U.S. patent application number 13/926920 was filed with the patent office on 2013-12-26 for liquid metal thermal storage system and method.
The applicant listed for this patent is Thermaphase Energy Inc.. Invention is credited to K. Russell Carrington, Arlon J. Hunt.
Application Number | 20130340432 13/926920 |
Document ID | / |
Family ID | 49773244 |
Filed Date | 2013-12-26 |
United States Patent
Application |
20130340432 |
Kind Code |
A1 |
Hunt; Arlon J. ; et
al. |
December 26, 2013 |
LIQUID METAL THERMAL STORAGE SYSTEM AND METHOD
Abstract
Embodiments of the invention relate to systems and methods for
storing thermal energy from working fluid heated by a
high-temperature heat source and retrieving the thermal energy. The
heated working fluid is in thermal communication with heat
exchanger elements that can efficiently store thermal energy by,
for example, phase change in one or more metal alloys.
Inventors: |
Hunt; Arlon J.; (El Cerrito,
CA) ; Carrington; K. Russell; (San Francisco,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thermaphase Energy Inc. |
El Cerrito |
CA |
US |
|
|
Family ID: |
49773244 |
Appl. No.: |
13/926920 |
Filed: |
June 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61664643 |
Jun 26, 2012 |
|
|
|
Current U.S.
Class: |
60/643 |
Current CPC
Class: |
F01K 3/00 20130101 |
Class at
Publication: |
60/643 |
International
Class: |
F01K 3/00 20060101
F01K003/00 |
Claims
1. A system for storing and retrieving thermal energy from a fluid
heated by a high temperature source comprising: a chamber
containing heat exchanger elements, wherein the heated fluid is
passed through the chamber containing the heat exchanger elements,
which heat exchanger elements are in thermal communication with one
or more metal alloys that melt at a specific temperature between
about 577.degree. C. and 1414.degree. C. to store thermal energy;
and wherein a fluid to be heated is passed through said chamber
where the one or more metal alloys give up the thermal energy
stored.
2. A system for storing and retrieving thermal energy from a fluid
heated by a high temperature source comprising: a first chamber
containing one or more metal alloys that melt at a specific
temperature between about 577.degree. C. and 1414.degree. C. to
store thermal energy; a second chamber that is adapted to accept a
fluid that is heated by the high temperature source, said second
chamber in thermal communication with the first chamber; and a
third chamber this is adapted to accept a fluid that is to be
heated by the first chamber, said third chamber in thermal
communication with the first chamber.
3. A method using the system of claim 1.
4. A power generation plant that uses the system of claim 1 as a
source of energy.
5. A power generation plant that uses the system of claim 1 as an
alternative source of energy when a primary source of energy is
unavailable.
6. The system of claim 1 wherein said heat exchanger elements have
a plurality of compartments with each compartment having one or
more metal alloys that melt at a different specific
temperature.
7. The system of claim 2 wherein said first chamber has a plurality
of compartments, with each compartment having one or more metal
alloys that melt at a different specific temperature.
8. The system of claim 1 wherein the heat exchanger elements have a
plurality of compartments, with each successive compartment having
a higher specific temperature at which the one or more metal alloys
melt.
9. The system of claim 2 wherein the first chamber has a plurality
of compartments, with each successive compartment having a higher
specific temperature at which the metal alloys melt.
10. A method using the system of claim 2.
11. A power generation plant that uses the system of claim 2 as a
source of energy.
12. A power generation plant that uses the system of claim 2 as an
alternative source of energy when a primary source of energy is
unavailable.
Description
PRIORITY CLAIM
[0001] This application claims the benefit of priority to U.S.
Provisional Patent Application No. 61/664,643 filed Jun. 26, 2012
entitled "LIQUID METAL THERMAL STORAGE SYSTEM AND METHOD" which
application is incorporated herein in its entirety.
FIELD OF THE INVENTION
[0002] Embodiments of the present invention relate to systems and
methods for storing thermal energy.
BACKGROUND OF THE INVENTION
[0003] Market dynamics and government regulations are leading to
the development and deployment of next-generation energy
technologies that are more cost-competitive, efficient, and
sustainable than their predecessors. In particular, thermal
transport and conversion play an important role in more than 90% of
energy technologies, and there is opportunity to improve power
generation, delivery, and consumption by developing thermal
technologies.
[0004] For example, concentrated solar power (CSP), a
thermal-electrical conversion technology, is promising for power
plants because of its potential to meet cost, efficiency, and
sustainability targets. CSP uses solar collectors (e.g.,
heliostats, parabolic troughs, linear Fresnel reflectors, etc.) to
concentrate sunlight on solar receivers. The solar receivers
contain working fluids (e.g., steam, oil, liquid salt, liquid
alkali metal, gas, etc.) to collect and transfer heat to operate
thermodynamic cycle engines (e.g., Rankine, Brayton, Stirling,
etc.). The engines provide mechanical power to generators for
emissions-free, utility-scale electricity generation.
[0005] There are four primary arrangements of solar collectors,
solar receivers, and thermodynamic cycle engines in CSP power
plants: Fresnel, parabolic trough, parabolic dish, and power tower.
Fresnel, parabolic trough, and parabolic dish arrangements are
generally considered low-temperature CSP as their operating
temperatures are restricted to approximately 450.degree. C. for
Fresnel and parabolic trough, and approximately 750.degree. C. for
parabolic dish. In contrast, power tower arrangements enable higher
operating temperatures because their solar collectors and receivers
are more scalable. Power tower arrangements use dual-axis solar
collectors that track the sun and reflect sunlight onto one or more
central solar receivers atop towers. The working fluid from the
solar receivers flows through piping to operate thermodynamic cycle
engines that are typically located at ground level.
[0006] Thermal energy storage (TES) is beneficial to CSP and other
next-generation thermal technologies. Utilities generally require
that CSP and other power plants provide dispatchable power on the
order of 75% of the year. The sun is only above the horizon for 50%
of the year on average, so CSP needs TES to meet the utilities'
requirement by producing and storing excess thermal energy when the
sun is shining, and converting it into electricity when the sun is
below the horizon or obscured (e.g., by clouds). Some sources
indicate TES can increase CSP capital utilization from
approximately 30% to 60%.
[0007] TES can be accomplished by storing energy as sensible heat
or latent heat (or some combination thereof). There are two primary
implementations of sensible heat storage in CSP. In the first
implementation, the sensible heat of the working fluid is used to
collect, transfer, and store heat. The working fluid can be stored
in separate hot and cold tanks, or by using a thermocline
configuration, in which a single tank has a colder, denser bottom
layer and a hotter, less dense upper layer. In the second
implementation, the sensible heat of the working fluid is
transferred to a separate and distinct TES system that stores
energy as sensible heat. Oil and liquid salts are common in
sensible heat TES systems employed in CSP power plants.
