US3549943A - Rotating electrode and gas arc heater employing the same - Google Patents

Description

United States Patent (DOG) [72] Inventors Charles 11. Church Alexandria, Va.; Leslie S. Frost, Pittsburgh, Pa. [21] Appl. No. 748,120 [22] Filed June 25,1968 [45] Patented Dec. 22, 1970 [73] Assignee Westinghouse Electric Corporation Pittsburgh, Pa. a corporation of Pennsylvania Continuation-impart of application Ser. No. 435,624, Feb. 26, 1965, now abandoned. This application June 25, 1968, Ser. No. 748,120

[54] ROTATING ELECTRODE AND GAS ARC HEATER EMPLOYING THE SAME 14 Claims, 6 Drawing Figs.

[52] U.S.C1. 315/111, 13/10, 219/347, 219/383, 313/149, 313/231 [51] Int. Cl 1101i l/44, 1-101j7/24,1-105h 7/18 [50] Field olSearch 315/111; 313/149, 231; 219/284, 347, 383, 232, 69; 13/9, 10, 33, 35; 263/40, (inquired); l65/(lnquired), 133; 313/147; 13/11 [56] References Cited UNITED STATES PATENTS 739,921 9/1903 Pauling 31 3/149X 758,775 5/1904 Pauling..... 313/149X 1,097,895 5/1914 Thomson 219/47 1,128,640 2/1915 Von Wilmowsky 219/383 13 AIR m 1,465,241 8/1923 Townsend 219/87 1,735,161 11/1929 Dufour 313/149X 2,512,301 6/1950 Breese 431/261 2,519,616 8/1950 Watkins 263/40 2,707,744 5/1955 Meaker 219/384 2,785,280 3/1957 Eisler et al. 219/69 3,014,115 12/1961 lngersoll 219/273 3,103,574 9/1963 Chellis et al. 219/383 3,239,593 3/1966 Maier et a1... 13/9 3,316,444 4/1967 Mentz 315/111 3,338,808 8/1967 Johnson 2l9/69X 958,855 5/1910 Danne 313/149X 2,007,225 7/1935 Strobel 219/69 2,070,475 2/1937 Dufour..." 313/149X 2,796,452 6/1957 1(rall 13/35 3,420,939 1/1969 Schlienger 13/9X Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Attorneys-A. T, Stratton, Clement L. McHale and M. 1. Hull ABSTRACT: An electrode from which an arc takes place to a passing through the chamber a number of times thereby increasing the percentage of the energy of the emitted radiation utilized in heating the gas.

ROTATING ELECTRODE AND GAS ARC HEATER EMPLOYING THE SAME This application is a continuation-in-part of copending application Ser. No. 435,624, filed Feb. 26, 1965, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improvements in electric are heating apparatus and more particularly to an improved gas arc heater having rotating electrodes, and to an improved rotating electrode.

2. Description of the Prior Art In large gas are heater units such as are used in high temperature wind tunnels, a major problem is the loss of energy due to radiation emitted by the arc itself. This energy is not effective in heating the gas, and is usually lost to the surroundings.

SUMMARY OF THE INVENTION We have solved the problem of utilizing the radiated energy to assist in heating the gas in the arc chamber. In summary, in our gas are heater the arc is fixed in space and takes place between electrodes at least one of which is rotating. The are takes place in a chamber having a reflecting wall or walls, with the are being located at substantially the optical center of the spherical or cylindrical reflective enclosure, the radiation emitted by the are being reimaged by the spherical or cylindrical reflecting mirror or surface back into the arc and passing through the arc chamber a number of times. In passing through the arc chamber three times, for example, about 51 percent of the energy of the emitted radiation may be recovered and utilized in heating the gas passing through the arc chamber.

In more general terms, we have provided an improved rotatable electrode which we rotate to substantially continuously move the are spot over the arcing surface and reduce the rate of erosion of material from the arcing surface, and employ the electrode in combination with an'at least partially enclosed vessel containing material to be heated.

