IL32804A - Method and apparatus for desalination of salt water - Google Patents

Description

Method and apparatus r deaalination of ealt vater This invention relates to manufacturing fresh water from sea water or brackish water.

To obtain fresh water from sea water or brackish water, many processes are known some of which are based on an expansion evaporation. The sea water, which has first of all been heated, is allowed to expand in stages and the vapours produced are precipitated in condensers o The sea water is at the same time preheated. But these hitherto known processes have the disadvantage that the fresh water obtained is still too expensive for industrial utilisation ..owing to the generally high temperature difference between inlet and outlet temperatures before expansion.

According to the present invention a method of manufacturing fresh water comprises heating and ■ centrifuging sea water or brackish water to form a water ring, maintaining this ring whilst subjecting its inner surface to such pressure below atmospheric pressure as to cause vaporisation at said surface, and drawing off the vapour and condensing it to form fresh water.

According to a further aspect of the invention, apparatus for centrifuging liquid comprises a closed outer rotationally symmetrical chamber, an open-ended ro a ionally symmetrical chamber of shorter length disposed coaxially within the outer chamber so that the ends of the inner chamber are spaced from respective facing walls of he outer chamber, an inlet for sea water opening tangentially into the inner chamber, and an outlet extending through a facing wall of the outer chamber for drawing vapour from the inner chamber.

In use the sea water enters the evaporation space in the internal chamber tangentially and, under the action of centrifugal force, forms a clearly visible layer of water in the form of a ring, which with an appropriate low pressure partly evaporates at the internal surface in accordance with the boiling state. The evaporation heat/which is necessary for maintaining the phase change is taken 'from the non-evaporated portion of the water ring, with a simultaneous temperature drop, in a region of turbulent flow with very good heat transfer conditions. This fact permits evaporation in a very small space i.e. with the least outlay on apparatus. The phase change does not take place in an undefined manner at metal surfaces which the danger of forming encrustations, and the effects on heat transfer which this involves, but only in a relatively thin layer at the inner surface of the water ring.

It is advantageous if the sea water is deliver ed into the separating chamber by means of a pump from a container provided with heating means, and the outflowing steam is conducted through a condensation plant as a fresh water condensate into a condensate container provided with an evacuation pump.

The process described is suitable more particularly in combination wit a thermal power plant using fossil or nuclear fuel, since as a result hea due to energy losses and also waste steam heat can be made use of. The sea water can be conducted as a coolant through a turbine condenser serving as a preheater, and a part-flow of the cooling water branched-off before the turbine condenser can be used as coolant for the steam flowing out of the inner separating chamber. Normally, the condensation enthalpy of the steam is passed completely to the cooling water, without any recovery being possible. The centrifugal force evaporator o^ae des-cribed makes it possible in this connection arrangement, as in a heat pump, to recover this energy partly in the form of fresh water with slight energy.

However, instead of using the heating-up range in the turbine condenser, it is also possible to heat the sea water fo " example in a heat exchanger heated by turbine bleed steam.

In order that the invention can be more clearly understood various embodiments will now be described with reference to the accompanying drawings, in which:- Figure 1 is a longitudinal sectional view and a cross-sectional view through an appropriate centrifugal force vaporisation chamber, Figure 2 shows a connection arrangement for an installation incorporating such a centrifugal force chamber, Figure 3 shows an open circuit and Figure 4- a semi-open circuit wherein the sea water is heated in a turbine condenser, and Figure 5 shows heating of the sea water in a heat exchanger heated by bleed steam.

Referring to Figure 1, apparatus for obtaining fresh water from sea water or brackish water comprises primarily an external, rotationally symmetrical chamber 1 with lateral end walls 2· Coaxiall thereto there is arranged a separating chamber 3 of smaller diameter. This separating chamber 3 is somewhat shorter than the external chamber , so that an annular gap is formed in each case .between the ends of the separating chamber 3 and^the end * walls 2. The separating chamber 3 has at a mid point along its length a tangential inlet 5 for feeding in heated sea water. Axial insert pipes 6 for steam discharge extend through the end walls 2· The sea water flowing in through the tangential inlet 5 is rotated within the separating chamber 3, so that a ring of water 8 forms at the internal wall of this separating chamber. A portion of the water is vaporised at the internal surface of the water ring 8 which forms. The vapour produced flows out through the insert pipes 6 into a condensing device not shown in detail. Owing to the condensation of the vapour there occurs a considerable negative pressure which reacts back into the separating chamber 3. Owing to the centrifugal force acting on the inflowing water, this negative pressure is balanced. The centrifugal force must be so great that it maintains equilibrium with the geodetic height of the forming water column appropriate to the particular negative pressure. By appropriately increasing the speed of revolution of the water ring, with a negative pressure of 0.2 atmospheres absolute, evapor-ation can take place already at about 30 0. As a result only a small temperature difference is required between the inlet and outlet temperatures of the tan-gentially introduced sea water. The water running out through the annular slots collects first of all ■·. ' / in an annular chamber 10, defined between the walls of chambers 1 and 3» and then flows out --through an outlet 7· Since vaporisation takes place at a water surface and not at hot metal surfaces, formation of encrustations on any parts of the apparatus can be substantially avoided.