[0008] Latent heat storage is distinct from sensible heat storage
because it does not result in temperature change, and is
experienced through phase change such as solidification/melting and
condensation/vaporization. There are two fundamental advantages of
latent heat storage relative to sensible heat storage, particularly
for CSP. The first advantage is that latent heat storage is an
isothermal process. Isothermal energy storage results in a working
fluid at near constant temperature with which to operate
thermodynamic cycle engines at optimum conditions. The second
advantage is that latent heat stores significantly more energy than
sensible heat per unit of storage medium. The amount of energy
stored as specific heat is determined by the product of the
specific heat and the temperature change. For example, the specific
heat of water is 1 cal/g-.degree. C. so one gram of water releases
1 calorie of heat if the temperature is lowered by 1.degree. C. By
comparison, the latent heat of fusion (i.e., solidification) of
water is approximately 80 cal/g. Therefore, sensible heat storage
at quasi-isothermal conditions (i.e., 1.degree. C. temperature
change) near 0.degree. C. requires eighty-fold more water than
latent heat storage.
[0009] The current state-of-the-art TES systems in CSP power plants
based on a power tower arrangement use sensible heat storage in
liquid salts, which poses several challenges. First, sensible heat
capacities of liquid salts are relatively low compared to latent
heats of metals and metal alloys. For example, the specific heat
capacity of sodium and potassium nitrate mixtures, known as solar
salts, is approximately 0.35 cal/g-.degree. C.; in contrast, the
latent heat of fusion of silicon is approximately 430 cal/g.
Therefore over one thousand-fold more liquid salt is required to
store the same amount of energy at quasi-isothermal conditions
(i.e., 1.degree. C. temperature change) as silicon. Second, liquid
salts have relatively poor heat transfer properties compared to
metals and metal alloys: the thermal conductivity of solar salts is
on the order of 1 W/m-.degree. C. versus 237 W/m-.degree. C. for
aluminum. In addition, solidification of solar salts around heat
exchangers inhibits natural convection, which further deteriorates
heat transfer.
[0010] The operating temperatures of TES systems (and downstream
thermodynamic cycle engines) are also important to CSP and other
next-generation thermal technologies because they directly affect
conversion efficiency. Carnot's theorem states that the maximum
efficiency of a heat engine is determined by the temperature
difference of the hot and cold reservoirs between which it
operates. Operating TES systems at the highest temperature possible
results in maximum efficiency because ambient air is typically the
cold reservoir and its temperature is not easily controlled. The
TES systems based on liquid salts or oils described above are
impractical at high temperatures. Energy storage in working fluid
(e.g., steam, supercritical CO.sub.2, air, etc.) at high
temperatures is difficult because of very high pressures, and oils
and solar salts break down at approximately 400.degree. C. and
570.degree. C., respectively, although some fluoride salts are
stable between approximately 350.degree. C. and 850.degree. C. New
high-temperature TES systems are beneficial to utilizing
thermodynamic cycle engines with operating temperatures in excess
of 575.degree. C. (e.g., supercritical H.sub.2O, CO.sub.2 Rankine,
Brayton, etc.) for CSP and other next-generation thermal
technologies.
INCORPORATION BY REFERENCE
[0011] The following references are incorporated herein by
reference in their entireties: [0012] U.S. Provisional Application
No. 61/276,269, filed Sep. 10, 2009, by Arlon J. Hunt, entitled
"Liquid Metal Thermal Storage System"; [0013] U.S. patent
application Ser. No. 12/878,896, filed Sep. 9, 2010, by Arlon J.
Hunt, entitled "Liquid Metal Thermal Storage System"; [0014] U.S.
Pat. No. 4,512,388, issued Apr. 23, 1985, by Terry D. Claar et al.,
entitled "High-Temperature Direct-Contact Thermal Energy Storage
Using Phase-Change Media"; [0015] Simensen "Comments on the
Solubility of Carbon in Molten Aluminum" Metallurgical Transactions
A Vol. 20A January 1989, p. 191; [0016] Winter, Sizmann, @
Vant-Hull, Solar Power Plants, Chapter 6, Springer, Verlag 1991;
[0017] Guthy and Makhlouf "The aluminum-silicon eutectic reaction:
mechanisms and crystallography" Journal of Light Metals Vol. 1, No.
4, November 2001, pp. 199-218. [0018] Department of Energy Advanced
Research Projects Agency-ENERGY (DoE ARPA-E)--HEATS Funding
Opportunity Announcement (issued Apr. 20, 2011, retrieved Jul. 2,
2011) [0019] Metallurgical Transactions A Volume 15A, March
1984-467 [0020] Metals Handbook, 8th ed. (American Society for
Metals, Metals Park, Ohio, 1973), Vol. 8, p. 263 [0021] Energy
Conyers. Manag., 47 (2006), 2211
SUMMARY OF THE INVENTION
[0022] Embodiments of the system and method of the invention
include a system and a method for storing and retrieving thermal
energy from a working fluid heated by a high-temperature heat
source. The system comprises an insulated channel containing heat
exchanger elements, wherein the high-temperature working fluid is
passed through the channel containing the heat exchanger elements
that are in thermal communication with one or more metal alloys
that melt at specific temperatures between approximately
577.degree. C. and 1414.degree. C. to store thermal energy; and
wherein a working fluid to be heated is passed through said channel
where the thermal energy stored is given up by the metal
alloy(s).
[0023] Other embodiments include a system for storing and
retrieving thermal energy from a working fluid heated by a
high-temperature heat source comprising: first heat exchanger
elements containing one or more metal alloys that melt at specific
temperatures between approximately 577.degree. C. and 1414.degree.
C. to store thermal energy; a second insulated channel that is
adapted to accept a working fluid that is heated by the
high-temperature heat source, with said second channel in thermal
communication with the first heat exchanger elements; and a third
insulated channel that is adapted to accept a fluid to be heated by
the first heat exchanger elements, with said third channel in
thermal communication with the first heat exchanger elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The foregoing, forthcoming, and other aspects will be
readily appreciated by the skilled artisan from the following
descriptions of the preferred embodiments of the invention when
read in conjunction with the accompanying drawings.
[0025] FIG. 1a is a schematic side view illustration of the
parallel tube array for the pressurized TES embodiment of the
invention.
[0026] FIG. 1b is a schematic top view illustration of the parallel
tube array for the pressurized TES embodiment of the invention.
[0027] FIG. 1c is a schematic cross-section view illustration of
the parallel tube array for the pressurized TES embodiment of the
invention.
[0028] FIG. 2a is a schematic side view illustration of the
perpendicular tube array for the pressurized TES embodiment of the
invention.
[0029] FIG. 2b is a schematic top view illustration of the
perpendicular tube array for the pressurized TES embodiment of the
invention.
[0030] FIG. 2c is a schematic cross-section view illustration of
the perpendicular tube array for the pressurized TES embodiment of
the invention.
[0031] FIG. 3a is a schematic side view illustration of the pebble
bed array for the pressurized TES embodiment of the invention.
[0032] FIG. 3b is a schematic top view illustration of the pebble
bed array for the pressurized TES embodiment of the invention.
[0033] FIG. 3c is a schematic cross-section view illustration of
the pebble vessel bed array for the pressurized TES embodiment of
the invention.
[0034] FIG. 4a is a schematic perspective view illustration of
sample axial fins on vessels in the form of tubes of an embodiment
of the invention.
[0035] FIG. 4b is an end view illustration of sample axial fins on
vessels in the form of tubes of an embodiment of the invention.
