US1369451A - Method of and apparatus for reclaiming spent pickling solutions - Google Patents

Description

H. S. MARSH AND R. S. COCHRAN. METHOD OF AND APPARATUS FOR RECLMMING SPENT PICKLING SOLUTIONS. APPLICATION HLED SAN-9.1920.

1,369,451 Patented Feb. 22, 1921.

2 SHEETSSHEET l- WITNESSES INVENTQRS H. S. MARSH AND R S. C(JiHRAN.

METHOD OF AND APPARAHIS FOR RECLAIMING SPENT ?iCixLWG SULUHUNSJ APPLSCATION FILED JAN. aw;

Patented Feb. 22, 1921.

r SHEEIS SHEET 2- FIE-LE1.

WH'NESSE5 mvzmon 5 1 fin-MM,

PATENT OFFICE.

UNITED STATES HENRY S. AND BALI B. OOGHBAN, OF YOUNGSTOWN, OHIO.

Specification of Letters Patent.

Patented Feb. 22. 1921.

Application filed January 9, 1920. Serial No. 850,88

To all whom it may concern:

Be it known that we, HENRY S. MARSH and HALF S. COCHRAN, residing at Youngstown, in the county of Mahonmg and State of Ohio, both citizens of the United States, have invented or discovered certain new and useful Improvements in Methods of and Apparatus for Reclaiming Spent Pickling Solutions, of which improvements the followin is a specification.

ur invention relates to methods of and apparatus for reclaiming spent pickling so lutions. The pickling operation which is widely practised in the steel-making industry, being incidental to, all sorts of steelworking processes, is essentially an opera tion in which the surface of an iron or'steel article is cleaned of oxid, corrosion, or scale, and left bright. The operation is accom plished by submerging the coated article in a bath of acid, ordinarily dilute sulfuric acid. Chemical reaction ensues, the underlying iron is attacked by the acid, and the oxid, corrosion, or scale is loosened and falls away, leavin i exposed a clean surface of metallic iron. he chemical reaction produces a sulfate of iron (FeSOJH O) known as copperas, which being soluble, is, from its formation carried in solution in the bath.

In present-da practice in steel mills, the pickling bath, t e solution of acid in which the coated articles are immersed and cleaned, becomes, through. continued operation gradi ually enfeebled, slow in action, an -ultimately exhausted. Acid of course is consumed in the pickling operation; and, as acid is consumed, new supplies of more con-. centrated 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 solutiong and, while according to our understanding it is not neces sary to our application that theories be given, it is our belief that the phenomenon we have described, theincreasing sluggishcost of recover ness 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, whereby concentration either of the Fe element or of the SO, radical or of both effects a repression of ionization. But, whatever the cause, the pnenomenon is lain, and it is to the overcoming of the di culty here involved that our present invention is directed.

In present day practice the exhausted solution is thrown away as wastenot because its composition is unknown, nor because the components are valueless, but because the by recognized procedure is forbidding. very reason is against such waste. The components are valuable, if only the can be recovered economically; and, in ad itionto that, the disposal of the waste often becomes a serious matter. If a steel mill be located where law forbids pollution of streams, the mill may be obliged even at financial loss to reclaim its spent pickling solution.

As we have said, processes of reclamation are known. These earlier processes, however, so far as we are acquainted with them, are directed, all of them, primarily to the separation and recovery from the spent gickling solution of the copperas content. .ur process, as will presently appear, is primarily directed to "the reclalmin dilute acid. Copperas, of course, as market value; the aws of crystallization, of course, are known. It is known that a salt may be precipitated from a solution by reducing t e temperature till theline of saturation is crossed, and this principle has been applied, with the intention of recovering from spent pickling solutions their ciopperas content. A dlfliculty, however, is encountered, and it lies in this: that the crystals of co per-as as they form tend to occlude in t air mass pockets of the mother li uor. In consequence, the precipitate w on obtained is a sludgy mass, of weak crystalline structure,*permeated with dilute sulfuric acid. Further steps of purificaof the some localities to ractice even at a loss such operations'of rec amation. It will be understood that, incidentally, the solution from which the copperas is taken, is itself partiall consumed in the operation; indeed, c as has en said, in existing operations of reclamation, the vuncombined acid remaining in the bath is regarded as waste and is from this point forth dead loss.

