US2352051A - Method for azotizing calcium carbide and carbide mixtures - Google Patents

Description

R. wENDLAND'r ETAL Filed Maren-14. 1941 METHOD FOR AZOTIZING CALCIUM CARBIDE AND CARBIDE MIXWRES June 20, 1944.

Patented June 20, 1944 mamon Foa Azo'rrzmG cALcmM canamr AND emma inxrunas Rudolf Wendlandt, Gerhard Hoffmann.. `and 'Hans Fldner, Piesteritz, near Balle, Germany: vested in the Alien Property Custodian Application March 14, 1941, Serial No. 383,338 In Germany May 29, 1937 In connection with the azotizing of calcium carbideinto calcium cyanamide it is a wellknown practice to collect fused carbide flowing from a. carbide furnace in pans, and, in a given case, for the purpose of partial azotizing, press nitrogen through the walls of such pans and through the fused carbide, respectively; to subsequently inely grind the carbide partially azotizd while in complete fusion and then azotize it again. It is furthermore a well-known practice.' previous to azotizing to .add finished calcium cyanamide to cooled-down carbide. Another well-known method provides the disintegration of carbide by means of an innocuous stream of gas in connection with the rapid cooling of the carbide below the azotizing temperature. These methods involve the disadvantage of heavy wear and tear of the carbide receptacles required for partial azotizing, cumbersome meansof transportation, adverse material and energy balances, and diilicult adaptability to large-scale industrial operations respectively so that hitherto they could not assert themselves in the field of largescale technology. l

All these disadvantages are eliminated by the new invention which is characterized by the feature that fused carbide flowing from a carbide furnace and having been suitably finely disintegrated, by'means of centrifugal forces for instance, is conveyed to a revolving drum in any desired manner, especially by being hurled into such a drum, becoming at the same time, under emission of heat, congealed before reaching, or in, the forward part of the drum in the stream of nitrogen, andl subsequently and while in motion azotized by means of nitrogen of higher temperatures and conducted through it. It has been found that azotizing or partial azotizing under temperatures coming from above, such as passed during the cooling-down of carbide fusion,

. is feasible, surprising as it may seem, but it is feasible under full safety ofoperation only if the material is continuously kept in v`rolling motion, without, contrary to other methods, re-` 'quiring quickest possible cooling-down below asotizing temperature.v By the new invention not only the cooling of the carbide in a cooling room and the loss of carbide involved in such cooling is avoided andthe damage to the azotizing process, in the form of carbonic acid and water contents of the carbide, reduced, but a return of finished calcium cyanamide, for the purpose of its admixture to carbide filling material, as well as the admixture station of calcium A further remarkable advantage is to be found `in the fact that the capacity of. any calcium cyanamide plant isconsiderably increased by the new method, without requiring any increase in the number and size of the azotizing furnaces whatever type they may belong to. Provided, for instance, that the initial nitrogencontents of the carbide filling material be 5 to 'I per cent., thenthe capacity increase will approximate 25 to 40 per cent. The fact that any return of calcium cyanamideis avoided'not only results in shorter and simpler means'of conveyance, but also in the elimination of damage due to the absorption of water and carbonio acid, caused by the return, and to hitherto longer means of conveyance, so that by increased yield of azotized carbide further favourable results are attained.

A further advantage of the method according to the invention is to'be found in the improvement of the energy andmaterial balances of the azotizing process, Le. in the savingof current required for the operation of lmills and furnaces and of energy required for the transportation of material. A special merit is to be found in the fact that all these various advantages and improvements within one and the same apparatus can be effected in ,an especially simple manner.

