Coupling photovoltaic, concentrated solar power, and wind technologies for desalination

Abstract

Systems and methods for the desalination of water. A system includes a concentrated solar power (CSP) system, the CSP system operable to concentrate solar energy to increase temperature and pressure of a heat transfer fluid and operable to produce steam utilizing heat from the heat transfer fluid; a photovoltaic (PV) system, the PV system operable to collect solar energy to produce electricity; a desalination system in fluid communication with the CSP system and in electrical communication with the PV system, the desalination system operable to produce desalinated water from a salt water source utilizing the steam from the CSP system and electricity from the PV system; and a pump station in fluid communication with the CSP system and the desalination system, and in electrical communication with the PV system, the pump station operable to transmit the desalinated water to consumers for use.

Claims

1. A land-based desalination system for desalination of salt water, the desalination system comprising: a concentrated solar power (CSP) system, where the CSP system includes a solar trough field, where the CSP system concentrates solar energy to increase temperature and pressure of a heat transfer fluid and produces steam from a steam water supply utilizing heat from the heat transfer fluid, where an area of the solar trough field exceeds about 700,000 sq. meters, where thermal energy output from the solar trough field exceeds about 240 thermal megawatts, and where the CSP system utilizes CSP technology selected from the group consisting of: a parabolic trough, a Fresnel trough, a tower central receiver, a tower distributed receiver, and combinations thereof to produce steam; a desalination unit in fluid communication with the CSP system, where the desalination unit produces desalinated water from a salt water supply utilizing a portion of the total steam produced by the CSP system, and where the desalination unit utilizes desalination technology selected from the group consisting of: multi-stage flashing (MSF), multiple effect distillation (MED), and combinations thereof; and a pump station in fluid communication with the CSP system and the desalination unit, where the pump station receives the desalinated water from the desalination unit, where the pump station includes a turbine driven pump and transmits the desalinated water to consumers by driving the turbine driven pump utilizing a remaining portion of the total steam produced by the CSP system, the remaining portion of the steam sufficient to drive the turbine driven pump, where the desalination system is a stand-alone system and operates to produce desalinated water independent of an external electrical grid.

2. The system according to claim 1, further comprising a photovoltaic (PV) system, where the PV system includes PV cells and produces electricity in excess of about 15 megawatts by directly converting solar irradiation to electricity.

3. The system according to claim 2, where the desalination system is in electrical communication with the PV system, where the desalination unit produces desalinated water from a salt water supply utilizing electricity from the PV system, where the pump station is in electrical communication with the PV system, and where the pump station includes a motor driven pump and transmits the desalinated water to consumers in part by driving the motor driven pump utilizing electricity from the PV system.

4. The system according to claim 1, further comprising a wind power generation system, where the wind power generation system includes sufficient wind turbines to produce electricity in excess of about 15 megawatts by converting wind power to electricity.

5. The system according to claim 4, further comprising a reverse osmosis (RO) water purification unit to produce desalinated water, where the desalination system, the RO water purification unit, and the pump station are in electrical communication with the wind power generation system, where the pump station includes a motor driven pump and transmits the desalinated water to consumers in part by driving the motor driven pump utilizing electricity from the wind power generation system.

6. The system according to claim 5, where the CSP system and wind power generation system are located on the same parcel of land with wind turbines intermingled amongst the CSP system.

7. The system according to claim 6, further comprising a PV system.

8. The system according to claim 5, where the RO water purification unit provides exhaust low pressure steam to the desalination unit.

9. The system according to claim 5, where the system further comprises tanks for storage of a portion of the desalinated water, the tanks operable to store a sufficient amount of desalinated water to transmit to consumers while the desalination system is inoperable during periods of substantially no solar or wind activity.

10. The system according to claim 5, where the CSP system for the RO water purification unit and the pump station further comprises a heat exchanger that produces high pressure steam at between about 1 MPa and about 10 MPa.

