US2038088A - Heat exchanger - Google Patents

Description

2 Sheets-Sheet 1 INVENTOR ATTORN EYS Patented Apr. 21, 1936 HEAT EXCHAN GER Leslie Earl Sebald, Ridgewood, N. 5., assignor, by mesne assignments, to The Griscom-Russell Company, a corporation of Delaware Application May 8, 1934, Serial No. 724,494

6 Claims.

This invention relates to heat exchangers and more particularly to heat transfer apparatus suitable for evaporating liquids.

In many industrial operations it is necessary to subject liquids to an evaporation process, either for the purpose of concentrating the liquid, or for the purpose of separating certain constitutents such as valuable solvents which,. upon being reclaimed, may be employed again for their original purpose. lhe partial evaporation of liquids, whether for the purpose of concentrating the same or for separating certain constituents, must oftentimes be carried out under exacting conditions as to pressure, maximum temperature and permissible temperature variations, and it is an object of the present invention to provide apparatus whereby the necessary evaporation can be efiected in the most efficient manner.

For some purposes it is necessary or desirable to operate an evaporator under a high vacuum and with a low difference in temperature between the heating medium and the liquid being evaporated. Under such conditions the process cannot be carried out erficiently' where the static head of the liquid being evaporated is considerable, and my invention aims to increase the efficiency of operation under such conditions by maintaining the heated liquid in the form of a shallow body of low static head whereby a small diiference in temperature between the heating medium and the vapor is all that is required to evaporate the liquid at a rapid rate. Another feature of my invention is the continuous application of heat to the liquid at a substantially constant rate whereby the evaporation takes place continuously and under the most stable conditions of operation. My invention also contemplates the provision of apparatus constructed and arranged in such a manner that the vapor produced is promptly removed from the zone of evaporation, whereby a minimum quantity of the vapor is reabsorbed in the body of the liquid being treated. t

In general, the objects of my invention may be attained by providing means for holding a liquid in the form of a thin layer or shallow body in which heating elements are submerged. In this manner the static head of the liquid is maintained at a low value whereby very little resistance is oflered by the body of liquid to the efficient evaporation of the same at points below the surface of theliquid body. A heating medium of relatively low temperature may thus be efliciently employed, and no portion of the liquid being treated is subjected to excessively high temperatures. I prefer to provide means for removing the vapor from the surface of the liquid being treated so that little if any of the vapor is reabsorbed by the body of liquid. This may be accomplished by providing a collecting hood or enclosure having exhaust ports through-which the vapor may be rapidly conducted away from the zone or zones of vaporization.

In a preferred embodiment of my invention I provide a number of superimposed shallow trays 10 each of which is adapted to hold a liquid in the form of a thin shallow layer, and each tray contains a number of tubes through which a heating medium may be continuously passed for the purpose of maintaining the liquid at the desired teml5 perature for efficient evaporation. These trays may be arranged in such a manner that the liquid to be treated may be continuously supplied to oneof the trays and continuously discharged from this tray to a tray below the same. By using such a series of superimposed trays the static head of the liquid being treated may be maintained at all times at a low value although the quantity of liquid being treated within the relatively small space defined by the stack of trays may be considerable. The trays are preferably provided with inclined side walls so that considerable free space is provided along the edges for the discharge of vapor from each of the trays. The stack of trays is preferably enclosed within a shell having one or more vapor discharge ports, and this shell may be provided with means for supplying a heating medium such as steam to the pipes located within the trays, and with means for discharging the heating medium from the apparatus.

My improved apparatus is much more eificient than the usual type of evaporator comprising a shell containing a large tube bundle in which the fluid to be evaporated substantially fills the shell, for in such apparatus the static head on V the lower tubes is considerable. This greatly decreases the efficiency of the lower tubes. For example, if the operating conditions are such' that there is only a ten degree temperature difference between the vapor and the heating me- 5 the heating tubes may be used efficiently.

I prefer. to have the several trays arranged in such a manner that they may be readily removed and with this object in mind I contemplate a preferred arrangement in which the trays are secured at one end to a tube sheet which is fixed to a-shell with the other ends of the, trays supported one by another. With such an arrangement, the fixed tube sheet and the trays secured thereto may be removed as a unit from the shell. The floating head associated with the tubes may also form a part of this removable unit. The floating head or cap may have a return connection or conduit secured thereto and communicating with a chamber in the stationary head or cap and this return connection gray/ likewise form a .part of the removable unit within the shell.

