DE1059130B - Electric resistance furnace - Google Patents

Description

GERMAN

The subject of the invention is an electric resistance furnace for converting substance mixtures, which conduct electricity only a little when cold and at high conversion temperatures can only be brought to sinter and not to complete melt flow.

Mixtures of the oxides of silicon, titanium and similar metals with carbon as a reducing agent Agents have only a very low electrical conductivity. At temperatures at which the oxides are reduced by carbon, the reaction products become electrical conductors with specific Resistance values on the order of 0.4 to 400 ohms / cm. At temperatures above 1000 ° C the resistance values drop rapidly with increasing temperature. This falling in the resistance values when the temperature rises leads to instability of the electrical conditions, the current in the Oven flows in certain channels so that high temperature spots or channels are formed locally and as a whole, a material is created whose properties are uneven.

For the implementation of melting processes, in particular for the production of calcium carbide, are from the German patent 119 464 continuously operated electric resistance furnaces known in where several reaction centers lying one behind the other in the direction of flow and kept separate from one another available. The current is conducted from one reaction hearth to the next with intermediate electrodes made of carbon, which extend in the direction of the current and into the material to be treated are embedded.

The individual reaction centers are kept separate from one another in that the intermediate electrodes are arranged elongated in the direction of the electric current. The reaction mass thus remains proportionate along the intermediate electrodes cold and is not implemented.

Such continuously operated ovens are completely useless for reaction processes in which the The material to be treated is not caused to flow by melting and is thus continuously withdrawn can. Intermittent operation of these furnaces cannot give a uniform reaction product.

To avoid these disadvantages and to achieve the stated advantages, the electrical Resistance furnace for temperatures in the range from 1500 to 2200 ° C with a cross to the direction of the current carbon bars embedded at a distance from one another in the material to be treated Radiators for heating and converting finely divided, solid and, when cold, electrical ones Electricity of non-conductive substances according to the invention

Applicant:
Union Carbide Corporation,
New York, NY (V.St.A.)

Representative:

Dr. phil. Dr. rer. pole. K. Köhler, patent attorney,
Munich 2, Amalienstr. 15th

Claimed priority:
V. St. v. America March 11, 1955

Victor Carl Hamister, Lakewood, Ohio (V. St. A.),
has been named as the inventor

according to set up in such a way that the distance between the bars made of carbon continuously with a granular resistance material that still conducts the electric current even when cold, for example with granulated graphite, and that the bars of carbon down alone are supported by the sintering material, the heating current of the furnace being subject to such temperature conditions it is set so that only part of the material to be treated melts with each batch. In this way, separate reaction sources are avoided with certainty.

According to a preferred embodiment, the granular material in the furnace consists of an oxide and a reducing agent, the reducing agent being a carbonaceous material, e.g. B. granulated Coal, extremely suitable.

In another preferred embodiment, the granular material consists essentially in the oven from 64% titanium oxide, 28% petroleum coke, 4.5% wood flour and 3.5% water.

909 530/339

Claims (2)

