U.S. patent application number 13/048924 was filed with the patent office on 2011-09-22 for energy storage vessel, systems, and methods.
This patent application is currently assigned to BELL INDEPENDENT POWER CORPORATION. Invention is credited to John P. Bell, Joseph M. Bell, JR., Michael S. Bower, Gerard C. Walter.
Application Number | 20110226780 13/048924 |
Document ID | / |
Family ID | 44589513 |
Filed Date | 2011-09-22 |
United States Patent
Application |
20110226780 |
Kind Code |
A1 |
Bell; John P. ; et
al. |
September 22, 2011 |
ENERGY STORAGE VESSEL, SYSTEMS, AND METHODS
Abstract
A vessel for a thermal energy storage system comprising a bottom
wall joined to a surrounding side wall, and an inner liner disposed
within the bottom wall and side wall and comprising an inner liner
bottom and an inner liner side wall. One aspect of the inner liner
bottom and side wall is that they are configured to repeatedly
expand and contract during the thermal cycling of the storage
system. A thermal energy storage system comprising the containment
vessel and an array of heat exchangers is also disclosed. The heat
exchangers are disposed in the vessel, and arranged so as to
enclose a volume within the vessel. Each of the heat exchangers is
suspended by a suspension assembly. The assembly may be comprised
of a central support hanger, a spring loaded upper hanger, and a
lower hanger.
Inventors: |
Bell; John P.; (Bloomfield,
NY) ; Bell, JR.; Joseph M.; (Victor, NY) ;
Bower; Michael S.; (Fillmore, NY) ; Walter; Gerard
C.; (Penfield, NY) |
Assignee: |
BELL INDEPENDENT POWER
CORPORATION
|
Family ID: |
44589513 |
Appl. No.: |
13/048924 |
Filed: |
March 16, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61314313 |
Mar 16, 2010 |
|
|
|
Current U.S.
Class: |
220/565 ;
220/592.22; 220/646 |
Current CPC
Class: |
Y02E 60/14 20130101;
F28D 2020/0047 20130101; F28D 20/021 20130101; Y02E 60/145
20130101; F28F 1/14 20130101; F28D 1/0426 20130101; F28F 9/002
20130101; Y02E 60/142 20130101; F28F 2270/00 20130101; F28F 13/125
20130101; F28F 2265/26 20130101; F28D 1/05333 20130101; F28D
20/0034 20130101 |
Class at
Publication: |
220/565 ;
220/592.22; 220/646 |
International
Class: |
B65D 88/06 20060101
B65D088/06; B65D 90/04 20060101 B65D090/04; B65D 81/38 20060101
B65D081/38 |
Claims
1. A vessel comprising a bottom wall joined to a surrounding side
wall, and an inner liner disposed within the bottom wall and side
wall and comprising: a) an inner liner bottom comprising a central
plate surrounded by an array of radially arranged sector-shaped
plates, each of the sector-shaped plates joined at a radial portion
of its perimeter to a radial portion of the perimeter of an
adjacent sector-shaped plate by a radial flexible joint and joined
at an inner portion of its perimeter to the central plate by an
inner flexible joint; and b) an inner liner side wall joined to the
inner liner bottom and comprising a plurality of panels, each of
the panels joined at a lateral portion of its perimeter to a
lateral portion of the perimeter of an adjacent panel by a lateral
flexible joint.
2. The vessel of claim 1 wherein the vessel is cylindrical, and the
vessel bottom wall is circular.
3. The vessel of claim 1, wherein the central plate is
circular.
4. The vessel of claim 1, wherein the central plate is a
polygon.
5. The vessel of claim 1, wherein the number of radially arranged
sector-shaped plates is between three and twelve inclusive.
6. The vessel of claim 5, wherein the number of radially arranged
sector-shaped plates is eight.
7. The vessel of claim 1, wherein the radial flexible joint between
each pair of adjacent sector-shaped plates is an arcuate
member.
8. The vessel of claim 1, wherein the lateral flexible joint
between each pair of adjacent panels of the side wall is an arcuate
member.
9. The vessel of claim 1, wherein each of the lateral flexible
joints are integrally formed along one of the radial portions of
the perimeters of each of the sector-shaped plates.
10. The vessel of claim 1, further comprising an outer liner
comprising an outer liner bottom having an outer perimeter and an
outer liner side wall joined to the outer perimeter of the outer
liner bottom, the outer liner containing the inner liner therein
and separated from the inner liner by thermal insulation.
11. The vessel of claim 1, further comprising bottom thermal
insulation disposed between the bottom wall of the vessel and the
inner liner bottom, the bottom thermal insulation comprising a
plurality of support members of a first insulating material
interspersed within a second insulating material.
12. The vessel of claim 1, wherein the surrounding side wall is
comprised of a network of structural members, and the vessel is
further comprised of a plurality of insulating support members
disposed between the network of structural members and the inner
liner side wall.
13. The vessel of claim 12, further comprising thermal insulation
covering the plurality of insulating support members and the
network of structural members.
14. A vessel comprising a bottom wall joined to a surrounding side
wall, and a liner disposed within the bottom wall and side wall,
the liner comprising: a) a liner bottom comprised of means for
expanding radially outwardly when heated and contracting radially
inwardly when cooled; and b) a liner side wall joined to the inner
liner bottom and comprised of means for expanding radially
outwardly when heated and contracting radially inwardly when
cooled.
15-16. (canceled)
17. An expandable liner for a vessel, the expandable liner
comprising: a) a liner bottom comprising a central plate surrounded
by an array of radially arranged sector-shaped plates, each of the
sector-shaped plates joined at a radial portion of its perimeter to
a radial portion of the perimeter of an adjacent sector-shaped
plate by a radial flexible joint and joined at an inner portion of
its perimeter to the central plate by an inner flexible joint; and
b) a liner side wall joined to the liner bottom and comprising a
plurality of panels, each of the panels joined at a lateral portion
of its perimeter to a lateral portion of the perimeter of an
adjacent panel by a lateral flexible joint.
18. The liner of claim 17 wherein the liner side wall is
cylindrical, and the liner bottom is circular.
19. The liner of claim 17, wherein the central plate is
circular.
20. The liner of claim 17, wherein the central plate is a
polygon.
21. The liner of claim 17, wherein the number of radially arranged
sector-shaped plates is between three and twelve inclusive.
22. The liner of claim 17, wherein the radial flexible joint
between each pair of adjacent sector-shaped plates is an arcuate
member.
23. The liner of claim 17, wherein the lateral flexible joint
between each pair of adjacent panels of the side wall is an arcuate
member.
24. The liner of claim 17, wherein each of the lateral flexible
joints are integrally formed along one of the radial portions of
the perimeters of each of the sector-shaped plates.
25-45. (canceled)
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims priority from U.S. provisional
patent Application No. 61/314,313, filed Mar. 16, 2010, the
disclosure of which is incorporated herein by reference. This
application is also related to the following copending commonly
owned United States patent applications: application Ser. No.
12/033,604 of Geiken et al., filed Feb. 19, 2008; application Ser.
No. 12/172,673 of Flynn et al., filed Jul. 14, 2008; and
application Ser. No. 12/842,203 of Bell et al., filed Jul. 23,
2010. The disclosures of these United States patent applications
are incorporated herein by reference in their entireties.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The inventions disclosed herein relate generally to energy
storage and, more particularly, to thermal energy storage systems
and methods thereof.
[0004] 2. Description of Related Art
[0005] Worldwide, there are ever-growing demands for electricity
due to increasing populations, technology advancements requiring
the use of electricity, and the proliferation of such technology to
more and more countries around the world. At the same time, there
is an increasing push to harness reusable sources of energy to help
meet these increasing electricity demands and offset and/or replace
traditional carbon-based generators which continue to deplete
natural resources around the world.
[0006] Many solutions have been developed to collect and take
advantage of reusable sources of energy, such as solar cells, solar
mirror arrays, and wind turbines. Solar cells produce direct
current energy from sunlight using semiconductor technology. Solar
mirror arrays focus sunlight on a receiver pipe containing a heat
transfer fluid which absorbs the sun's radiant heat energy. This
heated transfer fluid is then pumped to a turbine which heats water
to produce steam, thereby driving the turbine and generating
electricity. Wind turbines use one or more airfoils to transfer
wind energy into rotational energy which spins a rotor coupled to
an electric generator, thereby producing electricity when the wind
is blowing. All three solutions produce electricity when their
associated reusable power sources (sun or wind) are available, and
many communities have benefited from these clean and reusable forms
of power.
[0007] Unfortunately, when the sun or wind is not available, such
solutions are not producing any power. In the case of solar
solutions, non-reusable energy solutions are often employed during
nighttime hours. Similar issues arise for wind turbines during calm
weather. Therefore, some form of energy storage is needed to store
excess energy from the reusable power sources during power
generation times to support energy demands when the renewable power
source is unavailable or unable to meet peak demands for
energy.
[0008] Solar mirror arrays generate and transfer heat as an
inherent part of their operation. Solar cells and wind turbines
which typically generate electricity can also selectively be used
to drive heaters to generate heat and/or transfer heat from
windings to a heat transfer fluid. Several solutions have been
developed to store heat from these renewable energy sources for use
in non-energy-generating times. In particular, one or more large
vessels of a liquid may be used to temporarily contain the sensible
heat contained by oil heated in a solar field, and delivered to the
liquid in the vessels by heat exchangers disposed therein. Hot oil
is delivered to heat exchangers in a vessel containing relatively
cold liquid, and the liquid in contact with the heat exchangers is
heated up. The liquid may initially be in solid form, with some
portion of the energy transfer being in the latent heat of fusion
in the solid to liquid transition.
