US2067043A - Vacuum crystallizer and method of crystallizing - Google Patents

Description

Jan. 5, l1937. -H. B.' CALDWELL 2,057,043

i VACUUM CRYSTALLIZER AND METHOD OF CRY-STALLIZING Filed OCT'. 25, 1935 w ff-L :5i

ma@ W, w j@ M W l' Patented Jan. 5, I

UNITED STATES :anni:

PATENT oFFic/B VACUUM CBYSTAILIZEB AND METHODOF "CBYSTALLIZIN umm n. oneven. 'New' rm. N. r., mami :o

Swenson Evapin'atoi' Company, Harvey corporation of Illinois Ill.,a

appnc'emn october g5, 193s, anni No. 695.095

' nomini. l(criss- 45) This invention relates to vacuum crystallizers by a suitable cooling fluid, which may be at a temperature substantially higher than the temperature of the solution from which the crystals are being deposited. v ,l lo One ot the principal objects oi the invention is to provide. an improved method of andapparatus for crystallization. A further object of the invention isto provide an improved method of and apparatus for crystalgo lization, which ,is substantially continuous and can be continued for prolonged periods o! time without ceasing operations. Other obiectsradvantages and capabilities of the invention will appear from the following dem scriptlon oi a preferred embodiment' thereof, I te. .n in commotion with .the accompanying u.: in whicha i '1 e 1 is a diagrammatic view ot a crystallizer embodying my invention, and

' a0 Pig. 2 is a sectional view taken on the line 2--2 when the shell is evacuated to a substantial degree,

for example. about 29 inches of mercury, the surface oi' the liquid in the shell I Il isat a relativelyl low point on the'cylindrical portion thereof, so that ample vapor space is provided above the .surl'aceior the ebullition which takes place. Suitable stirring means are provided for agitatlng the ,liquid wlthinthe shell l0. These'mcans 60 may?` suitably consist o! propellersv M mounted on shaits i! which -are driven by suitable means (not shown) 'so as to agltate the liquid thoroughly. The solution from which salts are to be crystallined is suppliedby a valved pipe Il. i, The mercado! the shell II isprovldedwlth an opening Il which communicates with a suitable device Il for creating a vacuum within the shell lil and compressing the vapors removed from the shell. This evacuating means may be any oi the pumps or electors known in' this art. 5 In the speciiic embodiment illustrated the ,evacug ating means l1 is a booster elector which is supi plied with high pressure steam through a pipe i8. y 'I'his steamis supplied to a steam chest I9 from which it passes through a chamber 20 through 10 nozzles 2|. The chamber 20 communicates with the opening ii. The nozzles 2| terminate in the converging portion ot a' venturi 22, which venturi delivers into a condenser 23.` Thecondenser 23 is shown by way of example as comprising a 15 `chamber through which passes a Icoil 24, through which suiti'ible cooling fluid is' passed. Said chamber communicates with the barometric leg 25 sealed by a trough 2G. The chamber is also Aconnected to a vacuum pump 2l which exhausts air introduced into the system with the liquid supplied or introduced byleakage.

With an eilicient evacuating means -Il of the type shown and 'an'e'ilicient condenser 2,3 'the apparatus thus far described is a very eiective 25 means for cooling liquid introduced into the shell Il l. For example, it is quite feasible to freeze water in the shell i0, notwithstanding thel fact that the cooling water available for use inthe coil 23 is at ordinary summer temperatures. 3@

-lin crystallizing salts from solutions containing them the solution is introduced by the pipe I5 and the booster ejector il is put into operation, likewise the vacuum pp 21. 'As a result of the high vacuum produced in the shell I0, for ex- 35 ample a vacuum of 29 inches of mercury when the atmospheric pressure stands at 30 inches, a certain amount of ebullition occurs within the shell l0 and the resulting evaporation cools the liquid to a point where crystals deposit to ade- 4@ sired extent.-

'Ihe vapors from the'ahell I0 together with the ,steam introduced bypipe I8 are commingled in.

