US3390219A - Electrode furnace - Google Patents

Description

" June 25,1968 I A,J.:HENRIKSEN ETAL 3,390,219

I ELECTRODE FURNACE Filed April 2a. was v 2 Sheets-Sheet 1 POWER CABLES FIG I ronic/5L5: h men can.

INVENTORS ARTHUR J. HENRIKSEN June 25, 1968 A, JQHENRIKSEYIN ET AL 3,390,219

ELECTRODE FURNACE 2 SheetsSheet 2 Filed April 26, l966 ELECTRODE mas I80 OPPOSED IINVENTORS mmun J. uenmxseu United States Patent 3,390,219 ELECTRODE FURNACE Arthur J. Henriksen, Pocatello, Idaho, and Dean F.

Thorpe, Westport, Conn., assignors to FMC Corporation, New York, N.Y., a corporation of Delaware Filed Apr. 26, 1966, Ser. No. 545,427 6 Claims. (Cl. 136) The present application is concerned with a furnace equipped with internal electrodes for maintaining precise control of temperature and fluidity of molten fluids and, more specifically, of molten slag.

In the process of melting mineral slag or other inorganic materials, e.g., glass, temperatures on the order of 2400 to 2800 F. must be reached. While many furnaces can reach these temperatures it is difficult to control the temperature and fluidity of the resultant molten fluid in the furnace within prescribed limits. The temperature and fluidity of the molten product removed from the furnace must be carefully regulated in order that subsequent operations with the melt, e.g., the spinning of mineral wool, may be carried out to yield a commercially acceptable product. In spinning mineral wool the temperature and fluidity of the molten product fed to a spinning apparatus must be' carefully controlled to obtain a mineral wool having desirable physical properties and with a minimum of skulls and shot; mineral slag not formed into fibers by a spinning apparatus is termed either shot (-l0 mesh spheres) or skulls (larger solidified melt particles).

It is an object of the present application to define a furnace for closely regulating the temperature of molten slag so that a slag product having the desired temperatures and fluidity can be obtained uniformly with a minimum heat loss in the furnace.

'These and other objects will be obvious from the following description.

We have now found that the above objects can be achieved by a furnace comprising an elongated tubular heating section having a feed section connected to one end and a discharge orifice connected to the opposite end thereof, said sections containing an inner layer of refractory composition held in place by outer support means and a jacket containing a cooling medium (preferably water) surrounding said support means, said elongated tubular heating section containing electrodes internally placed for heating, said elongated tubular he'ating section being inclined downwardly from said feed section whereby two thermal layers of molten product are for-med in said elongated tubula-r heating section in which an upper, hotter thermal layer flows toward the feed section and a lower, cooler thermal layer flows toward the discharge orifice, and means for altering the angle of inclination of said elongated tubular heating section whereby the rate at which molten product is discharged from said discharge orifice can be cont-rolled.

In operation the slag is passed into the feed section of the furnace and flows downwardly into the inclined, elongated tubular heating section which is connected to the feed section. The slag then contacts the electrodes and is heated by current passing through both. the electrodes and molten slag to a higher temperature than that present in the feed section. The heated slag then stratifies into two moving streams. That portion of the heated slag that is hotter than its surrounding counterpart rises to the upper surface of the inclined heating section and then flows upwardly toward the feed section. The somewhat cooler slag passes downwardly along the lower surface of the inclined heating section to the next pair of electrodes.

As the slag gravity-flows along the lower surface of the inclined heating section it is heated in part by contact with hotter slag in the lower portion of the inclined heating section and in part by resistance heating effected by the electrodes. By the time the slag reaches the' lower portion of the tube furnace it reaches the desired outlet temperature.

Throughout the heating process two thermal, moving layers of slag exist within the furnace that form strong thermal currents. The upper thermal layer, which is hotter and more fluid than that in the lower thermal layer, flows upwardly along the upper surface of the inclined heating section to the feed section; the molten slag, located in the lower thermal layer at the base of the inclined heating section, which is at the temperature desired, flows out the discharge orifice. The higher temperature slag mixes with the cooler molten material in the feed section of the furnace and is used to preheat the feed flowing into the inclined heating section.

The rate of flow of the molten slag through the furnace can be varied by adjusting the degree of inclination of the inclined heating section and/or by regulating the temperature of the slag which is discharged through a given orifice. The discharge orifice acts as a restrictive dam and maintains the elongated heating section full of slag up to any desired level in the feed section.

The furnace will now be explained with reference to the attached drawings. In the drawings:

FIG. 1 illustrates the feed section and elongated section of the furnace, while FIGS. 2 and 3 are cross-sectional views of the furnace.

In FIG. 1 molten mineral slag 2 is poured from slag ladle 4 into feed section 6 of the furnace. The slag flows by gravity into the elongated tubular heating section 8 equipped with electrodes 10 connected to a power source not shown. The feed section 6 and heating section 8 contain a refractory liner 12, supporting means 14 and a water jacket 18. In addition, the heating section can be inclined at various positions by means of a hydraulic piston, screw jack or other elevating means 20. Increasing the in clination of the heating section increases the hydraulic head of molten fluid which causes the fluid to flow through under greater pressure. Alternately, if the flow rate through the furnace is to be reduced the inclination can be decreased, thereby decreasing the hydraulic head, which results in lowering the rate of flow through the furnace.