11. A method for desalination of salt water, the method comprising the steps of: concentrating solar power on a solar trough field to increase temperature and pressure of a heat transfer fluid and to produce steam from a steam water supply utilizing heat from the heat transfer fluid; desalinating salt water using a portion of the steam obtained from the steam produced in the concentrating step to produce desalinated water from a salt water supply by vaporizing the salt water supply in process chambers in a desalination technology selected from the group consisting of: multi-stage flashing (MSF), multiple effect distillation (MED), and combinations thereof; communicating a remaining portion of the steam obtained from the steam produced in the concentrating step to a pump station, where the pump station receives the desalinated water and includes a turbine driven pump, where the remaining portion of the steam is sufficient to drive the turbine driven pump; and pumping the desalinated water with the pump station to consumers, where the method is carried out in a stand-alone system and operates to produce desalinated water independent of an external electrical grid.

12. The method according to claim 11, where the step of concentrating solar power comprises applying concentrated solar power (CSP) technology selected from the group consisting of: a parabolic trough, a Fresnel trough, a tower central receiver, a tower distributed receiver, and combinations thereof.

13. The method according to claim 12, further comprising the step of converting wind to produce electricity in excess of about 15 megawatts.

14. The method according to claim 13, further comprising the step of converting, directly, solar irradiation utilizing photovoltaic (PV) cells to produce electricity.

15. The method according to claim 13, further comprising the step of applying reverse osmosis (RO) water purification to produce desalinated water, and further comprising the step of using the produced electricity to transport desalinated water to consumers.

16. The method according to claim 15, where the desalinated water is potable water.

17. The method according to claim 16, the method further comprising the step of storing a portion of the desalinated water, the portion of desalinated water comprising a sufficient amount of desalinated water to transmit to consumers during periods of substantially no solar activity and no wind activity.

18. The method according to claim 15, where the step of applying reverse osmosis water purification includes the use of high pressure steam at between about 1 MPa and about 10 MPa.

19. The method according to claim 15, where the step of desalinating salt water comprises the use of low pressure exhaust steam at between about 0.1 MPa to about 0.6 MPa produced from the step of applying RO water purification.

20. The method according to claim 13, where electricity produced from converting wind is used in the step of desalinating salt water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 is a process schematic for producing desalinated water in one embodiment of the present disclosure.

(3) FIG. 2 is a process schematic for producing and transporting desalinated water in one embodiment of the present disclosure.

(4) FIG. 3 is a schematic for a stand-alone (electricity grid connection free) hybrid RO/thermal (MSF/MED) desalination and pumping system powered entirely by CSP and wind technologies.

(5) FIG. 4 is a schematic for a stand-alone (electricity grid connection free) hybrid RO/thermal (MSF/MED) desalination and pumping system powered entirely by CSP and wind technologies.

DETAILED DESCRIPTION

(6) So that the manner in which the features and advantages of the embodiments of systems and methods for using PV, CSP, and wind power generation technology for salt water desalination and transport, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

(7) Referring now to FIG. 1, a process schematic is shown for producing desalinated water in one embodiment of the present disclosure. In combined CSP desalination system 100, a solar trough field 102 concentrates solar energy into a heat transfer fluid. There are four main CSP types based on the sun ray concentrating principle, and these include parabolic trough, Fresnel trough, tower central receiver, and tower distributed receiver. Any suitable type and combination of CSP trough field can be used in the embodiment of FIG. 1 as long as enough solar energy is collected to product the requisite amount of steam, described as follows. Solar energy is concentrated to heat a heat transfer fluid.

(8) One example heat transfer fluid suitable for low pressure steam generation through solar trough collectors is thermal oil, and another is direct molten salt (DMS). In some embodiments, low pressure steam has an outlet temperature and pressure at about 120 C. and 2 bar, respectively, while medium pressure steam is about 230 C. and 18 bar.

(9) For an example CSP field arrangement, there are two streams of steam. One low pressure steam stream is for desalination, and one medium pressure steam stream is used to create vacuum. Each stream consists of solar collectors in loops, and a low pressure steam stream can utilize a majority of the CSP field exceeding 100 loops when considering large-scale seawater desalination. An example CSP field has a large area, considering the solar field size can be larger than about 700,000 m.sup.2. The energy yield and nominal thermal output from the CSP side can be greater than about 240 MWt (thermal megawatts). The PV field can supply more than 15 MW direct electricity for all auxiliary power consumption in the desalination plant necessary to sustain its large-scale production. Additionally or alternatively, wind power can supply more than 15 MW direct electricity for all auxiliary power consumption in the desalination plant necessary to sustain its large-scale production.

