GB2094813A - Energy storage system medium - Google Patents
Energy storage system medium Download PDFInfo
- Publication number
- GB2094813A GB2094813A GB8136762A GB8136762A GB2094813A GB 2094813 A GB2094813 A GB 2094813A GB 8136762 A GB8136762 A GB 8136762A GB 8136762 A GB8136762 A GB 8136762A GB 2094813 A GB2094813 A GB 2094813A
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- GB
- United Kingdom
- Prior art keywords
- potassium
- sulphate
- water
- polyethylene oxide
- sodium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 238000004146 energy storage Methods 0.000 title claims abstract description 26
- 229910001868 water Inorganic materials 0.000 claims abstract description 38
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 37
- 229920003171 Poly (ethylene oxide) Polymers 0.000 claims abstract description 35
- 150000003839 salts Chemical class 0.000 claims abstract description 25
- 238000000034 method Methods 0.000 claims abstract description 14
- 238000001879 gelation Methods 0.000 claims abstract description 13
- 235000002639 sodium chloride Nutrition 0.000 claims description 32
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 claims description 17
- 229910000406 trisodium phosphate Inorganic materials 0.000 claims description 17
- 239000001488 sodium phosphate Substances 0.000 claims description 16
- 235000019801 trisodium phosphate Nutrition 0.000 claims description 16
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 15
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 claims description 10
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims description 10
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 10
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical group [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 10
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Chemical compound [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 claims description 10
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 claims description 10
- NROKBHXJSPEDAR-UHFFFAOYSA-M potassium fluoride Chemical compound [F-].[K+] NROKBHXJSPEDAR-UHFFFAOYSA-M 0.000 claims description 10
- 238000010438 heat treatment Methods 0.000 claims description 9
- 238000012546 transfer Methods 0.000 claims description 8
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims description 6
- 239000004115 Sodium Silicate Substances 0.000 claims description 5
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 claims description 5
- 229910052943 magnesium sulfate Inorganic materials 0.000 claims description 5
- 235000019341 magnesium sulphate Nutrition 0.000 claims description 5
- 229910000027 potassium carbonate Inorganic materials 0.000 claims description 5
- 239000001103 potassium chloride Substances 0.000 claims description 5
- 235000011164 potassium chloride Nutrition 0.000 claims description 5
- 235000011118 potassium hydroxide Nutrition 0.000 claims description 5
- OTYBMLCTZGSZBG-UHFFFAOYSA-L potassium sulfate Chemical compound [K+].[K+].[O-]S([O-])(=O)=O OTYBMLCTZGSZBG-UHFFFAOYSA-L 0.000 claims description 5
- 229910052939 potassium sulfate Inorganic materials 0.000 claims description 5
- 239000001120 potassium sulphate Substances 0.000 claims description 5
- 235000011151 potassium sulphates Nutrition 0.000 claims description 5
- 239000001632 sodium acetate Substances 0.000 claims description 5
- 235000017281 sodium acetate Nutrition 0.000 claims description 5
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 5
- 235000017550 sodium carbonate Nutrition 0.000 claims description 5
- 239000011780 sodium chloride Substances 0.000 claims description 5
- 229910052911 sodium silicate Inorganic materials 0.000 claims description 5
- 239000007788 liquid Substances 0.000 claims description 4
- 235000011181 potassium carbonates Nutrition 0.000 claims description 4
- 239000011698 potassium fluoride Substances 0.000 claims description 4
- 235000003270 potassium fluoride Nutrition 0.000 claims description 4
- 235000019794 sodium silicate Nutrition 0.000 claims description 4
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 claims description 4
- 239000011686 zinc sulphate Substances 0.000 claims description 4
- 235000009529 zinc sulphate Nutrition 0.000 claims description 4
- 150000003841 chloride salts Chemical group 0.000 claims 1
- 239000000243 solution Substances 0.000 description 26
- 239000000499 gel Substances 0.000 description 22
- 238000005338 heat storage Methods 0.000 description 9
- 239000000203 mixture Substances 0.000 description 8
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 6
- 238000001816 cooling Methods 0.000 description 6
- -1 salt hydrates Chemical class 0.000 description 6
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 5
- 230000007704 transition Effects 0.000 description 5
- 239000002202 Polyethylene glycol Substances 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 230000015556 catabolic process Effects 0.000 description 4
