US3431179A - Distilland by-pass means multi-stage evaporators having - Google Patents

Description

March 4, l1969 R. STARMER 3,431,179

MULTI-STAGE EVAPORATOHS HAVING DSTILLAND BY-PASS MEANS Filed Dec. l5, 1966 JMW United States Patent O 3,431,179 MULTI-STAGE EVAPORATORS HAVING DISTILLAND BY-PASS MEANS Roy Starmer, Durham, England, assigner to Applied Research and Engineering Limited, Durham, England, a British company Filed Dec. 15, 1966, Ser. No. 601,961 Claims priority, application Great Britain, Dec. 21, 1965,

54,045/65 Us. ci. 2oz- 173 Int. Cl. Bold 3/42, 3/02 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a multi-stage evaporators in a distillation plant employed, for example, in the production of distilled or potable water from sea-water or brine.

More speciiically this invention is related to the control of the ow of liquid through the stages of the evaporator in order to control, for varying throughputs, the liquid levels in the various stages, some such control means being beneficial since it is found that a high rate of flow tends to produce too high a level in at least some stages and that a slow rate of ow may allow the condition which is termed undersealing According to the invention a multi-stage evaporator comprises a succession of stages, a submerged passage or aperture between each stage and the succeeding stage whereby a stream of liquid can ow through the succession of stages, and means for controlling the levels of the liquid in at least some of the stages, which means comprise a by-pass passage connecting two successive stages, in addition to the aforesaid passage or aperture between the two stages, and means for controlling the rate of flow of liquid through the by-pass passage.

In one form of the invention the rate of ow through the by-pass passage is controlled by an adjustable valve.

In another form of the invention the rate of flow through the by-pass passage is controlled by interchangeable members within the by-pass, each member having a different size or orifice.

The evaporator is preferably a flash evaporator.

The or each opening provided by the passage or aperture between each stage and the preceding stage of the evaporator yfor allowing the Huid to flow through the succession of stages of the evaporator, may be fixed or maybe adjustable.

An evaporator in accordance with the invention allows a faster rate of ilow at least between two of the evaporator stages than is possible with a similar evaporator which is not provided with the by-pass passage. Furthermore, the range of the rate of flow can be still further increased by reducing the size of the passage or aperture between the stages having the by-pass passage whereby, with the by-pass passage closed, the rate of ow would be slower than would otherwise be the case.

A by-pass passage may be provided between more than one set of two successive stages.

By way of example, a specific embodiment of a multistage evaporator in accordance with the invention will now be described with reference to the accompanying ICC diagrammatic drawings in which:

FIGURE 1 is a layout of the evaporator; and

FIGURE 2 is a perspective view of the dividing wall between two stages of the evaporator shown in FIGURE 1 to show means for adjusting the size of the orifice therein.

With reference to the drawings, the evaporator is a ash evaporator and comprises ve stages 9A through 9E, each stage having a lower associated portion 10A through 10E through which a stream of brine is fed and in which a part of the brine is flashed off, the steam evolved passing into their respective upper portions 11A through 11E in which portion the steam condenses on a condensing surface 12 to form a distillate. The part of the brine which is not ilashed otl" passes into the succeeding stage through an associated orifice 13 or 13a in the wall 14 which divides the two stages.

It is normal that the sizes of the orifices 13, 13a determine the level of the brine in the stages of the evaporator and it is desirable that the size of each orifice 13, 13a should be progressively greater than the preceding orifice (although, in practice, such increases are normally carried out in steps, there 'being a number of stages between each increase in the size of the orifice). A level controller, shown in FIGURE l as a ball-cock 15, is also provided in the last stage of the evaporator to assist in the control of the level of the brine.

Brine is fed into the evaporator at 17, the brine then passing through a number of tubes, which comprise the aforesaid condensing surface 12 of each stage, to la heater 18 and then to the lower portion 10A of the iirst stage of the evaporator. A pump 19 is provided for returning the brine that is not flashed off in any of the stages of the evaporator into the evaporator feed. The distillate is discharged at point 20. Also, the steam evolved in the last stage 9E of the evaporator is condensed on a condensing surface 23 cooled by a fluid which is independent of the evaporator feed.

