U.S. patent application number 13/305542 was filed with the patent office on 2012-05-31 for systems and methods of thermal energy storage and release.
Invention is credited to Sheldon M. Jeter, Jacob H. Stephens.
Application Number | 20120132398 13/305542 |
Document ID | / |
Family ID | 46125853 |
Filed Date | 2012-05-31 |
United States Patent
Application |
20120132398 |
Kind Code |
A1 |
Jeter; Sheldon M. ; et
al. |
May 31, 2012 |
SYSTEMS AND METHODS OF THERMAL ENERGY STORAGE AND RELEASE
Abstract
Thermal energy storage systems and devices comprise at least one
storage vessel, at least one heat transfer ramp adjacent to the at
least one storage vessel, and at least one heat transfer fluid
channel adjacent to the heat transfer ramp. Heat exchange occurs
between a heat transfer medium traveling down the heat transfer
ramp and a heat transfer fluid traveling through the heat transfer
channel. The heat transfer ramp may be angled with respect to the
storage vessel such that the heat transfer medium travels down the
heat transfer ramp assisted by force of gravity.
Inventors: |
Jeter; Sheldon M.; (Atlanta,
GA) ; Stephens; Jacob H.; (Tucson, AZ) |
Family ID: |
46125853 |
Appl. No.: |
13/305542 |
Filed: |
November 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12881102 |
Sep 13, 2010 |
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13305542 |
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61241909 |
Sep 13, 2009 |
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Current U.S.
Class: |
165/104.15 |
Current CPC
Class: |
F28D 20/0056 20130101;
F28D 11/02 20130101; Y02E 60/142 20130101; Y02E 60/14 20130101 |
Class at
Publication: |
165/104.15 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Claims
1. A system of thermal energy storage and release, comprising: at
least one storage vessel; at least one heat transfer ramp adjacent
to the at least one storage vessel; and at least one heat transfer
fluid channel adjacent to the heat transfer ramp such that heat
exchange occurs between a heat transfer medium traveling down the
heat transfer ramp and a heat transfer fluid traveling through the
heat transfer channel; wherein the heat transfer ramp is angled
with respect to the storage vessel such that the heat transfer
medium travels down the heat transfer ramp assisted by force of
gravity.
2. The system of claim 1 wherein the heat transfer medium is a
granular material.
3. The system of claim 1 wherein the at least one heat transfer
ramp comprises at least two ramps in a substantially parallel
layered configuration.
4. The system of claim 3 wherein the at least one heat transfer
fluid channel is disposed between the two ramps.
5. The system of claim 1 wherein the at least one heat transfer
ramp defines at least one slot.
6. The system of claim 1 wherein the at least one heat transfer
channel is coupled to one or more of: a side surface of the heat
transfer ramp, a top surface of the heat transfer ramp, or a bottom
surface of the heat transfer ramp.
7. The system of claim 1 wherein the at least one heat transfer
ramp comprises at least two ramps in a cascading configuration.
8. The system of claim 1 wherein energy is stored as heat gathered
by, or discharged to, a concentrating solar thermal power
plant.
9. A combined heat exchange and conveyance system, comprising: a
bundled heat transfer assembly including at least two stacked heat
transfer ramps and at least one heat transfer fluid channel
adjacent to the at least two stacked heat transfer ramps; wherein a
heat transfer medium is conveyed through the heat transfer ramps
such that the heat transfer medium travels down the heat transfer
ramps assisted by force of gravity and a heat transfer fluid is
conveyed through the at least one heat transfer fluid channel such
that heat exchange occurs in the bundled heat transfer assembly
between the heat transfer medium and the heat transfer fluid.
10. The system of claim 9 wherein the heat transfer medium is a
granular material.
11. The system of claim 9 wherein the heat transfer ramps define at
least one slot such that the heat transfer medium falls through the
at least one slot in a first heat transfer ramp to a second heat
transfer ramp below the first heat transfer ramp.
12. The system of claim 9 wherein the at least one heat transfer
fluid channel is disposed between the two stacked heat transfer
ramps.
13. The system of claim 9 wherein the at least one heat transfer
channel is coupled to a bottom surface of one or more of the heat
transfer ramps.
14. The system of claim 9 wherein the at least one heat transfer
channel is coupled to a side surface of one or more of the heat
transfer ramps.
15. A thermal heat transfer device, comprising: a combined heat
exchanger and conveyor including at least one heat transfer ramp
and at least one heat transfer fluid channel adjacent to the heat
transfer ramp; wherein a granular material is conveyed through the
at least one heat transfer ramp such that the granular material
travels down the heat transfer ramp assisted by force of gravity
and a heat transfer fluid is conveyed through the at least one heat
transfer fluid channel such that heat exchange occurs between the
granular material and the heat transfer fluid.
16. The device of claim 15 wherein the granular material is
sand.
17. The device of claim 15 wherein the heat transfer channel is
angled relative to the at least one heat transfer ramp.
18. The device of claim 15 wherein the at least one heat transfer
ramp comprises at least two ramps in a substantially parallel
layered configuration and the at least one heat transfer fluid
channel is disposed between the two ramps.
19. The device of claim 15 wherein the ramps define at least one
slot such that the heat transfer medium falls through the at least
one slot in a first ramp to a second ramp below the first ramp.
20. The device of claim 15 wherein the at least one heat transfer
channel is coupled to one or more of: a bottom surface of one or
more of the heat transfer ramps, a top surface of one or more of
the heat transfer ramps, or a side surface of one more of the heat
transfer ramps.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/881,102, filed Sep. 13, 2010, which is
hereby incorporated by reference in its entirety, which claims
priority to U.S. Provisional Patent Application Ser. No.
61/241,909, filed Sep. 13, 2009, which is incorporated by reference
herein in its entirety.
FIELD
[0002] The present disclosure is in the technical field of Thermal
Energy Storage (TES).
BACKGROUND
[0003] In concentrated solar power (CSP) or similar energy systems,
heat transfer fluid (HTF) is used to convey energy from the heat
source to and/or from the energy conversion or use system. In CSP
systems, the heat source is an array of concentrating solar
collectors, and the energy conversion system is typically a heat
engine such as a steam cycle or organic Rankine cycle. In CSP
systems in particular, the functionality and, potentially, the
economic worth of the system is enhanced by thermal energy storage
(TES). The benefit of TES comes from extending the operating time
of the energy conversion system or shifting the time of energy
production to a more favorable time when energy is more
valuable.