Our invention regards the situation from another angle; our chief object is to reclaim the pickling solution and render it available'and "'siwiceable again; incident tally, we recover .the'copperas, by an-economical method and in marketable condition.' M

We shall first dc; rile apparatus, in the use of which, and in a sing a; continuous,

and simple operation, we uuburden the spent solution of its load of copperas, leaving it suitable for service again; while in so doing we separate out the co in commercially pure condition. is apparatus, in which we conduct a commercial operation, is so far royisional, that it contains fea.- tures whic would be modified, and lacks features which would be added, when it this: that the outer one is heat character. and the. inner heatsconduc't ng,

comes to building apparatus totake car's of all the run of a large mill; but the essential features of our invention are herein illustrated, and u n this'showin suitable bases for Letters atent willbe ound. In the segue], wheh we come to description of the operation of the apparatus, in! rovements 'in method will be indicated, wierein also there is patentable subject-matter.

Figure I of thedrawings is a diagram matic view, partly in side elevation, piirtf y. in longitudinal sectionof the apparatusj. mentioned; Fig. II isa view in planet I; e-

troughs which form part of the appmt as shown in Fig. I; Fig. III is aviewinve 1 tical and medial seetiom'onthe' plane indi-' cated was 1am III-III, "Fig,.' Ir; a

Fig. I s'a vertical, transversesectiongoii the glans indicated'at IV.- IV, FigJL; T e apparatus includes two troughsl and 2 arranged one within-the other, spucebetweenonevery side; tm

are made 'of material. such asto resistffiacid attack and are further Acordi'n'gly, as'indica'ted in the drawin space within the outer tron the outer trough is heavy-walled and ma otwood, while the inper wall is thin-walled andmade of lead]. It n ht be madelfof other metal-f hdonel me for e gai'nple. The space 'mthmltheT-jnner fis tmuous from endto' ends the surrounding it and the inner is divided, rst, by'a water tight .partitionilwhich rises to-thelevel of 1 the upperedge of the inner troug and. then bv other barriersdesigned to control'circulation. "These uire a few words of more detailed descri tion. It will be observed by studying ig. III that the inner trouglh, rests on a succession of cross pieces whic raise it from the bottom of the outer trough one of these, as will be seen, forms part of the water-ti litpartition 3 referred to. Each of the ot er cross pieces is continued in baflle plates 4 bridging the space between the side walls of the two troughsthese baflie plates are of two unequaiheights,'alternately arranged; and the relative arrangement on the two sides is staggered-thatis to say, a 'hi h partition on one side and a low one on be other stand opposite. At this point the description of operation ma be sofar anticipated as to remark that t e efiect is to cause the liquid within the outer tank to circulate in a course indicated by the arrows in Fig. II--over a low baflle plate on one side, down, trans-f versely beneath the inner trough between two of the supports, as, over a; low baflle gllgte on the opposite si e, down again, etc.

is arrangement of baflle plates extends throughout the length of the outer trough, and on either side of partition wall 4.

Giving specific dimensions to which, of

are descri ing 16 feet'fi inches long overall, 14 inchUs wide, and22 inches deep. The inner dimensions r of this outer wooden trough are 15 feet 8 inches ion 8 inches wide, and i 17 inches deep. i e inner trough is 15 feet king, 4 inches wide, and winches deep. The partition wall 3 mentioned above rises has been saidto the rim of the inner tron that is to say, it is 15 iiiches hi h fromwthe bottom of the outer trou h. e bodies 4 mentioned rise sltel na' y 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 closech'with a removable wooden cover. The partition 3; in the outer-trough isin the actual a paratus which .we are describing, andord narily .it will be, arranged nearer one end thani the other. Itstands 4 feet 1 inch from one end and '11 feet 5 inches from the other. a

, Operation may be regulated by roviding marked, at elevated, temperature, and a heater iii-may be provided to keep the liquid in the'receivm tank atthe desired temperature. for intro notion into the meipitating apparatus. Spentpickling so ution is introducsd into the inner trough through ,a mlippl pipe 5. A. receiving tank being ,emp o tindous stream and at properly controlled rate, conveniently by gravity flow,thro uglplmrv iio .: the solutionflows from it in consupply pipe 5, into inner trough 2, and at one end thereof-the end farther distant from partition 3.

From the opposite end of the inner partition 3 toward the inlet end gwhich is the outlet end as well). The trans erence is conveniently effected through a siphon pipe 6, arranged as indicated in the drawin s.

