U.S. patent application number 14/394130 was filed with the patent office on 2015-03-19 for method for charging and discharging a heat accumulator and plant for storing and releasing thermal energy, suitable for this method.
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 | 20150075210 14/394130 |
Document ID | / |
Family ID | 48045500 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150075210 |
Kind Code |
A1 |
Reznik; Daniel ; et
al. |
March 19, 2015 |
METHOD FOR CHARGING AND DISCHARGING A HEAT ACCUMULATOR AND PLANT
FOR STORING AND RELEASING THERMAL ENERGY, SUITABLE FOR THIS
METHOD
Abstract
A method for charging and discharging a heat accumulator is
provided. A system by which the method can be performed is also
provided. By means of the heat accumulator, it is possible to
convert overcapacities of wind turbines, for example, into a
charging circuit as heat in the accumulator by a compressor. If
necessary, electricity can be stored into the network by a turbine
and a generator, wherein the heat accumulator is discharged. The
charging circuit and the discharging circuit are operated by a
Rankine cycle, wherein for example river water is available as a
reservoir for heat exchangers in order to cause evaporation of the
working medium in the charging circuit and condensation of the
working medium in the discharging circuit.
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: |
48045500 |
Appl. No.: |
14/394130 |
Filed: |
March 28, 2013 |
PCT Filed: |
March 28, 2013 |
PCT NO: |
PCT/EP2013/056659 |
371 Date: |
October 13, 2014 |
Current U.S.
Class: |
62/467 ;
62/77 |
Current CPC
Class: |
F03D 9/18 20160501; F03D
9/25 20160501; Y02E 60/16 20130101; F03D 9/22 20160501; Y02E 10/72
20130101; F25B 45/00 20130101; F03D 9/17 20160501; F22B 1/028
20130101; F03D 9/28 20160501; Y02E 60/17 20130101; F01K 3/185
20130101 |
Class at
Publication: |
62/467 ;
62/77 |
International
Class: |
F25B 45/00 20060101
F25B045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2012 |
EP |
12164480.1 |
Claims
1. A method for charging and discharging a heat accumulator,
comprising: during a charging cycle the heat accumulator is heated
by means of a working fluid, wherein before passing through the
heat accumulator a pressure increase is created in the working
fluid by means of a first thermal fluid energy machine which is
operated as a working machine, and after passing through the heat
accumulator the working fluid is expanded and during a discharging
cycle the heat accumulator is cooled by means of a working fluid,
wherein before passing through the heat accumulator a pressure
increase is created in the working fluid and after passing through
the heat accumulator the working fluid is expanded via a second
thermal fluid energy machine which is operated as a power machine,
or via the first thermal fluid energy machine which is operated as
a power machine, wherein both the charging cycle and the
discharging cycle are designed as a Rankine process in which the
working fluid is evaporated during the charging cycle via a first
heat exchanger and is condensed during the discharging cycle via
the first or a second heat exchanger, wherein the first heat
exchanger, and if the second heat exchanger is present, the second
heat exchanger also, create a temperature balance with the
environment.
2. The method as claimed in claim 1, wherein the working fluid is
ammonia or water.
3. A method for charging and discharging a heat accumulator,
comprising: during a charging cycle the heat accumulator is heated
by means of a working fluid, wherein before passing through the
heat accumulator a pressure increase is created in the working
fluid by means of a first thermal fluid energy machine which is
operated as a working machine, and after passing through the heat
accumulator the working fluid is expanded and during a discharging
cycle the heat accumulator is cooled by means of a working fluid,
wherein before passing through the heat accumulator a pressure
increase is created in the working fluid and after passing through
the heat accumulator the working fluid is expanded via a second
thermal fluid energy machine which is operated as a power machine,
or via the first thermal fluid energy machine which is operated as
a power machine, wherein both the charging cycle and the
discharging cycle are designed as a Rankine process in which the
working fluid is evaporated during the charging cycle via a third
heat exchanger, is condensed during the discharging cycle via a
second heat exchanger and during the charging cycle the third heat
exchanger is heated by means of another working fluid with lower
boiling point, wherein before passing through the heat exchanger a
pressure increase is created in the other working fluid by means of
a third thermal fluid energy machine which is operated as a working
machine and after passing through the heat exchanger the other
working fluid is expanded, wherein the first heat exchanger and the
second heat exchanger create a temperature balance with the
environment.