[0004] Various TES technologies have been developed, particularly
for CSP applications, including the two-tank TES system and the
single-tank thermocline, both of which have direct and indirect
variations (referring to whether the HTF and thermal storage medium
are the same or are segregated and interfaced through a heat
exchanger). Each of these technologies has pros and cons related to
system cost effectiveness, commercial history, and operational
attributes. For example, a two-tank system using HTF with high
vapor pressure requires plants at high temperature HTFs requires
costly pressurized storage tanks. Systems with molten salt
varieties as a HTF and/or thermal storage media require specialized
tanks and heat exchanger designs. The single-tank thermocline can
be a cheaper option due to reduced capital costs, yet must consider
the same issues with the type of HTF used. In general, current TES
technologies require heat transfer fluids and thermal storage
mediums with significant cost and design implications.
[0005] The use of granular material such as sand would expand
currently available thermal energy storage medium options. However,
because sand is an abrasive solid, this requires new technical
solutions to effectively utilize the material. Thus, there is a
need for thermal energy storage systems and methods that can
effectively use inexpensive granular materials as a storage medium
and are compatible with a variety of heat transfer fluids.
SUMMARY
[0006] Embodiments of the present disclosure provide alternatives
to, and alleviate many of the disadvantages of TES systems by
providing thermal energy storage devices, systems and methods which
utilize granular materials as a thermal energy storage medium that
is compatible with a variety of HTFs. Disclosed systems include
combined heat exchange and conveyance systems in which thin layers
of granular heat transfer material are cascaded down a network of
ramps adjoined to heat transfer fluid channels such that heat
transfer occurs between the heat transfer material and the heat
transfer fluid. This thin flow is particularly advantageous because
it boosts heat transfer effects by increasing the surface area of
the heat transfer medium contacting the heat transfer fluid.
[0007] At least one heat transfer ramp is adjacent to at least one
heat transfer fluid channel, and the heat transfer ramp is angled
such that a granular material travels down assisted by force of
gravity so heat exchange occurs between the granular material and a
flow of heat transfer fluid traveling through the heat transfer
fluid channels. Any number of ramps can be stacked in parallel or
in a zig-zag configuration with heat transfer fluid channels in
between the ramps or linked to the sides of the ramps to optimize
heat transfer. Embodiments of the present disclosure effectively
use sand, a relatively inexpensive and environmentally benign
material, as a thermal storage medium while also providing heat
transfer and heat exchange capabilities. Alternative granular
materials would include any particles capable of acceptably
handling the temperature parameters in a given application, whether
it be a heating or cooling application.
[0008] Other advantages of the disclosed systems and methods
include, but are not limited to: (1) use of sand or other
inexpensive and inert granular material as the storage medium,
which is environmentally benign, inexpensive, non-volatile,
acceptable in thermal properties, (2) delivery of a constant
temperature heat from the silos since a relatively constant
temperature will be maintained in the bins irrespective of current
sand volume, (3) compatibility with a variety of HTF fluids, as the
design is adaptable to various HTFs and TES media, (4) achievement
of high "round trip thermal efficiency" since energy loss is
minimal, and (5) applicability to other CSP technology and other
thermal systems.
[0009] Exemplary embodiments of a system of thermal energy storage
and release comprise at least one storage vessel, at least one heat
transfer ramp adjacent to the at least one storage vessel, and at
least one heat transfer fluid channel adjacent to the heat transfer
ramp such that heat exchange occurs between a heat transfer medium
traveling down the heat transfer ramp and a heat transfer fluid
traveling through the heat transfer channel. The heat transfer ramp
is angled with respect to the storage vessel such that the heat
transfer medium travels down the heat transfer ramp assisted by
force of gravity. In exemplary embodiments, the heat transfer
medium is a granular material. In exemplary embodiments, the
storage vessel may be insulated to govern its contents' heat
exchange with the surrounding environment.
[0010] In exemplary embodiments, the system may further comprise a
distribution mechanism operatively connected to the heat transfer
ramp to evenly spread the granular material. The at least one ramp
could comprise at least two ramps in a substantially parallel
layered configuration or at least two ramps in a cascading
configuration. The at least one heat transfer fluid channel may be
disposed between the two ramps. In exemplary embodiments, the at
least one heat transfer channel is coupled to one or more of a side
surface of the heat transfer ramp, a top surface of the heat
transfer ramp, or a bottom surface of the heat transfer ramp. In
exemplary embodiments, the at least one ramp defines a textured or
channeled surface or defines at least one slot. The ramp could also
vibrate to assist flow of the heat transfer medium.
[0011] The at least one heat transfer fluid channel may comprise a
system of tubes or parallel plates linked to the ramps. In
exemplary embodiments, the system further comprises at least one
height adjustment mechanism operatively connected to at least one
of the at least one ramp(s) to change the flow direction of and/or
regulate the rate of flow of the heat transfer medium. The at least
one storage vessel may comprise a first and second storage vessel
and the at least one ramp comprises a first ramp removing the
granular heat transfer medium from the first storage vessel and a
second ramp delivering the heat transfer medium to the second
storage vessel. In exemplary embodiments, energy is stored as heat
gathered by, or discharged to, a concentrating solar thermal power
plant.
[0012] Exemplary embodiments include methods of storing thermal
energy comprising providing a granular material and a heat transfer
fluid. The methods include conveying the granular material through
at least one ramp angled with respect to a storage vessel such that
granular material travels down the heat transfer ramp assisted by
force of gravity and conveying the heat transfer fluid through at
least one heat transfer fluid channel such that heat exchange
occurs between the granular material and the heat transfer fluid.
The granular material may travel in overall counterflow to a flow
of heat transfer fluid, or flow could be generally concurrent or
cross-current. In exemplary embodiments, the granular material is
sand. Exemplary methods may further comprise evenly distributing
the granular material in the ramp.
[0013] In exemplary embodiments, methods further comprise adjusting
the height of at least one of the at least one ramp(s) to change
the flow direction and/or speed of the granular material. Exemplary
methods also include providing a first and second storage vessel,
removing the granular material from the first storage vessel, and
delivering the granular material to the second storage vessel.
