US1902668A - Electric furnace - Google Patents

Description

March 21, 1933. c. c. scHwr-:GLER

ELECTRIC FURNACE FiledvMay 14, 1932 2 Shees-Sheel 2' ATTQRNEY less of thevapor may not be Patented 21, `19.33;.

UNITED ys'rlvrss PATENT l OFFICE COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION 0F MICHIGAN ELECTRIC Application filed May 14,

The present invention relates to electric furnaces for the manufacture of carbon bisulphide, and has particular regard to im'- provements in means for /controlling the op- 5 eration of such furnaces.

The general process for the electrothermic production of carbon bisulphide is carried out, as is well knoiwn, by charging an electric furnace, commonly of the shaft type, with a body of wood charcoal or othersuitable carbon material'which surrounds and covers the furnace electrodes and provides a conductive material to carry the current between the electrodes; heating the charcoal in .the electrode zone to a red hea-t by passing the electric current therethrough; introducing sulphur into such hot zone wherein reaction between sulphur and carbon takes place; and finally removing and condensing the vapors of carbon bisulphide thereby formed. In order to improve the conductivity of the charcoal' it has been the practice to miX therewith pieces of hard carbon or graphite, such as broken electrodes. A relatively large body of carbon material is maintained in the furnace, which feeds downwardly by gravity into the reaction zone, and is replenished from time to .time by additions of more material. The sulphur may be introduced either in solid, liquid or vapor form, but for the best control of temperature in the furnace it is preferable to vaporize the sulphur outside of the furnace and to introduce the vapors into the hot reaction zone.

'5 On account of local changes in the density and conductivity of the charge in the furnace, or other causes, the hot reaction zone does not remain in a fixed position relative to the electrodes, but tends toshift or migrate both laterally and vertically within the body of charcoal constituting the charge. This condition exists in greater degree in furnaces of large capacity employing a number of electrodes in `which a plurality of current paths is formed.` Various disturbances in the operation of the furnace are causedby the shifting of the hot reaction zone. For instance, if the reactionzone is moved away from the location of the sulphur vapor inlet, more or brought in .con-

FURNACE- 1932. seria1m.e11,313. l

of entry of the sulphur vapor, the greater is.

the loss in yield fof product due to escape of unreacted sulphur. The condition does not 'j CLARENCE C. SCHWEGLER, OF MIDLAND, MICHIGAN Q ASSIGNOR T0 THE DOW' CHEMICAL correct itself, but once started tends to become continually worse, and if the hot zone approaches closely to the furnace walls may cause fusion and slagging thereof.

I have found that the diiiiculties arising Y from the aforementioned tendency for dis` placement of the hot reaction zone may be counteracted or prevented by providing means for varyin the distribution of elec` tric current within the charge, as vwell 'as for selectively controlling the introduction of sulphur vapor thereto. A further advantage is that I may control positively the displacement of the reaction zone. In my prior application Serial No. 487,449, filed Oct. 9, 1930, I have described and claimed an improved electric furnace wherein the sulphur vapor is introduced at a plurality of inlets distributed at a level below the electrodes. Such arrangement has been found disadvantageous for the reason that the residual ash of the carbon material consumed in the reaction melts and forms a slag, which, although it may be tapped off periodically as required,l nevertheless tends to congeal around the walls of the furnace below the electrode zone, thereby often stopping up the inlet ports for the sulphur vapor. The present application describes a modification of the furnace disclosed in said prior application, wherein the inlet ports forsulphur vapor are located at or above the level of the electrodes. Means are alsoprovided to facilitate the removal of the slag from the furnace. The invention, then,'consists in 'the' improved ,electric furnace illustrated in the annexed drawings and hereinafter fully described and particularly pointed out inthe claims. f

In said annexed drawings Fig. l shows in vertical section on the line l-lof Fig. 2 a preferred form of 'electric furnace according tothe invention. Fig. 2 100 is a horizontal cross section on the line 2 2 of Fig. 1. Figs. 3 and 4 show alternative electrode arrangements.