'Ihe level of the brine in the stages of the evaporator has been described above as being dependent on the sizes of the orifices 13, 13a and the level controller 15. The evaporator shown in FIGURE 1, however, also has a bypass passage 21 between the second and third stages, 9B, 9C, respectively, which passage 21 is provided with means 22 for controlling the rate of flow therethrough. 'Ihe means 22, in this example is an adjustable valve but it could comprise a set of plates for insertion into the passage, each plate having an orice therein of la different size except yone plate which has no oriiice and comprises a blanking-ol plate.

In addition, the orifice 13a in the wall 14 dividing the second stage 9B and the third stage 9C is of a smaller size than would normally be employed. Thereby, when the bypass valve 22 is shut-01T, the level of the brine in at least the preceding stage, is greater than would otherwise be the case. Similarly when the valve 22 is fully open, the level of the brine in at least the preceding stage 9B is less than for an evaporator that is not provided with the bypass passage 21 and that has the orifice 13a between the second and third stages of normal size. The size of the orifice 13a may be iixed or, as shown in FIGURE 2, may be adjustable by means of vertical adjustment of a plate 24 within the guideways 25` The vertical position of this plate 24 may be adjusted by means of a vertical rack 30 opstanding from the plate, and a pinion 31 in mesh with the rack, the pinion being mounted on a shaft 32 which passes through a bearing 33 xcd to the respective wall 14, and projects out of the lower portion 10. A wheel 34 is fitted to the free end of the shaft 32 to cause rotation of the pinion 31 and hence vertical movement of the rack 30 and the plate 34.

The levels of the brine in the various stages 9A through 9E, as shown in FIGURE 1, are appropriate for an evaporator in which the valve 22 is in a substantially shut-oli position, i.e., the rate of flow between the second stage 9B and the third stage 9C is reduced. It is estimated that if the size of the orifice 13a in the dividing wall 14 between the second and third stages is, or is adjusted so that it is, 15% smaller than would normally be the case and if the by-pass passage 21 is capable of passing 30% of the flow between these stages 9B, 9C, then operation of the control means 22 enables a depth control corresponding to a ow control of 15% above and below the range of depth control of an evaporator that is not provided with the by-pass passage 21 and that is not provided with the smaller orifice 13a.

The invention is not restricted to the specic details of the evaporator described above. For example, the sizes of some or each of the orifices 13 may be adjustable. Also, in the case of an evaporator lhaving tive stages 9A through 9E, as shown in FIGURE l, a by-pass passage between the second stage 9B and the third stage 9C in addition to the level controller (with or without the orifices being adjustable), is suicient to provide the necessary control to the depth of the brine in the iive stages. However, when more stages are added it may be necessary to provide one or more additional by-pass passages between other pairs of stages.

I claim:

1. A multi-stage evaporator comprising a shell, a plurality of spaced, upright partitions within said shell thereby forming a succession of evaporator stages, each of said partitions at their bottom ends having an aperture extending across the full length thereof to permit a stream of liquid to ilow from each said stage to its succeeding stage, at least one open-ended by-pass conduit attached to the bottom of said shell directly beneath at least one of said partitions with an end of said conduit positioned on either side thereof for connecting at least one of said stages to a succeeding stage and, means in said at least one conduit for controlling the tlow rate of tiuid therethrough, whereby a dierence in levels of liquid between the stages connected by said conduit can be controlled.

2. An evaporator according to claim 1, wherein said control means comprises an adjustable valve.

3. An evaporator according to claim 1, wherein said control means comprises a plate having an orifice therein of a size depending on the specific rate of ow desired through said conduit.

4. An evaporator according to claim 1, further including means for adjusting the size of one of said partitioned apertures.

5. An evaporator according to claim 1, wherein two open-ended by-pass conduits attached to the bottom of said shell are provided.

References Cited wrLBUR L. BAsCoMB, 1R., Primary Examiner.

U.S. Cl. X.R.

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