4. The method as claimed in claim 3, wherein the working fluid is
water and the second working fluid is carbon dioxide.
5. The method as claimed in claim 1, wherein water is used as the
heat transfer medium from the environment.
6. A plant for storing and releasing thermal energy comprising: a
heat accumulator, wherein the heat accumulator can release the
stored heat to a charging circuit for a working fluid and to a
discharging circuit for a working fluid, wherein in the charging
circuit the following units are interconnected in the specified
sequence by means of lines: a first thermal fluid energy machine
which is operated as a working machine, the heat accumulator, a
device for expanding the working fluid, especially a first throttle
and a first heat exchanger, wherein in the discharging circuit the
following units are interconnected in the specified sequence by
means of lines: the heat accumulator, a second thermal fluid energy
machine which is operated as a power machine or the first thermal
fluid energy machine which is operated as a power machine, the
first heat exchanger or a second heat exchanger and a pump, wherein
the first heat exchanger, and if the second heat exchanger is
present, the second heat exchanger, ensure an exchange of heat with
the environment of the plant.
7. A plant for storing and releasing thermal energy comprising: a
heat accumulator, wherein the heat accumulator can release the
stored heat to a charging circuit for a working fluid and to a
discharging circuit for a working fluid, wherein in the charging
circuit the following units are interconnected in the specified
sequence by means of lines: a first thermal fluid energy machine
which is operated as a working machine, the heat accumulator, a
device for expanding the working fluid, especially a first
throttle, and a third heat exchanger, wherein in the discharging
circuit the following units are interconnected in the specified
sequence by means of lines: the heat accumulator, a second thermal
fluid energy machine which is operated as a power machine or the
first thermal fluid energy machine which is operated as a power
machine, a second heat exchanger and a pump, wherein in an
additional circuit the following units are interconnected in the
specified sequence by means of lines: a third thermal fluid energy
machine which is operated as a working machine, the third heat
exchanger, a device for expanding the working fluid, especially a
second throttle and a first heat exchanger, wherein the first heat
exchanger and the second heat exchanger ensure an exchange of heat
with the environment of the plant.
8. The plant as claimed in claim 6, wherein the charging circuit
and the discharging circuit extend through the same line, at least
in certain sections.
9. The plant as claimed in claim 8, wherein the same lines are
provided for the charging circuit and the discharging circuit, at
least inside the heat accumulator.
10. The method as claimed in claim 3, wherein water is used as the
heat transfer medium from the environment.
11. The plant as claimed in claim 7, wherein the charging circuit
and the discharging circuit extend through the same line, at least
in certain sections.
12. The plant as claimed in claim 11, wherein the same lines are
provided for the charging circuit and the discharging circuit, at
least inside the heat accumulator.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2013/056659 filed 28 Mar. 2013, and claims
the benefit thereof. The International Application claims the
benefit of European Application No. EP12164480 filed 17 Apr. 2012.
All of the applications are incorporated by reference herein in
their entirety.
FIELD OF INVENTION
[0002] The invention relates to method for charging and discharging
a heat accumulator, in which the following steps are carried out,
preferably in an alternating manner. During a charging cycle, the
heat accumulator is heated by means of a working fluid, wherein
before passing through the heat accumulator a pressure increase is
created in the working fluid by means of a first thermal fluid
energy machine which is operated as a working machine, and after
passing through the heat accumulator the working fluid is expanded.
During a discharging cycle, the heat accumulator is cooled by the
same, or another, working fluid, wherein before passing through the
heat accumulator a pressure increase is created in the working
fluid and after passing through the heat accumulator the working
fluid is expanded via a second thermal fluid energy machine which
is operated as a power machine, or via the first thermal fluid
energy machine which is operated as a power machine.
