova South Africa (Pty) Ltd
Priority date: 2016-06-29
Filing date: 2017-06-28
Publication date: 2018-01-04
Also published as: ZA201802539B

Abstract

This invention relates to an element for use in a non-ferrous smelting apparatus and more particularly, but not exclusively, to a fluid cooled copper element suitable for use in a non-ferrous smelting apparatus. The element includes a copper body and a calorization layer formed in the copper body. The invention also extends to the use of a calorized copper element in a non-ferrous smelting application in order to prevent or at least reduce the occurrence of sulphidation corrosion.

Description

A-

ELEMENT FOR USE IN NON-FERROUS SMELTING APPARATUS

BACKGROUND TO THE INVENTION

THIS invention relates to an element for use in a non-ferrous smelting apparatus and more particularly, but not exclusively, to a fluid cooled copper element suitable for use in a non-ferrous smelting apparatus.

Cooled copper elements are used in a variety of applications in the non- ferrous smelting environment. These range from tapping blocks, launders, internal wall coolers, refractory coolers and other functional elements. Copper elements need to be cooled in the furnace environment as the operating temperature inside a furnace is typically above the melting point of copper, i.e. above 1085°C. The aim of the cooling process is to limit the cooled copper element temperature to be!ow 400°C in order to maintain the structural integrity of the element, as well as the structural stability of the arrangement of which the element forms part. Temperature excursions in the copper elements can occur due to normal or upset conditions in the furnaces, and these excursions may result in localized wearing of the surface of the copper elements. This wear results in a decrease in the life of the elements and also increases the downtime of furnaces as a result of the replacement time of the damaged elements. Cooled copper elements in particular applications, for example those relevant to direct smelting of platinum group metal concentrates, have shown very low life due to a combination of condensation of the labile sulfur, volatile chlorine bearing species, and moisture in the feed materials in the furnaces. This is a form of su!phidation, also referred to as chloride- accelerated suiphidation, and occurs at relatively low temperatures with severe acceleration of the corrosion rate above 110°C (Shaw et al., 2012). In contrast to high temperature slag or matte attack on the cooled copper elements, this form of sulphtdation corrosion attack on the cooled copper elements typically occur above the furnace slag and matte bath, and adjacent to the concentrate feed layer drifting on top of the furnace bath. There is therefore a particular need to extend the life of these components.

Typically the approach applied in industry to prolong the life of cooled copper elements has been to increase the heat removal capacity of the copper elements. This is achieved through design improvements to the copper blocks. Design improvements include increasing the quantity and configuration of the cooling water passages, and also using copper alloys for the tubes, which in turn creates smoother passage shapes that minimize formation of air pockets or imperfections. The addition of refractory anchoring or refractory casting within the copper has been used as a method for improving life and corrosion, as for example disclosed in patent US5785517. The heat removal capacity can, however, only be improved up to a limit, because the general dimensional structure and structural strength requirements of the copper blocks also has to be taken into account, and the design of the copper elements and blocks are not determined by the heat transfer issues in isolation.

Another approach has been to use surface protection methods in order to protect the copper elements. For example, it has been proposed to use nickel plating of copper elements. However, nickel plating of cooled copper elements result in diffusion of the nickel coated layer into the base copper metal over time, which means it loses its protective strength. Similar disadvantages are associated with other coating materials.

Calorizing (also known as aluminizing, alonizing or ceramalloying) is a diffusion metallizing process. More particualrfy, it is a thermochemical treatment that involves enriching the surface layer of an object with one or more metallic elements. Specifically, calorizing is the diffusion of aluminum into the surface of a base metal through high temperature vapors. The process results in an alloy with the surface properties of aluminum while retaining the base metal's inherent strength and rigidity. Therefore, calorizing does not change the high-temperature mechanical properties of the base metal, which is the advantage of calorizing over simply creating an aluminum alloy. The calorising metal is diffused into the base metal, which also differentiates the process from plating, where two discrete layers are perceptible.

The use of calorizing on cooled copper elements in furnaces or metallurgical smelting vessels is known in industry. However, previous use has been limited to the ferrous or steel industry with the aim of improving abrasion and corrosion resistance of blast furnace tuyeres and basic oxygen furnace lances. Examples include US3069760, DE2543659, US3977660, US4043542, US4189130 for tuyeres, and US3036929, US3292662 and US4901983 for basic oxygen furnace lances. Calorizing of cooled steel elements has also been applied in the steel industry, for example as disclosed in US6563855.

