U.S. patent application number 14/346729 was filed with the patent office on 2014-11-20 for installation for storing thermal energy.
This patent application is currently assigned to SIEMENS AKTIENGESELLSCHAFT. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Daniel Reznik, Henrik Stiesdal.
Application Number | 20140338329 14/346729 |
Document ID | / |
Family ID | 46980931 |
Filed Date | 2014-11-20 |
United States Patent
Application |
20140338329 |
Kind Code |
A1 |
Reznik; Daniel ; et
al. |
November 20, 2014 |
INSTALLATION FOR STORING THERMAL ENERGY
Abstract
An installation for storing thermal energy which can be
obtained, for example, at times of overcapacities, from
regenerative energy and then be stored is provided. The energy
stored in a heat accumulator, a cold accumulator and in an
additional heat accumulator can be, when needed, reconverted into
electrical energy by circuits via a generator (G) while using a
compressor and a turbine. The working gas is humidified by a
humidification column, ideally until saturation, whereby,
advantageously, a greater mass flow can be obtained at a lower
volume flow. For this reason, more economical components can be
used while simultaneously a high yield of the installation is
achieved.
Inventors: |
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: |
46980931 |
Appl. No.: |
14/346729 |
Filed: |
September 25, 2012 |
PCT Filed: |
September 25, 2012 |
PCT NO: |
PCT/EP2012/068858 |
371 Date: |
March 23, 2014 |
Current U.S.
Class: |
60/659 |
Current CPC
Class: |
F01K 21/04 20130101;
F01K 3/12 20130101 |
Class at
Publication: |
60/659 |
International
Class: |
F01K 3/12 20060101
F01K003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2011 |
EP |
11183267.1 |
Claims
1. An installation for storing thermal energy, comprising: a
circuit for a working gas, wherein, in the circuit, the following
units are connected to one another in the stated sequence by a line
for the working gas: a cold accumulator, a first thermal fluid
energy machine, a heat accumulator and a second thermal fluid
energy machine, wherein, as viewed in a throughflow direction of
the working gas from the cold accumulator to the heat accumulator,
the first thermal fluid energy machine is positioned as work
machine and the second thermal fluid energy machine is positioned
as prime mover, wherein a humidification unit for the working gas
is provided in the line between the first thermal fluid energy
machine and the heat accumulator.
2. The installation as claimed in claim 1, wherein a water
separator is arranged in the line downstream of the second thermal
fluid energy machine.
3. The installation as claimed in claim 2, wherein the water
separator is connected to the humidification unit via a feed
line.
4. The installation as claimed in claim 1, wherein the line leading
away from the second thermal fluid energy machine leads through a
heat exchanger situated in the humidification unit.
5. The installation as claimed in claim 1, wherein an auxiliary
heat accumulator is provided in a branch line, wherein the branch
line that leads away from the auxiliary heat accumulator leads
through a heat exchanger situated in the humidification unit.
6. The installation as claimed in claim 1, wherein a heat exchanger
is provided in the line downstream of the second thermal fluid
energy machine, with water for the humidification unit being fed as
coolant to said heat exchanger.
7. The installation as claimed in claim 1, wherein the heat
accumulator is connected between a third thermal fluid energy
machine and a fourth thermal fluid energy machine by a second line,
wherein, as viewed in the throughflow direction of the working gas
from the third thermal fluid energy machine to the fourth thermal
fluid energy machine, the third thermal fluid energy machine is
positioned as a work machine and the fourth thermal fluid energy
machine is positioned as a prime mover.
8. The installation as claimed in claim 7, wherein the cold
accumulator is connected downstream of the fourth fluid energy
machine as viewed in the throughflow direction as per claim 7 by
the second line.
9. The installation as claimed in claim 1, wherein an auxiliary
heat accumulator is connected between a fifth thermal fluid energy
machine and a sixth thermal fluid energy machine by an auxiliary
line, wherein, as viewed in the throughflow direction of the
working gas from the fifth thermal fluid energy machine to the
sixth thermal fluid energy machine, the fifth thermal fluid energy
machine is positioned as a work machine and the sixth thermal fluid
energy machine is positioned as a prime mover.