Accordingly, a primary object of our invention is to provide a new and improved gas arc heater offering advantages over any now existing in the art.

Another object is to provide a new and improved gas arc heater employing a rotating electrode or electrodes.

A further object is to provide a new and improved gas are heater in which the position of the arc remains substantially unchanged during the heating process; the arc is located at the optical center of spherical chamber, or at the axis of a cylindrical reflective enclosure, so that the radiation is reirnaged through the arc chamber.

Still another object is to provide an improved rotating electrode.

Still a further object is to provide improved electric arc heating apparatus.

These and other objects will become more clearly apparent after a study of the following specification, when read in connection with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a sectional view of our invention according to the preferred embodiment thereof;

FIG. 2 is a fragmentary view of nonsegmented electrodes according to a second embodiment of our invention;

FIG. 3 is a fragmentary view of electrodes according to a third embodiment of our invention;

FIG. 4 is a view of high current electric arc furnace apparatus in which our rotating electrode according to one configuration thereof is used to special advantage;

FIG. 5 is a fragmentary view partially in elevation and partially in section along the line V-V of FIG. 4; and

FIG. 6 is a fragmentary view partially in elevation and partially in section showing our rotating electrode with a different configuration used in high current electric arc furnace apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings for a more detailed understanding of the invention, and in particular to FIG. 1 thereof, there is shown at If) the wall of an arc heater 9 having an arc chamber generally designated ll. It will be understood that in accordance with conventional practice the wall 10 of the arc chamber may be fluid cooled, for example, by a plurality of conduits embedded in, or passageways disposed in, the metal forming the wall 10, and having a cooling fluid flowing therethrough under pressure. It will also be understood that the arc chamber ll shown as having a wall 10 may be enclosed in a housing, not shown, ruggedly constructed to withstand high operating pressures in the arc chamber, any convenient housing being provided if desired. The arc chamber generally designated II has air or other gas admitted thereto through the passageway in inlet 12 communicating with opening I3 in the wall It). Inlet 12 may have a flange portion 16 secured to wall It) as by bolts 17. Inlet 12 may be water cooled if desired. In accordance with the conventional practice of admitting air or other gas, which can be under pressure, into an arc chamber at a number of points around the wall of the chamber to insure proper mixing of the gas and heating of the gas to a uniform temperature, gas admitted through the inlet 12, which is symbolical, may in fact be admitted at a number of smaller inlets at spaced positions around the wall of the chamber 11.

The wall 10 of the arc heater generally designated 9 is seen to have an opening 14 therein communicating with an exhaust nozzle 15. Nozzle 15 has flange portion 23 secured by bolts 26 to the chamber wall. In accordance with conventional practice, the nozzle 15 may be watercooled, and, for example, may have a plurality of water headers communicating with a plurality of longitudinally extending passageways, such as an arrangement similar to that shown and described in the copending application of Raymond M. Mentz for Arc Heater For Use With Three Phase Alternating Current Source and Chamber andElectrode Structure for Use Therein," Ser. No. 374,701, filed June 11, 1964, now U.S. Pat. No. 3,316,444, issued Apr. 25, 1967, and assigned to the assignee of the instant invention. Any other convenient means of cooling the nozzle 15 may be employed.

The shape of the arc chamber II is generally spherical or cylindrical, and the optical center or center axis of the cylinder thereof is substantially at or through the point 18, where an are 19 is seen taking place between electrodes or poles 21 and 22. Electrode 22 is one of a number of peripherally spaced radially extending electrodes on a conductive rotating electrode wheel 24, which is mounted for rotation in any convenient manner by means, not shown for convenience of illustration, within the arc chamber 11. The electrode wheel 24 may, for example, be fixed for rotation with a shaft 25 journaled for rotation in suitable bearings, not shown, and having a lead 27 electrically connected to slip ring or other means 28 for bringing a potential to the electrode wheel 24 and electrodes 22, it being understood that the wheel 24 and the shaft 25 are composed of conductive material. Grommetlilte insulator means 29 is provided for lead 27.