the venturi 22 and are ilnally condensed in the condenser 23. In practicing crystallization in 45 this manner I have found that` a considerable amount oi salt is deposited on the walls of the shell Il above the liquid level, this deposit resulting from the splashing of the chilled solution upon these walls.-V Here the iilm oi liquid is suboo I lected to the full effect of the vacuum and the water evaporates therefrom rapidly so that the deposit grows as the crystallization is continued. I have also found that the overhead carries with it a certain amount oientrainment which builds 66 up on the nozzles 2|, which nomles are at high temperature owing to the passage of steam therethrough. The entrainment hitting these nonies is immediately deprived of its water content so that the salts build up thereon.

In order to render the operation continuous I provide within the shell I0, preferably at a position as high as possible therein, a spray Pipe 2s which is preferably annular in form and provided with spray openings adapted to distribute liquid around the whole surface of the cylindrical wall of the shell. This liquid is adapted to iiow downwardly over this surface and remove any salts deposited thereon or prevent the deposition of any salts thereon. 'I'he pipe 2. communicates with .one or more valved pipes 2l so that a controlling supply of liquid can be supplied to pipe 28 continuously or at intervals. The nature of the liquid supplied to the pipe 2l will depend upon the nature of the precipitate on the walls. or the salt or substance which isbeing crystallized. The solvent in the solution being evaporated is always suitable. In many cases where the solution being evaporated is relatively dilute,

a certain portion of the feed supplied to the shell lil may be introduced by the pipe 2l. In order to remove the, deposit of salts or the like upon the nozzles 2| I provide a valved pipe 3l adapted to deliver water or other suitable liquid upon these homes. In the embodiment of the invention illustrated I have shown the pipe 3l delivering into the top wall of the chamber 2l.

' In addition to the supply of liquid by means of the pipe 30, I prefer to provide in opposite walls of the chamber 2li, openings 3l for the supply of further quantities of liquid. .'llheL openings ll are preferably located near the level of the lowest nozzles 2| so that the. overhead can'ies the spray with it over the outer surfaces of the noazles whereby the deposit of solute is effectively prevented or removed. supplied with said liquid by means oi valved pipes 32. It is to be understood that it is not intended to limit the invention to this disposition of the means for supplying liquid to the ejector, since such means may be located in any position whereby they are effectively adapted to remove or prevent deposit of the solute on the nonies 2i. While the liquid supplied to the ejector may suitably be a solvent for the solute, this is not necessary since the removal of the deposit is at least partially mechanical due to great changes of temperature fracturing the deposit. I nnd that after running for one hour, that by turning on the liquid supply for three minutes and then turning on the steam the deposit is substantially fractured and falls from the noles.

In the preferred manner of operating, I prefer to supply a small amount 'of liquid continuously by the pipes 2l, that is, an amount of liquid which will keep any entrainment striking the walls from depositing crystals thereon or which will cause crystals on the walls to.remain slushy and become washed down by the stream of liquid.

As stated above, it is preferred to supply liquid by pipes 3l and I2 for short periods at comparativeLv long intervals, for example, periods oi' about three minutes at intervals of about one hour. l

Although the invention has been described in connection with the specific details of a prei'erred embodiment thereof, it is not intended that such details should be considered limitative of the invention except so far as set forth in the accompanying claims.

The openings 3i are' ,ooaoss Having thus described my invention I declare that what I claim is: v

l, A vacuum crystallizer comprising a chamber.

adapted to contain solution and provide a vapor space thereabove, means for withdrawing vapors to create a vacuum in the chamber and compress the withdrawn vapors, cooling means for condensing said compressed vapors, and means for injecting liquid upon surfaces within the vapor space oi' said chamber in order to prevent accumulation of solute thereon.

