AU2004269087B2

AU2004269087B2 - Electric reducing furnace

Info

Publication number: AU2004269087B2
Application number: AU2004269087A
Authority: AU
Inventors: Jurgen Kunze
Original assignee: SMS Siemag AG
Current assignee: SMS Siemag AG
Priority date: 2003-07-31
Filing date: 2004-06-21
Publication date: 2010-05-20
Anticipated expiration: 2024-06-21
Also published as: CL2004001844A1; CN1829891A; ZA200510205B; DE10335847A1; DE502004005447D1; CN100537784C; BRPI0413109A; EP1658467B1; ES2293277T3; MXPA06001136A; ATE377740T1; WO2005022062A1; AU2004269087A1; CA2534623A1; CA2534623C; EP1658467A1

Abstract

Electric arc reduction furnace (1) comprises a charging opening (3) for charging material which simultaneously acts as an exhaust gas line opening for the gas produced.

Description

TRANSLATION (HM-687PCT -- original): WO 2005/022,062 Al PCT/EP2004/006,687 ELECTRIC ARC REDUCTION FURNACE The invention concerns an electric arc reduction furnace for carrying out reduction processes, especially for reducing slag to recover metallic constituents, by means of electric energy, which is introduced into the interior of the furnace by at least one electrode. The reduction furnace has an opening in the wall or roof of the furnace for charging the charge material and an opening for exhausting the gas that forms during the reduction process from the furnace. The slag to be purified is charged into the furnace and reduced. The metals charged with the slag are in the form of oxides (e.g., Cu 2 O), sulfides (e.g., Cu 2 S), and pure metals (e.g., Cu). The oxide constituents are reduced to metals by the addition of a reducing agent. The sulfides and the pure metallic constituents settle on the bottom of the furnace due to their different densities. In reduction furnaces of this type for reducing or purifying slags, it is well known that the process gas, such as 1 CO, remains partly or entirely in the furnace and is burned. The CO-containing process gas is burned in the furnace above the melt or slag with air, which is drawn in through suitable openings in the furnace shell or furnace roof, and then cooled to a certain temperature, which is predetermined by the type of downstream dust catcher. This is associated with the following disadvantages. First, in the case of partial combustion of the process gas, there is the danger of a CO explosion or the escape of the poisonous CO gas into the furnace house. Second, due to the combustion of the gases and of gaseous metal vapors in the furnace, there is increased electrode consumption and increased consumption of the reducing agents, such as coke, coal, etc. This in turn results in high energy losses, which can be on the order of 3-5 metric tons of coke per day and 0.5-0.8 kg of electrode material per metric ton of charge. In a furnace installation that purifies about 1,000 metric tons of slag per day, these additional costs amount to US$1,000 to US$1,500 per day. The production of this additional waste gas by the unwanted combustion of the electrodes and reducing agents necessitates dust catchers designed for larger volumes of waste gas. In addition, the lining in the gas space of the furnace, especially 2 the roof lining, is subjected to strong thermal loads. The Japanese document 2000-039,118 A discloses an electric arc reduction furnace for reducing slag. Powdered charge material is introduced by a charging system through a suitable charge opening in the side wall of the furnace at the level of the slag layer and melted down electrically. Gases that form during the reduction, CO gas in particular, are removed by an exhaust system through a separate exhaust line in an opening in the furnace roof. Proceeding from the prior art, the objective of the invention is to modify an electric arc reduction furnace in such a way that the aforementioned disadvantages are avoided. According to one aspect of the present invention, there is provided a submerged arc furnace for carrying out reduction processes, particularly for the reduction of slag in order to reclaim metallic components, by means of electric energy that is introduced into the furnace interior by means of at least one electrode, with the reduction furnace featuring a charging aperture for charging material that is transported by means of a charging device, as well as an aperture for discharging the gas produced during the reduction process from the furnace, and with the charging aperture for the charging 3 22604851 (GHMatters) 27/04110 material simultaneously serving as waste gas line aperture for the gas being produced, wherein the furnace is realized in the form of an airtight construction and the charging device is provided with a cover outside the furnace, with said cover being sealed relative to the furnace vessel and featuring a chimney pipe in the proximity of the furnace which serves for discharging the gas and is realized in the form of a waste gas chimney toward the top, and with the charging device protruding into the furnace interior through the common charging and waste gas aperture or ending at the aperture, and wherein the charging device, consists of a charging chute and the transport of the charging material into the furnace is realized via the charging chute with the aid of the gravitational force or promoted with mechanical means such as vibrators or rotating rollers, with the furnace featuring a furnace roof and at least one charging pipe that serves for charging the furnace with reducing agent and/or solid slag and protrudes into the furnace interior through the furnace root and with a post-combustion chamber being connected to the chimney pipe downstream thereof. The crux of the invention is the realization of a furnace with an air-sealed design in which the charge 3a 22604851 (GHMatters) 27104110 material, especially liquid slag, is charged through an airtight opening in the furnace, and at the same time the furnace gas is exhausted or drawn off through the same airtight opening in the furnace. In this way, the furnace is provided with optimum protection against unwanted penetration of air. Oxidation of the electrodes and/or the reducing agents is prevented. 3b 22604851 (GHMatters) 27/04/10 In a preferred embodiment of the invention, the charging system, which is preferably designed as a charging chute and extends into the interior of the furnace through the common charge and waste gas exhaust opening, has a cover. This cover is sealed from the furnace shell and formed as a waste gas chimney towards the top. This embodiment allows the charging of slag with a simultaneous airtight seal and simultaneous prevention of unwanted consumption of electrodes and reducing agents. The cover allows continuous charging, because it is permanently operative. With a furnace mode of operation under a slight positive pressure, the process gas leaves the furnace via the charge opening in the furnace shell through the waste gas chimney formed by the charging chute and its cover. In principle, however, it is also possible to seal this common opening for charging and gas exhaust by means of a slide gate. However, this can be considered only if charging is not being performed continuously. The chimney shape of the cover is preferably formed in such a way that the cover of the charging system has a chimney flue for gas exhaust more or less close to the furnace, and that the chimney flue is followed by a post-combustion chamber. Partial combustion of the process gases can occur in this chimney flue, 4 because it is not entirely possible to prevent air from also being drawn into the chimney flue from the charging side through the charging system. However, the entrance of air into the furnace is completely prevented. Specifically, as a result of the chimney effect, air that is drawn in is not drawn into the furnace but rather into the flue formed by the cover. In the combustion chamber that follows the chimney flue, the controlled supply of additional air completes the combustion of the process gases and cools the combusted waste gas to the lower temperatures that are required. The conveyance of the charge material into the furnace by the charging system in the form of a charging chute is preferably accomplished by gravity or fluid force. However, the invention also includes the possibility of supporting this conveyance by mechanical means, such as vibrators and rotating rolls. The slags that are used are present mostly in liquid form. Liquid slags are charged through the common charge and waste gas exhaust opening. Solid, lumpy slag is also charged at the same time. In one embodiment of the reduction furnace, this charge material is charged together with the reducing agent by means of charging tubes that extend into the interior of the furnace through the furnace roof. 5 In another embodiment, it is also possible to charge solids through the common charge and waste gas exhaust opening. This is advantageous especially for the reducing agent, because the oxide constituents of the slag are then already being intensively mixed with the reducing agent as they are being charged to the furnace. All together, the following additional advantages are achieved by the invention: -- reductions of operating expenses of US$300,000 to US$400,000 per year; -- lower investment costs for the dust catcher, since.the waste gas volume arising from the combustion and the cooling air for the coke and electrodes is eliminated; -- reduced thermal load on the furnace roof due to the elimination of the latent heat, since no combustion occurs in the furnace; -- a simpler design of the electrode bar, since adjustment of the electrodes is greatly reduced; -- assurance of a reducing furnace chamber atmosphere, which is advantageous for recovery of the valuable materials, which are present in the form of oxides.