- 238000006731 degradation reaction Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- MTHSVFCYNBDYFN-UHFFFAOYSA-N diethylene glycol Chemical compound OCCOCCO MTHSVFCYNBDYFN-UHFFFAOYSA-N 0.000 description 3
- 239000012530 fluid Substances 0.000 description 3
- 229920000642 polymer Polymers 0.000 description 3
- 229910052938 sodium sulfate Inorganic materials 0.000 description 3
- 235000011152 sodium sulphate Nutrition 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 238000013517 stratification Methods 0.000 description 3
- 239000004698 Polyethylene Substances 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- HFCSXCKLARAMIQ-UHFFFAOYSA-L disodium;sulfate;hydrate Chemical compound O.[Na+].[Na+].[O-]S([O-])(=O)=O HFCSXCKLARAMIQ-UHFFFAOYSA-L 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 150000004677 hydrates Chemical class 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 229920000573 polyethylene Polymers 0.000 description 2
- 229920001223 polyethylene glycol Polymers 0.000 description 2
- 239000011435 rock Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229920001169 thermoplastic Polymers 0.000 description 2
- 239000004416 thermosoftening plastic Substances 0.000 description 2
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 1
- 239000001828 Gelatine Substances 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 239000001110 calcium chloride Substances 0.000 description 1
- 229910001628 calcium chloride Inorganic materials 0.000 description 1
- 239000012876 carrier material Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000374 eutectic mixture Substances 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 229920000159 gelatin Polymers 0.000 description 1
- 235000019322 gelatine Nutrition 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 1
- 229910017053 inorganic salt Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910000403 monosodium phosphate Inorganic materials 0.000 description 1
- 235000019799 monosodium phosphate Nutrition 0.000 description 1
- 239000002667 nucleating agent Substances 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 235000019353 potassium silicate Nutrition 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- AJPJDKMHJJGVTQ-UHFFFAOYSA-M sodium dihydrogen phosphate Chemical compound [Na+].OP(O)([O-])=O AJPJDKMHJJGVTQ-UHFFFAOYSA-M 0.000 description 1
- FQENQNTWSFEDLI-UHFFFAOYSA-J sodium diphosphate Chemical compound [Na+].[Na+].[Na+].[Na+].[O-]P([O-])(=O)OP([O-])([O-])=O FQENQNTWSFEDLI-UHFFFAOYSA-J 0.000 description 1
- 229910000162 sodium phosphate Inorganic materials 0.000 description 1
- 235000011008 sodium phosphates Nutrition 0.000 description 1
- 229940048086 sodium pyrophosphate Drugs 0.000 description 1
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 description 1
- 235000019345 sodium thiosulphate Nutrition 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 235000019818 tetrasodium diphosphate Nutrition 0.000 description 1
- 239000001577 tetrasodium phosphonato phosphate Substances 0.000 description 1
- NCPXQVVMIXIKTN-UHFFFAOYSA-N trisodium;phosphite Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])[O-] NCPXQVVMIXIKTN-UHFFFAOYSA-N 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
- 229920003169 water-soluble polymer Polymers 0.000 description 1
- LRXTYHSAJDENHV-UHFFFAOYSA-H zinc phosphate Chemical compound [Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O LRXTYHSAJDENHV-UHFFFAOYSA-H 0.000 description 1
- 229910000165 zinc phosphate Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
- C09K5/02—Materials undergoing a change of physical state when used
- C09K5/06—Materials undergoing a change of physical state when used the change of state being from liquid to solid or vice versa
- C09K5/063—Materials absorbing or liberating heat during crystallisation; Heat storage materials
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/14—Thermal energy storage
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Combustion & Propulsion (AREA)
- Thermal Sciences (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Compositions Of Macromolecular Compounds (AREA)
Abstract
An energy storage medium that can be raised to a high energy state is disclosed which comprises a gel of polyethylene oxide, water, and a salt which causes gelation of polyethylene oxide and water at or below 90 DEG C, and method for storing energy with the medium.
Description
SPECIFICATION
Energy storage medium
The present invention relates to energy or heat storage media having high heat capacity which render them potentially useful to systems with facilities for the storage of energy or heat along with requisite heat transfer equipment.
Heat storage reservoirs are provided in cases where the amount of heat supply and heat demand differ from each other within given time periods. In many instances, the heat energy is available for a short period of time, while the heat consumption is more or less continuous. The use of solar energy for heating and for industrial processes is an example of this situation. Time unsteady industrial processes would be another.
