US1972730A - Method and apparatus for evaporating and cooling liquids - Google Patents

Description

p ,4 93 e. A. CONNELL ET AL 1 1,972,730

METHOD AND APPARATUS FOR EVAPORATING' AND COOLING LIQUIDS Filed Sept. 18, 1931 INVENTOPS .THoMAs M. Gunmen Geoaac' A.CONNGLL BY HARoLo L ATTORNEY Patented Sept. 4, 1934 METHOD AND APPARATUS FOR EVAPORAT ING AND COOLING LIQUIDS George A. Council, San l edro, and Thomas M,

Cramer, Long Beach,

Calif., and Harold B.

Caldwell, Chicago, Ill., assignors to Pacific Coast Borax Company, a corporation of Nevada Application September 18, 1931, Serial lilo. 563,558

16 Claims.

This invention has to do in a general way with the art of evaporating and cooling liquids, and is more particularly related to improvements in processes for concentrating solutions and the like by evaporation and precipitating crystals .from solution by virtue of the reduction in temperature which attends such evaporation.

It is well known to those familiar with the art that various vaporizing apparatus have been designed ior use in cooling and concentrating liquids. The general principle upon which such vaporizing apparatus operates comprises the introduction of the hot solution to be cooled or concentrated into a chamber which is maintained under reduced pressure.

In certain instances, attempts have been made to produce processes of this type which are continucus in their nature. In other words, attempts have been made to cool or concentrate solutions by continuously introducing into a vacuum chamber, a hot solution and continuously removingfrom the chamber a cooled or more concentrated solution in Which crystallization has started to takeplace. 1 In any process of this nature, it is necessary for successful continuous operation, to prevent the deposition of crystals on the interior of the chamber shell and also to prevent such deposition within the conduits leading to and from the shell. Although there is little danger of crystals accumulating in the outlet passage of apparatus of this character, there is constant danger of such crystals building up in the inlet, and this together with the deposition of crystals on the shell wall, have been the major difliculties encountered in the use of apparatus of this character.

It is a characteristic feature of the prior methods and apparatus with which we are familiar, that the hot liquid is introduced into the evaporator shell in a manner such that fluid circulation is established and in the circulatory system thus set up the hot liquid is carried into direct engagement with the shell wall. Under these conditions we have found that eddy currents are set up along the wall which are attended by reduction in pressure and regional ebullition. We have found that in the case of a solution or a liquid carrying a small amount of some dissolved salt as an impurity, that this is followed by a precipitation of salt in the regions of the eddy currents, the crystals'as they build up increase the currents and consequently accellerate the precipitation. Furthermore'the engagementof the hot liquid with the cooler shell wall, even though the latter is exteriorly insulated, efiects a regional reduction of temperature immediately adjacent the shell wall which also promotes the deposition of crystals on the interior of the chamber.

It-is another characteristic of the prior apparatus with which we are familiar, that the introduction of the hot liquid into the chamber, in the event there is a substantial pressure differential between the chamber and the incoming liquid, is attended by ebullition in the inlet conduit. This ebullition is naturally attended by the formation of a crystalline deposit within the conduit which soon impairs the efliciency of the apparatus.

It is a primary object of the present invention, to prevent the deposition of crystals on the shell walls, and it is a further object of the in- Y vention to prevent ebullition and the consequent deposition of crystals in the inlet conduit.

The process contemplated by this invention consists in a general way of introducing the hot feed liquid into a body of cooler liquid which is contained in a closed chamber. When the process is being practiced for cooling or evaporating the liquid it is preferable that the chamber be maintained under a vacuum or a pressure less than that of the incoming liquid. The body of cooler liquid in the chamber is maintained in rotation by means which are entirely independent of the injected hot solution. Such means maybe in the form of a mechanical stirrer or any other suitable means. For example we may maintain rotation in the solution by withdrawing a part of the cooler liquid from the body of liquid contained in the chamber, and tangentially returning same into the chamber at a point below the level of the liquid therein. This last mentioned. method will be used herein as an example for illustrating this step in the invention.

