US3442765A - Multistage flash evaporator-condenser arrangement - Google Patents

Description

May 6, 1969 L EvrrE 3,442,765

MULTISTAGE FLASH EVAPORATOR-CONDENSER ARRANGEMENT A TTRNE YJ,

' G. LEVITE May 6, 1969 MULTISTAGE FLASH EVAPORATOR-CONDENSER ARRANGEMENT Sheet Filed OCC. 5, 1966 GIDEON av United States Patent U.S. Cl. 202-173 7 Claims ABSTRACT OF THE DISCLOSURE A multi-stage flash evaporator, wherein the condenser means for a given stage is located below the portion of the evaporator wherein flashing of distilland to vapor occurs, whereby a decrease in pumping requirements for the entire evaporator is realized.

'Ihis invention relates to the construction of ash evaporators. Moreparticularly, this invention relates to a novel arrangement of internal elements in ash evaporators.

It is well-known to distill saline fwater or waters having other dissolved impurities by means of ash evaportion to obtain pure distillates. Thus, in the past, it has been the usual practice to evaporate sea water, scrub entraned droplets from the resulting vapor, pass the vapor around a condenser medium, and collect the resulting condensate beneath the condenser medium. IIn the past, numerous types of evaporation apparatus have been proposed wherein the unevaporated portion of the saline or turbid water is mixed with incoming water and recycled through the apparatus.

A shortcoming of prior art apparatus has been high capital costs, particularly due to high shipping costs, or alternatively, high costs of on site construction. Thus, the interior portions of conventional evaporators, particularly the condenser section, which includes a large bundle of tubular members, is heavy and relatively fragile. Accordingly, such element requires particular care in shipping. Moreover, since in conventional practice the condenser section is located at the top of the apparatus, relatively heavy underpinnings must be built into the evaporator to support the condenser section. Such heavy construction increases the cost of material and labor in manufacture, and results in higher shipping costs. Moreover, to successfully handle hot recycle liquid, it has been necessary to place recycle pumps in deep wells beneath the apparatus, thereby further increasing the cost of construction.

Another shortcoming of conventional evaporators using recycle techniques has been the need for high pumping energy. The pump used to recycle the unashed liquid must, in the usual case, supply sucient pressure to overcome line pressure losses and to prevent premature flashing of the recycle liquid in the lines.

Accordingly, it is one object of the present invention to provide a liash evaporator wherein the requisite pumping energy is reduced.

It is another object of the present invention to provide an evaporator construction having decreased construction and installation cost.

It is still another object of the present invention to provide a ilash evaporator capable of easier shipping than evaporators heretofore known.

Other objects will appear hereinafter.

The present invention resides in a ash evaporator construction wherein a condenser section is located within an evaporator shell, below an evaporator section. Such a construction results in inherently lower pumping energy requirements, lower construction costs and a lighter weight ice structure, with attendant savings in material, labor and shipping costs.

lFor the purpose of illustrating the invention there are shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FlGURE l is a longitudinal cross-sectional view of a conventional ash evaporator of the multi-stage type.

BIGURE 2 is a transverse cross-sectional view of the evaporator of FIGURE 1 taken along line 2 2 in FIG- URE 1.

FIGURE 3 is a transverse cross-sectional view of one form of an evaporator in accordance with the present invention.

FIGURE 4 is a transverse cross-sectional view of another form of an evaporator in accordance with the present invention.

FIGURE 5 is a transverse cross-sectional view showing stillanother form of a flash evaporator in accordance with the. present invention.

EIGURE 6 is a partial cross-sectional view comprising a llsh evaporator embodying the principles of the present invention with a typical prior art evaporator.

Referring to the drawings in detail, wherein like numerals indicate like elements, there is shown in FsIGURE l a, conventional llash evaporator designated generally by the reference numeral .10. The flash evaporator 10 includes heat rejection stage or stages i12. The ash evaporator 10 also includes a series of heat recovery stages 14, the number of stages being variable.