Many different energy storage media have been used in the past. Stones, rocks, concrete blocks, bricks, gravel and the like are relatively inexpensive but have the disadvantage of a very low heat capacity. Water is one of the most commonly used media. It has a reasonably high heat capacity and good heat transfer properties. The difficulty with water is that an enormous volume of it is needed to store a reasonable amount of heat.
Metal salt hydrates or the eutectic mixture of such hydrates with other hydrates or with iongenerating compounds are also suitable as energy storage media. Examples of such energy storage substances are sodium thiosulfate or sodium phosphate when the storage media are to be used for heating purposes. Examples of storage media used for cooling purposes are sodium sulphate mixed with sodium chloride or calcium chloride and water. Crystallizing solutions have discontinuities in their cooling curves as a consequence of the change in phase from liquid to solid. Usually, during the change in phase large amounts of energy are absorbed or released and usually this phase transition occurs over a relatively narrow temperature range. Thus, the storage of energy must also take place in a narrow temperature range, usually from 25 to 50"C.
In addition, salts present severe heat transfer problems with resultant low thermodynamic efficiency in the overall storage systems in which they are used. Finally, these salts suffer greatly from cyclical losses due to stratification.
U.S. Patent No. 4,153,105 discloses the use of aqueous solutions of potassium flouride and sodium sulphate hydrate as heat storage media. In the description of prior art in such patent, salt hydrates are disclosed which include added nucleating materials which do not dissolve in the medium but which substantially increase the number of nuclei formed and also include the addition of an organic (for example, gelatine) or inorganic (for example, water-glass) colloidal carrier material which assists in finally dispersing the nucleating agents throughout the heat storage medium by solidifying the heat storage medium in the form of a gel. The patent goes on to say that gels of this kind age comparitively quickly and their thermal conductivity is very low.
The gels which are utilized in the present invention have a long life and their thermal conductivity is relatively high.
According to the present invention there is provided an energy storage medium which can be raised to a high energy state and which comprises a solution of polyethylene oxide and a salt in water which forms a gel upon heating. Typical salts which may be useful in this invention are sodium chloride, potassium chloride, sodium acetate, potassium flouride, potassium hydroxide, lithium sulphate, zinc sulphate, magnesium sulphate, potassium sulphate, sodium silicate, potassium carbonate, sodium carbonate, and trisodium phosphate, among others. Any salt which will cause gelling of polyethylene oxide in water at or below 90"C can be used in this invention.
Also in accordance with the present invention is a method for using the above energy storage medium. Such method comprises heating a solution of polyethylene oxide, water, and one of the salts described above to a temperature at or below 90or, thereby forming a gel at a high energy state. The energy (heat) stored by gelation can be released by cooling the mixture. This energy can be used in any number of applications. A major advantage of the medium of this invention is that it can be used repeatedly without suffering degradation whereas salt hydrates suffer greatly from cyclical losses due to stratification.
The present invention will be further illustrated, by way of example, with reference to the accompanying drawings. in which:
Figure 1 is a plot of the gelation temperature versus the concentration of the salt in a solution of polyethylene oxide and water for various salts; and
Figure 2 is a plot of the specific heat versus temperature. It compares the overall heat capacity of the energy storage medium of the present invention versus that of two prior art energy storage media.
An acceptable and functional energy storage medium must have the characteristics listed below. The energy storage medium of the present invention possesses these characteristics:
a) A high energy storage capacity as evidenced by a high specific heat.
b) A high specific heat over a broad temperature range.
c) High thermal conductivity so that it can absorb heat rapidly.
d) Low viscosity.
e) Low corrosivity.
f) Low vapor pressure.
g) Moderate to high density.
h) Low freezing point and high boiling point.
i) Lack of degradation at the operating conditions under which it is utilized.
We have found that an organic or inorganic salt can be added to an aqueous solution of polyethylene oxide to form a superior energy storage medium that can be raised to a high energy state. When a salt such as a trisodium phosphate is added to an aqueous solution of polyethylene oxide and the solution is heated to a temperature at or below 90"C, the solution forms a gel. The energy which was neccessary to create the gel can be released by cooling the medium. The temperature range over which gelling occurs is much broader than the usable range for any other phase change energy storage media. Because of this and the fact that the specific heat of the medium remains high over the range, the overall energy state of the energy storage medium of the present invention, as evidenced by its heat capacity, is very high.