[0009] During nighttime, or on overcast days when the solar field
is down, the flow through the heat exchangers in the thermal energy
storage vessel is directed to a steam generator which drives a
turbine, which in turn is connected to an electrical generator.
Heat is transferred from the heated liquid back into the oil in the
heat exchangers, which is pumped to the steam turbine, to drive the
turbine and generate electrical power.
[0010] One suitable energy storage medium is a molten inorganic
salt, with a liquid phase temperature range from about 400 to 750
degrees Fahrenheit (.degree. F.). This temperature range is
effective for providing high pressure steam to drive large scale
steam turbines for electrical power generation. Additionally,
inorganic salts typically have a substantially higher specific
gravity than water or organic heat transfer oils, in the range of
about two to about four times that of water. On a volumetric basis,
a molten inorganic salt can contain more sensible heat than an
equal volume of a typical organic heat transfer oil, and is thus
preferred in this regard.
[0011] Thermal energy storage systems which use molten salt are
known, such as the "Solar Two" system which was built near Barstow,
Calif., and was operational from about 1994 to 1999. This system
used molten salt comprised of a combination of about 60% sodium
nitrate and about 40% potassium nitrate as an energy storage
medium, which was circulated from a cold storage tank, through the
solar field where it was heated, to a hot storage tank. A summary
of a similar system is described and shown in FIG. 2 of the
aforementioned copending U.S. patent application Ser. No.
12/033,604 of Geiken et al.
[0012] Another known thermal energy storage system is the
single-tank thermocline energy storage system, which is also
described in the aforementioned patent application Ser. No.
12/033,604 of Geiken et al., and shown in FIG. 3 thereof. The
thermocline tank of this system contains a hot molten salt in the
top portion thereof and a relatively cool molten salt in the bottom
portion thereof. When the solar field 52 is active, a hot heat
transfer fluid is pumped from the solar field to a heat exchanger.
The relatively cool molten salt is pumped from the bottom of the
thermocline tank out to the heat exchanger where it is heated by
proximity to the hot heat transfer fluid from the solar field. The
heated molten salt is then returned to the top of the thermocline
tank. When the solar field is not active, the flow to and from the
thermocline tank is reversed. Heated molten salt is pumped out of
the top of the thermocline tank to the heat exchanger, where it
transfers its heat to the heat transfer fluid. The heat transfer
fluid is pumped to a steam turbine system for generating
electricity. The molten salt which gave up some of its heat in the
heat exchanger is then returned to the bottom of the thermocline
tank. While this system takes advantage of a vertical temperature
gradient within the thermocline tank to enable simplification to a
single tank, challenges with respect to the pumping, valving, and
delivery of molten salt through a complex network of piping to the
solar field, and to the power generator remain present.
[0013] It is therefore preferable to have a thermal energy storage
system in which the molten salt is simply contained within a vessel
as the thermal storage medium, and not pumped throughout the
overall system. Instead, the thermal energy is transferred from the
solar field to the vessel of molten salt by the circulation of a
heat transfer fluid, such as an organic heat transfer oil, from the
solar field through one or more heat exchangers immersed in the
molten salt in the vessel. In like manner, during nighttime or
overcast days, the thermal energy is transferred from the vessel of
molten salt to the power generator by the circulation of the heat
transfer fluid therebetween. The handling of heat transfer fluid by
standard pumps, valves and piping is much simpler than the
equivalent handling of a molten inorganic salt, which is corrosive,
and which is abrasive if some portion of solid phase salt
(crystals) is present, and which can solidify in the pumps, valves,
and piping at temperatures lower than 400.degree. F., thus
requiring a disruptive thawing process step to restart the
system.
[0014] By using a heat transfer fluid to perform the energy
transfer from the solar field to the thermal storage vessel, and
from the vessel to the power generator, the problems to be
addressed are simplified to those relating to containment of the
molten salt, and heat transfer to and from the molten salt. This
simplification notwithstanding, the problems of containing the
molten salt, and transferring thermal energy to and from it are
significant, particularly at the scale needed by a public utility
for an economically viable thermal energy storage process. The main
problems are summarized briefly as follows: [0015] 1. The
containment vessel is of economic necessity quite large, and the
molten salt contained therein is quite dense, on the order of two
to four times the density (or specific gravity) of water.
Consequently, the structural loads on the vessel bottom and side
wall are very high. [0016] 2. The molten salt within the vessel may
reach temperatures of up to about 750.degree. F. Therefore, the
containment vessel bottom and side walls must retain the required
structural strength to contain the molten salt at temperatures much
higher than the ambient environment. [0017] 3. The containment
vessel undergoes repeated thermal expansion and contraction, and
must be able to accommodate such extreme thermal cycling. During
system fabrication, the vessel is constructed at substantially
ambient temperature, and is then cycled up to as high as
750.degree. F. during startup and operation. The vessel is then
cycled between its minimum operating temperature (about 400.degree.
F. to about 500.degree. F.) to its maximum operating temperature of
about 750.degree. F. on a daily basis when in operation. The vessel
may also be occasionally cycled back down to ambient temperature of
between about 0.degree. F. and about 90.degree. F. during process
shutdowns. Given the requisite size of the containment vessel (on
the order of 25 feet in diameter by 30 feet high in one
embodiment), the dimensional changes of the vessel (and any
insulation contained therein or applied thereto) over the full
temperature range are significant, and must be accommodated.
Accordingly, the repeated cycles of thermal expansion and
contraction must occur without any structural failures of the
vessel, which could result in leaks of the molten salt therefrom
and/or collapse of the vessel. [0018] 4. The heat exchangers
contained within the vessel must also be able to withstand the
above-described thermal cycling, and must remain securely fixed
within the vessel during such cycling. [0019] 5. Many environments
where a thermal energy storage system may be located are
seismically active. Accordingly, the containment vessel and heat
exchangers must be able to withstand seismic events such as
earthquakes without significant damage, and without any leakage of
the molten salt. [0020] 6. Heat transfer rates are reduced when
solid salt forms on the heat exchanger. [0021] 7. For greatest
energy efficiency, it is desirable that the containment vessel of
the thermal energy storage system has as much insulation as
possible, thereby minimizing heat loss while still accommodating
the expansion and contraction of the vessel during thermal
cycling.
[0022] It is further noted that at minimum, for any thermal energy
storage system that comprises a molten inorganic salt as a thermal
storage medium, the above problems 1-4 must be simultaneously
addressed or otherwise rendered inconsequential by the features and
capabilities of the system. A system that further addresses
problems 5, 6, and/or 7 will be further advantageous.
SUMMARY
[0023] In accordance with the present disclosure, the problem of
containing a large mass of molten salt, which undergoes repeated
extreme thermal cycling in a thermal energy storage system is
solved by providing a vessel comprising a bottom wall joined to a
surrounding side wall, and an inner liner disposed within the
bottom wall and side wall and comprising an inner liner bottom and
an inner liner side wall. One aspect of the inner liner bottom and
side wall is that they are configured to repeatedly expand and
contract during the thermal cycling of the storage system in a
manner that avoids stress concentrations within the liner, which
could otherwise cause fractures and leaks in the liner. The liner
bottom and side wall are both comprised of means for expanding
radially outwardly when heated, and contracting radially inwardly
when cooled, without producing stress concentrations.
[0024] The inner liner bottom may be comprised of a central plate
surrounded by an array of radially arranged sector-shaped plates.
Each of the sector-shaped plates may be joined at a radial portion
of its perimeter to a radial portion of the perimeter of an
adjacent sector-shaped plate by a radial flexible joint and joined
at an inner portion of its perimeter to the central plate by an
inner flexible joint. The inner liner side wall is joined to the
inner liner bottom and may be comprised of a plurality of panels.
Each of the panels may be joined at a lateral portion of its
perimeter to a lateral portion of the perimeter of an adjacent
panel by a lateral flexible joint. The vessel may be cylindrical,
with the bottom wall of the vessel correspondingly being
circular.
[0025] The inner liner contained within the vessel is constructed
so as to be able to expand and contract under the loading thereof
with the molten salt, and in particular, due to the thermal
expansion and contraction caused by contact with the molten salt at
temperatures up to about 750.degree. F. During thermal cycling, the
radial and inner flexible joints of the liner bottom and the
lateral flexible joints of the liner side wall flex and accommodate
the thermal expansion and contraction of the sector shaped plates
and arcuate panels, so as to prevent localized stress
concentrations in the liner. The central plate may be circular, or
the central plate may be a polygon. The number of sides of the
polygon may be equal to the number of sector-shaped plates. The
number of radially arranged sector-shaped plates may be between
three and twelve, or more, depending upon the size of the vessel. A
flexible joint which joins a sector shaped plate at a radial
portion of its perimeter to a radial portion of the perimeter of an
adjacent plate may be comprised of an arcuate shaped member formed
and joined to the adjacent plates.
[0026] Depending upon the particular molten salt, the inner liner
may be made of a material selected from, but not limited to, plain
carbon steels; steels alloyed with copper, manganese, molybdenum,
nickel, silicon, tungsten, titanium, vanadium and chromium,
individually or in any combination thereof such as
chromium-molybdenum, or nickel-chromium-molybdenum; and stainless
steels. In one embodiment, the inner liner is made of 316 stainless
steel.
