WO1997032047A1

WO1997032047A1 - Hermetically closeable smelting/refining furnace

Info

Publication number: WO1997032047A1
Application number: PCT/IB1996/000156
Authority: WO
Inventors: Peter George Dunkel
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-03-01
Filing date: 1996-03-01
Publication date: 1997-09-04
Anticipated expiration: 1998-09-01

Abstract

A furnace for smelting and retiring metallic and non-metallic ores comprising a chamber (9) for processing said ore and an electric heating means (6) arranged in said chamber (9), characterised in that said chamber (9) is hermetically closeable. The smelting furnace can operate at high temperatures up to 3000 °C and process ores with an unexpectedly low consumption of energy.

Description

HERMETICALLYCLOSEABLESMELTINGREFININGFURNACE

Background of the invention

1. Field of the invention

The present invention relates to an electric furnace which is sealed when smelting and refining ores. A method for obtaining refined metals using this electric furnace is also included. The smelting furnace according to the invention allows, under closed conditions, to work at high temperatures of e.g. 3600°C and to process metallic and non-metallic ores with a surprisingly low energy consumption.

2. Description of the prior art

The smelting of ores has an overriding significance m the industrialised world because it provides the elementary and refined metals which are indispensable for manufacturing corresponding metal parts of any kind for a whole variety of sectors of the manufacturing industry.

The best known smelting methods are involving the production of, among others, iron, copper, tin, aluminium and lead from their corresponding ores. The respective metallic elements are usually m their oxidised form present in their corresponding ores, e.g. as oxides or sulphides, and need to be liberated therefrom by a reduction of the oxidised form to the elementary metal. In most cases, the method to obtain the elementary metal involves high temperatures and a reductive agent like for instance coal or carbon monoxide, so that the metal, once formed, can be removed from the furnace as a distinct phase, usually as a liquid.

As a matter of fact, a whole variety of different smelting methods are available to obtain the elementary metals from their corresponding ores, like for example the:

a) reverberatory smelting furnace, b) rotary smelting furnace, c) blast smelting furnace and/or d) electric smelting furnace.

The above smelting methods differ essentially in the temperature range at which they are operated. For example when it comes to the smelting of tin-containing ores, most smelting methods involve operational temperatures ranging between 1000 to 1200°C. -The electric furnace smelting method, however, allows to achieve higher temperatures of up -to 3500°C, thus increasing the reaction rate for the reduction, shifting the equilibrium to the side of the unoxidised metal products and diminishing the viscosity of the slag which is formed during the smelting method. Of further importance is that the electric conductivity of the slag is increasing at higher temperatures which facilitates the electron transfer from the electrode in an electric arc process to the oxidised metal within the molten slag.

The Australian Patent 502, 603 discloses an example of a method for manufacturing pure tin metal, whereby tin concentrates are mixed with a carbonaceous reducing agent and a lime flux by means of an electric smelting furnace. One major drawback of traditional electric smelting furnace methods is the fact that they are considered to be energy-intensive, which renders the method itself only possible at places where cheap and abundant electric energy supply is available.

Furthermore, traditional electric smelting furnaces are fed with reductive gases so that the furnace needs to be left open, usually by operating it without any cover, so that a more or less considerable amount of metal can evaporate, depending on the metal's boiling or sublimation point. For this reason and furthermore because of the considerable consumption of energy, the electric smelting furnace methods according to the state of the art ultimately avoid to operate at high temperatures (3000°C to 3600°C) .

Another characteristic of traditional smelting methods is the fact that the obtained metal is more or less impure so that an ensuing energy intensive and time consuming refining step turns out to be inevitable in order to obtain a high quality material.

Summary of the invention

Hence, it is a general object of the present invention to provide a furnace and a method for smelting and refining metal- and non-metal ores with low energy consumption.

Now, in order to implement these and still further objects of the invention, which will be more readily apparent as the description proceeds, the furnace for smelting and refining metallic and non-metallic ores is manifested by the features that it comprises a chamber for processing said ore and an electric heating means arranged in said chamber wherein said chamber is hermetically cioseable.

