ZA200510205B

ZA200510205B - Electric reducing furnace

Info

Publication number: ZA200510205B
Application number: ZA200510205A
Authority: ZA
Inventors: Juergen Kunze
Original assignee: Sms Demag Ag
Priority date: 2003-07-31
Filing date: 2005-12-14
Publication date: 2006-10-25
Also published as: EP1658467A1; DE10335847A1; EP1658467B1; ATE377740T1; AU2004269087A1; WO2005022062A1; CA2534623A1; CN100537784C; AU2004269087B2; CN1829891A; CA2534623C; BRPI0413109A; MXPA06001136A; CL2004001844A1; ES2293277T3; DE502004005447D1

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):

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., Cuz0), sulfides (e.g., cuss), 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

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

USS1,000 to US$1,500 per day.

The production of this additional waste gas by the unwanteqd : 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 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.

This objective is achieved by the furnace with the features of Claim 1. Advantageous further developments are described in the dependent claims.

The crux of the invention is the realization of a furnace with an air-sealed design in which the charge 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.

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,

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.

. 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 UsS$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 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 0i, 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 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 § (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-

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 (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.

List of Reference Symbols ’ 1 electric arc reduction furnace . 2 furnace wall 3 charge opening

C4 charging system 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

Claims

) 1. Electric arc reduction furnace (1) for carrying out . reduction processes, especially for reducing slag to recover metallic constituents, by means of electric energy, which is introduced into the interior (01) of the furnace by at least one electrode, wherein the reduction furnace (1) has a charge opening (3) for charging the charge material, which is conveyed by a charging system (4), and an opening (3) for exhausting the gas that forms during the reduction process from the furnace, characterized by the fact that the furnace is realized with an air-sealed design in which the charge opening (3) for the charge ‘material simultaneously serves as the waste gas exhaust opening (3) for the gas that forms during the process.
2. Electric arc reduction furnace in accordance with Claim ° 1, characterized by the fact that the charging system extends into the furnace interior (oi) through the common charge and waste gas exhaust opening (3) or terminates at the opening (3), that this charging system (3) is provided with a cover 7 outside the furnace, and that the cover (7) is sealed from the furnace shell and is formed as a waste gas chimney towards the top. :
] 3. Electric arc reduction furnace in accordance with Claim 1 or 2, characterized by the fact that the cover (7) for the charging system (3) has a chimney flue (10) near the furnace for exhausting gas, and that the chimney flue (10) is followed by a post-combustion chamber (11).
4. Electric arc reduction furnace in accordance with any of Claims 1 to 3, characterized by the fact that the combustion chamber (11) is connected with an air supply channel (12) for the controlled introduction of air and for the controlled post combustion of the process gases.
5. Electric arc reduction furnace in accordance with any of Claims 1 to 4, characterized by the fact that the common charge and waste gas exhaust opening (3) is arranged in the oo furnace wall (2) or in the furnace roof, and that the charging system (3) with the cover (7) is connected airtight with the common charge and waste gas exhaust opening (3) on the outside of the furnace.
6. Electric arc reduction furnace in accordance with any of Claims 1 to 5, characterized by the fact that the charging system is a charging chute (5). E
7. Electric arc reduction furnace in accordance with Claim 6, characterized by the fact that the conveyance of the charge material into the furnace by the charging chute (5) is accomplished by gravity or is supported by mechanical means, such as vibrators or rotating rolls.
8. Electric arc reduction furnace in accordance with any of Claims 1 to 7, characterized by the fact that liquid slag can be charged through the common charge and waste gas exhaust opening.
9. Electric arc reduction furnace in accordance with any of Claims 1 to 8, characterized by the fact that solid materials, such as solid slag and/or reducing agent, can be charged through the — charge and waste gas exhaust opening.
10. Electric arc reduction furnace in accordance with any of Claims 1 to 9, Characterized by the fact that the furnace, which has a furnace roof, has at least one charging tube that extends into the interior of the furnace through the furnace roof for charging