Further details and advantages of the invention are specified in the dependent claims. The invention is explained 6 in greater detail below with reference to the specific embodiment of the invention illustrated in the sole drawing, which shows a cross section of a schematically indicated reduction furnace wall with an opening that serves simultaneously as a charge and waste gas exhaust opening. The electric arc reduction furnace 1 is indicated by the furnace wall 2. An electric arc reduction furnace 1 of this type is used, for example, to carry out recycling processes, such as oxidic waste processes, and especially to purify slags for the purpose of recovering metallic constituents. To this end, at least one electrode (not shown) is inserted in the furnace interior Oi, and the charge material is melted down or raised to high temperatures by the electric energy introduced into the furnace, so that the reduction processes can proceed with the aid of the reducing agents that are introduced, such as coal and coke. The furnace wall 2 has a charge opening 3. A charging system 4, here in the form of a charging chute 5 or slag feed chute, which is supported by a frame 6, extends through the charge opening 3. Slag is charged into the furnace by means of the charging chute 5 (arrow I). At the same time, this opening 3 also serves as an exhaust opening for the process gases that are formed during the reduction, which are designated here as CO 7 and as {Zn} to reflect the gaseous metal vapors, such as Zn (arrow II). This opening 3 is basically the only waste gas exhaust opening. However, an emergency chimney for the waste gas can be provided for emergencies. The charging chute 5 is sealed airtight from the furnace wall 2. For this purpose, it is provided with a cover 7 in the form of a metal housing, which extends from the furnace wall 2 to the inlet 8 of the charging chute 5. On the side of the inlet 8, the cover 7 is bent up somewhat to provide room for the charge material. Close to the furnace, a chimney flue 10 extends from an opening 9 in the cover 7 upward and away from the cover 7. In this way, the cover 7 is formed as an exhaust gas chimney in the upward direction. The chimney flue .10 is followed in the direction of waste gas flow by a post-combustion chamber 11, into which an air supply channel 12 opens for feeding air into the post-combustion chamber 11. The process will now be explained. Charge material, such as liquid slag, is continuously charged into the furnace interior by means of the charging chute 5 (arrow I). Reducing agent is charged through separate charging tubes in the furnace roof or possibly by the charging chute 5. At the same time, process gases flow through the same opening 3 into the chimney 8 like cover 7 in the opposite direction (arrow II) from the charging direction. They flow off through the chimney flue (arrow III). Air (arrow IV) that is drawn in along with the charge material is likewise discharged through the chimney flue 10 (arrow V). Partial combustion of the gases can occur in the chimney flue 10 with this air. However, the actual post combustion with a controlled air supply occurs in the downstream post-combustion chamber 11, into which the controlled air supply is fed (arrow VI). All together, the invention creates a closed electric arc reduction furnace for purifying liquid slags. Its closed construction is a result of the fact that the furnace is provided with only one gas opening, through which liquid slag is charged and the furnace gas is simultaneously drawn off. This prevents any secondary air from penetrating to the interior of the furnace. 9 List of Reference Symbols 1 electric arc reduction furnace 2 furnace wall 3 charge opening 4 charging system 5 charging chute 6 frame 7 cover 8 inlet 9 opening in the cover 10 chimney flue 11 post-combustion chamber 12 air supply channel Oi furnace interior arrow I slag and reducing agent charge direction arrow II process gas exhaust direction arrow III flow of the process gases through the chimney arrow IV air drawn in from the charging side arrow V discharge through the chimney of the air drawn in from the charging side arrow VI controlled air supply for post combustion 10 It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 11 2260485 1 (GHMatters) 27/04/10

