IE43925B1 - Desalination apparatus - Google Patents

Abstract

1533316 Multiple effect desalination apparatus SNAMPROGETTI SpA 12 July 1976 [15 July 1975] 28952/76 Heading B1B In a multiple effect apparatus of the type described in Specification 1396074 and comprising a series of vertically superimposed chambers, condensate passes from one chamber to that below through one or more fall tubes 4 surrounded at the bottom end by a closed sleeve provided with one or more apertures 2 above the level of the end of the tube. The tanks 5 which communicate with the vertically disposed evaporator tubes may be divided by a horizontal partition H, the upper and lower compartments being connected by similar fall tube assemblies E. The apertures 2 may be of such a size that partial evaporation of the saline solution takes place within the sleeve. A further, similar, fall-tube assembly E' acts as an overflow to prevent excessive accumulation of liquid in the upper region of tank 5.

Description

This invention relates to apparatus, for-the desalination of a saline solution, for example sea water.

Erjsh.patent Specifications-Nos. 37,827 and 42,835, > in the name of the present Applicants, disclose apparatus for carrying out a multi-stage distillation process for sea water. The present invention relates to means for regulating the levels of fresh water and brine in such multistage desalination processes.

According to the present invention there is provided multiple effect apparatus suitable for recovering water from a saline solution, which apparatus comprises:(a) at least one vertically or substantially vertically disposed column divided into a plurality of compartments one above another: (b) a plurality of vertically or substantially vertically disposed evaporator tubes which are intended to act as film evaporators and which are provided in each compartment, apart 43935 from the lowermost compartment of the or each column: (c) at least one tank provided in each compartment wherein (ij each tank, apart from that or those in the lowermost compartment of the or each column, is an communication at its lower end region with the interior of the upper end region of the evaporator tubes in the same compartment; (ii) each tank, apart from that or those in the uppermost compartment of the or. each column, is in communication at its upper end region with the interior of the lower end region of the evaporator tubes in the immediately overhead compartment; (iii ) each tank, apart from that or those in the uppermost compartment of the or each column, is provided in an upper region of the tank side wall with at least one aperture; (d) means for conveying condensate from the lowermost region of each compartment, apart from the lowermost compartment of the or each column, to the next lower compartment, which means comprise at least one vertical fall tube communicating at .its upper end with the lowermost region of the respective, compartment and having its lower end region enclosed by a sleeve which is closed at its top and bottom ends and has an internal diameter greater than the external diameter of the fall tube, the sleeve being provided with one or more apertures, at a region above the lower end of the fall tube which aperture(s) afford communication between the lower end of the fall tube and the respective next lower compartment: (e) means for introducing saline solution into the tank(s) in the uppermost compartment of the or one column: (£) means for introducing steam into the uppermost compartment of the or one or each column: (g) means for discharging water from the lowermost compartment of the or each column: (h) means for discharging saline solution from the tank(s) of the lowermost compartment of the or each column; and (i) means accommodated within at least one of the compartments for preheating, by heat exchange with hot water vapour in those compartments, saline solution prior to its introduction into the tank(s) of the uppermost compartment of the or one column: the arrangement of the apparatus'being such that, in use, saline solution passes as a film in the evaporator tubes from one tank, in one compartment to one tank in the next lower compartment and is heated by hot water vapour in said one compartment, which hot water is condensed and conveyed at condensate to said next lower compartment, and some of the saline solution passing to the tank in said next lower compartment evaporates to produce hot water vapour which passes through said aperture(s) and heats the evaporator tubes in said next lower compartment.

In a preferred embodiment in accordance with the present invention, the upper region of each tank is separated from the lower region of that tank by a partition, and at least one further vertical fall tube is provided in each tank, the upper end of each further fall tube communicating with the upper region of the respective tank and the lower region of each further fall tube being enclosed by a sleeve which.is closed at its bottom end and has· apertures desposed above the level of the lower end.of the further fall tube to afford communication between the lower end of the further fall tube and the lower region of the respective tank.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made by way of example, to the accompanying drawings, in which: Figure 1 shows a component in apparatus in accordance with the present invention under a first operating conditions: Figure 2 shows the component of Figure 1 under a second operating condition; Figure 3 shows the component of Figure 1 under a third 4 operating condition; and Figure 4 shows a compartment of apparatus in accordance with the present invention, including the component of Figure 1 to 3.