Exemplary methods may also include releasing stored thermal energy
comprising providing a granular material and a heat transfer fluid.
The granular material is conveyed through at least one ramp angled
with respect to a storage vessel such that granular material
travels down the heat transfer ramp assisted by force of gravity.
The heat transfer fluid is conveyed through at least one heat
transfer fluid channel such that heat exchange occurs between the
granular material and the heat transfer fluid.
[0014] Exemplary embodiments include a combined heat exchange and
conveyance system comprising a bundled heat transfer assembly
including at least two stacked heat transfer ramps and at least one
heat transfer fluid channel adjacent to the at least two stacked
heat transfer ramps. A heat transfer medium is conveyed through the
heat transfer ramps such that the heat transfer medium travels down
the heat transfer ramps assisted by force of gravity, and a heat
transfer fluid is conveyed through the at least one heat transfer
fluid channel such that heat exchange occurs in the bundled heat
transfer assembly between the heat transfer medium and the heat
transfer fluid.
[0015] The heat transfer medium may be a granular material. The
heat transfer medium travels in overall counterflow to a flow of
heat transfer fluid or in overall co-current flow to a flow of heat
transfer fluid. In exemplary embodiments, the heat transfer ramps
define at least one slot such that the heat transfer medium falls
through the at least one slot in a first heat transfer ramp to a
second heat transfer ramp below the first heat transfer ramp. The
system may further comprise at least one storage vessel, wherein
the heat transfer ramps are angled with respect to the storage
vessel. The at least one heat transfer fluid channel may be
disposed between the two stacked heat transfer ramps. In exemplary
embodiments, the at least one heat transfer channel is coupled to
one or more of a side surface of the heat transfer ramp, a top
surface of the heat transfer ramp, and/or a bottom surface of the
heat transfer ramp.
[0016] In exemplary embodiments, a thermal heat transfer device is
provided comprising a combined heat exchanger and conveyor
including at least one heat transfer ramp and at least one heat
transfer fluid channel adjacent to the heat transfer ramp. A
granular material is conveyed through the at least one heat
transfer ramp such that the granular material travels down the heat
transfer ramp assisted by force of gravity, and a heat transfer
fluid is conveyed through the at least one heat transfer fluid
channel such that heat exchange occurs between the granular
material and the heat transfer fluid. In exemplary embodiments, the
granular material is sand.
[0017] The heat transfer channel may be angled in relation to the
at least one heat transfer ramp. In exemplary embodiments, the ramp
comprises at least two ramps in a substantially parallel layered
configuration, and the at least one heat transfer fluid channel may
be disposed between the two ramps. The ramps may define at least
one slot such that the heat transfer medium falls through the at
least one slot in a first ramp to a second ramp below the first
ramp. In exemplary embodiments, the ramp comprises at least two
ramps in a cascading configuration. In exemplary embodiments, the
at least one heat transfer channel is coupled to one or more of a
side surface of the heat transfer ramp, a top surface of the heat
transfer ramp, and/or a bottom surface of the heat transfer
ramp.
[0018] Exemplary embodiments include a heat exchanger that is
comprised of an Archimedes screw conveyor design to transport sand
over an internal HTF tube bundle, which contains heat transfer
fluid used to store and remove heat from the sand. In exemplary
embodiments a system of energy storage and release comprises at
least one storage vessel and a combined conveyor and heat transfer
device linked to the at least one storage vessel by at least one
discharge device. The combined conveyor and heat transfer device
includes a rotatable conveyor drum and at least one heat transfer
fluid channel within the rotatable conveyor drum. A granular
material travels from the at least one storage vessel to the
combined conveyor and heat transfer device via the at least one
discharge device. The rotatable conveyor drum moves the granular
material therethrough in counterflow to a flow of heat transfer
fluid traveling through the heat transfer fluid channel. In
exemplary embodiments the granular material is sand.
[0019] In exemplary embodiments, the rotatable conveyor drum may be
an Archimedes screw and may comprise one or more vanes fixed to an
inner surface of the drum. The one or more vanes may be spiral
shaped, longitudinally straight, substantially T-shaped or
substantially V-shaped in cross-section to distribute the granular
material over the heat transfer fluid channels. The at least one
heat transfer fluid channel may comprise a plurality of tubes
arranged in a bundle. In exemplary embodiments, when the rotatable
conveyor drum rotates the granular material pours over the at least
one heat transfer fluid channel such that heat exchange occurs
between the granular material and the heat transfer fluid. The one
or more vanes may pick up and rain the granular material over the
at least one heat transfer fluid channel.
[0020] In exemplary embodiments, the at least one storage vessel
comprises a first and second storage vessel, and the first storage
vessel has a higher temperature than the second storage vessel. The
at least one storage vessel may be located above or below ground
level and may have at least one angled wall. In exemplary
embodiments, the stored energy is heat gathered by, or discharged
to, a concentrating solar thermal power plant.
[0021] Exemplary embodiments include methods of storing thermal
energy. Exemplary methods comprise providing a granular material
and a heat transfer fluid. The heat transfer fluid has a
temperature relatively higher than a temperature of the granular
material. The granular material and the heat transfer fluid are
conveyed such that the granular material continually pours over a
tube carrying the heat transfer fluid such that heat exchange
occurs between the granular material and the heat transfer fluid. A
set of vanes may direct the pouring of the conveyed granular
material, and the granular material may be sand. The granular
material may travel in overall counterflow to a flow of heat
transfer fluid or in overall cocurrent flow to the flow of heat
transfer fluid.
[0022] Exemplary methods may further include methods of releasing
stored thermal energy comprising providing a granular material and
a heat transfer fluid. The granular material has a temperature
relatively higher than a temperature of the heat transfer fluid.
The granular material and the heat transfer fluid are conveyed such
that the granular material pours over a tube carrying the heat
transfer fluid such that heat exchange occurs between the granular
material and the heat transfer fluid. The result of this exchange
is that the granular material is cooled and the HTF is heated.
[0023] In exemplary embodiments, a combined conveyor and heat
transfer device comprises a rotatable conveyor drum and at least
one heat transfer fluid channel within the rotatable conveyor drum.
