Patent Application
20140262739
The availability of low-cost energy storage at utility scales would address a number of issues relating to the energy grid. In particular, the deployment of renewable power generators, such as wind and solar, may be limited by a difficulty in these technologies providing a reliable supply of power at predictable times or during periods of high demand.
Energy storage systems utilizing compressed gas as a storage medium, can allow for the effective use of renewable power generators. Such energy storage systems may rely upon underground caverns for the storage of large volumes of compressed gas.
Embodiments relate to techniques for forming underground caverns, and also to desalinization processes that may be employed in conjunction therewith. Particular embodiments form a salt cavern by introducing heated water into a salt formation, followed by removal of the resulting brine to leave a salt cavern. The injected water is provided as a result of a desalinization process of the brine. Concentrated brine resulting from the desalinization process, is used to form a solar pond whose stored thermal energy provides the heat source for the injected water. The resulting underground cavern may be employed to house large volumes of materials such as pressurized natural gas, liquid hydrocarbons, or compressed gas for energy storage. Also disclosed is a particular desalinization process based upon a Regenerative Evaporative Distiller (RED) structure, which efficiently leverages low grade heat available from the solar pond, by relying primarily upon a latent heat of evaporation and condensation.
Underground caverns may be useful in storing large volumes of certain materials, such as gases. Conventionally, one technique for forming underground caverns is to introduce pressurized heated water at a depth within a naturally-occurring salt formation such as a salt dome or bedded salt deposit. The salt of the formation becomes dissolved in the water to form brine, creating a cavity. The brine may then be flowed from the cavity to form the cavern.
Such conventional approaches to underground cavern formation may offer certain drawbacks inhibiting their adoption. One potential difficulty is the consumption of energy to heat the water that is used to dissolve the salt. Often, fossil fuels are burned for this purpose, adding cost and introducing carbon into the atmosphere.
Another potential drawback of conventional approaches is the expense associated with having to drill multiple wells into the ground. Specifically a first well is used to introduce the heated water underground. A second well may be used to recover water from an aquifer, but it is also possible to use water from a river or municipal supply, or even have the water be trucked in to the site. A third well may be used to reject the waste brine, but the first well may also be used for this purpose.
Still another potential drawback associated with conventional approaches, is environmental contamination. In particular, owing to the high concentration of dissolved salt present in the extracted brine, it may have deleterious effect on plants and animals and hence must be remediated or kept segregated from the surrounding environment.
Embodiments as described herein relate to methods of forming underground caverns that obviate one or more drawbacks mentioned above. In particular, embodiments employ cavern formation in conjunction with a desalinization process driven by heat from a solar pond that is created from extracted brine. The extracted brine is subjected to a desalinization process resulting in greater concentration of salt. At the same time, the desalinization process lowers a concentration of salt in another water source.
The concentrated brine may then be flowed to a solar pond that is used to store thermal energy. Thermal energy from the solar pond may be harnessed to drive one or both of the desalinization process and/or heating of the water introduced for cavern formation.
Brine 110 containing the dissolved salts exits the cavern via a second well 112 that leads to the surface. At the surface, the brine is exposed to a desalinization process 114.
Water with low salt content may be provided to the desalinization process an initial or ongoing additional input 190. A variety of water sources can be used for this purpose, including but not limited to: aquifer wells, municipal/existing plumbing sources, rivers, and water transported in by ground (e.g. pipeline, by road).
As a result of this desalinization process, low salinity water 116 with low or negligible salt concentration is produced.
Concentrated brine 118 is also produced as a result of this desalinization process. The concentrated brine is flowed from the second well into a solar pond 120.
Solar pond 120 comprises a body of water in which low salinity water floats on top of high salinity water. As a result of the increasing salinity gradient, solar energy penetrating into the lower depths of the solar pond becomes trapped therein. The temperature gradient is in the opposite direction as the salinity gradient, and the surface of the solar pond remains cool and evaporation is minimally enhanced by the stored thermal energy.
The thermal energy 130 stored within the solar pond, is communicated (e.g. via a heat exchanger 132) to the diluted water 116 from the desalinization process, to form the heated water 106. This is the heated water that is injected into the ground for purposes of cavern formation.
Alternatively, or in conjunction with heating water for injection, the thermal energy from the solar pond could also be communicated to drive the desalinization process.
While
Another potentially useful end product of the process of
Still another potentially useful end product of the process of
Finally, it is noted that once the solution mining is completed, there will exist an underground cavern and a salt pond at the surface. This combination of elements could be used for pumped hydro energy storage.