[0027] The vessel may further include an outer liner comprising an
outer liner bottom and an outer liner side wall joined to the outer
perimeter of the outer liner bottom. The outer liner contains the
inner liner within it, and is separated from the inner liner by
thermal insulation.
[0028] The vessel may further include thermal insulation disposed
between the bottom wall of the vessel and the inner liner bottom.
The bottom thermal insulation may be comprised of a plurality of
support members of a first insulating material interspersed within
a second insulating material. The support members of the first
insulating material provide structural support to the liner bottom,
thereby enabling the second insulating material to have a higher
R-value without needing to provide significant structural support.
Hence the combination of the first and second insulating materials
provided in this manner solves the problem of having insulation
that has the required structural strength and the required high
R-value insulating capability. In embodiments in which an outer
liner is provided, the thermal insulation is disposed between the
bottom wall of the vessel and the outer liner bottom.
[0029] The bottom wall of the vessel may be made of concrete, and
preferably, steel-reinforced concrete. The bottom wall of the
vessel may be formed upon a mud slab that is formed in the
supporting ground. The side wall of the vessel may be comprised of
a network of structural members. A plurality of insulating support
members may be disposed between the network of structural members
and the inner liner side wall. In embodiments in which an outer
liner is provided, the insulating support members may be disposed
between the network of structural members and the outer liner side
wall. The vessel may further include thermal insulation covering
the plurality of insulating support members and the network of
structural members.
[0030] In accordance with the invention, a thermal energy storage
system may include the instant vessel comprising a bottom wall
joined to a surrounding side wall, and an inner liner disposed
within the bottom wall and side wall as described above; a roof
structure disposed on the surrounding side wall; and a heat
exchanger assembly comprising a heat exchanger comprised of an
upper region, a central region, and a lower region, a central
support hanger connected to the central region of the heat
exchanger and suspended from the roof structure, a spring loaded
upper hanger connected to the upper region of the heat exchanger
and suspended from the roof structure, and a lower hanger suspended
from the central support hanger and connected to the lower region
of the heat exchanger. The heat exchanger assembly may include an
array of heat exchangers disposed in the vessel and arranged so as
to enclose a volume within the vessel. Each of the heat exchangers
may be comprised of an upper manifold connected to a lower manifold
by a plurality of heat exchanger tubes. The heat exchangers of the
array may be connected in series. The system may be further
comprised of a mixer comprising a shaft and at least one impeller
disposed within the volume enclosed by the array of heat
exchangers.
[0031] The inner liner of the vessel and the heat exchanger
suspension system of the thermal energy storage system may be
separately useful in other applications involving high temperature
material processing. Accordingly, there is provided an expandable
liner for a vessel comprising a liner bottom comprising a central
plate surrounded by an array of radially arranged sector-shaped
plates, each of the sector-shaped plates joined at a radial portion
of its perimeter to a radial portion of the perimeter of an
adjacent sector-shaped plate by a radial flexible joint and joined
at an inner portion of its perimeter to the central plate by an
inner flexible joint; and a liner side wall joined to the liner
bottom and comprising a plurality of panels, each of the panels
joined at a lateral portion of its perimeter to a lateral portion
of the perimeter of an adjacent panel by a lateral flexible
joint.
[0032] There is also provided a heat exchanger assembly comprising
a heat exchanger comprising an upper region, a central region, and
a lower region, and a suspension system suspendable from a
structure and connected to the heat exchanger. The suspension
system may be comprised of a central support hanger proximate to
the central region of the heat exchanger and suspendable from the
structure, a spring loaded upper hanger connected to an upper
region of the heat exchanger and suspendable from the structure,
and a lower hanger suspended from the central support hanger and
connected to a lower region of the heat exchanger. The heat
exchanger may be comprised of an upper manifold connected to a
lower manifold by a plurality of heat exchanger tubes.
[0033] In accordance with the invention, methods for using thermal
energy are also provided. The methods may include storing the
thermal energy received from a source and delivering the thermal
energy to a power generating station. In one embodiment, a method
comprises providing a thermal energy storage system as recited
above, connecting at least one heat exchanger of the system to a
thermal energy source, and delivering heated heat transfer fluid
from the thermal energy source to the heat exchangers, thereby
heating a thermal energy storage substance contained in the vessel.
The method may further comprise connecting the heat exchanger to a
power generating station and delivering heated heat transfer fluid
from the heat exchanger to the power generating station.
[0034] In another embodiment, a method comprises providing a
thermal energy storage system comprised of a vessel containing a
heat exchanger, connecting the heat exchanger to a first thermal
energy source, charging the vessel with a solid thermal energy
storage substance, and delivering heated heat transfer fluid from
the first thermal energy source to the heat exchanger, thereby
heating and melting the thermal energy storage substance contained
in the vessel. The charging of the vessel with a solid thermal
energy storage substance and delivering heated heat transfer fluid
from the first thermal energy source to the heat exchanger may be
performed simultaneously. The first thermal energy source may be a
solar array. The thermal energy storage substance may be an
inorganic salt. The method may be further comprised of mixing the
thermal energy storage substance. The method may be further
comprised of connecting the heat exchanger to a second thermal
energy source and delivering heated heat transfer fluid from the
second thermal energy source to the heat exchanger. The second
thermal energy source may be a solar array.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The present disclosure will be provided with reference to
the following drawings, in which like numerals refer to like
elements, and in which:
[0036] FIG. 1 is a schematic illustration of a thermal storage
system and method in accordance with the present disclosure;
[0037] FIG. 2 is a perspective view of a containment vessel and
thermal oil delivery unit of the thermal storage system, with the
vessel shown enclosed in thermal insulation;
[0038] FIG. 3 is a perspective view of the vessel of FIG. 2 shown
with the thermal insulation removed;
[0039] FIG. 4 is a perspective cutaway view of the containment
vessel of FIG. 3, showing the heat exchanger array contained
therein;
[0040] FIG. 5 is a side elevation cross-sectional view of a thermal
storage system, including a containment vessel, heat exchangers,
and a mixer, taken through a vertical plane passing through the
center of the vessel;
[0041] FIG. 6 is a plan view of the containment vessel of FIG. 2,
with the roof support structure, top cover, and top insulation
removed;
[0042] FIG. 7 is a detailed cross sectional single-plane elevation
view of a central plate of the liner bottom, taken along the line
7-7 of FIG. 6;
[0043] FIG. 8 is a detailed cross sectional elevation view of a
lateral flexible joint between arcuate panels of the inner liner
side wall, taken at the location indicated in FIG. 6;
[0044] FIG. 9 is a detailed cross-sectional plan view of the vessel
liners and insulation at a structural column of the vessel, taken
at the location indicated in FIG. 6, along line 9-9 of FIG. 11;
[0045] FIG. 10 is a plan view of the bottom of the containment
vessel with the liner bottom removed, showing the locations of a
plurality of insulating support members;
[0046] FIG. 11 is a side elevation cross-sectional view of a
containment vessel, including vessel liners, insulation, and a
vessel bottom foundation;
[0047] FIG. 12A is a detailed cross-sectional elevation view of the
junction of the vessel bottom and side wall, taken at the location
indicated in FIG. 11;
[0048] FIG. 12B is a detailed cross-sectional elevation view of
insulation of the side wall of the vessel at the junction of a
structural column and ring channel, taken at the location indicated
in FIG. 11;
[0049] FIG. 12C is a detailed cross-sectional elevation view of
insulation of the side wall of the vessel at a ring channel
only;
[0050] FIG. 12D is a detailed cross-sectional elevation view of the
junction of the vessel top and side wall, taken at the location
indicated in FIG. 11;
[0051] FIG. 13 is a perspective view of a heat exchanger array of
the thermal energy storage system;
[0052] FIG. 14A is a top view of the thermal storage system of FIG.
5 shown with the top cover and roof structure removed, and
including the heat exchanger array of FIG. 13, and a mixer;
[0053] FIG. 14B is a top cross sectional view of the thermal
storage system of FIG. 14A, taken approximately halfway down the
heat exchanger of FIG. 14A;
[0054] FIG. 15 is a detailed cross-sectional side elevation view of
the heat exchanger array of the thermal energy storage system of
FIG. 5, including a suspension system for supporting the array;
[0055] FIG. 16A is a side elevation view of a suspension system for
a heat exchanger;
[0056] FIG. 16B is a detailed side elevation view of a spring
loaded suspension member of the suspension system of FIG. 16A;
and
[0057] FIG. 17 is a flow chart depicting a method of storing and
releasing thermal energy using the applicants' thermal energy
storage system.
[0058] The present invention will be described in connection with a
preferred embodiment, however, it will be understood that there is
no intent to limit the invention to the embodiment described. On
the contrary, the intent is to cover all alternatives,
modifications, and equivalents as may be included within the spirit
and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION
[0059] For a general understanding of the present invention,
reference is made to the drawings. In the drawings, like reference
numerals have been used throughout to designate identical
elements.
[0060] FIG. 1 is a schematic illustration of a thermal storage
system and method in accordance with the present disclosure. The
thermal energy storage system 100 is comprised of a containment
vessel 101, which contains a heat exchanger or an array 400 of heat
exchangers immersed in a molten salt. The system 100 is further
comprised of a liquid transfer unit 490 (that may be of a modular
design), which circulates a heat transfer fluid through the heat
exchangers during operation of the system 100. The liquid transfer
unit 490 is comprised of liquid piping, various switching and
control valves, a pump 492, and a pressure relief tank (not shown).
