SYSTEM AND METHOD FOR DESALINATION OF WATER USING A GRAPHITE FOAM MATERIAL
A condenser or heat exchanger includes a circulation system for moving a cooling fluid, and a graphite foam in thermal communication with the circulation system. The condenser or heat exchanger can be used to remove water, or more particularly freshwater from water vapor or steam produced from seawater.
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This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/568,605, filed on Dec. 8, 2011, which is incorporated by reference herein.
TECHNICAL FIELDVarious embodiments described herein relate to a system and method for desalination of water using a graphite foam material. The system and method includes the use of heat to produce steam from seawater and condensation of the steam to produce a source of freshwater for human consumption.
BACKGROUNDAn increase in worldwide population has led to the increase in demand for freshwater for human consumption and irrigation. Over 99% of the world's freshwater comes from tapping a diminishing source of the world's rivers, lakes, and groundwater locations that are becoming less dependable as some are reaching maximum capacities. With only 1% of the world's water supply available for human use in a constantly expanding worldwide population, clean water is becoming the most important commodity in water-stressed regions. The increase in demand for freshwater has been most evident in dry areas where rainwater is scarce and groundwater sources are drying up such as: the Middle East, Australia, and the American West and Southwest, to name a few.
Clean water is necessary for irrigation in arid regions where occupants rely on importing most of their food because agriculture is too expensive or not possible. Although clean water is basic utility in water-rich and developed regions, the arid and less developed regions of the world do not have access to clean water.
Most of the earth's surface, about 71%, is covered with water. However, most of the water is in saltwater oceans. Of course, salt water is unfit for human consumption. Water can be desalinated. The two most common options for water production include non-thermal/pressure/membrane processes, and thermal processes. The non-thermal/pressure/membrane processes include reverse osmosis (RO), filtration, sludge, and the like. The thermal processes include multi-stage flash (MSF) evaporation, multi-effect distillation (MED), and low-temp thermal desalination (LTTD). Generally, water treatment and desalination methods require capital intensive equipment and facilities that become more expensive in regions that are arid and underdeveloped. In addition, the thermal processes require energy which is also expensive. Large amounts of energy are necessary for both operation and sustainment of a multi-stage flash evaporation plant or a multi-effect distillation plant. The energy and cost requirements many times eliminate these types of plants as desalination solutions unless there is a source of waste heat near the site. Increasing the efficiency would bring down the cost of operation. In addition, reducing the capital expenditures would also add the MSF and MED solutions to other desalination solutions. Adding additional desalination solutions reduces the chances that people resort to drinking water from polluted sources. Consumption of polluted water affects the health of approximately 1.2 billion people and contributes to 5 million deaths each year from water-related diseases such as cholera, schistosomiasis, and malaria.
The MSF and MED plants generally have a condenser which is used to condense or distill water from the water vapor in the MSF or MED device. Condensers used for MSF and MED plants generally employ shell and tube technology. Expensive materials, such as copper, nickel, aluminum brass, stainless steel and titanium, are also used in these plants. These materials drive up the capital expenditure associated with an MSF or MED plant and also may price such a plant so that it is no longer a choice for a desalination solution.
In operation, cool or cold seawater is pumped through the stages 110, 112, 114. Cold seawater is pumped through the heat exchanges 310, 312, 314 which transfers heat to the incoming water en route to the brine heater 124. The cold water is heated while some of the flashed or evaporated water is condensed out on the heat exchanger surfaces of the heat exchangers 310, 312, 314. When the MSF plant 100 is operating in steady state, feed water or the seawater at the cold inlet temperature flows, or is pumped, through the heat exchangers 310, 312, 314 in the stages 110, 112, 114 and warms up during each stage. When the seawater reaches the brine heater 124 at the hot end, it already has a raised temperature making the heat transfer more efficient. At the brine heater 124, an amount of additional heat is added. After the brine heater 124, the seawater/brine mixture flows through valves back into the stages 114, 112, 110 which each have progressively higher salinity, lower pressure and temperature. As the seawater or brine flows back through the stages the fluid mixture is now called brine, to distinguish it from the inlet seawater. In each stage, as the brine enters, its temperature is above the boiling point at the pressure of the stage, and a small fraction of the brine water boils (“flashes”) to steam thereby reducing the temperature until a liquid-vapor equilibrium state is reached. The resulting steam is warmer than the feed water in the heat exchanger. The steam cools and condenses against the heat exchanger 310, 312, 314 heat transfer surfaces, thereby heating the feed water as described earlier.