Specifically, water flowing from the pond through a (perhaps) re-purposed drill shaft through a pump/motor operating as a motor, into the cavern, would generate power. The same device operating as a pump could send the brine back up to the pond, thereby storing power.
In such an embodiment, the pond may no longer be useful for thermal storage. Accordingly, an alternative embodiment could utilize a second cavern located at a different depth below the ground for such hydro energy storage, instead of a salt pond at the surface. Such an embodiment could be desirable if a permanent salt pond is not wanted, or if the solar pond is desired to be retained for use.
Embodiments of cavern-forming techniques as in
It is noted that the thermal energy collected and stored by solar ponds, is typically relatively low-grade in nature (e.g. <˜100° C.). To significantly exceed that temperature would create bubbling in the solar pond, disrupting the salinity gradient necessary for its operation.
Accordingly, described now in connection with the
In particular, embodiments of desalinization approaches as described herein may utilize some amount of specific heat (ΔT) transferred from the solar pond, the bulk of which drives desalinization processes which evaporate and condense water. As described below, this may be accomplished utilizing a structure referred to herein as a Regenerative Evaporative Distiller (RED).
The desalinization apparatus is demarcated into a first region I and a second region II, by the location (X=0) of a source of specific heat 203. The first region I comprises a counter-flow heat exchanger in which heat, but not mass, are configured to be transferred between the flowing liquids.
The second region II comprises the RED. In the RED, the both heat and mass are transferred between the flowing liquids. In particular, as shown in the simplified cross-section of
In some embodiments, the head space may be at substantially at the same, atmospheric or near atmospheric pressure along its entire flowing length. In particular embodiments, partitions (see
Returning to
Application of the specific heat ΔT to the brine flow A at point X=0, initiates a desalinization process.
In particular, heating of the flow A causes the evaporation of water therefrom in the RED of Region II. This evaporated water condenses in the opposite flow B in the Region II, owing to its lower temperature. Depending on the concentration of salts and dissolved minerals, the ΔT necessary to drive this net evaporation from the saline stream and distillation in the pure stream will differ, as water molecules have differing affinities for one another in the presence of certain dissolved salts and minerals.
Due to the mass transfer of water occurring in the RED, the salt content in the flow A becomes concentrated, while the water mass of flow B increases. If flow B has any salt concentration to speak of initially, it becomes further diluted. Thus in
The latent heat associated with this transfer of mass may contribute the bulk of the thermal energy transfer in region II. Here, the ratio of sensible heat capacity of the fluid to the latent heat capacity, is related directly to the fraction of evaporated water to transported water possible in each pass. The counter-flowing stream of water can be of approximately equal mass flow in to the device, as the evaporated, saline stream of water flow out of the device. Such a configuration may realize thermodynamically efficiency.
The desalinization structure of
The partitions segregating air regions of the evaporating and condensing water may be thermally insulating. The air gap can be designed to assist convection (specifically convection rising from the evaporator). The water depth in any part of the evaporator or condensor may be minimized, in order to minimize heat transfer along the water's flow direction.
While the specific embodiment of
As shown, a heat conduction structure 302 may extend to transfer heat to a portion of the corresponding opposite liquid flow located directly across therefrom. As also shown in
The particular linear layout of the distillation structure of
According to embodiments, the flow of evaporating or condensing water can be horizontal or nearly so. This contrasts with many conventional humidification/dehumidification cycles that are vertical in nature (e.g. using cooling towers, etc.) Where liquid flows are gravity fed, near-horizontal embodiments configurations are possible utilizing very shallow slopes.
It is also noted that in alternative embodiments, the counterflow heat exchanger exchanging heat from liquid to liquid, could be included in the evaporator condenser. In one embodiment 600 shown in simplified form in
That use of the stream of low or negligible salinity water (flow B) as a heat transfer medium in
Specifically, the embodiment of
Such a design calls for more circulation of water, and involves more devices. However, a benefit is that the evaporator/distiller can be made partly or solely of insulating material, and the counterflow heat exchanger can be cost effective to maintain as a separate device.
As described above, the RED device may utilize liquid flow through adjacent channels that may be of small size. Under such circumstances, flow may be inhibited by the surface tension of the liquid within the channel.
Accordingly, in order to encourage liquid flow and avoid stagnation, certain embodiments may introduce a solid wicking material to the channel. As shown in
The wick may function to promote flow according to one or more of at least four separate underlying physical mechanisms:
disruption of surface tension within the liquid;
gravity;
a siphon (also “syphon”) effect arising from a pressure differential;
capillary action.
