U.S. patent application number 14/394141 was filed with the patent office on 2015-03-05 for system for storing and outputting thermal energy and method for operating said system.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Ursus Kruger, Daniel Reznik, Henrik Stiesdal.
Application Number | 20150059342 14/394141 |
Document ID | / |
Family ID | 48190472 |
Filed Date | 2015-03-05 |
United States Patent
Application |
20150059342 |
Kind Code |
A1 |
Kruger; Ursus ; et
al. |
March 5, 2015 |
SYSTEM FOR STORING AND OUTPUTTING THERMAL ENERGY AND METHOD FOR
OPERATING SAID SYSTEM
Abstract
A system for storing and outputting thermal energy and a method
for operating the system are provided. The system operates
according to the Brayton cycle, wherein a heat accumulator is
charged by a compressor and a cold accumulator is charged by
turbines. The cycle is reversed for discharging. In addition, the
cold accumulator supplies a cooling circuit, which provides the
cooling for a superconducting generator by a cooling unit. A
favorable generator weight can thereby be advantageously achieved
in particular for wind turbines, because the generators are limited
regarding the weight thereof due to being housed in the nacelle of
the wind power plant. Thus, advantageously higher power can be
converted in the wind power plant.
Inventors: |
Kruger; Ursus; (Berlin,
DE) ; Reznik; Daniel; (Berlin, DE) ; Stiesdal;
Henrik; (Odense C, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Munich |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
48190472 |
Appl. No.: |
14/394141 |
Filed: |
March 28, 2013 |
PCT Filed: |
March 28, 2013 |
PCT NO: |
PCT/EP2013/056735 |
371 Date: |
October 13, 2014 |
Current U.S.
Class: |
60/650 ;
60/659 |
Current CPC
Class: |
F25B 2400/14 20130101;
F25B 9/004 20130101; F01K 3/12 20130101; F25B 2400/24 20130101;
F25B 2400/053 20130101; F25B 9/06 20130101; F01K 3/06 20130101 |
Class at
Publication: |
60/650 ;
60/659 |
International
Class: |
F01K 3/12 20060101
F01K003/12; F01K 3/06 20060101 F01K003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2012 |
DE |
10 2012 206 296.3 |
Claims
1. A plant for storing and releasing thermal energy, comprising: a
charging circuit and a discharging circuit for a working gas,
wherein in the charging circuit the following units are
interconnected in the specified sequence by means of a line for the
working gas: a first thermal fluid energy machine, a heat
accumulator, a second thermal fluid energy machine, and a cold
accumulator, wherein the first thermal fluid energy machine is
operated as a working machine and the second thermal fluid energy
machine is operated as a power machine, as seen in the flow
direction of the working gas from the heat accumulator to the cold
accumulator, wherein the cold accumulator is adapted to be
connected into a cooling circuit which is separated from the
aforesaid circuits and in which the following units are
interconnected in the specified sequence by means of a line for a
cooling medium: the cold accumulator, a cooling unit, and a cold
consumer which is to be cooled.
2. The plant as claimed in claim 1, wherein the cold consumer is an
electric machine with superconducting components.
3. The plant as claimed in claim 2, wherein the electric machine is
a generator.
4. The plant as claimed in claim 3, wherein the generator is
installed in a wind power plant.
5. The plant as claimed in claim 2, wherein the electric machine is
a motor which is mechanically coupled to the first thermal fluid
energy machine.
6. The plant as claimed in claim 2, wherein the electric machine is
a generator which is coupled to the first thermal fluid energy
machine, or to a third thermal fluid energy machine, wherein the
third thermal fluid energy machine is connected in parallel with
the first thermal fluid energy machine and a fourth thermal fluid
energy machine is connected in parallel with the second thermal
fluid energy machine in the charging and discharging circuit,
wherein a valve mechanism is provided in each case between the
first and the third thermal fluid energy machines and between the
second and the fourth thermal fluid energy machines.
7. The plant as claimed in claim 2, wherein a high-temperature
superconductor is used for the superconducting components.