The heat rejection stage 12 includes a condenser section 18, which contains condenser tubes 20. Also, the heat rejection stage y12 includes an evaporator section 22 and a Acondensate collection pan 24.

IReferring now to the extreme left of FIGURE 1, distilland, usually raw sea rwater, is conducted to the apparatus through a conduit 26. The conduit 26 is in fluid communication with one end of the condenser tubes 20 of the condenser section 118i. The opposite ends of the condenser tubes 20 are in fluid communication with the conduit 28. A branch conduit 30 joins the conduit 28 and serves as a bleed. A recycle conduit 32 interconnects a lower portion of the evaporator section 22 with the conduit 28 for a purpose to be made clear shortly. A bleed conduit 36 emanates from the recycle conduit 32.

A product conduit 38 is in communication with one of its ends with the condensate collection pan 24. A product pump 40 serves to remove the product from the product conduit 38.

Referring now to the heat recovery stages 14, it is seen that such stages are contained within an outer shell or pressure vessel 42. The vessel 42 contains spaced vertically oriented transverse Walls or partitions, which divide the vessel into a series of stages. Each stage comprises a condenser section 46 and an evaporator section 50i. Condenser tubes 48 run through the vessel 42. Thus, the condenser tubes 48 run through the respective condenser section of each heat recovery stage. A condensate pan S2 extends the length of the vessel 42, and likewise, passes through each of the stages.

In operation, raw distilland enters the apparatus through the conduit 26, passes through the condenser tubes 20 and conduit 28, and the condenser tubes 48. Also, the uid from the recycle conduit 32 joins the incoming distilland in conduit 28. Thus, the combined distilland and recycle liquid serve as a condenser medium for each stage of the device. From the condenser tubes 48 the distillandrecycle mix passes to a brine heater 16, a conduit 54 and a pressure reducing valve 56 The valve 56 prevents premature llashing of the combined distilland and the recycle liquid downstream of the recycle pump. The liquid then re-enters the vessel 42. It should be understood that the initial heat recovery stage is maintained at a pressure below the saturation pressure corresponding to the temperature of the incoming liquid, and accordingly, as the liquid enters the stage, a portion is flashed to vapor. Such vapor rises upwardly into the condenser section 46, wherein it comes into contact with the relatively cool condenser tubes 48, and condenses. Resulting condensate falls to the condensate pan 52. Thus, referring to FIGURE 2, it is seen that in rising to the condenser section 46, the vapor passes through tine mesh screens 58, which serve to remove any entrained liquid particles. The screens 58, it should be understood, are one example of acceptable vapor scrubbing means. Those skilled in the art will recognize that alternative constructions may be used, or in some instances, the scrubbing means may be omitted.

The remaining mixture flows through a pressure reducing and sealing baie 60 in the wall or partition 44 into the next stage, wherein it re-ashes. In a similar manner, the remaining mix passes from stage to stage of the heat recovery stages 14, and then through the conduit 62 to the evaporator section of the heat rejection stage 12.

Similarly, the condensate in the condensate pan 52 ows through pressure reducing and sealing bafes 64 to successively lower stages of the heat recovery stages, and then through the conduit 66 to the condensate pan 24 of the heat rejection stage.

A common shortcoming of prior art evaporators of the type shown in FIGURE l stems from the need to locate the recycle pump 34 low enough to avoid ashing of liquid in the conduit 32 upstream of the pump. The present invention, as embodied in FIGURES 3 to 6 represents a simple and economical solution to the above problem.