The outlet for the now relaimed pic ling solution is from the outer trough, at the end adjacent the inlet, through the pipe 7. The flow of pickling solution through the apps.- ratus 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 artitions already described, (cf. F i U the gravity flow desired may be e ected; 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 diflerence in level. The serpentine course of the stream through the outer trough has been indicated in describing loaflle plates 4.

Through the escape pipe 7 the reclaimed pickling solution may be carried directly back to the pickling vat, or it may conven- ,iently accumulate in a suitable tank 14.

The portion of the outer trough at one side of partition 3, at the end opposite the inlet and outlet pipes, is not traversed by the solution, but it is occupied b a refrigerating medium. This medium wi lordinarily,

though not necessarily, be a circulating medium. This circulating refrigeratin medium may be derived from suitable re rigerating 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 arrangement of these being the same throughout the length of trough 1), be the serpentine course already described.

Apparatus for agitating the pickling so lution while advancing through the inner trough, taking preferably the form of an air-spray, appears in the pipe 10 which extends alon the bottom of the inner trough, substantially from end to end. It is a pi e of suitable material free from attack y acid, and is conveniently made of Monel metal. In the actual apparatus which we are describing, this pipe is a 1-inch pipe and drilled throu hout its length with holes 1/64 of an inc in diameter, spaced at intervals of four inches. Air is supplied to this long, perforated pipe from a suitable source of supply, indicated diagrammatically as a compressed-air tank 17 through pipe 18; from it a lead 11 extends, and, as shown 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 pickling solution enters trough 2 at one end through pipe 5 and at the other end is drawn off through siphon 6. While in trough 2, and throughout all the length of its gra ual progress through trough 2, the body of the solution is constantly agitated by jets of inblown air, and throughout the ually cooled.

Our invention here does not end with coolign across the line of saturation of copperas in solution nor is the whole stor told 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 copper-as in such quantity that the line of saturation lies within the temperature ranges of our operationfrom 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 1s precipitated. When it is cooled to 20, some ice separates. 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 formin and falling to the bottom of the troug At this temperature, below the freezing point, cooling through one degree will efi'ect recipitation of as much copperas as a cooling through several degrees immediately above the freezing point. The reason, so far as we have 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 precipitation effect is obtained which is superadded to that due to cooling alone. Of course a point is quickly reached in the reduction of temperature, at which the quantity of floating ice crystals renders further cooling impracticable, and

llt

.carry the cooling.

this point, varying somewhat-since we are dealing with a material of somewhat variable composition-is the point to which we The temperature limit, then,'to which in thepractice of our invention. the liquid under treatment is brought will lie between the point where ice er stals begin to form (approximately 21 F. and the point where accumulation of ice crystals, increasing as operation progresses, will interfere with the operation (this will be at a temperature'one or two degrees below that first indicated). It should be said that the crystals of ice formed in the continually agitated li uid, are, as theirformation begins, very t in; and they easily siphon over .to the outer trough.

scooped out, as we now operate. There is possibility here, of course, as elsewhere, for rearrangement and addition to instrumentalities, for handling the material in large quantities in economicalmanner.

The cooling means have been alluded to. Cooling is primarily accomplished by a cooling medium (preferably a circulating medium) in the outer trough on one side of partition 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 iclding solution in trough 2 as the latter vances from the inlet toward the oppositeend of the trough. The liquid in the inner trough is throughout the length of the trough giving up heat; the two bodies of liquid circulating in the outer trough 1 are absorbing heat from the liquid in inner trough 2. The two bodies of liquid in the outer trough clrculate in serpentine course. back and forth across the outer surface of the inner troughso that a maximum of heat transference is attained. The agitation of the liquid'within trough 2 by cooled air tends to the 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 apparatus. Provision is made for serpentine flow of the this granu ar e talline mass is from time to time remove were to become coated with (32 812818, the

conductivity of these walls for eat trans- ,ference would be impaired.

