U.S. patent application number 14/345247 was filed with the patent office on 2015-09-10 for thermal energy storage system with input liquid kept above 650.degree.c.
This patent application is currently assigned to SHEC ENERGY CORPORATION. The applicant listed for this patent is James Thomas Beck. Invention is credited to James Thomas Beck.
Application Number | 20150253084 14/345247 |
Document ID | / |
Family ID | 47882485 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150253084 |
Kind Code |
A1 |
Beck; James Thomas |
September 10, 2015 |
THERMAL ENERGY STORAGE SYSTEM WITH INPUT LIQUID KEPT ABOVE
650.degree.C
Abstract
A thermal energy storage system has an insulated storage
container filled with a particulate earth material. A heat input
conduit circuit is buried in the earth material and transfers heat
from an input liquid flowing in the heat input conduit circuit to
the earth material. A heat output system is operative to transfer
heat from the earth material in the storage container to an
external heat consumer. During operation the input liquid enters
the inlet port of the heat input conduit circuit at an input
operating temperature and leaves the outlet port at an output
operating temperature, and the output operating temperature is
above about 650.degree. C. The input liquid remains liquid at the
input and output operating temperatures under atmospheric pressure.
Energy is stored at a relatively high temperature compared to the
prior art, and provides increased efficiency for heat consuming
processes.
Inventors: |
Beck; James Thomas;
(Saskatoon, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Beck; James Thomas |
Saskatoon |
|
CA |
|
|
Assignee: |
SHEC ENERGY CORPORATION
Saskatoon
SK
|
Family ID: |
47882485 |
Appl. No.: |
14/345247 |
Filed: |
September 14, 2012 |
PCT Filed: |
September 14, 2012 |
PCT NO: |
PCT/CA2012/000836 |
371 Date: |
May 26, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61535391 |
Sep 16, 2011 |
|
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|
Current U.S.
Class: |
165/10 |
Current CPC
Class: |
F28D 2020/0078 20130101;
F28D 2020/0065 20130101; Y02E 60/14 20130101; Y02E 60/142 20130101;
F28F 2265/12 20130101; F28D 20/0056 20130101 |
International
Class: |
F28D 20/00 20060101
F28D020/00 |
Claims
1. A thermal energy storage system comprising: an insulated storage
container substantially filled with a particulate earth material; a
heat input conduit circuit buried in the earth material and
configured to transfer heat from an input liquid flowing in the
heat input conduit circuit to the earth material, the heat input
conduit circuit having an inlet port and an outlet port, each port
defined in one of a top, bottom, and side wall of the storage
container; a heat output system operative to transfer heat from the
earth material in the storage container to an external heat
consumer; wherein during operation the input liquid enters the
inlet port of the heat input conduit circuit at an input operating
temperature and leaves the outlet port at an output operating
temperature; wherein the output operating temperature is above
about 650.degree. C.; and wherein the input liquid remains liquid
at the input and output operating temperatures under atmospheric
pressure.
2. The system of claim 1 wherein the earth material comprises one
of sand and crushed lava rock.
3. The system of claim 1 wherein the storage container is sealed
and contains a substantially inert gas atmosphere with the earth
material, and wherein a purge and makeup regulation system is
operative to selectively release inert gas from the storage
container and add inert gas to the storage container to maintain
atmospheric equilibrium therein during thermal expansion and
contraction of the inert gas atmosphere as temperature changes.
4. The system of claim 3 wherein the storage container is formed by
an inner wall and an outer wall with an insulation space between
the inner and outer walls, and wherein the insulation space
contains the same substantially inert gas atmosphere, and wherein a
purge and makeup regulation system is operative to selectively
release inert gas from the insulation space and add inert gas to
the insulation space to maintain atmospheric equilibrium therein
during thermal expansion and contraction of the inert gas
atmosphere as temperature changes.
5. The system of claim 3 wherein the substantially inert gas
atmosphere comprises at least one of nitrogen, carbon dioxide,
helium, and argon.
6. The system of claim 1 wherein walls of the storage container
comprise stainless steel.