Disintegration of the fused carbide flowing from the carbide furnace can be achieved in any desired manner, so for instance by spraying the duid stream of carbide by means of nitrogen, in which connection, however, during and after disintegration excessive cooling down of the sprayed carbide, caused by excessive extraction of heat, must be avoided. It is especially advantageous to effect disintegration by-means of a rotating roller or disc, a centrifuge, or the like,` and to convey the so finely distintegrated carbide to a drum in any desired manner, preferably |by hurling it directly into the rotatingdrum, in such a manner that' the rotating roller,'or the like,

represents the means of both disintegration and transportation. If desired, the rotating drum is wholly or partly provided with guide vanes; or with winding guiderecesses -in its masonry lining, /or thelike, and/or arranged inclined in front \or rear, so. that disintegrated carbide,

hurled into it for instance, is made 'to pass through it. In the forward part, the carbide, if necessary, is made `to congeal under emission of heat. whereupon partial .azotizing of the disintesrated. congealed carbide-according to the invention coming from higher temperatures- Wnamide proper. are rendered superfluous in, takes place, while in motion, by means of nitrogen which moves in opposite direction (countercurrent) to'the carbide. However, parallel-current or partly parallel-current and partly counter-current motion may be applied; so for instance in connection with the disintegration of the carbide by spraying it by means of nitrogen. -For partial/azotizingA either `pure nitrogen, or residuary nitrogen derived from carbide or calcium cyanamidel mills or from azotizing furnaces, or the like, may lbe used, or vice versa.

It is an astonishing fact that in this manner it is possible during an only short time of stay to fill the carbide \with quantities of nitrogen, 3 to per cent. for instance, favourably influencing subsequent final azotizing. It is another astonishing fact that with partial azotizing in the sense of the present-invention, while the carbide is in motion,' the disintegrated carbide does not agglomerate but passes. through the apparatus without sticking, and the like. The carbide which in the form of porous material similar to coking duif results from the'use of'a sprayingroller is especially adapted for partial azotizing, and under temperatures in the sense of the present invention will surprisingly readily and to a large extent absorb nitrogen within a short time, that is to say, more than five per cent. of nitrogen in less than minutes. The absorbed quantities of nitrogen can be smaller or larger, and they depend not only on the time of stay in the azotizing zone, but also on the temperature conditions surrounding partial azotizing, the admixtures or the mixtures added, the size and the composition of the grain,` the percentage of the carbide, the conditions under which the carbide is generated, the conditions under which the disintegrated carbide is generated, etc. Partly, these conditions can be regulated,.so for instance by the use of a disintegrating devicekbased on the the carbide in motion and coming from`=`higher temperatures will absorb the desired quantity of nitrogen.

In ,the sense of the invention it has proved'of advantage for'partial azotization at atmospheric pressure to keep the range of temperature between 2912 and 2192 F., and in particular bev theless, temperatures of from 2552 to 2812 1"., and in excess thereof, may be used in connection with partial azotizing.

Naturally, the absorption of nitrogen is the quicker and themore uniform the more uniform and iinerthe splitting up of the calcium carbide stream- It would be erroneous, however, to believe that the process in question be practicable only in connection with dimcult measures of disintegration. ,It has proved a surprising fact that with comparatively coarse and ununiform disintegration favourable .degrees of absorption can be obtainedtoo.Y` In one case for instance-40 per cent. of the carbide by a rapidly rotating roller had a size of grain of up to 5 millimeters, and 83 per cent. a size 0f grain of up to 10 millimeters. In the case of admlxtures being used, nitrogen contents of 2 per cent. were obtained at a temperature of 2552 to 2372 F. in the zone of partial azotizing, and during la.` time oi stay of 5 minutes. During a time of stay of 10 minutes, 5 per cent. of nitrogen were obtained ywith iluorite, while during 20-25 minutes time of stay, in connection with the use of admixtures, '1.7 and 9.6 per cent. respectively .were obtained. An approximately equal admixture of fiuorlte and calcium cyanamide has also proved advantageous. i

After azotizing, the partially azotized carbide is preferably cooled, so forinstance'by means of enlarging the free cross sectional area of the drum, by external cooling, by free fall through spaces rinsed with protective gas, by cooling coils, or the like. After having cooled down to a temperature commensurable to its further treatment,

the azotized carbide can be ground together with or Without any admixed material enhancing or rarefying the reaction of azotizing, and then azotized. It also is possible to produce partially azotized carbide of higher nitrogen contents than required, and to add suitable quantities of preliminarily crushed or ground carbide of lower nitrogen contents, or to admix such carbide in a finely divided form after the grinding of the partly azotized carbide. Other admixing materials too must not be admixed until after the partially azotized carbide has been ground.

