US2615793A - Crystallization apparatus - Google Patents

Description

1952 J. A. WEEDMAN CRYSTALLIZATION APPARATUS Filed Aug. 22, 1949 IN VEN TOR.

J. A. WEEDMAN BY #MMB A T TORNE KS Patented Oct. 28, 1952 UNITED STATES PATENT OFFICE I 2,615,793 CRYSTAL LIZATION APPARATUS John A. Weedman, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application August 22, 1949, Serial No. 111,618

crystallization. In another aspect, it relates to an apparatus for eificiently moving a granular mass of crystallized material through a fractional crystallizer.

In the separation of mixtures of compounds by fractional crystallization, various types of apparatus have been constructed for establishing contact between a mass or the crystallized material moving in one direction and a mother liquor moving in the opposite direction. Usually these devices employ a flight conveyor or auger for moving the crystals. In most horizontal type crystallizers, a higher-melting fraction is removed from one end, a lower-melting fraction is removed from the opposite end and the feed is introduced at an intermediate point. The apparatus may be jacketed to abstract heat through the walls and form crystals in the liquid body, which usually fills the apparatus. The crystals that form in contact with a mother liquor are, ordinarily, the higher-melting fraction. In the case of eutectic mixtures, the crystals may or may not be the higher-melting component but will be that component present in excess of the eutectic ratio.

One of the principal difficulties with the devices of the prior art is that the crystal movers are not efiicient if the ratio of solid to liquid becomes too high. When the amount of solid material is too high, the flights of the conveyors bridge over with crystals and no crystal movement occurs. It is necessary, if separation is to occur, that the crystals or solid granular material be continuously moved toward the outlet for the higher-melting fraction and that the remaining liquor be displaced toward the opposite end, where the lower-melting fraction is withdrawn.

I have discovered a solid-moving device which operates efiiciently in any slurry of crystals in liquid and which does not become bridged over with the material being crystallized. 'My inven-' tion is particularly adapted to use in a crystallizer that is totally enclosed and has a freezing section near one end and an adiabatic section through which the crystals must be moved before reaching the product outlet.

The principal object of my invention is to provide a simple and eflicient apparatus for moving crystals through a liquid-full container and displacing liquid in the opposite direction.

Another object is to provide a conveyor for use in multi-stage crystallization apparatus.

Another object is to provide a crystal conveyor for moving the solids of a slurry to one end of 2 from a study of the following drawings, de'sc'zription and claims. q n Figure 1 is a longitudinal sectional view of a horizontal type crystallizer showing my crystal conveyor in elevation.

Figure 2 is a cross sectional View of Figure 1 taken along line 2-2.

Figure 3 is a detailed view, part sectional and part elevational, taken along line 3-3 of Figure 2'.

Figure 4 is a cross sectional view of a ylindri cal crystallizer showing a modification of a crys' tal mover in elevation.

In Figure 1, a reciprocating rod 6 extends through the end wall of crystallizer l longitudi nally into said crystallizer. Close-fittin'gpistons 8 are spaced along rod 6 and secured thereto. Stufiing box 9 seals the space around rod 6 ,"which is caused to reciprocate by the movement of crank H and connecting rod [2, which are actuated by a driving means, not shown. A bar l3 is' secured to rod 6 and extends transversely to form a stop for the foldable pistons 8. The reciprocating rod may be made up as a unit or it may be made up in sections which are joined together bymeans of couplings as shown at M, Product outlets l6 and I! are at opposite ends of the apparatus and feed inlet I8 is intermediate said ends. Cooling jacket 19 forms a freezing section on one end and heating jacket 2! forms a melting section on the opposite end. Cylinder 22 and piston 23 communicate with crystallizer 1 by means of a pas-' sageway 24 to make possible the maintenance of a desired pressure within said crystallizer;

In Figure 2, the cross sectional wall of crystal-' lizer I is shown, inside of which is a collapsible piston which is made up of a close' -fitting ring 26 which is secured to" reciprocate rod 6 by means of vertically-extending spokes 21. A pair of semi circular flaps 28 are loosely secured to said vertically-extending spokes by means of loops 29. Horizontal bar l3 serves to stop the folding of" In Figure 4, the perforate piston 32, which is secured to reciprocating rod 6, is provided with flaps 33 which close the large openings through said piston.