8. A method for storing and releasing thermal energy, comprising:
passing a working gas through a charging circuit or a discharging
circuit, wherein in the charging circuit flow passes through the
following units in the specified sequence: a first thermal fluid
energy machine, a heat accumulator, a second thermal fluid energy
machine, and a cold accumulator, operating the first thermal fluid
energy machine as a working machine and the second thermal fluid
energy machine as a power machine, connecting the cold accumulator,
when required, into a cooling circuit which is separated from said
circuits, wherein in the cooling circuit a cooling medium flows
through the following units in the specified sequence: the cold
accumulator, a cooling unit, and a cold consumer which is to be
cooled.
9. The method as claimed in claim 8, wherein nitrogen is used as
cooling medium.
10. The plant as claimed in claim 7, wherein Bi2223 or YBCO is used
for the superconducting components.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2013/056735 filed Mar. 28, 2013, and claims
the benefit thereof. The International application claims the
benefit of German Application No. DE 102012206296.3 filed Apr. 17,
2012. All of the applications are incorporated by reference herein
in their entirety.
FIELD OF INVENTION
[0002] The invention relates to a plant for storing thermal energy
which has a circuit for a working gas. In the circuit in this case
the following units are interconnected in the specified sequence by
means of a line for the working gas: a first thermal fluid energy
machine, a heat accumulator, a second thermal fluid energy machine
and a cold accumulator.
[0003] The first thermal fluid energy machine is operated as a
working machine and the second thermal fluid energy machine is
operated as a power machine, as seen in the flow direction of the
working gas from the heat accumulator to the cold accumulator.
[0004] Furthermore, the invention relates to two methods for
operating this plant. In one method for storing thermal energy,
passage through the circuit is in the direction of the heat
accumulator to the cold accumulator, which corresponds to the
sequence of the modular units specified above. According to a
further method, to which the invention also refers, stored thermal
energy from the plant can also be converted into mechanical energy,
for example. In this case, passage through the units is in the
reverse sequence, in other words the flow direction of the working
gas is reversed. This working gas then passes first of all through
the cold accumulator and then through the heat accumulator, wherein
in this case the first thermal fluid energy machine is operated as
a power machine and the second thermal fluid energy machine is
operated as a working machine.
BACKGROUND OF INVENTION
[0005] The terms power machine and working machine are used within
the scope of this application so that a working machine absorbs
mechanical work in order to fulfill its purpose. A thermal fluid
energy machine which is used as a working machine is therefore used
as a compressor or fluid compression machine. Compared with this, a
power machine performs work, wherein a thermal fluid energy machine
for performing the work converts the thermal energy which is made
available in the working gas. In this case, the thermal fluid
energy machine is therefore operated as a motor.
[0006] The term "thermal fluid energy machine" constitutes a
generic term for machines which can extract thermal energy from a
working fluid--a working gas within the context of this
application--or can feed thermal energy to this. Both heat energy
and cold energy are to be understood by thermal energy. Thermal
fluid energy machines can be designed as piston machines, for
example. Hydrodynamic thermal fluid energy machines, the impellers
of which allow a continuous flow of the working gas, can preferably
also be used. Axially acting turbines or compressors are preferably
used.
[0007] The principle specified in the introduction is described
according to US 2010/0257862 A1, for example. In this case, piston
machines are used in order to implement the method which is
described above. According to U.S. Pat. No. 5,436,508, moreover, it
is known that by means of the plants for storing thermal energy
which are specified in the introduction over-capacities can also be
temporarily stored when wind energy is being utilized for producing
electric current in order to retrieve this again when required.
SUMMARY OF INVENTION
[0008] An object of the invention is to disclose a plant for
storing thermal energy of the type specified in the introduction
and methods for conversion of thermal energy (for example
conversion of mechanical energy into thermal energy with subsequent
storage or conversion of the stored thermal energy into mechanical
energy) by means of which a utilization of the stored thermal
energy which is as efficient as possible is enabled.