The molten mineral slag 2 passes from the feed section 6 into the heating section 8 by gravity flow. There it is heated by a moving thermal layer of higher temperature, less viscous slag which flows upwardly along the upper section of the heating section 8 into the feed section 6. As the feed slag proceeds down the inclined heating section 8, it is also heated by resistance heating as it flows between opposing sets of electrodes 10. Thereafter, the heated slag continues to stratify into two moving streams, an upper stream which is hotter and more fluid, and a lower stream which is cooler and more viscous. The upper, hotter, more fluid stream rises up the inclined slope of the upper surface of tubular heating section 8 until it flows into the feed section .6 and preheats the incoming slag. The lower, more viscous stream of slag fiows downwardly along the lower surface of the inclined heating section 8 of the furnace. This stratification into hotter and cooler streams takes place at each of the electrode pairs along the entire length of the heating section 8 until the downwardly flowing stream at the orifice has reached the desired temperature and viscosity. By virtue of the configuration of the heating section of the instant furnace, the temperature of the molten slag which flows out of discharge orifice 16 can be very closely controlled. Any molten slag in the furnace which has a temperature higher than that desired normally rises to the top of the -furnace and flows away from the discharge orifice toward the feed section 6.

In the present furnace the water jacket 18 cools the refractory layer 12 thereby helping to maintain the iife of the refractory lining. In the preferred embodiment of the invention the rate of cooling is adjusted so that some of the slag which is in contact with the refractory is cooled sufiiciently so that it forms an inner, nonfluid layer in contact with the refractory layer. In this way a cooled annular layer of slag remains between the refractory layer 12 and the molten slag within the tubular inclined heating section 8. This promotes additional life of the refractory layer 12 since the refractory can be maintained at lower temperatures than if it is in direct contact with the molten slag, and because it eliminates the erosion which results when the dense molten slag flows in direct contact over the refractory material lining the furnace. If desired, a cooled annular layer of slag can be used as the refractory composition per se without the need for an additional refractory layer intermediate the molten slag and the supporting means.

The following examples are given to illustrate the present invention and are not deemed to be limiting thereof.

Example 1 A furnace having the configuration of FIG. 1 was constructed as follows: a feed section was constructed having a mouth 36 x 36 in. square and 36 in. deep. A metal pipe having a 24 in. ID. was fitted into one of the lower edges so that material added into the mouth of the feed section would travel downwardly and into the metal pipe section. The cylindrical portion of the feed section was then attached to an elongated tubular section made up from a metal pipe having a 24 in. LB. cross-section and 7% ft. in length. The base of the elongated tubular section was fitted with an orifice 1.25 in. in diameter. The feed section and the elongated tubular section were lined with a 4 in. thick layer of silicon carbide brick. This decreased the interior dimensions of the feed section to 28 in. square and the elongated tubular section to an internal diameter of 16 in. Three pairs of electrodes having a total of 108 sq. in. of effective electrode surface were placed along the length of the elongated section and each pair of electrodes was connected to a power source. The feed section and the elongated tubular section were encased in a metal jacket and water was passed into the jacket to cool both the feed section and elongated tubular section of the furnace. Molten slag having an input temperature of 2500 F. was then passed into the feed section of the furnace. The molten slag was added to fill up the entire furnace until its level reached about 8 in. from the top of the feed section. Thereafter, molten slag was added into the feed section at a rate of 8 gal/min. (about 172.5 lbs. of slag per min.).

Molten slag was removed from the outlet orifice at a rate of 8 gal/min. at a temperature of 2600 F. A total of 21.75 lbs. of melt was passed through the furnace and had an average retention time of 12.65 min. exclusive of start up. Total power input to the furnace was 652.4 kw. The heat loss from the furnace was found to be about 4.3 kw./hr./sq. ft. Examination of the furnace indicated that a solidified slag layer about /2 in. thick was maintained in contact with the refractory layer throughout the heating. Further, temperature profiles obtained in the furnace indicated that the temperature of the melt layer near the upper surface of the elongated tubular section was from 300 to 500 F. hotter than the slag layer at the lower surface. The temperature differential was greatest at the feed section end of the elongated tubular section and diminished gradually until it had the lowest temperature differential at the discharge end. The presence of this temperature differential indicated the presence of strong thermo currents within the elongated tubular section of the furnace. The slag recovered from the orifice 4 outlet was found to be within 20 F. of the desired 2600 F. discharge slag temperature.

Example 2 A furnace having the configuration of FIG. 1 was constructed as follows: A feed section having a refractory brick liner was constructed 2 ft. sq. and 2 ft. deep. To one side of this feed section was attached two concentric tubes, the inner tube having a 12 in. ID. The annular space between the tubes was provided with necessary bafiies and seals to provide for the flow and circulation of cooling water. The discharge end of the inner tube was fitted with a plate containing a. centrally disposed orifice 1.5 in. in diameter. The plate containing the orifice was fitted with an annular shell to permit water cooling. Into the side of the tubular portion of the furnace were installed two opposing electrodes in a horizontally disposed plane running through the center line of the tubes. The electrodes were positioned within threaded studs extending through the two concentric tubes and protected by refractory sleeves. The electrodes were then connected to a power source. A refractory brick liner was not used in the tubular section of the furnace.