10. The installation as claimed in claim 1, wherein the first
thermal fluid energy machine and the second thermal fluid energy
machine are, by bypass lines, connected such that the heat
accumulator is situated upstream of the cold accumulator in the
throughflow direction of a working fluid.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2012/068858 filed Sep. 25, 2012, and claims
the benefit thereof. The International Application claims the
benefit of European Application No. EP11183267 filed Sep. 29, 2011.
All of the applications are incorporated by reference herein in
their entirety.
FIELD OF INVENTION
[0002] The invention relates to an installation for storing thermal
energy, the installation having a circuit for a working gas. The
circuit may be of open configuration such that it draws in air from
the environment as working gas and discharges said air into the
environment again; that is to say the environment forms part of the
circuit. A closed circuit is also possible in which any desired
working gas (including air) may be used. In the circuit, the
following units are connected to one another in the stated sequence
by a line for the working gas: a cold accumulator, a first thermal
fluid energy machine, a heat accumulator and a second thermal fluid
energy machine. Here, as viewed in the throughflow direction of the
working gas from the cold accumulator to the heat accumulator, the
first thermal fluid energy machine is positioned as work machine
and the second thermal fluid energy machine is positioned as prime
mover.
BACKGROUND OF INVENTION
[0003] The expressions "prime mover" and "work machine" are used
within the context of this application with the following meanings:
a work machine absorbs mechanical work in order to perform its
task. A thermal fluid energy machine that is used as a work machine
is thus operated as a compressor. By contrast, a prime mover
performs work, wherein a thermal fluid energy machine for
performing work converts the thermal energy that is available in
the working gas. In this case, the thermal fluid energy is thus
operated as a motor.
[0004] The expression "thermal fluid energy machine" is an umbrella
term for machines that can extract thermal energy from a working
fluid, in the context of this application a working gas, or supply
thermal energy to said working fluid. Thermal energy is to be
understood to mean both heat energy and also cold energy. Thermal
fluid energy machines (also referred to hereinafter for short as
fluid energy machines) may for example be designed as piston-type
machines. It is preferably also possible for use to be made of
hydrodynamic thermal fluid energy machines whose rotors permit a
continuous flow of the working gas. Use is preferably made of
axially acting turbines and compressors.
[0005] The principle specified in the introduction is described for
example in US 2010/0257862 A1. In said document, piston-type
machines are used to perform the method described above. Moreover,
it is known from U.S. Pat. No. 5,436,508 that, by the installations
specified in the introduction for storing thermal energy,
overcapacities in the case of the utilization of wind energy for
producing electrical current can be temporarily stored in order to
be drawn upon again if required.
SUMMARY OF INVENTION
[0006] It is an object of the invention to specify an installation
for storing thermal energy of the type specified in the
introduction (for example conversion of mechanical energy into
thermal energy with subsequent storage or conversion of the stored
thermal energy into mechanical energy) in which high efficiency can
be achieved with simultaneously reasonable expenditure for the
structural units that are used.
[0007] With the installation, specified in the introduction, this
object is achieved according to aspects of the invention in that a
humidification unit for the working gas is provided in the line
between the first thermal fluid energy machine and the heat
accumulator. In the context of this invention, a humidification
unit is to be understood to mean a device through which the working
gas can flow and in which water vapor is supplied to the working
gas. Here, the air should be humidified with water vapor up to at
most the saturation limit. The use of humidification of the working
gas (for example air) has the advantage that the power output at
the fluid energy machine that operates as work machine can be
increased while maintaining the same structural size. For a
demanded power output, it is thus possible to use smaller and thus
cheaper components for the installation. Furthermore, it is
possible for the hot humidified air exiting the second fluid energy
machine to be utilized for supplying heat into the water used in
the humidification unit, such that said energy is not lost from the
process as a whole. In this way, the efficiency of the installation
according to the invention can be advantageously increased.
[0008] The circuit of the installation according to aspects of the
invention for storing thermal energy serves, with its
humidification unit, to convert the energy stored in the heat
accumulator and cold accumulator into mechanical energy by the
second thermal fluid energy machine. Said mechanical energy may for
example be used for driving an electrical generator. Then, in times
of high demand for electrical energy, the stored thermal energy is
used for the provision of said electrical energy by the
installation.
