US2310649A - Evaporating apparatus - Google Patents

Description

Feb. 9, 1943. V D, PEEBLES 2,31%,649

EVAPORATING APPARATUS Filed Aug. 2, 1940 2 Sheets-Sheet 2 1 47' 4e INVENTOR David 0. Peek/es ATTORNEY Psaaad Feb. 9,19

oFFIc David D. Peebles, Berkeley, @aliih, assignor to Golden State Company, Ltd; San Francisco, Calif a corporation or Delaware Application August 2, 194Il, Serial No. 349,417

" 4. Claims.

This invention relates generally to apparatus and methods for the concentration of various liquid materials by evaporation.

Itis an object of the invention to provide an improved evaporating apparatus and method applicable to a wide variety of materials, including materials containing substantial amounts of solids in suspension such as tomato pulp, as well as materials such as milk products.

Another object of the invention is to provide evaporating apparatus capable of concentrating materials like tomato pulp to paste-like consistency, without causing undue retention or accumulations of the material in difierent parts of the equipment.

A further object of the invention is to eliminate or minimize clogging or incrustation of evaporating tubes, such as is troublesome in conventional equipment when certain types of materials are handled.

Another object of the invention is to provide evaporating apparatus which .will afford utmost capacity for a given size of equipment and for a given number of evaporating tubes.

Further objects of the invention will appear from the following description in which the preferred embodiments of the invention have been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

Fig. 1 is a side elevational view, diagrammatically illustrating evaporating apparatus incorporating the present invention;

Fig. 2 is an enlarged detail, partly in cross section, illustrating the upper portion of the first evaporating unit:

Fig. 3 is an enlarged side elevational detail, illustrating the upper portion of the left hand unit of Fig. 1; and I v Fig. 4 is an enlarged cross sectional detail showing a possible modified form of distributing or plenum chamber.

Although thepresent invention can be incorporated in a single eflect evaporator, the drawings illustrate equipment incorporating two units A "and B. As will be presently explained, each unit utilizes two sets of evaporating tubes which are disposed within a common heating jacket.

Referring flrst'to the construction or the first unit A, it consists of a heating jacket III which surrounds the two groups of upright evaporating I tubes II and I2. Theupper and lower ends of these tubes are secured to the tube sheets I3 and I. The heater jacket is provided with a portion ii at its upper end which accommodates for unequal expansion or contraction. The tubes I I are grouped about the longitudinal axis of the Jacket l0 and occupy a substantially cylindrical space. The tubes I2 are disposed in an annular space about the group I I. Disposed below the lower tube sheet it there is a liquid inlet chamber It, whereby liquid material can be introduced into the lower ends of tubes II. The lower ends of the tubes I2 discharge into the collecting and separating chamber 5?.

Mounted upon the upper tube sheet I 3, there is a plenum chamber it which serves to establish communication between the upper ends of the two sets of tubes. According to the details of Fig. 2, the chamber I8 is cylindrical and of adequate diameter for positioning over the tubes. The lower end oi the plenum chamber is shown removably clamped by bolts I9, to the short extension'neck 2I, which in turn is clamped upon the upper side of the tube sheet I3. It will be noted that the chamber is relatively high compared to its diameter..

Within the chamber I8 there is a deflector means 22 which serves to maintain a liquid-free vapor space 23 in the upper part of the chamber. This deflector means in this instance consists of a tapered nozz1 24 in conjunction with a semitoroidal deflector 25. The nozzle 24 has its lower end supported by spaced pins 26, which in'turn rest upon the tube sheets I3. The lower part of the nozzle is also provided with an inner spider 21 which is secured by stud '28 to the central part of the tube sheet. The diameter oi the lower end or the deflector nozzle is such that it receives the discharge jetting from the upper end of the tubes I I, without obstructing downflow of material into the upper ends of the outer group of tubes I2.

