US3127462A

US3127462A - Device for the removal of smoke from electric furnaces and the like

Info

Publication number: US3127462A
Application number: US88982A
Authority: US
Inventors: Erni Enrico; Luscher Fritz
Original assignee: Von Roll AG
Current assignee: Von Roll AG; Von Roll Holding AG
Priority date: 1960-02-17
Filing date: 1961-02-13
Publication date: 1964-03-31
Anticipated expiration: 1981-03-31
Also published as: CH379659A; LU39748A1; GB914112A; AT241140B; NL261045A

Description

March 31, 1964 E RNl ETAL 3,127,462

E DEVICE FOR THE REMOVAL OF SMOKE FROM ELECTRIC FURNACES AND THE LIKE Filed Feb. 13. 1961 A 18 1/ J L17 f Fig.2

1NV5NToRs= E uuco RN/ no ATTORNEY United States Patent 3,127,462 DEVICE FGR THE REMOVAL OF SMOKE FRUM ELECTRIC FURNACES AND THE LIKE Enrico Erni and Fritz Liischer, Gerlafingen, Switzerland,

assignors to Gesellschaft der Ludw. von Rollschen Eisenwerke A.G., Gerlafingen, Switzerland, a corporation of Switzerland Filed Feb. 13, 1961, Ser. No. 88,982 Claims priority, application Switzerland Feb. 17, 1960 13 Claims. (Cl. 13-3) The present invention relates to an improved device for the removal of smoke from electric furnaces, and more specifically, to a novel design and construction of a smoke hood readily suitable for exhausting smoke and combustion gases from a furnace interior.

Electric furnaces, particularly those presently widely employed for metallurgical purposes, are provided with at least one electrode and an electric arc is formed between the electrode and the stock to be melted. In the melting processes carried out in such a manner, large quantities of smoke gas are generally generated which may partly originate from the melting stock and partly from the burnt-off electrode. The effective removal of these produced gases constitutes a major problem for industry. It is necessary that these gases be removed as completely as possible, not only to protect the operators against the toxic components of the gases (CO from the consumption of carbon electrodes), but also because of the considerable dust content generally present in the gas and, the necessity imposed thereby of cleaning the gases from dust prior to their escape into the atmosphere. Various proposals have been made in order to solve this problem with open-hearth electric furnaces by providing a movable smoke hood. In closed electric furnaces, openings for the removal of smoke gases have been proposed in the coverof the furnace; such openings, however, are arranged independently of and separate from the electrode opening. This separate arrangement of the gas escape openings has various operational disadvantages; of particular importance is the virtual impossibility of entirely preventing smoke from issuing along the electrodes. While it would, as such, be possible to prevent the smoke gas from escaping in the region of the electrodes by adequately raising the suction operating on the furnace interior, such may cause air to enter into the furnace. This is a disadvantage for several reasons, one of which is the danger of burning the electrode at its shaft. It has also been found that the flow conditions in the known exhausting devices for the smoke gas are not always very favorable.

The device according to the present invention is designed to eliminate the disadvantages encountered when employing the heretofore known smoke removal installations, and more particularly, those used with closed electric furnaces. The smoke removal device according to the present invention is provided with an annular housing which substantially coaxially encloses an electrode at the point where'it emerges from the furnace and, further, is provided witha suction slot which communicates with an exhaust duct in the interior of the housing.

The device according to the present invention enables the smoke to be collected immediately above the region where its development is most pronounced. It is to be appreciated that the generation of smoke and gases is most pronounced at the point where the electrode enters the charge. However, as a practical matter the smoke cannot be effectively removed immediately at this point. The gases and air which collect about the surface of the electrode are caused to rise in temperature and form an upwardly directed current which finally collects underneath the furnace cover at the point where the electrode piercingly enters this cover member. It is at this locality that the device of the present invention operates to remove smoke therefrom. Thus, the normal upward draft of the smoke gases and the like situated about the electrode is a factor directly contributing to the effective removal of smoke and the like. It is to be understood that a separate device for the removal of smoke and combustion gases or the like is preferably associated with each electrode of the furnace in practical operation.

