US1321892A - Island - Google Patents

Description

A. I". CROVVELI., IR.

FURNACE 'FOR NITROGEN FIXATION.

APPLICATloN FILED MAR.7.19|a.

Patented Nov. 18, 1919.

fw @MAW .@tZARIA-I FOSTER CROWELL, JR., OF SALTVILLE, VIRGINIA, PRODUCTS COMPANY, OF PROVIDENCE, RHODE ISLAND, A.

ISLAND.

ASSIGNOR TO NITROGEN CORPORATION OF RHODE FURNACE FOR NITROGEN FIXATION.

ieeasae.

Specification of Letters Patent.

Patented Nov, 18, 1919.

Application filed March 7, 191e. Serial No. 221,053.

To all whom t may concern.'

lie it known that I, AzAniAii lfosfriiii CROW- iiiiL, Jr., a citizen of the United States, residing at Saltville, in the county of Smyth and State of Virginia, have invented certain new and useful Improvements in `Furnaces for Nitrogen Fixation, of which the :following is a specification.

vThis invention relates to furnaces used in' effecting the fixation of free or atmospheric nitrogen, and more particularly concerns an improvement in the retorts used in such furnaces, especially where such retorts are of the eontinously feeding type. l

Une of the principal objects of my invention is to improve the delivery of the charge past critical feeding points in retorts of this and likedescription; and another obJect is to prolong the lives of such retorts, and at the saine time maintain their cost substantially at a minimum.

These and other objects of my invention will be hereinafter referred to and the novel combinations of means and elements whereby said objects may be attained will be more particularly pointed out 1n the claims appended hereto.

lin the patent to John E. Bucher, No. 1,120,682, dated December 15, 1914:, there 1s described a process for fixing nitrogen in the form of metal cyanid; an alkali metal, c. g. sodium, being preferred as the base of the cyanogen compound to be formed.

This processl preferably involves the formation of briquets comprising suitable proportions o'f finely divided carbon and iron,

or the like, intimately mixed and bound together with sodium carbonate or its equivalent. These briquets are introduced atthe top and feed through the retort by gravity,

to be removed from the cooling section of the apparatus at the bottom.

1While passing through the heat zone they are subjected to nitrogen which has been preheated, as by coming in contact with the briquets being cooled in said cooling section,-and the gaseous reaction products as cend from the heat zone to prelieat the incoming briquets.

As the briquets attain a temperature of preferably from about 900 to about 1100o C. while Vpassing through the reaction Zone,- when sodium cyanid is the product sought, they become rather plastic; but normally not so much so as will cause them to be seriously mashed out of shape.

lf, under such conditions, their progressI through the retort is not otherwise interfered with, they will tend, by gravity, to feed through quite smoothly; but there is a factor which hitherto has caused great trouble and expense in this connection; this factor being, as l have discovered, the action of the cyanid formed in the charge, when said cyanid is eongealing or solidifying.

lt could not for a long time be apprehended that the product itself was the priucipal cause of feed troubles, the difficulty being attributed to the sodium carbonate or like material used as a binder for the briquets. llt occurred to me, however, that on account of the relatively low fusing point of the cyanid, e. about 540 C. for sodium cyanid (a low red heat for potassium cyanid), as compared to the melting point of, for example, sodium carbonate-about 850 C. (or 880 C. for potassium carbonate),-the cyanid itself might be, in large part at least, the cause of said trouble.

ll have now found this to be true and that the reason therefor is apparently as follows:

Assuming that a given briquet adjacent the wall of the retort has entered the heat zone, then cyanid will begin to forni in this briquet; such formation being usually supplemented by some condensed cyanid which had been formed elsewhere in the charge and been volatilized-to be thereafter condensed in said given briquet, for example, before the latter entered the heat zone,

ln any case, cyaiiid normally tends to accumulate in the selected briquet, as the latter moves down through the reaction or heat zone, and this cyanid` probably is wholly molten, although retained iny the pores of the briquet by capillai'ity. So long as this cyanid is liquid, however, it does not tend to adhere to the surface past which it is sliding when the briquet containing it comes .in contact with said surface; but when said briquet has cooled to, as nearly as 1 can determine, somewhat below 6000, the cyanized briquet becomes more or less adherent or sticky and tends to stick fast to whatever it encounters. This sticking of the cyanized briquets obviously ehokes the feed and the downward flow of the charge is first im peded and thereafter wholly stopped.

It has hitherto in such case been found to be necessary to remove the retort from its |furnace, allow it to cool and, with great difficulty, then remove the charge.

Having located the source of the trouble, I then discovered that it could be most satisfactorily overcome by providing an abrupt offset in the wall of the retort at about this critical point; so that just when the briquets became adhesive, they would enter a space in the retort of greater cross-sectional area than that through which they had been passing,-the retort walls being, in e'ect, abruptly removed, so that the briquets could not adhere to them.