The liquid transfer unit 490 may further include a heater loop 494
comprising an oil heater 496 and an expansion tank (not shown) for
heating and circulating heat transfer fluid through the heat
exchanger array 400 when the system 100 is not online.
[0061] In daytime operation of the system 100, the control valves
of the liquid transfer unit 490 are positioned such that heat
transfer oil is recirculated by the pump 492 from the solar field
10, through the heat exchanger array 400 in the vessel 101, and
back out to the solar field 10. In the solar field 10, the heat
transfer fluid passes through piping in the solar collectors, which
collect and concentrate the solar radiation by suitable means such
as mirrors and/or lenses onto the piping. The heat transfer fluid
passing therethrough is heated to a high temperature of as much as
800.degree. F. This hot heat transfer fluid is then pumped through
the heat exchanger array 400 in the containment vessel 101. Heat
from the hot heat transfer fluid is transferred into the molten
salt contained in the vessel 101, and the heat transfer oil is
cooled. The relatively cold heat transfer oil is recirculated back
to the solar field 10 for reheating. During a startup condition,
the solid salt in the vessel is heated and melted into a liquid
(molten) state, and is then further heated up beyond its melting
point. The molten salt thus contains energy in the form of the
latent heat of fusion of the salt, as well as the sensible heat of
the heated liquid. It is also noted that during the delivery of hot
oil from the solar field 10 to the system 100, some portion of the
hot oil may be routed directly to a power generating station 20 by
pumps, piping, and valving (not shown) for driving the power
generating station 20.
[0062] On overcast days and during nighttime, this sensible and
latent heat is available to be transferred back into the heat
transfer oil, and delivered to an electrical power generating
station or "power block" 20. During this portion of the operation,
the control valves of the liquid transfer unit 490 are positioned
such that heat transfer oil is recirculated by the pump 492 from
the power block 20, through the heat exchanger array 400 in the
vessel 101, and back out to the power block 20. In the power block
20, the heat transfer fluid passes through a steam generator, which
produces high pressure steam that is used to drive a turbine, which
drives an electrical generator. The heat transfer fluid passing
therethrough is cooled substantially as its thermal energy is
transferred to produce steam. This relatively cold heat transfer
fluid is then pumped through the heat exchanger array 400 in the
containment vessel 101, where it is reheated and delivered back to
the power block 20. This cycle may continue, with the thermal
energy contained in the molten salt that was transferred from the
solar field being used to generate electrical power during
nighttime or overcast days, for as long as the molten salt contains
enough thermal energy to heat the heat transfer fluid to a
temperature suitable for producing steam in the steam turbines of
the power block 20.
[0063] The salt used for thermal energy storage may be a salt
mixture, or a eutectic salt mixture. Suitable salts include,
without limitation, lithium nitrate, potassium nitrate, sodium
nitrate, sodium nitrite, calcium nitrate, lithium carbonate,
potassium carbonate, sodium carbonate, rubidium carbonate,
magnesium carbonate, lithium hydroxide, lithium fluoride, beryllium
fluoride, potassium fluoride, sodium fluoride, calcium sulfate,
barium sulfate, lithium sulfate, lithium chloride, potassium
chloride, sodium chloride, iron chloride, tin chloride, and zinc
chloride, and mixtures and solutions thereof.
[0064] A thermal energy storage system containing a molten salt
will be particularly useful in the commercial generation of
electrical power if it can contain a minimum of 3,400 MMBTU
(million British Thermal Units) for transfer to the power block 20
during nighttime or overcast days. Such a system would have the
capacity to maintain generating operation of a 50 megawatt power
block for about 6 hours.
[0065] This need for large thermal capacity in a thermal energy
storage system results in the previously recited problems of vessel
size, related structural loads, high operating temperatures, and
repeated thermal cycling. These problems are solved in the thermal
energy storage system, containment vessel, heat exchanger array,
and related suspension system.
[0066] The containment vessel is comprised of a bottom wall joined
to a surrounding containment side wall, and an expandable liner
disposed within the bottom wall and side wall and comprising a
liner bottom and a liner side wall. The expandable liner bottom may
be comprised of a central plate surrounded by an array of radially
arranged sector-shaped plates. Each of the sector-shaped plates may
be joined at a radial portion of its perimeter to a radial portion
of the perimeter of an adjacent sector-shaped plate by a radial
flexible joint and joined at an inner portion of its perimeter to
the central plate by an inner flexible joint. The liner side wall
is joined to the outer perimeter of the liner bottom and may be
comprised of a plurality of arcuate panels. Each of the panels may
be joined at a lateral portion of its perimeter to a lateral
portion of the perimeter of an adjacent arcuate panel by a lateral
flexible joint. An array of heat exchangers is contained within the
vessel. The heat exchangers are suspended from a roof structure by
a suspension system configured to accommodate the thermal expansion
of the heat exchangers resulting from the large temperature
fluctuations that occur during the thermal process. The vessel may
further include a second, outer liner comprising an outer liner
bottom and an outer liner side wall joined to the outer perimeter
of the outer liner bottom. In such an embodiment, the outer liner
contains the inner liner within it, and is separated from the inner
liner by thermal insulation.
[0067] In the following disclosure, the containment vessel, liners,
and thermal insulation of the thermal energy storage system 100
will be described first, followed by descriptions of the heat
exchanger array and mixer. The respective relationships between
these components and sub-assemblies to form the overall thermal
storage system 100, and methods for making and assembling the
system 100, vessel, liners, and heat exchanger array will also be
provided.
[0068] Turning first to FIG. 2, the thermal energy system 100 is
shown in perspective view, with the containment vessel covered in
insulation. The system 100 is comprised of the containment vessel
101 and a liquid transfer unit 490. Referring also to FIGS. 3-5,
only the vessel 101 is shown, without the liquid transfer unit 490.
(Additionally, in FIGS. 3-4, the thermal insulation on the vessel
side wall and roof is not shown.) In the embodiment depicted in
FIGS. 3-5, the containment vessel 101 is cylindrical, with the
bottom wall of the vessel correspondingly being circular, although
other vessel shapes may be employed. The vessel 101 is comprised of
a bottom wall 110 joined to a surrounding containment side wall
120. The bottom wall 110 may be made of concrete, and preferably,
steel-reinforced concrete comprised of steel rebar (not shown)
embedded in the concrete. The bottom wall 110 of the vessel 101 may
be formed at a constant thickness as shown in FIG. 5, or it may be
formed so as to decrease in thickness from the central region
thereof to the perimeter region thereof as shown in FIG. 3 of the
aforementioned U.S. Provisional Application No. 61/228,351.
[0069] The bottom wall 110 may be formed upon a mud slab 112, which
in turn is formed in the ground. The mud slab 112 may be comprised
of an engineered fill. For simplicity of illustration, the outer
edge 116 of the mud slab 112 is shown as being terminated at the
same location as the outer edge 114 of the bottom wall 110 in FIGS.
2-4; however, it is to be understood that the mud slab 112 may
extend beyond the edge 114 of the bottom wall 110. Additionally,
the ground 2 (soil, rocks, etc.) would be backfilled against the
edges of the mud slab 112 and bottom wall 110 after construction
thereof as shown in FIG. 11, but such ground 2 is also not shown in
FIGS. 2-4.
[0070] The containment side wall 120 may be comprised of a network
of structural members. The structural members may be structural
steel members, such as steel I-beams and steel channels. In the
embodiment depicted in FIGS. 3 and 4, the network of steel members
is comprised of a plurality of vertical I-beams 121A-121H, and a
plurality of arcuate channels 131A-131E, 132A-132E, 133A-133H (see
also FIG. 6), and additional arcuate channels on the back side of
the vessel 101 not shown. The arcuate channels are disposed between
pairs of vertical I-beams and joined to the I-beams by suitable
means such as welding. The arcuate channels thus form a set of
radially constraining rings 131-133 that serve to support and
prevent radial expansion of the vessel liner 200 contained therein.
For added rigidity, the vertical I-beams 121A-121H may be anchored
or embedded in the concrete slab bottom wall 110. Alternatively,
referring to FIG. 12A, a thick structural ring 118, such as a steel
ring may be embedded in the concrete or secured to the concrete
vessel bottom 11 by anchor bolts 124 and 126 and nuts 125 and 127,
with the vertical I-beams 121A-121H joined thereto by suitable
means such as welding. Additionally, a network 140 of roof
structural members is joined to the upper ends of the vertical
I-beams 121A-121H. The roof network 140 serves to join the I-beams
121A-121H together, as well as to provide a structure for
suspension of the heat exchanger array 400, as will be described
subsequently herein.
[0071] The roof structure 140 may further include a bottom sheet
covering 142 which provides a protective barrier to prevent
personnel from falling into the containment vessel during
inspection and service, and also provides a structural support,
upon which thermal insulation 330 (FIG. 11) can be disposed, to
further conserve the heat energy contained within the vessel 101.
The roof structure 140 may be further provided with a salt fill
port (not shown), which extends downwardly through the bottom sheet
142. The salt fill port may be provided with a removable cap (not
shown). In that manner, the vessel 101 can be filled with granular
solid salt through the fill port at the time of startup of the
thermal storage system 100. One aspect of the roof structure 140 is
that it may be of modular construction.