Accordingly, it is an important object of the present invention to provide means for effectively removing smoke and the like from the interior of electric furnaces.

Another important object of the present invention is to provide means for removal of smoke from electric furnaces in such a manner as to prevent depositing of solid or foreign particles in the flow channels provided for the removal of such smoke.

Still a further object of the present invention is to provide means for effectively removing smoke gases from a furnace interior with the velocity of flow of the gases to be removed being maintained as uniform as possible.

These and still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In the drawings:

FIGURE 1 is a cross-sectional, fragmentary view of a smoke removal device carried by the upper portion of a closed electric furnace in the region where the electrode enters the furnace interior; and

FIGURE 2 is a cross-sectional view of the smoke removal device shown in FIGURE 1, taken along line AA thereof.

It is to be understood that only enough of the structure of the present device has been shown which will enable one to have a clear understanding of the teachings of the present invention. The details of the electrode and the furnace have been omitted for the sake of clarity in explanation.

Referring now to the drawing and, more particularly to FIGURE 1, there is shown a cover member 1 provided for an electric furnace and having an annular or circular opening 2 arranged to receive an electrode adapted to be inserted through said annular opening. The smoke removal device 3 comprises an annular housing 4 communicating with an exhaust conduit 5. A flange member 6 connects the conduit 5 with an exhaust system for the furnace, generally designated by reference numeral 7. The annular housing 4 may be arranged in the annular opening 2 of the electric furnace and, generally, comprises a lower base portion 8, an upper housing portion 9 and an intermediate connecting wall portion 17. The lower base portion 8 of the housing 4 includes an arcuate wall portion 8a having a downwardly, annular extending wall 8b which extends into the annular opening 2 and is adapted to bear against the inner wall 2a thereof to partly protect this annularopening 2. The upper housing portion 9 consists of an upper annular wall Qa and a downwardly extending wall portion 9b. The wall portion 9a inclines upwardly in the direction of the conduit 5, whereas the downwardly extending wall portion 9b continually widens in the direction of the conduit 5. The lower edge of the wall portion 9b is spaced a predetermined distance from the inner wall of the base portion 8 to define an annular slot 10 through which the smoke gases or the like, collecting in the space 11 at the point where the electrode passes through the cover 1, may be passed into an annular flow channel 18 formed between the upper and 'lower wall portions 9 and 8 respectively. The flow chansmoke gases removed should be maintained as uniform as possible and of sufficient magnitude to ensure that the solid particles are carried along in the flow stream and do not deposit themselves in the flow channel. The minimum velocity of flow necessary to obtain the so-called dragging effect of the solid particles is determined by a number :of factors; particularly by the type, size and distribution .of the solid material being handled, as for example dust. It has been found that in electric furnaces used for the processing of iron and for removing the dust or fine particles resulting therefrom, a minimum velocity of flow of the'gasshould amount to approximately meters/sec. Additionally, suitable means such as vibrators, may be employed to prevent solid particles from being deposited on the walls of the smoke removal housing, which housing may be formed of individual segments.

In order to achieve a uniform velocity of the gases or smoke to be exhausted, the cross-sectional area of the flow channel 18 must be dimensioned such that it increases radially in linear relationship in the direction of flow. That is to say, radial planes taken through the flow channel 18 at various spatial points through this flow channel clearly show an increase of the cross-section area of the flowchannel in the direction of the exhaust conduit 5. Such an increase of cross-sectional area of the flow channel is effectively obtained in the embodiment of FIG- URE 1 since the wall portion b of the upper wall 9 is designed'to widen in an upward direction and exhibits a helical configuration, in the form of a half-turn of a screw, from the point where the cross-sectional area of the flow channel is smallest to that where it is largest. It is to be appreciated that the width of the annular intake slot 10 between the upper housing portion 9 and the lower housing portion 8 should be suitably dimensioned in order to accommodate the volume of smoke gas handled; into account must be taken the gas suction output available for the smoke or gas handled.