The upper and smaller end 01 the. nozzles 24 discharges directly against the under side of the deflector 25. The deflector 25 is shown carried by stud 3I, which in turn is secured to a spider 32 fixed within theupper end of nozzle 24.

A connection is provided to the upper end of chamber I8 for venting a portlonof the vaporfrom space 23. Thus, an outlet fitting 33 is shown mounted upon the upper end of chamber resents introduction of steam into jacket I0, and

lines 33 and 39 are for removal of non-condensu' ables and condensate respectively. Line 4| rep-1 resents the liquid fiow to the effect-A, and connects with the liquid chamber l8. Line 42 connects to the lower end of the collecting chamber l1 and serves to remove the concentrated liquid material. Line I! represents removal of vapor from the chamber i'l. This line connects to suitable condensing means as will be presently explained.

Operation of the evaporating unit described above can be outlined as follows: The liquid to be evaporated is preheated by means to be presently explained and is then delivered to the first unit A through line 4!. Assuming proper heating of the evaporating tubes by steam introduced into the heating jacket It, the liquid pumped through line 4| flows into the lower end of the inner group of tubes. Evolution of vapor occurs due to heat absorption through the walls of the evaporating tubes, and as a result vapor, together with dispersed liquid material, flows upwardly at high velocities through the tubes II, to be discharged in the form of jets from the upper ends of these tubes. Nozzle 24 directs this discharge against the upper side of the deflector 25, by means of which the flow is directed generally downwardly around the nozzle 24 and toward the upper ends of tubes i2. Some vapor finds its way upwardly into the space 23, from which vapor is continuously withdrawn through the orifice plate 34 and pipe 38. The material entering the upper ends of the downflow tubes i2 consists of droplets of the liquid material dispersed in the vapor, thus making for good distribution to the several tubes l2. In other words, there is no collection of liquid material as a pool upon the tube sheet I3, with the liquid from this pool running into the upper ends of the pipes l2. Formation of such a liquid pool is highly objectionable, in that it tends to give poor distribution of liquid into the several tubes, with uneven streams of liquid material, rather than even films upon the inner surfaces of the tubes. The annular gap 29 at the lower end of the nozzle enables passage of any collected liquid material.

It is possible to operate the apparatus described above without withdrawal of vapor through pipe 36. However, by withdrawing a certain amount of vapor through this pipe, and from the vapor space 23, it is possible to decrease the amount of vapor entering the tubes I 2. Such bleed-of! of vapor makes it possible to so operate the apparatus that the amount of vapor entering the tubes l2 bears such a ratio to the amount of liquid carried by the vapor, that optimum evaporating conditions may take place within the tubes, without clogging or incrustation. Without such a bleed-01f, there would be too much vapor in proportion to the liquid material in the mixture entering tubes l2 to make for favorable evaporating conditions within these tubes, even though one might attempt to accommodate such an increased amount of vapor by utilizing a larger number of the tubes. It may be explained in this connection that if the velocity of vapor flowing through the evaporating tubes becomes too high, the filming of the inner walls of the tube is not proper for optimum operation, and incrustation and clogging results, particularly when evaporating certain viscous materials such as pulps or pastes. This is attributed to a-breaking or: tearing away of fllinsor causing the film to become so-excessiveiy'thin on the-inner surfaces off'the tubes by the extremely high velocities that the resulting very high rate-of heat transferactuailydries or so concentrates the liquid that incrustation results. Fcr'example if'it were attempted to secure concentration of tomato pulp by treatment in a single evaporating tube twice the length of tubes ii and I2, the velocity would become too high and as a result the inner surface -of the tube would accumulate an incrustation of solid material, particularly near the discharge end of the tube where the velocities are greatest. With the present apparatus the downflow tubes i2 would be subject to heavy incrustation and even finally to clogging if no vapor is withdrawn from chamber 23, and the deposit so formed would be more prevalent toward the discharge end of the tubes.