Figure 2 is a diagram explaining the operation of such- apparatus connected in circuit with other equipment. The sea water is first of all heated by a heating means 12 in a container 11, and then flows by way of a pump 13» a pressure valve and a quantity measuring device 15, through the tangential inlet 5 into the centrifugal force vaporiser 1'. 'Prom here, the vapour produced flows through a condensate conduit 16 first of all into a condenser 17» in which the vapour, is condensed, and then into a fresh water container 18, from which it can be removed by way of a service conduit 21. An evacuation pump 20 is also connected to the fresh water container 18. This pump 20 has the task of maintaining the boiling pressure in the separating chamber 3i removing the gas contained in the water.

Attention is now drawn to Figures 3 and 4 in connection with utilising the heat due to energy losses in a thermal power plant. Figure 3 first of all shows an open circuit. The sea water serving as coolant for a condenser 24 is conducted through a conduit 22 and a cooling water pump 23 into a/heat exchanger surface 25 of a turbine condenser" 2 . From here, the heated cooling water flows into an overflow tank 27 and is then fed by means of the pump 13 to the tangential inlets 5 of the centrifugal force evaporator 1 ' · In the downstream condenser 17i which is supplied by way of a conduit 29 with a portion of the cooling water branched-off from the turbine condenser, the outflowing vapour is condensed and conducted through the conduit 16 into the condensate collecting container 18. With this circuit arrangement, the water not yet vaporised from the centrifugal force vaporiser is discharged into the free atmosphere through a conduit 28 and the cooling water of the condensate condenser 1 likewise.

Figure 4 shows a semi-open circuit. Here, the non-vaporised sea water flows from the centrifugal force evaporator 1 ' first of all into the tank 27 and. is conducted from here, and heated, through the conduit 22 and the cooling water pump 23 into the turbine condenser 24. For cooling the vapour flowing out of the centrifugal force evaporator 1 · , there is used an additional quantity of sea water which is con This heating may be used solely, or additionally to the turbine condenser.

Usin the circuit arrangements indicated, it is also possible to carry out evaporation in several stages, since the sea water not vaporised always flows back again and can be collected* Thus, with the process and apparatus described, it is possible in a simple manner with little apparatus outlay and with the* use of exhaust' steam heat or heat due to energy losses, to obtain fresh 9 water economically. Owing to the simple construction of an installation of this kind, it is also possible to construct the entire apparatus to be transportable, and the apparatus requires only the energy for the pump and a small temperature difference between inlet and outlet temperatures*

Claims (11)

1. A method of manufacturing fresh water, comprising heating and centrifuging sea water or brackish water to form a water ring, maintaining this ring whilst subjecting its inner surface to such pressure below atmospheric pressure as to cause vaporisation at said surface, and drawing off the vapour and condensin it to form fresh water, :

2. * 2. A method according to claim 1 , wherein the sea water or brackish water is continuously fed.

3. · A method according to claim 2, wherein the low pressure is produced] in a downstream condenser connected to. receive the vapour.

4. ·:· A method according to claim 2 or claim 3, wherein prior to centrifuging, the fed water is heated in a turbine condenser, or is heated at least partially by turbine) bleed steam.

5. ,· A method according to claim 2, claim 3 or claim , ^wherein part of the fed water is not subjected to heating and centrifuging but is branched off and is caused to cool said vapour.

6. A method according to any preceding claim, wherein the centrifuging is carried out by pumping the sea water or brackish water tangentially into a cylindrical chamber so that it is /Caused to form a ring Iagainst the inside wall of the chamber.

7. · Apparatus for centrifuging liquid, comprising a closed outer rotationally symmetrical chambe an open-ended rotationally symmetrical chamber of shorter length disposed coaxially within the outer chamber so that the ends of the inner chamber are spaced from respective facing walls of the outer chamber, an inlet for sea water opening tangentially into the inner chamber, and an outlet extending through a acing wall of the outer chamber for drawing vapour from the inner chamber,

8. Apparatus, according to claim combination with a container for sea water, means for heating the; sea water, a pump for pumping the heated sea water to the inlet, a fresh water condenser and an evacuation pump for drawing vapour from said inner chamber through the outlet into the condenser.

9. The combination according to claim 8, wherein the means for heating the sea water -comprises a turbine conden rser. . -

10. The combination -according to claim 9» wherein a connection upstream from the turbine condenser connects with the fresh water condenser, whereby part of the sea, water when it is being fed will clrcul ate through thee fresh water condenser and act as a coolant therefore i

11. 5 The combination ^according to claim 9» comprising a coolan connection between the. fresh water condenser^ and a point upstream from the inlet,