[0009] Owing to the increased use of regenerative energy, a
situation may however also arise in which the total current
produced is not demanded at the time of production. In this case,
the installation for storing thermal energy may be used for
converting the electrical energy for example into mechanical energy
by an electric motor and into thermal energy by the fluid energy
machines. It should however be noted that the humidification column
is not used during the reverse process. Said humidification column
must thus be bypassed, for example by suitable bypass lines.
Another possibility includes providing a separate circuit in the
installation for the charging process of the cold accumulator and
of the heat accumulator. Said separate circuit may also be equipped
with additional fluid energy machines.
[0010] If the installation is provided with bypass lines, these
must be suitable for connecting the first thermal fluid energy
machine and the second thermal fluid energy machine such that the
heat accumulator is situated upstream of the cold accumulator in
the throughflow direction of the working gas. This may be achieved
by a reversal of the flow direction in the line system. Another
possibility includes the bypass lines issuing into the circuit in
each case directly upstream and downstream of the heat accumulator
and cold accumulator such that the flow direction of the working
gas is reversed only within the thermal accumulators. The reversal
of the flow direction in the thermal accumulators (cold accumulator
and heat accumulator) is of importance in order that, during the
charging and discharging of the thermal accumulator, the cold-hot
front in the storage medium of the thermal accumulator is moved in
the opposite direction in each case.
[0011] If an additional circuit is used for the charging of the
thermal accumulators, said additional circuit likewise passes
through the same heat accumulator and cold accumulator. By suitable
valve mechanisms, it is ensured that in each case only the circuit
for charging or the circuit for discharging is connected to the
thermal accumulators. Another possibility includes the thermal
accumulators comprising in each case two line systems for two
circuits. In this case, a switchover is not necessary, and it is
even possible in principle to realize simultaneous charging and
discharging of the thermal accumulators.
[0012] In one situation, however, the charging of the heat
accumulator and of the cold accumulator in the installation is
achieved in that the heat accumulator can be connected between a
third thermal fluid energy machine and a fourth thermal fluid
energy machine by a second line, wherein, as viewed in the
throughflow direction of the working gas from the third thermal
fluid energy machine to the fourth thermal fluid energy machine,
the third thermal fluid energy machine is positioned as work
machine and the fourth thermal fluid energy machine is positioned
as prime mover. This permits, in the manner already described, the
charging of the heat accumulator when the working gas flows through
the second line in the stated throughflow direction. Furthermore,
the cold accumulator may be provided in the second line downstream
of the fourth thermal fluid energy machine, which cold accumulator
is then fed with the working gas exiting the fourth fluid energy
machine and can absorb the cold energy stored in the working
gas.
[0013] In a further refinement of the invention, it is provided
that a water separator is arranged in the line downstream of the
second thermal fluid energy machine. Owing to expansion and cooling
of the working gas, the absorption capacity thereof for water vapor
also decreases, such that said water vapor condenses. Said water
vapor can then be captured in said water separator, wherein the
separated-off water is still at a temperature of approximately
50.degree. C. Said temperature level is thus still higher than
ambient temperature, such that the thermal energy stored in the
captured water can be supplied back to the process. If the water
vapor were discharged into the environment and, instead, feed water
from the environment were used for the humidification column, said
thermal energy would be lost from the process. The water separator
thus serves to increase the efficiency of the process realized by
the installation according to the invention. In order for the water
from the water separator to be provided back to the process, it is
advantageously provided that the water separator is connected to
the humidification unit via a feed line.
[0014] In another refinement of the installation according to
aspects of the invention, it may be provided that the line leading
away from the second fluid energy machine leads through a first
heat exchanger situated in the evaporator. The working gas exiting
the second fluid energy machine is at temperatures of approximately
200.degree. C. Said heat can be utilized for providing heat energy
to the humidification column, which heat energy is required for the
evaporation of the water situated in the humidification column.
Said heat energy is thus advantageously provided back to the
process and thus does not escape unused into the environment. This
advantageously increases the efficiency of the process realized by
the installation. Furthermore, owing to the cooling of the working
gas that has taken place in the humidification column, a water
separator connected downstream thereof can operate more
effectively, because the water can be separated off more easily
from the cooled working gas.
