US1820065A - Evaporator - Google Patents

Description

H. L. GUY

EVAPORATOR Aug. 25, 1931.

2 Sheets-Sheet 1 Filed May 17, 1929 INVENTOR BY 175L601.

ATTORNEY Aug; 25, 1931.

H. L. GUY

EVAPORATOR Filed May 17, 1929 2 Sheets-Sheet 2 INVENTOR liL. Gux

WITNESS ATTORNEY Patented Aug. 25, 1931 UNITED STATES PATENT QFFICE HENRY LEWIS GUY, F HALE, ENGLAND, ASSIGNOR TO WESTINGHOTTSE ELECTRIC 8; MANUFACTURING COMEANY, A CORPORATION OF PENNSYLVANIA EVAPORATOR Application filed May 17, 1929, Serial No. 363,862, and. in Great Britain May 19, 1928.'

This invention relates to evaporators such as are employed, for example, for distilling hard or impure water in order to obtain make-up water for steam power plant.

' The object of the invention is to provide '15 ly upon baflies or such like devices for separating the liquid particles from the vapor, as has hitherto generally been necessary.

The maximum permissible rate of heat transmission through the heating tubes to the i liquid in an evaporator is limited in practice to a value immediately below that at which objedionable priming occurs. This priming is mainly due to the spray caused by the bursting of large bubbles of steam formed by the coalescence of the smaller bubbles as they rise to the surface of the water past successive layers of tubes. The tendency of the bubbles to coalesce depends upon the freedom with which the small bubbles can escape to the surface, and this in turn depends upon the width of the vertical passes between the tubes.

The invention results from the appreciation of the fact that for a given maximum superficial area of tubular heating surface and a given size and shape of evaporator a greater width or horizontal spacing between the tubes may be obtained by the use of tubes of elliptical cross-section instead of the usual tubes of circular cross-section, and that there- KQ fore for a given size and shape of evaporator the maximum evaporative capacity that may be obtained by the use of circular tubeswhich maximum results from a substantial uniform distribution of the tubes throughout (T the liquid space-may be exceeded merely by substituting elliptical tubes for the circular ones.

Accordingly the invention provides an evaporator of the horizontal tube type K throughout the liquid space of which are distributed heating tubes of elliptical or oval I 4 cross-section disposed with their major axes vertical, the arrangement of the tubes being such that substantial similar vertical passes between the tubes areafl'orded throughout the liquid space. Sustantially straight heating tubes will generally be employed in carrying out the invention, the use of curved tubes in most cases resulting in an unevendistribution of the tubes throughout the liquid space, which is at variance with the principles of the invention. Tubes of U-shape or like configuration, the major portions of which are straight may be regarded as straight tubes for the purpose of this invention.

The tubes may be disposed throughout the whole of the liquid space with their axes substantially equi-distant and are preferably vertically aligned so that vertical passes ex.- ist through which the bubbles can rise without obstruction. Moreover, as far as practical circumstances permit, the vertical passes between the tubes, and between the tubes and the sides of the evaporator casing may all have the minimum width which may normally be permitted without leading .to objectionable priming as explained above.

If desired, certain tubes which lie at or about the normal liquid level may be omitted or these tubes made of smaller size in order to increase-the width of the aforesaid steam passes in the upper region. Similarly the bottom layer or layers of tubes may, if desired, consist of larger tubes or tubes of circular cross-sectional or elliptical tubes disposed with their major axes horizontally, the raw liquid being supplied to the evaporator preferably below said lower layers of tubes. The depth of the tube bank is also preferably substantially equal throughout the evaporator. Thus, in cases where the evaporator casing is of cylindrical form its axis being horizontal, it may be desirable to omit certain of the tubes in the central upper region of the liquid space.

In order further to prevent moisture from passing with the vapour to the evaporator outlet, according to a further feature of the invention one or more horizontal banks of heating tubes may be provided spaced above the normal liquid level. Spray or entrained particles of liquid coming into contact with these banks of tubes, which form in effect a hot grid, will be vaporized and thus add to the volume of vapour generated. The heating grid may be formed of either circular or elliptical tubes and in the latter case the major axes of the tubes are preferably horizontal so that a relatively large area of heated surface is presented to the vapour rising from the liquid surface, which vapour is constrained to pass between relatively narrow spaces between said tubes. The hot grid is advantageously composed of two superposed layers of tubes disposed in staggered relation.

