US2592517A

US2592517A - Closed electric furnace

Info

Publication number: US2592517A
Application number: US189402A
Authority: US
Inventors: Ingelsrud Arne Hildor
Original assignee: Elektrokemisk AS
Current assignee: Elektrokemisk AS
Priority date: 1944-06-16
Filing date: 1950-10-10
Publication date: 1952-04-08
Anticipated expiration: 1969-04-08
Also published as: CH254393A; AT164253B; ES172689A1; DE824813C; GB613949A

Description

April 8, 1952 A. H. INGELSRUD 2,592,517

cLosED ELECTRIC FURNACE Filed oct. 10. 195o s sheets-sheet 1 @j vf '14 INVEV TOR.

April 8, 1952 A. H. INGELSRUD CLOSED ELECTRIC FURNACE Filed oct". 10, 195o 3 Sheets-Sheet 2 RM n o# m ww. m E m/ rQA MM j@ April 8, 1952 A. H. INGELSRUD CLOSED ELECTRIC FURNACE Filed 00L l0, 1950 INVENTOR.

/Jfwd #Trop/vm Patented Apr. 8, 1952 CLOSED ELECTRIC FURNACE Arne Hildor Ingelsrud, Oslo, Norway, assignor to Elektrokemisk A/ S, a corporation of Norway Application October 10, 1950, Serial No. 189,402 In Norway Junev 16, 1944 Claims.

This invention relates to closed electric furnaces of the type adapted for use in making calcium carbide, ferro-alloys and other products demanding high temperatures.

The furnace of my invention has a main body portion above which is suspended a metal roof. The electrodes pass through the roof.

Ordinarily the roof will be made with a substantlally flat portion and side portions running down to meet the body of the furnace. These roof members preferably are water-cooled and may be supported in any desired way. For example, they may be suspended from a superstructure associated with the furnace unit. For electrical reasons the roof must be made of separate sections electrically insulated from each other and a field with magnetic insulation should also be introduced to reduce the inductive loss or voltage as much as possible at the points where the electrodes pass through the roof. This is an added reason for making the roof in separate sections which may be exchanged individually and bolted together. The roof is electrically insulated from the electrodes and preferably from the suspension mechanism and from the furnace body on which the edges of the roof ordinarily rest.

With furnaces of this type great dimculty has been found in so arranging the charging shafts that proper flow of the material is obtained and the escape of the developed gases so taken care of that explosions within the furnace are avoided as Well as extensive leakage directly around the electrode. The present invention relates to an apparatus in which the escape of the developed gases is taken care of and at the same time the eiciency of the furnace is maintained.

In order to prevent the formation of crust-s and resulting craters in the charge, it is desirable that the charge be introduced into the furnace zone at a distance from the electrode so that there is a continuous flow of material from the mouth of the charging shaft downwardly and inwardly toward the electrode. The gases can readily escape through this moving surface. In such cases the gases surround the electrode but they must be withdrawn at a distance from the electrode, as it is highly inefficient to have them burned where the ignition will directly affect the electrode.

I have succeeded in solving these problems by running down from the furnace roof a ring approximately concentric with the electrode but spaced outwardly from it. The clamps that suspend the electrode and carry current to it preferably go down into this ring zone and are provided with a circular jacketing member which makes a gas-tight joint with the electrode and which preferably is water-cooled. This member is concentric with the electrode and its surface is such that it can be maintained quite smooth. A sliding contact can then be maintained between the surface of this member and the ring member referred to so that a relatively good gas-tight joint can be maintained between the electrode and the ring member while permitting continuous vertical movement or agitation of the electrode.

This ring member serves as the inner limit of the charging shafts for the .material to ce introduced into the furnace and the flow of the charge will be from this ring member toward the electrode surface so that the gas can escape directly up into the space between the electrode and the ring member.