7. The system of claim 1 wherein the storage container is buried in
the ground such that the ground supports walls of the storage
container.
8. The system of claim 1 wherein the heat input conduit circuit is
divided into at least first and second input zones and is
configured such that the flow of input liquid can be directed
through one of the first input zone, the second input zone, and
both input zones to transfer heat to earth material in one or both
corresponding first and second earth material zones.
9. The system of claim 8 wherein the heat output system is
operative to transfer heat from the earth material in one of the
first earth material zone, the second earth material zone, and both
earth material zones to the external heat consumer.
10. The system of claim 1 wherein at least one conduit of the heat
input conduit circuit comprises a main conduit and at least one
auxiliary conduit arranged in proximity to the main conduit,
wherein the input liquid flows in the main conduit, and wherein an
auxiliary liquid flows in the at least one auxiliary conduit such
that heat transfers from the auxiliary liquid to the input liquid,
and wherein a melting temperature of the auxiliary liquid is less
than a melting temperature of the input liquid.
11. The system of claim 10 wherein the auxiliary conduit is inside
the main conduit.
12. The system of claim 10 comprising first and second auxiliary
conduits, wherein the first auxiliary conduit is arranged in
proximity to the main conduit such that heat is transferred from a
first auxiliary liquid flowing in the first auxiliary conduit to
the input liquid, and wherein the second auxiliary conduit is
arranged in proximity to the first auxiliary conduit such that heat
is transferred from a second auxiliary liquid flowing in the second
auxiliary conduit to the first auxiliary liquid, and wherein a
melting temperature of the first auxiliary liquid is less than a
melting temperature of the input liquid and wherein a melting
temperature of the second auxiliary liquid is less than a melting
temperature of the first auxiliary liquid.
13. The system of claim 12 wherein the first and second auxiliary
conduits are inside the main conduit.
14. The system of claim 13 wherein the second auxiliary conduit is
inside the first auxiliary conduit.
15. The system of claim 10 wherein a boiling temperature of the
auxiliary liquid at atmospheric pressure is greater than the input
operating temperature.
16. The system of claim 12 wherein a boiling temperature of the
first auxiliary liquid at atmospheric pressure is greater than the
input operating temperature.
17. The system of claim 12 wherein the second auxiliary liquid has
a melting point lower than ambient temperature at a location of the
system.
18. The system of claim 17 wherein the second auxiliary liquid is
water, and the first auxiliary liquid is a metal alloy.
19. The system of claim 18 wherein the melting temperature of the
metal alloy is below a boiling temperature of the water in the
second auxiliary conduit.
20. The system of claim 19 wherein pressure is maintained in the
second auxiliary conduit to increase the boiling temperature of the
water in the second auxiliary conduit.
21. The system of claim 18 comprising a valve operative to
selectively release pressure from the second auxiliary conduit such
that the water in the second auxiliary conduit boils out of the
secondary auxiliary conduit.
22. The system of claim 1 wherein the heat output system comprises
a heat output conduit circuit buried in the earth material and
configured to transfer heat from the earth material in the storage
container to an output liquid flowing in the heat output conduit
circuit.
23. The system of claim 22 wherein a temperature of the output
liquid delivered to the external heat consumer is controlled by
adjusting one of a bypass mixing valve and a variable output pump
circulating the output liquid through the heat output conduit
circuit.
24. The system of claim 22 wherein the heat output conduit circuit
is connected to circulate through an input loop of a heat exchanger
and wherein an output loop of the heat exchanger is connected to a
boiler, and wherein the output liquid in the heat output conduit
circuit and the input loop of a heat exchanger is sodium, and
wherein a boiler liquid in the output loop of the heat exchanger is
not sodium.
25. The system of claim 1 wherein the input liquid is one of
aluminum, sodium, and tin.
Description
[0001] This invention is in the field of thermal energy and in
particular systems for storing thermal energy, such as that
generated by solar collection.