Giving specific temperatures, the spent solution enters through conduit 5 at substantially 110 F., more or less;,in co uence of cooling by the agencies indicated, t e 1e claimed solution leaves trough 2 at a temperature of about 20 F., and after traversmg the outer trough it makes its exit at a. temperature not far removed from the temperature of introduction, 100 F., more or essu The temperature at the partition 3 is, within the inner trough, ap roximatel 30 F. From that oint to 5m end 0 the trough, and within the region of direct action of the refrigeration apparatus, there is a fall of about 10,-that is, to approximatelly 20 F. At this temperature the liqui is transferred from the inner to the outer trough and to a. point beyond the partition, and, beginning its tlow 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 quantity of copperas remaining is negligible. Ordinarily, this reclaimed solution will be of pickling strength (:1 to 10%), at least. The solution in the pic ing bath is initially of that strength; and when, as picklin progreases, new amounts of acid are add they must be such in quantity that the percentage of acid shall rise for as copgeras increases, a higher percentage of aci is needed in order to maintain a racticable rate of action within the pic ing bath. According to present-day practice this percentage of acid may increase to 20%; in eration, the picklin capacity of the bath would not be force to this limit' freshly purified solution would constantly be avai able; and the strength of the acid in solution would not be carried beyond 10- 15%. The copperas, when recipitated, carries with it water of crystal izatlon. It

\ is for these reasons that the solution when reclaimed will be of more than requisite strength for pickling.

Viewed see who e, it will be seen that, while the copperas' is removed, onlfv a portion of the excess heat is removed mm the our opsolution; 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 1n the practice of our invention pickling 5 solution may circulate through pickling vat and reclaiming apparatus in continuous stream.

In our operation practically all the acid is accounted for, either in the form of coperas, or in acid returned from the reclaimlng apparatus to the pickling vat.

It should have been said in proper place, although it will be understood by those who practice the art, that, upon withdrawing 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 at t We 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 pne portion of such stream to the solution at another portion, whereby preci itation is efi'ected 1n the portion whence eat is taken.

2. The method herein described of reclaiming a spent pickling solution which consists in causing the solution to flow counter current in loop form, the branches of the loop in heat-interchan ing relation one to the other, applying re rigeration to the turn of the loop, and a 'tatin the solution as it advances along t e in ow branch of the loop with inblown cool air.

3. The herein described method of reclaiming spent pickling solutions, which consists in causing the solution to flow counter current in oop form, the branches of the loop in heat interchanging relation one to the other, and applying refrigeration to the turn of the loop.

4. The herein described method 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 interchan ing relation one to the other, applying re rigeration to 65 the turn of the loop, and agitating the solution as it advances along the inflow branch of the loop.

5. In apparatus for reclaiming spent ickling solution, the combination of a conuit through which the solution flows in 100p 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 05 the loop, substantially as described.

6. In a paratus for reclaiming spent pickling so ution, 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, means for refrigerating the solution as it passes through the 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 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, 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 refrigerating 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 heattransmitting material, a dam across the outer trough at a point intermediate its length, refrigerating means located in the outer trough on one side ofsaid dam, connection from the inner trough to the outer at a oint in the outer trough on the side of the am opposite that where the refrigerating means are located, means for mtroducing'the solution to the inner trough, and for conducting it away from the outer trough, and means for agitating the solution within the inner trough, 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 trou h at a point intermediate its length, re rigerating means located in the outer trough on one side of said dam, connection from the inner trou h to the outer at a oint in the outer troug on the side of the am opposite that where the refrigerat- 116 ing 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 outertrough and 120 thence to the inner trough and being there provided with an escape orifice, substantially as described. 0

10. A paratus for reclaiming spent pickling so utions including two troughs arranged one within the other with a space between, a succession of strips set in the bottombf the outer trough and upon which the inner rests, and a corresponding succession of pairs of baflle plates arranged in the s aces between the side walls of the tronglis forming vertical continuations of said strips, every second plate in succession longitudinally of the troughs bein lower than those immediately adjacent and plates of each pair being unequal in height, substantially as described.

11. A ling soutions including two troughs arranged one within the other with a space between, the inner being formed of heatconducting material, a dam across the outer trough at a point intermediate its length, means within the outer trough on one side of said partition for elfectmg cooling of solution within the inner trou h, and a siphon leading from the end of the inner trough where the cooling means are located to the outer trough on the other side of the partition. substantially as described.

12. Apparatus for reclaiming spent pick ling solutions including two troughs arparatus for reclaiming spent pickranged one within the 0th r with a space between, the inner being ormed of heattransmitting material, a dam across the outer trough at a point intermediate its length, refrigerating means located in the outer trough at one side 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, an air pipe leading throu h the refrigerating means in the outer trougi and extending into the inner trough, and there provided with a vent orifice, substantially as described.

In testimony whereo'f we have hereunto set our hands.

HENRY S. MARSH,

. RALF S. COGHRAN.

Vitnesses:

Cam. Amour, Lao Ptmonm.

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