WO2005085735A1

WO2005085735A1 - Device for intake, processing and offtake of gases in an arc furnance

Info

Publication number: WO2005085735A1
Application number: PCT/SI2005/000002
Authority: WO
Inventors: Srecko Prislan
Original assignee: Srecko Prislan
Priority date: 2004-03-03
Filing date: 2005-01-07
Publication date: 2005-09-15
Also published as: SI21762A

Abstract

A device for the intake, processing and offtake of gases in an arc furnace conceived of a housing (1) with openings (5) through which electrodes (6) are positioned and an opening (11) to which an exhaust duct (12) is connected, said duct being - normally outside the room equipped with the arc oven - introduced into a dust filter (13), behind which there is a suction fan (14). Between each electrode (6) and the opening (5) through which the electrode runs there is a circular gap (7), whereas the fastening of the housing (1) on the furnace lid (2) is provided with spacers (8), due to which the lower edge of the housing (1) is distant from the lid (2), so that there are gaps (10) between them. Toxic gases and fumes are collected and electrodes are cooled by this arrangement.

Description

DEVICE FOR INTAKE, PROCESSING AND OFFTAKE OF GASES IN AN ARC FURNACE

Subject of Invention

The subject of the present invention is a device for the intake of gases in an arc furnace, processing of said gases into environmentally friendly gases and offtake of same into the environment.

Technical Problem

The technical problem solved by the invention is how to conceive such device for intake, processing and offtake of gases in an arc furnace that will be simple, without additional accessories and devices that would require an utterly precise and demanding construction to withstand this hot and mechanically demanding environment to avoid causing any interruptions and poorer operation of the electric arc furnace due to its possible malfunction, whereby the device of the invention should also process the environmentally toxic gases originating in an arc furnace to gases representing less burden for the environment and are led along gas ducts to a mechanical filter and the device should simultaneously also create improved conditions for the operation of electrodes in the arc furnace to extend their life span thus lowering those quantities of carbon in steel, which emerge due to the burning-off of electrodes into a melt, under consideration of the fact that the device should also be low-energy consuming and cost efficient.

Prior Art

Known devices for the intake and offtake of gases in an electric arc furnace consist of a housing enveloping the lid of the furnace and taking in the gases escaping through the slots lying near the electrodes into the environment. With the electrodes being taller than the housing, the housing also has openings for the exit of electrodes.

Due to high temperature of the furnace lid, the heat also transfers to the housing of the device for the intake of gases. Sealing rings near the electrodes are therefore conceived in a specially demanding way. Fans near the device must withstand high temperatures, because the gases escaping from the furnace are extremely hot. A special problem is how to conceive exhaust ducts of gases, which must be flexible to follow the opening of the furnace lid and the device for the intake of gases. All the above-mentioned contributes to the construction of the device for the intake of gases to be very complicated. Due to hot exhaust gases also the housing of the device and the exhaust duct are very hot, which increases the temperature of the working environment to a level that is uncomfortable for people.

There is a need for a simpler device of this type, which will be less prone to possible breakdowns and last but not least, its lower price would contribute to lower manufacturing costs of steel. Since people are more and more conscious of the environment, the quality of gases discharged into the environment is also subject to more strict requirements.

Solution to the Technical Problem

The described technical problem is solved by a new device for the intake and offtake of gases from an arc furnace, the essential characteristic of which lies in the fact that the housing covers the furnace lid at a distance, so that there is a narrow gap conceived between them. The openings for electrodes are also larger having a circular gap between the electrodes and the housing. The gases are discharged through the exhaust duct only by means of subatmospheric pressure produced by suction fans behind a filter located outside the room with the furnace. The quantity of the sucked air is many times bigger than the expected quantity of gases discharged from the furnace. Thus suction of the environmental air through the gaps between the device and the furnace lid and also through the gaps near the electrodes is provided for. The subatmospheric pressure in the device prevents the gases from the device to escape into the environment but through the exhaust duct. Additional oxygen in the device carried in by sucked-in air causes the gases discharged from the arc furnace to burning in the device itself, so that they become substantially less burdening to the environment.

A relatively high temperature in the device (around 700 - 900°C) due to the burning of gases discharged from the furnace and from the air sucked-in from the environment additionally heat the furnace. The environmental air coming into the device prevents the electrodes from heating beyond 700 - 900°C, i.e. they do not glow and thus the ratio of burning-off of graphite of electrodes is substantially much lower due to oxidation when the environmental air comes in. Based on this fact, the thickness of new electrodes can be smaller for the same actual electric power intended for melting in the furnace.

The device of the invention has also proved to allow additional forced intake of air or oxygen directly into the furnace due to strong suction of gases from the device and cooling of electrodes, thus speeding up the melting of the contents without any damage on electrodes. The capacity of the furnace is therewith increased.