The method is manifested by the steps of placing the ore in a chamber in said furnace and heating electrically said chamber, wherein the method comprises at least one reaction step of hermetically enclosing said ore in said chamber while heating said chamber.

Temperatures of between about 3000°C and about 3600°C can be reached under closed conditions using the Dunkel furnace, thus making the smelting and refining metallic and non-metallic ores possible in an one-step method. The term "Dunkel furnace" shall denote the furnace according to the invention.

The loss of metal by evaporation or sublimation can be prevented, due to the possibility of sealing the chamber of the Dunkel furnace.

Furthermore, the Dunkel furnace was found to have an actual energy consumption far lower than traditional smelting methods to achieve the smelting of a given quantity of a metallic or non-metallic ores.

The furnace comprises preferably a steel made housing, whereby at least one of the top, surrounding and bottom walls is convex bulging outwards. The furnace can comprise a chamber with an inner surface lined with suitable refractories, whereby the chamber can be closed by means of a suitable cover. The inventive furnace is preferably heated by electric energy in the form of an electric current which is passing through an electrode which is comprising carbon.

The carbon electrode is preferably extending between two walls of said chamber, preferably in a horizontal position in order to heat a metallic or non- metallic ore placed inside the chamber of the furnace.

Brief description of the drawings

The invention will be better understood and objects other than those set forth will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

Figure 1 displays a side view of the smelting furnace according to the invention. Figure 2 displays a front view of the smelting furnace according to the invention.

Figure 3 displays a top view of the smelting furnace according to the invention.

Figure 4 displays a cross-section- of the smelting furnace according to the invention.

Description of the preferred embodiment

The figures show a furnace that can be used for smelting metallic and non-metallic ores. It comprises a steel made housing whereby at least one of the surrounding wall 1 and bottom wall 7 is convex, i.e. bulging outwards, whereby the inner surface is lined with suitable refractories 8, e.g. based on silicon. For the purposes of this application a cylindrical shape, such as the one of the surrounding walls, is considered to be convex. The furnace is mounted on supports 3 by means of a collar 4 which assures the possibility of tilting the inventive smelting furnace about a horizontal axis by mechanical means. The housing encloses a chamber 9 that can be sealed hermetically by securing a cover 2 which is substantially convex bulging outwards and which is on top of the furnace.

A carbon electrode 5 is horizontally extending across the chamber 9, i.e. between two points 11 and 12 on the wall of chamber 9 and is provided with the terminal 6 serving as a connection to a power supply.

A first end of the electrode 5 is electrically connected to the grounded housing and the second end of the electrode 5 is connected to a voltage supply by means of a terminal 6. The voltage supply generates a voltage between terminal 6 and the housing.

In a preferred embodiment, the electrode 5 which comprises carbon, is a carbon electrode, preferably it is a carbon rod, most preferred is a graphite rod.

The furnace according to the present invention and the ore which is placed inside the inventive furnace is heated by means of an electric current which is passing through the carbon electrode 5. The current in the carbon electrode 5 substantially exceeds any current in the ore to be processed. The current is generated by a voltage applied over the electrode 5 whereas no voltage is applied to the ore to be processed.

The carbon electrode 5 can be positioned in order to extend entirely through the furnace under any angle, i.e. with a tilted, a vertical or a horizontal longitudinal axis. The most preferred position is, however, the horizontal position, i.e. the carbon electrode 5 is preferably positioned horizontally within the furnace. The inventive furnace is suitable for smelting and refining metallic as well as non-metallic ores. The metallic ores are preferably selected from the group comprising iron-, copper-, nickel-, zinc-, tin-, lead-, manganese-, cobalt- containing ores or mixtures thereof. The tin containing ores are particularly preferred and cassiterite is most preferred.