Referring to the drawings, the furnace casing 3 consists of an upright steel shell the lower part of which is cylindrical up to a shoulder 4, and the upper part of which above the shoulder converges toward the top in the form of a truncated cone. The casing is provided with a sloping hearth 5 and a thick lining 6 of fire brick or other refractory material forming a chamber to contain the reaction materials. A tap-hole 7 is provided in the wall on the lowside of the hearth 5. A closable feeding hopper 8 for charging charcoal is located at the top, and an eXit ipe 9 for the reaction vapors. In the shoullder 4 are provided closable inlets 10 for charging conducting carbon. A plurality of carbon or graphite electrodes 11 are inserted horizontally through the side walls at a level a short distance above the bottom, the number thereof preferably, but not necessarily, being three, or a multiple of three, adapted for use with three-phase alternating current. A preferred arrangement consists of siX electrodes arranged in pairs equally spaced about the periphery `of the chamber, as shown in Fig. 2. An inlet 12 for sulphur vapor communicates with a conduit or header 13 which is set in the furnace lining as shown, such arrangement enablingA the header to serve also as a preheater for the vapor. A plurality of branches 14 for introducing sulphur vapor into the furnace are tapped off from header 13 at a point midway between the pairs of electrodes, each branch terminating in a port 15 which is controlled by a valve 16. Branches 14, which are preferably of refractory material, project a short dis' tance into the furnace chamber, and may be protected by corbeling of the brick linf ing, as shown. The sulphur inlet ports 15 are located at a level not lower than that of the electrodes 11, and preferably at about the same level-as the latter.

Each pair of electrodes 11`is connected by separate leads 17 to one phase of a three- Aphase source of alternating current. `Each lead wire iis provided with a switch 18, through which connection is made to the ter- Ininals of secondary- coils 19a, 196 and 190 of three transformers, one transformer serving one pair of electrodes. Primary coils 20a, 205 and 20c of the transformers are connected to a suitable high-voltage alternating current transmission line. coil is provided with a plurality of taps or vcontacts 21 from the lead wire whereby to vary the length of winding in circuit, and hencethe voltage induced in the secondary coil circuits. By means of switches 18 and taps 21 it is possible to cut in or out any electrode, or to vary the voltage thereof, at will.

Located near the bottom or hearth of the Each primary furnace, preferably close to the tap-hole 7, is

-195 of one of the transformers. The purpose of electrode 22 is to assist in fusing the ash accumulated in the bottom of the furnace, so asf to form a liquid slag which maybe tapped o To operate the apparatus, the furnace chamber is charged nearly full with charcoal through hopper 8, and a small proportion of conducting carbon, e. g. about 1/20 to`1/40 of the charcoal y by volume, is added to the charge through inlets 10, which are preferably located above the electrodes, so that the conducting carbon as it feeds downwardly with the furnace charge is brought intol contact with the electrodes. Electric current is passed through the charge between the electrodes at a suitable voltage, e. g. about 40 to 80volts, until the Zone in the vicinity of the electrodes is heated to a red heat, e. g. between about 600 and 800 C. Then sulphur vapor, from a vaporizer not shown, is introduced from inlet 12 through ports 15, the vaserved through sight-holes and by means of f pyrometers whereby to determine suitable handling of operating controls for maintaining the desired conditions. If the hot zone is observed to shift toofar toward the sidewall of the furnace, valves 16 may be operated to feed sulphur vapor on the hot side, and to shut it oi on the cold side. p At the same time one or more of the electrodes on the hot side may be cut out or the voltage thereon reduced, thus shifting the currentA How mostlv to the cold side. By combining the foregoing means of control, or by either of them, the migration of the hot reaction zone may be held within suitable limits to prevent injury to the furnace lining, while loss of sulphur is avoided by selectively introducing the same at the ports located close to the hot zone. l

With a combination of six electrodes arranged in closely spaced pairs of same polarity, as shown in Fig. 2, various advantages are gained. For instance, the dead or inactive space between electrodes of like polarity is reduced to a low figure, while the length of current path between the several pairs is approximately the same, thereby equalizing the thermal effect of the current flow therebetween and avoiding overheating' whichwould be caused if the current paths were of unequal length. If desired, however, an approximately equal spacing ofvthe electrodes about the periphery of the. furnace in a common plane may be employed, as shown in Fig.' 3. Instead of being spaced apart horizontally in the same plane, however, the electrodes may also be spaced one above the other in pairs, as shown in Fig. 4, with substantially the same beneficial results. A somewhat less flexible arrangement is provided by employing a ysingle electrode `in each phase, instead of two or more, b'ut in other respects a similar mode of. operation may be followed therewith, and a similar control of the furnace operation may be had. l