This devicei is'desig ned'for the purpose ofinio'v ing a mass of granular solid through a confined .body of the mother liquor, which is 'thereby'Ldisplaced in the direction countercurrent to the movement of the crystal This device eliminates- ;the' difiici'llty" resulting from-bridging" across the i flights which usually occurs with augers or flight conveyors.

By using thy-apparatus, thecrystal's formed in;

the freezin 'zone are-scraped from the walls'by the rigid outer ring and are pushed forward through the crystallizer by the perforate pistons. At the same time, liquid is displaced-in the.opposite direction and flows through the perforations in the piston. On the reverse strokathe fold; able flaps 28 fold forward to form an opening around the sides thereof of considerable size. These flaps are prevented from folding com pletely inward against the reciprocating rod by stop 13. This prevents the flaps from coming to rest on dead center andfailing to open on the forward stroke.- As the; forward. stroke. begins,

the resistance of the solid in the solutionforces theflaps'back-against stops 3i andtherehyifcrms a; piston again.

The pistons of my device are entirely auto-- matic and open and close freely with'the motion of the reciprocating rod. My device-is; operable as long asthe mixture in-the crystallizer ismaintained asa slurry. If theorystals are melted. and a portion of the melt is caused to fiow.-toward1the freezing end as reflux, my device will be operable under conditions of complete reflux. If the crystals are not melted in the apparatus but are removed as solid material, it isobvious that this. removal must occur at the same rate that. the material isdelivered to the end ofthe apparatus.

Otherwise, there wouldbe a building upeofsolid: material in the end-of theapparatus which could result in damage to the pistons. Then, as; set

forth hereinbefore, crystals resultingfrom-move-rment through myapparatus can. be. melted. in the melting. section and the resulting. melt removed through conduit ['6 as-a liquid, or the crystals can be partially melted and removed-through. conduit it as a slurry, or the crystals: can. be-

removed as such withoutmeltingthem.

The perforate piston may be made: ofany foraminousmaterialwhich will permit theifiow of liquid therethrough. without substantial: resist-- ance andatthe same time will retain granular, material. It does not effect the operation if.

some small crystals do pass through the. piston along with: the liquid. Thesecrystals are. probably impure and' more closely approximate the composition of the. liquid than dothe larger crystals. which are retained onthe piston. I; have found that a ZO to 30 mesh, screen isexcellent for this purpose.

The screen forv the flaps is.secured toa reinforcingring which has loops or eyelets to fit around the vertically extending spokes- The screen may be secured to the reinforcing ring; by any desired method-but I have found soldering' to be very convenient. The hinge. action of the loops around said spokes must be easy so that the resistance required. to open. and close the flaps will be negligible.

Insteadof stops 3t, which are soldered to the periphery of the. scraper ring 25,.any other con venient method for preventing the. backward folding of said flaps may be used.

In the. drawings, my apparatus is shown in a; horizontal position. However, it may be operated in a vertical or inclined position; and in some instances, such positions may be preferable. In operating with the crystallizer full, or substantially full of slurry, the slurry would ofier sufiicient resistance to the foldablepistons to cause said pistons to unfold on the pump stroke and fold on the intake stroke. apparatus is of my. inventionwill be. moreclear-ly demonstrated and understood from. a study of the; following: table.