Such of these briquets as lie in the cylindrical surface of the briquet column may `shortly afterward again encounter the surface of the retort; but by then the cyanid has congealed and does not materially tend to stick.

ft will be appreciated that a gradual taper of the retort wall, such as that shown in said patent to Bucher, will not nearly so well meet the above conditions as does the abrupt offset aforesaid,-because the material becoming tacky or adhesive, will, of course, gradually be pushed out to maintain its contact with the correspondingl gradually flaring or tapering wall and wi l hence stick to the latter as soon as it becomes sufficiently adhesive.

ll1`or similar reasons, it will not do to place the offset haphazardly along the length of the retort; but rather it must be at, or substantially at, the said critical point. rThis is normally disposed a short distance below the bottom of the heatzone, where cooling of the charge by incoming gas or by radiation, or preferably by both, has lowered the temperature of the descending material to where such material becomes adherent as aforesaid.

I have found, too, that it is desirable to somewhat similarly abruptly reduce the upper end of the retort, especially above, or at the entrance to, the heat zone, to restrict the too free admission of the briquets to said heat zone at this second point where choking is apt to occur. The point first mentioned is, however, by far the more important of the two, as the choking action at the top of the heat vZone is not nearly so pro,- nounced as at lthe bottom.

In the accompanying drawing which forms a part hereof, I have exemplified a preferred form of my invention; but as I am aware of various changes and modifications which may be made thereto without departing from the spirit of said invention, I desire to be limited only by the appended claims, broadly considered in the light of my disclosure.

Referring to the drawing:

Figure l is a side elevation of a preferred form of my improved retort, showing it in position in a nitrogen fixing furnace, the furnace proper being diagrannnatically rcpresented in dotted lines, the interior walls, only, being drawn in full lines.

Fig. 2 is a view of said retort drawn to a larger scale and partly broken away to show details thereof; and

Fig. 3 is a bottom view of said retort.

The furnace comprises the usual walls or inclosure l of refractory brick or the like; the chamber which receives and co-acts with the retort to form a heat zone in the latter, being designated 2. rlihe heat supplying gases are caused to travel toward the fiue in the direction of the arrows, as indicated.

rPhe retort section 3 disposed within the chamber 2, is preferably made of, or at least cxteriorly coated with, a heat-resisting, or refractory alloy ;-such as one of iron and nickel; or of iron, chromium, nickel and manganese, or the like ,-which is capable of withstanding the high temperature to which it is normally continuously subjected when in use in the process.

However, were it not for the ability of the alloy or treated metal (e. g. nickel-impregnated iron) to resist the destructive or oXidizing action of the conveniently applied exterior heating flame, I should much prefer to form the entire retort of iron, because of its markedly lower cost, and further, because I consider that there is slightly less tendency lfor the charge to stick or cause accumulations on the retort walls, if of iron, than if made throughout of such an alloy as that aforesaid. Moreover, as iron, provided that operating conditions are maintained at their best, will stand up for a number of hundred hours, I do not wish to be limited to the alloy section or retort, except where specifically indicated in certain of the claims.

In this connection, also, I may point out that whether a retort be of iron or of such an alloy, there is frequently a tendency to thus form a coating on its lnner walls, and here the provision of a reduced upper or in'- take portion 4, aids in the maintenance of proper feeding conditions; since the walls of the retort section 8 must build out considerably before the effective inside diameter of said section is reduced to that of the inside diameter of the upper section 4, or, in other words, to such an extent as will abruptly throttle the incoming parts of the charge.

There is comparatively little tendency to thus build up a coating in this upper section, because it is above .the heat zone; while further as it is not subjected to the relatively intense heat and oxidizing conditions frequently present in the chamber 2, it may preferably and conveniently, and indeed at material saving in cost, be made of iron pipe; while, as above noted, even where any slight interior coating or slag`-forming ac`- tion is present in section 4, there is somewhat less of this action on iron than on the alloy.

The intake section 4, being thus preferably smallerin cross-sectional area than the tegral, should, of course, be joined together,1

as by welding, to afford gas-tight joints. On account of the load imposed upon the lower joint, the heat resistant section 3 is preferably provided with a flange 6, which engages the upper edge of the pipe or section 5, as shown.

rlhe retort is removably mounted in the furnace, readily removable bri-ckwork 7 and gas seals -8 of kieselguhr or the like being provided to this end. rlhe lower end of the reto-rt is received into a recess 9 in the casing l0 of a suitable charge removing mechanism; but as the particular mechanism employed to remove the charge is not my invention, and since various types of apparatus for this purpose may be used (the Bucher patent aforesaid showing one), l have merely dotted in the outlines of said casing l0, except that portion thereof which receives the end of my retort.

