Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
High-temperature heat pump and method of using a working medium
in a high-temperature heat pump
The present invention relates to a high-temperature heat pump
having a fluid circuit for taking up thermal energy through the
fluid from at least a first reservoir while perfoLming
technical work and for emitting thermal energy through the
fluid to at least a second reservoir for heating the at least
one second reservoir. The present invention furthermore relates
to a method of using a working medium in such a high-
temperature heat pump.
A heat pump is a machine which, while performing technical
work, takes up thelmal energy from a reservoir at a relatively
low temperature and, together with the driving energy,
transfers it as useful heat to a system to be heated at a
relatively high temperature. The reservoir at a relatively low
temperature can be, for example, air from the environment or
liquid and rock in the earth when using geothermal energy.
However, it is also possible to utilize, inter alia, waste heat
sources in industrial processes.
Heat pumps can be used to heat buildings or to obtain heat for
technical processes in industry. High-temperature heat pumps
feed useful heat to a system to be heated which is at a high
temperature level. A high temperature level or relatively high
temperature is to be understood to mean, for example,
temperatures above 70 C. The temperatures which can be achieved
with the aid of heat pumps for heating depend largely on the
working medium used in the heat pump. The working medium is
generally a fluid, which is liquefied in the event of
compression under pressure and emits thermal energy. In the
event of expansion to form a gas, the fluid cools and can take
up thermal energy from the first reservoir. In the circuit, a
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quantity of heat can thus
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be transferred continuously or in pulses from a cooler
reservoir to a hotter reservoir with the application of
mechanical energy.
The temperature which can be achieved by a heat pump during
heating depends not only on the working medium used but also on
the pressure in the condenser. In the condenser, the working
medium is liquefied with take-up of a quantity of heat from the
first, relatively cool reservoir. For high-temperature heat
pumps, carbon dioxide is used as the working medium, for
example. The boiling point of carbon dioxide at 1 bar is, for
example, -57 C and the liquefying temperature at 26 bar is, for
example, -26 C. For reasons of environmental compatibility,
e.g. with respect to "Global Warming Potential" and "Ozone
Depletion Potential", although carbon dioxide is an ideal
working medium, the critical temperature of carbon dioxide is
merely 31 C. Above this temperature, carbon dioxide can no
longer be liquefied, even with the application of extremely
high pressures.
This results in specific features for the procedure beyond the
critical temperature. Thus, the heat is not emitted at a
certain temperature after compression, as in the case of
condensing working substances, but rather over a large
temperature range. This makes it harder for the heat to be
used, for example, for generating steam. The use of carbon
dioxide as the working substance in a heat pump is further
associated with very high pressures and therefore entails a
high apparatus cost on account of the substance properties.
Hydrocarbons such as butane or pentane are better suited to
providing heat at a high temperature level on account of their
physical properties. Butane has, for example, a boiling point
of -12 C at 1 bar and a liquefying temperature of 114 C at 26
bar. However, owing to their good combustibility, the use
thereof is problematic for safety-related reasons.
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It is an object of the present invention, therefore, to specify
a high-temperature heat pump and a method of using a working
medium in a high-temperature heat pump which are suitable for
providing heat at high temperatures, for example higher than
70 C, are environmentally friendly and can be operated easily,
at low cost and without a high risk, e.g. owing to a low
combustibility.
The object set forth is achieved by the features of claim 1 in
terms of the high-temperature heat pump and by the features of
claim 7 in terms of the method of using a working medium in a
high-temperature heat pump.
Advantageous configurations of the high-temperature heat pump
according to the invention and of the method according to the
invention of using a working medium in a high-temperature heat
pump become apparent from the respectively assigned dependent
subclaims. In this respect, the features of the alternative
independent claims can be combined with one another and with
features of the subclaims, and also features of the subclaims
can be combined with one another.
The high-temperature heat pump according to the invention
comprises a fluid circuit for taking up thermal energy through
a fluid from at least a first reservoir while performing
technical work and for emitting thermal energy through the
fluid to at least a second reservoir for heating the at least
one second reservoir. According to the invention, the fluid
circuit is filled with a hydrofluoroether or with fluoroketone
as the fluid or working medium. It is also possible to use
mixtures of hydrofluoroether and fluoroketone.
Hydrofluoroether or fluoroketone are incombustible and can
therefore be used safely, for example in processes at a high
temperature. Hydrofluoroether or fluoroketone are
environmentally friendly, since no contribution is made to
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global warming or to an increase in the
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ozone hole by these substance classes. The known
hydrofluoroethers or fluoroketones have higher critical
temperatures than, for example, carbon dioxide. As a result,
the majority of the quantity of heat taken up can be emitted
again at one temperature, specifically the condensation
temperature, after compression. This makes it easier to utilize
the heat, for example during process steam provision. With
hydrofluoroether or fluoroketone as the working medium, it is
possible for high-temperature heat pumps to be operated in
transcritical form to achieve very high temperatures at
relatively low pressures, compared for example to carbon
dioxide as the working medium. In this context, transcritical
means that, compared to a subcritical procedure, in which the
working medium is liquefied at a constant temperature, in a
transcritical procedure the heat is emitted smoothly in the
supercritical range, i.e. in the case of a change in
temperature.