In accordance with alternating current devices, rotor secondary means rotating with shafts 25 and/or 32 could be inductively coupled to stationary primary means, for obtaining current for the arc 19 while eliminating the need for slip rings.

Means for rotating the shaft 25 and electrode wheel or disc 24 may be disposed within the arc chamber II, but are preferably disposed external thereto, the shaft 25 passing through a suitable bearing, not shown, in the wall It) of the arc heater 9, andbeing insulated therefrom.

Disposed substantially above the electrode wheel 24 is an additional electrode wheel 31 having at spaced intervals around the periphery thereof a plurality of salient electrodes 21. It is noted that the axis of rotation of the wheel 31 is perpendicular to the axis of the wheel 24. Preferably wheels 31 and 24 are of the same diameter and rotate at the same speed, some convenient means preferably being provided for maintaining the wheels in synchronism if they are not driven from the same source. Electrode wheel 31 rotates with shaft 32 having lead 33 to slip ring or other contact means 34, the shaft 32 having supporting bearings 35 and 36 supported in any convenient manner, not shown, within the arc member. insulator means 37 is provided for lead 33 where the lead passes through the wall of the chamber. It is further seen that the shaft 32 extends to the wall of the arc chamber, and thence extends through the bearing means d1 retained in position in the wall as by bolts 42. Shaft 32 is driven by its own driving device, for example motor 38 having leads 39, or shaft 32 is driven in synchronism from the wheel 24 and shaft 25, any suitable mechanical driving linkage, not shown, being provided. Preferably shaft 32 is electrically insulated from the wall of the chamber, as by insulating coupling 70.

As previously stated, the are 19 takes place between the electrodes at a position which is substantially at the optical center 13 of the sphere. Gas in the area of the arc is ionized so that as two electrodes 21 and 22 approach each other as the discs or wheels 31 and 24 turn, an arc is'formed; the arc may be momentarily extinguished as the electrodes move away from each other, but is substantially immediately formed through a triggering means, if necessary, again as the next two electrodes of the wheels rapidly approach the normal arc position.

As previously stated the enclosure 11 has reflecting walls. A number of electrodes could be employed, depending upon the operating power level, the arcs between the other electrodes being displaced only slightly from the exact optical center. it will be understood that the electrode holders or wheels can, if desired, be cooled by water, or by the gas to be heated, these convenient means being well known in the present state of the art.

By having the are fixed in space, and using the spherical or cylindrical reflective enclosure with the are at the center or along the axis, the radiation emitted by the arc is reimaged by the spherical or cylindrical mirror wall in effect back into the arc. It is understood that the arc is substantially at the axis or optical center, or not far therefrom. If desired, alternating current may be used between the electrodes, and transformers used to couple the current into the rotating members. The actual geometry of the rotating electrodes depends upon design considerations, as will be readily understood by those skilled in the art.

Typical operating characteristics would be as follows: For a system with:

a. three symmetric mirrors, 85 percent reflecting,

b. absorption of 50 percent passing through the arc stream.

Therefore, the first pass may recover up to 32 percent of the emitted energy and 32 percent passes through; the second pass may recover 13 percent, and 13 percent passes through; the third pass may recover 6 percent. The total of the three passes would recover approximately 51 percent of the emitted radiation.

It will be readily understood by those skilled in the art that the amount of energy recovered depends upon the emissivity and absorptivity of the gas, and the pressure of the gas.

Water is a suitable cooling fluid, but other coolants can be employed.

Particular reference is made now to FIG. 2, where an electrode arrangement according to a second embodiment of our invention is shown, which differs from the embodiment of FIG. 1 in that the rotating wheel electrodes are not segmented. Electrode 51 rotates with shaft 52 having slip ring 50 or other means for carrying power, connected to lead 53 for bringing current thereto; electrode 54 rotates with shaft 55 having slip ring 58 connected to lead 57 for bringing current thereto, to produce are 61 which occurs at substantially the optical center of the reflective spherical or cylindrical wall of an arc chamber, not shown for convenience of illustration.