In the method of smelting and refining metallic and non-metallic ores by means of the furnace according to the invention, it is preferred that the heating procedure is divided into a preheating period, whereby the cover 2 of the furnace is removed and the furnace stays open, and a reaction heating period whereby the furnace is loaded and hermetically closed.

In a preferred method, the empty furnace is undergoing first a preheating period, whereby the cover is removed, and thereafter the chamber of the furnace is loaded with the ore and the furnace is hermetically closed and then heated again by passing an electric current through the carbon electrode 5. Afterwards, the furnace is left to cool down sufficiently, so that the cover 2 can be removed and the furnace is tilted to remove the slag on the surface and, if desired, also the tin metal. Thereafter the reloading procedure can be performed and the next operational run can be carried out.

The preheating or reheating periods of the unloaded or loaded chamber of the furnace at open conditions are ranging between 0.5 to about 4 hours, preferably about 2 hours.

The reaction heating periods of the loaded chamber of the furnace at closed conditions is ranging between at about 1 and 6 hours, preferably between 1.5 and 3 hours, most preferred are 2 hours.

The furnace is heated by electric energy by means of the carbon electrode 5 which is fed with currents of between about 0.5 and about 600 amps, and voltages of between about 0.5 and about 72 volts, depending on the ore to be refined. Temperatures ranging between about 2800°C and about 3800°C are being realised, preferably between about 2900°C and about 3700°C.

In the case of the cassiterite, for all smelting operations that were carried out, not more than 4 % of the carbon electrode was consumed for the smelting of 1000 kg of the ore (see example 1) .

The invention shall be better illustrated by the following examples which are not construed to be limiting to the scope of the present invention:

Example 1

The steel made smelting furnace, has a silicon based insulating material forming the inner lining 8 of chamber 9. The horizontally placed graphite rod is 15 cm in diameter and 3 m in length. The employed ore is cassiterite, a typical composition of which is containing the following metallic ions and oxides:

Sn 73.64% (in Sn0₂)

Al 0.27 (mainly oxides)

Fe 2.09 (mainly oxides)

Ag 0.71 (mainly suicides) Si0₂ 1.89 Lower quantities of oxides and suicides comprising As, Bi, Mo, W, Ta and Pb are also present in cassiterite.

The following steps 1) to 8) were performed:

1) 2 hours preheating furnace is open

2) 45 minutes loading of ore furnace is open

3) 2 hours reaction heating furnace is closed

4 ) 4 hours cooling (stage 1) furnace is closed

5) 4 hours cooling (stage 2) furnace is open

6) 30 minutes pouring furnace is open

7) 45 minutes loading of ore furnace is open

8) 2 hours reheating furnace is open

9) 2 hours reaction heating furnace is closed

then the steps 4 ] 6) and 7) can be repeated.

The empty and open furnace is preheated to about 500°C prior to be loaded with cassiterite ore for about two hours by passing a current through the graphite rod. Thereafter, cassiterite ore is placed into the furnace through the opening and the furnace is completely sealed. Then, the temperature within the furnace is gradually increased to about 3000°C by passing again a current through the graphite rod for two more hours. After said two hours, during which the smelting process was taking place, the furnace is cooled down in a two stage process. Stage 1 is for 4 hours with the Dunkel furnace closed and step 2 is for another 4 hours with the furnace open. After this cooling process the slag on the surface can be run off by tilting the furnace by mechanical means. Thereafter, more cassiterite ore is placed into the chamber 9 of the furnace and a reheating step is performed. After two hours of reheating, the furnace is closed and another two hours of process heating are carried out. Thereafter the slag and the metal are poured. In this procedure, i.e. steps 1 to 9, the total time expired is 18 hours. A total of 1000 kg of cassiterite is processed and the method provides a practical yield of 82% using the cassiterite with a typical composition in example 1.

After the first operational run, i.e. after step 6), the loading step 7) is preceded by the two stage cooling steps 4) and 5) . The reheating step 8) under open conditions takes 2 hours, as did the preheating step 1) in the very beginning.

