USRE15119E - Method oxi and apparatus for reclaiming spent pickling solutions - Google Patents

Description

APPLICAT'ON FIIED MAN 28, I92].

R0is-1nvd J iuw 7, 1921.

INVENmRs 3. flan-4 W! TNESS E S mgcvmw um'rao STATES PATENT OFFICE.

Y B- M m S. 600M, 0] YOUNGSTOWN, OHIO.

Specification of Beiuued Letters Patent. Reissued J 7, 1921,

Original Io. 1388,451, dated I'ebruary 88, 1821, Serial No. 850,888, filed January 9, 1980. Application tor reissue fled larch 28, 1921. Serial No. 456,805.

To all whom it may comm:

Be it known that we, HENRY S.. Mansn, and Ram S. Coomum, residing at Youngstown, in the county of Maho and State of Ohio, both citizens of the Umted States, have invented or discovered certain new and useful Improvements in Methods'of and Aparatus for Reclaiming Spent Pickling So- Futions, of which improvements the followin is a specification.

r invention relates to methods of and apparatus for reclaimi spent icklin solutlons. The method, primarily mtende for the purpose stated, is of wider applicability, as will eventually a pear. The pickling op.- eration which is wi ely practised in the steelmaking industry, bemg incidental to all sorts of steel-working is essentially an operation in which the surface of an iron or steel article is cleaned of oxid, corrosion, or scale, and left bright. The operation is accomplished by submerging the coated article in a bath of acid, ordinarily dilute sulfuric acid. Chemical reaction ensues, the underlyi iron is attacked by the acid, and the ox i corrosion, or scale 1s loosened and falls awa leaving exposed a clean surface of metal 'c iron. The chemical reaction roduces a sulfate of iron (FeSO,7H,O) o as copperas, which besoluble, is, from its formation carried in solution in the bath.

In present-da practice in steel mills, the pickling bath, e solution of acid in which the coated articles are immersed and cleaned, becomes, through continued operation, gradually enfeebled, slow in action, and ultimatel exhausted. Acid of course is, consume is the pickling operation; and, as acid is consumed, new supplies of more concentrated acid are in present-day practice added from time to time to the bath. But, as a given body of solution continues in service, with such changes as have been indicated going on within it, and with additions made to it from time to time, a point is reached beyond which it is not desirable to proceed; a point is reached where addition of new supplies of concentrated acid cease to avail to restore the bath to vigor. This failure is due, manifestly, to the presence of copperas in solution; and, while according to our understanding it is not necessa to our application that theories be given, it

is our belief that the phenomenon we have described, the lncreasingslu gishness of the bath and its increasing failure to respond to new additions of acid, is due to or connected with the law of mass action, where'by concentration either of the Fe element or of the S0, radical or of both effects a repression of ionization. But, whatever the cause,

the phenomenon is plain, and it is to the overcoming of the difliculty here involved that our present invention is directed.

In present day practice the exhausted solution is thrown awa as waste-not because its composition is un nown, nor because the components are valueless, but because the cost' of recoveryby recognized procedure is forbidding. Every reason is against such waste. The components are valuable, if only the can be recovered economically; and, in ad ition to that, the disposal of the waste often becomes a serious matter. If a steel mill be located where law forbids llution of streams, the mill may be oblige even at financial loss to reclaim its spent pickling solution.

As we have said, the processes of reclamation are known. These earlier p, however, so far as we are acquainted with them, are directed, all of them, primarily to the separation and recovery. from the spent pick ing solution of the cop ras content. Our process as will resent y appear, is primarily dlrectedto t e reclaimlng of the dilute acid. Copperas, of course, has

market value; the laws of crystallization, of course, are known. It is known that a salt may be precipitated from a solution by reducing the temperature till the line of saturation is crossed, and this princi 1e has been applied, with the intention o recovering from spent pickling solutions their copperas content. A difliculty, however, is encountered, and it lies in this: that the crystals of copperas as they form tend to occlude in then mass pockets of the mother liquor. In consequence, the precipitate when obtained is a sludgy mass, of weak crystalline structure, permeated with dilute sulfuric acid. Further steps of purification have to be resorted to, and the result is that the reclaiming of the copperas has heretofore proved an unprofitable undertaking. Nevertheless, the laws against stream pollution, e e ed to above, have made it 0b said, in. existing ligatory upon steel companies in some localities to practise even at a loss suchoperations of reclamation. It will be understood that,

uncombined and remaining in the bath 1S regarded aswaste andis from this point forth dead loss. Our invention: regards the situation from another angle; our chief object is to reclaim the pickling solution. andrender it "available! and serviceable again; I incidentally, we recover the copperas, by an economical method and in marketable condition.