(10) The heat transfer fluid is transported to a boiler 104 (also referred to as a steam generator) in which water is heated by the heat transfer fluid to produce steam. The heat transfer fluid, once the heat has been transferred to the water to produce steam in the boiler 104, is returned to solar trough field 102 by recycle line 105 to collect more heat/solar energy from the sun's rays. Steam produced in the boiler 104 is transferred to MSF chamber 106 to carry out multi-stage flashing. One or more steam streams at low pressure, medium pressure, or high pressure can be supplied from boiler 104 to MSF chamber 106, depending on the steam requirements of MSF chamber 106. Desalinated water is produced from multi-stage flashing.

(11) As MSF and MED processes depend largely on steam to heat and vaporize salt water in desalination chambers, CSP technology has the advantage of producing steam which can supply steam to MSF and MED processes. Solar trough field 102 is operable to increase the temperature of the heat transfer fluid to reach a high temperature and a relatively high pressure by reflecting and focusing the sunlight onto one or more tubes which contain the heat transfer fluid.

(12) For large-scale thermal desalination with MSF and MED, an incremental vacuum in the chambers is needed, as the temperature generally drops in the middle and latest chambers of the system. A vacuum enables these systems to eliminate a high boiling point and forces flashing to take place, which reduces the risk of corrosion in the system (the risk of corrosion brought about because seawater has a high total dissolved solids (TDS) count at greater than about 40,000 ppm). Implementing CSP provides the capability to generate superheated steam which is operable to drive large MSF and MED units to supply large, rural communities with fresh water. In other words, a vacuum across the desalination chambers must be created through ejectors that are supplied with medium pressure steam from the CSP field. The CSP systems disclosed here are operable to supply sufficient steam to one or more desalination units to build sufficient vacuum and operate independently of an electrical grid connection.

(13) Certain assumptions for steam temperatures, pressures, and flow rates to be used for MSF/MED vary significantly and depend on the plant capacity and location parameters (for example Direct Normal Irradiance rate). In one embodiment, low pressure steam is supplied at 120 C. and 2 bar at 330 ton/hr. In one embodiment, medium pressure steam is supplied at 230 C. and 18 bar at 10 ton/hr.

(14) Referring now to FIG. 2, a process schematic is provided for producing and transporting desalinated water in one embodiment of the present disclosure. FIG. 2 provides one embodiment of using CSP and PV technology in seawater desalination without involvement of a power generation block or connection to an electrical power grid. CSP has not been used for the sole purpose of water desalination before, as countries with high implementation of CSP technology generally do not lack water resources and availability. In combined CSP and PV desalination system 200, CSP system 202 uses solar trough field 204 to collect solar energy. The solar energy is concentrated into a heat transfer fluid to increase temperature and pressure of the heat transfer fluid. The heat transfer fluid is used to heat water and produce steam in CSP system 202.

(15) A PV system 206 collects solar energy to produce electricity. Desalination unit 208 receives steam, optionally including superheated steam, high pressure steam, medium pressure steam, or low pressure steam, from CSP system 202 and electricity from PV system 206. Desalination unit 208 can include any one of or any combination of desalination units such as MSF, MED, and RO. Desalinated water, steam, and electricity are communicated to a pump station 210. Pump station 210 can fluidly convey desalinated water to end users and consumers. FIG. 2 shows one embodiment for implementing CSP and PV technology for a large-scale water desalination plant to cope with a large increase in demand for clean water. Many countries suffer from lack of water resources and un-environmentally friendly installation of water desalination facilities using fossil fuel-fired MSF plants.

