IE47266B1 - Desalination apparatus - Google Patents

Abstract

In a multiple effect desalination apparatus as described and claimed in U.K. Specification 1396074, the adoption of a vertical preheater 5 for preheating the saline solution, instead of horizontal preheaters, affords considerable savings of costly construction materials such as cupro- nickel alloys, facilitates the assembly and dismantling of tube bundles, and permits a saving in electric power consumption in use.

Description

This invention relates to an apparatus suitable for the recovery of water from a saline solution, for example from sea Via ter.

Our Patent Specification No. 37,827, to which another application is one for a patent of addition, describes and claims, in Claim 1, a multiple effect apparatus (as hereinafter defined), 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 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; wherein (i) 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 upper end region of the 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 tubes in the immediately overhead compartment; - 2 47266 (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: (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 lowermost compartment of the or each column; and (ij 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 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 evaporates to produce hot water vapour which - 3 47266 passes through said aperture(s) and heats the tubes in said next lower compartment.

Claim 5 of our Patent Specification Mo. 37,827, which is appendant to Claim 1 thereof, specifies that each preheating means (1) includes a plurality of horizontally or substantially horizontally disposed pipes.

The term multiple effect apparatus is used herein to mean an apparatus in which, in use, it is intended that in the or each column, each compartment taken in a downward direction works at a progressively lower temperature and pressure.

Our Patent Specification No. 42,835 describes and claims a modification of the apparatus according to claim 1 of our Patent Specification No. 37,827, in which modification the means (i) for preheating saline solution, instead of being accommodated within at least one compartment (outside the tank), is accommodated within the tank(s), thus in that modification the means (i) is accommodated within at least one of the tanks for preheating, by heat exchange with hot water vapour in that or those tank(s), saline solution prior to its being subjected to its first evaporating step.

This has the advantage that, with a column having a circular cross-section, the tubes (b) can be arranged in one bundle, preferably also of circular cross-section, because the preheating means (in each compartment in which it is present) is now at different height, in each compartment, from the tubes. Although this can have the effect of reducing the bulk of the column, thus resulting in a useful economy, nonetheless the provision of the preheaters within the tanks makes the construction of the tanks more complicated. - 4 47366 According to the present invention, there is provided a modification of the apparatus according to Claim 5 of our Patent Specification No. 37,827, wherein the preheating means (i) for preheating saline solution, instead of being horizontally disposed within at least one compartment, extends vertically or substantially vertically through at least some 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 present invention can afford savings in initial outlay during construction and also in consumption of electricity during use.

In the apparatus of the present invention, the or each column is of circular cross-section and tubes (b) are arranged in a plurality of bundles, each of which has a horizontal cross-section in the form of a sector of a circle, and the preheating means in each of those compartments in which it is present is accommodated within a sector of the same circle as the circle partially defining the sectors occupied by the tube bundles but being a sector not occupied by the tube bundles. In this case, preferably each tank (c) has a horizontal cross-section corresponding approximately to that of the bundle with which it is associated.

The preheating means comprises a plurality of ducts in end-to-end relationship and in communication with each other, the lower end region of each duct standing on a plate which separates two adjacent compartments and the upper end region of each duct being joined by a thermal expansion joint to the lower end region of the duct in the compartment immediately above. 547266 Preferably the apparatus of the present invention also includes in the lowermost compartment of the or each column a horizontally disposed condenser for condensing vapour in the lowermost compartment(s). Preferably the or each condenser includes a plurality of horizontally or substantially horizontally disposed pipes extending between two pipe plates located in diametrically opposed regions of the column.

The apparatus may also include means for transferring inert gases from one compartment to the next compartment.

Preferably the apertures in the tank walls are provided with liquid removers or demisters.

Preferably the apparatus also includes means for dissipating the pressure difference between the interior of the tank(s) in one compartment and the interior of the tubes in the next compartment. Conveniently the or each dissipation means comprises a plate for separating an upper region of the tank from a lower region of the tank, whilst still permitting communications between the upper and lower regions of the tank.