A considerable surplus of fresh air taken into the device does not only cause the burning of gases into environmentally friendly gases, moreover, it also lowers the temperature thereof to around 300°C at the exit from the device. The device therefore needs much less water cooling as is the usual procedure with known devices of this type in order for their external surface temperature be bearable for the workers. The temperature of gases in the area of the filter and the fan decreases to around 80°C. A large quantity of environmental air - with respect to the gases discharged from the furnace - introduced into the device of the invention moreover assures that the quantity of solid dust particles per unit of discharged gases is small. The specific mass of the mixture of gases and particles does therefore not increase, which maintains high flow velocity through ducts. Dust particles do not fall to the bottom of ducts in higher quantities, especially in bends, they reach a filter, where they get separated from gases. This contributes to a long operating time of the device without any need for the cleaning of ducts.

Due to the increased temperature of gases in the filter, no condensate can form in it, solid particles in the filter therefore remain dry and do not clog into a pasty substance, which would otherwise substantially too quickly require the cleaning of filters and the work of the furnace would have to be interrupted.

With the device of the invention preventing the discharge of gases from the furnace into the environment, the quantity of environmental air, needed to mix gases from the furnace and suction both and mechanically filter them is at least 5- times smaller than the quantity of air and gases from the furnace in known variants for the same final effect, because the needed devices for suction and filtering are substantially smaller, cheaper and also energy saving.

When the furnace is charged with a raw material, the furnace lid is lift together with the device of the invention positioned thereon. The flexible part of the duct allows the housing to be turned. The housing with the lid is also turned in a similar way when the furnace is tilted to pour the melt out.

The essence of the invention will now be described in more detail by the following description of an embodiment and the enclosed drawing, in which Fig. 1 shows a schematic view of an arc furnace with a device for the intake, processing and offtake of gases of the invention.

A device for the intake, processing and offtake of gases in an arc furnace is conceived of a housing 1 only leaning against a lid 2 of an arc furnace 3. The housing 1 has two walls and is intended to be cooled with a cooling liquid via connections 4. The housing further contains openings 5 for electrodes 6, so that there is a circular gap 7 between the electrodes 6 and the opening 5. The housing 1 is fastened to the lid 2 of the furnace with spacers 8, which keep the lower edge of the housing 1 distant from the lid 2 providing gaps 10 between them. On the lid 1 there is an opening for connecting an exhaust duct 12 positioned at the opposite end, as a rule outside of the room with the furnace, said duct being introduced into a dust filter 13, behind which there is a suction fan 14. In the duct 12 there is an outlet 15 for an auxiliary duct 16, sucking gases from below the ceiling of the room preferably above the furnace, said gases escaping from the furnace when the melt is poured out. In the duct 12 between the housing 1 and the outlet 15 there are flexible bellows 17 allowing the tilting of the furnace and opening of the furnace lid with the housing, whereby the discharge duct is permanently connected to it.

The shape and the size of gaps 7 and especially the gaps 10 is optional and can be adjusted to individual needs. The common cross-section of gaps 10 preferably equals that of the duct 12.

Cooling of the housing can be conceived in an optional way, different from the one described above. Discharge cooling water can be led to a heat exchanger 18 and water heat energy can further be transferred to any medium by a known method. There are also special devices for the intake and offtake of gases from the furnace upon pouring the melt out of it. A connection of such devices does not have any influence on the device of the invention. The ducts, the filter and the fan may also be changed and adapted to individual conditions without influencing the contents of the present invention.

A man skilled in the art can also conceive other embodiments by knowing the above description without circumventing the essence of the invention defined in the appended claims.

Claims

1. A device for the intake, processing and offtake of gases in an arc furnace (3) conceived of a housing (1) with openings (5) through which electrodes (6) are positioned and an opening (11) to which an exhaust duct (12) is connected, said duct being - normally outside the room equipped with the arc oven - introduced into a dust filter (13), behind which there is a suction fan (14), characterized in that between each electrode (6) and the opening (5) through which the electrode runs there is a circular gap (7), and that in the housing (1) on the furnace lid (2) there are gaps (10) for the entry of the environmental air into the device of the invention.

2. A device according to claim 1, characterized in that the gaps (10) are provided at the edge of the housing (1), so that between the furnace lid (2) and the housing (1) there are spacers (8).

3. A device according to claims 1 and 2, characterized in that the common cross-section of gaps (10) preferably equals that of the duct (12).

4. A device according to claims 1 to 3, characterized in that under the ceiling of the space above the furnace there is an auxiliary duct (16) sucking gases discharged from the furnace upon pouring out of the melt from the furnace, said duct being preferably connected to an outlet (15) in the duct (12).

5. A device according to claims 1 to 4, characterized in that the ratio between the air sucked by a fan (14) from the environment of the furnace through the gaps (7 and 10) and the gases discharged from the furnace and collected by the device is approximately 20 : 1.

6. A device according to claims 1 to 5, characterized in that the housing (1) is subject forced cooling, preferably by water.