Claims

1. A submerged arc furnace for carrying out reduction processes, particularly for the reduction of slag in order to reclaim metallic components, by means of electric energy that is introduced into the furnace interior by means of at least one electrode, with the reduction furnace featuring a charging aperture for charging material that is transported by means of a charging device, as well as an aperture for discharging the gas produced during the reduction process from the furnace, and with the charging aperture for the charging material simultaneously serving as waste gas line aperture for the gas being produced, wherein the furnace is realized in the form of an airtight construction and the charging device is provided with a cover outside the furnace, with said cover being sealed relative to the furnace vessel and featuring a chimney pipe in the proximity of the furnace which serves for discharging the gas and is realized in the form of a waste gas chimney toward the top, and with the charging device protruding into the furnace interior through the common charging and waste gas aperture or ending at the aperture, and wherein 12 22604851 (GHMatters) 27104/10 the charging device, consists of a charging chute and the transport of the charging material into the furnace is realized via the charging chute with the aid of the gravitational force or promoted with mechanical means such as vibrators or rotating rollers, with the furnace featuring a furnace roof and at least one charging pipe that serves for charging the furnace with reducing agent and/or solid slag and protrudes into the furnace interior through the furnace root and with a post-combustion chamber being connected to the chimney pipe downstream thereof.

2. The submerged arc furnace according to Claim 1, characterized in that the post-combustion chamber is connected to an air supply channel for introducing air in a controlled fashion and for realizing a controlled post combustion of the process gases.

3. The submerged arc furnace according to Claim 1 or 2, characterized in that the common charging and waste gas aperture is arranged in the furnace wall or in the furnace roof, to which the charging device with the cover is connected in an airtight fashion on the outside of the furnace. 13 22604851 (GHMatters) 27/04/10

4. The submerged arc furnace according to one of Claims 1 to 3, characterized in that the furnace can be charged with liquid slag through the coming charging and waste gas line aperture.

5. The submerged arc furnace according to one of Claims 1 to 4, characterized in that the furnace can be charged with solid matter such as solid slag and/or reducing agent through the common charging and waste gas line aperture.

6. A submerged arc furnace for carrying out reduction processes substantially as herein described with reference to and as illustrated in the accompanying drawings. 14 22604851 (GHMatters) 27104/10