[0015] Yet another refinement of the invention provides that an
auxiliary heat accumulator is provided in a branch line, wherein
the branch line that leads away from the auxiliary heat accumulator
leads through a heat exchanger situated in the evaporator. The
energy stored in the auxiliary heat accumulator can thus
additionally assist the process of evaporation of the water in the
humidification unit. The introduction of thermal energy, which
takes place indirectly via the auxiliary heat accumulator, thus
advantageously leads to a further increase in air humidity in the
humidification unit. This leads to the already-described increase
in efficiency of the process realized by the installation according
to the invention.
[0016] The auxiliary heat accumulator, like the heat accumulator
and the cold accumulator, may be fed from external heat and cold
sources. Here, use may expediently be made of district heat from a
power plant, for example. It is however particularly advantageous
for the auxiliary heat accumulator and the heat accumulator and the
cold accumulator to be charged by separate heat pump processes. For
this purpose, it is advantageously possible for the auxiliary heat
accumulator to be connected between a fifth thermal fluid energy
machine and a sixth thermal fluid energy machine by an auxiliary
line, wherein, as viewed in the throughflow direction of the
working gas from the fifth thermal fluid energy machine to the
sixth thermal fluid energy machine, the fifth thermal fluid energy
machine is positioned as work machine and the sixth thermal fluid
energy machine is positioned as prime mover. A separate heat pump
circuit is thus advantageously made available for the charging of
the auxiliary heat accumulator, wherein the fifth and sixth fluid
energy machines can be optimized for the temperatures to be
generated in the auxiliary heat accumulator. It is self-evidently
also possible for the auxiliary heat accumulator to be charged by
the first or by the third fluid energy machine if suitable
interconnection by lines and/or bypass lines is permitted. Here, it
is always necessary to weigh up the outlay for components versus
the increase in efficiency for the individual processes. Economical
considerations are of primary importance in said weighing-up
process.
[0017] The working gas may optionally be conducted in a closed or
an open circuit. An open circuit always uses the ambient air as
working gas. Said ambient air is drawn in from the environment and
is also discharged again into the environment at the end of the
process, such that the environment closes the open circuit. A
closed circuit also permits the use of a working gas other than
ambient air. Said working gas is conducted in the closed circuit.
Since an expansion into the environment with simultaneous adoption
of ambient pressure and ambient temperature is omitted, it is
necessary in the case of a closed circuit for the working gas to be
conducted through a heat exchanger which permits a dissipation of
heat from the working gas to the environment.
[0018] It may for example be provided that the circuit for the
storage of the thermal energy in the cold accumulator and the heat
accumulator is in the form of an open circuit, and the thermal
fluid energy machine that operates therein as prime mover is
constructed from two stages, with a water separator for the working
gas being provided between the stages. Here, allowance is made for
the fact that air moisture is contained in the ambient air. An
expansion of the working gas in a single stage can have the effect
that, owing to the intense cooling of the working gas to
-100.degree. C., for example, the air moisture freezes and, in the
process, damages the thermal fluid energy machine. In particular,
turbine blades can be permanently damaged owing to icing. An
expansion of the working gas in two stages however makes it
possible for condensed water to be separated off, for example at
5.degree. C., in a water separator downstream of the first stage,
such that, upon further cooling of the working gas in the second
turbine stage, said water has already been removed and ice
formation can be prevented or at least reduced. The risk of damage
to the second fluid energy machine is advantageously reduced in
this way.
[0019] If a closed circuit is used and, as already described, a
heat exchanger is installed into the circuit, the use of a water
separator and of a two-stage fluid energy machine as prime mover
can then be omitted. In this case, too, it is possible for
dehumidified ambient air to be used as working gas, the
humidification of which is prevented by the closed nature of the
circuit. Other working gases may however also be used.
[0020] For the thermal charging of the heat accumulator and of the
cold accumulator, it is advantageous if the working gas flows
through the auxiliary heat accumulator before flowing through the
first or third (depending on configuration) fluid energy machine.
