AU620918B2

AU620918B2 - Method of and means for controlling the volume and salinity of water in a reservoir

Info

Publication number: AU620918B2
Application number: AU42711/89A
Authority: AU
Inventors: Lucien Yehuda Bronicki; Yona Yahalom
Original assignee: Solmat Systems Ltd
Current assignee: Solmat Systems Ltd
Priority date: 1988-10-27
Filing date: 1989-10-09
Publication date: 1992-02-27
Anticipated expiration: 2009-10-09
Also published as: RU2038108C1; AU4271189A

Description

7 I. iiu i l-7lrraar~PrsPl~oum~ S F Ref: 109098 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 2 0 COMPLETE SPECIFICATION 0

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: Related Art: 4*4r 4, 4 i# Name and Address of Applicant: Address for Service: Solmat Systems Ltd.

Yavne 70650

ISRAEL

Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Method of and Means for Controlling the Volume and Salinity of Water in a Reservoir The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/3 r -1 METHOD OF AND MEANS FOR CONTROLLING THE VOLUME AND SALINITY OF WATER IN A RESERVOIR The volume and salinity of water in a reservoir that receives brackish water is controlled by evaporating water from liquid drawn from the reservoir to form concentrated brine. The heat storage layer of a solar pond is utilized as a source of heat for enhancing the evaporation of water from the liquid drawn from the reservoir. Finally, the concentrated brine produced by the evaporation of water is disposed of, for example, in the building of a further solar pond.

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DESCRIPTION

Technical Field: This invention relates to a method of and means for controlling the volume and salinity of water in reservoir.

Background and Relevant Information In many places in the world, crops are irrigated with river water, or with water stored in reservoirs. This water usually contains a small amount of salts which are deposited in the irrigated soil as the crops are irrigated. These salts tend to build up to the detriment of crops.planted in the irrigated soil. To overcome this problem, the amount of irrigation water applied to the soil is increased above the level necessary for plant growth by flooding the fields thereby leaching the salts from the topsoil. In many places, a system of underground drainage pipes is provided for collecting the excess water containing the leached salts and conveying the brackish water into a system of drainage 20 canals. These canals gather and carry away the brackish agricultural water for disposal.

In some places, like the Imperial and Central Valleys of California, the brackish water is carried by a canal system into a man-made terminal reservoir, the Salton 25 Sea, Kesterson Reservoir, etc. Ideally, the brackish water in these reservoirs can be conveyed by canal to the ocean and thus disposed of. In places where the water cannot be easily be pumped or conveyed to the ocean, the reservoirs become enlarged and more and more concentrated causing various ecological problems associated with high salt concentrations. In addition, the presence of toxic pollutants in the soil which are leached therefrom over an extended period of time results in high concentrations of pollutants, like selenium, and other heavy metals in the reservoirs.

The magnitude of the problem in disposing of 2agricultural drainage water is illustrated by considering the Central Valley and San Joaquin Valley in California. In the San Joaquin Valley, the current requirement is the disposal of agricultural water amounting to 40-50 million gallons per day (or 44,800-56,000 acre feet per year). In the future, the estimate is that as much as 600,000 acre feet from the San Joaquin Valley, and as much as 2,000,000 acre feet from the Central Valley will have to be disposed of annually within the next 20 years.

One approach to this problem is to construct a canal and pump system for transferring brackish water from the reservoirs at the rates indicated into the sea. Such a system will be very costly and complex in both construction and operation by reason of the distances and elevations of the reservoirs relative to the sea. It is, therefore, an object of the present invention to provide a new and improved method of a means for disposing of brackish from S"i reservoirs which is more cost effective.

SUMMARY OF THE INVENTION According to the present invention, a method for controlling the volume and salinity of water in a reservoir that receives brackish water comprises the steps of evaporating water from liquid drawn from the reservoir to form concentrated brine, using a solar collector as a source of hot liquid, transferring heat from the hot liquid to P; enhance the evaporation process,s and then disposing of the resultant concentrated brine.

Experience shows that, at the reservoir, the salinity of the agricultural drainage water which must be disposed of is about 10,000 ppm. Because of the chemical composition of this brine, namely the inclusion of sodium sulfate, the brine probably can be concentrated to 350,000 ppm. This results in a liquid volume reduction of approximately This 35-fold reduction in volume significantly reduces the amount of liquid that must be disposed of in the sea or in other ways. Thus, the invention provides a way to quickly 3 materially reduce the volume of brine that must be disposed of regardless of the technique employed. The preferred technique for disposing of the resultant concentrated brine is in the construction of a salt water solar pond. A conventional salt water pond has an upper convective layer nominally about 25-50 cm. in depth, depending upon ambient weather conditions, an intermediate, stratified, nonconvective halocline, nominally about 1-2 m. deep, and a lower heat storage layer whose depth may vary from 2-5 m.