I have found that it is desirable to withdraw the gas from this gas-collecting space either through or below the lower edge of the ring member. To this end the charging shafts do not entirely surround the ring member but segmental vspaces are left between the charging shafts through which the gases can be withdrawn. The ideal condition for efficiency of the furnace would call for an equal charge being delivered completely around the electrode but gas removal makes this a practical impossibility. Wherever a space is left between the charging shafts the charge will reach the electrode surface at a point somewhat lower than the average, forming valleys at these points. The electrical eiciency of the furnace is a function of the distance between the point where the clamps are attached to the electrode and the average height of the reduction zone. If large valleys are formed this average distance is increased and the efficiency of the furnace is lowered. I have found in al1 cases the angular distance between the charging shafts should be less than and preferably not over 45. That is each space between the charging shafts should be less than one-sixth and preferably not more than one-eighth of the ring perimeter. A simple construction involves the use of three segmental charging shafts and in such case the charging shafts occupy a major proportion of the peripheral space about the ring member. However, it is keeping the angular distance between the charging shafts low which is of primary importance and by increasing the number of shafts the angular distance between them can be so reduced that eiiicient results can be obtained without actually having the charging shafts occupy a major proportion of the peripheral area. For example, if four equal charging shafts are employed that occupy exactly half the peripheral area, the angular distance between them will be only 45.

While the valleys formed between the charging shafts tend to interfere with the electrical eciency of the furnace, these valleys serve to supply passages for the escape of gas from the inner ring member to the general furnace area. At or near the point where minimum permissible efciency is had (where the angular distance between the passages approaches 60) the valleys may be big enough to permit all of the gas to escape, but inasmuch as smaller valleys are preferable, I have found that in most cases it is essential to provide separate passages for the removal of the gas from within the innerr ring member. Such passages may be in the form of notches at the bottom of the ring member, opening into the `spaces between the charging shafts or they may be actual holes through the ring members above the bottom edge. The gases that enter the spaces between the charging shafts may be led from them directly to points outside the furnace or they may go through these spaces into the general furnace area and then the gases may be withdrawn by appropriate passages through the roof of the furnace.

I have found that in some applications the design of the roof can with advantage be modiiled by leaving out the side portions of the roof, maintaining only the central flat portion of the roof leaving the peripheral part open, which gives the advantage of free access to theA charge for stoking in the charge when desired, and facilitates a close observation and supervision of the smelting conditions in the furnace. The gas can escape readily through the small valleys between the segmental charging shafts into the central portion of the furnace or may be withdrawn through one or more appropriate open- This invention can be readily understood by reference to the accompanying drawings in which Fig. 1 shows a section through a part of the furnace around the electrode; Fig. 2 shows a plan view partly in section of the same parts: of the furnace shown in Fig. 1; Fig. 3 is a viewcorresponding generally to Fig. 1 showing a modified form of construction; Fig. 4 is a plan view of the parts shown in Fig. 3; Fig. 5 is a sectional view showing one of the passages for the escape of gas in the charging material adjacent such passage; Fig. 6 is a development of the bottom of the inner ring member of the construction shown in Fig. showing the-relationship of the depth of valley to the angular distance between the charging shafts; Fig. 7 is a development of a similar ring member where three charging shafts are employed spaced approximately 60 apart and no passage is cut through the ring member for the escape of gases, and Fig. 8 is a development of a ring member where four charging shafts are employed occupying only about half the peripheral area of the ring member but with anv angular distance between them of only 45 and in this case the gas passages are holes through the ring member instead of notches cut in the bottom of the ring member.

Referring now to Fig. l, ID is the electrode. I2

is the contact member which supplies the electric current through the conductors I4. As is usual, these are made flexible so that the electrode can be raised and lowered. I6 `is a protecting casing surrounding the contact arrangement and is preferably water-cooled. The lower end of member I8 is the pressure ring I8 whose vertical position determines the pressure between the contact members I2 and the electrode I This arrangement insures a gas-tight jointbetween member I8 and the electrode I0.