[0072] In another embodiment depicted in FIGS. 5, 14A, and 14B, a
containment vessel 102 of a smaller size is provided in which the
network of steel members is comprised of vertical I-beams
122A-122D, and a plurality of upper arcuate channels 134A-134D, as
well as additional lower arcuate channels not shown, beneath
channels 134A-134D. A network 141 of roof structural members may be
joined to the upper ends of the vertical I-beams 121A-121H for
added rigidity and for support of a heat exchanger array 401.
[0073] In order to contain the liquid molten salt within the
containment vessel 101, a liner 200 is provided within the bottom
wall 110 and containment side wall 120. The liner 200 is comprised
of a liner bottom 201 and a liner side wall 230, both of which may
be configured to repeatedly expand and contract during the thermal
cycling of the storage system 100. Referring again to FIGS. 3-4,
and also to FIG. 6, the liner bottom 201 may be comprised of a
central plate 204, surrounded by an array of radially arranged
sector-shaped plates. The central plate 204 may be circular, or the
central plate may be a polygon. The number of sides of the polygon
may be equal to the number of sector-shaped plates, such that the
linear inner perimeter portions of the sector-shaped plates are
contiguous with the sides of the polygon.
[0074] The number of radially arranged sector-shaped plates may be
between three and twelve, or more, depending upon the size of the
vessel. In the embodiment depicted in FIG. 6, the liner bottom 201
is comprised of eight sector-shaped plates 202A-202H, and a
circular central plate 204. In the alternative embodiment depicted
in FIGS. 14A and 14B, the liner 250 of the vessel 102 is comprised
of a liner bottom 251 comprised of four sector-shaped plates
252A-252D, and a circular central plate 254.
[0075] Referring to FIGS. 4 and 6, the sector-shaped plates
202A-202H may be joined at radial portions of their perimeters to
radial portions of the perimeters of adjacent sector-shaped plates
by respective radial flexible joints 206A-206H. The sector shaped
plates 202A-202H may also be joined at the inner portions of their
perimeters (e.g., 208A and 208D) to the central plate 204 by an
inner flexible joint 210. Referring to FIG. 7, the inner flexible
joint 210 may be formed as an angular riser which transitions
upwardly from the plane of a sector shaped plate (e.g. plate 202C
or plate 202G) to the plane of the central plate 204. In like
manner, in the alternative embodiment depicted in FIGS. 14A and
14B, the four sector-shaped plates 252A-252H are joined at radial
portions of their perimeters to radial portions of the perimeters
of adjacent sector-shaped plates by respective radial flexible
joints 256A-256D. The sector shaped plates 252A-252D are also
joined at the inner portions of their perimeters to the central
plate 254 by an inner flexible joint 258.
[0076] Referring again to FIGS. 4 and 6, the liner side wall 230 is
joined to the outer perimeter of the inner liner bottom 201. The
liner side wall 230 may be comprised of a plurality of arcuate
panels 232A-232H. The panels 232A-232H may be joined to form the
side wall 230, wherein lateral portions of their perimeters are
joined to the lateral portions of the perimeters of adjacent
arcuate panels by respective lateral flexible joints 234A-234H. In
like manner, in the alternative embodiment depicted in FIGS. 14A
and 14B, the four arcuate panels 282A-282D of the liner side wall
280 are joined at lateral portions of their perimeters to lateral
portions of the perimeters of adjacent arcuate panels by respective
lateral flexible joints 284A-284D.
[0077] The inner flexible joint 210, radial flexible joints
206A-206H, and lateral flexible joints 234A-234H are means for the
liner to expand radially outwardly when heated, and contract
radially inwardly when cooled, without producing stress
concentrations. The radially arranged sector-shaped plates of the
liner bottom 201 and the panels of the liner side wall 230 may be
provided in substantially greater numbers than shown, with
corresponding flexible joints between them, to the point where the
liner side wall 230 and liner bottom 201 are provided essentially
as corrugated structures.
[0078] Depending upon the particular molten salt, the liner 200 may
be made of a material selected from, but not limited to, plain
carbon steels; steels alloyed with copper, manganese, molybdenum,
nickel, silicon, tungsten, titanium, vanadium and chromium,
individually or in any combination thereof such as
chromium-molybdenum, or nickel-chromium-molybdenum; and stainless
steels. In one embodiment, the liner is made of 316 stainless
steel.
[0079] The containment vessel may further include a second, outer
liner comprising an outer liner bottom and an outer liner side wall
joined to the outer perimeter of the outer liner bottom. The outer
liner contains the first, inner liner within it, and is separated
from the inner liner by thermal insulation. The outer liner serves
to provide secondary containment of the molten salt in the event
that the inner liner develops a leak and allows molten salt to pass
through it.
[0080] FIG. 11 is a side elevation cross-sectional view of a
containment vessel, including vessel liners and insulation. FIGS.
12A-12D are detailed cross sectional views at various locations of
the vessel wall and bottom, as indicated in FIG. 11. For the sake
of simplicity of illustration, the network of roof structural
members is not shown in FIGS. 11 and 12D. The second, outer liner
260 is comprised of a liner bottom 261 and a liner side wall 270.
Solid, substantially incompressible solid thermal insulation
material 301 is disposed between the inner liner bottom 201 and the
outer liner bottom 261. In like manner, solid insulation material
311 is disposed between the inner liner wall 230 and the outer
liner side wall 270. The solid insulation material 301 and 311
serves to keep the inner liner 200 and the outer liner 260
separated by a substantially constant distance while also limiting
the rate of heat transfer therebetween.
[0081] The outer liner 260 may be provided with flexible joints in
the bottom wall 261 and side wall 270 in a manner similar to that
described for the inner liner 200. Referring to FIG. 8, a first
outer arcuate panel 272B is joined along its lateral perimeter to
the lateral perimeter of a second arcuate panel 272C by a flexible
joint 274B. The flexible joint 274B of the outer side wall 270
follows substantially the same contour as the flexible joint 234B
of the inner side wall, and is thus separated from the inner
flexible joint 234B by a distance that is approximately the
thickness of the solid thermal insulation 311. In the event that
the solid thermal insulation is not easily formed or flexible, a
different insulating material 312, such as a ceramic blanket
insulation may be disposed between the inner flexible joint 234B
and the outer flexible joint 274B.
[0082] Although not shown, corresponding flexible joints may be
provided in the outer liner bottom 261, which follow the respective
contours of the flexible joints 206 of the inner liner bottom 201.
In such an embodiment, the outer liner bottom 261 is comprised of a
plurality of sector-shaped plates having substantially the same
shape as the sector shaped plates 202A-202H of the inner liner
bottom 201. Additionally, referring to FIG. 7, the outer liner
bottom 261 may be comprised of a central plate 264, and a flexible
joint 266, which may be formed as an angular riser which
transitions upwardly from the plane of an outer sector shaped plate
of the outer liner bottom 261 to the plane of the outer central
plate 264. In that manner, separation is maintained between the
inner central plate 204 and the outer central plate 264. Solid
thermal insulation 301 may be disposed between the plates 204 and
264, with a flexible batt-type or ceramic blanket insulation 302
disposed between the flexible joints 210 and 266. The volume 209
directly beneath the plates 204 and 264 may also be filled with
batt or ceramic blanket insulation.
[0083] Referring to FIGS. 5, 14A, and 14B, and in the alternative
embodiment depicted therein, the containment vessel 102 may be
further comprised of an outer liner 290 comprising a liner bottom
291 and a liner side wall 295. Referring also to FIGS. 14A and 14B,
the outer liner 295 may be provided with lateral flexible joints
that follow the contour of the lateral flexible joints 284A-284D of
the inner liner 280. In like manner, the radial flexible joints
(not shown) of the bottom 291 of the outer liner 290 follow the
contour of the radial flexible joints 256A-256D of the inner liner
280. Solid, substantially incompressible solid thermal insulation
material 302 is disposed between the inner liner bottom 251 and the
outer liner bottom 291. In like manner, solid insulation material
313 is disposed between the inner liner wall 280 and the outer
liner side wall 295.
[0084] The containment vessel may further include thermal
insulation disposed between the bottom wall of the vessel and the
inner liner bottom. In embodiments in which an outer liner is
provided, the thermal insulation is disposed between the bottom
wall of the vessel and the outer liner bottom. The bottom thermal
insulation may be comprised of a plurality of support members of a
first insulating material interspersed within a second insulating
material. This is best understood with reference to FIGS. 4, 10,
11, and 12A. A plurality of insulating support members 320 are
distributed upon the bottom wall 110 of the vessel 101 with a
substantially even spacing. A second, higher R-value insulation 322
is disposed in the volume between the outer liner bottom 261 and
the vessel bottom 110. The insulating support members 320 of the
first insulating material provide structural support to the liner
bottom 261, thereby enabling the second insulating material 322 to
be selected from a higher R-value material, without the need for
the second material to provide significant structural support.