The work done on the application of calorizing to cooled elements in the smelting industry is focused entirely on the ferrous industry. This work has involved improving cooled elements resistance to molten metal, abrasion and slag attack. However, the effect of sulfur containing molten metal phases (which is present in non-ferrous smelting applications) as well as suiphidation or chloride-accelerated sulphidation have not been investigated as these are not usually present in the ferrous industry.

The main chemical wear identified on water cooled copper elements in non- ferrous furnaces is due to sulfur from matte/concentrate. The inventors are not aware of any published material on how calorized copper elements respond to superheated molten metal sulfide matte flow, and the application of calorizing for protecting copper elements against superheated molten matte has not been investigated previously. One of the reasons for this is that the perception in the industry is that aluminum has a low melting temperature metal, at 660°C, and that it therefore would not be suitable for use inside a non-ferrous furnace, which operates well above 1000°C. The slags used in the non-ferrous industry have a high affinity and capacity for alumina (AI203) and therefore will dissolve it from refractory bricks in furnaces, this view would be applied to the alumina layer on the calorized copper surface. In addition, there is a further perception that any surface layer that imparts benefits to the copper ends up decreasing its thermal conductivity and therefore performance will be inferior compared to plain copper. For these reasons, skilled persons in the smelting industry has effectively come to the conclusion that calorizing is obviously not a useful solution in the non-ferrous smelting industry.

The inventors are further not aware of any published material on how calorized copper elements respond to a combination of condensation of labile sulfur, volatile chlorine bearing species, and moisture, and whether or not it will prevent or slow down the rate of sulphidation or chloride- accelerated sulphidation of copper at various temperatures.

Other methods for applying a protection layer to the copper elements and prevent either sulphidation or oxidation of the copper surface have been attempted in the past. As an example, nickel plating of copper cooling elements have been tested in the South African platinum industry furnace. After a number of industrial trials the tests and practice were abandoned as the copper element service life did not increase significantly whilst the cost of the plating is fairly high. To date no metal coating on furnace copper cooling elements, whether plated, diffused or otherwise applied, have been successful to prevent or significantly reduce industrial sulphfdation attack of the base copper element.

It is accordingly an object of the invention to provide an element for use in non-ferrous smelting apparatus that will, at least partially, alleviate the above disadvantages.

It is also an object of the invention to provide an element for use in non- ferrous smelting apparatus which will be a useful alternative to existing elements.

It is also an object of the invention to provide a new use of an existing surface treatment process.

It is a still further feature of the invention to provide a new use for a calorized copper element.

SUMMARY OF THE INVENTION

According to the invention there is provided an element for use in a non- ferrous smelting apparatus, the element including:

a copper body; and

a calorization layer formed in the copper body.

There is provided for the copper body to include a plurality of internal cooling channels. There is provided for the caiorization layer to include a uniform Cu-AI diffusion layer at the interface of the body and the layer, the diffusion layer having a thickness of between 10 and 40 pm, preferably between 20 and 30pm.

There is provided for the caiorization layer to include a middle layer consisting of intermeta!fics in a Cu-Ai matrix, the middle layer having a thickness of between 250 and 600pm, preferably between 350 and 450pm.

There is provided for the caiorization layer to comprise an outer aluminium oxide layer having a thickness of between 150 and 700 pm, preferably between 250 and 550pm.

According to a further aspect of the invention there is provided a non- ferrous smelting apparatus including:

a vessel for receiving non-ferrous material to be smelted; and at least one calorized copper element located in or forming part of the vessel.

There is provided for the calorized copper element to be selected from the group including tapping blocks, launders, internal wall coolers and/or refractory coolers.

According to a further aspect of the invention there is provided the use of a calorized copper element in a non-ferrous smelting application.

There is provided for the use of a calorized copper element in a non-ferrous smelting application in order to prevent or at least reduce the occurrence of sulphidation corrosion. There is provided for the ca!orized copper element to be used in a non- ferrous smelting application as a functional element designed to withstand corrosion.

The functional element may, for example, be selected from the group including tapping blocks, launders, internal wall coolers and/or refractory coolers.

The non-ferrous smelting application may be a non-ferrous smelting furnace.

There is provided for the copper element to be calorized as described above.

There is provided for the copper element to be exposed to matte, slag and/or gaseous phases containing among other elements sulphur.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by way of non-limiting examples, and with reference to the figures. In which:

Figure 1 show the comparison of wear between the calorized plate

(left) and the uncalorized plate (right).