When a plurality of columns is present, the apparatus includes means for transferring saline solution from the tank(s) in the lowermost compartment of one column to the tank(s) in the uppermost compartment of the adjacent column, and means for transferring vapour from the lowermost compartment of the adjacent column, and means for transferring vapour from the lowermost compartment of the said one column to the uppermost compartment of the said adjacent column.

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 drawing, in which:- 6 47266 Figure 1 is a vertical section through part of one embodiment of the apparatus of the present invention taken along the line B-B in Figure 2; and Figure 2 is horizontal cross-sectional view, taken along the line A-A in Figure 1.

In the following description, reference numerals in parentheses indicate those numerals used to identify corresponding components in the apparatus illustrated in Figures 2 and 3 accompanying our Patent Specification No. 37,827. Except as described below, the apparatus of Figures 1 and 2 of the accompanying drawing is identical to that illustrated in Figure 2 of the drawings accompanying our Patent Specification No. 37,827.

In Figures 1 and 2 of the accompanying drawing there is shown the cylindrical wall of the column (1) divided by a plurality of plates, only two of which are shown, into a plurality of compartments. Each plate is circular and supports three bundles of tubes 1 (8) each bundle having a horizontal cross-section resembling a sector of a circle. Each tube communicates with an upper region Z of a tank (4) below its respective plate. The side wall of the upper region 2 of the tank (4) is provided with a plurality of apertures 3 (7), and the lower region 4 of the same tank (4) communicates with a lower bundle of tubes 1 (8) at a tube end plate 8. Extending across the tank (4) on the border line between the upper and lower regions 2 and 4 is a lamination system 7 which is for dissipating the difference in pressure between the interior of the tank 2, 4 {4) in one compartment and the interior of the tubes 1 (8) in the next compartment; the system 7 nonetheless permits communication between the upper and lower regions 2,4. - 7 47266 Any condensate produced in the tank 2,4 (4) passes from there down through the tubes 1 (8) of the bundle immediately below that tank. Also, the vapour emerging through the apertures 3(7) if used to heat the tubes 1 (8) in the same compartment.

£ Extending vertically through the compartments is a preheating means for preheating saline solution which comprises a plurality of ducts 5 each standing on a respective plate and each connected at its upper end via a thermal expansion joint 6 to the lower end of the duct in the compartment above.

Two following Examples illustrate the present invention. In each Example two tests are made, one with a vertical preheater as shown at 5 in the accompanying drawings and the other with horizontal preheaters. EXAMPLE 1. 15 The operating data were: Salinity of the sea water 35,000 ppm (parts per million) pH of sea water at 20°C 8.1 Temperature of sea water 26°C Primary steam at inlet(s) 3 atmospheres and 135°C 20 Production of fresh water 1,500 cubic metres per hour Temperature of the fresh n water 46 C Salinity of fresh water 15 ppm The embodiment of the desalination apparatus with vertical preheaters was especially interesting in view of its relatively high 25 output based on the electrical input, as can be seen in the following Table 1 which reports a comparison between the main features of the -8 472C6 desalination apparatus for the two alternatives, i.e. with horizontal preheaters and with vertical preheaters, the heating efficiency being the same for both.

TABLE 1 Horizontal preheaters Vertical preheaters No. of compartments 15 15 No. of columns 2 2 Diameter of 1st column 8,000 millimetres 6,500 millimetres Diameter of 2nd column 8,000 millimetres 6,500 millimetres Height of 1st column 37,200 millimetres 41,400 millimetres Height of 2nd column 40,800 millimetres 45,000 millimetres Specific electricity consumption 2.35 kWh/cu.metre 1.86 kWh/cu.metre In addition to the comparison made hereabove it must be added that the horizontal preheaters require tube end plates having a diameter of 2,450 mm each, with serious attendant problems as regards their construction and the supporting of the bundles in the interior of the compartments, on account of their weight, and as regards sealing problems for the flanges with respect to air seeping into the column from the outside; also, and this is a most important aspect, there is a real difficulty of manipulating the bundles of preheater tubes of such a size, when slipping them into and out of the columns for maintenance and repair operations.