In the case of a special type of construction embodying the new method, the material, partial azotizing being completed, is further azotized in the rotating drum. Such further azotizing takes place at or below the temperatures applied `for partial azotizing. It is 0f particular advantage to extend the time of stay in the initial zones adjacent to the zone of partial azotizing to such vcoming out of the higher temperatures of azotizing can be further azotized, at temperatures b'etween 2372 and 1832 F. for instance. Without further input of energy, such complete azotizing is possible only by utilization of the heat contents of the glowing carbide being tapped and of the heat of reaction. Excessive heat of reaction can be utilized for any desired purpose, for the generation of steam for instance. However, under -certain conditions, especially towards the end of complete azotizing, or in connection with discontinuous operation for instance, it is possible to also apply additional input of energy.

Another advantageous form of application of y the new process in `connection with partial or 1 continued azotizing is that zones of 'increasedtemperatures due to heat of reaction and zones of vconstant temperature respectively are followed by cooling zones, or vice versa. If partial` azotizing takes place at higher temperatures, then the absorbable` quantities of nitrogen arel physicoe chemicallylimited, while in the case of cooling to lower temperatures, new absorption of nitrogen will'start again.' It conforms to the sense of the invention for instance that temperature increase and cooling occur vseveral times in succession, or:

losses ln connection with the discharging or dis- 'as may be desired. In this manner, the presentprocess provides a regulation of the absorption of nitrogen, excluding any and all danger of overheating. v

Preferably, admixing substances enhancing azotizing and partial azotizing respectively are added tothe carbide by feeding them onto the spraying roller, the disc, or the like, or into the rotating drum. For the purpose of partial azotizing and in order to obtain shorter times of stay of the material in the drum. for partial azotizing,

preferably such admixing material is used as will result in especially rapid initial absorption of nitrogen. Such admixig substances include for instance chloride and fiuorides of alkalies, chlorides of\alkaline earths, calcium cyanamide itself, or mixtures composed of such substances or of such substances and other substances. If, however, further azotizing and final azotizing respectively in one and the same drum'be simultaneously desired, then admixing substances simultaneously enhancing these two parts of azotizing should be used; uorite for instance. Fluorite may be used for partial azotizing also.

feeding them onto a Water-cooled spraying roller, disc, or the like, or into the forward part of the rotating drum., but only after partial azotizing in the cooling zone or prior to the carbides passing or after its having passed the. mills. A suitable form of adding admixing substances or a mixture of admixing substances consists of blowing them in a iinely dvded condition, bymeans of a stream integrated carbide are fully excluded, the attendants eectually protected from any and all trouble, and practically a iree-from-loss utilization of the nitrogen is attained. Special atten- V tion is drawn to the fact that the nitrogen can Y be used again or pumped oi, and, if need be, after its plu'ication conducted again into the rotating drum, the tapping chamber and the mills respectively. The chamber, water-cooled if required or desired, is provided with oriiices for burning open the tap hole and for removing pieces of `carbide which may have dropped down. Continuous tapping provided, this type of construction represents one single aggregate continuously producing preliminarily azotized, granular carbide and finished granular calcium cyanamide respectively directly from uid carbide, at highest utilization of the nitrogen, without any loss of carbide and without any additional input of energy.

The adding of such substances enhancing further and nal azotizing respectively can also be effected by of gas-a stream of nitrogen for instance-onto, o

the disintegrating device or into tht,` rotating drum. In doing so, the gas stream carrying the admixing substance can for instance be made to travel in the direction of ow of the material, and the stream of gas supplying the drum., in a direction opposite to the iiow of the material, so

that the bathing with nitrogen takes place partly minimum consumption of nitrogen and without any restriction of the passage of material.