Referring now to FIGURE 3, there is seen a crosssection of a flash evaporator in accordance with the present invention. The flash evaporator 10 includes an outer shell or pressure vessel 68 in which the trough 70 is disposed. It should be understood that the vessel 68 is `divided by walls or partitions 72 into stages, in a manner not unlike the recovery stages 14 of the evaporator 10. Condenser tubes 74, the construction and functions of which are similar to the aforementioned condenser tubes 48, extend through the vessel 68 below the trough 70. The mixture flows in the trough 70 in vapor contact with the interior of the vessel 68 in each successive stage. A portion of the mixture owing in the trough 70, upon entering a given stage, ashes to vapor. Such vapor moves downwardly into contact with the condenser tubes 74. The condenser tubes 74, it will be understood, contain a liquid condensing medium. Thus, vapor in contact with the condenser tubes 74 is condensed, and eventually drops to the bottom portion 78 of the vessel 68. Such bottom portion defines a means whereby liquid distillate may be collected. Fine mesh screens 80 or other scrubbing means may be provided in connection with the trough 70 for removing entrained droplets of unilashed liquid from the vapors rising fromthe trough.

A conduit 82 is connected to the trough 70 and the recycle pump 84. The pump 84 discharges into a conduit 86, which in turn is in uid communication with the condenser tubes 74. Thus, the trough 70 is in fluid communication with the condenser tubes 74 through the conduit 82, pump 84 and the conduit 86.

An important aspect of the present invention is illustrated by the line A-C-B in FIGURE 3. Thus, the distance A-B denotes the vertical distance from the surface of liquid in the trough 70 to the inlet of the recycle pump 84. Those skilled in the art will appreciate that the difference in static tluid pressure at the two extremes of the line A-B may be expressed as the mass density of the uid times the vertical distance A-B. Such difference in pressure is of great importance in the operation of the device, since liquid removed from the trough 70 is at its saturation pressure and hence, a real danger of dashing in the conduit 82 and pump 84 exists. Flashing in the conduit 82 would interfere with the ow of recycle liquid and flashing in the pump itself results in cavitation, and consequently, the possibility of severe mechanical damage, As was indicated above, prior art apparatus such as the evaporator 10 overcame the problem by placing the recycle pump 84 in a deep well below the evaporator, and accepted the disadvantage of increased capital costs due to the deep well. With the present novel arrangement of elements, the vertical distance from A to the bottom of the vessel 68, which is wholly above ground, represents an inherent saving in well depth. Furthermore, the distance A-C, that is the difference between the level of the liquid in the trough 70 and the condenser tubes, represents a pressure head for preventing premature ashing downstream of the pump 84. Such head is almost wholly recoverable, and this, a saving in pumping energy is realized. By comparison, referring to FIGURE 6, with conventional structure the distance from the surface of the distilland in evaporator section 22 to the inlet of the recycle pump 34, equivalent to the distance A-B, would be almost entirely outside the evaporator and almost wholly located in a deep well. The valve 56, shown in FIGURE l, prevents ashing downstream of the pump, but the head due to such valve is not recoverable.

FIGURE 4 shows yet another evaporator construction embodying the principles of the present invention. In the embodiment shown in FIGURE 4, the evaporator 10" includes troughs 88 and 90, each disposed above the condenser tubes 92. Fine mesh screens 94 and 96 are provided to scrub entrained liquid from vapors rising from the troughs 88 and 90 in the previously described. The embodiment of FIGURE 4 represents a convenient way of increasing the capacity of an evaporator constructed in accordance with the principles of the present invention.

Yet another evaporator in accordance with the present invention is set forth in FIGURE 5. The evaporator 98 set forth in FIGURE 5 comprises a shell or pressure vessel 100, containing a trough 102. Also disposed in the vessel 100 are condenser tubes 104 and a condensate receiving tray 106. It should be apparent that the bottom portion 108 of the pressure vessel 100 serves as a further means for conducting distilland through the several stages of the evaporator 98. Thus, in operation, the distilland is simultaneously conducted through the pressure vessel 100 by the trough 102 and bottom portion 108, thereby creating two sources of vapor. Scrubbers` and 112, which may take the form of fine mesh screens are associated with the trough 102 and with the bottom portion 108 for removing entrained liquid droplets from the vapor. Those skilled in the art will appreciate that the embodiment shown in FIGURE 5 represents somewhat of a hybrid development, and contains certain features of the prior art devices, while partaking of the advantages inherent in the construction shown in FIG- URE 3.