Table WITHAUGER RatcaniL/mln. P SIliggiQK ercent High-Melting. Product Low- Low- ;Higli=-- Feed Melting, Feed Melting .Melting; Product -Vol. Product Product Rate percent of'ieed 3508 2:64 0.44 14 46.4 14.5 :3v 2. 77 2.51 0.26. 9.0 463-2 14:0 87.54 6 3 6.0 0.3 4.8 59.5 v 18.5 90.10. 6 1 (1.0 0.1 116 r 56.2 24:6 9820 WITH: POROUS E FIS'IZONS" 18.30 14.0 4.30' 23.5 75.8 55.9 QQLZ 1 24.6 18.9 5.7 23.2 75:9 6352 9859 35.0 23.3 =ll.70. 33.5 ;73.9 r 5331 99:

EXAMPLE The following tests were carried out to determine the maximum amount of high purity benzene to. be obtainedv by. crystallization. from. a benzene, n-heptane. feed in. a. crystallizer using, first an. auger-type. conveyor, and; then. a porous. pistonl-type conveyor, suchas that showninl ig ures.1,,2.; andiBl. Thecrystallizer tubewasa 101 foot section of inch tubing witha coolingjacket adjacent one end'and' a heater at the opposite end.

In the first testsit was. found that the augfir.

. conveyor wouldnotoperateifthe amount of'crystals in the mixture exceeded about per. cent of the mixture. The output of high-melting,prodiuct (benzene). dropped off rapidly. as. th purity. of the product increased. At .98 percentpuritm, Whichis notliigh enough, the high-melting prodnot was 1.6.volume per centof'the feed; which. is a. negligiblequantity for such a process. From. these results, it is obvious; that thecrystallizer was being operated atabout the maximumoutput for the purity of the product.

With. the. porous. piston conveyon. the.- purity of. the highrmelting product was appreciably, higher than that obtained with. they auger. con..-- veyor. The rat'eof output of the high-melting. product increased as the feedrat'e. wasincreasedl. Evenat a 33.5 volume per cent; output, the. puritit remained at 99 per cent,.which is. considerably.

'better than the 98 per cent purity obtainedat;a.

1.6 volume per cent. output with. the augerrtype conveyor. It. is. believedthat'. the output from. the porous piston crystallizer could. be. increased; evenmore without sacrificing purity of. theprod uct.

The data. in the following tableare. there sults of the tests just. described. Theadvantages If desired, an indicator may be installed in connection with said flaps to indicate when the.

great-.- Such an indicating device entirely within the scope'of my invention, which is defined by the following claims.

2 Having described my invention, I claim:

1. A fractional crystallization apparatus. which comprises, in combination, an elongated enclosed container, a product outlet adjacent each end of 'saidcontainer and a feed inlet intermediate said ends;means for adding heat to said container adjacent one end thereof, means for abstracting heatfrom said container along a portion thereof between said feed inlet and the unheated end, and: means for moving solid granular material through said container from the cooled to the heated end which comprises a reciprocating rod extending axially into said container, a plurality of foldable pistons comprising foraminate members-hinged at spaced intervals to said rod, said foldable pistons being adapted to close on the intake stroke and open on the pump stroke of said piston;

2. In a crystallizer of the type described comprising an elongated vessel having a first product outlet conduit in one end portion A of said vessel, a second product outlet conduit in a second end portion B of said vessel, a feed inlet conduit between said product outlet conduits and means for removing heat from said vessel between said feed inlet conduit and said end portion B, an improved solid-conveyor for moving solids toward end portion A which comprises, in combination, a reciprocating rod extending axially into said crystallizer,'a plurality of foldable perforate pistons comprising a screen having a plurality of perforations disposed at spaced intervals along said rod and secured thereto, and means to prevent rearward folding of said pistons during the forward stroke of said rod.

3. In a crystallizer of the type described comprising an elongated vessel having a first product outlet conduit in one end portion A of said vessel, a second product outlet conduit in a second end portion B of said vessel, a feed inlet conduit between said product outlet conduits and means for removing heat from said vessel between said feed inlet conduit and said end portion B, an improved solid-conveyor for moving solids toward end portion A which comprises, in combination, a reciprocating rod extending from one end longitudinally into said crystallizer, a plurality of foldable, foraminate pistons disposed at spaced intervals along said rod and secured thereto, means to prevent rearward folding of said pistons during the pumping stroke of said pistons, a rigid band at the periphery of said pistons for scraping solidified material from the wall of said crystallizer and means for actuating said reciprocating rod.