We shallfirst describe a paratus, in the use of which, and in ash e, continuous, and

simple operation, we un urden the spent solution of its load ofcopperas, leaving it suitablefor service again; whilein so doing we separate out the co ms in commercially pure condition. his apparatus, in which weoonduct a commercial operation, is sofar rovisional, that it contains fea- 'tures whic would be modified, and lacks features which would be" added, when it comes to building apparatus to take care of all the runofa large mill; but the essential featuresof our invention are herein illustrated, and u n this showing suitable bases for Letters atent will be found. In the sequel, when we come to description of the operation of the apparatus, improvements in method will be indicated, wherein also there is patentable subject-matter. y

Figure I of the drawings is a diagram matic view, partly in side elevation, partly in longitudinal section of the apparatus just mentioned; Fig: II is a view, in plan of the troughs which form part of the apparatus, as shown in- Fig. I; Fig. III is a view in vertical and medial section, on the plane indicated by the line IIIIII, Fig. .11; and

IV is a vertical, transverse section, on the plane indicated at IV-IV, Fig. II.

' The apparatus includes two troughs 1 and 2 arranged one within the other, with free space between on every side., These troughs are made of material such as to reacid attack, and are further character-. ized by this: that the. outer one is heat insulating in character and the inner heatcon- Accordingly, as indicated in the drawings, the outer trough is heavy-walled and made of wood, while the inner wall is thin-walled and made of l'ead. It mi ht be made of other metalMonel metal, or ex-. ample. The space within the inner trough is continuous from endtoend; the surrounding space within the outer. trough and between it and the inner isdivided, first, by a water-tight partition 3 which rises to the level of the upEer edge of the inner trough,- and then by ot er barriers designed to 00!;-

trol circulation. Thesegrequire a few words ofmore detailed description. It will be observed by studying, FigQIII that the inner trough rests on a succession of cross pieces which raise it from the bottom of the outer trough; one of these, as will be seen, forms part of the water-tight partition 3 referred to. Each of the other cross pieces is continued in baflle plates 4 bridging the space between the side walls of the two troughs; these baflie plates are of twounequal heights, alternately arranged; and the relative arrangement on the two sides is staggered that is to say, a hi h partition on one side and a low one on t e other stand opposite. At this point the descri tion of operation may be so far anticipated as to remark that the eflect is to cause the .liquid within the outer tank to circulate in a course indicated .by the arrows in Fig. IIover a low baflie plate on one side, down, transversely beneath the inner trough between two of the supports, up, over'a low baflie' plate on the opposite side, down again, etc. This arran ement of bafll plates extends throughout t e length of the outer trough, and on either side of partition wall 4. a

Giving specific dimensions (to which, of course, our invention is not limited), the outer trou h is in the installation which we are descri ing 16 feet 6 inches long'overall, 14 inches wide, and 22 inches deep; The inner dimensions of this outer wooden trough are 15 feet 8 inches long, 8 inches wide, and 17 inches deep. The inner trough is 15 feet long, 4 inches wide, and 13 nches deep. The partition wall 3 mentioned above rises as has been said to the rim of the inner trough; that is ,toJsay, it is 15 inches high from the bottom of the outer trough. The baflies 4 mentioned rise "alternately to the heights of 12 and 14 inches from the bottom of the outer'trough. The inner trough is open above, the outer trough is closed, witha removable wooden. cover. The partition 3 in. the outer trough is in the actual appaperature for introduction'into the precipitating apparatus. Spent pickling solution is introduced into the inner trough through a supply pipe 5. receiving tank' being employed, the solution flows from it in continuous stream and at properlycontrolled rate, conveniently by gravity. flow, through Supply pipe 5, into inner trough 2, and at one end thereof-the end farther distant from partition 3.

From the o riosite end of the inner trough the stream i uid (from which, as will presently be exp ained, the burden of copperas has in its course through the inner trough been removed) is transferred to the outer trough at a point beyond the partition 3-that is to say, on the side of partition 3 toward the inlet and which is the outlet end as well). The trans erence is conveniently efiected through a siphon pipe 6, arranged as indicated in the drawings.