Into the vertically inclined furnace described above was fed molten slag until the feed section and tubular furnace were filled. Thereafter, slag was fed through the furnace at a rate of about 8 gal/min. Total electric power input to the furnace was 168 kw. and heat loss was 4.86 kw./ sq. ft. of surface area. During operation of the furnace the inner tube contained an annular solidified slag coating about in. thick at the top of the furnace and 5% in. thick at the bottom of the furnace. This solidified slag coating acted as the refractory surface to protect the metal wall of the furnace from the molten slag. Molten slag was removed from the orifice at a controlled temperature of 2640 :20 F. at a flow rate of about 8 gal/min.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure otherwise than as specifically described and exemplified herein.

What is claimed is:

1. A furnace comprising an elongated tubular heating section having a feed section connected to one end and a discharge orifice connected to the opposite end thereof, said sections containing an inner layer of refractory composition supported by outer supporting means and a jacket containing a cooling medium surrounding said supporting means, said elongated heating section containing electrodes iternally placed for heating, said elongated tubular heating section being inclined downwardly from said feed section whereby two thermal layers of a molten product are formed in said elongated tubular heating section in which an upper, hotter thermal layer flows upwardly toward the feed section and a lower, cooler thermal layer flows downwardly toward said discharge orifice, and means for altering the angle of inclination of said elongated tubular heating section whereby the rate at which molten product is discharged from said discharge orifice can be controlled.

2. The apparatus of claim 1 wherein said inner layer of refractory composition is formed of cooled refractory product and is maintained in a solid state by sufiiciently cooling the said furnace by means of said jacket and said cooling medium.

3. The apparatus of claim 1 wherein the cooling medium of said jacket sufiiciently cools the inner layer of refractory composition and molten product in contact therewith to form an annular coating of cooled product intermediate the inner layer of refractory composition and molten refractory product within said furnace.

4. Process of heating an inorganic mixture comprising passing said mixture into the feed section of a furnace, said furnace comprising an elongated tubular heating section having a feed section connected to one end and a discharge orifice connected to the opposite end thereof, said elongated tubular heating section being inclined downwardly from said feed section, preheating said mixture in said feed section by contact with a thermal layer of said molten mixture flowing along the upper surface of said elongated tubular heating section into said feed section, passing the preheated mixture from said feed section into said elongated tubular heating section, heating the preheated mixture in said elongated tubular heating section, forming two thermal layers of said mixture in said elongated tubular heating section in which an upper, hotter thermal layer flows upwardly along the upper surface of said elongated tubular heating section into said feed section and a lower, cooler thermal layer flows down- 2 wardly toward said discharge orifice, discharging said mixture in a molten state from said discharge orifice, adjusting the degree of inclination of said elongated tubular heating section whereby the rate at which said mixture is discharged from said discharge orifice is controlled.

5. Process of claim 4 wherein said elongated tubular heating section is cooled sufficiently to form an anular coating of cooled, non-fluid inorganic mixture surrounding the molten mixture in said furnace.

6. Process of claim 4 wherein said inorganic mixture is a mineral slag from a phosphorous furnace.

References Cited UNITED STATES PATENTS 2,513,242 6/1950 Inman 219l0.51 2,578,760 12/1951 Strickland 219-1051 2,641,621 6/1953 Greene 1329 2,937,789 5/1960 Tarna 13-31 X 3,190,997 6/1965 Rothacker 219l0.51 3,354,256 11/1967 Vaughan et a1. 13- 6 X BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

Claims (1)

1. A FURNACE COMPRISING AN ELONGATED TUBULAR HEATING SECTION HAVING A FEED SECTION CONNECTED TO ONE END AND A DISCHARGE ORIFICE CONNECTED TO THE OPPOSITE END THEREOF, SAID SECTIONS CONTAINING AN INNER LAYER OF REFRACTORY COMPOSITION SUPPORTED BY OUTER SUPPORTING MEANS AND A JACKET CONTAINING A COOLING MEDIUM SURROUNDING SAID SUPPORTING MEANS, SAID ELONGATED HEATING SECTION CONTAINING ELECTRODES INTERNALLY PLACED FOR HEATING, SAID ELONGATED TUBULAR HEATING SECTION BEING INCLINED DOWNWARDLY FROM SAID FEED SECTION WHEREBY TWO THERMAL LAYERS OF A MOLTEN PRODUCT ARE FORMED IN SAID ELONGATED TUBULAR HEATING SECTION IN WHICH AN UPPER, HOTTER THERMAL LAYER FLOWS UPWARDLY TOWARD THE FEED SECTION AND A LOWER, COOLER THERMAL LAYER FLOWS DOWNWARDLY TOWARD SAID DISCHARGE ORIFICE, AND MEANS FOR ALTERING THE ANGLE OF INCLINATION OF SAID

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