US3725206A

US3725206A - Desalination plant

Info

Publication number: US3725206A
Application number: US00070816A
Authority: US
Inventors: N Foley
Original assignee: Auscoteng Pty Ltd
Current assignee: Valuepace Ltd
Priority date: 1969-09-11
Filing date: 1970-09-09
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03
Also published as: GB1321448A; DE2044918A1; CA939629A; FR2062178A5

Abstract

A desalination plant to distill water from sea water at ambient temperature without the addition of heat, wherein a condenser is formed in an evaporator in heat exchange relation therewith. A blower evacuates the evaporation and transfer steam to the condenser, and two combined liquid-vacuum pumps are provided, one to remove dense brine and air from the evaporator, the other to remove condensate and air from the condenser. A high vacuum is thus produced in the evaporator sufficient to cause boiling at ambient temperature.

Description

April 3, 1973 N. L. FOLEY DESALINATION PLANT Filed Sept. 9, 1970 |A.| Ill l l 5x63 Nueve@ ...l I ESE IAI I... M. UMQM Sum 36k btaq l. III'. mh xQ K All D923 @kim Tfr"` IIIIII 3,725,206 DESALINATION PLANT Norman Leslie Foley, Clovercrest, Modbury, South Australia, Australia, assignor to Auscoteng Pty. Ltd., Wayville, South Australia, Australia Filed Sept. 9, 1970, Ser. No. 70,816 Claims priority, application Australia, Sept. 11, 1969, 60,784/ 69 Int. Cl. B01d 1/00, 3/00, 3/10, 3/14, 3/42; C02b 1/04 U.S. Cl. 202-205 3 Claims ABSTRACT OF THE DISCLOSURE A desalination plant to distill water from sea water at ambient temperature without the addition of heat, wherein a condenser is formed in an evaporator in heat exchange relation therewith. A blower evacuates the evaporator and transfers steam to the condenser, and two combined liquid-vacuum pumps are provided, one to remove dense brine and air from the evaporator, the other to remove condensate and air from the condenser. A high vacuum is thus produced in the evaporator sufcient to cause boiling at ambient temperature.

This invention relates to an improved desalinisation plant. i

We have already proposed to use a desalinisation plant in which ambient temperatures are used to produce the required production of steam from sea water or the like, this being achieved by utilising a' vacuum which is sufficient to cause boiling of the water at ambient temperatures.

lProblems exist of course in the drawing of vacuums of this degree but in copending Australian patent application No. 60,784/69 and U.S. Ser. No. 70,823, a simple and effective vacuum pump has been described which enables the necessary vacuum to be drawn without any resultant problems, and the object of this invention is to generally provide an improved system by means of which a simple and effective unit will be provided which wil comprise basically only an evaporator and condenser formed as a single unit with blower means between the two sections of this unit to move the steam or vapour in the required manner, a pair of pumps being used one being to produce the necessary vacuum and the other to draw olf the heavy brine liquid as required to ensure that the supply of sea water or the like to the unit is maintained at a value where effective distillation of the water can take place with the heavier brine being removed as required in a quantity suicient to maintain the evaporator liquid at a required value.

As described in Ser. No. 70,1823, the pumps capable of producing high vacuum while pumping either gaseous or liquid tuids comprise water sealed gear pumps having a liquid trap at the outlet and recirculation tubes extending from the liquid trap to the inlet of the pump and the bearing means supporting the drive shaft. The bearing means has a substantially cylindrical wall disposed about the shafts of the pump and has an annular recess intermediate its ends. One of the recirculation tubes serves as the conduit means for supplying the sealing liquid from the liquid trap to the recess. A first clearance between the wall and the drive shaft is greater between the recess and the gears of the gear pump than a second clearance between the wall and the drive shaft over the remainder of the portion of the bearing means exteriorly of the recess. Thus, the inward passage of a small quantity of the liquid from the liquid trap blocks the flow of any other uid longitudinally of the shafts and allows a high vacuum to be produced. The second clearance serves as at least a portion of the seal to block outward passage of the liquid from the liquid trap longitudinally of the shaft exteriorly of the recess.