Figure 2 shows an experimental set-up for use in testing the protection of the calorized copper blocks against sulphidation; and

Figure 3(a) and 3(b) show the results of the experiment of Figure 2, PESCRIPTION OF THE INVENTION

A solution was sought to improve the life of elements used in non-ferrous smelting application, in particular cooled copper elements in non-ferrous smelting furnaces where temperatures may exceed 1000 °C. The inventors are of the view that caiorization of these copper elements will result in prolonged service life of the copper elements. Although aluminum has a low melting temperature metal {approximately 660°C) and although it would therefore appear as if caiorization would not be suitable for use inside a furnace which operates well above 1000°C, the inventors are of the view that this is not the case because the surface of the ca!orizing layer will immediately oxidize to form alumina (Al₂0₃) which has a melting point of over 2000°C, thus providing the resistance required.

Another perception in industry, based on the previously trialed solutions for coating copper, is that any surface layer that imparts benefits to the copper ends up decreasing the thermal conductivity of the copper, and therefore performance will be inferior compared to plain copper. The inventors are of the view that this is not the case with calorizing of copper elements in the ferrous industry, and the inventors therefore set out to show that this long standing perception also does not hold true in the non-ferrous smelting environment. Experimental work has shown that the characteristic benefits of the base metal are indeed maintained in the non-ferrous industry when calorized copper elements are subjected to molten superheated matte.

The inventors are further of the view that caiorization of these copper elements will result in improved resistance to sulphidation or chloride- accelerated sulphidation sometimes encountered in non-ferrous smelting furnaces due to condensation of labile sulfur, volatile chlorine bearing species, and moisture in the feed materials in the furnaces. ln use, calorizing is performed on the hot face or faces of element(s) that interfaces with the molten and gaseous phases, or alternatively on the copper element as a whole. The calorized copper elements are then installed as per standard copper elements in service in non-ferrous furnaces. These elements can be newly designed for a particuiar purpose or designed to match an existing arrangement and be calorized before service.

It is foreseen that the optimal thickness of the calorized copper layer will be between 750-900um, although a layer of up to or greater than 1Q00um wili be achievable. In a typical example, three layers will be present in a calorized copper element, being:

a uniform thin Cu-AI diffusion layer at the interface: 20-30um;

a thick middle layer consisting of intermetaiiics in Cu-AI matrix: 350-

450um; and

- an aluminium oxide layer: 250-550um.

These copper elements are designed and used to extract heat from a furnace lining system, and either form a frozen slag layer to prevent or limit wear of lining system, or reduce the temperature of the refractory used in the lining system to a level that will reduce the wear rate. The addition of a calorization layer, that includes a low conductivity aluminium oxide {Al₂0₃) outer layer, historically raised the question from practitioners in the industry as to how this low conductivity layer will affect the copper elements ability to remove heat from the lining system, and the perception in the past has been that the impact will be significant. However, the inventors have found that through heat transfer calculations it can be shown that the additional thermal resistance due to the approximately 1 mm thick calorized layer is insignificant. The thermal resistance per area of a layer is a function of its thickness, x in meters, and its thermal conductivity, k in W/mK:

Thermal resistance R_T = x/k The thermal conductivity of the outer aluminium oxide layer at 30 W/mK is expected to be the lowest of the three layers formed during the caiortzation of copper. If it is assumed that the thermal conductivity of a 1 mm thick calorized layer is at worst 30 W/mK, the thermal resistance can be calculated as 0.000033 m²K/W. This is equivalent to an additional copper element thickness of 10 mm with a conductivity of 300 W/mK, usually achieved for copper castings. It will be appreciated that the addition of 10 mm thickness to the copper element, or say an additional 10 mm copper between the element hot face and the element cooling channel, will neither adversely affect the copper element's ability to form a slag freeze lining on its hot face neither nor its ability to cool a surrounding refractory lining. As such, the calorized layer will neither affect the cooling efficiency of the copper element.