The total evaporation in all the stages 110, 112, 114 can be up to approximately 15% of the seawater flowing through the system, depending on the range of temperatures used. It should be noted that three stages are shown and there may be more or less stages for a particular MSF plant. With increasing temperature in the stages, there are growing difficulties of scale formation and corrosion. A maximum appears to be 120° C., although scale avoidance may require temperatures below 70° C.
The feed water carries away the latent heat of the condensed steam, maintaining the low temperature of the stage. The pressure in the chamber remains constant as equal amounts of steam are formed when new warm brine enters the stage and steam is removed as it condenses on the tubes of the heat exchanger. The equilibrium is steady state, because if at some point more vapor forms, the pressure increases and that reduces evaporation and increases condensation.
In the final stage the brine and the condensate have a temperature near the inlet temperature. Then the brine and condensate are pumped out from the low pressure in the stage 110 to the ambient pressure. The brine and condensate still carry a small amount of heat that is lost from the system when they are discharged. The heat that was added in the heater makes up for this loss.
The heat added in the brine heater 124 usually comes in the form of hot steam from an industrial process co-located with the desalination plant. The steam is allowed to condense against tubes carrying the brine on the shell-side of a conventional shell and tube heat exchanger (similar to the stages).
MSF distillation plants, especially large ones, are often paired with power plants in a cogeneration configuration. Waste heat from the power plant is used to heat the seawater, providing cooling for the power plant at the same time. This reduces the energy needed by one-half to two-thirds, which drastically alters the economics of the plant, since energy is by far the largest operating cost of MSF plants.
The graphite foam material is a material having highly ordered graphitic ligaments and is as thermally conductive as bulk aluminum, at 20% the weight. Graphite foam is dimensionally stable and has a low coefficient of thermal expansion (˜2-4 in/° C.). Graphite foam also is open porous, absorbs sound, and reflects or scatters RF/EMI/EMP. Thus, graphite foam is a lightweight thermal management material that enables designers to manage multiple aspects of a design problem with one material. It is believed that this material has many applications and will lead to radically new concepts in thermal, acoustic, RF/EMI signature management. Potential applications for the graphite foam material include power electronics cooling where a ten-fold increase in cooling potential over traditional heat sinks has been demonstrated. Other uses include transpiration/evaporative cooling for electronics and leading edges. The graphite material can also be used in radiators for all types of vehicles, such as heavy vehicles, racing vehicles, aircraft, fuel cell vehicles, and space vehicles. The material can be used to shield EMI (electromagnetic interference), and for thermal and acoustic signature management. Still another application is for batteries and battery cooling.
Turning back to
This process is repeated in a series of cells or effects 410, 412, 414 (thus the name Multiple Effect Distillation).
The condenser 500 is a highly efficient Graphite Foam Heat Exchanger (GFHX) using a hybrid heat exchanger (HX) in a shell & plate-fin configuration. The condenser 500 includes a first tubesheet 550 and a second tubesheet 552. The first tubesheet 550 includes openings for various tubes that will be attached to the openings.
Similarly, the second tubesheet 552 includes openings for various tubes that will be attached to the openings. The first tubesheet 550 corresponds to one end of a tube and the second tubesheet 552 corresponds to the other end of the tube attached between the first tubesheet 550 and the second tubesheet 552. Graphite foam surrounds the tubes between the two plates. The graphite foam is in thermal communication with the tubes as shown in
A structure 570 formed by the first tubesheet 550 and the second tubesheet 552, the tubes and the graphite material is placed in a shell 530. The shell 530 has a seawater inlet 532 at one end and a seawater outlet 542 at the other end. The shell 530 also has a steam inlet 534 and a condensate outlet 544 Water that is condensed on the graphite foam passes out outlet opening 544 of the shell 530. It should be noted that the shell 530 can be made of any material. In low pressure systems, the shell does not have to be a pressure vessel and can be made out of less expensive materials, such as fiberglass. Of course, the structure 570 must include a substructure to fit tightly to the shell 530, in one embodiment, so as to prevent a bypass condition where the incoming steam does not pass over the tubes, such as tubes 510, 512, 514, in the structure 570.