The depositionof crystals on the shell wall below the liquor level, is prevented by introducing the hot liquor into the body of cooler liquor at a substantial distance below the surface of the liquid and at a substantial distance from the walls of the chamber, preferably in a general direction toward the zone of reduced'pressure including and immediately surrounding the vortherethrough, a velocity sufflcient to maintain the pressure in the nozzle itself and in the assoart, that the static liquor head in the evaporating chamber above the opening of the nozzle, co-

operates with the pressure which attends the passage of liquid through a nozzle to maintain struction, and

a sufllcient pressure in the nozzle to prevent boiling in the inlet pipe. It is important in this connection that the velocity and its attendant pressure at the tip of the nozzle be sufficient to cooperate with the static head in maintaining a total pressure in the nozzle sufficient to prevent boiling of the solution at the temperature under which it is being introduced regardless of the absolute pressure in the chamber.

vIt was pointed out above that the preferred means of maintaining the liquor body in rotation was to remove a part of the solution/from the evaporator shell and introduce it tangentially into the shell at the point below the liquor level. In this connection it isa further feature of our invention, that means are provided for classifying the solution which is returned to the evaporator shell. The purpose of such means is to permit the larger crystals which have formed through the cooling and concentration of .the solution, to be withdrawn from the solution leaving thechamber before it is introduced back into the body of the liquor in the chamber. This is accomplished 'by providing the outlet pipe, which is preferably situated in the central portion of the bottom of the chamber, with an, upwardly extending connection, such connection being connected through the medium of a pump and suitable conduit with the circulating inlet.

It is a further object of this invention to sup press the formation of eddy currents in the rotating body and pursuant to this object, we provide thenozzle'through which the hot liquor is introduced into the shell, with a stream lined covering. Further with a view to preventing the deposition of crystals in the feed nozzle, we prefer to make such covering of an insulating material. It is a still further object of this invention to prevent the accumulation of crystals on the shell wall above the liquor level, by delivering to the shell, a spray of wash liquid which may comprise condensed vapor or any other suitable liquid, and which is directed against the inner shell wall at a substantial distance above the boiling zone.

The various steps followed in the practice of our process, and the details in the construction of a preferred form of apparatus contemplated by this invention, will be best understood from the following description of the accompanying drawing in which:

Fig. 1 is an elevational view with parts broken,

away showing a preferred form of apparatus contemplated for this invention;

Fig. 2 is a plan view which may be considered as having been taken in a plane represented by the line 2-2 in Fig. 1;

Fig. 3 is a fragmentary view with parts broken away showing a preferred form of nozzle con- Fig. 4 is a sectional view which may be considered as having been taken in a plane repre-' sented by the line 4-4 in Fig. 3.

More particularly describing the invention as denser and the vaporv outlet. being associated with any suitable means for withdrawing vapors from the shell or applying vacuum thereto, such means not being shown. The condenser 14 has an outlet pipe 15 which may be in the nature of a barometric leg leading to a condensate receiving tank 16.

The bottom portion 17 of the shell 11 is preferably made in the form of a funnel which communicates through a suitable valve 18 with an- 'outlet conduit 19. The outlet conduit 19 is shown as being connected through a suitable reducing nipple 20 with a connection 21 which leads to a discharge pump or barometric leg, nowshown. The outlet connection 19 is also provided with an upwardly projecting arm 22 which is shown as being connected through an inverted U pipe 23 with a leg 24 which leads to the inlet of a circulating pump 25. The outlet of the pump 25 is connected through a pipe 26 to a cooled liquor inlet connection 27 mounted on the shell 11 and arranged so that the discharge therefrom is tangentiallyinjected into the shell at a point substantially below the static liquor 'level L.

From the construction so far described it will be seen that when the pump 25 is in operation, the body of liquor in the shell is maintained in rotation, such rotation being effective to form a central zone of reduced pressure and peripheral zone of increased pressure in the body.