BACKGROUND
[0002] A significant problem with solar energy development is the
cyclical nature of the energy collection due to day and night
cycles, and the variability in the amount of energy collected due
to cloud cover. For most practical uses it is necessary to have a
steady supply of energy. Some uses, for example electrical power
consumption, are also themselves cyclical in nature, with peak
demand often twice the minimum demand.
[0003] It is therefore desirable to store thermal energy collected
from the sun and draw the energy when needed. Present technology
uses oil or molten salt as a thermal energy transfer medium. Molten
salt is also used as a thermal energy storage medium. A molten salt
presently being used is a mixture of 60 percent sodium nitrate and
40 percent potassium nitrate, and has certain desirable properties.
It is liquid at atmosphere pressure, it provides an efficient,
low-cost medium in which to store thermal energy, its operating
temperatures are compatible with today's high-pressure and
high-temperature steam turbines, and it is non-flammable and
nontoxic.
[0004] The salt melts at 221.degree. C. and can be maintained in a
liquid state in a "cold storage tank at about 280.degree. C., then
circulated through a solar collector apparatus where the
temperature is increased to about 560.degree. C., then it flows
into a heavily insulated "hot storage tank, where it can be stored
for up to a week. When needed, hot molten salt is drawn from the
hot storage tank and circulated through a conventional steam
generator creating steam to operate a conventional steam turbine to
generate electrical power. It is calculated that a 100-megawatt
turbine would need tanks of about 30 feet (9.1 m) tall and 80 feet
(24 m) in diameter to drive it for four hours by this design.
[0005] Conventional solar towers can increase the temperature of
the molten salt to about 560.degree. C., however the temperature of
the molten salt drops in the steam generator such that the
temperature of the generated steam is only about 280.degree. C.
Conventional steam turbines operating at this temperature have
substantially reduced efficiency when compared to a higher
temperature steam turbine operating at about 560.degree. C.
[0006] Solar collectors are also known which can generate thermal
energy at increased temperatures of about 850.degree. C. Such a
collector is described for example in United States Published
Patent Application Number 20080184990 of Tuchelt. Increasing the
temperature of a storage medium to this increased temperature of
850.degree. C. in the system described above, or higher, would
allow steam to be generated with a temperature of about 560.degree.
C., which is an ideal temperature for conventional steam turbines,
and which would provide significantly improved efficiency, and
therefore increased electrical production from collected solar
energy and reduced cost of electricity.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a
thermal energy storage system that overcomes problems in the prior
art.
[0008] The present invention provides a thermal energy storage
system comprising an insulated storage container substantially
filled with a particulate earth material. A heat input conduit
circuit is buried in the earth material and is configured to
transfer heat from an input liquid flowing in the heat input
conduit circuit to the earth material. The heat input conduit
circuit has an inlet port and an outlet port, each port defined in
one of a top, bottom, and side wall of the storage container. A
heat output system is operative to transfer heat from the earth
material in the storage container to an external heat consumer.
During operation the input liquid enters the inlet port of the heat
input conduit circuit at an input operating temperature and leaves
the outlet port at an output operating temperature, and the output
operating temperature is above about 650.degree. C. The input
liquid remains liquid at the input and output operating
temperatures under atmospheric pressure.
[0009] The high input operating temperature transfers heat energy
to the earth material, which is generally a poor conductor,
primarily by radiation. The high storage temperature allows heat to
be removed at a higher temperature than conventional systems, which
higher out put temperature provides greater efficiency for
operating steam turbines and the like.