In the present invention, the depth of the heat storage layer depends on the amount of concentrated brine that is to be disposed of. Generally, as disclosed in.U.S. Patent No.

4,377,071, the disclosure which is hereby incorporated by reference, the salinity of the convective or wind mixed S 15 layers is less than about 5% while the salinity of the halocline changes with depth from about 5% at the top to around 30% at the bottom. The salinity of the heat storage layer is uniform with depth at around In a conventional salt water solar pond, solar radiation penetrates into the pond heating the water in the wind mixed layer, in the halocline, and in the heat storage oO* layer. Because the wind mixed layer is convective, o ,f practically all the heat absorbed therein is returned to the atmosphere by conduction; and for this reason, this layer o i0 25 should be kept as shallow as possible. Heat absorbed in the 4444 halocline is trapped therein because the halocline is non- S convective and acts as an insulator for the heat storage layer. After a period of time, the temperature profile of *0 the pond will closely match its density profile.

Eventually, the temperature in the heat storage layer may reach over 100 0

C.

The present invention contemplates that the heat contained in the heat storage layer is available for heating the liquid drawn from the reservoir for the purpose of enhancing its rate of evaporation. Preferably, water is evaporated from the liquid drawn from the reservoir by 4 spraying the liquid into the air forming a droplet shower.

To maximize the evaporation process, the techniques disclosed in U.S. Paten No. 4,704,189 and 4,351,849, both of which are incorporated by reference, can be utilized, preferably those specified in the '189 patent. As described in the '189 patent, the size of the droplets in the droplet shower and their elevation with respect to a reservoir for collecting the droplets are selected such that the droplets in the shower interact with the air so that practically all of the heat and vapor transfers occur under the condition that the latent heat flux due to the evaporation of liquid from the droplets is substantially equal to the sensible heat flux to the droplets from the air. Stated otherwise, 000.,.

most of the liquid that evaporates does so under conditions 15 of constant enthalpy. The result is a rapid and efficient evaporation process whose only energy cost is that of pumping the water into a spray at a predetermined height.

on In order to efficiently employ the heat from the heat h0 storage layer of the solar pond for the purpose of enhancing evaporation from the evaporation pond which receives water from the reservoir, a power plant may be associated with the o solar pond. Such power plant operates on the Rankine cycle to and includes a vaporizer responsive to brine from the heat storage layer of the solar pond for vaporizing an organic working fluid, a turbo-generator responsive to vaporized 0#40 working fluid produced by the vaporizer for producing power S° and heat depleted working fluid, a condenser for condensing o the heat depleted working fluid and producing condensate that is returned to the vaporizer, and an arrangement by which liquid is exchange between the condenser and the evaporation pond. In this way, the heat source for the power plant is constituted by the heat contained in the heat storage layer; and the heat sink for the power plant is constituted by the evaporation pond. The power plant generated power which can be used to drive the various pumps necessary for the spraying and transfer of liquids between the reservoir, the evaporation pond, and the system for disposing of the concentrated brine so that the overall system is energy efficient. Moreover, the heat rejected by the condenser is utilized to enhance the evaporation of water from the evaporation pond.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention is shown by way of illustration in the accompanying drawing whose single figure illustrates apparatus according to the present invention wherein a solar pond is constructed using an evaporation pond whose operation is enhanced by the use of heat rejected from a power plant associated with the solar pond.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawing, reference numeral designates apparatus according to the present invention for controlling the volume and salinity of water in reservoir 11 which is an open body of brackish water exposed to ambient conditions. The reservoir receives rain and gives up water by evaporation. In addition, agricultural water flows into the reservoir as indicated in the drawing. Reservoir 11 is a terminal lake such as the Salton Sea. The inflow of agricultural water greatly exceeds the outflow due to evaporation. As a consequence, the size of the lake, as well as its salinity, increase with time.

Apparatus 10 includes water intake 12 which receives water from reservoir 11 and operates as a settlement region within which sediment brought from the reservoir settles.