It was pointed out in the fore part of the specification that one of the most important features of this invention resides in the manner of introducing the hot liquid into the bodyof cooled liquid in theshell. The means for introducing the hot liquid are shown in the drawing as comprising a nozzle member 30 which is connected with an extension 31 having its upper end situated a substantial distance below the static liquor. level L. The nozzle is connected to a conduit 32- which leads to a pump 33 or any other suitable source of hotliquor supply capable of delivering the liquid to the nozzle under the proper pressure. In view of the fact that the socooler than the liquid which is entering the shell through the nozzle, we prefer to construct the nozzle as shown in Fig. 3, wherein the pipe 31 is covered with insulation 34. This insulation is preferably stream lined, as indicated in Fig. 4, so as-to suppress the formation of eddy currents in the rotating body of solution as it passes the insulation coating.

It will be observed that the nozzle 30 is eccentrically disposed with relation to the central portion of theshell so that the jet of hot liquid projected therefrom is not directed vertically upward through the zone of lowest pressure at.

the center of rotation.- If arranged in this latter bent slightly either into or opposing the di-- rection of rotation. In this manner the hot solution is directed into the main body of the liquid at a slight angle with the vertical and into a region in which it will boil before it has an opportunity to contact any part of the shell surface. The crystals which may be released or precipitated during evaporation, are drawn downwardly into the outlet, and by the time the newly introduced hot liquid reaches the shell wall it has cooled to a point at which no farther boiling takes place under the conditions existing at the shell walls.

In any apparatus of this character there is always a certain amount of crystalline deposit formed on the shell wall at the boiling zone. For the purpose of preventing the accumulation of such crystals we provide a spray ring 35 which is situated above the boiling zone and is provided with a plurality of outlets through which a wash liquid is sprayed against the interior of the shell. This wash liquid may be pure water or it may, as shown, comprise a condensate drawn from the condensate receiving tank 16 and deliveredto the ring 35 by means.

of a pump 36.

It will be apparent from the foregoing description that the process contemplated by this invention is one which assures a rapid cooling and evaporation of a hot liquid in a manner such that all of the precipitated salts are removed from the evaporating or cooling chamber by virtue of the position at which they are precipitated. The apparatus shown for practicing the process is of simple form and construction and its operation may be easily controlled.

It will occur to those familiar with the art that apparatus of the type described above may be arranged in several stages in which the solution leaving the discharge of one stage will be delivered to the injector nozzle of the next stage, the various stages being of progressively lower pressure.

It is to be understood that the scope of our invention is not confined to the specific example given above, but includes within its scope whatever changes fairly come within the spirit of the appended claims.

We claim as our invention:

1. A method of evaporating and cooling a solution which comprises: introducing the solution to be cooled as a jet directly into a body of cooled solution contained in a chamber under reduced pressure; and rotating the body of cooled solution by withdrawing solution from the bottom of said body and introducing solution tangentially into the side of said body.

2; A method of evaporating and cooling a solution which comprises: introducing the solution to be cooled as a jet directly into a body of cooled solution contained in a .chamber under reduced pressure; and rotating the body of cooled solution by withdrawing solution from said body and reintroducing part of the withdrawn solution tangentially into the side of said body.

3. A method of evaporating and cooling a solution which comprises: introducing a jet of the solution to be cooled directly into a body of cooled solution contained in a chamber under reduced pressure at a substantial distance below the surface of the liquid therein and above thebottom of the chamber; continuously withdrawing solution from the bottom of said body; classifying said withdrawn solution; and tangentiallyintroducing a part of the classified solution into the side of said body for effecti a rotation of said body. 0

4. An apparatus of the class described embodying: a shell having a vapor outlet; means for withdrawing cooled liquor from the bottom portion of said shell; means for tangentially introducing cooled liquor into said shell at a. point below the liquor-level therein; and means for introducing hot liquor into said shell at apoint between the center of the shell and the inner surface thereof and at a substantial distance below the surface of the liquor therein.

