US20140245763A1

US20140245763A1 - High-temperature heat pump and method of using working medium in a high-temperature heat pump

Info

Publication number: US20140245763A1
Application number: US14/348,795
Authority: US
Inventors: Bernd Grommoll; Jochen Schäfer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2011-09-30
Filing date: 2012-09-21
Publication date: 2014-09-04
Also published as: CN103827599A; EP2742298A1; CA2850396A1; WO2013045361A1; DE102011086476A1; RU2014117522A; JP2014528053A

Abstract

A fluid circuit in a high-temperature heat pump absorbs thermal energy through the fluid from at least a first reservoir while performing technical work and outputs thermal energy through the fluid to at least a second reservoir, thereby heating the at least one second reservoir. The working medium may be hydrofluoroether or fluoroketone.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International Application No. PCT/EP2012/068645, filed Sep. 21, 2012 and claims the benefit thereof. The International Application claims the benefit of German Application Nos. 102011083840.6 filed on September 30, 2011, and 102011086476.8 filed on Nov. 16, 2011, of which all applications are incorporated by reference herein in their entirety.

BACKGROUND

Described below is a high-temperature heat pump having a fluid circuit for taking up thermal energy through the 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. Also described below is 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 thermal 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 quantity of heat can thus 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.

SUMMARY

Described below are 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 high-temperature heat pump described below has 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. Accordingly, 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 global warming or to an increase in the 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 described below has 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, e.g. from DE 10 2007 010 646 A1. 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.
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 C_xF_y−O—C_mH_n, 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(OC₂H₅)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(O)CF(CF₃)₂as the fluid. As the working medium in the high-temperature heat exchanger, it is also possible to use other hydrofluoroethers or fluoroketones with good thermal properties, and also mixtures of different hydrofluoroethers or fluoroketones.
The method 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, 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.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments and advantageous developments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic illustration of a high-temperature heat pump, and

FIG. 2 is a schematic illustration of a high-temperature heat pump as shown in FIG. 1 additionally with multi-stage compression and an economizer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.
FIG. 1 shows a schematic illustration of an exemplary embodiment of a high-temperature heat pump. The high-temperature heat pump includes 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 C_xF_y—O—C_mH_n, 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(OC₂H₅)CF(CF₃)₂or CH₃CHO(CF₂CFHCF₃)₂, or, as fluoroketone, consideration is given to a substance having the chemical formula CF₃CF₂C(O)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 T₂of the second reservoir 3. In the case of a high-temperature heat exchanger, the temperature T₂can 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.
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 p₁to a value p₂. The working medium at the elevated pressure p₂from the compressor 5 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 T₁to the second reservoir 3 at the relatively high temperature T₂, 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 p₂via a throttle valve 7 back into the evaporator 4 at a pressure p₁. 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 p₁to p₂, and the pressure is reduced from p₂to p₁by 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 p₁, 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 includes the evaporator 4 and the high-pressure side includes the condenser 6.
As is shown in FIG. 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 the gaseous working medium at the outlet of the evaporator 4.
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 makes it possible to achieve secure, environmentally friendly and effective pumping of heat from the first reservoir 2 at a low temperature T₁into 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 have a series of advantages over the prior art, where typical working media include butane, pentane or carbon dioxide. The exemplary embodiments described above can be combined with one another and with exemplary embodiments from the related art.
A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).

Claims

1-13. (canceled)

14. A high-temperature heat pump coupled to at least one first reservoir and at least one second reservoir, comprising:

a fluid circuit taking up thermal energy, through a fluid working medium of hydrofluoroether or fluoroketone, from the at least one first reservoir while performing technical work and emitting thermal energy through the fluid to the at least one second reservoir, thereby heating the at least one second reservoir.

15. The high-temperature heat pump as claimed in claim 14, wherein said fluid circuit includes at least one evaporator, at least one compressor, at least one condenser and/or at least one throttle.

16. The high-temperature heat pump as claimed in claim 15, wherein said fluid circuit includes a two-stage compressor.

17. The high-temperature heat pump as claimed in claim 16, wherein said fluid circuit includes an economizer.

18. The high-temperature heat pump as claimed in claim 17, wherein the fluid circuit is closed or completed.

19. The high-temperature heat pump as claimed in claim 18, wherein the fluid working medium is a hydrofluoroether having the chemical formula CxFy-O—CmHn, 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

20. The high-temperature heat pump as claimed in claim 18, wherein the fluid working medium is a hydrofluoroether having the chemical formula C3F7CF(OC2H5)CF(CF3)2, or in that the hydrofluoroether is a hydrofluoroether having the chemical formula CH3CHO(CF2CFHCF3)2, or in that the fluoroketone is a fluoroketone having the chemical formula CF3CF2C(O)CF(CF3)2.

21. A method of using a working medium in a high-temperature heat pump coupled to at least one first reservoir and at least one second reservoir, comprising:

circulating a working medium of hydrofluoroether or fluoroketone through a fluid circuit, absorbing thermal energy from the at least one first reservoir while performing technical work and emitting thermal energy to the at least one second reservoir, thereby heating the at least one second reservoir.

22. The method as claimed in claim 21, further comprising at least one of compressing the working medium in a predetermined range of condensation temperature of the working medium, and utilizing the thermal energy in producing steam, prior to emitting the thermal energy to the at least one second reservoir.

23. The method as claimed in claim 22, wherein the thermal energy is emitted to the at least one second reservoir, which is at a temperature of greater than 70° C.

24. The method as claimed in claim 23, wherein the high-temperature heat pump is operated in transcritical form to achieve temperatures at a low pressure.

25. The method as claimed in claim 24, wherein the working medium is compressed in two stages.

26. The method as claimed in claim 25, wherein the working medium is superheated and in each of the two stages, compression is completed entirely upstream of a wet-steam zone of a high-temperature heat exchanger.

27. The method as claimed in claim 26,

wherein an economizer superheats the working medium, and

wherein said method further comprises transferring heat from the high-pressure heat exchanger to an outlet of the working medium at the evaporator.