A s previously indicated, the hot reaction zone may tend to rise upwardly as well as laterally with respect to the position of the electrodes. yI have found it advantageous to control such vertical displacement in a positive manner, which I am enabled to accomplish by appropriate manipulation of the ,operating controls of the furnace hereindescribed. F orexample, the voltage on the electrodes may be increased, thereby increasing the current and, as a result, the heating effect caused by the current, which increases the temperature of the hot lzone above thef normal. The hot zone is thus enlarged and spreads upwardly until it reaches a level considerably above that of the electrodes. When the hot zone has reached a suitably high level, the voltage ymay be reducedl to normal again, and the supply of sulphur vapor may also be increased. This has the elfect of lowering the temperature of the lcharge in the immediate vicinity of the electrodes, since the temperature in the direct path `of the current depends upon the strength of the current modified by the cooling effect of the sulphur vapors as they are introduced. I have found, however, that the upper part of the hot zone is less sensitive to changes in conditions adecting the temperature, so that the upper part thereof. if sufficiently elevated above the level of the electrodes, may remain at a higher temperature after the charge adjacent the electrodes has been lowered in temperature. Under such a condition the elevated hot zone, in which the reaction of carbon and sulphur principally takes place, becomes'more or less separated and detached from direct contact with the electrodes, and may-be maintained in such a position at a suitable temperature largely by the heat of reaction of the carbon andy sulphur. Operating in this way, the portion of the charge in the direct path of the current between the electrodes becomes mostly .a preheating zone for the sulphur vapors to raise the sa'me up to reaction temperature. By causing the hot 4reaction zone to be maintained at a higher level than that of the electrodes, heat losses from the furnace by conduction through the electrodes y are greatly reduced. Another advantage is that, after operation as aforesaid is once established, a lower power input is sufficient for operating the furnace than when the reaction is centered in the electrode zone it` self. Still further, the electrodes are less rapidly attacked and consumed, so that they remain in serviceable condition for much longer periods.

Due to the mineral content ofthe carbon material there is a gradual accumulation of ash in the furnace below the reaction zone. This may be removed periodically as required by temporarily increasing the power input sufficiently to melt the ash and form a fluid slag whichA runs down into the bottom of the furnace and may be tapped off. To assist removing the slag, auxiliary electrode 22 may be switched on, thereby producing additional heat below the principal electrode zone whereby to prevent the molten slag from congealing and to maintain it in fluid condition to drain od properly when the tap-hole is opened.A Except when -so used, electrode 22 would notl be connected in service.

In operating an electric furnace of the type, and in the manner, described I have found it possible to maintain the same uninterruptedly in service over a period of many months. rlhe invention upon which the aforementioned advantages depend, concisely stated, consists in an improved electric furnace of the shaft type for the manufacture of carbon bisulphide which is provided with a plurality of electrodes laterally inserted in a belt or zone in the lower part of the shaft, a plurality of inlet ports for sulphur vapor at approximately the same level as the electrodes, such ports branching from a common header which is preferably encased within the furnace wall or lining, means for selectively varying the'voltage of the electrodes or for disconnecting the same individually and means for selectively and independently controlling the introduction of sulphur vapor at each of the inlet ports therefor, together with accessory means for melting and drawing ofl' slag at suitable intervals.

Other modes of applying the principle .off

my invention may be employed instead of the one explained, change being made as regards the apparatus herein disclosed. provided the means stated by any of the following claims or the equivalent ofvsuch stated means be emtrodes laterally inserted through the walls of said chamber, a source of electric current for sald electrodes, switch means to control each electrode independently, a plurality of inlet.

a chamber enclosed by walls of refractory heat-insulating material, three, or a multiple thereof, electrodes laterally inserted through the walls of said chamber', a three-phase source of electric current, transformer means comprising primary and secondary coils, electrical connections from said secondary coils to each of said electrodes, switch means to control each electrode independently, a plurality of inlet ports for introducing sulphur vapor into said chamber, said ports being at a level not substantially below that of the electrodes, a header connecting said inlet ports for supplying sulphur vapor thereto, and valve means for independently controlling said inlet ports.

3. In an electric furnace for the manufacture of carbon bisulphide, the combination of a chamber enclosed by walls of refractory heat-insulating material, three, or a multiple thereof, electrodes laterally inserted through the walls of said chamber, a A three-phase source of electric current, transformer means comprising primary and secondary coils, electrical connections from said source of current to said primary coils including adjustable contacts for varying the number of windings thereof connected in circuit, other electrical connections from said secondary coils to each of said electrodes, switch means to control each electrode independently, a plurality of inlet ports for introducing sulphur vapor into n said chamber, said ports being at a level not substantially below that of the electrodes, a

header connecting said inlet ports for supplying sulphur vapor thereto, and valve means for independently controlling said inlet ports.

