US1158899A - Electric furnace intended chiefly for the manufacture of nitrids. - Google Patents

Description

G. COUTAGNE.

ELECTRIC FURNACE INTENDED CHIEFLY FOR THE MANUFACTURE OF NITRIDS. APPLICATION. FILED MAY2I.19I4.

1,158.899. Patented Nov. 2, 1915.

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GEoiiGEs ICOUTAGNE, or- LYON, FRANCE.

ELECTRIC FURNACE INTENDED CHIEELY FOR THE MANUFACTURE OF NITRIDS.

Specification of Letters Patent.

Patented Nov. 2, 1915.

Application filed May 21, 1914. Serial No. 839,963.

tric Furnaces Intended Chiefiy for the.

Manufacture of Nitrids, of which the following is a specification. Thomas Leopold Willson patented 'in England as No. 217 55 of November 15, 1895,

.. the manufacture of aluminium nitrid by heating in an electric furnace in the presence of nitrogen a mixture of carbon and alu- On heating in a small electric furnace, ar-- ranged as described and shown by Willson, a mixture of bauxite and coal such as coke or. anthracite and by blowing generator gas into the incandescent mass, it is indeed possible to obtain a more or less abundant amount of aluminium nitrid. If one tries to use this process of manufacture on an industrial scale however by using the one or the other of the four devices shown by I'Villson, on having enlarged the same and even on having considerably modified the relative proportions of the various parts, no satis-' factory result is obtained.

A great number of devices that differ considerably from those of Willson and most of which are very ingenious have been contrived, patented and tried during these last years. The difficulties to be overcome are such however that the manufacture of aluminium nitrid has not been practicable hithereto on anindustrial scale. It appeared preferable thereafter to go back to WVillsons process and simply improve the furnace with intermittent working proposed by the American inventor in 1895, without tryingtocontrive a furnace with continuous working. After a great many tests really practical results have at last been ob The' aluminousmaterial to be used Generator gas has besides altained with the furnace described and shown in the present specification. This furnace is derived from the device of Figure 1 of Willsons patent comprising essentially as an vupper electrode a cylindrical solid vertical and movable electrode, as a lower electrode a mass of agglomerated carbon in theform of a crucibleand for the introduction of. the generator gas an axial channel in the lower electrode. In these original arrangements that have. been retained four modifications or new features have been made that are all very important, and a The same are as follows:

1. The lower electrode is made of a large tube A (see the accompanying figure of the present specification), which is vertical, cylindrical or polygonal, very thick and constitutes an electrode-of agglomerated coal. The inside space of this tube is filled with coke B, and a layer O of refractory material forming a bad conductor of electricity, for instance ordinary crushed bauxite reduced tosand, surrounds the tube A. The tube A must be fairly high so that the hearth of steel which supports the tube and through which the currentis fed is never heated too strongly. The inside of tube A must be large enough that the generator gas which is supplied under pressure through tube D and first spreads out in the annular space E. can rise in the mass of coke in fairly large.

quantity and without too high aspeed.

2. The furnace is entirely surrounded by a metal casing composed of cast iron or cast steel parts or of iron or steel plates with air tight joints, so that the nitrogenized gas may on the one hand be injected under pres-v sure and can overcome the resistance caused by the mass of material treated in the furmace and in order that the residual gases consisting chiefly of carbon monoxid and a bsolutely essential.

little nitrogen that has not been combined can on the other hand be collected, passed out and used any distance away from the furnace. These gases pass out at the opening G; The latter may be arranged at any other placeinstead of the one shown, provided it is always at the upper part of the furnace. pended on a steel rod I which slides in a stuffingbox. Openings K are arranged in a suitable number all'around the electrode on the metal lid of the furnace and serve for introducing the mixture ofbauxite and coal. These openings must be provided with The movable electrode H is sus-.

lids or any other contrivance' that will'prevent the gases from passing out. In-

sulating-joints are provided between the sev- "-"eral shell rings of sheetiron thatare built;

' aup to fo'rm -the casing of the'furnaeef It has been found for instance that a good a1"- rangement is obtained by making two insuatNN.

lating joints, one at the bottom of, the fur nace between the first and the second shell ring, at M M,'and the other at the top Where come. On carefully studying the conditions of working of the new furnace described in the present specification it will be 'understood moreover that by localizing the 'work of the electric current in the v-axis'of the furnace, 'the mixture of bauxite and coalwhich is next to the sheet iron casing is not penetrated by the currentand does not'undergo the reaction, so that it remains'in the state of a pulverulent mixture or a mixturethat is slightly agglomerated and only conducts heat to a slight extent, so that it is perfectly apt to act as a non-conducting materlal. 4

/ 4. The upper shell rings of the furnace have to be arranged so that they can be .so as to be able to remove the mass of aluminium nitrid formed after each opera- 40 taken down and removed easily and quickly,

tion and take it, over to another workshop. In industrial furnaces of high power each shell ring can be made of several parts. In-

stead of using superposed cylindrical shell rings the metal casing maybe made in any other manner, for instance of walls, all of which or part only can readily be removed.