DESCRIPTION OF THE DRAWINGS
[0010] While the invention is claimed in the concluding portions
hereof, preferred embodiments are provided in the accompanying
detailed description which may be best understood in conjunction
with the accompanying diagrams where like parts in each of the
several diagrams are labeled with like numbers, and where:
[0011] FIG. 1 is a schematic top view of an embodiment of a thermal
storage system of the present invention, and also showing a heat
output system that is provided by a heat output conduit circuit
buried in the earth material of the thermal storage system;
[0012] FIG. 2 is a schematic side view of the thermal storage
system and heat output system of FIG. 1;
[0013] FIG. 3 is a schematic top view of another embodiment of a
thermal storage system of the present invention, where the storage
container is divided horizontally and vertically into zones;
[0014] FIG. 4 is a schematic side view of the thermal storage
system of FIG. 3;
[0015] FIG. 5 a schematic sectional view of a portion of the heat
input conduit circuit with an auxiliary conduit carrying an
auxiliary liquid for melting the input liquid in the main conduit
where the auxiliary conduit is adjacent to the main conduit;
[0016] FIG. 6 a schematic sectional view of a portion of the heat
input conduit circuit with an auxiliary conduit carrying an
auxiliary liquid for melting the input liquid in the main conduit
where the auxiliary conduit is inside the main conduit;
[0017] FIG. 7 a schematic sectional view of a portion of the heat
input conduit circuit with an first and second auxiliary conduits
carrying a first and second auxiliary liquids for melting the input
liquid in the main conduit, where the first and second auxiliary
conduits are adjacent to the main conduit;
[0018] FIG. 8 a schematic sectional view of a portion of the heat
input conduit circuit with an first and second auxiliary conduits
carrying a first and second auxiliary liquids for melting the input
liquid in the main conduit, where the first and second auxiliary
conduits are inside the main conduit
[0019] FIG. 9 a schematic sectional view of a portion of the heat
input conduit circuit with an first and second auxiliary conduits
carrying a first and second auxiliary liquids for melting the input
liquid in the main conduit, where the first auxiliary conduit is
inside the main conduit and the second auxiliary conduit is inside
the first auxiliary conduit;
[0020] FIG. 10 is a schematic view of a heat consumer for
connection to the thermal storage system of FIG. 1, where the heat
output conduit circuit is connected to an input loop of a heat
exchanger, and the output loop of the heat exchanger is connected
to a boiler
[0021] FIG. 11 schematically illustrates a purge and makeup
regulation system for use with a sealed storage container
containing an inert gas atmosphere.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0022] FIGS. 1 and 2 schematically illustrate an embodiment of a
thermal energy storage system 1 of the present invention. The
system 1 comprises an insulated storage container 3 substantially
filled with a particulate earth material 5. The earth material 5
will typically be a material such as sand, crushed lava rock, or
the like that is available in the local area to reduce costs.
[0023] A heat input conduit circuit 7 is buried in the earth
material 5 and is configured to transfer heat from an input liquid
9 flowing in the heat input conduit circuit 7 to the earth material
5. The heat input conduit circuit 7 has an inlet port 11 and an
outlet port 13 defined in one of a top, bottom, and side wall of
the storage container 3.
[0024] It is contemplated that the heat source 15 of the heat input
liquid 9 will commonly be a solar energy collector capable of
raising the temperature to the desired temperature above about
750.degree. C. to 900.degree. C., however it is also contemplated
that other energy sources could provide the input liquid 9 at the
required temperature as well. During operation, the input liquid 9
enters the inlet port 11 of the heat input conduit circuit at an
input operating temperature and leaves the outlet port 13 at a
lower output operating temperature. The input operating temperature
is above about 750.degree. C. to 900.degree. C., and at this
elevated temperature heat is transferred primarily by radiation.
The earth material 5 in the storage container 3 is a poor conductor
of heat, and so in order to effectively transfer energy to the
earth material, the input liquid 9 must be at a relatively high
temperature.
[0025] The energy transferred from the input liquid 9 to the earth
material is proportional to the fourth power of the absolute
temperature of the input liquid 9. Thus it can be seen that at
800.degree. C. or 1073 kelvins (K), power output of the input
liquid will be 1.325X , while at 750.degree. C. or 1023 K the power
output of the input liquid 9 will be only 1.095X , or 83% of the
power output at 800.degree. C., and at 700.degree. C. or 973 K the
power output of the input liquid 9 will be only 0.896X, or 67% of
the power output at 800.degree. C. At 650.degree. C. or 923 K the
power output of the input liquid 9 will be only 0.726X, or 55% of
the power output at 800.degree. C.
[0026] Also it can be seen that increasing the input operating
temperature will increase the rate of transfer of energy from the
input liquid 9 to the earth material 5. For example at 900.degree.