EXAMPLE 1

In one example used to test the principle, an induction furnace was used to bring multiple lots of approximately 5 kg of low iron nickel matte up to a temperature of 1400°C. This represented a matte super heat of approximately 500°C. The molten matte was then poured onto uncooled plain copper plate (12 mm in thickness) and calorized copper plates (calorized copper layer between 750-900um) in a controlled manner. The plates were placed at an angle during the pouring process so that the rear surfaces of the plates could be observed with a camera in order to confirm burn through. The plain copper plate failed 5 seconds into the matte pour. The calorized copper plate survived the matte pour for a period of greater than 15 seconds without significant damage. This represented a substantial increase in resistance to the molten matte when compared to the plain copper plate. To eliminate any variables in the matte temperature between the pours, due to the induction furnace heat cycle, a plain copper plate and a caiorized copper plate were then placed in a V-configuration and the matte was poured on the contact point between the two plates. The plain copper plate had a mass loss of 7.77wt% whilst the caiorized copper plate mass loss was 0.64wt%. This represents an order of magnitude difference in the resistance of the caiorized copper to matte attack compared to plain uncalorized copper. Figure 1 show two different views of the comparison of wear between the caiorized plate (left) and the uncalorized plate (right).

EXAMPLE 2 in another example, the experimental setup of which is shown in Figure 2, specifically related to the principle of improved resistance of copper to suiphidation or chloride-accelerated suiphidation, six copper blocks sized 4cm by 5.2 cm by 7 cm were exposed to controlled levels of sulphur vapour as well controlled levels of HCI 40. Specifically, the partial pressure of the sulphur vapour was controlled at a level of 20% and the partial pressure of the HCI was controlled at a level of 5%. Three of the six blocks were subjected to caiorized treatment as described above. The blocks 20 were machined and drilled to allow the control of the block temperature 50 using oil circulation 30. A thermocouple 10 imbedded in the copper block was used for this purpose. Two different block temperatures were tested: 90°C and 125°C respectively. Another thermocouple was used to control the sulphur vapour temperature and as such the sulphur partial pressure. Each block was tested and subjected to the sulphadizing conditions for 5 consecutive days, 24 hours per day. All of this was done to simulate the typical conditions experienced in practice resulting in copper suiphidation or chloride-accelerated suiphidation. The corrosion of the uncaiorized copper block was highest at 125°C. At the same temperature the caiorized copper block showed minimum corrosion. The difference between the caiorized Figure 3(a) and uncalorized Figure 3(b) copper blocks post testing for 5 days at 125°C are clearly visible. Virtually no corrosion took place on the caiorized copper block Figure 3(a), with a pure condensed sulphur build-up (yellow) forming on top of the block during the test but not resulting in any corrosion. In comparison, the uncalorized copper block Figure 3(b) corroded significantly, with a thick corrosion layer forming on the outside surface, consisting mostly copper sulphide.

The copper mass loss due to corrosion for the uncalorized block was 3.98% over the 5 days, whilst the copper mass for the caiorized block actually increased by a very small amount, or 0.11%. This small increase is potentially due to build-up in the cooling channels, or otherwise measurement error. In both cases the blocks were cleaned and the corrosion and build-up layers carefully removed before measurement.

Claims

CLAIMS:

1. An element for use in a non-ferrous smelting application, the element including:

a copper body; and

a calorization layer formed in the copper body.

2. The element of claim 1 including a plurality of internal cooling channels.

3. The element of claim 1 or claim 2 in which the calorization layer includes a uniform Cu-Ai diffusion layer at the interface of the body and the layer, the diffusion layer having a thickness of between 10 and 40 μηη, preferably between 20 and 30 m.

4. The element of any one of the preceding claims in which the calorization layer includes a middle layer consisting of intermetallics in a Cu-AI matrix, the middle layer having a thickness of between 250 and δθθμητι, preferably between 350 and 450μιη.

5. The element of any one of the preceding claims in which the calorization layer comprises an outer aluminium oxide layer having a thickness of between 150 and 700 μηι, preferably between 250 and 550pm.

6. A non-ferrous smelting apparatus including:

a vessel for receiving non-ferrous material to be smelted; and

at least one calorized copper element located in or forming part of the vessel.

7. The non-ferrous smelting apparatus of claim 6 in which the copper element is selected from the group including tapping blocks, launders, internal wail coolers and/or refractory coolers.

8. Use of a caiorized copper element in a non-ferrous smelting apparatus as a functional element designed to withstand corrosion.

9. Use of a caiorized copper element in a non-ferrous smelting apparatus as a functional element designed to withstand sulphidation corrosion

10. Use of claim 8 or 9 in which the element is the element of any one of claims 1 to 5.

11. Use of claim 8 9 or 10 in which the functional element is selected from the group including tapping blocks, launders, internal wall coolers and/or refractory coolers.