[0003] The invention also relates to a plant for storing and
releasing thermal energy using a heat accumulator, wherein the heat
accumulator can release the stored heat to a charging circuit for a
working fluid and to a discharging circuit for another, or the
same, working fluid. In the charging circuit, the following units
are interconnected in the specified sequence by means of lines: a
first thermal fluid energy machine which is operated as a working
machine, the heat accumulator, a device for expanding the working
fluid, especially a first throttle, and a first heat exchanger. In
the discharging circuit, the following units are interconnected in
the specified sequence by means of lines: the heat accumulator, a
second thermal fluid energy machine which is operated as a power
machine, or the first thermal fluid energy machine which is
operated as a power machine, the first heat exchanger or a second
heat exchanger, and a pump. The method which is specified in the
introduction, or the plant which is suitable for implementing the
method, can, for example, be used in order to convert
over-capacities from the electricity network by means of the
charging cycle into thermal energy and to store said thermal energy
in the heat accumulator. When required, this process is reversed so
that the heat accumulator is discharged in a discharging cycle and
by means of the thermal energy electric current can be generated
and fed to the network.
BACKGROUND OF INVENTION
[0004] 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
operated 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.
[0005] The term "thermal fluid energy machine" constitutes a
generic term for machines which can extract thermal energy from a
working fluid or can feed thermal energy to this. Both heat energy
and cold energy are to be understood by thermal energy. Thermal
fluid energy machines (also referred to as fluid energy machines
for short in the following text) 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.
[0006] The principle specified in the introduction is described
according to WO 2009/044139 A2, for example. In this case, piston
machines are used in order to implement the method described
above.
[0007] According to U.S. Pat. No. 5,436,508, it is known, moreover,
that by means of the plants specified in the introduction for
storing thermal energy over-capacities can also be temporarily
stored utilizing wind energy for generating electric current in
order to retrieve this again when required.
SUMMARY OF INVENTION
[0008] An object is to disclose a method for charging and
discharging a heat accumulator or a plant for implementing this
method, by means of which storing and recovery of energy can be
carried out with comparatively high efficiency and a comparatively
low cost of components is incurred in the process.
[0009] This object is achieved according to the invention by means
of the method referred to in the introduction by both the charging
cycle and the discharging cycle being designed as a Rankine
process, in which the working fluid is evaporated during the
charging cycle via a first heat exchanger and is condensed during
the discharging cycle via the first or a second heat exchanger. In
the process, the first heat exchanger, and if the second heat
exchanger is present, this also, creates, or create, a temperature
balance with environment. In this case, it is to be noted that
depending on whether separate circuits are provided for the heat
exchangers in the case of the discharging cycle or of the charging
cycle or both cycles take place in one and the same circuit, one or
two heat exchangers can be provided. The same applies to the fluid
energy machines. The advantage of using two different fluid energy
machines has the advantage that the one can be optimized to the
charging cycle and the other to the discharging cycle. As a result
of this, especially the aim of an increase in the overall
efficiency is achieved. If a single fluid energy machine is used,
expectations regarding efficiency certainly have to lowered, for
which such a method may be implemented with a less expensive plant
since a saving can be made in components.
[0010] The Rankine process, which synonymously is also referred to
as the Clausius-Rankine process, can especially be operated using a
steam-heat pump or using a steam turbine. The working medium exists
in this case in a gaseous state and a liquid state alternately, as
a result of which the specific cyclic working process can be
advantageously increased. The features of the process, referred to
as Rankine process for short in the following text, are explained
in more detail below.
