US2752410A - Electrical reduction furnace having means to protect the walls thereof from heat within the furnace and to utilize otherwise wasted heat - Google Patents

Description

2,752,410 OTEIC June 26, 1956 S. M. J. OLSSON ELECTRICAL REDUCTION FURNACE HAVING MEANS TO FR THE WALLS THEREOF FROM HEAT WITHIN THE FURNACE AND TO UTILIZE OTHERWISE WASTED HEAT 4 Sheets-Sheet 1 Filed June 20, 1955 (MJMQV iwn M i 5/5502? Juhe 26, 1956 s M J OLSSON 2,752,410

ELECTRICAL REDUCTION FURNACE HAVING MEANS To PROTECT THE WALLS THEREOF FROM HEAT WITHIN THE FURNACE AND TO UTILIZE OTHERWISE WASTED HEAT Filed June 20. 1955 4 Sheets-Sheet 2 June 26, 1956 s. M. J. OLSSON 2,752,410

ELECTRICAL REDUCTION FURNACE HAVING MEANS TO PROTECT THE WALLS THEREOF FROM HEAT WITHIN THE FURNACE AND TO UTILIZE OTHERWISE WASTED HEAT Filed June 20, 1955 4 Sheets-Sheet 3 iwzzMi 55022 June 26, 1956 s. M. J. OLSSON 2,752,410

ELECTRICAL REDUCTION FURNACE HAVING MEANS TO PROTECT THE WALLS THEREOF FROM HEAT WITHIN THE FURNACE AND TO UTILIZE OTHERWISE WASTED HEAT 4 Sheets-Sheet 4 Filed June 20, 1955 0 O O O O O O O O O O O O O 5mm Mi 17/5502? United States Patent-O ELECTRICAL REDUCTION FURNACE HAVING MEANS TO PROTECT THE WALLS THEREOF FROM HEAT WITHIN THE FURNACE AND TO UTILIZE OTHERWISE WASTED HEAT Sven M. J. Olsson, Mount Vernon, N. Y., assignor to Sunrod Manufacturing Corporation, New York, N. Y., a corporation of Delaware Application June 20, 1955, Serial No. 516,652

3 Claims. (Cl. 13-9) This invention relates to electric reduction furnaces and the like, and has as its general purpose to improve such furnaces and render them safer and considerably more economical in operation.

The furnaces to which this invention appertains are generally huge structures consisting essentially of an open-topped crucible to contain the ore, minerals, or other material to be reduced and melted, and large carbon electrodes supported from above and extending down into the crucible to be embedded in its contents. During the operation of the furnace, extremely high heat is developed and fumes and gases are produced.

Heretofore attempts have been made to collect the fumes and gases resulting from the reduction process by means of a hood spaced above the open top of the crucible and connected to a stack; but such expedients not only were ineffective for the purpose intended, but had the very serious objection of wasting a considerable amount of heat to say nothing of contaminating the atmosphere into which the gases were discharged.

In other electric furnaces of the past, attempts were made to overcome the objections inherent in the use of collecting hoods or the like, by tightly covering the top of the crucible and drawing off the gases. That arrangement was particularly employed in situations where it was desired to collect and refine the gases drawn off, but there was always the constant danger that these gases would ignite and explode within the covered crucible.

The present invention may be said to constitute a compromise between these two past expedients in that it utilizes a cover which closes the top of the crucible but does not attempt to make the enclosure gas tight. On the contrary, means are expressly provided for the admission of combustion supporting air, and instead of attempting to carry off the gases resulting from the reduction process, the combustible fraction thereof which constitutes the major part, is burned in the covered cru'cible and the products of combustion plus any other residual gases are carried off to the stack.

Those skilled in the art will of course, readily appreciate that some means must be provided to protect the cover against the extremely high heat to which it is subjected. Protection could of course, be provided by a refractory lining for the inner walls of the cover, but with a view toward rendering the operation more economical, the means provided by this invention for protecting the walls of the cover against the intense heat not only serves that function, but in addition, achieves the very important advantage of utilizing the otherwise wasted heat through the generation of steam which may be employed for power production purposes and other uses.

Accordingly, it is another object of this invention to provide the inner Walls of the cover with a lining consisting of closely spaced tubes through which a steamwater emulsion is circulated.

' With a view toward abstracting all possible heat energy ice from the hot gases emanating from the operation of the furnace, this invention has as another of its objects to provide a gas withdrawal duct or passage leading from the cover to a stack and which passage is lined with tubes or pipes through which a steam-water emulsion is also circulated, and which passage at another portion thereof, contains several sets of coils, one of which may serve as a superheater, another as convection heating surfaces, and a third as an economizer to preheat the water fed to the system.