[0036] FIG. 4c is a schematic perspective view illustration of
sample radial fins on vessels in the form of tubes of an embodiment
of the invention.
[0037] FIG. 5a is a schematic side view illustration of a planar
configuration for the unpressurized TES embodiment of the
invention.
[0038] FIG. 5b is a schematic cut-away perspective view
illustration of a concentric configuration for the unpressurized
TES embodiment of the invention with high-temperature working fluid
inside the TES annulus.
[0039] FIG. 5c is a schematic cut-away perspective view
illustration of a concentric configuration for the unpressurized
TES embodiment of the invention with high-temperature working fluid
outside the TES annulus.
[0040] FIG. 5d is a schematic side view illustration of sealed
hollow tube containing a relatively small amount of working fluid
in the unpressurized TES embodiment of the invention.
[0041] FIG. 5e is a schematic side view illustration of a planar
configuration for the electrical unpressurized TES embodiment of
the invention.
[0042] FIG. 5f is a schematic cut-away perspective view
illustration of a concentric configuration for the electrical
unpressurized TES embodiment of the invention with high-temperature
working fluid inside the TES annulus.
[0043] FIG. 5g is a schematic cut-away perspective view
illustration of a concentric configuration for the electrical
unpressurized TES embodiment of the invention with high-temperature
working fluid outside the TES annulus.
[0044] FIG. 6a is a schematic side view illustration of a ceramic
or superalloy vessel in an embodiment of the invention.
[0045] FIG. 6b is a schematic side view illustration of a clad
graphite or vitreous carbon vessel in an embodiment of the
invention.
[0046] FIG. 7a is a schematic perspective view illustration of a
vessel of an embodiment of the invention during charging; the
vessel is in the form of a tube, oriented parallel to flow, and
divided into compartments of cascading Al/Si metal alloy
composition.
[0047] FIG. 7b is a schematic perspective view illustration of a
vessel of an embodiment of the invention during charging; the
vessel is in the form of a tube, oriented parallel to flow, and
divided into compartments of cascading Al/Si metal alloy
composition.
[0048] FIG. 7c is similar to FIG. 5a with the vessel provided with
compartments.
[0049] FIG. 8a shows a schematic illustration of a CSP power plant
based on a power tower arrangement.
[0050] FIG. 8b shows the components in a CSP power plant based on a
power tower arrangement incorporating an embodiment of the
invention.
[0051] FIG. 8c shows the flow of working fluid during TES charging
for an embodiment of the invention in a CSP power plant based on a
power tower arrangement.
[0052] FIG. 8d shows the flow of working fluid during TES
discharging for an embodiment of the invention in a CSP power plant
based on a power tower arrangement using an upcomer.
[0053] FIG. 8e shows the flow of working fluid during TES
discharging for an embodiment of the invention in a CSP power plant
based on a power tower arrangement using a bypass.
[0054] FIG. 9a shows a schematic side view illustration of an
embodiment of the invention supported by a horizontal section in a
CSP power plant based on a power tower arrangement.
[0055] FIG. 9b shows a schematic cross-section view illustration of
an embodiment of the invention supported by struts in a CSP power
plant based on a power tower arrangement.
[0056] FIG. 10a shows a schematic illustration of the pressurized
TES embodiment of the invention in a wind or hydro power plant.
[0057] FIG. 10b shows a schematic illustration of the electrical
pressurized TES embodiment of the invention in a wind or hydro
power plant.
[0058] FIG. 11 is an equilibrium phase diagram for pure
aluminum-silicon metal alloys.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0059] The invention is illustrated, by way of example and not by
way of limitation, in the figures of the accompanying drawings in
which like references indicate similar elements. References to
embodiments in this disclosure are not necessarily to the same
embodiment, and such references mean at least one. While specific
embodiments are discussed, it is understood that this is done for
illustrative purposes only. A person skilled in the relevant art
will recognize that other components and configurations may be used
without departing from the scope and spirit of the invention.
[0060] In the following description, numerous specific details will
be set forth to provide a thorough description of the invention.
However, it will be apparent to those skilled in the art that the
invention and embodiments thereof may be practiced without these
specific details. In other instances, well-known features have not
been described in detail so as not to obscure the invention.
[0061] Embodiments of the invention relate to the use of phase
change in metal alloys to store (and release) energy as latent
heat. Certain metal alloys store very large amounts of energy as
latent heat at temperatures suitable for operating high-temperature
thermodynamic cycle engines for CSP and other next-generation
thermal technologies.
[0062] In a first embodiment of the invention, at least one metal
alloy is contained in at least one vessel located within an
insulated channel through which working fluid is circulated. This
embodiment is referred to as the pressurized TES embodiment. The
pressurized TES embodiment is charged by flowing high-temperature
working fluidthrough the insulated channel to heat and induce phase
change (e.g., melting) in the metal alloy(s) contained in the
vessel(s). The high-temperature working fluid is heated by solar
receivers or other heat sources such as electrical resistance
heating wires that can be powered by, for example, wind or hydro
power. The pressurized TES embodiment is discharged by flowing
working fluid to be heated through the same insulated channel to
cool and induce phase change (e.g., solidification) in the metal
alloy(s) contained in the vessel(s).
[0063] In a second embodiment of the invention, at least one metal
alloy is contained in at least one vessel located outside at least
one insulated channel through which working fluid is circulated.
Heat transfer rods provide thermal communication between the
vessel(s) and the insulated channel(s). This embodiment is referred
to as the unpressurized TES embodiment. The unpressurized TES
embodiment is charged by transferring heat via heat transfer rods
from high-temperature working fluid flowing through an insulated
channel to heat and induce phase change (e.g., melting) in the
metal alloy(s) contained in the vessel(s). The high-temperature
working fluid is heated by solar receivers or other heat sources
such as electrical resistance heating wires that can be powered by,
for example, wind or hydro power. The unpressurized TES embodiment
is discharged by transferring heat via the same or different heat
transfer rods to working fluid to be heated flowing through the
same or a different insulated channel to cool and induce phase
change (e.g., solidification) in the metal alloy(s) contained in
the vessel(s).
[0064] In a third embodiment of the invention, at least one metal
alloy is contained in at least one vessel located within an
insulated channel through which working fluid is circulated.
Electrical resistance heating wires wrapped around the vessel(s)
supply energy to the metal alloy(s) through resistive heating. This
embodiment is referred to as the electrical pressurized TES
embodiment. The electrical pressurized TES embodiment is charged by
flowing electrical current through the electrical resistance
heating wires to heat and induce phase change (e.g., melting) in
the metal alloy(s) contained in the vessel(s). The electrical
pressurized TES embodiment is discharged by flowing working fluid
to be heated through the insulated channel to cool and induce phase
change (e.g., solidification) in the metal alloy(s) contained in
the vessel(s).
[0065] In a fourth embodiment of the invention, at least one metal
alloy is contained in at least one vessel located outside an
insulated channel through which working fluid is circulated.
