US1693786A - Process for the crystallization of solid substances in a coarse granular form from solutions - Google Patents

Description

PROCESS lFOR THE CR Dec. v4, 1928.

Patented u 4, 1928.

UNITED STAT-Es :sax Isaacnsan, or osLo,

, 1.693.186. P.vraN'roFFlcl-z.

NORWAY, AssIeNoa To urrnsnnsxnrnr xmrszrnr., .or osLo, Noaway.

IPBOGESS FOB THE CBYBTALLIZIATION OI SOLID SUBSTANCES IN A COABSE GRANULAB` FORM FROM SOLUTIONS.

Application med September 10, 1925, lerial No. 55,802, and in Norway September 17,'1924.

with very great drawbacks, among other` things because the creation of new small kernels in the apparatus has taken place.

completely uncontrolled. If the intensity of production is maintained onl moderately igh, the liquidwill become sov ighly heaped with crystalsJthat the contents lof the a paratus will form a thick mass before t e separate granules have obtained moderately large dimensions. If, for instance, the separate granules were cause to grow from` '25 llOO mm. to 4 mm. in average diameter,

eir total volume would increase to the (iLOOOOOO-double one.` Therefore, it has been necessar either to remove the precipitationsl before the granules have attained larger dimensions, such as used in vacuum apparatus for the manufacture of common salt, or it has been necessary to operate the apparatus intermittentl with a low intensit vveach time new kernels ad to be created an as long as they were still small, such as has been proposed in respect of vacuum apparatus for' sugar. Otherwise, a su erlluous numbery of new kernels would be ormed, because any changerequires a comparativel o owing to the lar e quantities of apparatus, and t ese small lkernels will thereafter grow quite catastrophically, as just intimated. 4

In addition, one had not by a` constrained guiding ofthe liquid-circulation taken carey of maintaining the granules in., suspensionv until they were large enou h.

The present invention oes away with these inconveniences bycombining three elements fomerly known separately but never utilized simultaneously hitherto.

1. A constrained .guiding ofthe circulating stream of liquid wherein the kernels are long time. quid'in the suspended, with so high velocities that the kernels can nowhere deposit before they have attained the-desired size'. v f 4 2. A. regular removal of kernels which havev rown to the size desired. f

' 3. regulation of the number ofthe small kernels by introducing regularly smallsker-so nels or causing them to form automatically in the apparatus or by removing them according as the mass of. kernels in the a paratus is increasing or decreasing durab y.

l The removal of large kernels and the regulated introduction of small kernels in the apparatus need not be quite constant. Small variations play no part. v y

The important point consists in takin care that the totalsuperficial area of kerne s "10' in the apparatus, in spite of the re ular' rethe read -grown ones, is a ways so large that the sai area at afull intensity of the o eration can take up the most essential part f the crystallizations.

If the present surface of kernels should be too small and thereby the new formation of small kernels so great that the constant increase ofthe latter lcannot be regulated by the present means for taking out smallkernels, the catastrophical growth of these small kernels will transform the contents of the apparatus into a thick mass, before the larg` est kernels have attained the desired size.

The accompanying drawin illustrates as examples two uti izations of t e methoddiagrammatically. Figurel showsan apparatus for continuous manufacture of coarse-gran` ular precipitations by cooling, and Figure 2 an apparatus for continuous manufacture of coarse-granular precipitations by the evap-` oration of a solution.

`In Figure` 1, w is a vessel havin thel shape of a closed annular channel and eing vfilled with a solution and a suspension of larger or smaller kernels of the substance to be precipitated. b is a propeller which passes the solution in the direction indicated by the arrows. 0 is a cooling device consisting of pipes through` which the contents ofthe apparatus are passing. y j

The cross sectional areas of the vessel are all over so small that the suspension is taken along and circulates with the liquid.

All superfluous small crystals are removed before having time to grow up, by a pipe d los - large spaces f these small kernels facing its funnel-shaped opening e against the stream so'that a portion of the solutionv will takevits-waythrough thepipe d, the

space f and the aperture g. As the propeller b produces a rotation of the column of liquid, so that the coarser crystals .will be forced towards the wall of the vessel by the rcentrifugal force, the solution passing into the centrally disposed funnel e will contain only crystals of smaller dimensions. The quantity `of liquid-passing through d may be regulated by a cock lw. In comparatively will sink down -more or less completely and may be taken out through the cock h. The liquid passes on throughth'e aperture g into the main stream again.

When the main stream passes by the'aperture g1, a portion of the largest crystals will fall down through p g and the pipe i to.the

'conveyor'ls which removes them from the apparatus. The stream of liquid. coming from e through d prevents smaller crystals which have 4still not grown to the desired size from falling down through the aperture g.

l is a cross which smooths the rotation of liquid produced by the propeller, so that the crystalsinthe lower `part of the apparatus will not be flung against the wall, where they would 'be less completely 'taken along by the stream of liquid.

At m solution is taken out continuously,

at 'nf-new solution with a higher temperature and a higher proportion of the dissolved substancev is introduced continuously, vand at n, new, small crystals are introduced,

apparatus. In other words, care is taken systematically that only the same number of small kernels are allowed to o'row as the number of large kernels-'desired to remove. Each small kernel, namely, grows into. a large one, and if, therefore, the number of the kernels are not limited while they are small, diculties must arise.

In Figure 2, a is a ain a vessel of such a sha as to form a c osed annular channel. It 1s filled with a solutioncarrying a suspension of larger and smaller kernels of the substance or substances to be precipitated. A propeller b passes the contentsA in' the direction indicated by the arrows, ol is a superheater consisting of pipe through which the liquid and sus nsion are passing. At the level p the liqui is boiling and the steam passes out through g.

From a place r, -where the larger crystals will not arrive owing to an enlargement of the vessel a, a pump s sucks a solution mixed with small crystals out through va sedimentation compartment t, wherein a greater or smaller-part of the small crystals aresinking down and may be removed through the -cock h. Atu the liquid is then passed into` the vessel again. w is also a cock by which the quantity'of the liquid passing lthrough may l bev regulated.

From the same place r anotherpump lv sucks liquid which is free of largercrystals,

and drives them up through the-removalaperture g :for large crystals. The large crystals will fall down through the 'pipe i into the conveyor k.

Instead of removing the small crystals by sedimentation in t, other known methods may be used, such as for instance a throwing-out in a centrifugal separator, or filtration. Also the known peculiarity may be utilized that small crystals are more easily 4soluble than large ones, by'dissolving the lsmall crystals by passing under-saturated solution into the compartment t. v

New lsolution is introduced through the pipen.-

If the apparatus does notcreate' itself a suicient number of new small crystals, no

crystals are removed-through r t h, but-small crystals are introduced from outside through the aperture fnq.

These small crystals introduced from outside, may also be produced in a separate portion of the same apparatus, a higher supersaturation being vcreated here than'innother parts for instance by extra cooling. 1

The method of crystallizing out solid substances from supersaturated solutions thereof wherein the solution and a sus ension of granules of the substances circu ate cyclically which comprises circulatin the solution and suspension as a stream o relatively small ycross sectional area whereby the granules are normallyV positively carried along by the circulating stream', regulating the number of granules before they have.

vmaterially increased in size, and removing granules from the circulating stream -at esignated places therein.

In testimony that I claim lthe foregoing as my invention, I have signed my name.

ISAK ISAACHSEN.

losy

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