Advantages of the unsegmented electrodes are that it is not necessary to rotate the electrodes in synchronism, and the are continuously transfers to new electrode surfaces.

In FIG. 3, to which particular reference is made, electrodes 51' and 54- are in the same plane, being secured for rotation with shafls 52 and 55 respectively, the shafts being rotated in synchronism, if necessary by synchronous motors 63 and M respectively connected by leads 65 and 66 to the same alternating current source.

Electrodes 51' and 54' can be segmented if desired, with any convenient similar numbers of salient poles.

Where segmented electrodes are employed, conventional triggering means may be provided for starting the are each time a pair of salient poles approach each other.

Whereas the wall it) of the furnace chamber is shown in FIG. 1 as having two openings 13 and M, it is apparent that one of these openings may be omitted, and the invention practiced with a partially enclosed chamber into which material to be heated is introduced and after heating may be removed through the same opening through which it was introduced, the heating of material being repetitive or periodic rather than continuous. Particular reference is made to FlGS. l, 5 and 6 where furnace apparatus corresponding to the immediately above description is shown, and the particular advantages resulting from employmentof our rotating electrodes are in part illustrated.

in FIG. 4, a furnace is generally designated 67, and is seen to have no cover so that it is apparent that it operates if desired at atmospheric pressure neglecting the increase in pressure therein which may result from the intensely hot gas (air and/or impurities escaping from the melt in the form of gases), which, even though the top of the furnace is open, may result in a slight pressure differential between the surface of melt 70 and the open top 81 of the furnace.

Whereas only the refractory lining 63 of the wall of the furnace is shown, it will be understood that an additional metal wall portion exterior to refractory portion 68 may be provided to give the needed mechanical strength. A melt 70, composed at least partially of electrically conductive material, is shown in the furnace, with the upper surface 36 thereof having an arc 73 thereto from rotating electrode 74. In the bottom of the furnace is an electrode 71 for making good electrical contact with the melt, having lead 72 connected thereto for connecting the electrode and the conductive melt to a terminal of one polarity of a source of potential. Spout 69 is provided for periodically tapping or emptying the furnace as desired, any suitable tipping means and means for rotating the furnace about an axis preferably radially passing therethrough at a desired position from the bottom, not shown for convenience of illustration, being provided.

Most materials to be heated in an electric arc furnace contain impurities which, when the material is melted, rise to the top and form a slag layer as shown; slag, if formed, may be periodically removed through spout 69.

Rotatable electrode 74 is seen, FIG. 4, to be solid and of very substantial thickness. The melting of metals may require arc currents of the order of many thousands of amperes. Electrode 74 is made as large in volume as possible, because the intensely hot are spot where are 73 momentarily attaches to electrode 74 is the major contributor to the temperature rise of the electrode, even radiation and convection from the hot metal playing a secondary role in raising electrode 74 to some average temperature; the greater the exposed area of the electrode the better the cooling and the less the average temperature to which the electrode is raised.

As is well known in the arc furnace art, the lower the average temperature of an electrode, the less the material lost from the electrode by are action. The intensely hot are spot may momentarily increase the surface temperature at the site of the are spot at least, several thousand degrees, the temperature being a function of the arc current and the dwell time of the are spot at that site until the are, as a result of rotation of the electrode, moves to another site on the electrode.

Ideally, the instantaneous temperature at the site of the arc spot is never allowed to reach a value at whichevaporation or sublimation of material from the electrode occurs. Nevertheless, the arc is almost certain to momentarily increase the temperature at the site of the are spot above the melting temperature of the material; the lower the instantaneous temperature reached at the arc spot site, which temperature represents an instantaneous temperature increase at the arc site above the average electrode temperature, the better the chance that melted material will cool and remain'in and form part of the electrode.