, To prevent this, the mount of vapor which should be bled of! from chamber II in proportion to the amount of vapor discharged from the tubes I I, to secure good results, will depend upon various factors, including the concentration being obtained, the amount of water being removed from a given amount of feed material, the ratio between the cross sectional flow area afforded by the upflow and downflow tubes, the ratio between the cross sectional area of each tube and its inner circumference, and the properties of the material being handled. In practice, where a suitable bleed-oil? orifice has not been previously determined for a given installation, a hand throttling valve is inserted in line 38 and the fixed orifice plate removed. The hand valve is then adjusted until when operating at desired capacity, incrustation or clogging does not take place or is reduced to a minimum, and optimum operation is secured. Thereafter an equivalent fixed orifice can be substituted for the throttling valve. In a number of installations for the evaporation of tomato pulp, where the pulp is being concentrated from 6% to 14% solids in unit A, and where the tubes are 1% inches inside diameter and about 20 feet long, with thirty four of tubes ii, and twenty seven of tubes l2, good results are secured by diverting about 25% of the vapor discharged into chamber 18 from the upflow tubes II. In other instances, under different conditions of design and operation, the amount of vapor diverted for best results may vary over a, substantial range, as for example from 10 to 70%.

The deflector 25 serves the purpose of providing a space 23 above this deflector, which is relatively free of entrained liquid and from which vapor alone can be withdrawn through pipe 35.

The second unit B is similar in some respects to the unit A, but it does not make use of an entrainment separator, and it is not provided with a bleed-oi! for vapor from the upper plenum chamber. Briefly, the unit 13 includes the heater jacket 44, which surrounds the upflow tubes 46 and the downflow tubes". The ends of these tubes connect with the upper and lower tube plates 48 and 49. The plenum chamber 5|, mounted upon the tube plate 48, is similar to the chamber is for the effect A, except that in the embodiment of Fig. 3 its interior is unobstructed. The lower end of downflow tubes discharge into the collecting chamber 52, and liquid collected in this chamber is removed through pipe 53, and vapor through conduit 5!. Line 55 represents introduction of heating steam to jacket 44. Lines 51 and 58 represent, respectively, removal of noncondensables and' condensate. Liquid in the chamber 59 communicates with the lower ends of the upflow tubes, and this chamber is shown being supplied'with material from the first unit A, through pipe 42- and pump 5|.

As auxiliary equipment which can beused with the two units A and B, one can employ a preheater 62 for heating liquid being supplied to the first eiiect A. This heater can be of the closed tube type, with the tubes being .heated by vapor from conduits 43 and 44. Vapor discharged from the preheater by line 63 is shown merging with the vapor being vented through pipe 36- to bleed oil vapor from the chamber, because the material being handled is relatively concentrated and the amount of. vapor evolved is insufflcient to cause detrimental eflects such as described in connection with unit A.

The use of a relatively high plenum chamber serves to prevent plastering of the top wall of this chamber with liquid material being concentrated. This can be better understood when it is considered that the material jetting from the upper ends of the upflow tubes 48 consists oi liquid, solids suspended in the same, and vapor. or in other words liquid material dispersed as small droplets in the vapor. material leaving the upflow tubes are propelled upwardly at considerable velocity, and if these droplets are permitted to impact the top wall of the plenum chamber, they serve to plaster this wall instead of remaining in entrainment with the vapor. When such plastering occurs large masses of the material accumulate and occasionally slough ofi thus overloading some of the tubes. Such plastering i particularly detrimental to operation of the apparatus, because it causes a certain amount of the material undergoing concentration to be subjected to the treatment temperatures for unduly long periods of time, and in addition it makes for poor redistribution of the liquid material in the downflow tubes 41. It will be evident that material sloughing off or streaming down the inner side walls of the plenum chamber 5| will not be re-distributed as droplets in the vapor entering the downflow tubes 41, but will flow as uneven streams of liquid material into the downflow tubes.