Electrical resistance heating wires wrapped around the vessel(s)
supply energy to the metal alloy(s) through resistive heating, and
heat transfer rods provide thermal communication between the
vessel(s) and the insulated channel. This embodiment is referred to
as the electrical unpressurized TES embodiment. The electrical
unpressurized TES embodiment is charged by flowing electrical
current through the electrical resistance heating wires to heat and
induce phase change (e.g., melting) in the metal alloy(s) contained
in the vessel(s). The electrical unpressurized TES embodiment is
discharged by transferring heat via the heat transfer rods to
working fluid to be heated flowing through the insulated channel to
cool and induce phase change (e.g., solidification) in the metal
alloy(s) contained in the vessel(s).
[0066] In any of the embodiments, there is a wide choice of
available metal alloys. Metal alloys are formed from a combination
of two or more elements with phase change temperatures determined
by the fraction of each element present. The phase change
temperatures are chosen to correspond to the desired operating
temperatures of CSP and other next-generation thermal
technologies.
[0067] Metal alloys composed of aluminum, silicon, and optional
trace elements, referred to as Al/Si metal alloys, can be chosen in
the embodiments because of their desirable thermodynamic and heat
transfer characteristics relative to other thermal storage media
such as liquid salts or oils. The phase change temperatures of
Al/Si metal alloys free of trace elements range from approximately
577.degree. C. to 1414.degree. C. depending on the relative
composition of aluminum and silicon. Therefore Al/Si metal alloys
enable the delivery of working fluid to thermodynamic cycle engines
across a broad temperature range, in contrast to the limited
temperature range enabled by liquid salts or oils.
[0068] Another advantage of Al/Si metal alloys relative to liquid
salts or oils are their high latent heats. While the latent heat of
fusion of aluminum is relatively high compared to other pure
metals, the latent heat of fusion of silicon is among the highest
known of any material. As described above, the latent heat of
fusion of silicon is approximately 430 cal/g; in contrast, the
specific heat capacity and latent heat of fusion of solar salts
(i.e., liquid salts) are approximately 0.35 cal/g-.degree. C. and
100 cal/g, respectively.
[0069] Al/Si metal alloys also have very good heat transfer
properties that enable faster charging/discharging than liquid
salts or oils. The thermal conductivity of aluminum just below its
melting temperature of 660.degree. C. is approximately 237
W/m-.degree. C., and the thermal conductivity of pure silicon is
149 W/m-.degree. C. at 27.degree. C. These values are considerably
higher those of liquid salts or oils; for example, the thermal
conductivity of solar salts is on the order of 1 W/m-.degree.
C.
[0070] The materials of the vessels containing the metal alloy(s)
are considerations in the embodiments. The vessel materials can be
ceramics such as alumina, magnesia, or zirconia, superalloys (i.e.,
metal alloys with strong performance at high temperatures) such as
Inconel and Waspalloy, or clad graphite or vitreous carbon.
Graphite and vitreous carbon must be clad in ceramics or
superalloys if the working fluid is air or another oxidizing gas
(e.g., carbon dioxide) because carbon allotropes oxidize at high
temperatures. Cladding can be accomplished by chemically bonding
ceramics or superalloys to graphite or vitreous carbon, or slip
fitting ceramics or superalloys around graphite or vitreous carbon.
To be specific, slip fitting refers to creating ceramic or
superalloy vessels that are geometrically similar to, but slightly
larger than, the graphite or vitreous carbon vessels. The graphite
or vitreous carbon vessels are then placed inside the ceramic or
superalloy vessels, which are sealed closed (e.g., through welding)
so no oxidizing gases can penetrate. The graphite or vitreous
carbon inner vessels can be in physical contact with the ceramic or
superalloy vessels, or separated by small spacers of ceramics,
superalloys, graphite, or vitreous carbon that help accommodate
thermal expansion and mitigate any potentially adverse interactions
between the inner and outer vessel materials. The void space in the
sealed ceramic or superalloys vessels (i.e., the space not filled
by the metal alloy(s), graphite or vitreous carbon, or optional
spacers) can be filled with helium, argon, or another non-reactive
gas to promote heat transfer and help balance the pressure
differential inside and outside the sealed ceramic or superalloy
containers.
[0071] The heat transfer rods of the unpressurized TES embodiment
can be made from solid ceramics, superalloys, or clad graphite or
vitreous carbon. They can also be sealed hollow tubes made from
ceramics, superalloys, or clad graphite or vitreous carbon that
contain a relatively small amount of working fluid. The working
fluid in the sealed hollow tubes should change phase from liquid to
vapor at a temperature above the phase change temperature of the
metal alloy(s) with which they are in thermal communication for
tubes communicating with the high-temperature working fluid. The
working fluid is vaporized in the lower ends of the tubes by the
high-temperature working fluid, and condenses in the upper ends of
the tubes that are embedded in the metal alloy(s) in the insulted
vessel(s). For communicating with the working fluid to be heated,
the working fluid in the sealed closed hollow tubes should change
phase from liquid to vapor at a temperature below the phase change
temperature of the metal alloy(s) with which they are in thermal
communication. The working fluid is vaporized in the lower ends of
the tubes that are embedded in the metal alloy(s) in the insulted
vessel(s), and condenses in the upper ends of the tubes by the
working fluid to be heated. Considerations for the heat transfer
rods of the electric unpressurized TES embodiment are the same as
those of the unpressurized TES embodiment that communicate with the
working fluid to be heated.
[0072] The electrical resistance heating wires in the electrical
pressurized and unpressurized TES embodiments are also
considerations. The heating wire materials should have high
electrical resistivity, high melting temperatures, high corrosion
(i.e., oxidation) resistance, and other desirable properties. By
way of example, Nichrome or Constantan are candidate heating wire
materials.
[0073] The preferred embodiments of the invention are illustrated
in the context of a Brayton thermodynamic cycle engine operating in
a CSP power plant based on a power tower arrangement. The skilled
artisan will readily appreciate, however, that the systems and
methods disclosed herein apply in a number of other
high-temperature TES contexts. For example, the embodiments can be
incorporated into wind or hydro power plants to convert electricity
into heat, and store the heat for future thermal-electrical
conversion in a thermodynamic cycle engine. The pressurized and
unpressurized TES embodiments can be charged by heating working
fluid with electrical resistance heating wires, and the electrical
pressurized and unpressurized TES embodiments can also be charged
by heating the vessel(s) and metal alloy(s) directly with
electrical resistance heating wires.