Each of these mechanisms is now discussed in turn.
As mentioned above, the presence of the physical wick within the channel with the liquid, may disrupt surface tension that causes the water to pool. Such surface tension can play a particularly large role in inhibiting flow and low flow rates. The wick effectively breaks the surface tension of the water and prevents it from pooling.
Under a second separate mechanism, gravity can act on the liquid to move it from a first (higher) location relative to the center of the earth, relative to a second (lower) location. Such a situation may occur where the liquid inlet is at a greater height than the liquid outlet.
Under a third separate mechanism, a siphon effect may act on the liquid to move it from a first (high pressure) environment to a second (lower pressure) environment. A difference in a height of the liquid in a conduit hose drives the action. Gravity pulls on the lower part of the liquid, and all the liquid moves. Otherwise, a gap would open up, creating a vacuum, and the section of liquid that has vacuum on one side and air pressure on the other will move to close the gap. A siphon can pull a fluid in any direction, as long as it follows a pressure gradient. For example, a siphon action can pull a fluid up 1 meter, and then down 2 meters. By contrast, gravity flow is limited to moving a fluid in a downward direction.
Under a fourth separate mechanism, a wicking action and/or capillary effect may act on the liquid to move it from one location to another. This wicking action is based upon intermolecular forces between the liquid phase and the surrounding solid phase (e.g. the wick itself). In particular, the solid wick comprises a plurality of pores configured to receive the liquid and offering a large surface area to define a liquid-solid interface. Forces operating at that liquid-solid interface can operate to flow the liquid through the wick in a particular direction.
Depending upon the specific application, the wick may comprise any number of different types of porous materials. Owing to the relatively high uniformity of porosity exhibited by natural products such as cotton, wool, flax, hemp, or others, those materials may be favored to serve as wicks. However this is not required, and artificial porous materials (such as polyester or others) could alternatively be employed to perform a wicking function.
The following table lists the four different mechanisms that may operate independently to provide a liquid flow.
This table also indicates the various factors that may influence the magnitude of the liquid flow.
It is further noted that certain embodiments may dispense with separate channel(s) entirely, relying instead upon the transfer of heat and mass between liquid flows taking place through the solid wicking materials under the influence of gravity, siphon, and/or wicking action. One example of such an embodiment is shown and described in connection with
In particular,
Specifically, device 800 transfers heat and mass from a hot liquid stream 802 flowing through a first wick 804, and a cold liquid stream 806 flowing through a second wick 808.
In the device of
A solid but porous wick structure may also be useful to evenly distribute liquids at low flow rates, where pressure is not sufficient to adequately drive the liquid streams. For example, as mentioned above, sub-division of streams into low flow rates may be inhibited by surface tension.
Accordingly,
It is further noted that forces may be applied to control the thermal and mass exchange occurring between the liquid streams. For example, in certain embodiments an electric potential difference could be caused to arise between the liquid flows. In some embodiments, this potential difference could be applied from a power supply to electrodes present in the liquid flow channels. Alternatively the potential could be applied directly to the channels themselves or to wick(s) present therein, or to just the wick(s) if used without channel(s).
The resulting electric field could promote the movement of mass between the liquid flows. For example, water evaporating from a warm channel could be drawn by the field in the direction of the colder channel, thereby establishing an enhanced flow.
It is further noted that the application of a potential difference may also promote heat transfer by disrupting thermal boundary layers that can arise in the liquid. Such enhanced thermal transfer will also aid in evaporation resulting from the heating of the liquid flow.
Another possible force that could be applied to control distillation performance, is a reduction in gas pressure in the space overlying the liquid flows. In particular, imposition of reduced pressure in the head space (e.g., using a vacuum pump or other element) could promote evaporation, enhancing the rate of distillation in a manner similar to that described below in connection with
A numerical model of the RED system indicates that, for the same inlet conditions, a reduction in gas pressure increases the amount of water obtained from RED.
Physical features may also serve to control liquid flows and distillation resulting therefrom.
Physical features other than roughening may be used. One example is a crump feature used in weirs of aqueducts in order to control liquid flow. In particular,
Another example of a physical feature used for distillation, could include a step-like feature configured to control a flow rate in conjunction with gravity feed.