4. In a crystallizer comprising an elongated container having product outlet conduit A and B in the end portions thereof, a feed inlet conduit between said outlet conduits, means for abstractingheat from a portion of said container between said outlet conduit B and said feed inlet conduit, means for adding heat to a portion of said container between said outlet conduit A and said 6 feed inlet conduitv and means for moving solids therethrough toward outlet conduit A in countercurrent contact with a liquid, an improved crystal-conveyor which comprises, in combination, a

" reciprocating rod extending axially into said con-' tainer, a plurality of perforate pjstons comprising a screen having a plurality of perforations secured to-said rods at spaced intervals, a plurality of openings through said piston, a corresponding 10 plurality of hinged flaps covering said openings and adapted to open on the intake stroke to allow passage of solids through said openings and to close onthe pumping stroke to move the solids through said container, and means to effect the reciprocation of said rod.

5. In a fractional crystallizer comprising anelongated container having product outlet con-- duits A and B in the end portions thereof, a feed inlet conduit between said outlet conduits, means for abstracting heat from a portion of said container between said outlet conduit B and said feed inlet conduit, means for adding heat to a portion of said container between said outlet conduit A and said feed inlet conduit and means for moving granular solids therethroug-h toward outlet conduit A in countercurrent' contact with a liquid, an improved solid-conveyor which comprises, in combination, av reciprocating rod extending longitudinally into said container and parallel to the axis of said container, a plurality of pistons formed by paired, semi-circular, flaps comprising a screen having a plurality of perforations transversely disposed along said rod at spaced intervals and secured thereto, saidfiaps being hinged and rotatable, means to stop the-rotation of said flaps at the transverse position on the forward stroke and means to stop said rotation at an angle less than 90 degrees from the transverse position on the return stroke.

6. In a crystallizer comprising an elongated cylindrical container having product outlet conduits A and B in the end portions thereof, a feed inlet conduit between said outlet conduits, means for abstracting heat from a portion of said container between said outlet conduit B and said feed inlet conduit, means for adding heat to a portion of said container between said outlet conduit A and said feed inlet conduit and a crystal-conveyor for moving crystals toward outlet conduit A, an improved conveyor which comprises, in combination, a reciprocating rod extending axially into said container, a plurality of perforate pistons which comprise rings transversely positioned within said cylinder at spaced intervals along said rod, spokes extending inwardly from said rings and secured to said rod, a pair of semi-circular foraminate flaps rotatably hinged to the spokes of each ring and adapted to assume a transverse position and close the openings within said ring, a boss on the inner periphery of each ring to stop the rotation of said flaps at the fully extended position, a forward stop for each pair of flaps which comprises a transverse, horizontal bar secured to said rod in front ofthe corresponding piston, and means to actuate said reciprocating rod.

7. In a cylindrical, multi-stage crystallizer having a product outlet in each end and a feed inlet intermediate said ends, an improved conveyor for moving granular solids through said crystallizer countercurrently to the liquid therein which comprises, in combination, a reciprocating rod extending axially into said crystallizer, a plurality of closely-fitting rings transversely positioned within said crystallizer at spaced intervals along said: 110d: andisecuredi thereto by means trans= verse; ba'fs extending: outwardly-from saith rod; a: cornesponding: plurality. of; paired; semiecimular; ioraminato; flaps rotate-lilysecured along: theisnonecircular edges to said: transversebarsg meanst tcwstion said fiapsettheinfulhzextendedr position; and meanstoactuate saintreciproeating rod;