It is to be understood that my invention is not limited to any physical embodiment thereof but may be utilized in various forms for example, I may provide one or more shallow trays within a cylindrical shell in which event the shell is provided with one or more discharge ports for removing the vapor from the surface of the liquid as the. vapor is formed. I prefer to employ apparatus constructed and arranged in such a manner that the vapor does not have to-pass through any body of liquid after it leaves the tray or trays where it is formed. The trays .within the shell may contain heating tubes all of which may be secured to a tube sheet mounted at one end of the shell. According toone aspect of my invention the trays may be regarded as means for dividing the space between the tubes into a plurality of separate compartments each adapted to hold a shallow body of the liquid to be treated. I prefer to provide means such as overflow pipes or the like arranged in such a manner that the liquid may overflow-from one trayto another and where the trays are mounted within a shell the liquid may be finally discharged into the bottom of the shell from which it may be withdrawn through any suitable pipe connection.

The various objects of my invention will be more apparent upon considering the following detailed description and the accompanying drawings illustrating one embodiment of the invention.

In the accompanying drawings:

Fig. 1 is a longitudinal sectional view of one form of apparatus embodying my invention;

Fig. 2 is a transverse sectional view taken on line 2-2 of Fig.1 showing details of construction and 4 k Fig. 3 is a transverse sectional view taken on line 3-3 of Fig. i also illustrating details of construction.

The apparatus illustrated in the accompanying drawings comprises a dylindrical -shell l which may be provided with an integral head 2 at one end thereof and with a removable cap or cover, plate 3 at the other end thereof. A tube sheet 4 may be clamped between the cap 3 and the end of the cylindricalshell. A tube bundle comprising. a plurality of tubes 5 is provided within the shell with one end 05 each oi the tubes secured to the tube sheet 8. The other end of each tube is secured to a floating tube sheet 6. The removable cap 3 is provided with an inlet 7 for steam or some other beating medium and inasmuch as this cap is in direct communication with all of the tubes, this cap serves as ameans for supplying a heating medium to all of the tubes simultaneously. A cap 8 is mounted on the floating tube sheet 6 the rim of the cap being bolted to the edge 01 this tube sheet as shown at 9. The cap 8 has a discharge plates l5 and partition l3 may be welded or otherwise secured at one end to the-stationary tube sheet 4, and at the other end to an end plate 14. These several elements form a tray; and by means of "a plurality of such trays placed one above the other,'-the space around the tube bundle may be regarded as being divided into a plurality of compartments. -The side plates 15 in all except the top tray re inclined in such a manner that the width of the tray at the bottom is narrower than at the top, so that onlya portion of the area at the top of any tray is covered by the bottom of the tray above. Within eachtray may be provided at one or more points tube supports 26 of such dimensions as not to objectionably impede the flow of liquid through the tray.

The end plates M are provided with openings through which pass the tubes 5. I prefer to make such openings of slightly larger diameter than the tubes passing therethrough in order that no strain may be caused by the difference in the linear expansions of the tubes and of the relatively colder trays under operating conditions.

Located near one end of the top tray is a pipe connection l6 through which is supplied the liquid to be concentrated or from which a volatile constituent is to be separated. At the opposite end of the top tray is an overflow outlet i8 communicating with a discharge conduit I! which directs the overflowing liquid into the tray directly below. Similar overflow outlets i8 and discharge conduits I9, .20, and ii are arranged at alternate ends of the lower trays. A discharge port 22 may be provided to withdraw from the bottom of the shell i the liquid overflowing the bottom tray." Discharge ports 23 and 24 are provided for withdrawing vapors formed within the apparatus.

