Coupling photovoltaic and concentrated solar power technologies for desalination

Abstract

Systems and methods for the desalination of water are disclosed. 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 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; a desalination unit in fluid communication with the CSP system and in electrical communication with the PV 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 electricity from the PV 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, and in electrical communication with the PV system, where the pump station receives the desalinated water from the desalination unit, where the pump station includes a turbine driven pump and a motor 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, and driving the motor driven pump utilizing electricity from the PV system, where the desalination system is a stand-alone system and operates to produce desalinated water independent of an external electrical grid.

2. The desalination system according to claim 1, where the desalination 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 activity.

3. A method for desalination of salt water, the method comprising the steps of: concentrating solar power on a solar trough field exceeding about 700,000 sq. meters 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, where thermal energy output from the solar trough field exceeds about 240 thermal megawatts; converting, directly, solar irradiation utilizing photovoltaic (PV) cells to produce electricity in excess of about 15 megawatts; desalinating salt water using a portion of the steam obtained from the steam produced in the concentrating step and the electricity to produce desalinated water from a salt water supply by applying 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, and a separate portion of the electricity obtained from the electricity produced in the converting step, to a pump station, where the pump station receives the desalinated water and includes a turbine driven pump and a motor driven pump, where the remaining portion of the steam is sufficient to drive the turbine driven pump and the separate portion of the electricity drives the motor 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.

4. The method according to claim 3, 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.

5. The method according to claim 3, where the desalinated water is potable water.

6. The method according to claim 3, where the step of desalinating salt water comprises flashing sea water stored in multiple stages.

7. The method according to claim 3, 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.

8. The method according to claim 3, the method further comprising the step of splitting the portion of the steam into a low pressure steam stream and a medium pressure steam stream, where the low pressure steam stream is introduced in the desalinating step for thermal desalination, where a portion of the total medium pressure steam stream is introduced in the desalinating step to build sufficient vacuum used in the desalination technology, and where a remaining portion of the total medium pressure steam stream is introduced in the communicating step to drive the turbine driven pump.

9. The method according to claim 8, where the low pressure steam stream has temperature at about 120 C., pressure at about 2 bar, and steam flow rate of 330 tons per hour, and the medium pressure steam stream has temperature at about 230 C., pressure at about 18 bar, and steam flow rate of 10 tons per hour.

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.

DETAILED DESCRIPTION

(4) So that the manner in which the features and advantages of the embodiments of systems and methods for using combined PV and CSP 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.

(5) 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.

(6) 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.

(7) 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 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.

(8) 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.

(9) 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.

(10) 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 sea water 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.

(11) 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.

(12) 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.

(13) 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.

(14) 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.

(15) 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.

(16) 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 sea water 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 sea water and hence collect distillate from a condensate collector. As temperature decreases, the vacuum increases in the stages corresponding to the boiling points of sea water in order to keep the sea water 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 sea water 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.

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

(18) In the drawings and specification, there have been disclosed embodiments of systems of and methods for using combined PV and CSP 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.