2. A vacuum crystallizer comprising a chamber adapted to contain solution and provide a vapor space thereabove, means for withdrawing vapors to create a vacuum in the chamber and compress the withdrawn vapors, cooling means for condensing said compressed vapors, and means for injecting liquid upon the internal surfaces of the vapor withdrawing means in order to prevent accumulation of solute thereon. Y 3. A. vacuum crystallizer comprising a shell adapted to contain solution and provide a vapor space thereabove, means for withdrawing vapors tocreate a vacuum in the chamber, and means for injecting liquid upon the internal surfaces of the vapor withdrawing means in order to prevent accumulation of solute thereon.

4. 'Ihe method of crystallizing solute Lfrom solutions which consists in supplying said solution to a closed chamber, maintaining a vapor space above said solution in said chamber, withdrawing vapors from said space and maintaining a substantial vacuum therein thereby causing a fall of temperature below that necessary for the precipitation oi' crystals, injecting -liquid upon surfaces within said vapor space to prevent accumulation of solute thereon andwithdrawing said crystals from said chamber.

5. 'Ihe method of crystallizing solute from solutions which consists in supplyin said solution to a closed chamber provided with an ejector communicating with the .upper portion of said chamber, withdrawing vaporsfrom said space by said ejector and maintaining a substantial vacuum therein thereby causing a fall of temperature below that necessary for the precipitation of crystals, injecting liquid into said ejector to prevent accumulation of solute therein. and withdrawing said crystals' from said chamber.

8. A vacuum crystalliser comprising a chamber adapted to contain solution and provide a vapor space thereabove, means for withdrawing vapors to create avacuum in the chamber and compress the withdrawn vapors, said means including ejector tubes adapted to convey steam at high temperature, cooling means for condensing said compressed vapors and steam, and means for injecting liquid upon the outer surfaces of said ejector tubes for the purpose oi' removing accumulated solute therefrom.

7. A vacuum crystallizer comprising a shell adapted to contain solution and provide a vapor space thereabove, means for withdrawing vapors to create a vacuum in the chamber, said means comprising ejector tubes adapted to convey steam at hightemperature, and means for injecting liquid upon the exterior vsurfaces of said ejector tubes, for the purpose of removing accumulated solute therefrom.

8. The continuous method of crystallizing solute from solutions which consists in supplying said solution continuously to a closed chamber so as to pass over unsubmersed portions of the wall thereof so as to prevent deposition of solute thereon, maintaining a Por space above said solution in said chamber, continuously withdrawing vapors from said space and maintaining a substantial vacuum therein, thereby causing a fall of temperature below that necessary for the precipitation of crystals, and continuously withdrawing said crystals from said chamber.

9. The continuous method of crystallizing so-y lute from solutions which consists in supplying 'said solution to a closed chamber, maintaining a vapor space above said solution in said chamber, continuously withdrawing vapors from said space and maintaining a substantial vacuum therein, thereby causing a fall of temperature below that necessary for the 'precipitation of crystals, continuously injecting liquid upon surfaces within said vapor space to prevent accumulation of solute thereon, and continuously withdrawing said crystals from said chamber.

10. The continuous method of crystallizing solute from solutions which consists in continuously supplying said solution to a closed chamber provided With an ejector communicating with the upper portion of said chamber, said ejector comvprising an ejector tube conveying steam at high temperature, continuously withdrawing vapors from said space by said ejector and maintaining a substantial vacuum therein, thereby causing a fall of temperature below that necessary for the precipitation of crystals, intermittently injecting liquid upon said ejector tubes to remove solute deposited thereon, and continuously withdrawing said crystals from said chamber.

11. A continuous method of crystallizing solute fromsolutions which consists in continuously supplying said solution to a closed chamber provided with an ejector communicating with the upper portion of said chamber, said ejector comprising an ejector tube adapted to convey steam at high temperature, continuously withdrawing vapors from said space by said ejector and maintaining a substantial vacuum therein, thereby causing a fall of temperature below that necessary for the precipitation of crystals, injecting liquid into said chamber so as to cause the injected liquid to flow down the unsubmerged walls thereof and prevent accumulation. of solute thereon, intermittently injecting liquid upon the exterior of the ejector tubes for the purpose of removing solute deposited thereon, and continuously removing said crystals from said chamber.

HAROLD B. CALDWELL.

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