Referring to Fig. 2, the heat capacity is the area under the curve of the plot of specific heat versus temperature. It can be seen from the area under the polyethylene oxidetrisodium phosphate curve is much greater than the areas under the water and sodium sulphate hydrate curves. Obviously then, the polyethylene oxide-trisodium phosphate gel is a much better heat storage medium than the other two known heat storage media.
As stated above, thermal conductivity is an important characteristic of a good energy storage medium. The thermal conductivity of the medium of the present invention is relatively high as indicated by a measurement of the thermal conductivity of one of the possible formulations. In this case, the thermal conductivity of a solution of 10 percent polyethylene oxide with a molecular weight of 20,000, one percent of trisodium phosphate, and 89 percent of water was determined to lie between 0.0005 calories per centimeter-seconds-degrees centigrade, the thermal conductivity of methanol, and 0.0015 calories per centimeter-seconds-degrees centigrade, the thermal conductivity of water.
The energy stored in the gel of the present invention can be removed from the gel by exposing it to a suitable temperature gradient. As the gel cools because of the transfer of heat energy via the temperature gradient, there is a phase transition in the gel from solid to liquid which releases the stored energy which is then transferred to whatever medium is causing the temperature gradient. The means for establishing temperature gradients are well-known. This cycle can be repeated many times without the medium of the present invention suffering from degradation or stratification. Several examples are provided here. First, the gel of this invention could be contained in a large storage tank of conventional design and in which is placed a heat exchanger.Preferably, this exchanger would have a high surface area (high effectiveness) on the gel side with conventional channels for the heat exchange fluid (such as water or water/glycol mixture) on the other. The so-called 'extended surface' heat exchanger is an example of such a configuration. Another method would be to encapsulate the gel in numerous relatively small containers which are suitably sealed from the environment. The heat transfer medium such as water or air would then be circulated past the exterior surfaces of these containers in a suitable fluid-tight chamber.
There are many examples of how such a storage facility could be used and two examples are provided here. First, the gel media of this invention could obviously be used in a solar-thermal facility. In the winter months, the excess solar heat collected during the day could be stored in the gel and released in the evening hours after facility heating. Another example would be the use of this gel to store low grade process waste heat during daytime operation to be released at night for facility heating.
Any salt which will cause polyethylene oxide to gel is water at or below 90"C can be used in the energy storage medium of the present invention. If a salt will only cause a gelling above 90"C, it generally is not acceptable beacuse the temperature will be too close to the boiling point of the solution resulting in a change in chemical composition and/or overpressuring of the system.
Fig. 1 shows the gelation temperature for various concentrations of various salts in a 0.5 percent by weight aqueous solution of polyethylene oxide. This graph shows that trisodium phosphate is he preferred salt for use in the present invention since it promotes gelation at lower temperatures and lower salt concentrations. Other salts which are effective in the- present invention include sodium chloride, potassium chloride, sodium acetate, potassium fluoride, potassium hydroxide, lithium sulphate, zinc phosphate, magnesium sulphate, potassium sulphate, sodium silicate, potassium carbonate, and sodium carbonate.
Polyethylene oxide is a crystalline, thermoplastic, water-soluble polymer with the general formula HOCH2(CH2OCH2)nCH20H or H(OCH2CHA,OH. The end groups are said to be hydroxyl groups in the case of the lower molecular weight species. Unlike most polymer systems, polyethylene oxide is commercially available in an extraordinarily wide range of molecular weights from ethylene glycol, diethylene glycol, and so on, up to polymers that have molecular weights many times greater than a million. The lower molecular weight members of the series with n up to about 1 30 (molecular weight from 200 to 6000) are generally known as polyethylene glycols while the higher members (molecular weight greater than 6500 up to 100,000 to several million) are known as polyethylene oxide, polyoxyethylene, or polyoxirane.
The preferred polyethylene oxide polymers for use in the present invention have a molecular weight of at least 6500 and, theoretically, there is no maximum.
The higher (polyethylene oxide) and lower (polyethylene glycol molecular weight members of this series differ sufficiently in properties as to form two classes. The lower members range from relatively viscous fluids to wax-like solids while the higher members are true thermoplastics capable of being formed into tough, molded shapes. The property differences of these two classes are due principally to large differences in molecular weight and the relatively greater importance, therefore, of the end groups in the low molecular weight class. The viscous fluids are generally unsuitable for use in this invention because they do not form gels.