The invention results in additional advantages, provided, the carbidefurnace tap, the disintegrating device and the head of the rotating drum, or at least the distintegrating device and the -rotating drum, are interconnected by means of' an easily. accessible nitrogen-bathed chamber which,

if necessary or desired, is sealed against the rotating parts (rotating drum, drive shaft of the disintegrating device, etc.). With this type of construction, the stream of carbide'iiows exclusively within the nitrogen-bathed chamber which is tightened against both carbide furnace Y and rotatingdrum. In this-manner, calculation furnacev having a tapping snout 2 through which molten carbide leaves the furnace. The numeral Another form of application of the 4new method consists of subdividing the .drum into two or more drums, in which case the different drums assume the respective functions of the original drum parts. By doing so, the individual drums servfing for azotizing., partial azotizing and cooling respectively, can be regulated in such a manner, as far as speed oi rotation, pitch, diameter, etc., are concerned, that at smallest power consumption most favourable effects of azotizing and cooling respectively can be attained, irrespective of how heavily the quantities vof material passing through may vary.

The apparatus aspect of the invention is illus-- trated in the accompanying drawing, in which the single gure is a diagrammatic view, partially in section, of apparatus adapted for carrying out the above described process. In the drawing, the numeral i designates the calcium carbide 2a designates a gutter for leading molten carbide from the tapping snout 2 of the carbide furnace to the disintegrating and azotizing apparatus of the invention. Numeral 3 designates a conically shaped roller disposed partially within,

Molten carbide falling from gutter 2a onto the u surface of rapidly rotating roller -3 is disintegrated (aneiy divided) by the naar; simultaneused at the same time fr driving the drum. It Y is provided internally, at least in part, with a heat-insulating lining 9.

In the front part of the drum D, a retaining "chambeaj-n 'is formed by the built-1n b'ame wan fit of material greatly resistant to heat, and in;l

this retaining chamber the glowing hot carbide" is-backed up for the purpose of lengthening the time that Iit remains in this tempera ture zone. The divided up or granular carbide enters the retaining chamber Il through the opening I2, is

backed up in the retaining chamber itself, and

' thereafter passes out through the opening Il and enters the other part of the drum through which it moves on slowly (from right to left in the iigure). In the retaining chamber Il, the temperature oi the carbide is still so great that azotizing to calcium cyanamide occurs at least partially. 'I'he retaining chamber can be extended over any desired length of the drum.

As soon as the carbide has left the opening I3, there is stillanother absorption of nitrogen on its path through the drum with descending temperatures, so that according to the speed of rotation, length of the drum, heat insulation of the lining 9, iineness of the division of the carbide by thespraying drum i, etc., more-or less partial or complete azotization can be produced.

In order to maintain a nitrogen environment in the drum D (including the retaining chamber I I), nitrogen is admitted into .thev drum from the left by known means, and thereby flows in counter-current to the path oi the carbide.

-The more or less completely azotized carbide leaves the drum D at Il, and enters a conveyor I5, by means of which it is available for further use. Ii it is suiliciently finely divided it is azotized completely in an azotizing furnace of a suitable type, or else it is led, after thorough cooling,

as semi-azotized carbide, to carbide mills and,

the known type. revolving furnaces or the like, and, as high-percentage lime nitrogen, is completely azotized.

We claim:

1. A process for. producing partially azotized disintegrated calcium carbide which comprises subjecting liquid carbide to the action of centrifugal force to disintegrate the same and contacting said liquid disintegrated carbide in a zone of `rotary motion with nitrogen heated in a zone removed therefrom-while subjecting said carbide to continuous agitation while solidifylng and partially azotizing, said nitrogen` being supplied at a temperature sumcient to maintain said carbide undergoing partial azotization at a temperature between 2282 F. and 2552 F., v

RUDOLF WENDLANDT.

after being finely ground. to vertical furnaces ofI

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