The invention is illustrated in the accompanying drawings wherein, Fig. 1 is a longitudinal section through the shell of an evaporator suitable for carrying out the invention,

most of the tubes being omitted in this view;

Fig. 2 is an end view corresponding to Fig. 1, the left hand portion being a section on line IIII of Fig. 1 and the right hand portion being an end elevation with one of the end boxes removed; Fig. 3 represents in section and to an enlarged scale the two end portions of an evaporator tube for use according to the invention, a crosssection of the tube being also illustrated in this figure, and Fig. 4 shows diagrammatically a cross-section similar to Fig. 2 of an evaporator embodying certain further modifications according to the invention. I i In the construction shown in Figs. 1 and 2 the body of the evaporator has a usual form, comprising a cylindrical shell 1 upon the ends of which are mounted the tube plates 2, 3, braced by stay bolts 41. The inlet box 5 for steam or other heating fluid to be supplied to the tubes is secured over the tube plate 2 and an oulet box 6 is similarly mounted over the tube plate 3. The cylindrical shell 1 is surmounted by a vapour dome 7 containing separator plates 8 above which is the vapour outlet 9, and suitable valve controlled drain outlets 10 are provided at the bottom of the evaporator shell. 7

The heating tubes which are secured horizontally between the tube plates 2, 3 and directly connect the inlet and outlet boxes 5 6, are arranged as shown more clearly in Fig. 2. They comprise banks of vertically aligned tubes 11 of substantially elliptical cross-sectional form disposed with their major axes vertical. The tubes are distributed in a uniform manner throughout the liquid space, the normal liquid level of which is indicated by the broken line A in Fig. 2, so that similar vertical passes 12 are left between the banks 11, and through these passes the bubbles of vapour formed canrise without obstruction.

At the lower region of the evaporator are disposed tubes 13, also of substantially elliptical form, these tubes being arranged with their major axes horizontal. More effective heating of the liquid in the lower part of the evaporator may thereby be obtained.

Arrangements of a usual character may be employed to maintain the liquid level substantially constant during the operation of the evaporation. A float operated valve, the float chamber of which is connected by pipes 16, 16 with the upper and lower parts of the evaporator may admit the liquid to be treated through a pipe 17 below the tubes 13 "at such times as the surface of the liquid in the these passes would have if the tubes were of circular form throughout. It therefore follows that for a given size and shape of liquid space and given superficial area of tube surface, a higher rate of evaporation may be obtained by the use of elliptical tubes than would be possible with circular tubes, since with the latter priming will occur more readily on account of the difiiculty with which the vapor can escape through the passes between the tubes. Conversely it may be stated that for a givenminimum width of pass between the tubes, a greater superficial area of tubular heating surface may be provided in a given space by the use of elliptical instead of circular tubes.

Moreover, with the uniform distribution of the tubes throughout the liquid space, evaporation will take place substantially uniformly in all parts thereof. Hence all parts may be brought to the priming point practically simultaneously and a very high evaporative capacity may be obtained.

In some cases it may be desirable to modify the arrangement of the tubes in order to obtain the most advantageous evaporative effect in 'all parts ofthe evaporator. The vertical passes 12 may, for example, be made wider towards the upper part of the liquid space, the tubes at the top of the vertical banks being of smaller dimensions than those at the bottom. Also in order to ensure a substantially equal depth of the tube banks, instead of leaving a space below the tubes as in Figs. 1 and 2, the banks of tubes may be carried completely to the bottom of the cylindrical shell as shown in Fig. 4 and certain of the tubes in the upper central region 21 of the liquid space of the evaporation may be omitted.

The so-called hot grid provided according to the invention in order to further reduce the possibility of Wet vapour being delivered due to priming is constituted by a horizontal bank of tubes 22 (Fig. 2) or by more than one bank as shown in Fig. 4. The tubes 22 are spaced above the normal liquid level just out of reach of the majority of the splashes that are likely to arise when the priming point is reached. Any spray or entrained liquid particles passing upward to the vapour outlet must pass through the hot grid and in so doing may be completely vaporized. The usual collecting dome and liquid separating plates or other devices may even be rendered superfluous by the use of such a hot grid.