With a plenum chamber of suflicient height. as for example of the order of 3% feet high for tubes 1 inch inside diameter and about 20 feet long,

' the liquid material projected upwardly from the in the liquid material, the weight of the solids,

the viscosity of the material and the velocity, with which vapor is discharged from the upflow tubes.

In addition to the type of plenum chamber shown in Fig. 3, it is possible to utilize a chamber of lesser height in conjunction with means for checking and difiusing the material jetting from the upflow tubes 36. Such an arrangement is shown in Fig. 4. The plenum chamber 56. in

this instance is relatively short compared to the height of chamber 5i in Fig. 3, and within the plenum chamber there are a plurality of screens Droplets of liquid 3 81 which are carried by the removable ring v88. These screens extend across the upper ends 01 the evaporating tubes, and they are impacted by the vapor and liquid material jetting from the upfiow.tubes. Because of the checking and diffusing action of the screens 61, the upward velocity component of particles or liquid material issuing from the upflow'tubes i reduced before such particles can impact the top wall or the plenum chamber. Thus, in this instance plastering of the top wall of the plenum chamber is likewise prevented, and the liquid material is properly distributed into the downflow tubes.

To brieifiy review operation of the complete apparatus shown in Fig. 1, the material to be concentrated, such as tomato pulp, is supplied by pump M to the preheater 62, after which the heated material is supplied to the upflow evaporating tubes of the first unit A. Material jetting from the upper ends of the upflow tubes of unit Ais deflected downwardly within the plenum chamber I8, and re-enters the downflow evaporating tubes l2. A certain amount of vapor is continuously bled oil? from the upper portion of the plenum chamber l8, through the line 36.

Partially concentrated liquid material is removed from the first unit through line 42 and pump 6i, and is delivered to the secondunit B. The other liquid material is further concentrated by evaporation in the manner previously d'escribed, and the final concentrate removed through pipe 53. Vapor evolved in the two effects is utilized to heat the preheater 62, and in addition this preheater serves as a partial condenser for the two units.

I claim:

1. In an evaporating method for the concentration of liquid materials wherein liquid material to be evaporated is passed at high velocities through heated evaporating tubes, the improvement comprising causing the liquid material interspersed with evolved vapor to pass upwardly through one set of evaporating tubes, causing the liquid material and a substantial part of the vapor discharged from the first set of tubes to enter the second set of tubes, and diverting the remaining part of the vapor discharged from the first set of tubes.

2. In an. evaporating methodlior the concentration of liquid materials wherein liquid material to be evaporated is passed at high velocities through heated evaporating tubes, the improvement comprising causingthe liquid material interspersed with evolved vapor to pass upwardly through one set of evaporating tubes, separating a part of the vapor discharged from the first set of tubes from the mixture ofliquid material and vapor, causing the mixture of liquid material and remaining vapor to be introduced into the second set of tubes, and removing the-separated vapor.

3. In evaporating apparatus, two sets of generally upright evaporating tubes, the second set of tubes being grouped about the first set, means for introducing liquid material to be evaporated into the lower end of the first set of tubes, means for receiving evaporated material and evolved vapor from the lower end of the second set of tubes, a chamber serving to transfer evolved vapor and dispersed liquid from the upper end of the first set of tubes to the upper end of the second set of tubes, a deflecting nozzle disposed within the chamber and having its lower open end overlying the upper end of the first set of tubes. and a deflector overlying the upper open end of the nozzle and serving to deflect material downdispersed liquid from the upper end of the first 10 set of tubes to the upper end of the second set of tubes, means in said chamber for deflecting liquid, and vapor discharged from the upper end of the first set of tubesedownwardly toward the 5 upper end or the second set of tubes, and means for continuously bleeding from said chamber a portion of the vapor discharged from the first set of tubes.

DAVID D. PEEIBLES.

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