[0085] The side wall of the liner (or liners, if an inner and outer
liner are provided) may be supported by the network of structural
members of the containment vessel so as to prevent expansion and
contraction of the liner(s) during thermal cycling. However, it is
preferable that the liner(s) not be in direct contact with the
structural members; because the structural members are made of
steel or another high thermal conductivity material, any such
contact would cause a substantial heat loss through the vessel side
wall 120. To address this problem, a plurality of insulating
support members may be disposed between the network of structural
members and the inner liner side wall. In embodiments in which an
outer liner is provided, the insulating support members may be
disposed between the network of structural members and the outer
liner side wall. The vessel may further include a second thermal
insulation material covering the plurality of insulating support
members, the network of structural members, and the portions of the
exterior of the liner wall that are not covered by the insulating
support members. In a manner similar to the thermal insulation of
the bottom of the vessel liner, the insulating support members of
the first insulating material provide structural support to the
liner side wall, thereby enabling the second insulating material to
be selected from a higher R-value material, without the need for
the second material to provide significant structural support.
[0086] This is best understood with reference to FIGS. 11-12D.
Referring first to FIG. 11, the network of structural members may
comprise a plurality of vertical I-beams surrounding the vessel
liner(s), including I-beams 121C and 121G. (See also FIG. 4.) FIGS.
12A, 12B, and 12D depict detailed cross-sectional elevation views
of the vertical I-beam 121C, the inner and outer liner side walls
230 and 270, and insulating support members disposed between
vertical I-beam 121C and the outer liner side wall 270, for the
bottom, middle, and top regions of the vessel 101, respectively.
For the sake of simplicity of illustration, the second
non-supporting wall thermal insulation is not shown covering I-beam
121C in FIGS. 12A, 12B, and 12D.
[0087] Referring now to FIGS. 12A and 12B, a first solid insulation
member 304A is disposed between the lower portion of vertical
I-beam 121G and the outer liner wall 270. The solid insulation
member 304A extends from the lower arcuate channel 131B to the
middle arcuate channel 132B. Referring to FIGS. 12B and 12D, a
second solid insulation member 304B is disposed between the upper
portion of vertical I-beam 121G and the outer liner wall 270. The
solid insulation member 304B extends from the middle arcuate
channel 132B to the upper arcuate channel 133B. Referring also to
FIG. 9, which is taken along line 9-9 of FIG. 11, but oriented as
indicated in FIG. 6, the solid insulating members such as
insulation member 304B may be formed to have the same width as the
corresponding I-beam 121G. In like manner, first and second solid
insulation members may be disposed between the outer liner wall
270, and the other vertical I-beams 121A-121G and 121H.
[0088] Each of the lower and middle arcuate channel sections (e.g.
sections 131A and 132A of FIG. 4) and the upper arcuate channel
sections 133A-133H are provide with solid insulation members
disposed between them and the outer liner wall 270. By way of
illustration, referring to FIG. 12A, a solid arcuate insulation
member 306A is disposed between arcuate channel section 131B and
the outer liner side wall 270; referring to FIG. 12B, a solid
arcuate insulation member 306B is disposed between arcuate channel
section 132B and the outer liner side wall 270; and referring to
FIG. 12C, a solid arcuate insulation member 306C is disposed
between arcuate channel section 133B and the outer liner side wall
270. It can be seen in FIGS. 12A, 12C, and 12D, and in FIG. 12B in
particular, the height of the solid arcuate insulation member 306B
may be made to be the same as the height of the side of the
corresponding arcuate channel section 132B.
[0089] Referring again to FIGS. 11 and 12A-12D, a second thermal
insulation material 324 is provided, which covers the plurality of
insulating support members, the network of structural members, and
the portions of the exterior of the liner wall that are not covered
by the insulating support members. As can be seen particularly in
FIG. 12C, in regions of the outer liner side wall 270 that are not
adjacent to any of the I-beams or arcuate channel sections, such as
regions 276, the second thermal insulation material 324 is disposed
directly onto such surfaces. In that manner, with the second
thermal insulation material 324 being of a higher R-value than that
of the solid insulation members in contact with the network of
structural members, heat loss from the containment vessel 101 is
minimized.
[0090] A wire mesh 326, or other supporting material may be
attached to the network of structural members to provide support to
the second thermal insulation material 324 during fabrication of
the vessel 101 and operation of the thermal storage system 100. The
second thermal insulation material 324 may be covered with a layer
of waterproof and weather-resistant protective material 328 to keep
the insulation material 324 dry, thereby maintaining its high
R-value.
[0091] The liners within the vessel, and the inner liner in
particular are constructed so as to be able to expand and contract
under the loading thereof with the molten salt, and in particular,
due to the thermal expansion and contraction caused by contact with
the molten salt at temperatures up to about 750.degree. F. During
thermal cycling, the radial and inner flexible joints of the liner
bottom and the lateral flexible joints of the liner side wall flex
and accommodate the thermal expansion and contraction of the sector
shaped plates and arcuate panels. Having described the construction
of the vessel walls, liners, and insulation, the manner in which
the vessel liners expand and contract during thermal cycling will
now be explained.
[0092] The network of structural members, and the solid
substantially incompressible thermal insulation members disposed
between the structural members and the liner side wall serve to
dimensionally constrain the liner side wall and prevent substantial
radial thermal expansion of the vessel liner(s) during the heating
portion of thermal cycling. Accordingly, each of the sector-shaped
plates 202A-202H of the inner liner bottom 201 is prevented from
significant expansion radially outwardly along its outer arcuate
perimeter portion. Thus during heating, each sector-shaped plate is
free to expand along the radial portions of its perimeter, and
radially inwardly at its inner perimeter portion. Along the radial
portions of the perimeters of the sector-shaped plates, a radial
flexible joint accommodates the circumferential or angular thermal
expansion by flexing. At the inner perimeter portions of the
sector-shaped plates, the flexible joint 210 which borders the
central circular plate 204 accommodates the radially inward thermal
expansion by flexing as well.
[0093] By way of illustration, referring to FIGS. 6 and 8, the
circumferential thermal expansion of sector-shaped plates 202B and
202C is indicated by arrows 212. The radial flexible joint 206B
flexes to accommodate this expansion, with its bend radius
increasing as a result. The radially inward thermal expansion of
sector-shaped plate is indicated by arrow 214. Referring also to
FIG. 7, the flexible joint 210 bordering the central circular plate
204 accommodates this radially inward thermal expansion by flexing
radially inwardly, as indicated by arrows 216.
[0094] In a similar manner, the thermal expansion of the arcuate
panels 232A-232H is accommodated by the lateral expansion joints
provided between them. Again by way of illustration, referring to
FIGS. 6 and 8, the lateral (circumferential) thermal expansion of
arcuate panels 232B and 232C is indicated by arrows 236. The
lateral flexible joint 234B flexes to accommodate this expansion as
indicated by arrows 238 and 239, with its bend radius increasing as
a result.
[0095] Referring also to FIG. 12D, the arcuate panels 232A-232H of
the liner wall 230 are terminated at the upper ends 231 thereof
below the supporting plate 142 of a vessel cover 240. In that
manner, the side wall 230 of the vessel is free to expand and
contract vertically during thermal cycling as indicated by
bidirectional arrow 233.
[0096] It will be apparent that the thermal expansion of the outer
liner 260, constructed similarly with sector-shaped plates in the
bottom 261 thereof, and arcuate panels in the side wall 270
thereof, is accommodated in a similar manner by its respective
radial and lateral flexible joints.
[0097] Referring back to FIG. 1, the thermal energy storage system
may include an array of heat exchangers. The array of heat
exchangers are disposed in the vessel and arranged so as to enclose
a volume within the vessel. Each of the heat exchangers may be as
shown for heat exchanger 402 of FIG. 4, comprising an upper
manifold 403 connected to a lower manifold 404 by a plurality of
heat exchanger tubes 405. The tubes may also include fins (not
shown) to increase the rate of heat transfer between the heat
exchanger and the surrounding environment. The heat exchangers may
be constructed of a variety of materials, for example, but not
limited to plain carbon steels; steels alloyed with copper,
manganese, molybdenum, nickel, silicon, tungsten, titanium,
vanadium and chromium, individually or in any combination thereof
such as chromium-molybdenum, or nickel-chromium-molybdenum; and
stainless steels.
[0098] An exemplary heat exchanger array and heat exchanger
suspension system will now be described with reference to FIGS. 5
and 13-16B. Referring first to FIGS. 5 and 13-14B, a heat exchanger
array 401 is suspended in the containment vessel 102. The heat
exchangers are arranged so as to enclose a volume within them and
within the vessel. In the embodiment depicted in FIGS. 13-14B, the
heat exchanger array 401 is comprised of four heat exchangers 412,
414, 416, and 418 arranged in a square pattern, and enclosing a
rectangular volume. Each of the heat exchangers 412-418 is
comprised of an upper manifold connected to a lower manifold by a
plurality of heat exchanger tubes 411, the tubes 411 also
optionally including fins 409. In an alternative embodiment, a
single heat exchanger may be provided comprising upper and lower
manifolds and connecting tubes therebetween, formed so as to
enclose a volume within the heat exchanger. The heat exchangers of
the array may be connected in parallel or in series. In the
embodiment depicted in FIGS. 13-14B, the heat exchangers 412-418
are connected in series, with the lower manifolds 415 and 417 of
heat exchangers 414 and 416 connected to each other, and the lower
manifolds 413 and 419 of heat exchangers 412 and 418 connected to
each other. In that manner, the flow of heat transfer fluid within
successive heat exchangers around the array is in vertically
opposed directions, as indicated by the flow arrows provided in
FIG. 13. Other heat exchanger connection arrangements may be
suitable.