For a general understanding of the operation of the type of desalination apparatus to which the present invention relates, reference is directed Irish Patent Specification No. 37,827.

The component shown in Figure 1 to 3 comprises a vertical fall tube 4 and a coaxial sleeve 3 which encloses the lower end region of the fall tube. The sleeve 3 is provided with apertures 2 at a level above the lower end of the fall tube.. The internal diameter of the sleeve is greater than the external diameter of fan tube. The upper end of the fall tube 4 communicates with a compartment of multiple effect apparatus, the interior of which compartment is at a pressure P. The lower end of the fall tube 4 communicates, through the apertures 2, with another compartment of the apparatus the interior of which is at a pressure Ρ-Δρ. The two compartments are separated by plate 1.

The cross-sectional area of the apertures 2 (which are formed as slots) is such that, under normal operating conditions (i.e, when the flow rate from one compartment to the next is equal to that for which the apparatus was designed), the surface of the liquid in the fall tube 4 is at a height of above the level of the apertures 2. Under these conditions, shown in Figure 1, the difference in pressure head across the apertures 2 is Λ.Ρ Δ H] + Y. where Y_ is the product of the,density.and the gravitational constant g. The actual pressure in the space between the fall tube 4 and the sleeve 3 is thus greater than P-Δρ, and, under these conditions, no evaporation of the liquid will occur until the liquid issues from the apertures 2.

If the operating conditions change so that the flow »rate of liquid down the fall tube 4 decreases, the level of the surface of the liquid in the fall tube will drop. In Figure 2, the level of the surface of the liquid has dropped to a height of δΗ^ below the level of the apertures 2. Under these conditions, the difference in pressure, head across the apertures is ΔΡ --ΔΗμ Y and the pressure in the space between the fall tube 4 and the sleeve 3 is below Ρ—Δ J?. Evaporation of the liquid in this space then occurs, and the resulting water vapour effectively restricts the flow cross-section of the apertures 2 due to.its larger specific volume. This prevents the fall tube 4 from being completely emptied and prevents steam being transferred from one compartment to another.

Under the operating conditions represented in Figure 3, which occur less frequently than those represented in Figure 2, the flow rate through the fall tube 4 has increased so that the level of the liquid in the fall tube has risen.

The magnitude of the permissible fluctuations in this level will depend on the length of the fall tube. It is possible to provide an overflow tube to prevent an unduly large accumulation of liquid in the upper compartment of it cannot be transferred to the lower compartment quickly enough through the.fall tube 4, and if there is not enough space in which to accommodate a sufficiently long fall tube.

Alternatively, the apertures can be given a cross-sectional area such that, under normal operating conditions, the liquid evaporates in the space between the fall tube 4 and the sleeve 3, as represented in Figure 2. 433SS Figure 4 shows a whole compartment of the apparatus Including a fall tube 4 for transferring fresh water from an upper compartment (stage n) to the compartment shown (stage n+1). The compartment also includes a heat exchanger 6 and two tanks 5 which act..as evaporators for brine flowing in from stage n. Each tank 5 is divided by a partition H into an upper region, which is the boundary between liquid and vapour and a lower region 7 from which liquid flows to the next lower stage. The upper region communicates with lower region 7 by way of an assembly E comprising a further fall tube 8 having a sleeve 9 with apertures 2. This assembly E operates in the same way as that shown in Figures 1 to 3 and maintains a constant level L in the lower region 7. The height of the compartment shown in Figure 4 is about, four or five metres, which means that the fall tube 4 can be long enough to absorb large fluctuations in flow rath. However, the fall tube 8 must be shorter, and so it may be necessary to design the apertures 2 in the sleeve 9 so that the assembly E, under normal operating conditions, operates in the manner represented in Figures 2, i.e. with evaporation occuring between the fall tube 8 and the sleeve 9.