4. In an electric furnace for the manufacture of carbon bisulphide, the combination of a chamber enclosed by walls of refractory heat-insulating material, three, or a multiple thereof, electrodes laterally inserted through 'the walls of said chamber, a three-phase source of electric current, transformer means comprising primaryl and secondary coils, electrical connections from said source of current to said primary coils including adjustable contacts for varying the number of windings thereof connected in circuit, other electrical connections from said secondary coils to each of said electrodes, switch means to control each electrode independently, a

plurality of inlet ports for introducing sulphur vapor into said chamber, said ports being at a level not substantially below that of the electrodes, a header connecting said inlet ports for supplying sulphur vapor thereto, valve means for independently controlling said inlet ports, and means including an auxiliary electrode for melting and removing slag from the furnace.

5. In an electric furnace/for the manufacture of carbon bisulphide, the combination of a chamber in the form of a shaft enclosed by walls of refractory heat-insulatingmaterial, three,or a multiple thereof, horizontal electrodes inserted through the walls of said chamber, a three-phase source of electric current, transformer means comprising primary and secondary coils, electrical connectlons from said secondary coils to each of said electrodes, switch means to control each electrode independently, a plurality of inlet ports for introducing sulphur vapor into said chamber, said ports being at a level not substantially below that of the electrodes, a header connecting said inletv ports for supplying sulphur vapor thereto, said header being encased within the walls of said chamber, and

valve means for independently controllingv said inlet ports.

6. In an electric furnace for the manufacture of carbon bisulphide, the combination of a chamber in the form of a shaft enclosed by walls of refractory heat-insulating material, three, or a multiple thereof, horizontal electrodes inserted through the walls of said chamber, a three-phase source of electric current, transformer means comprising primary and secondary coils, electrical connections from said source of current to said primary coils including adjustable contacts for varying the number of windings thereof connected in circuit, other electrical connections from said secondary coils to each of said electrodes,- switch means to control each. electrode independently, a plurality of inlet ports for introducing sulphur vapor into said chamber, said ports being at a level not substantially below that of the electrodes, a header connecting said inlet ports for supplying sulphur vapor thereto, said header being encased within the Walls of said chamber,

and valve means for independently controlling said inlet ports. f

7 In an electric furnace for the manufacturev of carbon bisulphide, the combination of a chamber in the form of a shaft enclosed by walls of refractory heat-insulating material, three, or a mltiple thereof,horizonta electrodes inserted through the walls of sai chamber, a three-phase source of electric current, transformer means comprising primary and secondary coils, electrical connections from said source, of current to said primary coils including adjustable contacts for varying the number of windings thereof connected in circuit, other electrical connections from said secondary coils to each of said electrodes, switch means to control each electrode independently, a plurality of inlet ports for introducing sulphur vapor into said chamber, said ports being at a level not substantially below that of the electrodes, a header connecting said inlet ports for supplying sulphur vapor thereto, said header being encased Within the Walls of said chamber, valve means for independently controlling said inlet ports, and means including an auxiliary electrode for melting and removing slag from the furnace.

8. Apparatus claimed in claim in which six electrodes are employed and disposed in pairs that are approximately equallyfspaced in a common pla-ne about the periphery of the chamber.

9. Apparatus claimed in claim 6 in which six electrodes are employed and disposed in y pairs that are approximately equally spaced 1n a common plane about the periphery of the chamber.

10. Apparatus claimed in claim 7 in which six 4electrodes are employed and disposed in pairsithat are approximately equally spaced in a common plane about the periphery of thechamber.

l1. Apparatus claimed in claim 5 in Which six electrodes are employed and disposed in pairs that are approximately equally spaced l in a common plane about the periphery of the chamber, and in which the inlet ports for sulphur vapor are located in the same plane between the pairs of electrodes.

12. Apparatus claimed in claim 6 in which six electrodes are employed and disposed in pairs that are 'approximately equally spaced in a common plane about the periphery of the chamber, and in which the inlet ports for sulphur Vapor are located in the same plane between the pairs of electrodes.

13. Apparatus claimed in claim 7 in which six electrodes are employed and disposed in pairs that are approximately equally spaced in a common plane about the periphery of the chamber, and in which the inlet ports for sulphur vapor are located in the same plane between the pairs of electrodes.

Signed by me this 9 day of May 1932.

' CLARENCE C. SCHWEGLER.

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