During the operation of the furnace, a field of force 'is formed about the electrode which produces induced currents in a metallic and magnetic material which may cause operational trouble. The materials handled by the furnace and which generate the smoke to be removed, include non-magnetic materials such as ceramic materials or non-magnetic metals such as brass, and magnetic materials such as iron because of its favourable thermal stability and relatively low cost. If magnetic materials are used an intermediate layer formed of a non-magnetic material may be provided according to one embodiment of the invention. Such a layer is provided to counteract the formation of induced currents. For this purpose a layer formed of non-magnetic material is incorporated between the wall portions of the housing segments, preferably at the narrowest point of the cross-section of the flow channel 18 provided in the annular housing 4. The layer at least partially separates the two halves of the housing 4, that is to say, the respective portions located in front of and behind the plane of the drawing of FIGURE 1. This non-magnetic layer may also be in the form of a sheet arranged so as to divide the flow channel 18 into two halves. Such an arrangement may be of considerable advantage with respect to the conditions of flow provided that this partition is accurately located at the point where the velocity of flow is smallest. In FIGURE 2 we have shown such a partition member 20 which is formed of a non-magnetic material. If the smoke removal device is formed of a material which is not readily capable of withstanding the thermal stresses due to the heat from the furnace and the electrode, a cooling system may be provided therewith. In the embodiment according to FIG- URE 1, the housing 4 may-be provided with a cooling compartment 1h formed between the inner and outer walls of the housing in the form of a cooling jacket. A cooling medium such as water may be passed through the compartment 19 formed between these two walls.

In FIGURE 2 there is shown a cross-sectional view taken along line A-A of FIGURE 1. An outer furnace wall 12 supports the smoke removal device 3. An electrode member, schematically illustrated in cross-section by the phantom lines 15, passes through the central aperture 14 of the smoke removal device 3 into the furnace interior. The outer periphery of the electrode 15 is spaced from the edge 9c of the upper housing portion 9 and defines an airgap 16 between the electrode and'the annular upper portion 9 of the housing 4. This airgap 16 may be sealed by means of a loosely arranged sealing ring if provision can be made that no short circuit will occur between the electrode and ground. However, since the provision of an effective seal between the electrode and the furnace constitutes a problem which has not been satisfactorily resolved up to the present, a preferred embodiment of the invention provides a solution for such a sealing problem. This is done by arranging a control member between the electrode 15 and the housing 4 of the smoke removal device. This control member may be, for example, a pressure probe which responds to the conditions of gas flow. As a result, it is possible to automatically control the gas removal output in such a manner that the flow velocity of the fluid medium appearing in the airgap 16 between the electrode 15 and the housing 4 practically amounts to zero. A zero value of flow velocity at this point indicates that gas cannot emerge from the furnace nor air enter into it. Since practical operation of the furnace may possibly render it difiicult when employing several electrodes, such as three or six electrodes, to avoid varying flow conditions in the individual gas exhaust ducts, each smoke removal device provided for the individual electrodes is preferably connected'to its own dust removal device and suction unit (exhaust system). The suction effect of each exhausting or suction unit may be controlled by the pressure probe provided for each respective suction unit. Such an arrangement is designed to ensure that the entry of air and the escape of gases at the electrodes is effectively inhibited even if several electrodes are employed.

Having thus described the present invention, what is desired to be secured by United States Letters Patent, is:

'1. A device for removal of smoke gas and the like from the interior of a furnace adapted to encircle an electrode at the region where said electrode enters said furnace, said device comprising an annular housing provided with an outlet conduit for removal of said gas and an internal annularly arranged flow'channel communicating with said outlet conduit, with the cross-sectional area of said annularly arranged flow channel increasing in the direction of said outlet conduit, said housing being. provided with annular slot means in registry with said flow channel permitting movement of smoke gas into said flow channel.

2. A device according to claim 1, wherein partition means are arranged atthe region of smallest cross-sectional area of said flow channel-to divide said flow channel into two substantially symmetrical segments.

3. A device according to claim 1, wherein said annular housing is constructed to provide an annular airgap adapted to receive a control member responsive to the gas flow.