In particular, RED device 1200 of
Thermal and mass transfer takes place between the gravity-fed flow 1202 and a second flow 1210 moving in an opposite direction. Here, the second flow is driven by a siphon effect, but this is not required and other forces (including combinations thereof) could drive the second liquid flow. While the particular embodiment of
Physical features within the head space enclosing liquid flows, could also serve to influence the nature of the distillation process. This is shown in
Finally, it is noted that the manner of introduction of liquid for flow, may calculated to promote higher flow rates. For example,
Where the channel is narrow, surface tension may inhibit the flow rate. Such surface tension, however, may be counteracted by introducing the liquid to the reservoir (e.g. by pumping) in a direction Vp, where Vp intentionally includes a component (VX) lying along the X-axis. That component forces the liquid down the channel, thereby overcoming a resistance offered by surface tension.
Returning now to
The caverns are in selective fluid communication with one another through conduit 410 and surface compressor/expander (C/E) 420, that is in communication with a motor/generator (M/G) 430. Operation of the system of
In an energy storage mode, the motor/generator functions as a motor, driving the compressor/expander as a compressor to compress and flow gas from the large chamber for storage at high pressure in the smaller chamber. Such a storage mode could occur during off-peak hours, for example.
In an energy recovery mode, the motor/generator functions as a generator driven by the compressor/expander operating as an expander. In particular, the gas stored at high pressure in the smaller cavern is flowed through the compressor/expander, where its expansion drives the expander and results in the generation of electricity by the generator. Such an energy recovery mode could occur during peak electricity consumption hours, when electrical prices are at a premium.
In certain embodiments, gas compression and/or expansion may take place in an adiabatic manner. Such embodiments may benefit from economies of scale resulting from the compression and expansion of relatively large gas volumes (e.g. about 100 m3 to about 1,000,000 m3) to relatively low maximum pressures (e.g. about 10 atmospheres to about 300 atmospheres). Such embodiments may also benefit from the use of existing compression and expansion technologies.
Alternatively, embodiments may perform gas compression and/or expansion in a manner that is isothermal or near-isothermal. Such operation may confer enhanced efficiency according to certain thermodynamic principles.
In some embodiments, it is possible for the compressor/expander to perform in a near-isothermal manner. Incorporated by reference herein for all purposes is U.S. Patent Publication No. 2011/0115223 (“the Publication”), which is incorporated by reference in its entirety herein for all purposes. According to the Publication, gas may be compressed in the presence of liquid water as a heat exchange medium. That is, heat generated from the compression of gas is transferred across a gas-liquid boundary (e.g. fine droplets), such that the temperature experienced by the gas remains within a relatively small range over the course of the course of the compression cycle. This enhances the thermodynamic efficiency of the compression process. The transferred heat of gas compression may be retained in the heated water, and may be available for other uses.
A compressor as described in the Publication, may utilize a reciprocating or rotating moveable member for gas compression. An example of the former is a solid piston connected to a mechanical linkage comprising a piston rod and rotating shaft (e.g. crankshaft), and incorporated by reference herein for all purposes is the U.S. Patent Publication No. 2013/0098027. An example of the latter is a rotating turbine, screw, or other structure connected to a mechanical linkage comprising a rotating shaft, and incorporated by reference herein for all purposes is the U.S. Patent Publication No. 2013/0192216.
In certain embodiments as described in the Publication, liquid may be introduced directly into the compression chamber for heat exchange. In certain embodiments, liquid may be introduced to gas in a mixing chamber upstream of the compression chamber.
It is noted that the isothermal or near-isothermal compression/expansion as described in the Publication, has potential applicability to desalinization as discussed in connection with
Specifically, in the apparatus 500 of
In certain embodiments, waste heat and or heat of condensation may be recycled into the salty water to aid evaporation. Alternatively, atmospheric heat may be added to the salty water to prevent it from growing too cold. As another possible variation, air may be largely excluded from the head space.
According to still another possible variation, instead of a sealed container as a source of gas for the compressor, atmospheric air is taken in. However, before the air enters the compressor, it passes through an evaporator, which could be an evaporation pan or an evaporation tower. The evaporator both cools the air (increasing thermodynamic efficiency) and concentrates the brine.
Separation of the liquid from the compressed gas occurs in separator 550, with the resulting compressed gas being stored in storage unit 552. Storage unit 552 may be an underground cavern, and that underground cavern may be formed as a result of the process of
Large underground caverns, the formation of which has been described herein, may be used to contain a variety of materials. As described above in connection with
Underground caverns created according to embodiments may offer particular value in the storage of compressed natural gas at elevated pressure, as well as of compressed natural gas stored at supercritical pressure (hereafter referred to as “supernatural” gas). In particular, the caverns may offer a repository accommodating large quantities natural gas over the course of long- or short-term swings in market price therefor, allowing for an owner to wait until prices rise in order to recoup an initial drilling investment.