[0099] Referring to FIG. 5, the thermal energy storage system may
be further comprised of a roof structure 141 disposed on the top of
the containment side wall 123, wherein each of the heat exchangers
412-418 is suspended from the roof structure 141.
[0100] FIG. 15 is a detailed view of the heat exchanger array 401
contained within the vessel 102 of FIG. 5, depicting suspension
systems 420 for suspending the heat exchangers 412-418 within the
vessel 102. FIG. 16A is a detailed view of the suspension system
suspending one of the heat exchangers 416. (For the sake of
simplicity of illustration, only the upper manifold 408, a central
vertical tube 407 and fins 409, and the lower manifold 417 of heat
exchanger 416 are shown. Additional vertical tubes 411 parallel to
the central tube 407 are not shown.)
[0101] The suspension system 420 is comprised of a central support
hanger 422 suspended from the roof structure 141 proximate to the
central region 441 of the heat exchanger 416, a spring loaded upper
hanger 424 suspended from the roof structure 141 and connected to
an upper region 443 of the heat exchanger 416, and a lower hanger
426 suspended from the central support hanger 422 and connected to
a lower region 445 of the heat exchanger 416. The central support
hanger 422 may be comprised of a horizontal support member 428 that
is suspended from the roof structure 141 by threaded rods 429 and
nuts 430. The lower hanger 426 may be comprised of a threaded rod
427 secured to the horizontal support member 428 by nuts 421.
[0102] Referring also to FIG. 16B, the spring loaded upper hanger
424 may be comprised of a container 431 holding a spring 432
disposed on the container bottom 433. A suspension member 434 such
as a threaded rod extends upwardly through the container bottom,
through the spring 432, and through a retainer plate 435 disposed
on the top of the spring 432. A nut 436 on the threaded end of the
suspension member 434 secures the retainer plate 435 to the top of
the spring 432. The suspension member 434 extends downwardly and is
joined to the upper region 443 of the heat exchanger 416. The
container 431 is provided with a top lug 437, which may be engaged
with an eyebolt 438 that is joined to the roof structure 141.
[0103] In the embodiment depicted in FIGS. 15 and 16A, in which the
heat exchanger 416 is comprised of an upper manifold 408 connected
to a lower manifold 417 by vertical tubes 407, the spring loaded
upper hanger 424 may be connected to an upper pipe hanger 425 which
supports the upper manifold 408, and the lower hanger 426 may be
connected to a lower pipe hanger 423 which supports the lower
manifold 417. The heat exchanger 416 may further include a tube
guide plate 447, and the horizontal support member 428 may be
connected to the guide plate 447.
[0104] When the heat exchanger array 401 is installed in the
containment vessel 102, each of the heat exchangers 412-418 is
provided with a support system 420. During installation, when the
heat exchanger 416 is first suspended from the central and lower
support hangers 422 and 426, all of the weight of the heat
exchanger is supported by those hangers. But when the spring loaded
upper hanger 424 is added to the support system 420, and the nut
436 is turned down on the support rod 434, then the spring 432
begins to compress, and an increasing amount of the weight of the
heat exchanger 416 becomes carried by spring loaded upper hanger
424. The nut 436 may be turned down sufficiently such that
approximately half, or slightly more than half of the weight of the
heat exchanger 416 is borne by the spring loaded upper hanger 424,
with the remainder of the weight being borne by the central and
lower support hangers 422 and 426. The container 431 of the spring
loaded upper hanger 424 may be provided with indicia 439 of a
compression scale of the spring 432, and the retainer plate 435 may
be provided with a pointer 440 proximate to the indicia, so that
adjustment of the spring 432 can be made quantitatively. In that
manner, when the weights of the heat exchangers 412-418, spring
constant of the springs 432, and dimensions of the heat exchangers
412-418 and suspension system 420 are known, the adjustments of
spring compression can be made according to the indicia, without
the need for individual tension measurements of the support hangers
422, 424, and 426.
[0105] In operation of the thermal energy storage system 100, when
the molten salt is thermally cycled, the heat exchanger suspension
systems 420 provide for expansion of the heat exchangers in both
vertical directions, and also prevent stress of the heat exchangers
due to any difference in thermal expansion coefficients of the heat
exchanger tubes and the hanger rods 427, 429, and 434. Some of the
thermal expansion of the heat exchangers 412-418 will be in
downward from the horizontal support member 428, and some of the
expansion will be in upward from the horizontal support member 428
by the action of the spring loaded upper hanger 424.
[0106] The system 100 or 102 may be further comprised of a mixer
comprising a shaft and at least one impeller disposed within the
volume enclosed by the array of heat exchangers. In the embodiment
depicted in FIGS. 5, 14A, and 14B, the mixer 450 is comprised of a
drive motor 452 mounted on the vessel roof support 141, a shaft
454, and upper and lower impellers 456 and 458. Referring also to
FIG. 15, the impellers 456 and 458 may be configured to cause flow
of molten salt downward through the internal volume of the heat
exchanger array 401, and upward along the exterior of the array 401
as indicated by arrows 459. The motor 452 may be made rotationally
reversible so that the direction of flow through the heat exchanger
array 401 may be reversed.
[0107] Details of one exemplary design of the applicants' thermal
energy storage system and containment vessel will now be provided.
These details are to be considered as exemplary only, and not
limiting. Many other designs of the system and vessel are possible,
and are within the scope of the present invention. In this
embodiment, the side wall 120 of the vessel may be about 23 feet in
diameter and about 22 feet high. The bottom wall 110 of the vessel
may be of steel rebar reinforced concrete about 24 inches thick.
The mud slab 112 beneath the bottom wall 110 may also be about 24
inches thick. The concrete used in the bottom wall 110 may be 4000
psi (pounds per square inch) concrete. The vertical I-beams 121 of
the vessel wall 120 may be 8-inch.times.8-inch steel I-beams, and
the ring channels 131, 132, and 133 may be formed from 8-inch wide
steel channel.
[0108] The plates of the inner liner bottom 210 and the arcuate
panels of the side wall 230 of the liner 200 are preferably made of
metal, which provides sufficient structural strength at high
temperatures, and which is joinable at the job site by suitable
means such as welding. The particular metal must also be resistant
to corrosion by the molten salt. Suitable metals include stainless
steel, titanium, and other metals and metal alloys previously cited
herein with regard to the liner. In one embodiment, the inner liner
200 may be made of 304 stainless steel having a thickness of about
1/4 inch. The outer liner, which serves as secondary containment in
the event of a leak through the inner liner, is not directly
exposed to the molten salt. In one embodiment, the outer liner is
made of carbon steel.
[0109] The flexible joints of the liner bottom 201 and liner side
wall 230 may be made by suitable forming means such as a metal
brake, or by stamping with a die. The flexible joints may be made
of the same material as the sector shaped plates 202A-202H and the
arcuate panels 232A-232H.
[0110] The Applicants have determined that modularity of the
instant thermal storage system is preferred. In construction of the
vessel and overall thermal energy storage system, a system that is
of a modular design is more cost effective. In a modular system, a
major portion of the system components can be fabricated in a shop
environment, which is better equipped and controlled, and then
shipped to the job site. Final construction and assembly can then
be done on the job site.
[0111] Accordingly, one aspect of the liner 200 of the containment
vessel 101 is that it may be designed in a modular manner, i.e.
such that the various pieces of the liner bottom 210 and liner side
wall 230 may be cut and formed in a workshop or factory, and then
transported to the job site to be assembled. The panels of the side
wall 230 may be formed from upper and lower arcuate panels that are
pre-formed in a shop and welded together at the job site. In one
embodiment, the lower panels may be thicker than the upper panels
to contain the higher fluid pressures near the bottom of the
containment vessel 101. The respective sector plates 202A-202H,
center plate 204, radial flexible joints 206A-206H, and center
plate perimeter joints 210 may also all be pre-cut and formed in a
shop.
[0112] Other configurations of the sectoral portions of the liner
bottom 201 are also possible. In one embodiment, each sectoral
section 202A-202H may be provided with a flexible joint formed
along one radial edge, with the other radial edge being a simple
straight edge. In that manner, when the sectoral plates are joined
together, a flexible joint is provided between each of them.
Additionally, the center plate 204 could be formed with its
perimeter flexible joint 210 integrally formed therewith. Many
other configurations are possible, with the operative requirement
being that the respective adjacent plates are separated by flexible
joints to accommodate the expansion and contraction of the liner
200 during thermal cycling.
[0113] The thermal insulation of the containment vessel 101 will
now be described. Referring first to FIGS. 11 and 12A, the
substantially incompressible solid thermal insulation material 301
that is disposed between the bottoms 201 and 261 of the inner and
outer liners 200 and 260 may be made from one inch thick sheets of
MARINITE.RTM. 1 insulation manufactured by BNZ Materials, Inc. of
Littleton Colo. This insulation is primarily comprised of calcium
silicate. In like manner, the thermal insulation material 311 that
is disposed between the side walls 230 and 270 of the inner and
outer liners 200 and 260 may be made of two-inch thick
MARINITE.RTM. 1 insulation. The sheets may be scored or routed
vertically to facilitate their being formed to conform to the
arcuate panels of the liner side walls.
[0114] The insulating support members or piers 320 beneath the
liner bottom walls 201 and 261 may also be made of MARINITE.RTM. I
insulation. In one embodiment, the piers 320 are 12 inches in
diameter, 16 inches high, and are distributed as shown in FIG. 10
over the 23-ft. diameter vessel bottom. The second insulation 322
that is disposed in the volume between the outer liner bottom 261
and the vessel bottom 110 may be Foamfrax.RTM. insulation
manufactured by the Unifrax Corporation of Niagara Falls N.Y.