5. An apparatus of the class described embodying: a shell having a vapor outlet; means for withdrawing cooled liquor from the bottom of said shell; means for tangentially introducing cooled liquor into saidshell at a point below the liquor level therein; and means comprising a nozzle for introducing hot liquor into said shell at a point between the center of the shell and the inner surface thereof and at a substantial distance below the surface of the liquor in said shell. I

6. An apparatus of the class described embodying: a shell having a vapor outlet; means for withdrawing cooled liquor from the bottom of said shell; means for tangentially introducing cooled liquor into said shell at a point below the liquor level therein; and. means for introducing hot liquor into .said shell comprising an insulated nozzle having its outlet positioned between the periphery and the center of said shell and at a substantial distance below the surface of the liquor therein.

7. An apparatus of the class described embodying: a shell having a vapor outlet; means for withdrawing cooled liquor from the bottom of said shell; means for tangentially introducing cooled liquor into said shell at a point below the liquor level therein; and means comprising a substantially vertical nozzle having an inclined upper end for introducing hot liquor into said shell at a, substantial distance below the surface of the liquor therein.

8. An evaporator cooler of the class described embodying: a shell having a vapor outlet and a liquid outlet; a cooled liquor inlet pipe tangentially mounted in the side of said shell below the liquor level therein; means for delivering a part of the cooled liquor from the outlet to the cooled liquor inlet pipe; a hot liquor inlet connection mounted in the bottom portion of said shell and terminating within the body of liquor in the shell at a substantial distance below the surface of said body of liquor; and means for delivering a hot liquor to said hot liquor inlet connection. 1

9. An evaporator cooler of the class described embodying: a shell having a vapor outlet and a liquid outlet; a cooled liquor inlet pipe tan-- gentially mounted in the side of said shell below the liquor level therein; means for delivering a part of'the cooled liquor from the outlet to the cooled liquor inlet pipe; a hot liquor inlet nozzle mounted in the bottom portion of said shell and terminating within the body of liquor in the shell at a substantial distance below the surface of said body of liquor; and means for delivering a hot liquor to said hot liquor inlet liquor inlet pipe; said last mentioned means comprising an upwardly inclined connection hav ing an inlet at its lower end communicating with said outlet pipe, and liquor circulating means connecting said inclined connection with said cooled liquor inlet; a hot liquor inlet connection mounted in the bottom portion of said shell and terminating within the body of liquor in the shell at a substantial distance below the surface of said body of liquor; and means for delivering a hot liquor to said hot liquor inlet connection.

11. A method of treating aliquid which comprisesz. maintaining a r tating body of solution in a chamber under red ced pressure; and independently introducing the solution to be treated directly into said body as a jet which is located between the center and the periphery and above the bottom and below the'top of the body and is angularlydisposed relative to the plane of rotation and the axis of said body.

12. An apparatus of the class described embodying: a shell having a. vapor outlet; means for maintaining a rotating body of cooled liquor in said shell; means for withdrawing cooled liquor from said shell; and means for introducing hot liquor into said shell at a point between the periphery of the shell and the center thereof and between the surface of said liquor and the bottom of the shell.

13. An apparatus of the class described emintroducing hot liquor into said shell at a point between the periphery of the shell and the center thereof and between the surface of said liquor and the bottom of the shell.

15. An apparatus of the class described embodying: a shell having a vapor outlet; means for maintaining a rotating body of cooled liquor in said shell; means for withdrawing cooled liquor from said shell; and means for introducing hot liquor into said shell at a point between the periphery of the shell and the center thereof and between the surface of said liquor and the bottom of the shell, said last mentioned means comprising a nozzle, the outlet end of which is inclined relative to theaxis of rotation and a plane of rotation of said body of liquor.

16. A method ofcooling a hot solution by evaporation which comprises: maintaining a rotating body of cooled solution under vacuum; and introducing said hot solution into said rotating body of cooled solution at a point which 105 is spaced inwardly from all bounding surfaces of said rotating .body, and is spaced outwardly from the center of said rotating body.

GEORGE A. CONNELL.

IHOMAS M. CRAMER. .HAROLD B. CALDWELL.

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