C. or 1173 K the power output of the input liquid 9 will be 1.893X
, or 142% of the power output at 800.degree. C.
[0027] As the input liquid 9 circulates from the inlet port 11 to
the outlet port 13 energy moves from the input liquid 9 to the
earth material 5 and the temperature of the input liquid 9 drops
from the input operating temperature to the output operating
temperature. The rate of transfer of energy to the earth material 5
is much reduced when the temperature drops and it is contemplated
that the temperature of the input liquid 9 in the heat input
conduit circuit 7 should not fall below about 650.degree. C. or
insufficient heat transfer will occur to heat the earth material
5.
[0028] The temperature of the input liquid 9 falls generally
proportional to the time it is in the heat input conduit circuit 7.
The output temperature can thus be controlled by increasing or
decreasing the rate of flow of the input liquid through the heat
input conduit circuit 7. Thus for example where the input operating
temperature is 800.degree. C., the input liquid may be circulated
at a rate of X gallons per minute to result in an output operating
temperature of 650.degree. C., but where the input operating
temperature is only 750.degree. C., the input liquid will need to
be circulated at a higher rate of X+ gallons per minute to result
in the desired output operating temperature of 650.degree. C.
[0029] A heat output system is operative to transfer heat from the
earth material 5 in the storage container 3 to an external heat
consumer 21, such as a boiler or like apparatus that will utilize
the heat energy. Similarly to the input mechanism described above,
and again because the earth material 5 is a poor conductor, the
heat is drawn out of the earth material also primarily by
radiation. While the earth material 5 is a poor conductor, it is
also very cheaply available in the very large quantities
contemplated as necessary for electric power generation or like
large scale uses, and in the system 1 of the present invention
using the high temperature input liquid 9, an economical storage
system for heat energy is provided, and available to be drawn out
for various uses.
[0030] It is contemplated that the heat output system would
typically be a heat output conduit circuit 17 with an output liquid
19 flowing therethrough, and arranged similar to the heat input
conduit circuit 7 to absorb heat energy radiated from the heated
earth material 5. The temperature of the output liquid 19 will be
significantly lower than the input liquid 9, and so the output
liquid 19 will typically be a different liquid than the input
liquid 9 with a lower melting temperature. It is also contemplated
that the heat output system could comprise heat pipes or other
systems known in the art to move heat energy from the earth
material 5 to a heat consuming process 21 such as a boiler.
[0031] The input liquid 9 is selected so that it will remain liquid
at the input and output operating temperatures under atmospheric
pressure. One possible choice that has several advantages is
aluminum, with a melting point of 660.degree. C. and a boiling
point above the operating temperature range. It is relatively
economical and very light weight thereby reducing the energy needed
to circulate it. It is also contemplated that in order to provide a
significant portion of the world's energy from solar power, a great
deal of this input liquid will be required, and aluminum also has
the advantage of being very plentiful, as it is the third most
abundant element in the earth's crust at about 8.1%.
[0032] Another possible choice for the input liquid 9 is sodium,
which has a melting point of just 98.degree. C. and an atmospheric
boiling point 883.degree. C. which is above the contemplated
operating temperatures. Sodium is also very light weight,
inexpensive, and plentiful, but has the major drawback that it
becomes explosive when mixed with water and poses a significant
danger in the event of a failure. A further possible choice for the
input liquid 9 is tin, which has a melting point of 232.degree. C.
and a boiling point also above the operating temperature range, but
tin is more costly, and less plentiful. It is contemplated other
materials may be found to be suitable as well. Tin and sodium may
be suitable for use as the output liquid 19, as both have a
relatively low melting temperature.
[0033] Thus the only pressure in the heat input conduit circuit 7
is that exerted by the pumps circulating the input liquid. At the
high operating temperatures of the present system 1, the metal of
the pipes forming the heat input conduit circuit 7 is susceptible
to failure, and by keeping the pressures inside low, the risk of
failure, leakage, and the like is reduced. Operating at low
pressure also allows for the use of less costly conduit materials
than those required for both high temperature and high pressure
operation.