[0009] This object is achieved according to the invention by means
of the plant specified in the introduction by the cold accumulator
being able to be connected into a circuit for a cooling medium,
which differs from the aforesaid circuit, by the following units
being interconnected in the specified sequence by means of a line
for a cooling medium: the cold accumulator, a cooling unit and a
cold consumer which is to be cooled. The cooling medium is normally
different from the working gas which accounts for the fact that the
cooling circuit is different from the circuit. In order to avoid
cleaning during a change of the operating state, it is particularly
advantageous if in the cold accumulator the passages used for heat
transfer also form two passage systems and if in this respect each
of the passage systems can be connected to one of the circuits. The
cooling circuit therefore uses the one passage system, whereas the
charging circuit uses the other passage system. The charging
circuit, however, can share the passage system in the cold
accumulator--and possibly also other parts of the line associated
with this--with a discharging circuit (more about this below).
Whereas the charging circuit is responsible for storing the thermal
energy, the thermal energy can be released again to the working gas
via a discharging circuit.
[0010] The cooling unit is required in order to be able to set the
necessary temperature level for the cold consumer which is to be
cooled because the storage temperature of the cold accumulator is
higher than the necessary temperature level. However, by means of
the cold accumulator precooling of the cooling medium can be
carried out so that a smaller temperature difference has to be
overcome in the cooling unit. This also advantageously reduces the
power demand for the cooling unit. Process cold, which accumulates
anyway in the plant for storing thermal energy, can be utilized.
This is admittedly no longer available during discharging for the
purpose of releasing thermal energy, for which this does not have
to be produced separately, however, for operation of the cold
consumer which is to be cooled. The overall energy balance of the
plant for storing and releasing thermal energy and of the cold
consumer is advantageously improved as a result.
[0011] The charging circuit (and discharging circuit) can be
operated as an open or closed circuit (more about this below). In
the case of an open circuit, air forms the working gas which can be
extracted from the atmosphere and then fed again to this. As a
cooling unit, any form of unit can be used. The use of a
thermosiphon, which advantageously achieves comparatively low
temperature levels, is particularly advantageous.
[0012] The cold consumer is equipped according to a specific
embodiment of the invention with a superconducting component. As
cooling medium, nitrogen can be used here, especially when
high-temperature superconductors, for example Bi2223 or YBCO, are
being used. This has to be brought to a temperature level of
approximately 50 to 60 K. A precooling via the cold accumulator to
approximately 180 K simplifies the cooling process and reduces the
power consumption on the cooling unit.
[0013] According to another embodiment of the invention, it is
provided that the electric machine is a generator which in
particular can be installed in a wind power plant. This application
offers particular advantages since electric machines can be
constructed with superconducting components (especially the winding
of an electrically excited rotor in a synchronous generator) with a
lower mass. The mass of the generator, however, constitutes the
limiting factor in the design of wind power plants since the
generators have to be installed at great height in the nacelle of
the wind power plant. In the case of conventional generators, the
mass of the applied generators increases more quickly, however,
than the output, wherein approximately a power of 1.6 lies within
this ratio. Therefore, at present the economical limit for an
increase of the generator output in wind power plants is
approximately 6 MW. On the other hand, the construction of wind
power plants exposed to strong winds requires the installation of a
larger generator capacity in the nacelle. This can be achieved
according to the invention by using generators with superconducting
components. If the wind power plant is coupled to the plant
according to the invention of storing and releasing thermal energy,
then this has the advantage that the cold accumulator can be
expediently used in order to minimize the losses which become
necessary on account of the required cooling of the superconducting
generator windings. At the same time, this plant for storing
thermal energy can also be used in order to temporarily store, in a
known manner per se, over-capacities in the electricity network and
to convert them again into electric current, by releasing the
thermal energy, in the event of consumption peaks in electric
energy. It therefore involves the utilization of a synergy effect
which altogether increases the efficiency during operation of the
plant especially wind power plants. However, the plant can also be
operated for example with pump storage power plants or with
conventional power plants, such gas-turbine power plants.
[0014] It can furthermore be advantageously provided that the
electric machine is a motor which is mechanically coupled to the
first thermal fluid energy machine. This fluid energy machine has
to be operated specifically during the charging process of the cold
accumulator and of the heat accumulator (possibly also of an
additional low-temperature heat accumulator) in order to bring the
thermodynamic charging process into operation. It is particularly
advantageous to also construct this motor as an electric machine
with a superconducting winding if the infrastructure for cooling
this machine is available on account of using a superconducting
generator, for example in the wind power plant. With this, a
further efficiency increase for the plant is possible.