The rotatable conveyor drum moves a granular material therethrough
in counterflow to a flow of heat transfer fluid traveling through
the heat transfer fluid channel. The rotatable conveyor drum may be
an Archimedes screw. When the rotatable conveyor drum rotates, the
granular material pours over the at least one heat transfer fluid
channel such that heat exchange occurs between the granular
material and the heat transfer fluid. The rotatable conveyor drum
may be capable of rotating at one or more speeds.
[0024] Accordingly, it is seen that thermal energy storage devices,
systems and methods are provided which effectively use granular
materials as a thermal storage media while also providing heat
transfer and heat exchange capabilities. These and other features
and advantages will be appreciated from review of the following
detailed description, along with the accompanying figures in which
like reference numbers refer to like parts throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a perspective view of an embodiment of the present
disclosure, showing a thermal energy storage and release system
with above ground storage vessels containing sand thermal storage
medium;
[0026] FIG. 2 is a front view of an embodiment of a rotatable
conveyor drum containing the heat transfer tube bundle in
accordance with the present disclosure;
[0027] FIG. 3A is a side view of an embodiment of a rotatable
conveyor drum containing an embodiment of a heat transfer tube
bundle in accordance with the present disclosure;
[0028] FIG. 3B is a side view of an embodiment of a rotatable
conveyor drum containing an embodiment of a heat transfer tube
bundle in accordance with the present disclosure;
[0029] FIG. 4 is a top view of an embodiment of a supply and return
piping arrangement for a heat transfer tube bundle in accordance
with the present disclosure;
[0030] FIG. 5 is a perspective view of an embodiment of a thermal
energy storage and release system with in-ground storage vessels
containing sand thermal storage medium in accordance with the
present disclosure;
[0031] FIG. 6 is a side view of an embodiment of a thermal energy
storage and release system with in-ground storage vessels during
the thermal energy storage charging process in accordance with the
present disclosure;
[0032] FIG. 7 is a side view of an embodiment of a thermal energy
storage and release system with in-ground storage vessels during
the thermal energy discharge process in accordance with the present
disclosure;
[0033] FIG. 8 is a side view of an embodiment of a storage vessel
of a thermal energy storage and release system in accordance with
the present disclosure;
[0034] FIG. 9 is a perspective view of an embodiment of a combined
heat exchanger and conveyor in accordance with the present
disclosure;
[0035] FIG. 10A is a side view of an embodiment of an energy
storage and release system in accordance with the present
disclosure;
[0036] FIG. 10B is a side view of an embodiment of an energy
storage and release system in accordance with the present
disclosure;
[0037] FIG. 10C is a perspective view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0038] FIG. 11A is a cross-sectional view of an embodiment of a
heat transfer ramp and heat transfer channels in accordance with
the present disclosure;
[0039] FIG. 11B is a cross-sectional view of an embodiment of a
heat transfer ramp and heat transfer channels in accordance with
the present disclosure;
[0040] FIG. 11C is a cross-sectional view of an embodiment of a
heat transfer ramp and heat transfer channels in accordance with
the present disclosure;
[0041] FIG. 11D is a cross-sectional view of an embodiment of a
heat transfer ramp and heat transfer channel in accordance with the
present disclosure;
[0042] FIG. 11E is a cross-sectional view of an embodiment of a
heat transfer ramp and heat transfer channel in accordance with the
present disclosure;
[0043] FIG. 11F is a cross-sectional view of an embodiment of a
heat transfer ramp and heat transfer channel in accordance with the
present disclosure;
[0044] FIG. 12A is a perspective view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0045] FIG. 12B is a perspective view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0046] FIG. 12C is a perspective view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0047] FIG. 13A is a side view of an embodiment of an energy
storage and release system in accordance with the present
disclosure;
[0048] FIG. 13B is a perspective view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0049] FIG. 14 is a side view of an embodiment of an energy storage
and release system in accordance with the present disclosure;
[0050] FIG. 15 is a perspective view of an embodiment of an energy
storage and release system in accordance with the present
disclosure;
[0051] FIG. 16A is a perspective view of an embodiment of an energy
storage and release system in accordance with the present
disclosure;
[0052] FIG. 16B is a side view of an embodiment of an energy
storage and release system in accordance with the present
disclosure;
[0053] FIG. 17A is a top view of an embodiment of a heat transfer
ramp in accordance with the present disclosure;
[0054] FIG. 17B is a top view of an embodiment of a heat transfer
ramp in accordance with the present disclosure;
[0055] FIG. 17C is a top view of an embodiment of a heat transfer
ramp in accordance with the present disclosure;
[0056] FIG. 17D is a top view of an embodiment of a heat transfer
ramp in accordance with the present disclosure;
[0057] FIG. 17E is a top view of an embodiment of a heat transfer
ramp in accordance with the present disclosure;
[0058] FIG. 17F is a top view of an embodiment of a heat transfer
ramp in accordance with the present disclosure;
[0059] FIG. 18A is a cutaway view of view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0060] FIG. 18B is a cutaway view of view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0061] FIG. 19 is a cutaway view of view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0062] FIG. 20 is a cutaway view of view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure;
[0063] FIG. 21 is a cutaway view of view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure; and
[0064] FIG. 22 is a cutaway view of view of an embodiment of a
combined heat exchanger and conveyor in accordance with the present
disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0065] In the following paragraphs, embodiments will be described
in detail by way of example with reference to the accompanying
drawings, which are not drawn to scale, and the illustrated
components are not necessarily drawn proportionately to one
another. Throughout this description, the embodiments and examples
shown should be considered as exemplars, rather than as limitations
of the present disclosure. As used herein, the "present disclosure"
refers to any one of the embodiments described herein, and any
equivalents. Furthermore, reference to various aspects of the
disclosure throughout this document does not mean that all claimed
embodiments or methods must include the referenced aspects.
[0066] With reference to FIGS. 9-22, exemplary embodiments of
systems of storing and releasing thermal energy utilizing gravity
assisted flow of heat storage materials will now be described.
Embodiments of disclosed systems are sometimes referred to as a
"Ramp SandShifter" or "Column SandShifter." An exemplary Column
SandShifter is shown in FIG. 15 and may also include one or more
ramps. A schematic overview of an exemplary thermal energy storage
and release system 110, or Ramp SandShifter, can be seen in FIGS.