[0011] A further essential feature of the invention is that an
exchange of heat with the environment is provided for the heat
exchanger. The environment is to be understood as being a part
outside of the running process. The heat exchanger can be used both
for absorbing and releasing thermal energy if the running process
is set so that the working fluid can be evaporated by absorbing
heat from the environment in order to be able to then be compressed
via the first fluid energy machine, and in the case of the
discharging cycle can be condensed by releasing heat to the
environment after the working fluid has performed work via the
second fluid energy machine. This can be carried out by choosing
ammonia or water as working fluid, for example. In this case,
ammonia has the advantage that for example at an ambient
temperature of 15.degree. C. a superheating of the ammonia vapor
can be ensured. The choice of water as working fluid has the
advantage that its use involves low risks for the environment.
[0012] According to an alternative solution of the problem, it can
also be provided in the method specified in the introduction that
both the charging cycle and the discharging cycle are designed as
the Rankine process, in which the working fluid is evaporated
during the charging cycle via a third heat exchanger and is
condensed during the discharging cycle via a second heat exchanger.
Furthermore, during the charging cycle the third heat exchanger is
heated by means of another working fluid with lower boiling point,
wherein before passing through the heat exchanger a pressure
increase is created in the other working fluid by means of a third
thermal fluid energy machine which is operated as a working
machine, and after passing through the heat exchanger the other
working fluid is expanded. In this case, it is provided according
to the invention that the first heat exchanger and the second heat
exchanger create a temperature balance with the environment.
[0013] By means of the alternative solution according to the
invention, the advantages already quoted above are achieved. An
exchange of heat with the environment is also possible, as a result
of which a saving can be made in components. The advantage of
ammonia as working fluid being able to be dispensed with and
therefore water being able to be used in the circuit of the third
heat exchanger without the possibility of superheating having to be
dispensed with, can additionally be achieved. This is achieved by
means of a two-stage charging cycle, wherein the charging cycle
can, for example, be advantageously operated with carbon dioxide in
the first heat exchanger which is in communication with the
environment. In this case, it also involves a substance the use of
which is harmless with regard to risks to the environment. This,
however, can already be superheated at lower temperatures, wherein
by conducting the Rankine process in the carbon dioxide circuit
heating of the third heat exchanger is a carried out. The energy
which is made available by the third heat exchanger lies above the
temperature level of the environment, however, so that in the water
circuit a superheating of the water vapor can be carried out under
technically realizable pressure conditions.
[0014] A particularly advantageous embodiment of the invention is
achieved if water is used as a heat transfer medium from the
environment. This water can be extracted from a river, for example.
This has the advantage that water, especially flowing water, is
subjected to smaller temperature fluctuations than the air, for
example. As a result, the process can be conducted both in summer
and winter within a smaller temperature window. Furthermore, the
water can be introduced into the first or the second heat exchanger
in a simple manner.
[0015] An object is otherwise achieved according to the invention
by means of the plant specified in the introduction by the first
heat exchanger, and if the second heat exchanger is present, this
also, ensuring an exchange of heat with the environment. This
advantageously enables the plant to make the method specified above
realizable. The aforesaid advantages therefore correspondingly
apply.
[0016] The same also applies to the alternative solution of the
problem by means of the plant specified in the introduction by the
following units being interconnected in an additional circuit in
the specified sequence by means of lines: a third thermal fluid
energy machine which is operated as a working machine, the third
heat exchanger, a device for expanding the working fluid,
especially a second throttle, and a first heat exchanger. The first
heat exchanger and the second heat exchanger ensure an exchange of
heat with the environment of the plant, as a result of which the
advantages already mentioned above can be achieved and the plant is
especially put in a position to implement one of the previously
specified methods.
[0017] According to an advantageous embodiment of the plant, it can
be provided that the charging circuit and the discharging circuit
extend through the same lines, at least in certain sections. Meant
by this is that there is passage of flow through the lines both in
the discharging cycle and in the charging cycle. This can therefore
be provided because the plant is always used either only for
storing thermal energy or for releasing thermal energy by means of
the heat accumulator (corresponds to the charging cycle and to the
discharging cycle). This is therefore to be based on the fact that
either the state exists in which surplus energy is available for
charging the heat accumulator or the requirement arises in which
the stored energy from the heat accumulator is to be converted into
electric energy, for example. An operation both of the charging
cycle and of the discharging cycle at the same time is technically
therefore not advisable. By using the same lines, at least in
certain sections, a saving in material is advantageously made and
the cost of components is further reduced. In particular, it is
possible to realize the charging and discharging circuit completely
by means of the same line system if the same thermal fluid energy
machine is also to be used for charging and discharging. Otherwise,
different fluid energy machines and necessary throttles and pumps
can be integrated into the circuit by means of suitable bypass
lines and valves.