[0074] The arrays of one or more heat exchange elements in the
preferred pressurized TES embodiment and electrical pressurized TES
embodiment are discussed first. It is to be understood that the
structures, such as the vessels, the tubes and the spheres, may,
from time to time, be referred to as heat exchanger elements
generally. Three examples of arrays of heat exchanger elements are:
(1) an array of one or more vessels in the form of tubes parallel
to the working fluid flow, referred to as the parallel tube array;
(2) an array of one or more vessels in the form of tubes
perpendicular to the working fluid flow, referred to as the
perpendicular tube array; and, (3) an array of one or more vessels
in the form of spheres in a pebble bed, referred to as the pebble
bed array. FIG. 1a to FIG. 1c are side, top, and cross-section
views of a 3-tube parallel tube array; FIG. 2a to FIG. 2c are side,
top, and cross-section views of an 8-tube perpendicular tube array;
and FIG. 3a to FIG. 3c are side, top, and cross-section views of a
7-sphere pebble bed array. FIG. 1a to FIG. 1c show the channel 100
through which working fluid flows, the vessels (heat exchanger
elements) 102 containing the metal alloy(s), the insulation 104
surrounding the channel, and electrical resistance heating wires
105 (for the electrical pressurized TES embodiment); FIG. 2a to
FIG. 2c show the channel 200 through which working fluid flows, the
vessels (heat exchanger elements) 202 containing the metal
alloy(s), the insulation 204 surrounding the channel, and
electrical resistance heating wires 205 (for the electrical
pressurized TES embodiment); FIG. 3a to FIG. 3c show the channel
300 through which working fluid flows, the vessels (heat exchanger
elements) 302 containing the metal alloy(s), the insulation 304
surrounding the channel, and electrical resistance heating wires
305 (for the electrical pressurized TES embodiment). The vessels
can have fins or other appendages or structures that maximize heat
transfer, particularly in the parallel and perpendicular tube
arrays; the appendages or structures on the vessels 402 could have
axial (FIG. 4a and FIG. 4b) or radial orientations (FIG. 4c). The
vessels in FIG. 4a, FIG. 4b, and FIG. 4c are shown without
electrical resistance heating wires, but vessels with electrical
resistance heating wires can also have fins or other appendages or
structures.
[0075] Vessels in the preferred unpressurized TES embodiment are
illustrated next in FIG. 5a, FIG. 5b, and FIG. 5c. FIG. 5a is a
side view of one vessel 502 containing the metal alloy(s) 506, the
high-temperature insulated channel 500h, the low-temperature
insulated channel 500l, and the insulation 504 surrounding the
channels in a planar configuration. FIG. 5b is a side view of one
vessel 502 containing metal alloy(s) 506, the high-temperature
insulated channel 500h, the low-temperature insulated channel 500l,
and the insulation 504 surrounding the channels in a concentric
configuration; FIG. 5c is identical to FIG. 5b except the
high-temperature insulated channel 500h and low-temperature
insulated channel 500l are switched. In FIG. 5a, FIG. 5b, and FIG.
5c, the metal alloy(s) 506 thermally communicate with the insulated
channels 500h and 500l through heat transfer rods 508 and 510,
respectively. The heat transfer elements are made from solid
ceramics, superalloys, or clad graphite or vitreous carbon, or from
sealed hollow tubes made from ceramics, superalloys, or clad
graphite or vitreous carbon that contain a relatively small amount
of working fluid. If the heat transfer rods 508 are sealed hollow
tubes, then the working fluid is selected to change phase from
liquid to vapor at a temperature above the phase change
temperature(s) of the metal alloy(s) 506. By way of example, the
working fluids within the heat transfer rods 508 could be magnesium
(vaporization temperature of 1090.degree. C.) or lithium
(vaporization temperature of 1342.degree. C.). The working fluid is
vaporized in the lower ends of the heat transfer rods 508 by
absorbing heat from the high-temperature working fluid flowing
through the insulated channel 500h; the working fluid then releases
heat by condensing in the upper ends of the heat transfer rods 508
that are embedded in the metal alloy(s) 506. If the heat transfer
rods 510 are sealed hollow tubes, then the working fluid is
selected to change phase from liquid to vapor at a temperature
below the phase change temperature(s) of the metal alloy(s) 506.
The working fluid is vaporized in the lower ends of the heat
transfer elements 510 by absorbing heat from the metal alloy(s)
506; the working fluid then releases heat by condensing in the
upper ends of the heat transfer rods 510 in the insulated channel
500l containing working fluid to be heated. By way of example, the
working fluids within the heat transfer elements 510 could be
potassium (vaporization temperature of 760.degree. C.) or sodium
(vaporization temperature of 883.degree. C.). FIG. 5d shows a
sample sealed hollow tube heat transfer rod 508 (or 510) containing
a relatively small amount of working fluid 512.
[0076] Vessels in the preferred electrical unpressurized TES
embodiment are illustrated in FIG. 5e, FIG. 5f, and FIG. 5g. The
vessels in the preferred electrical unpressurized TES embodiment
are similar to those in the preferred unpressurized TES embodiment,
but include the electrical resistance heating wires 505 and lack
the high-temperature insulated channel 500h and associated heat
transfer elements 508 of FIG. 5a, FIG. 5b, and FIG. 5c.
[0077] The preferred embodiments can be oriented vertically,
horizontally, or slantingly. A vertical orientation of the
preferred embodiments is especially attractive for two reasons.
First, it enables the preferred embodiments to be incorporated into
vertical piping from solar receivers to avoid additional cost
associated with piping, insulation, etc. Second, it enables natural
convection within the metal alloy(s) to promote beneficial mixing
during phase change. For the preferred unpressurized TES embodiment
and the electrical preferred unpressurized TES embodiment, the heat
transfer elements always have a vertical component to promote
natural convection.
[0078] The vessels in the preferred embodiments are numbered,
sized, spaced, and oriented to simultaneously maximize metal alloy
volume and heat transfer, and minimize pressure drop in the working
fluid. This is accomplished by considering working fluid flow and
temperature, which can be characterized by one or many
dimensionless numbers such as the Reynolds number, Nusselt number,
and Grashof number. The Reynolds, Nusselt, and Grashof numbers are
determined by the properties and temperature of the working fluid
and metal alloy(s), and the characteristic dimensions of the
vessels. The Reynolds number is the ratio of inertial forces to
viscos forces; lower Reynolds numbers indicate laminar flow
characterized by smooth, constant fluid motion, while higher
Reynolds numbers indicate turbulent flow characterized by chaotic
eddies, vortices, and other flow instabilities. Pressure drop in
the working fluid does not monotonically increase or decrease as a
function of the Reynolds number, and therefore the number, size,
spacing, and orientation of the preferred vessels are selected to
target Reynolds numbers in the laminar flow regime and the
turbulent flow regime. The Nusselt number is the ratio of
convective heat transfer to conductive heat transfer across a
boundary (e.g., the boundary between the working fluid and the
vessels); lower Nusselt numbers indicate convection is limiting
heat transfer, while higher Nusselt numbers indicate conduction is
limiting heat transfer. The number, size, spacing, and orientation
of the preferred vessels are selected to target higher Nusselt
numbers so convective heat transfer into and out of the working
fluid, and into and out of the metal alloy(s), is not limiting TES
charging and discharging. The Grashof number is the ratio of
buoyancy force to viscous force, and is primarily used in
understanding the degree of natural convection in a fluid; lower
Grashof numbers indicate relatively less natural convection, while
higher Grashof numbers indicate relatively more natural convection.
The number, size, spacing, and orientation of the preferred vessels
are selected to target higher Grashof numbers so natural convection
in the metal alloy(s) supports heat transfer and TES charging and
discharging.
[0079] The choice of metal alloy(s) in the preferred embodiments is
influenced by many factors including, by way of example: phase
change temperatures and kinetics, latent heats, thermal
conductivity, expansion/contraction during phase change and
associated natural convection, stability during cycling, chemical
reactivity with vessel materials and heat transfer elements,
effects of contaminants, and current and future prices of the metal
alloy(s).