The composition of the present invention is prepared by dissolving the proper amount of polyethylene oxide in a measured amount of water. This may be accomplished by any conventional method, but we have found that simply mixing the polyetnylene oxide in warm water (30"C to 70"C) is sufficient to provide the desired composition. The addition of the salt may be accomplished by simply mixing the salt with the polyethylene oxide solution.
The following non-limitative examples are given by way of illustration.
Example 1
A solution of 120 grams of water, 1.5 grams of polyethylene oxide with a molecular weight 900,000, and 0.5 grams of trisodium phosphate was made by adding the polyethylene oxide and salt water and stirring until they were dissolved. Gelation occurred below 90"C. The heat storage capacity of this solution was determined using a Differential Scanning Calorimeter. Over the temperature range of 27"C to 92"C, the solution had a heat storage capacity of about 110 calories per gram, substantially greater than that of water. Because of its initial liquid state, this material is a good heat transfer material and requires substantially less volume or weight for the same storage capacity as water.
Example 2
Three solutions were made according to the procedure of Example 1. The solutions each contained 100 grams of water and 30 grams of polyethylene oxide with a molecular weight range of 7000 to 9000. Three solutions had 0.5 grams, 1.0 gram, and 1.5 grams of trisodium phosphate, respectively. Gelation occurred below 90"C. All of t:ie solutions had a heat capacity of about 65 calories per gram over a temperature range of 32"C to 90"C, just slightly greater than that of water.
Example 3
A solution of 100 grams of water, 30 grams of polyethylene oxide with a molecular weight range of 7000 to 9000, and 3.5 grams of trisodium phosphate was made according to the method of Example 1. The heat capacity was determined to be approximately 300 calories per gram over a temperature range of 32"C to 92"C. The solution was cooled and showed a strong exothermic peak. The solution was then cycled through four additional heating and cooling cycles. In each heating, the solution went through a transition at about 55"C. Upon cooling, the transition occurred at 35"C. The heat capacity of this mixture between 32"C and 60"C is 62 calories per gram.The mixture was then cycled repeatedly for about 40 cycles over a four-day period. There was no deterioration or degradation of the solution.
Example 4
In the following example, the properties of the solution of Example 3 were compared with the properties of three known energy storage media whose thermodynamic properties were determined by conventional thermodynamic techniques. A Differential Scanning Calorimeter was used. The following table shows the results of this experiment:
Sodium PEO
Rocks Water Sulphate Soln
Usable Temp. Range ("C) Varies 0-100 25-50 25-55
Specific Heat Btu/Lb. 0.2 1.0 .55 1.9
Heat of Phase
Transition Btu/Lb. - N.A. 90 45
Heat Capacity-Btu/Lb.
(11'CRange) 4 20 101 85
Heat Capacity-Btu/Lb.
(22'CRange) 8 40 112 122
Weight Need to
Store 106 Btu, Lb. 25 X 104 5X104 1X104 8.2 X 103
Volume Needed to
Store 106 Btu, Ft3 2,150 1,000 125 150
The polethylene oxide and trisodium phosphate solution has the highest specific heat and it has a higher heat capacity in both temperature ranges than rocks or water. It also has a higher heat capacity than sodium sulphate over the broad temperature range. Furthermore, it requires the least amount of weight to store 1,000,000 Btu's per pound of energy.