?Water from intake 12 is transferred via pump 13 and filter 14 to condenser 15 of power plant 16. Water form condenser 15 is transferred via conduit 17 to evaporation station 18 adjacent to reservoir 11. Alternatively, if preferred, water from condenser 15 can be transferred directly to spray system 19.

Associated with evaporation station 18 is a pond and elevated spray system 19 which receives liquid by operation of pump 20. Thus, at evaporation station 18, liquid from 6 the pond, which had served to cool condenser 15, is sprayed into the air as droplets. Water is evaporated from the droplets as they fall back into the pond and form a more concentrated. brine. The construction of spray system 19 may be in accordance with the disclosure of U.S. Patent No.

4,704,189 because the apparatus and method disclosed in this patent is an efficient way in which to concentrate the heated brine discharged from the condenser. The vapor pressure of the heated brine is increased facilitating the evaporation of water contained in the brine. As a result, the evaporation process is enhanced.

got*#: System 19 evaporates a great deal of water from the o liquid in the reservoir producing a very concentrated brine 0, which is then transferred by pump or other means to 15 crystallization pond 21. in the latter pond, the concentration is so great that less soluble salts, such as sodium chloride, precipitate from the solution. The result is that the concentration of liquid contained in pond 21 will exceed 30%. The highly concentrated brine is then oo:: 20 piped into depression 22 and forms a part of a potential S 0 solar pond. When the depression is almost full, the O concentrated brine may be mixed with fresher water to create *Gott, a halocline. When this pond is completed, it becomes available for generating electricity, and the process is repeated to construct a new solar pond.

In summary, brackish water contained in reservoir 11 is Go first quickly and efficiently concentrated by elevated spray system 19. Sodium chloride, and other less soluble salts are precipitated in crystallization pond 21, and very concentrated brine is available for constructing the heat storage layer and the halocline of a solar pond.

Associated with apparatus 10 is operating solar pond 23 which includes wind-mixed layer 24, halocline 25 and heat storage layer 26. The salinity profile of this pond is shown by curve 27. From a practical standpoint, the salinity in wind mix layer 24 is uniform at about 5% and, ~1~1 7 within the halocline, the salinity increased from about near the top to around 30% near the bottom. The concentration in the heat storage layer is around 30% or more.

As is well known and is described in the patents incorporated by reference, the temperature profile of pond 23 will approach that of the salinity profile after a period of time. When this occurs, the water contained in heat storage layer 26 will approach 100 0 C and is capable of acting as a heat source for power plant 16.

Power plant 16 is preferably a Rankine cycle organic o fluid power plant. To this end, power plant 16 includes vaporizer 28 which receives hot brine from heat storage •layer 26 and discharges cooler brine into the storage layer 7 15 at a level consistent with the temperature of the brine.

;Vaporizer 28 contains an organic working fluid such as Ott. Freon which is vaporized by the heat exchange process that occurs in the vaporizer. The vaporized organic fluid is applied to turbine 29 of turbo-generator 30. Expansion of 20 the vaporized working fluid occurs in turbine 29 causing Sgenerator 31 to produce electricity. After expansion in turbine 29, the heat depleted working fluid is exhausted ,o into condenser 15 which rejects heat into evaporation pond 18 by reason of the operation of pump 20 and the connection of the condenser to reservoir 11 via operation of pump 13.

As shown, brackish water from reservoir 11 also provides o make-up water to solar pond 23 to account for evaporation.

Finally, regardless of the thermodynamic cycle or type of working fluid utilized in the power plant, an essential feature of the present invention lies in providing a heat engine in which heat is rejected into the pond of station 18.

In the operation of apparatus 10, solar pond 23 is operational, and a new solar pond is being constructed as indicated at 22 using the brine that is concentrated in pond 18. Brackish water from reservoir 11 is first greatly -8concentrated by reason of the operation of spray system 19 for producing concentrated brine that is used to form the heat storage layer and the halocline of the new solar pond.

The energy required to drive the various pumps is obtained at the output of generator 31 of power plant 16 which utilizes heat stored in heat storage layer 26 of the operating solar pond. The rejection of heat from condenser into evaporation pond 18 greatly enhances the operation of the evaporation process. As a consequence, the present invention provides an expeditious way to efficiently concentrate the brackish water contained in the reservoir.

The greatly reduced volume of water is disposed of in constructing further solar pond. Great quantities of brackish water are efficiently reduced in volume by the present invention. Moreover, the solar ponds so constructed can be used to generate electricity to help pay for the project. Furthermore, the concentrated brine produced by the operation of system 19 is available for use in stabilizing the halocline in operational solar ponds, such as pond 23, as described in U.S. Patent No. 4,440,148.