2|) is a ring-like shaft for introduction of the raw materials. rlhe inner rim of this shaft is formed by the cylinder wall or" ring member 22 which is preferably water-cooled. Preferably the bottom of this ring is above the furnace wall 23 as this simplifies inspection and possible stoking. 24 is a pipe connecting the furnace hoppers with the shaft. 26 is a packing arrangement forming an electrically insulated packing between the inner shaft ring 22 and the protecting casing I6 surrounding the contact arrangement I2. Since casing I6 is water-cooled and has a smooth cylindrical surface, a much better sliding contact can be made against it than against the surface of the electrode. In order to prevent the deposition of dust between contact members and the protecting casing, the space between them is preferably kept under pressure slightly above atmospheric; for example, by returning some furnace gas to this area. The numeral 28 represents the furnace roof which may be water-cooled and 30 indicates the exit pipes for the gas. Two such exit pipes are shown, one running outwardly and downward tok the side, and the other extending upwardly from the center of the furnace. suspension iron for the roof which may be connected at any convenient point to the xed structure surrounding the furnace but this should be electrically insulated from such structure and the connection should allow some flexibility as indicated by the spring 34. Preferably three such suspension members are provided and are connected to a magnetically insulated roof section forming a single part of the furnace roof 36.`

In the example illustrated, as shown in Fig. 2, the charging ring is subdivided into three segments by gas conduits as indicated at 38 which take up a minor portion of the circumferential area. Each of these conduits is provided with a door 40 through which the interior of the furnace is inspected and adjusted. The lid over each such door is constructed to act as an explosion valve. Other explosion and inspection doors 42 are positioned at suitable places in the roof.

As shown in Fig. 1 gas passages 31 are cut in the cylinder wall 22 opposite each of the gas conduits 38. It will also be noted (and this is particularly shown in Fig. 5) `that the charging material coming in to the side of each such conduit will slope toward the center of such conduit making a relatively small valley so as to keep Y the material around the electrode nearly even.

Even though these valleys are relatively small, they supply some area for gas escape, and asv their size is increased within permissible limits (as illustrated later), the area of the passages through ring 22 may be reduced in size but it is only rarely and in an extreme case that the gas passages through ring 22 can be eliminated. In this example the gas conduits 38 take the gas to the general furnace area from which it can be withdrawn through the pipes 3U.

The structure shown in Figs. 3 and 4 is similar 32 shows a to that shown in Figs. 1 andv 2 except that here the electrode Il is provided with the clamping members I3 and the pressure ring I 9 all of which are above the furnace roof. In `this case a special closure ring 44 is provided with a separate packing ring 4E and these two together act to insulate the electrode from the furnace roof. In these figures the outer ring of the charging shaft is designated as 2l and the inner ring as 23.

In Fig. 5 the relationship of the gas conduits is shown as has previously been described.

In Fig. 6 I show a development of the bottom portion of the ring member 22 and it is obvious that in this case where the space between adjacent charging shafts is only about 40 and where these shafts occupy the major proportion of the area immediately around the ring member 22, the valleys formed because of the charging shafts will be small. This makes for highly efficient electrical operation but it will be seen that the valley itself will only offer a small area for the escape of gas. Accordingly the bottom of the ring is cut away as indicated at 3l to increase the size of the passage for gas iiow.

In Fig. 7 the ring member is designated as 22a and in this case again three charging shafts are shown but the space between the charging shafts is substantially equal to the peripheral area occupied by the charging shafts which means that the space between adjacent charging shafts reaches the permissible maximum of about 60. The electrical efficiency is lowered somewhat but is still way above that had with previous types of furnaces. In this case the area of the valley is large enough so that there is no serious danger of building up gas pressure and it is possible to operate such a furnace without cutting separate passages through the ring member 22a for the escape of gas.

In Fig. 8 a similar development is shown, with the ring member designated as 22h. In this case four charging shafts are shown, and again the charging shafts occupy approximately one-half of the peripheral area around the ring member but due to their increase in number, the distance between adjacent charging shafts is only about 45. In this case a separate opening for the withdrawal of gas is formed above the bottom of the ring member 22h for each space between the shafts and is designated by the numeral 44. As most of the gas will escape through these passages 44 it may, if desired, be conducted directly to the exterior of the furnace by appropriate passages not shown.