That is to say that the working gas is fed into the first fluid
energy machine having been heated by the auxiliary heat
accumulator. In this way, the auxiliary heat accumulator can
perform a further task in addition to the heating of the
humidification unit. The use of the auxiliary heat accumulator has
the following advantages. If the installation is used for the
storage of thermal energy, the flow passes through the auxiliary
heat accumulator before passing through the first/third fluid
energy machine that operates in this case as work machine
(compressor). In this way, the working gas is already heated to a
temperature higher than ambient temperature. This has the advantage
that the work machine does not need to absorb as much power to
achieve the demanded temperature of the working gas. Specifically,
the heat accumulator should be heated to over 500.degree. C.,
wherein, following the preheating of the working gas, this can
advantageously be realized even by commercially available
thermodynamic compressors which permit a compression of the working
gas to 15 bar. It is therefore advantageously possible, for the
structural units of the installation, to resort to components that
are commercially available without expensive modifications. It is
advantageously possible for the working gas to be heated to a
temperature between 60.degree. C. and 100.degree. C., particularly
advantageously to a temperature of 80.degree. C., in the auxiliary
heat accumulator. By contrast, for the supply of heat into the
humidification column, heating of the working gas to approximately
190.degree. C. is particularly advantageous.
[0021] As already mentioned, the working gas can be compressed to
15 bar in the circuit of the heat accumulator and of the cold
accumulator, whereby temperatures of the working gas of up to
550.degree. C. can be achieved.
[0022] Finally, according to one particular embodiment of the
invention, it may be provided that a heat exchanger is provided in
the line downstream of the second thermal fluid energy machine,
with water for the humidification unit being fed as coolant to said
heat exchanger. In this way, an even greater amount of heat energy
can be extracted from the working gas flowing through the line,
which heat energy is used to preheat the feed water for the
humidification unit. In this way, said energy is also provided back
to the process, whereby the efficiency of said process is
advantageously further increased. In particular in the case of the
provision of an open circuit, the humidification unit requires a
relatively large amount of feed water, because the water is at
least partially discharged back into the environment after passing
through the circuit. Even in the case of a closed circuit, however,
leaks in the circuit and drying of the ducts in the heat
accumulator and the cold accumulator in the event of a switchover
from discharging operation to charging operation can have the
effect that new feed water must be introduced into the
humidification unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Further details of the invention will be described below on
the basis of the drawing. Identical or corresponding elements in
the drawing are in this case denoted by the same reference signs in
each case, and will be explained multiple times only where
differences exist between the individual figures. In the
drawing:
[0024] FIG. 1 shows, in the form of a circuit diagram, an exemplary
embodiment of the installation according to the invention with
bypass lines, and
[0025] FIGS. 2 and 3 show, on the basis of further circuit
diagrams, another exemplary embodiment of the installation
according to the invention with separate circuits for the charging
and discharging of the thermal accumulators.
DETAILED DESCRIPTION OF INVENTION
[0026] An installation for the storage of thermal energy as per
FIG. 1 has a line 11 by which multiple units are connected to one
another such that a working gas can flow through them in an open
circuit. The working gas is drawn in from the environment via a
valve A and flows through a first thermal fluid energy machine 13
which is in the form of a hydrodynamic compressor. Furthermore, the
line then leads via a valve B to a heat accumulator 14. The latter
is connected by the line 11 and via a valve C to a second thermal
fluid energy machine 15, which is in the form of a hydrodynamic
turbine. From the turbine, the line 11 leads via a valve D to a
cold accumulator 16. From the cold accumulator 16, the line opens
into the environment. In the operating state described, the valves
A to D are thus open. Valves E to H are closed (more in this regard
below).
[0027] The first and second fluid energy machines 13 and 15 are
mechanically coupled to one another via a shaft 21 and are driven
by an electric motor M which is powered by a wind turbine 22 for as
long as the electrical energy generated is not demanded in the
electrical grid. During said operating state, the heat accumulator
14 and the cold accumulator 16 are charged, as will be explained in
more detail further below, and the installation is traversed by
flow through the line 11, wherein flow passes through the units in
the above-stated sequence.
[0028] If the demand for electrical energy is greater than the
amount of electrical energy presently being generated, then the
current generated by the wind turbine 22 is fed directly into the
grid. Furthermore, the installation, in another operating state,
assists the generation of electricity by virtue of the heat
accumulator 14 and the cold accumulator 16 being discharged and a
generator G being driven by the fluid energy machines 18 and 19 via
the shaft 21. For this purpose, the valves A to D are closed, and
instead, the valves E to H are opened. As a result, flow no longer
passes through regions of the line 11, and instead the bypass lines
19 thereof are opened, which change the flow of the working
gas.