Foamfrax.RTM. is a monolithic three-component insulation system
comprised of bulk ceramic or soluble fibers, an inorganic binder,
and an organic foaming binder which may be applied by spray gun. In
the side wall 120 of the vessel 101, the various members 304A-304C
and 306A-306C of solid thermal insulation material may also be made
of MARINITE.RTM. I insulation having a thickness of about two
inches. The second thermal insulation material 324 of the side wall
120, and the roof insulation 330 may also be made of Foamfrax.RTM.
insulation, applied to a thickness of between about 12 and 16
inches.
[0115] The heat exchangers 402 of the system 100 may be made of
"21/4 Cr-1 Mo alloy," (also known as ASME SA-213-T22 tubing), a
steel alloy containing molybdenum and chromium, which is
particularly suitable for high temperature pressure vessels in
corrosive environment. The upper and lower manifolds of the heat
exchangers may be 8-inch diameter pipes, with 31 rows of five tubes
connecting them. The tubes may be 3/4-inch diameter and have twelve
fins each.
[0116] A method of making the applicants' thermal energy storage
system 100 may be substantially as described in the aforementioned
U.S. Provisional Patent Application No. 61/228,351 of Bell et al.,
except that the preparation of the system site such that the system
my be partially submerged in the ground would likely not be
performed.
[0117] FIG. 17 is a flow chart depicting a method of storing and
releasing energy from the applicants' thermal energy storage
system. It is to be understood that although the steps of the
method 500 of FIG. 17 are illustrated in a serial order, the method
is not limited to being done in the order depicted in FIG. 17.
Certain steps of the method 500 may be performed in parallel,
and/or in orders other than depicted in FIG. 17.
[0118] One aspect of the instant system 100 and method 500 is that
the latent heat contained in the system 100 will be extracted in an
optimal manner. In transferring thermal energy out of the system
100, when most of the sensible heat has been removed from the
molten salt and the salt is near its freezing point, the salt will
begin to freeze on the outside of the heat exchanger tubes 411. The
molten salt will be agitated by the mixer 450 to bring hotter
molten salt in contact with the cooler solidified salt on or near
the heat exchanger tubes 411, thus allowing maximum heat removal
from the salt bath. The heat transfer oil within the heat
exchangers will have a lower temperature rise across the salt bath,
but can still be utilized overnight to heat oil in the solar field
10 or to preheat components in the power generating station 20.
[0119] From calculations, it is estimated that approximately 15% of
the latent heat in the salt bath can be recovered for producing
power, and the oil temperature from thermal storage will be below
520.degree. F. The low grade heat that is not hot enough to produce
steam in the power generating station 20 can be used to preheat the
oil in the solar field 10 and to preheat feed water in the power
generating station 20. This will enable a faster daily startup of
the power generating station 20, which will bring the turbine cycle
of the station 20 to full load sooner and increase the daily energy
production of the station 20.
[0120] A method for storing thermal energy using the applicants'
thermal energy storage system will now be described. Referring in
particular to FIGS. 1 and 20, as a first step 510 of the method
500, a thermal energy storage system comprising a vessel, a heat
exchanger or heat exchanger array, and a heat transfer fluid
delivery system is provided. The thermal energy storage system may
be the system 100 as described herein. The system 100 may be
fabricated according to a method substantially as described, or
similar to that described and shown in FIG. 12 of the
aforementioned U.S. Provisional Patent Application No. 61/228,351
of Bell et al. The system is connected 520 to a thermal energy
source such as a solar field 10 and a power generating station 20.
The fluid delivery system including the piping to and from the
solar field 10 and the power generating station 20, and the heat
exchanger array 400 is filled 530 with heat transfer fluid. The
heat transfer fluid may be circulated through the heat exchanger
array 400 at normal operating pressure or higher pressure to
confirm that the entire system is leak-free.
[0121] To facilitate the startup process of the thermal energy
storage system 100, the Applicants have determined that it is
desirable that the initial melting of the salt be performed in the
containment vessel, rather than melting the salt at a remote
location and pumping it to the containment vessel, as is widely
practiced in the art currently. Accordingly, in step 540, the
vessel 101 is charged with solid phase salt. The solid salt is
typically in a coarse granular state, and is delivered through a
charging port (not shown) in the top of the vessel 101. The salt
may be delivered manually, or the system may be provide with a
temporary or permanent hopper and/or auger, or other conveying
means (not shown) to deliver the granular salt into the vessel 101.
In one embodiment, as the incoming granular salt contacts the lower
regions of the heat exchangers 412-418, the melting process can be
started. Valves 495 and 497 of heater loop 494 are positioned to
circulate heat transfer fluid through heater 496, and through the
heat exchanger array 400, and back to the heater loop 494. The heat
transfer oil is heated to above the melting point of the salt by
the heater 496, and then circulated through the heat exchanger
array 400, such that the initial granular salt contacting the heat
exchangers 412-418 is melted early in the charging process. As the
liquid salt level rises, it submerges the lower impeller 458, such
that the mixer functions to circulate a slurry of liquid salt and
solid granules as the melting process proceeds. With mixing and
therefore enhanced heat transfer occurring during almost the entire
salt melting process, the initial salt melting process is
accelerated. This melting process is also beneficial in that if the
vessel 101 were fully filled with granular salt and then melted, a
second charge of salt would need to be added. This is because the
granular salt has a large void volume, and once that first charge
of granular salt were melted, the vessel would not be full to
capacity, thus requiring a second charge of salt.
[0122] Once the salt is completely melted, or nearly so, such that
the mixer 450 can circulate substantially the entire contents of
the vessel 101, the contents may be maintained 550 in the
pre-heated state by using the heater loop 494 if necessary until
thermal energy is available 555 from the solar field 10 or other
thermal source. The various valves of the fluid delivery system 490
are switched, circulating hot heat transfer fluid from the solar
field 10 through the heat exchanger array 450 and back, thereby
delivering 560 thermal energy to the vessel from the solar field
10. Any remaining solid salt in the vessel is fully melted, and the
molten salt is heated further, typically to a temperature of as
much as 800.degree. F. When the molten salt is at its maximum
operating temperature, the vessel 101 is at its maximum thermal
capacity 565. This maximum thermal energy is available to deliver
to the power generating station 20.
[0123] This is typically needed from evening to morning, or during
cloudy periods of the day. The various valves of the fluid delivery
system 490 are again switched, circulating hot heat transfer fluid
through the heat exchanger array 450 in the vessel 101 to the power
generating station 20 and back, thereby delivering 570 thermal
energy from the vessel 101 to the power generating station 20. The
heat transfer rate from the molten salt to the heat transfer fluid
in the heat exchangers 412-418 is enhanced by use of the mixer 450.
This may continue until the molten salt in the vessel 101 is cooled
to a point where it begins to solidify on the upstream portion of
the inlet heat exchanger 414, at which point the available thermal
energy in the vessel 101 is substantially depleted. It is
preferable that the system 100 not be operated such that the molten
salt completely freezes and encloses the heater exchangers 412-418.
This is because the enhanced heat transfer provided by the fluid
flow caused by the mixer would then no longer be available. After
depletion of the thermal energy in the vessel 101, the salt is
maintained 550 in a heated state with minimal heat loss by virtue
of the substantial amount of thermal insulation surrounding the
entire vessel. In the event that it is necessary to completely shut
down the process, or to interrupt the process for a prolonged
period of time, it is permissible to allow some or all of the
entire contents of the vessel to solidify. The solid salt in the
vessel can be re-melted by resuming the circulation of hot heat
transfer fluid through the heat exchangers 412-418.
[0124] It is also noted that it is not necessary to have the vessel
fully charged to maximum thermal capacity 565 before delivering 570
thermal energy to the power generating station 20, as indicated by
dotted line arrow 568. If conditions warrant, a partial thermal
charge may be delivered 570 to the power generating station 20.
Additionally, even if the temperature of the molten salt in the
vessel 101 is relatively low, and only a small amount of thermal
energy is available in the vessel 101, that energy may still be
beneficially used. As described previously, the low grade heat that
is not hot enough to produce steam in the power generating station
20 can be used to preheat the oil in the solar field 10 and/or to
preheat feed water in the power generating station 20. This will
enable a faster daily startup of the power generating station 20,
which will bring the turbine cycle of the station 20 to full load
sooner and increase the daily energy production of the station
20.
[0125] It is, therefore, apparent that there has been provided, in
accordance with the present invention, a vessel for containing a
thermal energy storage liquid, a thermal energy storage system
comprising such vessel, and methods for making and using the vessel
and thermal energy storage system. Having thus described the basic
concept of the invention, it will be rather apparent to those
skilled in the art that the foregoing detailed disclosure is
intended to be presented by way of example only, and is not
limiting. Various alterations, improvements, and modifications will
occur and are intended to those skilled in the art, though not
expressly stated herein. These alterations, improvements, and
modifications are intended to be suggested hereby, and are within
the spirit and scope of the invention. Additionally, the recited
order of processing elements or sequences, or the use of numbers,
letters, or other designations therefore, is not intended to limit
the claimed processes to any order except as may be specified in
the claims. Accordingly, the invention is limited only by the
following claims and equivalents thereto.
* * * * *