During normal operation of the apparatus illustrated in the accompanying drawings the liquid to be treated is continuously supplied to the top tray through the pipe connection it. This liquid flows from one end of this tray to the other and then back through the tray immediately below the top tray and from this second tray the liquid is discharged to the third tray from which it flows along the tubes therein toward the floating tube sheet 6. The liquid is then discharged into the bottom tray in which it flows back toward the stationary tube sheet :3 and it is then discharged into the bottom oi the shell from which the liquid is ultimately wlth-= drawn through the pipe connection 22. The heating medium entering through the cap 3 passes through all of the tubes -5 and is then discharged from the apparatus through the re turn pipe I and the discharge connection 52. The liquid being treated flows continuously from one shallow tray to another and because of the fact that the liquid is thusmaintained in the form of a,thin layer the static head on the heating tubes is low at all points in the apparatus, thus facilitating the formation of vapor. The

insuring eflicient operation. The exposed upper side portions of each tray permit the vapor to escape freely from the surface of the liquid in each of the lower trays and the vapor is thus removed from the surface of the liquid without having the vapor pass through any body of liquid after it leaves the tray. The shell serves as a means for collecting the vapor and promptly removing the same from the zones of evaporation. The return pipe l for the heating medium is preferably located at the bottom of the shell where it may produce some evaporation of the liquid discharged into the bottom of the shell before this liquid 'is finally withdrawn through the discharge port 22.

The apparatus illustrated in the accompanying drawings not only provides an eflicient means for concentrating or partially vaporizing liquids but it has the virtue of simplicity because of the fact that it can be made of simple and inexpensive parts which can be readily assembled. Furthermore the apparatus can be easily taken apart whenever this becomes necessary for cleaning the apparatus or making necessary repairs. bolts 3', or the like, by means of which the removable cap 3 is secured to one end of the shell I may be removed and then the tube sheet 4, the tube bundle, the trays, floating tube sheet 6, cap 8 and the return pipe l0 may all be withdrawn from the shell as a unit. If desired, a manhole cover, such as that shown at 25, may be provided for facilitating inspection, adjustment or repair of the apparatus without the necessity for removing the tube bundle and the elements associated therewith from the shell.

It is to be understood that my invention is not limited to the particular embodiment herein illustrated and described but includes such modifications thereof as fall within the scope of the appended claims.

I claim:

1. Apparatus of the type described comprising a shell, a tube sheet associated therewith, means forming a plurality of shallow trays within said shell, said trays having side and end walls, a plurality of tubes secured to said tube sheet and extending through the end walls of said trays remote from said tubesheet, the said tubes being loosely mounted in said end walls to permit relative displacement of the tubes with respect to said walls, means for supplying a liquid to said trays, and means for supplying a heating medium to said tubes.

2. Apparatus of the type described comprising a shell, a plurality of superimposed shallow trays within said shell, all of said trays below the upper- The.

most having inclined upwardly diverging side walls whereby the top portion of each tray is of greater extent than the bottom or the tray above it and each of said trays having an outlet at the upper edge of the side wall thereof, means for supplying a liquid to the uppermost of said trays, conduit means on the wall of each tray adjacent the outlet for causing the liquid discharged through the outlet to flow along the wall of the tray and a plurality of heating tubes disposed in each of said trays.

3. Apparatus of the type described comprising a shell, a tube sheet fixed with respect to one end of the shell, a floating tube sheet within said shell, a tube bundle having its ends secured to said tube sheets, and a plurality of superimposed trays dividing the space occupied by the tube bundle into a plurality of compartments, at least one-of said trays having one end secured to the fixed tube sheet and the other end supported by another of said trays.

4. Apparatus of the type described comprising a shell, a tube sheet removably secured to one end of the shell, a floating tube s eet, a tube bundle having its ends secured to sa tube sheets, and a plurality of superimposed trays dividing the space occupied by the tube bundle into a plurality of compartments, thetube sheets, tube bimdle and trays being removable as a unit from the shell.

5. Apparatus of the type described, comprising a. shell, a tube sheet secured thereto, a"floating tube sheet, a tube bundle having its ends secured to said tube sheets, a plurality of trays dividing the space occupied by said tube bundle into a plurality of compartments, a cap secured to the floating tube sheet for receiving fluid from the tube bundle, a cap secured to the other tube sheet and having a chamber therein, and a conduit for delivering fluid to said chamber from the cap secured to the floating tube sheet.

6. Apparatus of the type described, comprising a shell, a tube sheet secured thereto, a floating tube sheet, a tube bundle having its ends secured to said tube sheets, a plurality of trays dividing the space occupied by said tube bundle into a plurality of compartments, a cap secured to the floating tube sheet for receiving fluid from the tube bundle, a cap secured to the other tube sheet and having a chamber therein, and a conduit for delivering fluid to said chamber from the cap secured to the floating tube sheet, the said tube sheets, tube bundle and conduit being removable as a unit from said shell. I

LESLIE EARL SEBALD.

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