In fact, sales of futures in the natural gas that is to be initially stored within an underground cavern, could even provide the mechanism for financing the cost of constructing the cavern itself. Once the natural gas is sold, the cavern that remains could thereafter be employed at a profit for the storage of various materials (e.g. compressed air).
While the previous discussion has focused upon the storage of materials in the gas phase, embodiments are not limited to this. Underground caverns could store a variety of liquid (or even solid) materials, including but not limited to hydrocarbons and derivatives thereof.
In conclusion, it is noted that the RED embodiments shown and described in
For example, the liquid is not necessarily water.
Moreover, it is understood that the concentration being distilled away from need not necessarily be dissolved solid, but could be other fluids. Embodiments could be used in the fractional distillation of oils or alcohols. Accordingly, embodiments could be employed in the refining of petroleum products, for example.
1. A method comprising:
applying thermal energy to heat water;
introducing the heated water into a geological formation;
causing the heated water to dissolve a portion of the geological formation and form a cavern;
extracting brine from the cavern;
exposing the brine to a desalinization process to produce the water and a concentrated brine; and
forming a solar pond from the concentrated brine, wherein the thermal energy is stored in the solar pond.
2. A method as in claim 1 further comprising harvesting a dissolved mineral from the concentrated brine.
3. A method as in claim 1 wherein the desalinization process employs a Regenerative Evaporative Distiller (RED) involving mass transfer and heat transfer.
4. A method as in claim 3 wherein the desalinization process employs the RED in conjunction with a counterflow heat exchanger involving heat transfer.
5. A method as in claim 1 wherein the desalinization process creates a vacuum environment over the brine.
6. A method as in claim 1 wherein the desalinization process is driven by the thermal energy stored in the thermal pond.
7. A method as in claim 1 further comprising storing a material in the cavern.
8. A method as in claim 7 wherein the material comprises natural gas.
9. A method as in claim 7 wherein the material comprises compressed air.
10. A method as in claim 7 wherein the material comprises a hydrocarbon.
11. A method comprising:
in an energy storage phase,
storing gas in a first underground cavern at a first pressure,
compressing the gas to a second pressure higher than the first pressure, and
flowing the compressed gas to a second underground cavern; and
in an energy recovery phase occurring after the compression phase,
causing the compressed gas to expand in an expander and drive a generator, and
flowing the gas from the expander to the first underground cavern.
12. A method as in claim 11 wherein the gas comprises air.
13. A method as in claim 12 wherein the second pressure is at least 10 bar higher than the first pressure.
14. A method as in claim 12 wherein a volume of the first underground cavern is at least 2× greater than a volume of the second underground cavern.
15. A method as in claim 11 wherein at least one of the first underground cavern and the second underground cavern are formed by introducing desalinated water heated by a solar pond, into a salt formation.
16. A method as in claim 11 wherein compressing the gas comprises compressing the gas under adiabatic conditions.
17. A method as in claim 11 wherein compressing the gas comprises compressing the gas in the presence of a liquid for heat transfer.
18. A method as in claim 11 wherein the compressed gas is expanded under adiabatic conditions.
19. A method as in claim 11 wherein the compressed gas is expanded in the presence of a liquid for heat transfer.
20. A method comprising:
providing a first channel in gaseous communication with a second channel through a common head space
causing a first liquid to flow through the first channel in a first direction;
causing a second liquid to flow through the second channel in a second direction opposite to the first direction; and
applying specific heat to cause evaporation in the second channel and condensation in the first channel.
21. A method as in claim 20 wherein the specific heat is applied between:
a Regenerative Evaporative Distiller (RED) structure comprising the first and second channels and allowing both mass transfer and thermal transfer; and
a counterflow heat exchanger containing the first and second liquids and allowing only thermal transfer.
22. A method as in claim 20 wherein the specific heat is provided from a solar pond.
23. A method as in claim 20 wherein:
the first liquid comprises a first aqueous solution; and
the second liquid comprises a second aqueous solution.
24. A method as in claim 23 wherein:
the first aqueous solution comprises brine; and
the second liquid comprises a dilute aqueous solution.
25. A method as in claim 20 wherein the first liquid and/or the second liquid are flowed at least partially by gravity.
The instant nonprovisional patent application claims priority to the U.S. Provisional Patent Application No. 61/778,257, filed Mar. 12, 2013 and incorporated by reference in its entirety herein for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61778257 | Mar 2013 | US |