8; In. a fractional cliystailizerwhich comprises elongated: container" having product: outlet eonduitsA: and: BE in the end portions thereof; we feedinlet conduit between. said; outlet; conduits; meanszforabstracting heatfromta portionzofisaid; containen between saidioutletrconduittB- anciisaitf feed inlet conduit, meansfor adding. heat: to; a" portion of said container between saidoutletcorrduit A and said feed inletconduit? and as crystalconveyon for; moving cnystalstowardi outlet. conduit A, animgroved conveyor which: comprises: a;

reciprocatingrodextending axially 'intozsaid comtainen; av -plurality of periorate,-.pistons-comnrise ing; a screenhevinge, plurality of perforationsidisposed; along and: foldably; securedto said rod;- means to-stop the unfolding; ofsaid. piston-s at their fully extended-position during; the: advance stroke OfzSSid rod, endmeans: to. actuatesaidfrod;

9; In a-.multi-sta ge:orysta,l1izen comprising a: cylinderhaving a product outlet-in each end. and aaieed fillet-intermediate said: ends, an improved: cr'ysta-lnonveyor which comprises; inecombination; a 'eeiprocating rod-extending through said cy1in der and. parallel to the axis" of said cylinder-r, a; pluralityof perforate pistons disposed along;Saidv rod: and foldablysecured thereto; s-aidi pistons comprising paired, semi=circulan foraminate Nil members hinged: to rotate about-a v common. axis 35 83 of saidhinged: members: aboutzsaid axis: at: their i111!yxmened position 011217116 forward strokeiof thee.

rodimeanstostontherotation ofsaidsemieciroullarmembers on'the: reverse stroke; short ofa deade center-.positiomendmeansW cause said mite.-

reciprocate;

10:12 frwctionaicrystallization. apparatus whiclncomprises in combination, anze-longatedien closed oontainen, a; product outlet. adjacenteachx ondi of said' containersuch a. feed; inlet; inter-mes; diate said ends, means for adding: heat: twsaidi containeradjacent.- one; end: thereof; means: for abstracting,heatfromisaidflcontainet along apertion; thereof between said feed; inlet. and-1 thez-une heated end;, andmeans for moving: solid grams Ian material: through said; eontainen from; the coo'l'edtorthewheatedf end which :compniseseueeimmcating; rod; extending: serially: into. said con;-r tainenga: plurality ofperforatmpistons secureditm said= rod; and spacedl intervals; each: of:' said pistol-1s;- comprising, a; plurality: ofi' perforate members adapted to open: to permit passage of throughsaid pistons and-adantedxtooloseso asto. movesolids through said: containers-m1 the direee tion of the heated end;-

I REFERENCES GITED, The following references are of record in the file of "this: patent? UNITED- STAT-ES.

Numben

Claims (1)

1. A FRACTIONAL CRYSTALLIZATION APPARATUS WHICH COMPRISES, IN COMBINATION, AN ELONGATED ENCLOSED CONTAINER, A PRODUCT OUTLET ADJACENT EACH END OF SAID CONTAINER AND A FEED INLET INTERMEDIATE SAID ENDS, MEANS FOR ADDING HEAT TO SAID CONTAINER ADJACENT ONE END THEREOF, MEANS FOR ABSTRACTING HEAT FROM SAID CONTAINER ALONG A PORTION THEREOF BETWEEN SAID FEED INLET AND THE UNHEATED END, AND MEANS FOR MOVING SOLID GRANULAR MATERIAL THROUGH SAID CONTAINER FROM THE COOLED TO THE HEATED END WHICH COMPRISES A RECIPROCATING ROD EXTENDING AXIALLY INTO SAID CONTAINER, A PLURALITY OF FOLDABLE PISTONS COMPRISING FORMINATE MEMBERS HINGED AT SPACED INTERVALS TO SAID ROD, SAID FOLDABLE PISTONS BEING ADAPTED TO CLOSE ON THE INTAKE STROKE AND OPEN ON THE PUMP STROKE OF SAID PISTON.

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