The outlet for the now reclaimed pickling solution is from the outer trough, at the and adjacent the inlet, through the pipe 7. The flow of pickling solution through the apparatus is conveniently by gravity throughout, and it will be understood that by arranging the outlet 7 at suitable height relatively to the height of the partition already described (cf. Fig. IV) the gravity flow desired may be eflected; the level of pickling solution within the inner trough will be somewhat higher than in the outer trough, and, the rate of inflow through pipe 5 being properly adjusted, the siphon Wlll. automatically maintain the necessary difference in level. The serpentine course of the stream through the outer trough has been indicated in describing bafile plates 4.

Through the escape pipe 7 the reclaimed ickling solution may be carried directly Back to the pickling vat, or it ma conveniently accumulate in a suitable ta 14.

The portion of the outer trough at one side of artition 3, at the end opposite the inlet ans outlet pipes, is not traversed by the solution, but it is occupied by a refrigerating medium. 'This medium will ordinarily, though not necessarily, be a circulating medium. This circulating refrigerating medium may be derived from suitable refrigerating. apparatus 15 of any preferred sort. The ingress and egress of this circulating stream of refrigerating medium are indicated in pipe connections 8 and 9. In the inlet pipe 8 a pump 16 is indicated. The refrigerating medium will ordinarily be brine. Its course through the portion of the outer trough to which it gains access will, by virtue of the partitions 4 (the arrange.- ment of these being the same throughout the length of the trough 1), be the serpentine course already described.

Apparatus for agitating the pickling solution while' advancing through the inner trough, taking preferably the form 0f an air-spray, ap ars in the pipe 10 which extends alon t e bottom of the mner trough, substantiafiy from end to end. It is a pipe of suitable material free from attack by acid, and is conveniently made of Monel metal. In the actual apparatus which we are describing, this pipe is a l-inch pipe nd drilled throu hout its length with holes 1/64 of an inc in diameter, spaced at inter vals of 4 inches. Air is supplied to this long, perforated pipe from a suitable source of supply, indicated diagrammatically as a compressed air tank 17 through ipe 18; from it a lead 11 extends, and, as s own in Figs. III and IV, this lead extends along the bottom of the outer trough 1, throughout such part of trough 1 as is filled with refrigerating medium, before it makes connection, over the end of trough 2, with the blow-pipe 10.

The operation carries into practice the method wherein our invention in part resides. Spent ickling solution enterstrough 2 at one end t rough pipe 5 and at the other end is drawn off through siphon 6. While in trough 2, and throughout all the length of its gradual pro ress through trough 2, the body of the so ution is constantly agitated by jets of inblown air, and throughout the length of the trough this advancing body is as will presently more clearly appear gradually cooled.

Our invention here does not end with coolng across the line of saturation of cop eras m solution, nor is the whole stor to d in agitation during precipitation. e deal with actual temperatures, and within certain temperature limits results are attained which otherwise are not attainable. The spent solution as it comes from the. pickling vats contains about 10% free acid, and copperas in such quantity that the line of satu- 100 ration lies within the temperature ranges of our operation-from the temperature of pickling, 110 F., more or less, downward to about 20 F. The solution begins to freeze at about 21 F.

As the stream of spent pickling solution courses slowly through trough 2 from one end to the other, it grows gradually cold, and, as it cools, copperas is precipitated. When it is cooled to 20, some ice separates. 110 The ice crystals are of reasonably pure H O. These ice crystals float and do not mingle with the copperas crystals which meanwhile have been forming and falling to the bottom of the trough. At this tem- 115 perature, below the freezing point, cooling through one degree will efiect precipitation of as much copperas as a cooling through several degrees immediately above the freezing point. The reason, so far as we have 120 discerned it, is that the separation of ice crystals has the effect of increasing the degree of concentration, both of copperas and of sulfuric acid, and thus a preci itation efi'ect is obtained which is supera ded to 125 that due to cooling alone. Of course a point is quickly reached in the reduction of temperature, at which the uantity of floating ice crystals renders furt er cooling impracticable, and this point, varying somewhat 180 of ice crystals, increasing as 0 eratlon prohis will be at a tem erature one or two grees below that rst indicated). 7 It should be said that the crystals of ice' formed in the continually agitated liquid, are, as their formation begins, very th1n; and they easily siphon over to the outer trough.