After the last pouring step 6), steps 7) , 8) and 9) follow. The same steps after the step 6) pouring, i.e. steps 7), 8) and 9) are followed by steps 4) to 7) .

For the total of 18 hours i.e. steps 1) to 9) , a transformer with a maximum output of 220 kVA was used. The energy consumption was about 148.75 k h over said period of 18 hours of said heating. Thus the average power is amounting to 8.20 k . With the current being at 335 amps, the voltage was accordingly at 44.4 volts.

A direct comparison with existing, usual 1000 kVA furnaces requiring about 730 kWh per 1000 kg of cassiterite to be processed shows that the smelting furnace of the present invention is by far superior with regard to the energy consumption of the smelting method.

While there are shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practised within the scope of the following claims.

Claims

Cl aims

1. A furnace for smelting and refining metallic and non-metallic ores comprising a chamber (9) for processing said ore and an electric heating means (6) arranged in said chamber (9), characterised in that said chamber (9) is hermetically cioseable.

2. The furnace of claim 1, wherein said chamber (9) is surrounded by walls whereby at least one of a bottom wall (7) or surrounding wall (1) is convex bulging outwards.

3. The furnace of any preceding claims, wherein said chamber (9) has a lining of suitable refractories (8), preferably based on silicon.

4. The furnace of any preceding claims, wherein said heating means comprises an electrode (5) which is comprising carbon.

5. The furnace of claim 4, wherein said electrode (5) consists of carbon.

6. The furnace of one of the claims 4 or 5, wherein the electrode (5) is a graphite electrode, preferably a graphite rod.

7. The furnace of any of the claims 4 to 6, wherein it comprises a means for passing a current through the electrode for heating up the ore inside the furnace.

8. The furnace of any of the claims 4 to 7, wrerem the electrode (5) is extending between two points (11 and (12) on the wall of said chamber.

9. The furnace of any of the claims 4 to 8, wherein the electrode (5) is horizontally extended across the chamber.

10. The furnace of any of the claims 4 to 9, wherein a first end of said electrode (5) is electrically connected to a housing of said furnace and the second end of said electrode (5) is electrically connected to a voltage supply.

11. A method for smelting and refining ores by using a furnace comprising the steps of, placing the ore in a chamber in said furnace and heating electrically said chamber, characterised in that the method comprises at least one reaction step of hermetically enclosing said ore in said chamber (9) while heating said chamber.

12. The method of claim 11, wherein said chamber (9) is heated by passing an electric current through an electrode (5) arranged in said chamber.

13. The method of claim 12, wherein said electric current is between about 0.5 and about 600 amps and a voltage over said carbon electrode is between about 0.5 and about 72 volts.

14. The method of claim 12 or 13, wherein said current in said carbon electrode (5) substantially exceeds any current in said ore.

15. The method of any of the claims 12 to 14, wherein said current is generated by a voltage applied over said electrode.

16. The method of claim 15, wherein no voltage is applied to said ore.

17. The method of any one of the claims 11 to 16, comprising the step of tilting said chamber (9) after processing said ore for pouring the slag and the metal.

18. The method of claim 11 to 17, further comprising a step of preheating or reheating said filled or unfilled chamber (9) of the furnace at open conditions.

19. The method of claim 18, wherein said preheating of said chamber (9) lasts about 0.5 to about 4 hours, preferably about 2 hours.

20. The method of any of the claims 11 to 19, wherein said reaction step lasts between about 1 and 6 hours, preferably between 1.5 and 3 hours, most preferred are 2 hours .

21. The method of any of the claims 11 to 20, wherein the ore is cassiterite or any other Sn0₂- containing ore.

22. The method of any of the claims 11 to 21, wherein about 4% of the carbon electrode are consumed for the smelting of 1000 kg of cassiterite.

23. The method of any of the claims 11 to 22, wherein in said reaction step, said ore is heated to at least between about 2000°C and 3200°C, preferably between 2800°C and 3100°C.