= The high-temperature heat pump according to the invention can
comprise at least one evaporator, at least one compressor, at
least one condenser and/or at least one throttle as part of the
fluid circuit. The individual components are known from the
prior art, e.g. from DE 10 2007 010 646 Al. Moreover, expansion
valve can also be used as a synonym for the throttle, depending
on the function of the component. The fluid flowing in the
fluid circuit is compressed in the compressor, cools in the
condenser, emitting a quantity of heat to the second reservoir,
and flows, depending on the opening of the throttle, at a given
rate or with a given pressure reduction through the throttle
into the evaporator, where it expands and extracts a quantity
of heat from the first reservoir.
A multi-stage compressor, in particular a two-stage compressor,
can be used as the compressor. Multi-stage compression
increases the coefficient of performance of the high-
temperature heat exchanger.
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An economizer can be part of the fluid circuit. An economizer
is an additional intermediate heat exchanger in the fluid
circuit. It transfers some of the heat present in the liquid
working medium after the emission of heat to the second
reservoir to the gaseous, superheated working medium upstream
of the compressor. This makes it possible to achieve, for
example, intense superheating of the working medium = as a
suction gas, as a result of which compression in the wet-steam
zone of the working medium can be ensured. The economizer leads
to an increase in the efficiency of the high-temperature heat
exchanger.
The fluid circuit can be closed or completed. A completed fluid
circuit can be selected specifically with respect to the
avoidance of losses of working medium.
The hydrofluoroether can be a hydrofluoroether having the
chemical formula CFy-O-CH, where x is 3, y is 7, m is 1 and n
is 3, or x is 4, y is 9, m is 1 and n is 3, or x is 4, y is 9,
m is 2 and n is 5, or x is 6, y is 13, m is 1 and n is 3. The
hydrofluoroether can also be a hydrofluoroether having the
chemical formula C3F7CF (0C2H5) CF(CF3) 2 = Furthermore, the
hydrofluoroether can be a hydrofluoroether having the chemical
formula CH3CHO(CF2CFHCF3)2. It is also possible to use a
fluoroketone having the chemical formula CF3CF2C(0)CF(CF3)2 as
the fluid. As the working medium in the high-temperature heat
exchanger according to the invention, it is also possible to
use other hydrofluoroethers or fluoroketones with good thermal
properties, and also mixtures of different hydrofluoroethers or
fluoroketones.
The method according to the invention of using a working medium
in a high-temperature heat pump, in particular in a high-
temperature heat pump described above, includes the fact that
the working medium, as it flows in a fluid circuit,
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takes up thermal energy from at least a first reservoir while
performing technical work and emits thermal energy to at least
a second reservoir for heating the at least one second
reservoir. Here, hydrofluoroether or fluoroketone is used as
the working medium.
The thermal energy can be emitted to the at least one second
reservoir after compression of the working medium, at or in the
range of the condensation temperature of the working medium.
The thermal energy can be utilized for process steam provision.
The at least one second reservoir, to which the thermal energy
is emitted, can be at a temperature of greater than 70 C. The
high-temperature heat pump can be operated in transcritical
form to achieve high temperatures at a low pressure. The
working medium can be compressed in multiple stages, in
particular two stages.
The gaseous working medium can be severely superheated, so that
in each case the compression has been completed entirely
upstream of a wet-steam zone of the high-temperature heat
exchanger. The superheating can be performed by an economizer,
in particular with a transfer of the heat at the end of a high-
pressure heat exchanger or of the condenser to the outlet of
the working medium at the evaporator.
The advantages associated with the method of using a working
medium in a high-temperature heat pump are analogous to the
advantages which have been described above with reference to
the high-temperature heat pump.
Preferred embodiments of the invention with advantageous
developments as per the features of the dependent claims will
be explained in more detail hereinbelow with reference to the
figures, but without being limited thereto.
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In the figures:
Figure 1 shows a schematic illustration of a high-temperature
heat pump according to the invention, and
Figure 2 shows a schematic illustration of a high-temperature
heat pump as shown in figure 1 additionally with
multi-stage compression and an economizer.