In each of the above-described embodiments of the present invention, significantly lower capital costs than are currently typical for plants of the equivalent capacity are realizable. Such reductions in capital costs are due to several factors. Among these are the savings realized by eliminating the cost of construction of a deep well for the recycle pump. Also, a saving is realized through decreased pumping energy requirements. Moreover, the heaviest parts of each of these embodiments, namely the condenser tubes, are located relatively low in the structure. Accordingly, heavy structural parts, normally used to support the condenser tubes and located in the upper portion of the evaporator, are in some cases eliminated, and in all cases located at a lower portion of the structure. Such structures may therefore be made lighter than those heretofore known, and due to their lower centers of gravity, are stable during shipment. Accordingly, shipping costs are substantially reduced.

In view of the foregoing, it is evident that the novel flash evaporator constructions herein disclosed constitute a clear advance in the art.

The present invention may be embodied in other speciic forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than the foregoing specitication as indicating the scope of the invention.

I claim:

1. A flash evaporator comprising a generally horizontally disposed pressure vessel, a plurality of generally vertical partitions within said pressure vessel dividing said vessel into a plurality of horizontally spaced stages of successively lower pressure, means for conducting liquid distilland generally horizontally through said vessel from stage to stage in vapor contact with the interior of said vessel in each successive stage so that a portion of said distilland is made to Hash to vapor in each stage, condenser means comprising tubes for conducting a liquid condensing medium from stage to stage out of direct contact with the vapor, said condenser means being disposed below said means for conducting distilland, means disposed below said condenser means for collecting liquid distillate, said tubes of said condenser means being in fluid communication with said means for conducting distilland so that distilland may be initially pre-heated as the liquid condensing medium and then introduced into said means for conducting distilland, a recycle loop in uid communication with said means for conducting distilland and said tubes of said condenser means, and said recycle loop including a pump, said pump :being disposed below the surface of the distilland in said means for conducting distilland by a vertical distance sufficient to provide a static pressure head at the inlet of said pump to prevent flashing of distilland in the recycle loop.

2. A ash evaporator in accordance with claim 1 wherein said means for conducting distilland through said vessel comprises a trough.

3. A ash evaporator in accordance with claim 1 wherein said means for conducting distilland through said vessel comprises a generally horizontally extending trough, and scrubbing means associated with said trough for removing entrained liquid particles from the vapor.

, means and a bottom portion of said pressure vessel definingk a further means for conducting distilland from stage to stage.

7. A tiash evaporator in accordance with claim 6 and means associated with said bottom portion of said pres- Ysure vessel and said means for conducting distilland for removing entrained liquid particles from the vapor.

References Cited UNITED STATES PATENTS 3,342,697 9/ 1967 Hammond 203-11 2,289,956 7/1942 Gaus et al 202-188 X 3,330,739 7/1967 Roe et al. 203-11 3,096,256 7/ 1963 Worther et al 202-173 3,119,752 1/ 1964 Checkovich 202-173 X A 3,203,875 8/ 1965 Sturtevant 203-11 X 3,228,859 1/1966 Fankel et al. 202-173 3,245,883 4/1966 Loebel 203-11 X 3,304,242 2/1967 Lockman 202-173 3,320,137 5/1967 Jebens et al 203-11 X 3,334,024 8/1967 Zahavi 202-173 OTHER REFERENCES The Institution of Mechanical Engineers: Flash Evaporators for the Distillation of Sea Water by A. Frankel. (1960) pp. 5, 6, 9, 11 and 15.

NORMAN YUDKOFF, Primary Examiner. F. E. DRUMMOND, Assistant Examiner.

U.S. C1.X.R.

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