(16) Since rural areas and dry cities away from coasts struggle to fulfil their dramatic increase in water consumption, embodiments herein pump desalinated water to consumers through a pump station which is powered by solar energy. Pump station 210 depends on CSP system 202 for steam and PV system 206 for electricity in order to operate its pumps. One advantage is that no electrical grid connection is required for a stand-alone configuration in either of the desalination process or the operating pumps in order to send desalinated water to consumers. Pump station 210 can utilize steam from CSP system 202 to drive turbine driven pumps in addition to or alternative to using electricity from PV system 206 to operate motor driven pumps to send desalinated water to rural villages located very far from the coast, or other supply of salt water, with poor infrastructure.

(17) In one embodiment, the size of a CSP solar trough field can exceed about 700,000 m.sup.2 when considering a MSF/MED plant with a capacity of about 70,000 m.sup.3/day of desalinated water. The thermal energy output from the solar field is approximately 230 MWt, with a steam flow rate output of about 330 ton/hr of low pressure steam and about 10 ton/hr of medium pressure steam. The temperature and pressures of the streams are about 120 C. and 2 bar for the low pressure steam and 230 C. and 18 bar for medium pressure steam. As the amount of desalinated water produced and transported is a large quantity, in one embodiment about 70,000 m.sup.3/day, in order to determine the necessary steam flow and electricity for the pump station, one would need to consider the geographical situation (for example altitude, remoteness, mountain areas) and specific distance between the sending and receiving sides. However, as a generalization, systems and methods of the present disclosure require tons of medium pressure steam from the CSP to drive the turbine-driven pumps and a couple of megawatts of electricity from the PV system to drive motor-driven pumps.

(18) In some MSF water plants, desalination of salt water is achieved in a once-through configuration. In some embodiments herein, salt water is distilled to fresh water by flashing seawater stored in multiple stages. Such a process depends on increasing the water temperature and decreasing the pressure by building vacuum in the stages to maintain flashing of the seawater and hence collect distillate from a condensate collector. As temperature decreases, the vacuum increases in the stages corresponding to the boiling points of seawater in order to keep the seawater flashing. One source of heat in MSF is from steam passed through a heat exchanger, also known as a brine heater, which increases the temperature of the seawater pumped from the sea into the stages. In some embodiments, product water is stored in nearby tanks before pumping to customers, and blow down pumps pump any salt water back to the sea. One of ordinary skill in the art will understand other configurations will be suitable, and other process equipment such as pumps, blowers, condensers, valves, expanders, temperature and pressure meters, etc. can be required for the systems and methods of the present disclosure.

(19) FIG. 3 provides a schematic for a stand-alone (electricity grid connection free) hybrid RO/thermal (MSF/MED) desalination and pumping system powered entirely by CSP and wind power generation technologies, with no connection to an external electric grid. In stand-alone system 300, a CSP field and system 302, similar for example to CSP system 202 and solar trough field 204 from FIG. 2, generate steam, by directly heating water to steam in addition to or alternative to heating water to steam with a heat transfer fluid. Wind power generation field 304 generates electricity via one or more turbines powered by wind. CSP field and system 302 generates high pressure steam in steam line 306 for fluid communication to pump station 308 and generates high pressure steam in steam line 310 for fluid communication to RO unit 312, which includes turbine driven pumps. RO unit 312 produces fresh water, which flows via fresh water line 314 to product water tanks 316.

(20) In some embodiments, high pressure steam has a temperature range from about 220 C. to about 480 C., a pressure range from about 1 MPa to about 10 MPa, and for example systems and methods described, steam supply can range from about 20 tons/hour to about 120 tons/hour. Suitable sunlight (DNI) in some embodiments can be between about 800 kWh/m.sup.2 to about 2,500 kWh/m.sup.2, while a CSP can have a size range from about 80,000 m.sup.2 of land area to about 220,000 m.sup.2 of land area, or greater.

(21) Example RO systems can produce water at about 5,000 tons/day to about 25,000 tons/day, and example MSF/MED systems can produce between about 5,000 tons/day to about 25,000 tons/day. The provided ranges and suitable values depend on several parameters including plant configuration, equipment efficiency and size, location, elevation, ambient temperature, type of applied CSP technology (for example parabolic trough or central tower technology), and how far customers are located from the coast. Described systems and methods apply to a variety of desalination plants at different scales depending on potable water requirements.