.This furnace is used in the following manner: When the movable electrode has-been brought right down and even engaged a little in the central space inside tube A, the

current passes from one electrode to theother through the coke and this condition is maintainedfor some time, so as to thoroughly heat the annular hearth and the coke. The supply is'then started which is made thereafter at regular intervals through'the upper openings K, and. atthe 's'ame'time the 'lnjection' ofthe generator 'gas through tube D is begun. An operation lasts several days v and is finished when the whole inner cavity w or recess of the furnace is filled'.- The weights of eachfcharge are obtained by experience" as well asthe: interval between two 'consecutive charges that-is most suitable for the capacity and power of'each'furnace. Care must be taken particularlyeat the beginning of the operation to avoid feeding theifurnace too quickly with too'large quantities of the mixturefof bauxite: and coalfas other-- ,wise' a large metallic mass of an alloy. of

iron,'sil icium andaluminium is obtained on the tubular'hearth that'is: not easily pene-- tratedby the nitrogen, sothat this mass is only' partly transformed jat'its periphery -into aluminium nitrid.v If the. charges are supplied on the contrary at longer intervals and are reduced toan adequate extent,each

charge is partly brought to the temperature of the reaction and even partly transformed "-into nitrid when the following charge is fed,

and as the particles of metallic alloy'contained in the vmass are smalland dissemi--" n'ated in a mass permeableto gas, they grad 'ually allow their aluminium to combine with the nitrogen.

.The furnace could'evidently be supplied also in a continuous manner, but this would not be so simple. The example of blast furnaces shows that working on a large-scale can quite well be effected with discontinuous charges. Y When the operation is finished the electric current and the current of gas containing nitrogen are interrupted and on having cooled down and opened thefurnace a large cake ofaluminium nitrid is found that is surrounded by a slightly agglomerated layer of a mixture of bauxite and coal, that can easily be separated from the nitrid and can' bev put aside to be introduced again in the following operation together with the mixture of new. material.

The crude aluminium nitrid also contains I grains or small clusters of'metallic alloy ale. ferro-silicium with a varying amount of aluminium. On having reduced and crushed the mass these metallic parts can easily be certain purposes however such as the manufacture of annnonia in which the alumina 1s returned to 'the nitrid furnace, this separation is not necessary. These particles of metallic alloy and particularly the larger.

masses of this same alloy that are some- "separated by any suitable means, for instance by an electromagnetic separator. For

times found 'in the cake, principally in its lower part, moreover fall into dust after some time, particularly in moist air, prob ably owing totheaction of small quantities of aluminium carbid disseminated in the substance of these masses or particles. This property can therefore be used even together with the addition of water or a treatment with water vapor at atmosphericpressure;

this treatment does not decompose the alunitrid.- The reduction to dust can therefore be "accelerated, as the same. largelyfacilitates the separation of the various products mixed with the nitrid in the crude cake takeniout of the furnace.

' cess of. coal, in .the mixture of bauxite and In the parts of the cake that are nearest to the-electrode geodes are found that are covcred with Crystals of nitrid' and carborundum, which give an idea of the temperature attained in the furnace. It is known indeed that according to the experiments of Tucker and Lampen (Journal of the Amem'can 'Ukemicdl Society, 1906), carborundum only begins to assume a crystalline form toward 1950o 7 y When'using ordinary red bauxite an excoal; with regard to the amount calculated according to the chemical formulae as being necessary for completely .deoxidizing the bauxite, is not necessary either for increasing the permeability for the gases or for increasing the electric conducting properties of the'mixture. If another kind of bauxite is used however 01' other aluminous material an excess of coal is of advantage, as pro.-

posed already in 1896 by G. de Chalmot.

Generator gas containing about 35% of carbonmonoxid produces very satisfactory results; by using pure nitrogen however the yield would of course'be improved. According to the cost prices at which generator gas ornitrogen can be had in each case, it will be of advantage to use either the one or the other of these gases. As the nitrid remains subjected to a high temperature after the, moment it has, been formed till the end ofeach operation, the retrogression recently pointed out and studied by Fraenkel (Zeitsckrift f'eir Elektrochemie, April 15, 1913,

p.362-373) and that isparticularly importrodes being in the form of a tubular carbonaceous block and forming a part of the base of the furnace, and a filling of coke in said tubular block.

2. An electric furnace for the production of nitrids comprising a chamber havingelectrodes therein, the lower one of said electrodes bein in the form of ajtubular carbonaceous lock surrounded at its sides by refractory material and forming a part of the base of the furnace, and a filling of coke in said tubular block. v

3. An electric furnace for the production of nitrids comprising a chamber having electrodes therein, one of said electrodes being 5 in the'for'm of a tubular carbonaceous block, a filling of loose'carbonaceous material in said tubular block, and an inlet for a supply of nitrogen in communication with said furnace through said loose filling.

4. An electric furnace for the productionof nitrids comprising a'chamber, a pair of electrodes therein, one of said electrodes being in the form of a stick or pencil andthe other in the form of a tubular carbonaceous block, a filling of loose carbonaceous material in said tubular block, and an inlet for a supply of nitrogen in communication with -:said furnace through said loose filling.

5. An electric furnace for the production of nitrids comprising a chamber having electrodes therein, one of said electrodes being in the form of a tubular carbonaceous block,

a loose filling of coke in said tubular block, and said chamber above said tubular block being of relatively large capacity and the inner surface being of iron and unlined with refractory material.

6. An electric furnace for the production of nitrids comprising a chamber having electrodes therein, one of said electrodes being in the form of a tubular carbonaceous block, a loose filling of carbonaceous material in said tubular block, and an inlet for the supply of nitrogen in communication with said furnace through said loose filling, the tubular space in said tubular block being relatively large, the gas being capable of spreading out therein and passing through at a relatively low speed.

In witness whereof, I have hereunto signed my name in the presence of two subscribing witnesses.

GEORGES COUTAGNE.

Witnesses:

' JEAN MILLION,

VINCENT MILLIoN.

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