[0029] The working gas flows through the cold accumulator 16 and
passes via a bypass line 19 and via the valve E to the first fluid
energy machine (compressor). After exiting the compressor, the
working gas is conducted via a valve F through a humidification
unit 18, which is provided in a further bypass line 19 and which
leads to the heat accumulator 14. The heat accumulator 14 is thus
already fed with humidified air, which exits the heat accumulator
14 via the bypass line 19 through a valve G and is supplied to the
second fluid energy machine 15 (turbine). The mechanical energy for
driving the first fluid energy machine 13 (compressor) and the
generator is gained here. The working gas passes back into the
environment via the bypass line 19 and through a valve H, wherein
prior to that, the working gas is dehumidified by a water separator
17. The water which is separated off and which is at approximately
50.degree. C. is supplied by a feed pump 23a to the humidification
unit 18. It is additionally possible, for example, for heat derived
from a power plant as district heat to be introduced into the
humidification unit. This is indicated in FIG. 1 by a heat
exchanger 33a.
[0030] In the installation in FIG. 1, the heat accumulator 14 and
the cold accumulator 16 (and also the auxiliary heat accumulator as
per FIG. 3) are in each case of identical construction, said
construction being illustrated in more detail by way of an enlarged
detail based on the cold accumulator 16. A tank is provided, the
wall 24 of which is provided with an insulation material 25 which
has large pores 26. In the interior of the container there is
provided concrete 27 which functions as a heat accumulator or cold
accumulator. Pipes 28 are laid, so as to run parallel, within the
concrete 27, through which pipes the working gas flows, releasing
heat or absorbing heat in the process (depending on the operating
mode and accumulator type).
[0031] The thermal charging and discharging process will be
explained in more detail on the basis of the installation as shown
in FIGS. 2 and 3. FIG. 2 firstly illustrates a two-stage charging
process which functions on the basis of the principle of a heat
pump. The illustration in FIGS. 2 and 3 shows an open circuit which
could however be closed, as indicated by dash-dotted lines, through
the use of an optionally provided heat exchanger 17a, 17b. The
states of the working gas, which in the exemplary embodiment of
FIGS. 2 and 3 is composed of air, are presented in each case in
circles at the lines 30, 31, 32. The pressure in bar is indicated
at the top left. The enthalpy in kJ/kg is indicated at the top
right. The temperature in .degree. C. is indicated at the bottom
left, and the mass flow rate in kg/s is indicated at the bottom
right. The flow direction of the gas is indicated by arrows in the
respective line.
[0032] In the model calculation for the charging circuit of the
second line 31 as per FIG. 2, the working gas passes at 1 bar and
20.degree. C. into a (hitherto charged) auxiliary heat accumulator
12 and exits the latter at a temperature of 80.degree. C.
Compression by the third fluid energy machine 34, which operates as
a compressor, results in a pressure increase to 15 bar and, as a
result, also to a temperature increase to 540.degree. C. Said
calculation is based on the following formula:
T.sub.2=T.sub.1+(T.sub.2s-T.sub.1)/.eta..sub.c;
T.sub.2s=T.sub.1.pi..sup.(K-1)/K,
where [0033] T.sub.2 is the temperature at the compressor outlet,
[0034] T.sub.1 is the temperature at the compressor inlet, [0035]
.eta..sub.c is the isentropic efficiency of the compressor, [0036]
.pi. is the pressure ratio (in this case 15:1), and [0037] K is the
compressibility, which is 1.4 in the case of air.
[0038] The isentropic efficiency .eta..sub.c may be assumed to be
0.85 for a compressor.
[0039] The heated working gas now passes through the heat
accumulator 14, where the major part of the available thermal
energy is stored. During the storage process, the working gas cools
to 20.degree. C., whereas the pressure is maintained at 15 bar
(aside from flow-induced pressure losses). Subsequently, the
working gas is expanded in two series-connected stages 35a, 35b of
a fourth fluid energy machine 35, such that said working gas
arrives at a pressure level of 1 bar. In the process, the working
gas cools to 5.degree. C. after the first stage and to -100.degree.
C. after the second stage. The formula specified above serves as a
basis for this calculation too.
[0040] In the part of the line 31 that connects the two stages of
the fourth fluid energy machine 35a, 35b in the form of a
high-pressure turbine and a low-pressure turbine, there is
additionally provided a water separator 29. Said water separator
makes it possible for the air to be dried after a first expansion,
such that the air moisture contained in said air does not lead to
icing of the turbine blades in the second stage 35b of the fourth
fluid energy machine 35.