4. A device according to claim 1, wherein at least a portion of said annular housing includes means formed of a non-magnetic material for counteracting the formation of induced currents.

5. A device according to claim 4, wherein said means formed of non-magnetic material is located at the point of narrowest cross-section of said flow channel for counteracting the formation of induced currents.

6. A device according to claim 1, wherein said annular housing is provided with means permitting circulation of a cooling medium through said annular housing for cooling thereof.

7. A device according to claim 7, wherein said cooling means is a cooling compartment adapted to receive a cooling medium.

8. A device according to claim 1, wherein said annular housing includes a downwardly extending portion.

9. A device according to claim 1, wherein said outlet conduit is integral with said annular housing.

10. A device for removal of smoke gas and the like from the interior of a furnace adapted to encircle an electrode at the region where said electrode enters said furnace, said device comprising an imperforate annular housing provided with an outlet conduit for removal of said gas, said annular housing having an upper housing portion, a lower base portion and an intermediate wall portion interconnecting said upper housing portion with said lower base portion to define an annular flow channel, said upper housing portion including an upper wall portion and a downwardly extending wall portion terminating at a predetermined distance from said lower base portion to define an annular slot, said annular flow channel communicating with said outlet conduit with said annular slot in registry with said annular flow channel.

11. A device for removal of smoke gas and the like from the interior of a furnace adapted to encircle an electrode at the region where said electrode enters said furnace, said device comprising an annular housing provided with an outlet conduit for removal of said gas, said annular housing having an upper housing portion, a lower base portion and an intermediate wall portion interconnecting said upper housing portion with said lower base portion to define an annular flow channel, said annular flow channel increasing in cross-sectional area in the direction of said outlet conduit, said upper housing portion including an upper wall portion and a downwardly extending wall portion terminating at a predetermined distance from said lower base portion to define an annular slot, said annular flow channel communicating with said outlet conduit with said annular slot in registry with said annular flow channel.

12. A device for removal of smoke gas and the like from the interior of a furnace adapted to encircle an electrode at the region where said electrode enters said furnace, said device comprising an annular housing provided with an outlet conduit for removal of said gas, said annular housing having an upper housing portion, a lower base portion and an intermediate wall portion interconnecting said upper housing portion with said lower base portion to define an annular flow channel, said upper housing portion including an upper wall portion and a downwardly extending wall portion terminating at a predetermined distance from said lower base portion to define an annular slot, said upper wall portion inclining upwardly in the direction of said outlet conduit and said downwardly extending wall portion increasing in width in the direction of said outlet conduit such that said annular flow channel increases in cross-sectional area in the direction of said outlet conduit, said annular flow channel communicating with said outlet conduit with said annular slot in registry with said annular flow channel.

13. A device according to claim 12, wherein said widening, downwardly extending wall portion is helically curved in the manner of at least a portion of a screw line.

References Cited in the file of this patent UNITED STATES PATENTS 2,761,003 Richardson Aug. 28, 1956 FOREIGN PATENTS 198,225 Switzerland Sept. 1, 1938

Claims

1. A DEVICE FOR REMOVAL OF SMOKE GAS AND THE LIKE FROM THE INTERIOR OF A FURNACE ADAPTED TO ENCIRCLE AN ELECTRODE AT THE REGION WHERE SAID ELECTRODE ENTERS SAID FURNACE, SAID DEVICE COMPRISING AN ANNULAR HOUSING PROVIDED WITH AN OUTLET CONDUIT FOR REMOVAL OF SAID GAS AND AN INTERNAL ANNULARLY ARRANGED FLOW CHANNEL COMMUNICATING WITH SAID OUTLET CONDUIT, WITH THE CROSS-SECTIONAL AREA OF SAID ANNULARLY ARRANGED FLOW CHANNEL INCREASING IN THE DIRECTION OF SAID OUTLET CONDUIT, SAID HOUSING BEING PROVIDED WITH ANNULAR SLOT MEANS IN REGISTRY WITH SAID FLOW CHANNEL PERMITTING MOVEMENT OF SMOKE GAS INTO SAID FLOW CHANNEL.