In Figures 6, 7 and 8 the charge is not shown but in each of these figures the valleys below the spaces between the shafts is indicated by broken lines and the top line of the charge at the electrode is indicated by dot and dash lines.

This application is a continuation in part of my earlier application Serial No. 672,029 filed May 24, 1946, now forfeited.

What I claim is:

1. In a furnace of the type described a furnace casing, a roof for the casing above the furnace casing, a circular opening in the roof, a ring member in said opening extending down from the roof, an electrode movable within said ring of smaller diameter than the ring member, means for making a substantially gas-tight sliding connection between said electrode and said ring member so that the electrode may move in and out relative to the furnace casing while the pcripheral area within the ring member forms a gas chamber, segmental charging shafts extendingzthrough the roof with said ring member forming the 'inner boundaries thereof and with their outer boundaries inside the inner line of the furnacev casing, .and `segmental spaces between such charging shafts which are of an average width equal to not more than one-sixth `of the peripheral distance around the ring member so that the charging shafts largely surround `but are'spaced from the electrode with the result .that a charge introduced through such shafts will slope toward the electrode to surround the same with relatively shallow Valleys within thecharge below the ring member located below the segmental spaces between the charging shafts through which gases may escape from within the ring member.

2. A structure as specified in claim 1 in which the angular distance between adjacent charging shafts does not exceed 45 and in which passages are formed in the ring member to provide area for the withdrawal of gases in addition to the area of the valleys in the charge below the segmental spaces between the charging shafts.

3. A structure as specified in claim l in which a water-cooled cylindrical member is clamped around the electrode to form a gas-tight joint and the sliding connection is made between such cylindrical member and the said ring.

4. A structure as specified in claim 1 in which said ring member carries an internal packing ring adapted to rub against the face of the movable electrode to make a substantially gas-tight sliding connection between the electrode and said ring member.

5. A structure as specified in claim 1 in which the charging shafts occupy the major proportion of the area immediately around said ring and passages are formed in the ring member for withdrawing gases from within such ring in the line of the spaces between the charging shafts.

6. A structure as specified in claim l in which said ring member extends down from the furnace roof but does not extend below the top of the furnace casing.

7. A structure as specified in claim l in which there are a plurality of circular openings through the roof of the ring members and electrodes for each and a central passage is provided through the roof for withdrawing gases from within the furnace structure.

8. A structure as specified in claim 1 in which the roof has portions extending down to make a connection with the furnace casing.

9. In a furnace of the type described a furnace casing, a roof for the casing above the furnace casing having portions extending down to make a connection with the furnace casing, a circular opening in the roof, a ring member in said opening extending down from the roof, an electrode movable within said ring member of smaller diameter than the ring member, means for making a substantially gas-tight sliding connection between said electrode and said ring member so that the electrode may move in and out relative to the furnace casing while the peripheral area within the ring member forms a gas chamber, segmental charging shafts through the roof of the said ring member forming the inner boundaries thereof and with their outer boundaries inside the inner line of the furnace casing and occupying a major proportion of the peripheral space about said ring member, with spaces between such charging shafts so that the charging shafts largely surround but are spaced from the electrode, with the result that 'a charge introduced through such shafts will slope toward the electrode to surround the'same with relatively shallow valleys in the charge below the ring member, passages fori the escape of gas formed in the lower part of the ring member leading into the body of the furnace chamber, and means for withdrawing gas from within the furnace chamber.

10. A structure as specied in claim 9 in which the passages for the escape of gas formed in the lower part of the ring member extend to the bottom of the ring member so that they will cooperate with the valleys that may be formed in the charge to provide space for the escape of gases from within the ring member.

ARNE HILDOR. INGELSRUD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 826,742 Price July 24, 1906 842,099 Landis Jan. 22, 1907 u; 1,223,278 Helfenstein Apr. 17, 1917 1,496,232 Klugh June 3, 1924 2,286,732 Hardin June 16, 1942 FOREIGN PATENTS 15 Number Country Date 6,237 Norway May 2, 1898