The advantage is improved results achieved by the method and apparatus of the present invention are apparent from the foregoing description of the invention. It should be obvious that various changes and modifications may be made without departing from the spirit and scope of the A invention as defined in the claims which follow.

Claims

1. A method for controlling the volume and salinity of liquid in a reservoir that receives brackish water comprising the steps of: a) drawing liquid from the reservoir into an evaporation pond; b) evaporating water from the liquid in the evaporation pond; c) using a solar collector to form a source of o 10 hot liquid; d) transferring heat from the hot liquid to oaar S° enhance step and on °o disposing of the concentrated brine.

2. A method according to claim 1 wherein the solar CI~O o0 15 collector is a solar pond of the type having a halocline 0 interposed between a wind-mixed layer at the surface of the pond, and a heat storage layer at the bottom of the pond, and the method includes the step of transferring heat from 0o:o0 the heat storage layer to the liquid in the evaporation 00 o o a 20 pond. @o

3. A method according to claim 2 wherein the step of evaporating water from the evaporation pond is carried out @000 S by spraying the liquid in the evaporation pond into ambient air. oPo• 25

4. A method according to claim 3 including the step of generating power using the heat storage layer of the solar pond as a heat source, and using liquid from the reservoir as a heat sink.

A method according to claim 4 wherein power is generated by vaporizing a working fluid by transferring heat in the heat storage layer to the working fluid, expanding the vaporized working fluid in a turbine to generate power and to produce heat depleted working fluid, and condensing the heat depleted working fluid into condensate using liquid in the reservoir as a heat sink.

6. A method according to claim 1 wherein the concentrated brine is disposed of by constructing a solar pond.

7. Apparatus for controlling the volume and salinity of water in a reservoir that receives brackish water, said apparatus comprising: a) an evaporation station including an evaporation pond that receives liquid from said reservoir for evaporating water and forming concentrated brine; b) a solar pond of the type having a halocline interposed between a wind-mixed layer at the surface of the pond, and a heat storage layer at the bottom of the pond for o storing heat collected by the pond; *3 c) a power plant whose heat source is the heat o contained in the heat storage layer of said solar pond, and off' 15 whose heat sink, at least in part, is said evaporation pond; and d) means for disposing of the concentrated brine produced by said evaporation pond.

8. Apparatus accordi, ig to claim 7 wherein said 0 20 evaporation station includes means for spraying liquid from a0 said evaporation pond into ambient air thereabove. 00"

9. Apparatus according to claim 8 wherein said means *tot S for spraying is constructed and arranged so that the liquid from said reservoir forms a droplet shower within which heat 25 and vapor transfers take place, and the droplets in the shower interact with the air such that practically all of the heat and vapor transfers occur under the condition that tLh. latent heat flux due to evaporation of water from the droplets is substantially equal to the sensible heat flux to the droplets from the air.

Apparatus according to claim 8 wherein said power plant operates in the Rankine cycle and includes a vaporizer responsive to brine from the heat storage layer of the solar pond for vaporizing an organic fluid, a turbo-generator responsive to vaporized working fluid produced by said vaporizer for producing power and heat depleted working d t 11 fluid, a condenser for condensing said heat depleted working fluid and producing condensate that is returned to said vaporizer, and means for cooling the condenser with liquid from the reservoir. 4

11. Apparatus according to claim 10 wherein said means for disposing of said concentrated brine is a pond.

12. Apparatus according to claim 11 wherein the pond in which said concentrated brine is disposed of is a solar pond.

13. A method for controlling the volume and salinity of water in a reservoir that receives brackish water comprises evaporating water from liquid drawn from the reservoir to form concentrated brine, utilizing S° heat from the heat storage layer of a solar pond as a source of heat for enhancing the evaporation of water from the liquid drawn from the reservoir, and disposing of the concentrated brine.

14. A method for controlling the volume and salinity of water in a 0 0 o- o 15 reservoir substantially as hereinbefore described with reference to the drawing.

15. Apparatus for controlling the volume and salinity of water in a reservoir substantially as hereinbefore described with reference to the drawing. DATED this ELEVENTH day of DECEMBER 1991 Solmat Systems Ltd. Patent Attorneys for the Applicant SPRUSON FERGUSON KNrT o(LMM/587E