[0080] In the preferred embodiments, Al/Si metal alloys are chosen
because of their desirable thermodynamic and physical
characteristics. Some metal alloys with suitable melting
temperatures for TES, such as aluminum (melting temperature of
660.degree. C. and latent heat of fusion of 95 cal/g) and magnesium
(melting temperature of 650.degree. C. and latent heat of fusion of
88 cal/g), do not have sufficiently high latent heats for
commercialization. Other pure metals with high latent heats are
rare, expensive, radioactive, toxic, or have impractically high or
low melting temperatures. However, Al/Si metal alloys have tunable
phase change temperatures and latent heats of fusion that are
well-suited for high-temperature TES used in conjunction with a
Brayton thermodynamic cycle engine operating in a CSP power plant
based on a power tower arrangement or other next-generation thermal
technologies.
[0081] Al/Si metal alloys form a eutectic system with two distinct
phase changes from solid to liquid. The first phase change from
solid to mushy (i.e., partially solid, partially liquid) occurs at
the solidus temperature, which depends on the type and quantity of
trace elements present. For example, the solidus temperature is
approximately 577.degree. C. for pure Al/Si metal alloys free of
trace elements, but approximately 572.degree. C. for Al/Si metal
alloys with trace amounts of alkali metals. The second phase change
from mushy to liquid occurs at the liquidus temperature, which
depends on the relative composition of aluminum and silicon as well
as the type and quantity of trace elements present. For pure Al/Si
metal alloys free of trace elements, the liquidus temperature is
equal to the solidus temperature (i.e., phase change is from solid
to liquid) for the composition of approximately 87.4 wt. % aluminum
and 12.6 wt. % silicon. This composition is termed the eutectic
composition, and abbreviated as AlSi12. Compositions with
relatively less silicon content than the eutectic composition are
termed hypoeutectic compositions or hypoeutectics, and those with
relatively more silicon content than the eutectic composition are
termed hypereutectic compositions or hypereutectics. Liquidus
temperatures for hypoeutectics monotonically decrease from
660.degree. C., the melting temperature of pure aluminum, to
577.degree. C. for the eutectic composition as silicon content
increases. Liquidus temperatures for hypereutectics monotonically
increase from 577.degree. C. for the eutectic composition to
1414.degree. C., the melting temperature of pure silicon, as
silicon content increases. The equilibrium phase diagram for pure
Al/Si metal alloys free of trace elements is shown in FIG. 11 with
the solid, mushy, and liquid phases, and the solidus and liquidus
temperatures indicated. The presence of trace elements tends to
decrease the solidus and liquidus temperatures, and increase the
silicon content of the eutectic composition.
[0082] The latent heat storage of Al/Si metal alloys is dependent
on phase change, and therefore it is beneficial to understand the
solid, mushy, and liquid phases as functions of composition. The
solid phase is actually a solid solution: an aluminum and silicon
mixture at the eutectic composition (i.e., AlSi12) serves as the
solvent, and excess aluminum for hypoeutectics or silicon for
hypereutectics serves as the solute. The ratio of AlSi12 to excess
aluminum or silicon is dependent on composition. For example, the
composition of 50 wt. % aluminum and 50 wt. % silicon, abbreviated
as AlSi50, is approximately 57.2 wt. % AlSi12 and 42.8 wt. % excess
silicon because the 50 wt. % aluminum requires 7.2 wt. % silicon to
form AlSi12.
[0083] When transitioning from solid to mushy at the solidus
temperature, AlSi12 melts, but excess aluminum or silicon does not
change phase. Therefore the mushy phase is solid aluminum in molten
AlSi12 for hypoeutectics, and solid silicon in molten AlSi12 for
hypereutectics. When transitioning from mushy to liquid at the
liquidus temperature, the solid aluminum or silicon melts to form a
truly liquid phase. In the reverse transitions, excess liquid
aluminum or silicon solidifies at the liquidus temperature (i.e.,
liquid to mushy), and AlSi12 solidifies at the solidus temperature
(i.e., mushy to solid).
[0084] The solid, mushy, and liquid phases as functions of
composition directly affect the latent heat storage of Al/Si metal
alloys in the embodiments. The energy stored as latent heat during
phase change from solid to mushy at the solidus temperature is
attributable to melting AlSi12, which has a latent heat of fusion
of approximately 134 cal/g. Noncoincidentally, linear interpolation
between the latent heats of fusion of aluminum at 95 cal/g and
silicon at 430 cal/g suggests a latent heat of fusion of
approximately 137 cal/g for AlSi12. The energy stored as latent
heat during phase change from mushy to liquid at the liquidus
temperature is attributable to melting the excess aluminum fraction
for hypoeutectics, and melting the excess silicon fraction for
hypereutectics. For example, the latent heat of fusion for AlSi50
at the liquidus temperature is approximately 184 cal/g based on
42.8 wt. % excess silicon with the latent heat of fusion of silicon
at 430 cal/g.
[0085] Therefore the amount of energy stored as latent heat and the
temperature at which the energy is stored in Al/Si metal alloys can
be tuned by selecting a specific composition of aluminum and
silicon in the embodiments. The liquidus temperature can be tuned
from 577.degree. C. for the eutectic composition to 1414.degree.
C., the melting temperature of pure silicon. Likewise, the latent
heat of fusion at the liquidus temperature can be tuned from
approximately 95 cal/g to 134 cal/g for hypoeutectics (i.e., from
the latent heat of fusion of pure aluminum to that of the eutectic
composition), and from 134 cal/g to 430 cal/g for hypereutectics
(i.e., from the latent heat of fusion of the eutectic composition
to that of pure silicon). This enables the delivery of working
fluid at near constant temperature from 577.degree. C. to
1414.degree. C. to thermodynamic cycle engines for operation at
optimum conditions. The embodiments can also store latent heat at
several temperatures by varying the composition of aluminum and
silicon spatially. For example, each of the embodiments can have
one or more vessels, and each vessel can have one or more
compartments containing different compositions of aluminum and
silicon. This `cascading` strategy allows the embodiments to
maximize the temperature difference and heat transfer between the
Al/Si metal alloys and working fluids.
[0086] Al/Si metal alloys also have very good heat transfer
properties, are containable, and have low price points. The thermal
conductivities of pure aluminum and pure silicon at 25.degree. C.
are approximately 250 W/m-.degree. C. and 149 W/m-.degree. C.,
respectively. Al/Si metal alloys also transfer heat through natural
convection because of expansion/contraction during phase change.
Additionally, the expansion/contraction that promotes natural
convection in Al/Si metal alloys is not expected to rupture the
vessels in the preferred embodiments. Pure aluminum expands during
phase change from solid at 2.7 g/cm.sup.3 to liquid at 2.4
g/cm.sup.3. In contrast, pure silicon contracts during phase change
from solid at 2.4 g/cm.sup.3 to liquid at 2.6 g/cm.sup.3. Therefore
mushy is the least dense phase for hypereutectics because it is
solid silicon in molten AlSi12. Depending on composition, mushy is
between 0% and 10% less dense than the solid or liquid phases. The
mushy and liquid phases change shape to accommodate any vessel and
mushy contracts upon solidification to prevent rupturing. From a
practical perspective, Al/Si metal alloys are inexpensive, readily
available, and stable because no known degradation paths exist.