[0018] It is especially advantageous if the same lines are provided
for the charging circuit and the discharging circuit, at least
inside the heat accumulator. This substantially reduces the cost
for producing the heat accumulator since in this a surface which is
as large as possible has to be provided for a transfer of heat
through the lines. Also, the volume, which when using two line
systems has to be provided in the heat accumulator for one of the
line systems, can be filled with the heat accumulator medium in the
case of using one line system, as a result of which a more compact
constructional form is advantageously possible.
[0019] If the plants or methods according to the invention are
compared with those according to WO 2009/044139 A2, then it becomes
clear, moreover, that a saving can be made with regard to the
complete cold accumulator. This is achieved by the low temperature
level of the respectively running Rankine process lying at ambient
level so that the environment can be utilized as a cold
accumulator. This additionally has the advantage that the thermal
energy which is provided by the environment can be introduced into
the process. Furthermore, the component cost of a cold accumulator
no longer applies.
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 and
are repeatedly explained only insofar as differences arise between
the individual figures. In the drawing:
[0021] FIG. 1 shows an exemplary embodiment of the plant according
to the invention as a block schematic diagram,
[0022] FIGS. 2 and 3 show two exemplary embodiments of the method
according to the invention, which can be implemented with a plant
according to FIG. 1,
[0023] FIG. 4 shows an alternative exemplary embodiment of the
plant according to the invention as a block schematic diagram,
and
[0024] FIGS. 5 and 6 show an exemplary embodiment of the method,
which can be implemented with the plant according to FIG. 4,
wherein the methods are represented in a diagram with the
temperature T on the Y-axis and the entropy S on the X-axis.
DETAILED DESCRIPTION OF INVENTION
[0025] Apparent in FIG. 1 is a plant by means of which surplus
electric energy of a wind power plant 11 can be converted into
thermal energy which can be stored in a heat accumulator 12. The
heat accumulator, in a way not shown in more detail, can comprise a
cast body of concrete, for example, in which provision is made for
a passage system through which can flow a working medium. The
electric energy of the wind power plant 11 is fed to the plant via
a motor M. When required, the heat accumulator 12 can be
discharged, wherein ultimately electric energy can be generated via
a generator G. For converting electric energy into thermal energy,
and vice versa, a charging circuit 13 and a discharging circuit 14
are realized in the plant. These are schematically represented as
lines in which a working fluid, such as ammonia, can circulate. Via
valves 15, either the charging circuit 13 or the discharging
circuit 14 respectively is activated by a connection being made to
the heat accumulator 12. Furthermore, provision is made in the
charging and discharging circuits for a first heat exchanger 16
which can be fed with flowing water of a schematically indicated
river 17. Also, valves 18 are provided for the connection of the
first heat exchanger 16 so that this can be used in the charging
circuit 13 and in the discharging circuit 14. Instead of valves 18,
a second heat exchanger 19 can also be used, as shown by dash-dot
lines. In the region of the heat exchangers, two separate circuits
for the charging circuit 13 and discharging circuit 14 are created
in this way, as indicated in FIG. 1, which makes the valves 18
superfluous.
[0026] The respective flow directions of the charging circuit 13
and of the discharging circuit 14 are indicated by arrows. Also,
typical positions in the charging circuit 13 and discharging
circuit 14 are identified by numbers between 1 and 10, wherein
these typical positions of the running Rankine processes are also
apparent in FIGS. 2 and 3. These shall explain in more detail below
the conducting of the respective process.