[0034] The illustrated container 3 is formed by an inner wall and
an outer wall with an insulation space 23 between the inner and
outer walls that is filled with an insulating material.
[0035] FIGS. 3 and 4 schematically illustrate a different
embodiment of the thermal energy storage system 101 of the present
invention where the storage container 103 is buried in the ground
102 such that the ground supports walls of the storage container
103. This arrangement significantly reduces the structural strength
required of the container walls. Also the storage container 103 is
a cube with equal dimensions for length, width, and height, and
providing a maximum volume of earth material 105 with a minimum
wall surface area, thus reducing heat loss through the walls. The
storage container may also be cylindrical in shape as in the
embodiment of FIGS. 1 and 2. This cylindrical shape would be
particularly applicable for an above ground installation in which
the weight of the earth material 105 would want to naturally form
this shape. It also may be possible in some areas to dig the hole
required for the storage container 103 by removing suitable earth
material 105.
[0036] In the system 101, the heat input conduit circuit 107 from
the source 115 is divided vertically and horizontally into eight
substantially cubic input zones 129, as schematically illustrated
by dotted lines 131. By manipulating valves 133, the input conduit
circuit 107 can be configured such that the flow of input liquid
109 can be directed through selected input zones 129, or
combinations of the input zones 129, or through all the input zones
129 at once to transfer heat to earth material in corresponding
earth material zones 135.
[0037] The heat output system 117 may likewise be operative to
transfer heat from selected earth material zones 135, or
combinations of the earth material zones 135, or all the earth
material zones 135 to an external heat consumer 121.
[0038] Thus with the system 101, the output system 117 would draw
the temperature of the earth material in a zone 135 down by a
desired amount, for example 50.degree. C., and then the output
system 117 would be changed to draw from a different zone 135.
Similarly the heat input conduit circuit 107 could be configured to
circulate input liquid 109 through each zone 129 separately or in
combination, depending on the amount of heat available from the
source 115 and the heat being drawn out by the heat output system
117.
[0039] In either system 1 or 101, but referring for convenience to
system 1 of FIGS. 1 and 2, if the temperature of the input liquid
falls below its melting point the liquid will solidify in the
conduits of the heat input conduit circuit 7. For example where the
input liquid is aluminum, when the temperature thereof drops to
660.degree. C., the input liquid will turn to a solid. It is thus
desirable to provide a system for reheating the input liquid to the
melting point. Where the source 15 of the heat input liquid 9 is a
solar collection system, it is contemplated that, particularly
where the input liquid is aluminum with a higher melting point
compared to tin or sodium, the input liquid will solidify at least
periodically in some portions of the heat input conduit circuit 7
during the night or during cloudy periods.
[0040] Pumps, valves, junctions, and like areas of the heat input
conduit circuit 7 are typically heated to the melting point of the
input liquid 9 by electrical heaters. The entire heat input conduit
circuit 7 could also be heated by electricity however it is
desirable to be able to heat lengthy portions of the heat input
conduit circuit 7, such as those buried in the earth material 5 or
that connect the storage container 3 to the heat source 15,
directly with heat from the heat source 15.
[0041] FIG. 5 schematically illustrates a cross-section of a
portion of the heat input conduit circuit 7 that comprises a main
conduit 41 and an auxiliary conduit 43 arranged in proximity to the
main conduit 41. In operation the input liquid 9 flows in the main
conduit 41, and an auxiliary liquid 45 flows in the auxiliary
conduit, such that heat transfers from the auxiliary liquid 45 to
the input liquid 9. The auxiliary liquid is selected to have a
melting temperature that is less than a melting temperature of the
input liquid 9.
[0042] In operation then if the temperature of the portion of the
heat input conduit circuit 7 drops below the melting temperature of
the input liquid, the auxiliary will remain liquid until the
temperature of the auxiliary liquid also drops below its melting
temperature, which will be much lower, and so will not often be
encountered unless the heat source goes cold for an extended
period. While the auxiliary liquid 45 is liquid, it can be
circulated through auxiliary conduit 43 to the heat source 15 to
raise the temperature thereof well above the melting point of the
input liquid 9 and the heat from the auxiliary liquid 45
circulating in the auxiliary conduit 43 will be transferred to the
main conduit 41 to melt the input liquid 9. In order to avoid
building pressure in the auxiliary conduit 43, the auxiliary liquid
45 can be selected to have a boiling temperature at atmospheric
pressure that is greater than the input operating temperature.