The sleeves 3 and 9, with closed lower ends, and the fall lubes 4 and 8 preferably have circular cross-sections, but they may have rectangular, elliptical or other cross-sections.

A further assembly E' comprising a fall tube 10 and a sleeve 3 acts as an overflow to prevent an excessive accumulation of liquid in the upper region of the tank 5.

The present invention thus provides means whereby the levels of brine and fresh water in desalination apparatus may be automatically regulated. By determining the design flow rate of the apparatus, the cross-sectional areas of the apparatus 2 may be adapted to afford a selected pressure difference across the apertures thereby to determine whether or not evaporation of liquid occurs between the fall tubes 4 and 8 and the respective sleeves 3 and 9.

Claims (4)

1. Multiple effect apparatus suitable for recovering water from a saline solution, which apparatus comprises:(a) at least one vertically or substantially vertically disposed column divided into a plurality of compartments one above another: (b) a plurality of vertically or substantially vertically disposed evaporator tubes which are intended to act as film evaporators and which are provided in each compartment, apart from the lowermost compartment of the or each column: (c) at least one tank provided in each compartment: and (1) each tank, apart from that or those in the lowermost compartment of the or each column, is in communication at its lower end region with the interior of the 0 upper end region of the evaporator tubes in the same compartment: (ii! each tank, apart from that or those in the uppermost compartment of the or .each column, is in communication at its upper end region with the interior of the lower end region of the evaporator tubes in the immediately overhead compartment; (iii) each tank, apart from that or those in the uppermost compartment of the or each column, is provided in an upper region of the tank side wall with at least one aperture; (d) means for conveying condensate from the lower-most regions of each compartment, apart from the lowermost compartment of the or each column, to the next lower sompartment, which means comprise at least one vertical fall tube communicating at its upper end with the lowermost region of the respective compartment and having its lower end region enclosed by a sleeve which is closed at its top and bottom snds and has an internal diameter greater than the external liameter of the fall tube, the sleeve being provided with one sr more apertures at a region above the lower end of the fall ;ube which aperture(s) afford communication between the lower 43825 end of the fall tube and the respective next lower compartment; (e) means for introducing saline solution into the tank(s) in the uppermost compartment of the or one column; (f) means for introducing steam into the uppermost compartment of the or one or each column; (g) means for discharging water from the lowermost compartment of the or each column; (h) means for discharging saline solution from the tank(s) of the lower compartment of the or each column; and (i) means accommodated within at least one of the compartments for preheating, by heat exchange with hot water vapour in those compartments, saline solution prior to its introduction into the tank(s) of the uppermost compartment of the or one column: the arrangement of the apparatus being such that, in use, saline solution passes as a film in the evaporator tubes from one tank in one compartment to one tank in the next lower compartment and is heated by hot water vapour in said one compartment; which hot water vapour is condensed and conveyed as condensate to said next lower compartment, and some of the saline solution passing to the tank in said next lower compartment to produce hot water vapour which passes through said aperture(s) and heat the evaporator tubes in said next lower compartment.

2. Apparatus as claimed in claim 1, in which the apertures in tho sleeve of the or each fall tube have a total crosssectional area such that, in use of the apparatus with the intended normal flow rate of saline solution in the or at least one of the fall tubes, partial evaporation of the saline solution takes place in the sleeve or sleeves of that or those respective fall tubes.

3. Apparatus as claimed in claim 1 or claim 2, in which the upper region of each tank is separated from the lower region of that tank by a partition, and at least one further vertical fall tube is provided in each tank, the upper end of each further fall tube communicating with the upper region of the respective tank and the lower region of each further fall tube being enclosed by a sleeve which is closed at its bottom end and has apertures disposed above the level of the lower end of the further fall tube to afford commur-'ratior between the lower end of the further fall tube and the lower region of the respective tank. '

4. Apparatus for the desalination of salt water, part of which is substantially as specifically described herein with reference to the accompany!ng drawi ngs.