[0015] It can have an equally efficiency-increasing, advantageous
effect if a further generator with superconducting components (e.g.
the winding) is used as an electric machine. This is then coupled
to the first fluid energy machine and used if in times of increased
energy demand the heat accumulator and the cold accumulator are to
be discharged. It is alternatively also possible that the generator
is connected to a third thermal fluid energy machine, wherein the
third thermal fluid energy machine is connected in parallel with
the first thermal fluid energy machine and a fourth thermal fluid
energy machine is connected in parallel with the second thermal
fluid energy machine in the charging and discharging circuit. In
this case, a valve mechanism is provided in each case between the
first and the third thermal fluid energy machines and/or between
the second and the fourth thermal fluid energy machines. By
switching of the valve mechanism, the one or the other fluid energy
machine can now be advantageously selected in each case, depending
on the flow direction of the working gas. This has the advantage
that the respective fluid energy machine being used can be
optimized to the operating state which is to be selected. Since
when using only two fluid energy machines both have to be used both
as a working machine and as a power machine, depending on the flow
direction, only one constructional compromise can be selected
without the provision of additional fluid energy machines. Since,
however, both in the thermal charging operation and in thermal
discharging operation the aim is a highest possible level of
efficiency, the parallel connection of fluid energy machines allows
both the method for storing the thermal energy and the method for
conversion of the thermal energy to be undertaken with optimum
efficiency. Instead of using valves, separate lines can also be
provided for the charging circuit and the discharging circuit. The
configuration has the advantage that the fluid energy machines
being used in each case can be optimized to the respective
operating state during the charging process and the discharging
process. As a result of this, an increase of efficiency of the
system is achieved. This, however, is at the cost of higher
investment costs of the plant. An economical assessment has to be
made in this case.
[0016] By choice, the working gas can be conducted in a closed
circuit or an open circuit (this applies both to the charging
circuit and to the discharging circuit, but not to the cooling
circuit). An open circuit always uses the ambient air as working
gas. This is drawn from the environment and at the end of the
process is also released into this again so that the environment
closes the open circuit. A closed circuit also allows the use of a
working gas which is other than ambient air. This working gas is
conducted in the closed circuit. Since an expansion into the
environment with simultaneous adjustment of the ambient pressure
and the ambient temperature does not apply, the working gas, in the
case of a closed circuit, has to be conducted through a heat
exchanger which allows a release or absorption of the heat of the
working gas into or from the environment.
[0017] In addition, it can be provided that a low-temperature heat
accumulator is additionally provided in the circuit upstream of the
first fluid energy machine. This heat accumulator is referred to as
a low-temperature heat accumulator because the temperature level
which is reached as a result of storing the heat principally lies
below the temperature level of the heat accumulator. Heat is
defined in relation to the ambient temperature of the plant.
Everything above ambient temperature is heat, whereas everything
below the ambient temperature is cold. Therefore, it also becomes
clear that the temperature level of the cold accumulator lies below
the ambient temperature.
[0018] The use of the low-temperature heat accumulator has the
following advantages. If the plant for storing thermal energy is
used, then the low-temperature heat accumulator is passed through
before passage through the first fluid energy machine which in this
case works as a working machine (compressor). As a result of this,
the working gas is already heated above ambient temperature. This
has the advantage that the working machine has to absorb a lower
level of power in order to achieve the required temperature of the
working gas. In concrete terms, the heat accumulator is to be
heated to above 500.degree. C., which can advantageously also be
carried out, subsequent to the preheating of the working gas, using
technically available thermodynamic compressors which allow
compression of the working gas to 15 bar. Therefore, recourse may
advantageously be had to components for the modular units of the
plant which are obtainable on the market without costly
modifications.