Electrode 74 is secured to a rotatable shaft 77by anyconvenient means, not shown for convenience of illustration, shaft 77 being of substantial cross section and composed of material having a high electrical conductivity since it carries arc current to electrode 74, as well as having sufficient mechanical strength and having-a high melting point. Shaft 77 passes through opening 76 in furnace wall 68, and has brush 78 firmly in contact therewith, the brush being maintained in position by any suitable means, not shown, brush 78 having lead 79 connected thereto with variable resistor 97 in series therein symbolizing means for regulating the arc current. Lead 79 is connected to the terminal of opposite polarity to that of lead 72, and to the same source of potential.

Shaft 77 is rotated by a motor 83 mounted on bracket 82, with motor leads 84 and 85, one containing variable resistor 99 in series therein symbolizingmeans for adjusting the speed of the motor, leads 84 and 85 being connected to a source of motor energizing potential, not shown forconvenience of illustration.

ln FlG. 5, a view along the line V-V of FIG. 4, the circular arcing surface of the electrode 74 is seen, together with are 73, slag layer 80, and melt 70 having an upper surface 86.

In the operation of FIGS. 4 and 5, the arc 73 tends tofollow the lowest resistence path between electrode and melt, and accordingly, as the electrode 74 rotates, the arc tends to remain substantially in the position shown, with the result that the site of thearc spot on the arcing surface of the electrode moves substantially continuously, reducing the rate at which material is lost from the electrode, increasing the life of the electrode and also reducing the contamination of the material of melt 70 by the material lost from the electrode.

Additionally, are 73 tends to remain in the position shown because of the ionized gas in that area which tends to move much more slowly that the fast moving arcing surface, so that in effect an ionized path between electrode 74 and melt 70 is formed which tends to remain in the position shown.

Electrode 74 may be rotated in a direction opposite to that indicated by the arrow.

Particular reference is made to FIG. 6. Here a rotating electrode 90 has teeth or segments extending radially therefrom, are 92 taking place between the nearest adjacent segment or tooth 91 and conductive melt 93 shown covered by a thin slag layer 94.

Whereas we have shown and described our invention with respect to some embodiments thereof which give satisfactory results, it should be understoodthat-the drawings and the aforegoing written description are illustrative and exemplary only and should not be interpreted in a limiting sense.

We claim:

1. Arc heater apparatus comprising, in combination, means forming an arc chamber, the chamber being substantially spherical in shape and having a reflecting inner wall, means for admitting gas to be heated into the chamber, means for exhausting heated gas from the chamber, a first electrode disposed in the chamber, and a second electrode disposed in the chamber, at least one of the first and second electrodes rotating substantially continuously, the first and second electrodes being adapted to have a potential applied there across to produce an arc in the chamber, said are occurring at substantially the optical center of the spherical arc chamber, radiation from the are being reflected a plurality of times through the chamber by the reflecting inner wall thereof, said reflected radiation additionally heating the gas as the gas passes through the chamber.

2. Arc heater apparatus according to claim 1 in which the first and second electrodes are additionally characterized as being segmented.

3. Are heater apparatus according to claim 1 in which the first and second electrodes are additionally characterized as being similarly segmented, as being of the same diameter, and as both being rotated at the same speed in synchronism with each other.'

4. Apparatus according to claim 1 in which both the first and second electrodes are additionally characterized as being rotatable, and including in addition means operatively connected to the first and second electrodes for rotating the same at a predetermined speed.

5. Arc heater apparatus comprising, in combination, means forming an arc chamber, the inner walls of the chamber being formed with reflecting surfaces, the chamber having a predetermined shape, the walls forming a spherical optical reflector centered on an arc position, first and second rotatable electrodes rotatably mounted in the chamber in predetermined positions therein whereby an arc takes place between the electrodes at said arc position, means including at least one motor operatively connected to the first and second electrodes for rotating the same, means for admitting gas to be heated to the chamber, and means for exhausting heated gas from the chamber, radiation from the arc at the optical center of the spherical reflector being reflected a plurality of times through the chamber and assisting in heating the gas passing through the chamber.