Figure 1 shows a schematic illustration of an exemplary
embodiment of a high-temperature heat pump according to the
invention. The high-temperature heat pump comprises a fluid
circuit 1, in which a hydrofluoroether or fluoroketone flows as
the working medium. The hydrofluoroether or the fluoroketone is
a fluid which can be present in liquid or gaseous form. As
hydrofluoroether, consideration is given inter alia to
substances having the chemical formula CFy-O-CH, where x is
3, y is 7, m is 1 and n is 3, or x is 4, y is 9, m is 1 and n
is 3, or x is 4, y is 9, m is 2 and n is 5, or x is 6, y is 13,
m is 1 and n is 3, or substances having the chemical formula
C3F7CF(0c2H5)CF(CF3)2 or CH3CHO(CF2CFHCF3)2, or, as fluoroketone,
consideration is given to a substance having the chemical
formula CF3CF2C(0)CF(CF3)2. It is also possible to use other
hydrofluoroethers or fluoroketones with suitable physical
properties for providing heat at a high temperature level.
A first reservoir 2 is in thermal contact with an evaporator 4.
A second reservoir 3 is in thermal contact with a condenser 6
for the working medium. The first reservoir 2 is at a
temperature T1, which is lower than the temperature T2 of the
second reservoir 3. In the case of a high-temperature heat
exchanger, the temperature T2 can be higher than 70 C.
In the evaporator 4, upon expansion of the working medium, the
working medium takes up heat, which is withdrawn from the first
reservoir 2.
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A gaseous working medium is sucked in from the evaporator 4 by
a compressor 5 and compressed. The pressure of the working
medium thereby increases from a value pi to a value p2. The
working medium at the elevated pressure p2 from the compressor
flows into a condenser 6, where it is liquefied with emission
of heat to the second reservoir 3. A quantity of heat is
thereby transported or pumped from the first reservoir 2 at a
relatively low temperature T1 to the second reservoir 3 at the
relatively high temperature T2f with work being performed by
the compressor 5. The first reservoir 2 in this case serves as
a heat source and heat is fed to the second reservoir 3 via the
condenser 6 as a heater.
The working medium from the condenser 6 can flow at a high
pressure p2 via a throttle valve 7 back into the evaporator 4
at a pressure pi. The fluid circuit 1 is thus closed. If fluid-
tight devices 4, 5, 6, 7 and connections, for example pipes and
seals, are used, the fluid circuit for the working medium can
be completed, such that no working medium is emitted to the
environment or lost. The compressor 5 increases the pressure of
the working medium from pi to p2, and the pressure is reduced
from p2 to pi by way of the throttle 7 in the form of an
expansion valve. The fluid circuit can thus be divided into a
cold side at a low pressure pl, that is to say a low-pressure
side, and into a hot side at a high pressure p2, that is to say
a high-pressure side. The low-pressure side comprises the
evaporator 4 and the high-pressure side comprises the condenser
6.
As is shown in figure 2, an economizer 8 can be used to improve
the efficiency of= the high-temperature heat exchanger, that is
to say the ratio between a pumped quantity of heat and work
performed for pumping, e.g. in the form of mechanical work of
the compressor 5. The economizer 8 can be in the form of a heat
exchanger, which takes up a quantity of heat from the liquid
working medium at the outlet of the condenser 6 and emits it to
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the gaseous working medium at the outlet of the evaporator 4.
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It is thereby possible to achieve superheating of the gaseous
working medium, as a result of which it is possible to ensure
compression in the wet-steam zone of the condenser 6.
An increase in the coefficient of performance, the ratio
between useful heat obtained and driving energy used, of the
high-temperature heat exchanger is made possible by using
multi-stage compression, rather than single-stage compression,
of the working medium.
The use of hydrofluoroether or fluoroketone as the working
medium or fluid in the high-temperature heat exchanger and
method according to the invention makes it possible to achieve
secure, environmentally friendly and effective pumping of heat
from the first reservoir 2 at a low temperature Tl into the
second reservoir 3 at a high temperature T2-
Hydrofluoroether and fluoroketone are incombustible and can
therefore be used safely, for example in processes at a high
temperature and for compression. Hydrofluoroether and
fluoroketone are environmentally friendly, since no
contribution is made to global warming or to an increase in the
ozone hole by this substance class. The known hydrofluoroethers
and fluoroketones have higher critical temperatures than, for
example, carbon dioxide, as a result of which the majority of
the quantity of heat taken up can be emitted again after
compression. With hydrofluoroether and/or fluoroketone, it is
possible for high-temperature heat pumps to be operated in
transcritical form to achieve very high temperatures, as a
result of which only moderate pressures are required, e.g.
lower than in the use of carbon dioxide. Therefore, by using
hydrofluoroether and/or fluoroketone, high-temperature heat
exchangers and methods according to the invention have a series
of advantages over the prior art, where typical working media
include butane, pentane or carbon dioxide. The exemplary
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embodiments described above can be combined with one another
and with exemplary embodiments from the prior art.