10A-B. The system 110 includes one or more storage vessels 112a,
112b, at least one of which contains a heat transfer medium 115,
which could be a granular material that functions as a thermal
energy storage medium. The heat transfer medium 115 could be sand
or any other organic or inorganic materials in granular form that
can store energy in the form of heat or might be warm and provide a
benefit from being cooled. Exemplary granular materials include
sand such as silica sand or barytes sand (barium sulfate),
partially calcined clay, glass beads, and reclaimed petroleum
catalysts. The storage vessels 112 could be situated above or below
ground, and there could be a plurality of storage vessels used as
part of the system.
[0067] The system 110 further comprises a combined heat exchanger
and conveyor 111, which includes one or more heat transfer ramps
114 located adjacent to the storage vessels 112, or linked thereto,
and extending into each storage vessel 112. The ramps 114 may be
mechanically linked to the storage vessels 112 either indirectly
through attachment to one or more vertical conveyors 116 connecting
a pair of storage vessels 112 or directly through attachment of a
first end 118 of the ramp 114 to the interior bottom 120 of a
storage vessel 112. Supporting structures 119 of various sizes may
be provided to support the ramp 114 and achieve the desired angle
of the ramp 114. Additional linkages could be provided as well, and
it should be understood that any linking of the ramps 114 to the
storage vessels 112 could be used so long as the granular material
115 can pass freely between the ramps and the storage vessels.
[0068] As best seen in FIGS. 12A-C, the combined heat exchanger and
conveyor 111 further includes one or more heat transfer fluid
channels 122 in close enough relation to the ramps 114 to allow
heat transfer between the granular material 115 acting as a thermal
energy storage medium and a heat transfer fluid (HTF) 128. More
specifically, heat is exchanged between the shared walls of the
heat transfer ramps 114 and the heat transfer fluid channels 122 so
the heat transfer medium 115 is effectively heated or cooled. Any
known HTF could be used, including oil, water, steam, molten salt,
synthetic HTFs such as Therminol VP-1, or any other fluid or gas
with which heat exchange occurs. Many configurations of heat
transfer ramps and channels can be utilized so long as the granular
material and HTF are sufficiently close to permit effective heat
transfer. Multiple heat transfer ramps 114 could be arranged in a
substantially parallel layered, or stacked, configuration. As
discussed in more detail below, the layered configuration could
comprise two or more ramps 114 in a straight stack directly on top
of each other so the sides are flush, or could be in a parallel
cascading or zig-zag arrangement.
[0069] In some embodiments, the heat transfer channels 122 are
adjacent the ramps 114 or in direct contact with the ramps 114. The
heat transfer channels 122 could be enclosed tubes, open plates or
ramps, or spaces created in between the ramps 114 when the ramps
are in a stacked configuration. For high pressure HTF applications
(e.g., steam) the heat transfer channel 122 would likely be in the
form of an enclosed pipe. For lower pressure HTF applications, the
heat transfer channel 122 would likely be open, such as a thin,
flat channel, perhaps located parallel to the ramps 114. While
rounded pipes handle higher pressures better since there are no
uneven pressures that create deformities, either form of channel
could be used in either circumstance. As shown in FIGS. 11B and
12A, the channels 122 can be coupled to the bottom surface 121 of
each ramp 114 at any location along the bottom of the ramp.
Alternately, or in addition to bottom coupling, the channels 122
could be coupled to one or more of the side surfaces 123 of the
ramp 114, as shown in FIGS. 11A and 12B.
[0070] As illustrated in FIG. 12C, instead of running parallel to
the heat transfer ramp, the heat transfer channel 122 could be
configured at an angle relative the heat transfer ramp 114 so that
HTF 128 flows longitudinally up or down at an oblique angle
relative to the latitudinal flow of heat transfer medium 115. In
some embodiments, as shown in FIG. 11F, channels 122 could be
coupled to a top surface 125 of the ramp 114. In some embodiments,
as illustrated in FIGS. 11C-D, the ramp 114 may be hollow and
define one or more tubes or passages 130 within it through which
the HTF 128 flows. Alternately, the ramps 114 and heat transfer
channels 122 may be arranged side by side with the heat transfer
channels being flat ramps similar in structure to the heat transfer
ramps 114.
[0071] In exemplary embodiments, multiple heat transfer ramps 114
are joined together in various configurations to form a network of
ramps and heat transfer channels 122. Turning to FIGS. 9, 12A-B and
14, one example is a parallel layered configuration in which at
least two heat transfer ramps 114 are stacked on top of each other.
FIGS. 18A-B show a cutaway view of a straight parallel layered
configuration. Such a system of stacked ramps 114 has, alternately,
granular material 115 flowing through a ramp 114 with HTF 128
flowing through a channel 122 coupled to the bottom 121 or side 123
of the ramp 114, then granular material 115, then HTF 128, in
succession through any number of ramps and channels. The granular
energy storage material 115 flows down each ramp 114 while HTF 128
is either pumped upwards or flows downwards through the heat
transfer channels 122, shown here as externally linked tubes 132.
As shown in FIGS. 10-11, a system of ramps could be provided in
which one or more heat transfer ramps 114 are aggregated into a
collected assembly forming a bundle 108.
[0072] Two or more parallel heat transfer ramps 114 could also be
linked in a cascading, or zig-zag, configuration. As shown in FIGS.
13A-B, the ramps 114 employed in this arrangement may be shorter
plates to reduce the amount of space needed for the thermal energy
storage and release system 110. FIGS. 19 and 20 show close up views
of the angled ramps 114, with a smooth zig zag configuration in
FIG. 20. The granular energy storage material 115 flows down the
ramps or plates 114, zig-zagging from plate to plate while HTF 128
is pumped upwards through the heat transfer channels 122, shown
here as internal tubes 130. A cascading configuration could allow
for directional adjustment as the individual plates could "toggle"
directionally relative to each other to allow for direction change
of the granular material 115 and HTF 128 without moving the entire
ramp system. Indeed, a wide range of different angles between
cascading ramps could be employed depending on the application.
FIG. 21 shows a network of cascading ramps 114 with a corrugated
fin configuration.