[0043] FIG. 5 shows a heat input conduit circuit portion 7 where
the auxiliary conduit 43 is beside the main conduit 41, and FIG. 6
shows an optional arrangement where the auxiliary conduit 43 is
inside the main conduit 41.
[0044] The auxiliary liquid could be a metal alloy with a low
melting point, such as Field's metal with a melting temperature of
62.degree. C. or Woods metal with a melting temperature of
70.degree. C. Field's metal may be more suitable as same contains
no harmful lead or cadmium. The auxiliary liquid 45 may be
relatively costly compared to the input liquid 9, but could be
drained from the auxiliary conduit 43 and used in different heat
input conduit circuits at different times as required, so it is
contemplated that the cost will not be prohibitive.
[0045] While it is contemplated that the auxiliary liquid 45 will
not often fall below its melting temperature, means should
generally be provided to also melt the auxiliary liquid if it does
solidify. FIGS. 7-9 schematically illustrate a heat input conduit
circuit comprising the main conduit 41, and two auxiliary conduits
43A, 43B.
[0046] The first auxiliary conduit 43A is arranged in proximity to
the main conduit 41 such that heat is transferred from a first
auxiliary liquid 45A flowing in the first auxiliary conduit 43A to
the input liquid 9 in the main conduit 41, and the second auxiliary
conduit 4313 is arranged in proximity to the first auxiliary
conduit 43A such that heat is transferred from a second auxiliary
liquid 45B flowing in the second auxiliary conduit 43B to the first
auxiliary liquid 45A. The melting temperature of the first
auxiliary liquid 45A is less than a melting temperature of the
input liquid 9 and, in turn the melting temperature of the second
auxiliary liquid 45B is less than a melting temperature of the
first auxiliary liquid 45A.
[0047] The second auxiliary liquid 45B can conveniently be selected
to also have a melting point lower than ambient temperature at the
location of the system. Thus if the entire system goes cold, the
second auxiliary liquid 45B will remain liquid and can be
circulated through the heat source to raise the temperature thereof
to a level above the melting point of the first auxiliary liquid
45A, which in turn is circulated through the heat source as
described above to melt the input liquid 9.
[0048] The second auxiliary liquid 45B conveniently can be water.
The melting temperature of the metal alloy of first auxiliary
liquid 45A can be selected to be below the boiling temperature of
the water at atmospheric pressure, such that the water of the
second auxiliary liquid 45B in the second auxiliary conduit 43B is
not under pressure.
[0049] If the melting temperature of the metal alloy of first
auxiliary liquid 45A is above the boiling temperature of the water
at atmospheric pressure, some increased pressure could be
maintained in the second auxiliary conduit 43B to increase the
boiling temperature of the water in the second auxiliary conduit
43B. As schematically illustrated in FIG. 7, a valve 47 can be
provided to selectively release pressure from the second auxiliary
conduit 43B such that the water in the second auxiliary conduit 43B
simply boils out of the secondary auxiliary conduit 43B as the
temperature in the heat input conduit circuit 7 rises.
[0050] FIG. 7 schematically illustrates a heat input conduit
circuit 7 comprising the main conduit 41, and two auxiliary
conduits 43A, 43B placed adjacent to the main conduit 41. In the
embodiment of FIG. 8, the two auxiliary conduits 43A, 43B are
placed inside the main conduit 41, and in FIG. 9 the second
auxiliary conduit 43B is inside the first auxiliary conduit 43A
which in turn is inside the main conduit 41. It is contemplated
that placing the auxiliary conduits 43A, 43B inside the main
conduit 41 may make a convenient package and facilitate
installation and/or maintenance in the earth material filled
storage container.