[0027] Shown in FIG. 2 are a charging cycle 20 and a discharging
cycle 21, as can be conducted using ammonia as working fluid
(R717). In position 1 of the cycle, the working medium is at a
pressure of 5 bar. In this case, the boiling temperature of ammonia
lies at 4.degree. C. Therefore, the heat of the river water at
15.degree. C. can be used in order to evaporate the working medium
in the first heat exchanger 16. In this way, position 2 is reached.
As is to be gathered from FIG. 1, the working medium, by means of a
first fluid energy machine 22 which is operated as a hydrodynamic
compressor, with the aid of the motor M, is brought to a pressure
of more than 131 bar, for example 140 bar. In the process, the
working medium is heated to 320.degree. C. and reaches position 3.
This heat can then be introduced into the material of the heat
accumulator 12, wherein the latter functions as a heat exchanger.
In this process step, the working medium is isobarically cooled to
a temperature of less than 30.degree. C., as a result of which
position 4 of the cycle is reached. By means of a first throttle
23, the working medium can be expanded and in this way achieves a
pressure of 5 bar again. At this position, the simple component of
a throttle is advantageously sufficient. A turbine or the like is
not necessary.
[0028] The discharging cycle 21 proceeds as follows. The
condensation pressure can be set at 10 bar so that the boiling
temperature of the working medium (also ammonia) lies at 25.degree.
C., that is to say above the temperature level of the river at
15.degree. C. In position 5 of the discharging cycle 21, ammonia
exists in the liquid state and is brought to a supercritical
pressure via a pump 24. The working medium is heated by means of
the heat accumulator and supercritically brought to position 9. In
this case, the temperature level prevailing in the heat accumulator
12 cannot quite be achieved. Heating to 220.degree. C., for
example, is possible. From the working medium in the supercritical
state, mechanical energy can be generated via a second fluid energy
machine 25 in the form of a turbine and converted into electric
energy via the generator G. The mechanical connections between the
generator G and the second fluid energy machine 25 and also between
the motor M and the first fluid energy machine 22 are designed as
shafts 26. After expansion of the working medium, position 10 is
reached. The expanded working medium still exists in a gaseous
state and is condensed at 25.degree. C., wherein the river water is
heated in the process.
[0029] Shown in FIG. 3 is a charging cycle 20 and a discharging
cycle 21, as can be operated with a plant according to FIG. 1,
using water. In this case, river water at a temperature of
15.degree. C. is again to be used in the first heat exchanger. If
the water is to be condensed at a temperature of 25.degree. C., a
condensation pressure of 30 mbar is to be expected. An evaporation
temperature of the water of 5.degree. C. requires a pressure of 10
mbar. The following parameters for operating the charging cycle
result from this. From position 1 to position 2, the water is
evaporated at 10 mbar. Position 3 of the charging cycle is achieved
by the water vapor being compressed to 1 bar, wherein the
temperature rises to approximately 540.degree. C. The water is then
cooled to 99.degree. C. during passage through the heat accumulator
12, as a result of which the heat accumulator 12 is heated. During
this, position 4 is reached. The water vapor is expanded via the
throttle 23 to 10 mbar and in the process achieves the temperature
of 5.degree. C. again.
[0030] The charging cycle proceeds through the following positions.
In position 5, the water, which is now fully condensed at 30 mbar,
has a temperature of 25.degree. C. By means of the pump 24, the
water is brought to a working pressure and transported through the
heat accumulator 12, absorbs heat in the process, and reaches
position 7. In so doing, the water starts to boil and in the
process maintains the temperature in position 7 until this is
completely evaporated (position 8). In this case, it involves a
subcritical evaporation of the water. The temperature level in the
heat accumulator 12 then leads to superheating of the water vapor,
reaching position 9 at approximately 480.degree. C. Position 10 is
then reached by the water vapor being expanded via the second fluid
energy machine 25, the water temperature again achieving a
temperature of 25.degree. C. at a pressure of 30 mbar in the
process. In the first heat exchanger 16, the water is then
condensed again, as a result of which position 5 of the discharging
cycle is reached.