[0087] Specifically, hypereutectic Al/Si metal alloys are chosen in
the preferred embodiments. Hypereutectics have two distinct
advantages over hypoeutectics. First, they have a much broader
liquidus temperature range: their liquidus temperature range
includes that of hypoeutectics from 575.degree. C. to 660.degree.
C., and also liquidus temperatures from 660.degree. C. to
1414.degree. C. Second, they have much higher latent heats of
fusion at liquidus temperatures owing to their excess silicon
content. Furthermore, the preferred embodiments are designed to
store energy at the liquidus temperatures of hypereutectic Al/Si
metal alloys. The energy stored as latent heat at the liquidus
temperature is greater than at the solidus temperature for
compositions above approximately 34 wt. % silicon (abbreviated as
AlSi34) because of silicon's extremely high latent heat of fusion.
Additionally, storing energy at the liquidus temperatures of
hypereutectics avoids potential complications associated with
solidification of the Al/Si metal alloys.
[0088] In the preferred embodiments, the materials of the vessels
are simultaneously compatible with high-temperature hypereutectic
Al/Si metal alloys and oxidizing working fluid (e.g., air, carbon
dioxide, etc). Therefore the vessel materials of the preferred
embodiments are ceramics, superalloys, or clad graphite or vitreous
carbon. The preferred unpressurized TES embodiment and electrical
unpressurized TES embodiment also include heat transfer rods, which
can be made from solid ceramics, superalloys, or clad graphite or
vitreous carbon. They can also be sealed hollow tubes made from
ceramics, superalloys, or clad graphite or vitreous carbon that
contain a relatively small amount of working fluid; the selection
of working fluid in the sealed closed hollow tubes is discussed
above. In FIG. 6a, the vessels 602 is composed of ceramics or
superalloys contain metal alloy(s) 606. In FIG. 6b, the graphite or
vitreous carbon inner vessel 602a containing metal alloy(s) 606 is
protected from oxidizing working fluid by the ceramic or superalloy
outer vessel 602b and fit with optional spacers 612. In the
preferred electrical pressurized and unpressurized TES embodiments,
the electrical resistance heating wires are made from heating wire
materials that have high electrical resistivity, high melting
temperatures, high corrosion (i.e., oxidation) resistance, and
other desirable properties.
[0089] A representative preferred pressurized TES embodiment is a
vertically-oriented parallel tube array of vessels containing
hypereutectic Al/Si metal alloys; the vessels can have fins or
other appendages or structures that maximize heat transfer such as
those shown in FIG. 4a and FIG. 4b, or FIG. 4c. The vessels are
numbered, sized, spaced, and finned to target Reynolds numbers in
the laminar and turbulent flow regimes, higher Nusselt numbers, and
higher Grashof numbers to maximize Al/Si metal alloy volume and
heat transfer, and minimize pressure drop in the working fluid.
Each vessel is comprised of 2 or more compartments, with adiabatic
spacers between compartments to prevent thermal spillover. FIG. 7
shows the channel 700 through which working fluid flows, a
representative vessel divided into 3 compartments 702a, 702b, and
702c containing the Al/Si metal alloy(s), the Al/Si metal alloys
themselves 706a, 706b, and 706c, the adiabatic spacers 714, and the
insulation 704 surrounding the channel. Each compartment contains a
different composition of hypereutectic Al/Si metal alloy selected
such that the liquidus temperature of a given compartment is higher
than the compartment below it, which results in hypereutectic
compositions that cascade from more excess silicon to less excess
silicon. Additionally, the compositions are selected such that the
liquidus temperatures of all compartments are lower than the
temperature of the high-temperature working fluid as it enters the
channel, but higher than the temperature of the working fluid to be
heated as it enters the channel. FIG. 7a and FIG. 7b illustrate
such a cascading strategy: the liquidus temperature of the top
compartment 702a is higher than the middle compartment 702b, which
is in turn higher than the bottom compartment 702c. The liquidus
temperatures of compartments 702a, 702b, and 702c are lower than
the temperature of the high-temperature working fluid as it enters
the channel 700 from the top during charging, but higher than the
temperature of the working fluid to be heated as it enters the
insulated channel 700 from the bottom during discharging (i.e.,
T.sub.working,700,charging>T.sub.liquidus,702a>T.sub.liquidus,702b&-
gt;T.sub.liquidus,702c>T.sub.working,700,discharging). For
example, the aluminum-silicon composition of metal alloy 706a could
be AlSi50 with a liquidus temperature of approximately 1030.degree.
C., the composition of metal alloy 706b could be 55 wt. % aluminum
and 45 wt. % silicon (i.e., AlSi45) with a liquidus temperature of
approximately 980.degree. C., and the composition of metal alloy
706c could be 60 wt. % aluminum and 40 wt. % silicon (i.e., AlSi40)
with a liquidus temperature of approximately 930.degree. C. if the
high-temperature working fluid enters at 1050.degree. C. and the
working fluid to be heated enters at 400.degree. C.
[0090] This cascading strategy parallels a counter-current heat
exchanger to maximize heat transfer. During charging as shown in
FIG. 7a, high-temperature working fluid enters through the top and
thermally communicates first with the compartment containing the
hypereutectic with the highest liquidus temperature, and then
thermally communicates with one or more compartments containing
hypereutectics with increasingly lower liquidus temperatures.
During discharging as shown in FIG. 7b, working fluid to be heated
enters through the bottom and thermally communicates first with the
compartment containing the hypereutectic with the lowest liquidus
temperature, and then thermally communicates with one or more
compartments containing hypereutectics with increasingly higher
liquidus temperatures.
[0091] FIG. 7c is similar to FIG. 5a with similar numbering with
the chamber 502 divided into compartments 512a, 512b, and 513c and
with each compartment including different Al/Si alloys 516a, 516b,
and 516c. Adiabatic spacers 514 can divide the compartments as in
the manner shown in FIGS. 7a and 7b. A cascading strategy and/or
counter-current flow strategy similar to that demonstrated for the
embodiments of FIGS. 7a and 7b can be employed in the embodiment of
FIG. 7c.
[0092] During charging, high-temperature working fluid flows from
top to bottom through the channel because it originates in solar
receivers above the TES system and is destined for a gas turbine
below. During discharging, flow through the channel is reversed and
working fluid to be heated enters through the bottom and exits
through the top to maintain the counter-current parallel. The flow
directions also result in natural convection during phase change
from mushy to liquid. Phase change from mushy to liquid occurs more
quickly at the top of each vessel than at the bottom during
charging, and phase change from liquid to mushy occurs more quickly
at the bottom of each vessel than at the top during discharging.
Mushy is less dense than liquid so it will rise, creating a natural
convection loop that promotes beneficial mixing within each
vessel.
[0093] The TES system of the representative preferred pressurized
TES embodiment is placed in the downcomer connecting a solar
receiver to a turbine in a Brayton thermodynamic cycle engine
operating in a CSP power plant based on a power tower arrangement.