Example 5
The specific heats of water, a solution of polyethylene oxide with a molecular weight of 100, 000 in water, a solution of the same polyethylene oxide and trisodium phosphate in water with and without gelation, and sodium sulphate were determined over a temperature range of 35"C to 81 C by using a Differential Scanning Calorimeter.The following table shows the results of this experiment:
No Gelation Gelation Temp('C) H20 PEO Soln PEO 8 Na3PO4 PEO a Na3PO4 Na3S203 X 5H20 35 1.0 .93 - 0.58 37 1.0 .77 1.02 0.57 39 1.0 .91 - 0.71 41 1.0 .63 .73 3.04 .6 43 1.0 .76 - 4.07 1.06 45 1.0 .73 - 4.20 2.06 47 1.0 .71 .72 4.20 3.08 49 1.0 .59 - 5.00 4.5 51 1.0 .57 - 4.65 5.6 53 1.0 .61 .75 4.30 1.0 55 1.0 .51 - 3.30 .7 57 1.0 .36 63 3.30 .6 59 1.0 .35 - 4.51 .55 61 1.0 .32 - 5.46 ' .5 63 1.0 .19 .47 5.75 .5 65 1.0 .30 - 5.71 .5 67 1.0 .27 .42 5.07 .4 69 1.0 .32 - 5.44 .5 71 1.0 .28 - 4.79 .4 73 1.0 .34 .50 4.37 75 1.0 .20 - 4.00 77 1.0 .30 .68 2.90 79 1.0 .38 - 1.09 81 1.0 .33 - 0.45
It can be seen that the solution and gel in accordance with the present invention has the highest heat capacity over the broadest temperature range of any of the five energy storage media compared in the table. Furthermore, it has a much higher specific heat than polyethylene oxide and water alone. The specific heats for trisodium phosphate were unavailable, but the International Critical Tables of Numerical Data, Physics, Chemistry and
Technology, Volume V, published by the McGraw-Hill Book Company of New York in 1 929 gives the specific heats over a temperature range of 24"C to 55"C for sodium phosphite, sodium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium pyrophosphate on page 1 24. The specific heats were given for various concentrations of these materials in water and they ranged from 0.85 to 0.98. Thus, it can be seen that there is a synergistic effect by the use of trisodium phosphate and polyethylene oxide to form a gel.
Claims (9)
1. An energy storage medium that can be raised to a high energy state, said medium comprising a solution of polyethylene oxide, water, and a salt which causes gelation of the solution when the solution is heated to a temperature at or below 90"C.
2. An energy storage medium as claimed in claim 1, wherein the salt is selected from sodium chloride, potassium chloride, sodium acetate, potassium fluoride, potassium hydroxide, lithium sulphate, zinc sulphate, magnesium sulphate, potassium sulphate, sodium silicate, potassium carbonate, sodium carbonate, and trisodium phosphate.
3. An energy storage medium as claimed in claims 1 or 2, substantially as hereinbefore described, illustrated and exemplified.
4. A method of storing energy which comprises heating a solution of polyethylene oxide, water, and a salt which causes gelation of polyethylene oxide and water to a temperature at or below 90"C, thereby forming a gel with a high energy state.
5. A method as claimed in claim 4, wherein the salt is selected from chloride, potassium chloride, sodium acetate, potassium fluoride, potassium hydroxide, lithium sulphate, zinc sulphate, magnesium sulphate, potassium sulphate, sodium silicate, potassium carbonate, sodium carbonate and trisodium phosphate.
6. A method of storing energy as claimed in claims 4 or 5, substantially as hereinbefore described, illustrated and exemplified.
7. A method of energy storage and transfer which comprises the steps of:
a) contacting a solution of polyethylene oxide, water, and a salt which causes gelation of polyethylene oxide in water with a warm medium such that the temperature of the solution is raised to at or below 90"C, thereby forming a gel with a high energy state.
b) storing the energy transferred from the warm medium in the gel for a period of time, and
c) contacting the gel with a cool medium whereby the gel goes through a phase change to liquid form and the energy stored therein is transferred to the cool medium.
8. A method as claimed in claim 7, wherein the salt is selected from sodium chloride, potassium chloride, sodium acetate, potassium fluoride, potassium hydroxide, lithium sulphate, zinc sulphate, magnesium sulphate, potassium sulphate, sodium silicate, potassium carbonate, sodium carbonate, and trisodium phosphate.
9. A method of energy storage and transfer as claimed in claims 7 or 8, substantially as hereinbefore described, illustrated and exemplified.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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GB8136762A GB2094813A (en) | 1981-12-07 | 1981-12-07 | Energy storage system medium |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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GB8136762A GB2094813A (en) | 1981-12-07 | 1981-12-07 | Energy storage system medium |
Publications (1)
Publication Number | Publication Date |
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GB2094813A true GB2094813A (en) | 1982-09-22 |
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ID=10526407
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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GB8136762A Withdrawn GB2094813A (en) | 1981-12-07 | 1981-12-07 | Energy storage system medium |
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GB (1) | GB2094813A (en) |
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1981
- 1981-12-07 GB GB8136762A patent/GB2094813A/en not_active Withdrawn
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