[0073] As described in more detail herein, heat transfer from the
energy storage medium to the HTF is achieved by gravity assisted
flow of the granular material functioning as the storage medium
down or along the surface of the ramps. To effectively utilize
gravity to move the granular material, the ramps are deployed at
various angles relative to the ground and relative to the storage
vessels. The ramp angle could be anywhere from 0.degree. to
90.degree., or perpendicular to the ground, i.e., vertically
oriented. It should also be understood that the ramps could be
fixed or could have a height adjustment mechanism 132 to elevate or
lower the respective ends of the ramp and change the flow direction
of the energy storage medium. Height adjustment mechanisms could be
any known mechanical or electronic system including motors, etc. An
example of a combined heat exchange and conveyance system 111 at a
relatively steep angle is depicted in FIG. 10C.
[0074] Turning to FIGS. 17A-F, embodiments of the heat transfer
ramp 114 could have different surface features. For instance, the
surface 134 of the ramp 114 could define channels 136 therein for
facilitating the flow of the granular material 115, and the
channels 136 may have different patterns or features. Exemplary
channels may be straight, curved or zig-zag. A textured surface is
also possible having small protrusions 138 to create the texture.
The ramp surface could, of course, be smooth and without channels.
Another contemplated ramp feature that would aid in the flow of the
granular material 115 is that the ramp could have the ability to
vibrate, as shown in FIG. 14D. Such vibrations 117 could be
achieved via a motor or electromechanical mechanisms. As shown in
FIGS. 17E-F and 22, the heat transfer ramps 114 may define one or
more slots 127 or punctures. This feature is advantageous in
parallel stacked and cascading configurations as it allows the heat
transfer medium 115 to fall through the slots 127 from one ramp 114
to the next ramp 114 below. The slots and punctures may also offer
heat transfer advantages due to the thermal storage media's contact
with their enlarged and/or angled surface area as it passes
through.
[0075] In operation, high temperature HTF 128 is pumped to the site
of the energy storage and release system 110, having been heated,
for example, by a renewable energy facility such as a concentrating
solar thermal power plant 105. Meanwhile, vertical conveyor 116,
best seen in FIG. 15, lifts and conveys a granular material 115
having a temperature cooler than that of the HTF 128 from a first
storage vessel 112a up to a top entry point of a heat transfer ramp
114. The granular material 115 is then loaded into the heat
transfer ramp 114 and, assisted by the force of gravity, flows down
the ramp toward a second storage vessel 112b. In stacked parallel
configurations, whether straight or cascading, the granular
material 115 feeds from the end of one ramp 114 into the start of
another ramp 114. In addition, the granular material 115 may flow
from the sides 123 of one ramp 114 into a ramp below, as well as
through the above-described slots 127 from ramp to ramp. The
operator could optimize the loading process and initial descent of
the granular material 115 by using a distribution mechanism 113
such as a fan, sieve, plenum, shaped outlet, or a system of
channels to spread the granular material 115 in the desired manner,
such as an even distribution, at the top of the ramp 114.
[0076] As discussed above, additional ramp features such as
channels, a textured surface, or vibrations 117, could also aid the
flow of the granular material 115. It should also be noted that the
operator of the energy storage and release system 110 could change
the orientation and angle of the heat transfer ramp 114 to optimize
flow of the granular material 115. Any ramp angle, including a
90.degree. vertical orientation could be employed. Significant
advantages of the systems described, especially the various ramp
structures, features, and layouts, are that the conveyed granular
material 15, 115 is retarded so it moves in a soft flow, reducing
abrasiveness, and as the conveyed granular material 15, 115 falls
slowly in a thin layer, it provides increased time and surface area
contact to improve heat transfer to or from the granular
material.
[0077] In exemplary embodiments, the HTF 128 flows through one or
more of the heat transfer channels 122 in counterflow, co-current
flow, or cross-current flow to the granular material 115. As
discussed above, the HTF 128 could flow through heat transfer
channels 122 which are internal tubes 130 within the ramps 114 or
externally linked tubes 132. In this way, the HTF 128 adsorbs or
gives up heat, which is transferred to the granular material 15
functioning as a thermal energy storage medium. The granular
material 115, now hot from the heat transfer, exits the heat
transfer ramp 114 into the second storage vessel 112b, where it is
stored until the thermal energy is needed.
[0078] The thermal energy storage process would be similar when
employed using other exemplary embodiments described above, such as
parallel stacked or layered configuration of heat transfer ramps
114 or a cascading configuration of shorter ramps or plates. It may
be advantageous for the granular material 115 to travel in
cocurrent flow relative to the flow of HTF 128. In such
embodiments, the HTF 128 may flow downward through the heat
transfer channels 122 as the granular material 115 flows down the
heat transfer ramps 114, as illustrated in FIG. 16. It also should
be noted that the relative flow direction of the granular material
115 and the HTF 128 could be changeable so that it is neither
cocurrent nor in counterflow, but some relative flow direction in
between. Such cross-current flow could be implemented so the
granular material 115 and HTF 128 flow in any direction relative to
the other. As mentioned above, the system operator could "toggle"
or adjust the direction of one or more of the cascading ramps 114
or plates to change the flow direction of the granular material 115
relative to that of the HTF 128.
[0079] To release the thermal energy stored in the storage medium,
the hot granular material 115 is lifted by the vertical conveyor
116 from the second storage vessel 112b up to a top entry point of
a heat transfer ramp 114. The granular material 115 is then loaded
into the heat transfer ramp 114 and flows down the ramp toward a
second storage vessel 112b, with the aid of gravity. At the same
time, HTF 128 having a temperature cooler than that of the granular
material 115 is distributed through heat transfer channels 122 and
flows in counterflow to the hot granular material 115. Thus, the
granular material 115 exchanges heat with the HTF 128 as they flow
adjacent each other. The now cooler granular material 115 reaches
the lower end point of the heat transfer ramp 114 and exits into
storage vessel 112a where it awaits another round of thermal energy
storage. The now hot HTF 128 may be used to produce usable energy
by known methods such as providing steam for a turbine. It should
be noted that any of the variations discussed above could be
employed in the energy release mode, including different relative
flow directions of the granular material 115 and HTF 128, different
ramp angles and configurations, and different heat transfer channel
arrangements.
[0080] It also should be noted that thermal energy storage and
release are not the only functions provided by disclosed systems
and methods. Heat exchange could be conducted for non-energy
storage purposes such as use of the heated granular material 115 or
HTF 128 for industrial heat or cooling or to directly provide power
in various energy generation applications.