With the above and other objects in view, which will appear as the description proceeds, this invention resides in the novel method and combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate several complete examples of the physical embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

Figures la and 1b together, constitute a perspective view illustrating generally an electric furnace embodying this invention;

Figure 2 is a top plan view of the furnace with the electrodes in cross section and a portion of the cover wall broken away to illustrate one of the air inlets;

Figure 3 is a fragmentary sectional view through Figure 2 on the plane of the line 33;

Figure 4 is a sectional view through the top wall of the cover of the furnace at one of the electrodes and illustrating one way of sealing the port in the cover through which the electrode passes;

Figure 5 is a sectional view through Figure 4 on the plane of the line 55; and

Figure 6 is a view similar to Figure 4, but illustrating a modified embodiment of this portion of the structure.

Referring to the accompanying drawings in which like numerals indicate like parts throughout several views, the numeral 1 indicates generally the furnace proper which may be constructed in any suitable conventional way and generally is built up of refractory brick or the like. Essentially, the body of the furnace provides a huge crucible in which the material to be reduced is received, and into which a plurality of electrodes 2 depend. The electrodes, as is customary, are supported from above in a manner permitting them to be lowered as they are consumed during the operation of the furmace, and as is well known, the heat needed for the reaction is supplied by electric arcs which exist in operation between the electrode tips and a hearth electrode 2' in the bottom or" the crucible. I The top of the furnace or crucible is closed by a cover indicated generally by the numeral 3. This cover is substantially an inverted hood having side walls 4 and a top wall 5, the latter including a central portion 6 provided with ports 7 through which the electrodes pass. All walls of the cover are preferably reinforced metal shells filled with mineral wool or the like. Any suitable metal may be used except for the central portion 6 of the top wall, in which case the metal should be non-magnetic, for instance, austenitic steel, so as to reduce hysteresis losses caused by the magnetic fields set up by the current flowing in the electrodes.

Charging openings 3 in the center portion 6 of the top wall provide means for charging material into the furnace without disturbing the electrodes. These opening's are normally closed by slide doors 9; and to permit inspection of the furnace contents doors are provided in the side walls 4 of the cover.

The entire cover may rest on the furnace or its weight may be supported, at least partially, by any structure (not shown). If the cover is suspended from above the furnace may be rotated when such movement is necessary to better orient the electrodes with the furnace contents.

The ports 7 through which the electrodes pass, as best shown in Figure 2, are preferably slightly elongated, on lines radial to the axis of the furnace so as to accommodate some lateral adjustment of the electrodes, but in any event are considerably larger than the electrodes. Closure of the intervening space between the electrodes and the edges of the ports without interfering'with lateral adjustment of the electrodes, is accomplished in one embodiment of the invention by means of hollow collars 11 which closely fit the electrodes and are of a size to more than cover the ports 7. These collars are supported upon the top wall of the cover by refractory rings 12; and to cool the collars, suitable liquid coolant is circulated therethrough, entering the interior of each collar through a port 13 and leaving the same through a port 14. Baffles 15 arranged within the hollow collars assure an effective circulation of the cooling medium.

As an alternate for the hollow collars 12, the ports 7 may be equipped with refractory liners 16, as shown in Figure 6, and a refractory collar 17 encircling each electrode may be supported upon these refractory liners, as also shown in Figure 6.

As distinguished from those past constructions wherein a gas-tight enclosure was sought, the cover of the present invention not only permits air to leak into it, but in addition, air inlet nozzles 18 are specifically provided for positively introducing air into the furnace so as to insure combustion of the gases resulting from the process. Two of these nozzles are supplied with combustion air through air inlet ducts 19, and a third nozzle has air conducted to it through an air passage 20 which encircles the upper edge of the cover and is formed by parts of its structural framing; the air entering the passage 20 through an inlet duct 21. Attention is directed to the fact that the nozzles are positioned to effect a desirable turbulence of the gases in the furnace.

As noted hereinbefore, the temperatures which obtain inside the furnace during operation are extremely high. For instance, in the reduction of vanadium the temperature of the molten mass is approximately 3400 F., and of the burning gases approximately 2500 F. To protect the walls of the cover 3 against this intense heat obviously presents quite a problem. The protection perhaps could be afforded by an adequate refractory lining for the cover walls, but that expedient would still have the objection of wasting heat.

The present invention achieves the necessary protection for the walls of the cover in a manner which utilizes this otherwise wasted heat. To this end, all inner surfaces of the cover walls are lined with tubes 22 through which a steam-water emulsion is positively circulated. These tubes are secured to the cover walls in any suitable manner and are exposed directly to the radiant heat within the furnace. The tubes 22 thus constitute part of a steam generating system comparable to the steaming coils of a steam generating plant.

The steam-water emulsion is supplied to the tubes 22 from a-steam drum 23 by means of a circulating pump 24, and a feed line 25 leading from the pump to headers 26. A sufficient number of such headers 26 is provided to enable all of the tubes lining the inner walls of the cover to be adequately supplied. The discharge ends of the tubes are connected to headers 27, which in turn, are connected by means of a return line 28 to the steam drum 23, above the normal water level therein.