United States Patent O Because of the availability according to our invention of simple and effective pumps to handle the output from such a desalinisation unit and the association of the various circuits with heat exchangers, a very high efciency is obtainable from the unit which forms the basis of this invention, and it will be realised therefore that an object of the invention is to provide a desalinisation unit of high eliiciency and with a minimum of complications so far as mechanisation is concerned.

In order however that the invention will be fully appreciated one embodiment will now be described with reference to the accompanying drawing, but it is to be clear that the invention need not necessarily be limited to this embodiment, the scope being defined in the claims herein.

Referring to the single figure of the drawing, the unit according to this invention can conveniently comprise an evaporator 1 having a condenser 2 within it for heat exchange purposes, the water to be purified being drawn by means of a low pressure system from a supply tank 18, through a heat exchange tank. 3 and flowing through line 20 to various other heat exchangers 4, 5 and eventually entering the evaporator 1 through an air separation chamber 6, the air separation chamber in turn being connected by a line 7 and a heat exchanger to a brine pump 8 which serves the dual purpose of drawing olf any air which enters the system with the water and at the sa-me time drawing off a quantity of the brine and delivering it through line 21, so that the evaporator 1 will be held at the correct salinity and heavy brine will be removed from the system after giving up any heat remaining in it at the heat exchanger coil 17 in heat exchanger tank 3'- through which the incoming water rst passes.

The product water outlet line 9 goes from the condenser through a heat exchanger 5, in heat exchange with the incoming feed water, to a vacuum pump 10 which maintains the required vacuum within the system, and from the vacuum pump 10 the product water passes through a heat exchanger 11 which can be in the same heat exchanger tank 3 as the brine heat exchanger 17 so that all of the remaining heat is given up from not only the brine but also from the product water to the incoming Water for the evaporator.

The actual construction of the evaporator and condenser should be such that the simple and effective unit is provided which can be readily cleaned and therefore presents no problems when say the tubes must be exchanged, this is preferably achieved by having an outer shell which forms the evaporator itself and is adapted to contain the brine, and into this is placed from one end a nest of tubes provided with the necessary headers so that the header at one end is disposed within the evaporator while the header at the other end is formed as a closure means for that end of the evaporator, the header at the inner end having a tube projecting outwardly through a stuffing gland in the evaporator casing so that to position the unit it is only necessary to loosen the holding means and the gland and to withdraw the tube and header assembly, leaving an evaporator shell ready for cleaning, repositioning being simply a reverse of that and that it is only necessary to put the tube assembly back into the evaporator shell and secure it in position to seal the unit.

In the evaporator, the shell contains the liquid, and the tube assembly is adapted to contain the vapour or steam, the steam being drawn from the evaporator through liquid extractor baiiles 12 into a blower 13 driven by a motor 19, which then forces the steam or vapour through the tubes to the vacuum pump 10.

Actually of course the vacuum pump 10 draws the products of vapourisation through the circuit itself, but the purpose of the blower 13 is to maintain a pressure differential between the evaporator 1 and the condenser 2 so that the evaporator pressure will be lower than the condenser pressure to enhance the production of steam in the evaporator 1 and its passage in heat exchange with the evaporating liquid to the vacuum pump y which also serves as stated earlier to draw off the product water after such water has given up any remaining heat to the incoming water.

At this stage of course the vacuum pump 10 is used which has a water seal so arranged that a simple gear pump or the like can be used to produce the required vacuum, the gear pump or the like being sealed by means of the water flow which is appropriately recirculated from a liquid trap in the outlet section of the pump as described in the copending Australian patent application No. 60,7l83/ 69.