The cooling is effected by the refrigerating apparatus described, and ranges as has been said, from about 110 F., the temperature of the introduced 11 uid, to about 20 F., the temperature at w ich the liquid is carried through siphon 6 from the inner to the outer trough. Cooling efiects precipitation, and agitation brings it about that glasses, will interfere with t eoperation the copperas crystallizes in small ains which fall tothe bottom of the trou and lie there in a loose mass, from whic when removed the liquid will drain away. And, as operationprogresses, this granular c stalline mass is from time to time remove scooped out, as we now operate; There is possibility here, of course, as elsewhere, for rearrangement and addition of instrumentalities for handling the material in large quantities in economical manner.

The cooling means have been alluded to. Cooling is pnmarily accomplished by a c0oling medium (preferably a circulating medium) in the outer trough on one side 0 partion 3, but on the other side of the partition the cold, and now reclaimed pickling solution flows away to exit 7, and as it flows it is a secondary cooling medium, extracting heat from the pickling solution in trough 2 as the latter advances from the inlet toward the opposite end of the trou h. The liquid in the inner trough is throug out the len h of the trough giving up heat; the two bodles of liquid circulati 1n the outer trough 1 are absorb' heat rom the liquid in inner trough 2. e two bodies of liquid in the outer trou h circulate in serpentine course, back and orth across the outer surface of the inner trough so that, a maximum of heat transference is attained. The agitation of the li uid within trough 2 by cooled air tends to t e same end.

Thus it will be seen that the stream of pickling solution is caused to flow in a loop, the return branch of the loop inclosing and continuing in heat transferring contact with the entering branch, and in the turn of the loop is a refrigerating ap aratus. Provision is made for se ntine ow of the liquid in the return bran of the loop, while the become coated with crystals, the conductivity.

of these walls for heat transference would be impaired.

Giving specific temperatures, the spent solution enters throughconduit 5 at substantially 110 F., more or less; in con uenee of cooling by the agencies indicated,t e reclaimed solution leaves trou h 2at a temperature of about 20 R, an after traversing the outer trough it makes its exit at a temperature not far removed from the temperature of introduction, 100 F more or less. The temperature at the partition 3 is, within the inner trough, approximately 30 F. From that point to the end of the trou h, and within the region of direct action of 5m refrigeration apparatus, there is a fall of about 10,that is, to approximately 20 F. At this temperature the liquid is transferred from the inner to the outer trough and to a point beyond the partition, and, beginning its flow there at about 20 F., it finally emerges as has been said at a degree not far removed from the initial temperature.

The escaping liquid is dilute acid, practically free from copperas; the small quantityof copperas remaining is negligible. Or-

dinarily, this reclaimed solution will be of pickling strength (7 to 10%), at least. The solution in the pickling bath is initially of that strength; and when, as picklin progresses, new amounts of acid are adde they must be suchin quantit that the percentage of acid shall rise or as co creases, a higher percentage of aci is 'needed in order to maintain a practicable rate of action within the pickling bath. According to resent-day practice this percentage of eras in-- aci ma increase to 20%; in our operation,

the pick ing capacity of the bath would not be forced to this limit; freshly purified solution would constantly be available; and the strength of the acid in solution would notbe carried beyond 10-15%. The copperas, when precipitated carries with it water-of cr stallization. it is for these reasons that t e solution when reclaimed will be of more than requisite strength for picklin iewed as a whole, it will be seen that, while the cop eras is removed, only a portion of the excess eat is removed from the solution; the reclaimed solution passes on still heated and requiring but relatively small heat additions, to bring it again to pickling temperature. It is manifest that in the practice of our invention pickling solution may circulate through pickling vat and reclaimin apparatus in continuous stream.

Tn our operation practically all the acid is accounted for, either in the form of copperas, or in acid returned from the reclaimin apparatus to the pickling vat.

t should have been said in proper place, although it will be understood bg' those who practise the art, that, upon with rawing the spent pickling solution from the vat, and before introducing it in the reclaiming apparatus, it will have to be filtered, in order to separate from it solid particles of iron oxid, sawdust and such other matter as may incidentally accumulate in the pickling bath.

We have now described the invention in its application to the specific problem of reclaiming spent pickling solution. As we 1ntimated in the beginning, and as is now manifest, the invention is applicable to solutions generally, and will be found advanta ous, wherever the desirability appears of o taining precipitation with a minimum of loss of heat.

\Ve claim as our invention:

1. The method herein described of reclaiming spent pickling solutions which consists in causing hot solution to' flow in a stream, cooling the solution at an intermediate point in the course of the stream, and in transferring heat from the solution at one portion of such stream to the solution at another portion, whereby preclpitation is effected in the portion whence heat is taken.