In the power tower arrangement shown in FIG. 8a, the solar
collectors 804c reflect sunlight onto a central solar receiver 804
located atop a tower 804t. Working fluid flows between the central
solar receiver 804, TES system 806, and Brayton thermodynamic cycle
engine 804b (including the compressor 800, recuperator 802, and the
turbine 808) through piping 804p. FIG. 8b provides additional
detail on the solar receiver, TES system, Brayton thermodynamic
cycle engine, and piping: the compressor 800, recuperator 802,
solar receiver 804, TES system 806, and turbine 808 are shown, as
well as the flow valve.sub.a 810a, flow valve.sub.b 810b, flow
valve.sub.s 810c, compressor-recuperator piping 801,
recuperator-valve.sub.a piping 803a, valve.sub.a-receiver piping
803b known as the upcomer, receiver-valve.sub.b piping 805a,
valve.sub.b-valve.sub.c piping 807b known as the bypass,
valve.sub.b-TES piping 805c and TES-valve.sub.c piping 807a
collectively known as the downcomer, valve.sub.s turbine piping
807b, valve.sub.s valve.sub.a piping 807c, valve.sub.a-turbine
piping 807d, tubine-recuperator piping 809a, and recuperator
exhaust piping 809b.
[0094] FIG. 8c shows the CSP power plant during charging.
Compressed working fluid flows from the compressor 800 to the
recuperator 802 through the compressor-recuperator piping 801, is
preheated in the recuperator 802, and flows through the
recuperator-valve.sub.a piping 803a, valve.sub.a 810a, and the
upcomer (i.e., valve.sub.a-receiver piping 803b) to the solar
receiver 804. High-temperature working fluid from the solar
receiver 804 then flows through receiver-valve.sub.b piping 805a to
valve.sub.b 810b, which directs some or all of the high-temperature
working fluid through the TES system 806 via the downcomer (i.e.,
valve.sub.b-TES piping 805c and TES-valve, piping 807a) and the
balance of the high-temperature working fluid through the bypass
(i.e., valve.sub.b-valve, piping 807b). At valve, 810c, there are
three options for the working fluids flowing through the downcomer
805c/807a and bypass 807b to the turbine 808 in the preferred
embodiments: if flow is present in both the downcomer 805c/807a and
the bypass 807b, (1) the working fluids can be mixed before
entering the valve.sub.s turbine piping 807d; or (2) the working
fluid exiting the TES system 806 can be vented before reaching
valve, 810c; or (3) if flow is only present in the downcomer
805c/807a, the working fluid from the TES system 806 enters the
valve.sub.s turbine piping 807d. The working fluid from the
valve.sub.s turbine piping 807d is then expanded through the
turbine 808 to produce electricity. The bypass 807b enables the CSP
operator to separate charging the TES system from flowing working
fluid through the turbine for electricity production.
[0095] FIG. 8d and FIG. 8e show two options of the CSP power plant
during discharging. In FIG. 8d, compressed working fluid flows from
the compressor 800 to the recuperator 802 through the
compressor-recuperator piping 801, is preheated in the recuperator
802, and flows through the recuperator-valve.sub.a piping 803a,
valve.sub.a 810a, valve.sub.c-valve.sub.a piping 807c, valve, 810c,
and TES-valve, piping 807a to the TES system 806. Working fluid to
be heated enters the TES system 806, is heated, and then flows
through the valve.sub.b-TES piping 805c, valve.sub.b 810b,
receiver-valve.sub.b piping 805a, solar receiver 804,
valve.sub.a-receiver piping 803b, valve.sub.a 810a, and
valve.sub.a-turbine piping 807d to the turbine 808 to produce
electricity. This option, in which working fluid to be heated flows
through the downcomer and upcomer, minimizes additional cost
associated with piping, insulation, etc. by utilizing the
upcomer.
[0096] In FIG. 8e, compressed working fluid flows from the
compressor 800 to the recuperator 802 through the
compressor-recuperator piping 801, is preheated in the recuperator
802, and flows through the recuperator-valve.sub.a piping 803a,
valve.sub.a 810a, valve.sub.s-valve.sub.a piping 807c, valve, 810c,
and TES-valve, piping 807a to the TES system 806. Working fluid to
be heated enters the TES system 806, is heated, and then flows
through the valve.sub.b-TES piping 805c, valve.sub.b 810b, bypass
(i.e., valve.sub.b-valve, piping 807b), valve, 810c, and
valve.sub.s-turbine piping 807b to the turbine 808 to produce
electricity. This option, in which working fluid to be heated flows
through the downcomer and bypass, reduces the temperature
requirements of the upcomer.
[0097] The TES system can be positioned at any point in the
downcomer. If positioned at the base of the downcomer, it can be
supported by resting on the horizontal section of the downcomer; if
suspended above the base of the downcomer, it can be supported by
struts or other structures made of ceramic or superalloy. FIG. 9a
shows the TES system 906 resting on the horizontal section of the
channel 900 (i.e., downcomer) with surrounding insulation 904, and
FIG. 9b shows the TES system 906 supported by struts 916 composed
of superalloy in the channel 900 with surrounding insulation 904.
In the representative preferred pressurized TES embodiment, the TES
system is positioned at the base of the downcomer to minimize the
need for struts.
[0098] The preferred embodiments of the invention are also
illustrated in the context of a wind or hydro power plant. In the
embodiments, energy is converted from electricity to heat through
resistive heating, and stored as heat in the metal alloy(s) for
future thermal-electrical conversion in a thermodynamic cycle
engine. FIGS. 10a and 10b show the channel 1000 through which
working fluid flows, the vessels 1002 containing the metal
alloy(s), the insulation 1004 surrounding the channel, the
electrical resistance heating wires 1005, the wind or hydro power
block 1001, and the thermodynamic cycle engine (for example, a
Rankine or Brayton thermodynamic cycle engine) 1003. FIG. 10a is
consistent with the pressurized and unpressurized TES embodiments,
with the electrical resistance heating wires 1005 located in the
channel 1000 upstream of the vessels 1002. The working fluid in the
channel 1000 is heated with the electrical resistance heating wires
1005 from energy produced by the wind or hydro power block 1001,
and the heat stored in the vessels 1002 is subsequently used to
operate the thermodynamic cycle engine 1003. FIG. 10b is consistent
with the electrical pressurized and unpressurized TES embodiments,
with the electrical resistance heating wires 1005 wrapped around
the vessels 1002. The vessels 1002 containing the metal alloy(s)
are heated with the electrical resistance heating wires 1005
directly from energy produced by the wind or hydro power block
1001, and the heat stored in the vessels 1002 is subsequently used
to operate the thermodynamic cycle engine 1003.
[0099] The foregoing description of the preferred embodiments of
the present invention has been provided for purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed. Many
modifications and variations can be apparent to the practitioner
skilled in the art. Embodiments were chosen and described in order
to best explain the principles of the invention and its practical
application, thereby enabling others skilled in the relevant art to
understand the invention. It is intended that the scope of the
invention be defined by the following claims and their
equivalents.
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