[0041] In the further course of the process, the expanded and thus
cooled working gas extracts heat from the cold accumulator 16 and
is thereby heated to 0.degree. C. In this way, cold energy is
stored in the cold accumulator 16, which cold energy can be
utilized for subsequent energy production. Comparing the
temperature of the working gas at the outlet of the cold
accumulator 16 and at the inlet of the auxiliary heat accumulator
12, it is clear why the heat exchanger 17b must be provided in the
case of a closed circuit. Here, the working gas can be heated to
ambient temperature of 20.degree. C. again, whereby heat is
extracted from the environment, said heat being provided to the
process. Such a measure may self-evidently be omitted if the
working gas is drawn in directly from the environment, because said
working gas is then already at ambient temperature.
[0042] In order that preheating can be realized by the auxiliary
heat accumulator 12 in the cycle of the circuit of the first line
31, an auxiliary circuit is realized by an auxiliary line 30, by
which auxiliary circuit the auxiliary heat accumulator 12 can be
charged. It must therefore be possible for the auxiliary heat
accumulator 12 to be connected both to the circuit of the second
line 31 and also to the circuit of the auxiliary line 30. A
connection to the second line 31 is realized by the valves I,
whereas a connection to the auxiliary line 30 is ensured by opening
the valves K. In the cycle of the auxiliary line 30, the air is
initially conducted through a fifth fluid energy machine 36, which
operates as a compressor. The compressed air is conducted through
the auxiliary heat exchanger 12, wherein the throughflow direction
is, corresponding to the indicated arrows, the exact opposite of
that in the circuit formed by the second line 31. After the air has
been raised from ambient pressure (1 bar) and ambient temperature
(20.degree. C.) to 4 bar and a temperature of 188.degree. C. by the
compressor, the air is cooled again to 20.degree. C. by the
auxiliary heat accumulator 12. The air is subsequently expanded in
two stages by the stages 37a, 37b of a sixth fluid energy machine
37, which operates as a turbine. Here, too, a water separator 29 is
provided in the auxiliary line 30 that connects the two stages 37a,
37b, which water separator functions in exactly the same way as
that which is situated in the second line 31. After expansion of
the air by the sixth fluid energy machine 37, said air is at a
temperature of -56.degree. C. at ambient pressure (1 bar). If the
circuit of the auxiliary line 30 is of closed design, as
illustrated by the dashed-dotted line, it is therefore necessary
for a heat exchanger 17c to be provided in order that the air can
be heated from -56.degree. C. to 20.degree. C. by release of heat
to the environment.
[0043] The circuits of the second line 31 and of the auxiliary line
30 are set in operation independently of one another. The third and
fourth fluid energy machines are thus mechanically coupled via the
shaft 21 to a motor M1, and the fifth and sixth fluid energy
machines are mechanically coupled via the other shaft 21 to a motor
M2. In the event of overcapacities of the wind turbine 22, the
electrical energy can initially drive the motor M2 in order to
charge the auxiliary heat accumulator 12. Subsequently, by
operation of the motor M1 and simultaneous discharging of the
auxiliary heat accumulator 12, the heat accumulator 14 and the cold
accumulator 16 can be charged. Subsequently, by operation of the
motor M2, the auxiliary heat exchanger 12 can also be recharged.
When all the accumulators are fully charged, an effective
discharging cycle for the production of electrical energy can be
initiated (cf. FIG. 3). However, if the overcapacity of the wind
turbine 22 comes to an end without it having been possible for the
auxiliary heat accumulator 12 to be charged, the energy provided
therein can also be replaced by other heat sources (cf. FIG.
3).
[0044] Also conceivable is an auxiliary heat accumulator 12 which
can be fed through separate line systems for the second line 31 and
the auxiliary line 30. This would yield two independent circuits
without the use of valves I and K. In this way, it would be
possible for the auxiliary heat accumulator 12 to be charged and
discharged simultaneously. Simultaneous operation of the motors M1,
M2 is therefore also conceivable in this case. This operating
regime has two advantages. Firstly, even relatively large
overcapacities of the wind turbine 22 can be captured through
simultaneous operation of the motors M1, M2, resulting in greater
flexibility of the system. Furthermore, through simultaneous
operation of both motors, it would be possible to ensure that the
three thermal accumulators 12, 14, 16 are always charged
simultaneously and not in succession. The charging process can thus
be stopped at any time, with full operational capability of the
discharging process, when there are no longer overcapacities in the
electrical grid and, instead, there is a demand for additional
electrical energy.