(22) Wind power generation field 304 generates electricity, which is transmitted to RO unit 312 by electricity transmission line 318. Electricity is also transmitted in the embodiment shown to pump station 308 via electricity transmission line 320, and to MSF/MED unit 322 via electricity transmission line 324. Fresh water generated in MSF/MED unit 322, which incorporates either or both of MSF and MED, is transmitted to product water tanks 316 via fresh water line 326. Fresh water includes desalinated water, and can include potable water. As shown, RO unit 312 produces exhaust low pressure steam, which is transmitted via line 328 to MSF/MED unit 322. Pump station 308 transmits fresh water from product water tanks 316 to end users 330 a distance away from stand-alone system 300.

(23) In some embodiments for example, about 7 to about 15 wind turbines can produce about 15 to about 30 MW of power for systems of the disclosure. A suitable number of pumps for the example systems depends on the design, equipment sizes, and other parameters known to those of skill in the art. Exhaust low pressure steam in certain embodiments has a pressure from about 0.1 MPa to about 0.6 MPa and amounts to between about 20 tons/hour and about 120 tons/hour.

(24) As shown in FIG. 3, CSP field and system 302 can simultaneously provide both pump station 308 and RO unit 312 with high pressure steam, and RO unit 312 produces exhaust low pressure steam, which is transmitted via line 328 to MSF/MED unit 322.

(25) In the stand-alone hybrid desalination configuration of stand-alone system 300, there are two production streams for potable water, RO unit 312 and MSF/MED unit 322, such that potable water is continuously produced from CSP field and system 302 and wind power generation field 304. Many countries suffer from lack of water resources and the current un-environmentally friendly installation of water desalination facilities, particularly those facilities with large production, such as, conventional thermal and RO plants. Stand-alone approaches, such as that shown in FIG. 3, are suitable for domestic implementation and industrial implementation, for example to desalinate seawater and ship it to industrial cities located away from the coast or brackish water sources.

(26) Since rural areas and dry cities located far distances away from coasts struggle to fulfil increases in water demand, example systems and methods disclosed here for pumping desalinated, for example potable, water over long distances to consumers through a pump station powered by solar and wind energy have many advantages. As shown, pump station 308 applies electricity from wind power generation field 304 and high pressure steam from CSP field and system 302 to operate.

(27) One advantage of example systems and methods is that grid connections are not required for stand-alone configurations, for either the desalination processes or operating large pumps necessary to send desalinated water to consumers. Electricity from one or more wind turbines in wind power generation field 304 is applied to operate motor driven pumps, while high pressure steam from the CSP field and system 302 is applied to operate turbine driven pumps. The pumps are used to at least send water to consumers, for example rural villages located far from the coast with poor infrastructure.

(28) In addition, another advantage of systems and methods described here is to reduce and optimize plant land size by replacing photovoltaic fields with wind turbines to supply electricity. Wind turbines can be distributed within a CSP field. For example, in other embodiments a CSP field and system, such as CSP field and system 302, can be combined with a wind power generation field, such as wind power generation field 304, on the same plot of land with wind turbines intermingled amongst solar collectors. Moreover, wind turbines enhance overall performance of stand-alone system 300, since wind intensity proximate a coastal region is higher, and thus would strengthen the desalination unit reliability. In addition, in either the embodiments of FIG. 3 or 4, in certain other embodiments a PV system such as for example PV system 206 of FIG. 2 can be applied with wind power generation and/or CSP to directly collect solar energy to produce electricity, for example for meters, motor-drive pumps, and/or auxiliary systems.

(29) In CSP field and system 302, a heat transfer fluid delivers heat captured from solar collectors to a heat exchanger, which functions as a steam generator to produce high pressure steam from water. Then, high pressure steam is directed and distributed to first and second pass trains in RO unit 312 to drive its turbine-driven pumps. Afterward, RO unit 312 produces exhaust low pressure steam, which is transmitted via line 328 to MSF/MED unit 322, which has chambers to heat and vaporise the seawater to obtain desalinated water via thermal processes.