'lhis casing l0 is very conveniently employed as a means for directing or supplying a current of nitrogen to the lower end of the retort; the nitrogen flowing up through the casing toward said lower end, as indicated by the arrows, and receiving heat from the charge in course of removal.

A gas-tight connection between said casing and the cooling section of the retort is ed'ected by means of a loosely fitting re cessed ring ll which is pulled down by bolts to compact a packing 12 of kieselguhr or the like, against a corresponding part of the casing l0 and. against the outer wall of retort cooling section.

The briquets 13, some of which are shown entering the casing l0, are introduced into the feeding section 4 through a cap or hopper 14 which is loosely mounted upon the upper end of said feeding section. rllhey` then feed slowly down through section 4 and become preheated by the ascending gaseous reaction .produ-cts which-pass up through the hopper. 'lhe now hot briquets then enter the heat-zone section 3 where the cyanid forming reaction is ed'ected in them. The nitrogen for this reactionmay be supplied to the casing 10 in any desired manner and passes thence up through the cooling section 5,-where, as it is relatively cool upon its entrance into the latter, it cools the de- `sce'nding briquets emerging from the section 3.

I have found that a relatively shortl l initial cooling section 5 ameter thereof. The advantage of such a short cooling section over arelatively long one vis that while it is of sufficient extent to permit radiation and air cooling, coupled with the cooling effect of the incoming nitro- 'gem-to properly chill and harden the briquets following their emergence from the heat-zone, still it is not so long as to materially interfere with the feed of the briquets by gravity through the retort.

As the briquets pass from the heat-zone, their temperature rapidly falls, so that although they may have been at7 for example, 1000o C., at the point marked A in lig. 2, by the time that they arrive at B, they are usually nearly at a temperature at which u v`is' suificient,"tl1e length of thls section being preferably made' in practice but two or`three times the dithe cyanid with which they are impregnated and more or less coated, will begin to set or solidify. This temperature is, of course, the eutectic point of the mixture of fused cyanid and sodium carbonate, or the like. The dotted lines C, below the end of section 3 in Fig. 2, probably represent reasonably well the outer surface of the descending charge at this point; the exact rate at which said charge will slowly flow or bulge radially outwardly, depending obviouslyrupon the rate at which the charge cools, the amount of fused material present therein, etc.

Normally however while the briquets are about at the level of the point C', they will be most adhesive; but at such time, as indicated by the lines C, they will be spaced from the retort wall and only come in contact therewith at l), by which time they have lost most of their stickiness.

rllhe briquets, by now, cluttered and ad he-red together at their points of contact,-- but still with interstices therebetween,-feed on down until they are removed from the mouth of the retort by the chargeremoving mechanism aforesaid.

l may add in conclusion that atmospheric oxygen is preferably carefully excluded from the casing 10 and retort sections 5 and 3; ingress of air to the latter from the top being prevented by the ascending gaseous current in section 4.

Also, it will be well to point out that by the term abrupt as applied to the offset or offsets in the retort, l contemplate such a form of offset as will substantially free the retort walls at such point from close contact with the passing tacky material which would otherwise adhere to them; but that, while for cheapness of construction, the oifset adjacent C', for example, is made one of practically ninety degrees in cross-section, by reason of the end of the inserted retort section being fiat,itv is by nomeans necessary that the offsetting be quite so pronounced,sincc, as shown, there is an appreciable space between the line C- and the retort wall, and it is merely necessary to accord fair clearance to the charge at this critical point to prevent its close-adhesion to the adjacent retort walls. It will be understood that the length and contour of the lines C will depend upon the conditions present in the charge at this portion of its path of travel, i, c., cyanid content, rate of cooling, etc.

Having thus described my invention, what I claim is:

1. In apparatus for effecting the fixation ot' nitrogen, the combina-tion of a substantially vertical retort through which a briqueted charge to be treated is fed silbstantially continuously, means to deliver nitrogen to said retort, and means to constitute a heat zone in an interlnediate section of said retort, said retort comprising a cooling section below said intermediate section and an iii-take section above the latter, the intermediate section having its inner walls abruptly off-set, with respect to the inner walls of theA in-take section, to suddenly and materially increase the cross-sectional area of the retort at a point along the length of said retort which is near the upper end of said heat zone.