[0051] FIG. 10 schematically illustrates a heat consumer 21 for
connection to the heat output system of the energy storage system 1
of FIGS. 1 and 2 that includes a heat output conduit circuit 17
with an output liquid 19 flowing therethrough. The heat output
conduit circuit 17 is connected to a heat exchanger 51 which
transfers heat from the output liquid 17 to a secondary liquid 53
from the heat exchanger 51 to a boiler 55. The heat exchanger 51
maintains separation between the output liquid 19 and the boiler 55
which contains water. The separation allows the output liquid to be
more safely provided by sodium, which is relatively inexpensive,
and has a low melting temperature of 98.degree. C. With the sodium
flowing as the output liquid in the input loop of the heat
exchanger 51, and tin or some like non-hazardous as the secondary
liquid 53 flowing in the heat output loop of the heat exchanger 51
to the boiler 55, there is little risk of contact between the
sodium in the heat output conduit circuit 17 and the water in the
boiler 55.
[0052] With the earth material 5 in the storage container 3 at a
temperature of about 750.degree. C., it is calculated that the
boiler 55 could provide steam at a temperature of about 550.degree.
C. which is an efficient temperature for operating a modern
conventional steam turbine to produce electrical power. The
temperature of the output liquid 19 flowing to the heat consumer 21
can be controlled to a desired temperature, for example by
adjusting a bypass mixing valve 57, or by varying the rate of flow
of output liquid 19 through the heat output conduit circuit 17 with
a variable output pump 59.
[0053] Thus in a typical energy storage system 1 of the present
invention, the input liquid 9 is aluminum with a melting
temperature of 660.degree. C., the first auxiliary liquid 45A is a
metal allow such as Field's metal with a melting temperature of
62.degree. C., and the second auxiliary liquid 45B is water. The
first and second auxiliary conduit may remain empty until it is
necessary to melt the aluminum input liquid. Initially at start up,
the heat input conduit circuit 17 will be preheated with steam or
the like to a temperature approaching 660.degree. C. and then the
molten aluminum will be pumped through and substantially fill the
heat input conduit circuit 7. From this point, depending on the
operation of the heat source 15, the liquid aluminum 9 will
circulate until the temperature thereof drops below 660.degree. C.
The Field's metal 45A will remain liquid if present until the
temperature drops below 62.degree. C. The water 45B will not
usually be present in the auxiliary conduit 43B until it is needed
to heat the Field's metal 45A.
[0054] It is calculated that a volume of about 14,700 cubic meters
of earth material would provide sufficient thermal energy storage
for a 20 megawatt electrical turbine. The storage container 3 would
then be a cube about 11.4 meters on each side, with a heat input
conduit circuit buried therein with conduits of about five
centimeters (cm) in diameter spaced about 25 cm apart in a grid
throughout the earth material 5 filing the storage container 3.
[0055] The container 3, and insulation space 23 if desired, can
also be sealed and filled with a substantially inert gas atmosphere
of nitrogen, carbon dioxide, helium, argon, or the like which will
keep the earth material dry and reduce corrosion of the material of
the container walls. A suitable wall material is stainless steel,
which will resist corrosion. Where the storage container 3 and
insulation space 23 is sealed, as schematically illustrated in FIG.
11, the pressure inside them will rise and fall as the temperature
varies. To avoid excessive expanding and collapsing pressures being
exerted on the container walls, a purge and makeup regulation
system 61 is operative to selectively release inert gas from the
storage container 3 and insulation space 23 through a vent 63 to
the ambient atmosphere, and add inert gas from a pressurized gas
container 65 to the storage container 3 and insulation space 23, to
maintain atmospheric equilibrium therein during thermal expansion
and contraction of the inert gas atmosphere as temperature
changes
[0056] The foregoing is considered as illustrative only of the
principles of the invention. Further, since numerous changes and
modifications will readily occur to those skilled in the art, it is
not desired to limit the invention to the exact constriction and
operation shown and described, and accordingly, all such suitable
changes or modifications in structure or operation which may be
resorted to are intended to fall within the scope of the claimed
invention.
* * * * *