[0019] The achieving of an object is additionally managed by means
of the method referred to in the introduction for storing and
releasing thermal energy by the cold accumulator being connected,
when required, into a cooling circuit which differs from said
circuit, wherein in the cooling circuit cooling medium flows
through the following units in the specified sequence: the cold
accumulator, a cooling unit and a cold consumer which is to be
cooled. By means of this method, the advantages explained above for
the plant according to the invention are achieved, wherein the
method can be implemented with the aforesaid plant. As a
particularly suitable cooling medium, especially for
superconducting components, nitrogen can be used. This exists in
liquid form at the temperatures which are required for cooling
these superconducting components and can be brought to the required
temperature level in a thermosiphon, for example, as the cooling
unit. The precooling via the cold accumulator reduces the energy
expenditure in this case during operation of the cooling unit. This
can also be of smaller dimensions. This make this solution
particularly economical.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Further details of the invention are described below with
reference to the drawing. The same or corresponding elements of the
drawing are provided with the same designations in each case in
this and are repeatedly explained only insofar as differences arise
between the individual figures.
[0021] In the drawing:
[0022] FIG. 1 shows an exemplary embodiment of the plant according
to the invention as a schematic diagram, and
[0023] FIGS. 2 and 3 show exemplary embodiments of the method
according to the invention (Brayton process) with reference to
further schematic diagrams.
DETAILED DESCRIPTION OF INVENTION
[0024] A plant for storing thermal energy according to FIG. 1 has a
line 11 by means of which a plurality of units are interconnected
in such a way that a working gas can flow through these. The
working gas flows through a low-temperature heat accumulator 12 and
then through a first thermal fluid energy machine 13 which is
designed as a hydrodynamic compressor. The line then continues to a
heat accumulator 14. This is connected to a second thermal fluid
energy machine 15 which is designed as a hydrodynamic turbine. From
the turbine, the line 11 leads to a cold accumulator 16. The cold
accumulator 16 is connected to the low-temperature heat accumulator
12 by means of the line 11, wherein in this line section provision
is also made for a heat exchanger 17 via which the working gas can
release heat to the environment or absorb heat from the environment
(depending on the type of operation).
[0025] In FIG. 1, a closed circuit for the working gas is provided
in this respect. However, it is equally conceivable that the line
section between the cold accumulator 16 and the low-temperature
heat accumulator 12 together with the heat exchanger 17 are
dispensed with, in a way not shown. In this case, the circuit via
the environment would be closed, wherein the working gas, which in
this case comprises ambient air, would be drawn in at the
low-temperature heat accumulator 12 and be blown out again into the
environment downstream of the cold accumulator 16.
[0026] Also provided in FIG. 1 is a third thermal fluid energy
machine 18 in the form of a hydrodynamic turbine and a fourth
thermal fluid energy machine 19 in the form of a hydrodynamic
compressor. It is also to be noted that the first hydrodynamic
fluid energy machine 13 in the line 11 is connected in parallel
with the third hydrodynamic machine 18 and the second fluid energy
machine 15 in the line 11 is connected in parallel with the fourth
fluid energy machine 19. Valve mechanisms 20 by opening and closing
ensure that flow only passes through the first and second fluid
energy machines or the third and fourth fluid energy machines in
each case. The first and second fluid energy machines 13 and 15 are
mechanically intercoupled via a first shaft 21 and are driven by an
electric motor M which is fed from a wind power plant 22 as long as
there is no demand for the generated electric energy in the
electricity network. During this operating state, the heat
accumulator 14 and the cold accumulator 16 are charged, as is
explained in more detail later. If the demand for electric energy
is greater in relation to the currently generated quantity of
electric energy, then the electric current generated by the wind
power plant 22 is fed directly into the network. The plant
additionally supports power generation in another operating state
by the heat accumulator 14 and the cold accumulator 16 being
discharged and a generator G1 being driven by the fluid energy
machines 18 and 19 via a second shaft 23. The second shaft 23 is
mechanically coupled to the third fluid energy machine 18 and to
the fourth fluid energy machine 19 for this purpose.
[0027] The construction of the low-temperature heat accumulator 12,
of the heat accumulator 14 and of the cold accumulator 16 in the
plant according to FIG. 1 is the same in each case and is explained
in more detail by means of a detail enlargement based on the cold
accumulator 16. Provided is a container, the wall 24 of which is
provided with an insulating material 25 which has large pores 26.