The fact that with the embodiment according to the present invention the overall length of the two columns is 8,400 mm greater than in the case of the columns with horizontal preheaters must not be allowed to give a deceptive impression because, in view of the considerable reduction - 9 47266 in the diameter of the columns and the ability to dispense with the external manifolds for the preheaters, which manifolds were compulsorily made of an expensive material (e.g. Cu/Ni90/10), and with the connecting pipes which are also made of a costly material, the overall result is a considerable savings in the initial cost, a saving which is also seen in the following example. Notice also the lower consumption of electricity with the vertical preheaters.

EAXMPLE 2. ,000 ppm 8.1 26°C atmospheres and 135°C 535 cubic metres per hour 46°C ppm The operating data were: Salinity of the sea v/ater pH of sea water at 20°C Temperature of sea water Primary steam at inlet (5) Fresh v/ater production Fresh water temperature Salinity of fresh water The following Table 2 clearly shows that the lower output of 535 cu. metres per hour (compared to 1,500 cu. metres per hour in Example 1), which can be regarded as a medium-to-high magnitude, makes the advantages of the present invention less conspicuous than in the previous example but, this notwithstanding, the savings of materials is still significant as will be seen hereafter. - 10 47266 TABLE 2. Horizontal preheaters Vertical preheaters No. of stages 15 15 No. of stages 2 2 Diameter of 1st column 4,700 mm 4,350 mm Diameter of 2nd column 4,700 mm 4,350 mm Height of 1st column 37,200 mm 39,800 mm Height of 2nd column 40,800 mm 44,000 mm Specific electricity consumption 2.35 kWh/cu. 1.86kWh/cu metre metre In this case a closer comparison between the two alternatives has been made, and has permitted the actual economical advantages so achieved to be more accurately evaluated.

The overall weight of the two columns of the embodiment of the invention was reduced, compared to that of the apparatus with horizontal preheaters, by about 33 metric tons and, of these, 5.5 tons were of a costly material (Cu/Ni 90/10) and the remainder was carbon steel coated by a costly material.

It should be added that in the case of the apparatus with laterally withdrawable horizontal preheaters, external scaffolding must be provided outside the columns, with work stages opposite each compartment, as well as hoists for removing and installing the preheaters.

However, with the apparatus of the present invention, both the evaporating tube bundles and the preheaters can be withdrawn vertically from the column heads so that it is sufficient to cater for a hoist of proper strength above the heads of the columns, which hoist must be - II 47266 capable of servicing both columns and of resting on a platform fastened to the column heads.

By so doing, the saving in the scaffoldings required for servicing outside the columns can be estimated at about 140 metric tons, and the saving relating to the erection can be added thereto.

The powerful pump used for charging the evaporators (i.e. for introducing saline solution to the tanks) can be cheaper since, if the rate of delivery required is the same, then, because there are less reversals of flow when using vertical preheaters as compared with horizontal preheaters there is less pressure drop and the hydraulic head to be overcome can be reduced from 180 metres to 120 metres. In addition, with vertical preheaters there is also a reduction of the erection time of the apparatus.

In addition to the reduction of the weight of the materials, which means a resultant considerable reduction in the initial costs, a saving is also achieved in the running costs of the apparatus with vertical preheaters on account of the reduced consumption of electric power.

For a yearly output distributed over 330 working days and for a cost of electricity of 30It. Lira per kWh such a saving will be: (2.35 - 1.86) x 1,500 x 24 x 330 x 30 = 174,636,000 It. Lira yearly for Example 1 and, (2.35 - 1.86 x 535 X 24 x 330 x 30 = 62,286,840 It. Lira yearly for Example 2.