[0031] Shown in FIG. 4 is another exemplary embodiment of the
plant. This differs from the exemplary embodiment according to FIG.
1 mainly by the fact that the charging cycle is split into two
stages. The heating of the heat accumulator 12 takes place in the
charging circuit 13 which, unlike as in FIG. 1, is completely
separated from the discharging circuit 14. The charging circuit 13
with the first throttle 23, the heat exchanger 12 and the first
fluid energy machine 22, and the discharging circuit with the pump
24, the heat accumulator 12, the second fluid energy machine 25 and
the second heat exchanger 19, are constructed in a way similar to
FIG. 1. However, the heat accumulator 12 has two passage systems
which are independent of each other for the charging circuit and
the discharging circuit in each case, which are not shown in more
detail in FIG. 4.
[0032] The essential difference between FIG. 4 and FIG. 1, however,
lies in the fact that a third heat exchanger 27 is used in the
charging circuit 13. This is not supplied by river water at ambient
temperature for the purpose of heat exchange but is connected to an
additional circuit 28. The additional circuit 28 has the following
functions. In addition to the motor M1, which supplies the first
fluid energy machine 22, provision is also made for a motor M2
which via a shaft 26 drives a third fluid energy machine 29. This
is provided in the additional circuit 28 and compresses the working
fluid, for example carbon dioxide, which is heated as a result, and
releases the heat in the third heat exchanger 27 to the working
fluid (for example water) of the charging circuit 13. The working
fluid of the additional circuit 28 is then expanded via a second
throttle 30 and condensed via the first heat exchanger 16 which
releases its heat to the river 17.
[0033] The positions 1', 2', 3' and 4' are inscribed in FIG. 4 and
give the typical positions of the Rankine process which is shown in
FIG. 5. In this case, it involves an alternative charging cycle 20a
which represents the first stage of the two-stage charging process
according to FIG. 4. From position 1' to position 2', the carbon
dioxide is evaporated at a temperature of 5.degree. C. and a
pressure of 40 bar. In this case, the necessary energy comes from
the river 17 and is introduced via the first heat exchanger 16. Via
the third fluid energy machine 29, the carbon dioxide is compressed
to 97 bar and achieves a temperature of 80.degree. C. (position
3'). This heat can be released via the third heat exchanger 27 to
the charging circuit 13, wherein a temperature window of between 35
and 80.degree. C. is made available for this. After cooling of the
working medium to 35.degree. C., position 4' is reached, from where
a pressure of 40 bar is achieved (position 1') as a result of
expansion of the carbon dioxide via the second throttle 30.
[0034] The temperature level of 35.degree. C. in the third heat
exchanger makes it possible to operate with water as working medium
in the charging circuit 13 at a level which differs from that in
the case of FIG. 3. The condensation can be carried out at 30 mbar
at a temperature of 25.degree. C. (position 10 to position 5). The
temperature is therefore higher than in the case of FIG. 3. On the
other hand, the discharging cycle can be conducted similar to the
case according to FIG. 3 (position 1 to position 2). The
temperature level for the discharging cycle is therefore also
predetermined by the river 17 at 15.degree. C.
[0035] In principle, the method according to the invention is not
restricted to the working fluids which are specified in the
exemplary embodiments. For example, hydrocarbons, such as propane,
can also be used. If the exemplary embodiments of the plants
according to FIGS. 1 and 4 are compared, their elements can also be
combined with each other. For example, the charging circuit 13 and
discharging circuit 14 according to FIG. 4 can also be realized
according to FIG. 1 with partially the same lines and valves 15, as
a result of which only one passage system has to be provided in the
heat accumulator 12. In this case, however, the second heat
exchanger 19 is required in FIG. 1, whereas the first heat
exchanger 16 according to FIG. 1 would have to be replaced by the
third heat exchanger 27 and the additional circuit 28 with all the
components.
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