Thus it will be seen that the evaporator 1 and condenser 2 are a unitary structure which can be readily dismantled and reassembled and if scaling or the like occurs no problem results because these units are readily changed and cleaned.

The brine feed to the evaporator 1 of course passes through a control valve 14 which regulates the amount of ilow in relation to the high vacuum existing in the evaporator 1 and condenser 2, and as stated air separation is preferably effected by means of a separator 6 which has an inlet tube 1S projecting part way up a vessel 16 and the lower end of which vessel 16 leads to the inside of the evaporator shell 1, but the upper part of the vessel 16 which is above the normal water level in the evaporator has a vacuum applied to it by means of a second vacuum pump which we term the brine pump 8 and therefore any air which is entrained in the water owing into the circuit is drawn off at this point to ensure the maintaining of the required vacuum within the circuit.

The same brine pump 8 of course also connects to the evaporator shell via heat exchanger 4 at an elevated locality such that the tubes of the condenser are kept covered with brine, and this overflow brine is taken through the heat exchanger 4 in heat exchange with the incoming saline feed water to the brine pump 8 which is also supplied with a liquid trap and recirculation tubes to ensure that this 'brine pump in spite of its being a simple gear pump or the like is capable of drawing the necessary vacuum, the brine pump 8 passing its concentrated product in heat exchange with the incoming saline feed water to the dense brine outlet. The amount of flow through this pump `8 is so arranged that suicient water is drawn off to maintain the correct brine level in the evaporator shell 1.

Thus it will be realised that there is one vacuum pump 10 which directly maintains the condenser Z at the required low pressure and in doing so draws off the condensate and discharges it to the product water outlet through the necessary heat exchangers, while the second pump which is the brine pump 8 draws off the brine as well as any air released from the incoming water and discharges a regulated quantity to the -brine water outlet through a heat exchange coil 17 effective on the incoming water.

Thus it will be seen that the condenser 2 is kept at a low pressure immediately by suction applied by the main vacuum pump 10 but the evaporator is also coupled through the vacuum pump 8 which discharges a certain amount of brine, both of these pumps thus holding the relatively low pressures within the condenser 2 and evaporator 1, but the evaporator pressure is further lowered by the blower 13 between the evaporator 1 and condenser 2 so that there is the required differential which will enhance boiling of the liquid in the evaporator shell 1 due to the vacuum and as evaporation lowers the temperature the heat exchange with the condenser 2 is beneficial to produce a system which requires no outside supply of heat such as solar pan or the like -but because of the extremely low pressure existing in the evaporator 1 and condenser 2 the liquid is boiled at a high rate and while steam passes over to the condenser 2 and is eventually pumped away through the vacuum pump 10 to the product water outlet, the incoming brine is diluted by the brine pump 8 drawing off a certain quantity of the heavier brine to maintain a proper balance within the evaporator 1 and condenser 2.

If desired, the air separation chamber y6 may not be utilised, but instead the brine feed line may be connected directly to the evaporator, the control valve 14 regulating the flow and the two vacuum pumps 8 and 10 being effective to withdraw any air entering the System.

On starting up the plant, the vacuum produced by the blower 13 and the vacuum pumps v8 and 10 causes a chilling effect, and there will be a degree of heat ow into the evaporator from the surrounding air. During operation the only heat added to the system is the heat of compression by the blower, thus forming an entirely selfsupporting plant in which the plant is entirely self sustaining, and relies for its operation on the high vacuum produced.

yIt will be realised from the foregoing that a simple and effective unit is provided which has few problems in its construction and which is readily dismantled if such is required for servicing or the like.

It will also be realised that the blower which is disposed between the evaporator shell and the condenser can be of a type similar to the gear pumps suggested for the vacuum producing members in which case a simple drive is possible through the use of sealing water from the system itself.