[0045] FIG. 3 serves for illustrating the discharging cycle of the
heat accumulator 14 and of the cold accumulator 16, wherein
electrical energy is generated at the generator G. The first fluid
energy machine 13 and the second fluid energy machine 15, which
were not used in the above-described charging processes (see FIG.
2), are available for the discharging cycle. This permits an
optimization of the efficiency of the fluid energy machines but
also leads to higher investment costs for the acquisition of the
installation. It is therefore necessary to weigh up the higher
investment outlay for the use of additional fluid energy machines
versus the gain in efficiency achieved by virtue of the fact that,
if four fluid energy machines are used, each can be optimized for
the corresponding operating state. The heat accumulator 14, the
cold accumulator 16 and the auxiliary heat accumulator 12 are the
same as in FIG. 2, and are merely traversed by flow in the opposite
direction. FIGS. 2 and 3 thus illustrate the same installation,
wherein, for clarity, the illustrations show in each case only
those system components and lines which are involved in the process
taking place. Furthermore, the alternative of a closed circuit is
illustrated by means of dash-dotted lines.
[0046] The working gas is conducted through the cold accumulator
16. In the process, it is cooled from 20.degree. C. to -100.degree.
C. This measure serves to reduce the power consumption for
operating the first fluid energy machine that operates as a
compressor. The power consumption is reduced by a factor
corresponding to the temperature difference in Kelvin, that is to
say 293K/173K=1.69. In the example, the compressor compresses the
working gas to 10 bar. Here, the temperature rises to 89.degree. C.
A compression of up to 15 bar would also be technically feasible.
The compressed working gas flows initially through the
humidification unit 18 and then through the heat accumulator 14,
and is thereby heated to 145.degree. C. in the humidification unit
and to 530.degree. C. in the heat accumulator 14. The working gas
is subsequently expanded by the second fluid energy machine 15,
which thus operates as a turbine in this operating state. An
expansion to 1 bar takes place, wherein a temperature of
201.degree. C. still prevails in the working gas at the outlet of
the first fluid energy machine. It is therefore possible for the
working gas to be additionally conducted through a heat exchanger
33b in the evaporation unit in order to release heat therein for
the evaporation of the water. As a result of the further cooling of
the working gas, it is possible for at least a part of the air
moisture to be separated off by the water separator 17. The
separated-off water is still at a temperature of approximately
50.degree. C. and is pumped back into the humidification unit by a
feed pump 23b. The dehumidified air exits the circuit and is
discharged into the environment. It may alternatively be provided
that, as indicated by dash-dotted lines, a closed circuit is
realized by the line 32. In this case, a heat exchanger 17a serves
for cooling the working gas, which is still at a temperature of
50.degree. C., to ambient temperature (20.degree. C.). The heat
exchanger may also be used for heating fresh water that can be
pumped into the humidification unit by a feed pump 23c.
[0047] Heat is required in the humidification unit to effect the
evaporation of the feed water. To provide an additional energy
source here, it is possible, as already indicated in FIG. 1, for
the heat exchanger 33a to be connected to an external heat source.
Said external heat source may for example be district heat. It is
however also advantageous to utilize the charged auxiliary heat
accumulator 12. For this purpose, a branch line 38 is provided
which branches off from the line 32 upstream of the cold
accumulator 16. Said branch line runs through the auxiliary heat
accumulator 12 and subsequently through a heat exchanger 33c in the
humidification unit, such that the heat energy stored in the
auxiliary heat accumulator 12 can likewise be supplied to the
humidification unit. Downstream of the heat exchanger 33c, the
branch line 38 issues into line 32 downstream of the heat exchanger
33b. The mass flow of the working gas is thus split up at the
branch line 38, wherein 8.3 kg/s is conducted through the branch
line 38 and 4.8 kg/s is conducted through the cold accumulator 16,
humidification unit 18 and heat accumulator 14.
* * * * *