Provision is made inside the container for concrete 27 which
functions as a heat accumulator or cold accumulator. Pipes 28 which
extend in parallel are laid within the concrete 27 and the working
gas flows through these and in the process releases heat or absorbs
heat (depending on the type of operation and type of
accumulator).
[0028] The cold accumulator 16 also supplies a further line 31 with
the stored cold. For this line 31, a passage system--not shown in
more detail--is provided in the cold accumulator 16 and is
independent of another passage system (not shown either) which is
connected to the line 11. The line 31 is part of a cooling circuit
by means of which a cooling medium, such as nitrogen, can be
precooled. By means of a pump 32, this cooling medium is circulated
in the cooling circuit and also pumped through a cooling unit in
the form of a thermosiphon, which is not shown in more detail. Via
different valves 34, bypass lines 35, which are connected to heat
exchangers 36 in each case, can be connected into the cooling
circuit. The heat exchangers 36 in each case lead to the motor M,
to the generator G1 and to a generator G2 in the wind power plant
22. These generators are provided with superconducting components,
especially windings, comprising high-temperature superconductors.
The cooling medium is sufficient to hold these windings at a
temperature level which the superconducting properties
maintain.
[0029] Shown in FIG. 1 is a variant of the cooling circuit in which
the cooling unit is arranged outside of the wind power plant 22. In
order to keep the paths of the line 31 to be insulated as short as
possible, the cooling unit, however, is to be arranged in the
direct proximity of the wind power plant 22 and of the motor M and
also of the generator G1. Therefore, the cold accumulator 16 should
also be arranged in the vicinity of the wind power plant 22. Such a
cold accumulator 16 will advantageously be allocated in each case
to only one wind power plant 22, or to a few wind power plants 22,
of a wind park. On the other hand, the losses on account of
transporting the cold in the line 31 or the cost of thermal
insulation would be too high.
[0030] With reference to the plant according to FIGS. 2 and 3, the
thermal charging and discharging process shall be explained in more
detail. Shown first of all in FIG. 2 is the charging process which
functions according to the principle of a heat pump. Shown in FIGS.
2 and 3, in contrast to FIG. 1, is an open circuit which, however,
as indicated by dash-dot lines, could be closed using the
optionally provided heat exchanger 17. The states in the working
gas, which in the case of the exemplary embodiment of FIGS. 2 and 3
comprises air, are shown in each case in circles on the lines. At
the top on the left, the pressure in bars is indicated. At the top
on the right, the enthalpy in KJ/Kg is indicated. At the bottom on
the left is the temperature in .degree. C., and at the bottom on
the right the mass flow in Kg/s is indicated. The flow direction of
the gas is indicated by arrows in the line 11.
[0031] In the model calculation the working gas at 1 bar and
20.degree. C. makes its way into the (previously charged)
low-temperature heat accumulator and leaves this at a temperature
of 80.degree. C. As a result of compression by means of the first
fluid energy machine 13, working as a compressor, a pressure
increase to 15 bar takes place and consequently also a temperature
increase to 547.degree. C. This calculation is based on the
following formula
T.sub.2=T.sub.1+(T.sub.2-T.sub.1)/.eta..sub.c;T.sub.2s=T.sub.1.pi..sup.(-
K-1)/K,
wherein
[0032] T.sub.2 is the temperature at the compressor exit,
[0033] T.sub.1 is the temperature at the compressor inlet,
[0034] .eta..sub.c is the isentropic efficiency of the
compressor,
[0035] .pi. is the pressure ratio (in this case 15:1) and
[0036] K is the compressibility, which in the case of air is
1.4.
[0037] The isentropic efficiency .eta..sub.c can be assumed to be
0.85 in the case of a compressor.
[0038] The heated working gas now passes through the heat
accumulator 14 where the main part of the available thermal energy
is stored. While being stored, the working gas is cooled to
20.degree. C., whereas the pressure (apart from flow-inducted
pressure losses) is maintained at 15 bar. The working gas is then
expanded in two series-connected stages 15a, 15b of a second fluid
energy machine so that it arrives at a pressure level of one bar.
In the process, the working gas is cooled to 5.degree. C. after the
first stage and cooled to -114.degree. C. after the second stage.
The basis for this calculation is also the formula specified
above.