Thus, it will be seen that the circulating pump 24 positively circulates the steam-water emulsion through all of the tubes 22 and in so doing, protects the walls of the cover against the intense heat within the furnace, and at the same time utilizes the otherwise wasted heat. The steam generated is of course, useful for many purposes as will be readily apparent.

The products of combustion are carried off by a flue gas duct 29, which connects with the cover interior and leads to a flue passage 30, which in turn, opens to the inlet of a suction fan 31, or directly to a stack, not shown. Since the temperature of the combustion gases leaving the furnace is also still quite high, approximately 1800 F., the walls of the flue gas passage 29 are lined with tubes 32, which, like the tubes lining the cover of the furnace have a steam-water emulsion positively circulated therethrough to abstract heat from the gases flowing through the flue gas duct.

The flue gas passage 30 which connects the duct 32 with the stack, has three sets of coils 33, 34 and 35, arranged therein. The first of these sets of coils provides a superheater for the steam generated in the system, and to that end, is connected with the steam drum 23 by a line 36, and a line 37 leads from the superheater coils to the place of use of the superheated steam. The second set of coils 34 constitutes convection surfaces through which steam-water emulsion is circulated by the pump 24, and the third set of coils 35 provides an economizer to preheat the water fed to the system.

It should, of course, be understood that the specific arrangement of these various sets of coils and tubes and their connections into the complete steam generating system has been only generally illustrated. The important consideration, however, is that the heat abstracting coils or tubes lining the walls of the cover of the furnace have a dual function. Not only do they protect the cover walls against the intense heat within the furnace, but they also put that heat to useful purposes and thus make the entire operation far more economical than has heretofore been possible.

The steam generated by this otherwise wasted heat which emanates from one single reduction furnace is often sufficient to provide electric power for a good portion of the entire plant in which the furnace is located.

From the foregoing description taken in connection with the accompanying drawings, it will therefore, be readily apparent that this invention provides a substantial improvement in electric furnaces not only because it removes the hazard and danger connected with the operation of such furnaces in the past, but also because it utilizes most of the heat which is an inevitable concomitant of the operation of such furnaces, and which heretofore was wasted.

What is claimed as my invention is:

l. The combination with an electric furnace having a crucible to contain the material to be smelted and/or molten and electrodes extending down into the crucible to be embedded in the contents thereof: of a cover closing the top of the crucible and having ports through which the electrodes pass; and means to protect the walls of the cover against the intense heat emanating from the molten crucible contents and the combustion of gases thereabove, and at the same time utilize said heat for the generation of steam, said means comprising closely spaced tubes covering the inner surfaces of the cover and directly exposed to the radiant heat of the incandescent or molten crucible contents and the burning gases, and means for circulating a steam-water emulsion through said tubes.

2. The combination of claim 1 further characterized by a flue gas duct connected with and leading from the cover to carry off products of combustion, tubes lining the inner surfaces of said flue gas duct, and means for circulating a steam-water emulsion through said lastnamed tubes.

3. The combination of claim 2 further characterized by the provision of a flue gas passage connected to the 2,752,410 5 flue gas duct, a series of coils in said flue gas passage providing a superheater for the steam generated in the tubes lining the cover and th: flue gas duct, a second set of coils in said flue gas passage providing convection heat- 1234946 Sperhng July ing surfaces, and a third set of coils in the flue gas passage 5 gg g 3 1918 0 I J $5 3 an economlzer for sald steam g e t g 1,499,020 Leonarz June 24, 1924 2,116,202 Honegger May 3,

2,222,004 Smith NOV. 19,

2,672,491 Lamb M31. 17,

6 References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. THE COMBINATION WITH AN ELECTRIC FURNACE HAVING A CRUCIBLE TO CONTAIN THE MATERIAL TO BE SMELTED AND/OR MOLTEN AND ELECTRODES EXTENDING DOWN INTO THE CRUCIBLE TO BE EMBEDDED IN THE CONTENTS THEREOF: OF A COVER CLOSING THE TOP OF THE CRUCIBLE AND HAVING PORTS THROUGH WHICH THE ELECTRODES PASS; AND MEANS TO PROTECT THE WALLS OF THE COVER AGAINST THE INTENSE HEATING EMANATING FROM THE MOLTEN CRUCIBLE CONTENTS AND THE COMBUSTION OF GASES THEREABOVE, AND AT THE SAME TIME UTILIZE SAID HEAT FOR THE GENERATION OF STEAM, SAID MEANS COMPRISING CLOSELY SPACED TUBES COVERING THE INNER SURFACES OF THE COVER AND DIRECTLY EXPOSED TO THE RADIANT HEAT OF THE INCANDESCENT OF MOLTEN CRUCIBLE CONTENTS AND THE BURNING GASES, AND MEANS FOR CIRCULATING A STEAM-WATER EMULSION THROUGH SAID TUBES.

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