2. In apparatus for effecting the fixation of nitrogen, the combination of a subst-antially vertical retort through which a briqueted charve to be treated is fed substantially contmuously, means to deliver nitrogen to said retort, and means to constitute a heat zone in an intermediate section of saidretort, said retort comprising a cooling section below said intermediate section and an in-take section above the latter, the intermediate section having its walls abruptly off-set with respect to the inner walls of the in-take section, to suddenly and Amaterially increase the crossfsectional area of the retort at at least one point along the length of said retort, which point is near the upper end of said heat zone, the interior walls of said cooling section being similarly offset with respect to the interior walls of said intermediate section, to still further increase the cross-sectional area of the retort, at a point outside of the heat-zone proper and where perceptible congelation of a previously fluid part of the treated charge begins.

3. In apparatus for effecting thefixation of nitrogen, the combination of a sub stantially vertical retort through which a briqueted charge to be treated is fed substantially continuously, means to deliver walls an abrupt off-set to suddenly and materially increase the cross-sectional area of said retort, said off-set being located outside of said heat zone at a point along the length of said retort where perceptible congelation of a previously fiuid part of the treated charge begins.

4. In apparatus for effectinfY the fixation of nitrogen, the combination of a composite retort through which a briqueted charge is fed substantially continuously, means` to deliver nitrogen to said retort, and means to constitute a heat zone in van intermediate section of said retort, said retort comprising an iron cooling-section below7 said intermediate section and an iron in-take section above the latter, portions at least of said intermediate section being of material more heat-resistant than pure iron and autogenously united to the adjoining iron parts, said composite retort having a plurality of steps in its interior walls whereby its crosssectional area is abruptly increased at critical feeding points along its length.

In apparatus for effecting a nitrogenfixing reaction, the combination of a gravitationally fed retort with means to establish a heat zone therein, provisions to cool the charge traveling through said retort, upon the emergence of said charge from said heat zone, means to deliver to said charge the nitrogen to be fixed, and means to prevent adhesive accumulations on the Walls of said retort, resulting from said reaction, from hindering the downward movement of said charge.

6. In apparatus for effecting a nitrogenfixing reaction, the combination of a substantially vertical, continuously feeding retort with means to establish a heat zone therein, provisions to cool the material being treated in said retort, upon its emergence from said heat zone, and means to supply to said material the nitrogen to be fixed, said retort having a succession of steps in its walls to form relatively abrupt enlargements in its cross-sectional area at critical feeding points.

7. In apparatus for effecting a nitrogen fixing reaction, the combination of a substantially continuously feeding retort with means to establish a heat zone therein, and provisions to supply nitrogen to said retort and to establish a cooling zone in said retort contiguous to said heat zone, said retort having' in its Walls, outside of said heat zone, an offset to afford clearance space to said material as the latter arrives at a critical point where said material, when partly cooled, becomes especially tacky. Y

8. In apparatus for effecting a nitrogen' fixing reaction, the combination of a substantially continuously feeding retort with means to establish a heat zone therein, said retort being formed of vertically disposed,

partl telescoped sections, and provisions to supp y nitrogen to said retort and to estab lish a cooling zone in said retort contiguous to said heat zone, said' retort having in its walls, outside of said heat zone, an o'set to a'ord clearance space to said material as the latter arrives at a critical point Where said material, when partly cooled, becomes especially tacky, said offset being formed by telescoping a larger retort section over a smaller one, the larger section being the lower of the two.

9. lin` apparatus for e'ectingl a nitrogen xing reaction, the combination of a sub- Y stantially continuously feeding retort with means to establish a heat zone therein, said retort comprising. a section formed of heatresistant alloy Within which said heat zone is established, and a cooling section, portions of the walls of which are odset from those of the heat-zone section to free said off-set portions trom said material as the latter arrives at a critical point Where said materiaywhen partly cooled, becomes especially tac l0. ln apparatus for fixing nitrogen which includes a substantially vertical retort through which is ted a charge to react with free nitro en in said retort,-the improvement Whic consists in odsetting the Walls of said retort away from the passing charge, at a critical feeding point to prevent choking of said charge at such point.

11. In apparatus for fixing nitrogen which includes a substantially vertical retort through Which is fed a charge to react with free nitrogen in said retort and which retort comprises a heating zone and a coolingzone below said heating'zonef-the im rovement which consists in offsetting the Wa ls of said retort at a critical feeding point in said cooling zone. i

12. In apparatus for fixing nitrogen which includes a substantially vertical retort through which is fed a charge to react With free nitrogen in said retort and which retort comprisesa heating zone and a cooling zone below said hea-ting zone,-the improvement which consists in oiisetting the Walls of said retort at a critical feeding point in said cooling zone and thereafter continuing the offset Walls of said cooling zone down for but a proportionately short distance as compared to the over-all length 0f said retort.

ln testimony whereof ll have affixed my signature, in the presence of two Witnesses.

AZARIAH FOSTER CROWELL, JR. Witnesses:

LLOYD N. WATSON, J. M. Anoninn.

Images