[0081] Referring now to additional embodiments of the invention in
more detail, FIG. 1 depicts an exemplary embodiment of a thermal
energy storage system (sometimes referred to herein as a "Rotating
Drum SandShifter") that uses a very inexpensive and benign storage
medium: sand or similar granular material. Exemplary embodiments of
a sand-shifter thermal energy storage system consist of a higher
temperature above ground vessel 2 as well as a lower temperature
above-ground storage vessel 3, each filled with sand to function as
the thermal energy storage medium. The lower temperature above
ground storage vessel 3 contains only moderately warm sand that is
available to be heated and store energy, and the higher temperature
above ground storage vessel 2 contains hot sand after it has been
heated to store energy.
[0082] As shown in FIGS. 1-3B, a system of energy storage and
release 30 includes a combined conveyor and heat transfer device 40
comprising a conveyor 1, which may be an Archimedes screw conveyor
and heat transfer fluid inner heat transfer tube bundle 8. In
exemplary embodiments, the sand or similar granular material is
moved by the conveyor in a direction 35 roughly in counterflow to
the flow 38 of the heat transfer fluid 28, but cocurrent flow may
also be employed. The HTF 28 will be circulated through a heat
transfer tube bundle to contact the sand within the conveyor 1. The
heat transfer tube bundle 8 may be one of various designs including
a tube bundle of pipes, bare tubes, finned tubes, and/or plate heat
exchangers; where the design consists of the basic concept of
effectively transporting heat transfer fluid through the conveyor 1
to come into contact with the sand thermal energy storage medium.
FIG. 1 provides an illustration of how the HTF heat transfer tube
bundle 8 may be configured within the conveyor 1, which will pour
sand or similar granular material 15 over the HTF 28 to adsorb or
give up heat depending on whether the sand is being heated or
cooled. Sand or other granular material enters the conveyor 1 via
the horizontal discharge augers (or other suitable conveyor) 9, 10,
and sand is recovered to the top of the storage vessels via
vertical conveyors 6, 7.
[0083] It is understood that alternatively the granular material
might be moved between the top and the bottom of a single vessel.
It is also understood that the heat transfer tube bundle may employ
finned tubes to promote heat transfer and distribution of the
sand.
[0084] As shown in FIG. 1, when energy is being stored the lower
temperature sand is removed from the lower temperature above ground
storage vessel 3, heated by the heat transfer tube bundle 8
containing higher temperature HTF 28 from the solar collector field
4, 5 and transferred to the higher temperature above ground storage
vessel 2. When energy storage is complete, the higher temperature
above ground storage vessel 2 will be largely full of hot sand.
When stored energy is needed, hot sand will be returned to the
lower temperature above ground storage vessel 3 while stored heat
in the sand is recovered by warm outlet HTF. The practical design
shown allows free expansion and contraction of the metal parts to
account for thermal expansion.
[0085] An exemplary conveyor used to move the sand is a variation
of an Archimedes screw. The Archimedes screw is normally used as a
type of lift pump. In this case, it is used as a sand conveyor and
heat exchanger. As more specifically shown in FIGS. 2 and 3A-3B,
the Archimedes screw conveyor 1 is a rotating sand conveyor drum 11
with one or more spiral vanes 12 fixed to the inner surface of the
drum. As the drum turns, the spiral vane 12 pushes the sand 15
along the bottom of the rotating drum 11. The Archimedes screw has
no close sliding fits to achieve this pushing motion; indeed, there
is no sliding metal-to-metal contact at all. As the sand 15 is
conveyed by the spiral vane 12, a set of longitudinal straight
vanes 13 acts to simultaneously lift and convey the sand 15 over
the heat transfer tube bundle 8 containing the heat transfer fluid
(HTF) 28. By this action the HTF 28 flowing in the tubes 8 is made
to either adsorb or give up heat. As shown in FIG. 1, vertical
conveyors 6, 7 will top-load each storage vessel, and horizontal
discharge augers or other conveyors 9, 10 will unload them from
below.
[0086] The Archimedes screw sand conveyor 1 has the great advantage
that switching the direction of rotation changes the direction of
the motion of the sand. This feature makes it is easy to change the
direction of the motion of the sand as the system is switched
between the heat storage function and the heat recovery
function.
[0087] Details of the Archimedes screw conveyor 1 are shown in
FIGS. 2 and 3. The spiral vane 12 (the "screw" of the Archimedes
screw) is shown attached to the interior of a drum 11. Inside the
drum 11, is shown a heat transfer tube bundle 8 containing the HTF
28. As the drum 11 rotates, sand or other granular material 15 is
pushed along laterally by the screw spiral vane 12. An advantageous
feature is that the drum also carries a series of longitudinal
vanes 13 that pick up and rain the sand 15 over the tube bundle,
thus providing heat exchange as the sand 15 is conveyed (FIG. 3).
Note again that the Archimedes screw has no close sliding fits and
no sliding metal to metal contact at all, which is in contrast to
an auger or screw conveyor. As the HTF 28 passes through the heat
transfer tube bundle 8, the sand 15 pours over the pipes, either
charging the HTF 28 with heat from hot sand or, conversely,
charging the sand 15 with heat from the hot HTF 28. The tubes may
be equipped with longitudinal or transverse fins to increase the
outside heat-transfer area and to retard and redirect the fall of
the conveyed sand 15 providing adequate time for heat transfer to
or from the sand. In this application, the function of the tubes
and fins is analogous to the action of the so-called "fill" in a
cooling tower or packed column. The rotating drum 11 will be
insulated 14 to avoid heat losses.
[0088] Various types of extended surfaces such as longitudinal,
latitudinal, and/or corrugated fins may be used to increase the
heat transfer surface on the sand side. Furthermore, the fins may
have additional features to improve the contact between the flowing
sand and the base tubes. In addition the tubes may have elongated
or elliptical shapes to improve the contact and heat transfer with
the sand. Indeed, the preferred "tube" cross section may be more
plate like or similar to an elongated rectangular passage than a
generally circular "tube". These additional features enhance the
contact between tube and fins with the sand and heat transfer to or
from the sand may be included.