This has been a detailed description of some exemplary embodiments of the invention(s) contained within the disclosed subject matter. Such invention(s) may be referred to, individually and/or collectively, herein by the term “invention” merely for convenience and without intending to limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. The detailed description refers to the accompanying drawings that form a part hereof and which shows by way of illustration, but not of limitation, some specific embodiments of the invention, including a preferred embodiment. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to understand and implement the inventive subject matter. Other embodiments may be utilized and changes may be made without departing from the scope of the inventive subject matter. Thus, although specific embodiments have been illustrated and described herein, any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.
Claims
1. A vapor-fin heat exchanger comprising:
- aluminum multi-hollow extruded (MHE) tubes; and
- graphite foam thermally coupled to an exterior surface of the tubes.
2. The vapor-fin heat exchanger of claim 1 wherein a cooling fluid is moved through the tubes and water vapor condenses on the graphite foam.
3. The vapor-fin heat exchanger of claim 2 in use of thermal and non-thermal condensation of water for irrigation or drinking.
4. The vapor-fin heat exchanger of claim 1 used for flash evaporation in a multi-stage flash evaporation system.
5. The vapor-fin heat exchanger of claim 4 used to enhance distallation in a multi-effect distillation evaporation system.
6. The vapor-fin heat exchanger of claim 1 housed within a fiberglass shell.
7. The vapor-fin heat exchanger of claim 1 wherein the graphite foam has machined channels therein for increasing the surface area of the graphite foam.
8. The vapor-fin heat exchanger of claim 1 wherein the graphite foam has machined channels therein for fluid management.
9. The vapor-fin heat exchanger of claim 1 wherein the graphite foam is bonded to substantially round condenser tubes with thermally conductive adhesive, soldering, or brazing.
10. The vapor-fin heat exchanger of claim 1 wherein the graphite foam is bonded to substantially flat condenser tubes with thermally conductive adhesive, soldering, or brazing.
11. The vapor-fin heat exchanger of claim 1 wherein the graphite foam is used with a metallic foams to enhance heat transfer.
12. A vapor-fin heat exchanger comprising:
- an aluminum multi-hollow extruded (MHE) set of tubes; and
- graphite foam bonded on an exterior surface of the set of tubes; and
- a cooling fluid from a refrigeration cycle being moved through the set of tubes so that water condenses on the graphite foam and exterior surface to produce water for irrigation or drinking.
13. The vapor-fin heat exchanger of claim 12 within a flash evaporation system.
14. The vapor-fin heat exchanger of claim 12 within a distillation evaporation system.
15. The vapor-fin heat exchanger of claim 12 wherein, the vapor-fin heat exchanger is substantially horizontally in operation.
16. The vapor-fin heat exchanger of claim 12 wherein the vapor-fin heat exchanger is substantially vertically in operation.
17. The vapor-fin heat exchanger of claim 12 further comprising a polymer, the graphite foam including a polymer coating on the heat transfer surfaces.
18. The vapor-fin heat exchanger of claim 12 further comprising a polymer, the graphite foam can be bonded to heat transfer surfaces using the polymers and non-polymeric coatings.
19. The vapor-fin heat exchanger of claim 12 further comprising a plastic tube for carrying a cooling fluid, the graphite foam can be bonded to plastic tube using using polymeric, non-polymeric, or thermally conductive epoxy.
20. The vapor-fin heat exchanger of claim 12 further comprising a Diamond Like Carbon (DLC) coating on the graphite foam.
- A Closed Cycle Ocean Thermal Energy Conversion system which expends cold sea water, the system further comprising a flash evaporization system to produce low pressure steam, the system further comprising a heat exchanger that uses a portion of the system's expended deep sea cold water to produce fresh water for irrigation or drinking.
Type: Application
Filed: Dec 7, 2012
Publication Date: Jun 13, 2013
Applicant: LOCKHEED MARTIN CORPORATION (Bethesda, MD)
Inventor: LOCKHEED MARTIN CORPORATION (Bethesda, MD)
Application Number: 13/708,457
International Classification: F28F 21/08 (20060101);