Fig. 3 shows to an enlarged scale one manner of mounting the improved evaporator tubes. The tube has its ends circular and its intermediate portion elliptical in crosssection. The elliptical portion is advantageous eccentrically disposed with respect to the circular portion so that the bottom of the ellipse is in the same plane as the bottom of the circle. This form of tube has the ad'- vantage that it can be drained dry when the evaporator is out of operation and corrosion due to stagnant water is prevented.

The holes to receive the tubes are bored sufficiently large in one of the tube plates (3) to permit the tube to be passed therethrough. The said holes are each screwed to receive a bush 19 which is inserted after the pipe is placed in position. The ends of the tubes may be expanded into their apertures in the bush 19 and in the other tube plate (2) if desired, but preferably they are received in sliding engagement with gland members 20, as shown, so that they are free to expand or contract without danger of buckling.

Among the minor advantages of the invention may be mentioned the fact that by the use of elliptical tubes as suggested cracking off of the scale deposited upon the outside is facilitated, since the cross-sectional form of the tubes may be altered by chilling the hot tubes by the customary methods, whereby the scale is readily fractured and cast off.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

1. In an evaporator, the combination of a shell structure, an inlet disposed in the lower portion of the shell structure for the admis sion of liquid to be evaporated, an outlet dis posed in the upper portion of the shell structure for the vapor generated, and upper and lower layers of substantially elliptical tubes for circulating heating fluid longitudinally through the shell structure, the tubes in said upper layer being disposed with their major axes vertical and the tubes in said lower layer being disposed with their major axes horizontal.

2. In an evaporator, the combination of a shell structure partly filled with a liquid to be evaporated, an inlet disposed in the lower portion of the shell structure for said liquid, an outlet disposed in the upper portion of the shell structure for the vapor generated, and a series of layers of substantially elliptical tubes for circulating heating fluid longitudinally through the shell structure and so ar ranged that one or more layers form a hot grid above the surface of the liquid, the tubes of the layers above the liquid being disposed with their major axes horizontal and the tubes of the layers below the liquid being disposed with their major axes vertical.

3. In an evaporator, the combination of a shell structure, an inlet disposed in the lower portion of the shell structure for the admission of liquid to be evaporated, an outlet disposed in the upper portion of the shell structure for the vapor generated, and a series of layers of tubes substantially elliptical in cross-section for circulating a heating fluid through the shell structure, the tubes forming one or more of the upper layers and one or more of the lower layers being disposed with 7100 their major axes horizontal and the tubes forming the intermediate layers being disposed with their major axes vertical.

4. In an evaporator, the combination of a shell structure having a substantially circui505 lar cross-section, an inlet disposed in the lower portion of the shell structure for the admission of liquid to be evaporated, an outlet disposed in the upper portion of the shell D structure for the Vapor generated, and a series 0 of tubes for circulating heating fluid through the shell structure, said tubes being arranged inverical banks so grouped as to have a peripheral outline conforming to the shape of 15 the lower portion of the shell structure, the height of the banks being made substantially uniform by the omission of tubes in the central portion of the shell structure.

5. In an evaporator, the combination of a 120 shell structure, an inlet disposed in the lower portion of the shell structure for liquid to be evaporated, an outlet disposed in the upper portion of the shell structure for the vapor generated, a heating fluid distribution diam- 125 ber, and a series of tubes for circulating heating fluid extending longitudinally within the shell structure and communicating with the distribution chamber, said tubes being arranged in banks forming intervening passes 23 '10 circulating heating which "increase in width in a direction from the liquid inlet toward the vapor outlet.

6. In an evaporator, the combination of a shell structure, an inlet disposed in the lower '5 portion of the shell structure for the admission of liquid to be evaporated, an outlet disposed in the upper portion of the shell structure for the vapor generated, a heating fluid distribution chamber, and a series of tubes for fluid extending longitudinally within the shell structure and communicating with the distribution chamber, said tubes being arranged in banks with intervening passes, the tubes nearest the vapor out- 15 let having a smaller cross-sectional area than the tubes remote from the vapor outlet, whereby the passes formed between the banks increase in width in a'direction toward the vapor outlet. 7

In testimony whereof, I have hereunto subscribed my name this 2nd day of May, 1929.

HENRY LEWIS GUY.

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