What I claim is:

1. Apparatus for effecting desalination of saline water comprislng:

an evaporator;

supply means for supplying saline feed I'water to said evaporator;

a condenser disposed within the water space of the evaporator so that heat given up by a fluid condensing within the condenser is transferred to the saline water in the evaporator; and

first means for evacuating the evaporator to a high degree of vacuum suflicient to cause boiling of the water in the evaporator at temperatures no greater than ambient temperature, thus obviating the deposition of scale on the heat exchange surfaces due to temperature; said rst means including:

blower means including means for powering it so as to provide heat of compression and to establish a vapor flow from the evaporator to the condenser and to establish a lesser degree of high vacuum within said condenser such that the latent heat of vaporization of a uid condensing within the condenser will ow from the condenser into the saline water at said high degree of vacuum in said evaporator, second means to withdraw condensate and any entrained air from the condenser to maintain the condenser at said lesser degree of high vacuum, and third means to withdraw concentrated brine and any entrained air from the evaporator for maintaining said high degree of vacuum therein; said first means maintaining a pressure differential between the evaporator and the condenser so that the evaporator pressure is lower than the condenser pressure to enhance the production of steam in the evaporator; said first means also maintaining said high degree of vacuum and said lesser degree of high vaccum such th'at ambient temperature conditions and heat of compression of said blower means alone are sufficient for feasibly producing desalinised water without requiring a supplemental heat source for start-up or for operation;

said apparatus being characterized in that the second means to withdraw the condensate from the condenser and the third means to withdraw the concentrated brine from the evaporator each comprise a water sealed, gear-type vacuum pump having the capability of pumping both gaseous and liquid fluids and maintaining said high degree of vacuum;

said apparatus being further characterized in that first and second indirect heat exchangers are connected serially with said supply means and with said evapo- Iator to preheat feed therefor; said first heat exchanger also being connected with said second and third means and said second heat exchanger also being connected with said evaporator such that the saline feed water passes through said first heat exchanger in indirect heat exchanging relation with both the warm condensate and the warmer concentrated brine from said second and third means respectively, and is further heated by passing through said second heat exchanger in heat exchanging relation with the concentrated brine as it is withdrawn from the evaporator and before the concentrated brine passes to the first heat exchanger.

2. Apparatus for effecting desalination of saline water as defined in claim 1 wherein a third heat exchanger is serially connected with said second heat exchanger and said evaporator; said third heat exchanger being also connected with said condenser such that the saline feed water is finally heated by passing through said third heat exchanger in heat exchanging relation with the condensate as it is withdrawn from the condenser and before the condensate passes to the first heat exchanger.

3. Apparatus for effecting desalination of saline water comprising:

an evaporator;

supply means for supplying saline feed water to said evaporator;

first means for evacuating the evaporator to a high said first means maintaining a pressure differential between the evaporator and the condenser so that the evaporator pressure is lower than the condenser pressure to enhance the production of steam in the evaporator;

said first means also maintaining said -high degree of vacuum and said lesser degree of high vacuum such that ambient temperature conditions and heat of compression of said blower means alone are suicient for feasibly producing desalinised water without requiring a supplemental heat source for startup or for operation;

said apparatus being further characterized in that an air separation chamber is provided at the saline water feed inlet to the evaporator, the air separation chamber being connected by a vacuum line to the inlet of the third means to withdraw the air from said air separation chamber simultaneously with the concentrated brine from the evaporator.

References Cited UNITED STATES PATENTS 2,589,406 3/1952 Latham, Jr. 203--91 X 2,885,328 5/ 1959 Williamson 202-167 3,026,261 3/ 1962 Mayfield et al. 210-56 3,227,630 1/1966 [Beckman 202-205 2,236,748 2/ 1966 Pottharst, Jr 203--26 X i3,410,758 :l1/.1968 Coanda 159-24 R 3,471,373 10/ 1969 Pottharst, .l r. 203-26 X NORMAN YUDKOFF, Primary Examiner I. SOFER, Assistant Examiner U.S. Cl. X.R.