[0039] In the part of the line 11 which connects the two stages
15a, 15b of the second fluid energy machine in the form of a
high-pressure turbine and a low-pressure turbine, provision is
additionally made for a water separator 29. After a first
expansion, this enables the air to be dried so that the air
moisture which is contained in this in the second stage 15b of the
second fluid energy machine 15 does not lead to icing of the
turbine blades (necessary only for the case of an open
circuit).
[0040] In the further process, the expanded and therefore cooled
working gas extracts heat from the cold accumulator 16 and is
heated to 0.degree. C. as a result. In this way, cold energy is
stored in the cold accumulator 16 and can be utilized during a
subsequent energy generation. If the temperature of the working gas
at the outlet of the cold accumulator 16 and at the inlet of the
heat accumulator 12 is compared, then it becomes clear why the heat
exchanger 17 has to be provided for the case of a closed charging
circuit. In this case, the working gas can be reheated to an
ambient temperature of 20.degree. C., as a result of which heat is
extracted from the environment and made available to the process.
Such a measure can naturally be dispensed with if the working gas
is drawn directly from the environment since this already has
ambient temperature.
[0041] For the cooling, an embodiment which deviates from the
variant in FIG. 1 is shown in FIG. 2. The motor M and the generator
G1 do not have any superconducting components in this case. Only
the generator G2 in the wind power plant 22, which on account of
its installed height in the nacelle of the wind power plant is to
have a mass which is as low as possible, utilizes the advantages
which are associated with superconducting windings and their
smaller, necessary conductor cross sections. The line 31 therefore
leads without bypass lines directly to the wind power plant 22. The
cooling unit 33 is also accommodated in the nacelle of the wind
power plant 22 so that the paths of the cooling medium can be
advantageously minimized, at least at low temperature level.
[0042] By means of FIG. 3, the discharging cycle of the heat
accumulator 14 and of the cold accumulator 16 can be understood,
wherein electric energy is generated at the generator G1. Unlike as
in FIG. 1, in FIG. 3 the first fluid energy machine 13 and the
second (two-stage) fluid energy machine 15 are used both in the
charging cycle and in the discharging cycle. This does not impair
the functioning principle of the plant but, however, is at the cost
of lower efficiency. Therefore, the higher investment cost when
additionally using a third and a fourth fluid energy machine is to
be balanced against the gain in efficiency which is achieved when
using four fluid energy machines by each being able to be optimized
to the corresponding operating state. Also shown, by dash-dot lines
again, is the alternative of a closed circuit. The water separator
29 is not shown in the representation according to FIG. 3 since
this is not used.
[0043] The working gas is directed through the cold accumulator 16.
In the process, it is cooled from 20.degree. C. to -92.degree. C.
This measure serves for reducing the power consumption in order to
operate the second fluid energy machine which works as a
compressor. The power consumption is reduced correspondingly by the
factor of the temperature difference in Kelvin, that is to say
293K/181K=1.62. In the example, the compressor compresses the
working gas to 10 bar. During this, the temperature rises to
100.degree. C. A compression of up to 15 bar would also be
technically acceptable. The compressed working gas passes through
the heat accumulator 14 and is consequently heated to 500.degree.
C., wherein the pressure reduces slightly to 9.8 bar. The working
gas is then expanded by means of the first fluid energy machine
which therefore works as a turbine in this operating state. An
expansion to 1 bar is carried out, wherein at the outlet of the
first fluid energy machine a temperature of 183.degree. C. still
prevails in the working gas.
[0044] In order to be able to also utilize this residual heat, the
working gas is then directed through the low-temperature heat
accumulator and additionally cooled to 130.degree. C. as a result.
This heat has to be stored in order to serve for preheating of the
working gas to 80.degree. C. in a subsequent charging process of
the heat accumulator 14 and of the cold accumulator 16 (as already
described above). The low-temperature heat accumulator therefore
works as a temporary store and is always charged especially when
the two other accumulators, i.e. the heat accumulator 14 and the
cold accumulator 16, are discharged, and vice versa. As already
mentioned, the functioning principle of the plant and of the method
is not limited, however, if the low-temperature heat accumulator is
omitted.
* * * * *