[0089] Various additional features to enhance heat transfer to or
from the sand or from the tube to the internal heat transfer fluid
may be included. In some situations, for example, it may be
advantageous for the granular material to travel in overall
cocurrent flow to the flow of internal heat transfer fluid. FIG. 3B
illustrates an exemplary embodiment in which the sand or similar
granular material 15 is moved by the conveyor in a direction 35
roughly in cocurrent flow to the flow 38 of the heat transfer fluid
28.
[0090] An overhead view of the supply and return piping, including
the heat transfer tube bundle 8 is shown in FIG. 4. The heat
transfer tube bundle 8 is integrated into the plant via inlet and
outlet large central large diameter pipes 16, 17. These pipes are
connected to the heat transfer tube bundle 8 through left and right
hand large diameter pipes 18, 19, which are in turn connected to
left and right hand plenums 20, 21. The plenums 20, 21 handle the
transfer of HTF 28 between the large diameter pipes and the heat
transfer tube bundle 8. It should be noted that the structural
outriggers support the heat transfer tube bundle and both plenums
at each end. This allows free expansion from the central support to
account for thermal expansion.
[0091] It may be further understood that the option exists for the
sand-shifter system to employ in ground storage vessels or pits as
the storage volume as opposed to above ground storage vessels. FIG.
5 shows a perspective view of the sand-shifter thermal energy
storage system with an in ground storage vessel setup. The main
difference in this system is the need for vertical conveyors 24, 25
to transport sand out of the higher temperature in ground storage
vessel 22 and lower temperature in ground storage vessel 23.
[0092] Embodiments of charging processes to store thermal energy in
the sand are shown by a side view in FIG. 6. This process will be
largely similar regardless if practiced with in ground or above
ground storage vessels. Higher temperature heat transfer fluid
inlet from the solar collector field 5 flows into the sand-shifter
system by way of an inlet large diameter supply pipe 16. Next the
hot HTF 28 flows through the left hand large diameter pipe (LHLDP)
18 into the left hand plenum (LHP) 20. In the LHP 20, hot HTF is
distributed to the heat transfer inner flow core 8, and flows to
the right in counterflow to the conveyed sand 15. The lower
temperature sand is lifted out of the lower temperature in ground
storage vessel 23 via a vertical conveyor 24 and enters the
Archimedes screw sand conveyor 1 from a horizontal discharge auger
27 or other suitable conveyor. Heat transfer fluid 28 exchanges
heat with conveyed sand 15 roughly in counterflow until it reaches
right hand plenum (RHP) 21. HTF flows are combined in the RHP 21
and directed into the right hand large diameter pipe (RHLDP) 19,
which is now used as the return pipeline. The conveyed sand 15
exits the Archimedes screw and enters storage vessel 22 view auger
26. Warm HTF in the RHLDP 19 returns to the outlet central large
diameter pipe 17 and exits the Thermal Energy Storage system.
[0093] Embodiments of Discharging Processes to release stored
thermal energy and heat the HTF are shown by a side view in FIG. 7.
Again, this process will be largely similar regardless if practiced
with in ground or above ground storage vessels. The operation of
heating the HTF 28 is accomplished by using hot sand stored in the
higher temperature in ground storage vessel 22. Warm HTF 28 flows
in by way of an inlet large diameter supply pipe 16 and then flows
in the right hand large diameter pipe (RHLDP) 19 into the right
hand plenum (RHP) 21. In the RHP 21, warm HTF 28 is distributed to
multiple pipes in the heat transfer tube bundle 8 and flows to the
left in counterflow to the conveyed sand 15. The hot sand is
conveyed 15 from the higher temperature in ground storage vessel 22
into the Archimedes screw conveyor 1 via vertical conveyor 24 and
horizontal discharge auger 26 or other suitable conveyor and
exchanges heat with the warm HTF roughly in counterflow. When the
warm sand reaches the end of the Archimedes screw conveyor 1, it is
returned to the lower temperature in ground storage vessel 23 where
it awaits the Charging Process. The now hot HTF reaches the left
hand plenum (LHP) 20 and is directed into the left hand large
diameter pipe 18, now used as the return pipeline. Hot HTF then
returns to the outlet large diameter supply pipe 17 and exits the
Thermal Energy Storage system to produce usable energy.
[0094] Turning to FIG. 8, exemplary embodiments of storage vessels
102, 103 are illustrated in greater detail. The storage vessels
102, 103 may have angled walls 132 to facilitate flow of granular
materials 15 into and out of the storage vessels during operation.
In exemplary embodiments, the wall angle may be about 30.degree. or
greater. This advantageous configuration can be employed in either
above ground or in-ground storage vessels.
[0095] In concentrator solar thermal power, embodiments of the
disclosed systems and methods are used to store heat gathered
during the day that is not needed for power generation or that is
in excess of the heat needed for power generation at some time.
This heat will be stored and used to generate power when needed,
such as during afternoon peaking periods, or during the evening and
nighttime. The basic concept of the sand shifter may be applicable
in other applications in power generation cycles, in materials
processing, or in other heating, cooling, and/or mass transfer
applications.
[0096] It should be understood that good heat transfer performance
is obtained by raining the sand 15 over a heat transfer tube bundle
8 carrying the HTF used to convey heat alternatively from the
collector field or to a power conversion plant. Ideally, heat
transfer coefficients moderately approximating the performance seen
in similarly-agitated fluidized beds will be achieved. Good heat
exchange effectiveness means close approach of the thermal storage
medium to the inlet temperature of the HTF during charging of the
storage and close approach of the HTF temperature to the maximum
temperature of the storage medium during discharge. This good
effectiveness will be obtained by heating sand or alternatively
removing heat from the sand while moving the sand to or from a
higher temperature above ground storage vessel 2 in a novel
conveyor that doubles as a counter flow heat exchanger. The counter
flow arrangement promotes high effectiveness. The sand storage
containers will be simple and inexpensive insulated silos or bins
above ground or buried pits.
[0097] Thus, it is seen that systems and methods of storing and
releasing thermal energy are provided. It should be understood that
any of the foregoing configurations and specialized components or
chemical compounds may be interchangeably used with any of the
systems of the preceding embodiments. Although illustrative
embodiments of the present invention are described hereinabove, it
will be evident to one skilled in the art that various changes and
modifications may be made therein without departing from the
invention. It is intended in the appended claims to cover all such
changes and modifications that fall within the true spirit and
scope of the invention.
* * * * *