1 According to another preferred embodiment, the granular material in the furnace consists of silica sand and petroleum coke. The drawing shows in FIG. 1 a partially sectioned plan view of an electrical resistance furnace with a charged charge according to the invention, FIG. 2 shows a section according to 2-2 of FIG. 1, viewed in the direction of the arrows drawn, and FIG. 3 shows a section according to 3-3 or Fig. 2, viewed in the direction of the arrows drawn, with the charge after completion of the reaction. In one embodiment of practicing the invention, a charge 10 to be heated, e.g. B. a reaction mixture of titanium oxide and a carbon reducing agent, produced and filled into the electrical resistance furnace 12 with heat-resistant walls 14 and terminal electrodes 16 which pass through opposing walls of the furnace. The charge 10 is placed in the furnace so that its surface is level with the end electrodes 16; a plurality of conductive rods 18, e.g. B. made of carbon, is placed in the furnace across the current flow from electrode to electrode parallel to each other at a distance from each other. The end rods are arranged at an appropriate distance from the electrode ends of the furnace. Granular resistance material 20, e.g. B. crushed coal or graphite, introduced, this granular material is used in such an amount that its surface corresponds to the boundary surfaces of the rods 18. The furnace is then filled with the reaction mixture so far that the surface of the charged charge is substantially above the upper boundary surfaces of the conductive rods 18 and above these rods there is approximately the same mass of charge material as below these rods. An electric current is now passed through the electrodes 16 into the furnace, which passes through the granular resistance material 20, which is thereby heated and on the one hand heats the conductive rods 18 so that a heating element with a large heating surface is created in the charge of the reaction mixture. The following examples relating to the application of the invention to the production of carbides illustrate the practice of the invention. In a conventional oven with end electrodes 914 cm apart, carbon rods approximately 26.8 cm 2 in cross-section by 127 cm in length were embedded in a reaction mixture 10 cm apart. The spaces between the carbon rods were filled with granulated graphite (of a grain size that passes through a 10-mesh sieve and is retained by a 20-mesh sieve [sieve openings of 0.165 and 0.833 cm, respectively]). The reaction mixture consisted of about 64% titanium oxide, 28% petroleum coke, 4.5% sawdust and 3.5% water; the weight of the mass poured in was 39,000 kg. When an electric current was applied to the furnace, it was found that the temperature could be adjusted to a value between 1600 and 2200 ° C as required. The conductive rods and the resistance material formed a heating element with a heating surface of about 25.6 m2; the batch surrounding this heating surface was supplied with heat at a rate of 390 to 600 watts per dm2 of heating surface. 7 <j After the introduction of a total amount of heat of 61,270 kilowatt hours, the electricity was switched off; the stove cooled down for a week. After this cooling period, loose unreacted mixture was removed; What remained was a porous core 22 made of titanium carbide. The cross-section of this core was, as FIG. 3 shows, elliptical and of uniform cross-section over the entire length between the electrodes of the furnace. The resulting titanium carbide product weighed 12,670 kg. The properties of the product were essentially uniform throughout the mass. In another experiment, approximately 4490 kg of a reaction mixture of approximately the same composition as that of the previous example was treated at approximately 63,000 kilowatt hours for approximately 49 hours. Here, too, an elliptical core of titanium carbide of uniform porosity and uniform properties was obtained. About 13,600 kg of titanium carbide were obtained. About 5000 kg of a reaction mixture of silica sand and petroleum coke in a ratio of 10 parts by weight to 6 parts by weight of coke were placed in a somewhat smaller furnace than that used in the above examples to produce silicon carbide. This mixture also contained 3% sawdust and 3% moisture. A number of carbon rods measuring 5.08 x 5.08 x 5.08 cm were embedded in the charge as in the examples above; the spaces between the bars were filled with granulated graphite. A total of 10610 kilowatt hours were sent through the mass in about 36 hours. An elliptical core made of silicon carbide weighing 871 kg was obtained. The method of the invention is not only applicable to the heating of a reaction mixture to carry out a desired chemical reaction, but can also be used in all methods in which a solid substance is to be heated to temperatures above about 1500 ° C. “Coal” or “carbon” also means amorphous coal or graphite or amorphous carbon, namely a natural or artificially produced material. Patent claims: 1. Electric resistance furnace for temperatures in the range from 1500 to 2200 ° C with one embedded in the item to be treated transversely to the direction of flow at a distance from one another Bars made of carbon radiators for heating and moving finely divided, solid and, when cold, substances that do not conduct electricity significantly, thereby characterized in that the distance between the bars of carbon continuously with a granular resistance material that still conducts the electric current even when cold, for example with granulated graphite, and that the bars are made of carbon are supported downward solely by the sintering material and that the heating current of the furnace is set to such temperature conditions that only part of the good to be treated melts. 2. Electric resistance furnace according to claim 1, characterized in that the granular