(30) Wind power generation field 304 supports certain electrical equipment and some motor-driven pumps across the desalination processes of stand-alone system 300. In other words, CSP field and system 302 generates high pressure steam for RO unit 312 and steam generally for MSF/MED unit 322, while wind energy via wind power generation field 304 supplies electricity for intake and circulating pumps, and to operate auxiliary systems, for example auxiliary pumping systems, and meters or valves.

(31) FIG. 4 is a schematic for a stand-alone (electricity grid connection free) hybrid RO/thermal (MSF/MED) desalination and pumping system powered entirely by CSP and wind technologies. In stand-alone system 400, solar trough field 402 collects solar energy to heat a heat transfer fluid for transport via flow line 404 to CSP system 406. CSP system 406 produces high pressure steam for transport in line 408 to solar pump station 410, and for transport in line 412 to RO system 414. Exhaust steam (low pressure steam) from RO system 414 is provided via line 416 to MSF/MED system 418, which includes either or both of an MSF or MED system.

(32) Wind generation system 420, which includes one or more wind turbines, provides electricity via line 422 to RO system 414 and provides electricity via line 424 to MSF/MED system 418. Desalinated water from RO system 414 is provided via line 426 to solar pump station 410, and desalinated water from MSF/MED system 418 is provided via line 428 to solar pump station 410. Solar pump station 410 uses steam turbine driven pumps in the embodiment shown to transfer desalinated, optionally potable, water to end users via water line 430.

(33) RO includes desalination technology used to purify water using a semi-permeable membrane. It applies in part an osmosis phenomena, where the normal osmosis process is the movement of solvent naturally from low solute concentration into high solute concentration through a membrane until both sides are balanced. In RO water desalination, pressure is applied to seawater such that the pure solvent water becomes pure water after going through a semi-permeable membrane, with the salt or any particulates and ions being left behind on the membrane. In other words, pure water is concentrated. High pressure pumps are generally required for RO processes.

(34) An example RO process can include the steps described as follows. (1) Intake and pre-treatment, where a seawater supply is filtered (with a filter size up to about 5 microns), optionally with chemical dosing such as, for example, acid (H.sub.2SO.sub.4), coagulant (FeCl.sub.3), sodium bisulphate, and anti-scalant. Filtration and chemical dosing help maintain the pH level within about a range of about pH 6.9 to about pH 7.5. (2) The RO process itself, where a first pass and second pass occurs, and each unit in the first pass comprises a high pressure pump, for example at about 70 bar, membrane vessels, membrane elements, energy recovery exchangers and a booster pump. The second pass is similar to the first pass, but with lower pressure to filter the product water of first pass further. The second pass includes, for example, a medium pressure pump of about 17 bar, membrane vessels, and membrane elements. (3) Waste water treatment, where the waste water is back-washed from the media filter which is used in the pre-treatment of the seawater.

(35) With respect to MSF, certain MSF water plants used to desalinate seawater work in a once-through configuration. Seawater can be distilled by flashing the seawater stored in multiple stages. The process increases the water temperature and decreases pressure by building vacuum in stages to maintain flashing the seawater, and hence collect the distillate from the condensate collector. As temperature decreases, the vacuum increases in the stages corresponding to the boiling points of seawater in order to keep the seawater flashing.

(36) One source of the heat in MSF includes steam from a heat exchanger known as a brine heater, which increases the seawater temperature pumped from the sea into the stages. Product desalinated, optionally potable, water is stored in nearby tanks before pumping water to customers, and blow down pumps pump high mineral concentration water back to the sea. The process of pumping in some embodiments requires some electricity, for pumping and auxiliaries, for instance, and for control and metering systems. Such electricity can be provided by wind or solar power.

(37) Systems and methods of the present disclosure for stand-alone desalination systems provide environmentally efficient systems for the desalination of water without additional greenhouse gas emissions.

(38) The singular forms a, an, and the include plural referents, unless the context clearly dictates otherwise.

(39) In the drawings and specification, there have been disclosed embodiments of systems of and methods for using combined PV, CSP, and wind power generation technology for salt water desalination and transport, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.