6. Apparatus according to claim 5 wherein the rotating electrodes are additionally characterized as. being driven in synchronism, and are further characterized as being segmented with the segment of one electrode most closely approaching the segment of the other electrode at substantially the optical center of the spherical reflector.

7. Gas arc heater apparatus comprising in combination, means forming an arc chamber, the wall of the arc chamber being reflecting, said arc chamber having a predetermined shape and having at least one optical focal point, means for admitting gas to be heated into the chamber, means for exhausting heated gas from the chamber, means including first and second rotating electrodes for producing an are at substantially the optical focal point of the chamber, and means for applying a potential across said electrodes, the arc at substantially the optical focal point resulting in radiation therefrom being reflected back and forthfrom the wall of the chamber a number of times whereby the reflected radiation assists in heating the gas in the arc heater.

8. Arc heater apparatus comprising, in combination, means forming an arc chamber, the chamber being substantially spherical in shape and having a reflecting inner wall, means for admitting gas to be heated into the chamber, means for exhausting heated gas from the chamber, a first electrode disposed in the chamber, and a second electrode disposed in the chamber, at least one of the first and second electrodes rotatingsubstantially continuously, the first and second electrodes being adapted to have a potential applied there across to produce an arc in the chamber, said are occurring at substantially the optical center of the spherical arc chamber, the admitting means and the exhausting means being so disposed with respect to each other as to provide a gas path through the chamber of maximum length in accordance with the dimensions of the chamber, radiation from the are being reflected a plurality of times through the chamber by the reflecting inner wall thereof, said reflected radiation additionally heating the gas as the gas passes through the chamber.

9. Arc heater apparatus comprising, in combination, means forming an arc chamber, the chamber being substantially spherical in shape and having a reflecting inner wall, means for admitting gas to be heated into the chamber, means for exhausting heated gas from the chamber, a first electrode disposed in the chamber, and a second electrode disposed in the chamber, at least one of the first and second electrodes rotating substantially continuously, the first and second electrodes being adapted to have a potential applied there across to produce an arc in the chamber, said arc occurring at substantially the optical center of the spherical arc chamber, the positions of the admitting means and the exhausting means being chosen with respect to the position of the arc whereby the majority of the gas follows a path between the admitting means and the exhausting means in which the arc takes place, radiation from the are being reflected a plurality of times through the chamber by the reflecting inner wall, said reflected radiation additionally heating the gas as the gas passes through the chamber.

10. A Arc heater apparatus comprising, in combination, means forming an arc chamber, the chamber being substantially spherical in shape and having a reflecting inner wall, means for admitting gas to be heated into the chamber, means for exhausting heated gas from the chamber, a first electrode disposed in the chamber, and a second electrode disposed in the chamber, at least one of the first and second electrodes rotating substantially continuously, the first and second electrodes being adapted to have a potential applied there across to produce an arc in the chamber, said are occurring at substantially the optical center of the spherical arc chamber, the position of the admitting means 'with respect to the position of the are being so chosen that the location of the arc is substantially unchanged by gas flow within the chamber, radiation from the are being reflected a plurality of times through the chamber by the reflecting inner wall thereof, said reflected radiation additionally heating the gas as the gas passes through the chamber.

11. Apparatus according to claim 7 in which the first and second rotating electrodes are so disposed with respect to each other that the plane of rotation of the first electrode is nonparallel to the plane of rotation of the second electrode.

12. Apparatus according to claim 7 in which both the first and second electrodes are discshaped with smooth annular rim surfaces.

13. Apparatus according to claim 12 in which the first and second electrodes are so disposed with respect to each other that the plane of rotation of the first electrode is perpendicular to the plane of rotation of the second electrode.

M. Apparatus according to claim 12 in which the axes of rotation of the first and second electrodes are parallel.

Images