2. The method herein described of reclaiming a spent pickling solution which consists in causing t e solution to flow counter current in loop form, the branches of the loop in heat-interchanging relation one to the other, applying refrigeration to the turn of the loop, and agitating the solution as it advances along the inflow branch of the loop with inblown cool air.

3. The method herein described of reclaiming spent pickling solutions, which consists in causing the solution to flow counter current in loop form, the branches of the loop in heat interchanging relation one 'to' the ot er and applying refrigeration to the turn of the l 4. The herein described method of reclaiming spent picklin solutions, which consists in causing the so ution to flow counter current in loop form, the branches of the loop in heat interchanging relation one to the other, applying refrigeration-to the turn of the loop, and agitating the solution as it advances along the inflow branch of the loo 5. In apparatus for reclaiming spent plckling solution, the combination of a conduit through which the solution flows in loop form, the branches of the-loop being separated by a partition of heat-conducting material, and means for refrigerating the solution as it passes through the turn of the loop, substantially as described.

6. In apparatus for reclaiming spent pickling solution, the combination of a conduit through which the solution flows in loop form, the branches of the loop being separated by a partition of heat-conducting mater al, means for refri erating the solution as it passes through t e turn of the loop, and means for agitating the solution as it flows in the intake branch of the loop, substantially as described.

7. Apparatus for the reclaiming of spent pickling solutions includin two troughs arranged one within the ot er with a space between, the inner being formed of heat transmlttlng material, a dam across the outer trough at a. point intermediate its length, refrigerating means located in the outer trough on one side of said dam, and connection from the inner trough to the outer at a point in the outer trough on the side of the dam opposite that where the refrigeratlng means are located, substantially as described.

8. Apparatus for the reclaiming of spent pickling solutions including two troughs arranged one within the other with a space between, the inner being formed of heat-transmitting material, a' dam across the outer trough at a point intermediate its length, refrigerating means located in the outer trough on one side of said dam, connection from the inner trough to the outer at a point in the outer trough on the side of the dam opposite that where the refrigeratin means are located, means for introducing t e solution to the inner trough, and for conducting it awa from the outer trough, and means for a ltating the solution within the inner troug substantially as described.

9. Apparatus for the reclaiming of spent pickling solutions including two troughs arranged one within the other with a space between, the inner being formed of heattransmitting material, a dam across the outer trough at a point intermediate its length, refrigerating means located in the outer trough on one side of said dam, connection from the inner trough to the outer at a point in the outer trough on the side of the dam opposite that where the refrigerating means are located, means for introducing the solution to the inner trough, and for conducting it away from the outer trough, an air conductor leading through the refrigerating means in the outer trough and thence to the inner trough and being there provided with an escape orifice, substantially as described.

10. Apparatus for reclaiming spent pickling solutions including two troughs artom of the outertrough and upon which the inner rests, and a corresponding succession of pairs of bafile lates arranged in the spaces between the side walls of the troughs forming vertical continuations ofsaid striss, every second plate in succession longitu inally of the troughs being lower than those immediately adjacent and plates of each pair being unequal in height, substantially as described. a

11. Apparatus for reclaiming spent pickling solutions including two troughs arranged oue within the other with a. space between, the inner being formed of heatconducting materia1,-a dam across the outer trough at a point intermediate its length, means within the outer trough on one side of said partition for eil'ecting1 cooling of solution within the inner troug and a siphon leading from the end of the inner trou h where the cooling means are located to tie outertrough on the other side of the partition, substantially as described. a

12. Apparatus for reclaiming spent pickling solutions including two troughs arranged one within the other with a space between, the inner being formed of heattransmitting material, a dam acres the outer trough at one side said dam, connection from the inner tro point in the outer troug on the side of the dam opposite that where the refrigerating means are located, an air pipe leading through the refrigerating means in the outer trough and extending into the inner trough, and there provided with a vent orifice, substantially as described.

13. The method herein described of treating a solution which consists in causing the solution to flow in a stream, eflecting preci itation by withdraw' v heat from the so ution at oneppoint iri l he course of the stream, and transferring the heat so withdrawn and restorin it again to the liquid at a lower point in t e course of the stream.

14. The method herein described of treat ing a solution which consists in ca the so ution to flow counter current in loop orm, the branches of the loop in heat interchanging relation one to the other, and cooling the stream at the turn of the loop.

HENRY S. MARSH. RALF S. COCHRAN.

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