It is apparent from Example 2 as reported above that this invention can be applied with advantage, as outlined above, to apparati having a potential medium-to-high output, and probably also those apparati with outputs such as from 800 to 1,000 cu. metres per hour, and over: such high output apparatus are becoming increasingly widespread.

Claims (12)

1. A multiple effect apparatus (as hereinbefore defined), suitable for recovering water from a saline solution, which apparatus comprises:5 (a) at least one vertically or substantially vertically disposed column which is of circular cross-section and is divided into a plurality of compartments one above another: (b) a plurality of vertically or substantially vertically disposed tubes which are intended to act as film evaporators and 10 which are provided in each compartment, apart from the lowermost compartment of the or each column, the tubes in each compartment apart from the lowermost compartment being arranged in a plurality of bundles each of which has a horizontal cross-section in the form of a sector of a circle: 15 (c) at least one tank provided in each compartment wherein (i) 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 upper end region of the tubes in the same compartment; 20 (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 tubes in the immediately overhead compartment; 25 (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; - 13 47266 (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: (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 lowermost compartment of the or each column; and (i) preheating means extending vertically or substantially vertically through at least some 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 preheating means in each of those compartments in which it is present being accommodated within a sector of the same circle as the circle partially defining the sectors occupied by the tube bundles but being a sector not occupied by the tube bundles, and the preheating means comprising a plurality of ducts in end-to-end relationship and in communication with each other, the lower end region of each duct standing on a plate which separates two adjacent compartments and the upper end region of each duct being joined by a thermal expansion joint to the lower end region of the duct in the compartment immediately above: the arrangement of the apparatus being such that, in use, saline solution passes as a film in the tubes from one tank in one compartment to one tank in the next lower compartment and is heated by hot water - 14 47266 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 evaporates to produce hot water vapour which passes through said aperture(s) in the upper region of the side wall of the tank in said next lower compartment and heats the tubes in said next lower compartment.

2. An apparatus according to claim 1, wherein each tank (c) has a horizontal cross-section corresponding approximately to that of its associated bundle of tubes in the same compartment.

3. An apparatus according to any preceding claim, which also includes in the lowermost compartment of the or each column a horizontally disposed condenser for condensing vapour in the lowermost compartment(s).

4. An apparatus according to claim 3, wherein the or each condenser includes a plurality of horizontally or substantially horizontally disposed pipes extending between two pipe plates located in diametrically opposed regions of the column.

5. An apparatus according to any preceding claim, which also includes means for transferring inert gases from one compartment to the next compartment.

6. An apparatus according to any preceding claim, wherein the apertures in the tank walls are provided with liquid removers or demi sters.

7. An apparatus according to any preceding claim, which also includes means for dissipating the pressure difference between the interior of the tank(s) in one compartment and the interior of the tubes in the next compartment. - 15 47266

8. An apparatus according to claim 7, wherein the or each dissipation means comprises a plate for separating an upper region of the tank from a lower region of the tank, whilst still permitting communication between the upper and lower regions of the tank. 5

9. An apparatus according to any preceding claim, wherein a plurality · of columns is present, which apparatus includes means for transferring saline solution from the tank(s) in the lowermost compartment of one column to the tank(s) in the uppermost compartment of the adjacent column, and means for transferring vapour from the lowermost compartment 10. Of said one column to the uppermost compartment of the said one column to the uppermost compartment of the said adjacent column.

10. An apparatus according to claim 1, substantially as hereinbefore described with reference to, and as illustrated in Figures 1 and 2 of the accompanying drawings. 15

11. A process for recovering water from a saline solution, whenever effected in an apparatus as claimed in any preceding claim.

12. Water whenever removed from a saline solution in accordance with the process claimed in Claim 11. Dated this 13th day of September, 3Y:- - TOMKINS & CO., Applicants’ Agents