Patent Application
20250052457
The present invention relates to a heat pump method and a heat pump arrangement.
Closed-loop compression heat pumps are used to raise heat Qu from a lower temperature level Tu (heat source) to an upper temperature level To (heat sink). This requires work to be expended. The ratio Qo/W of the heat Qo that can be used at To to the work W is also referred to as the coefficient of performance (COP). We speak of high-temperature heat pumps when the upper temperature level To is higher than 80° C. or even higher than 100° C. The temperature difference To-Tu is also referred to as ΔTLift. A current list of technically achievable COP values depending on this can be found, for example, in the publication by Arpagaus Cordin et al., “High temperature heat pumps: Market overview, state of the art, research status, refrigerants, and application potentials”, Energy 152 (2018), 985-1010.
Against this background, the object of the present invention is to improve known heat pump methods and heat pump arrangements.
This object is achieved by a heat pump method and a heat pump arrangement having the features of the independent claims. Embodiments of the invention are specified in the dependent claims and the description below.
The present application uses the terms “pressure level” and “temperature level” to characterize pressures and temperatures, which is intended to express that corresponding pressures and temperatures in the method explained in each case or a corresponding arrangement do not have to be used in the form of exact pressure or temperature values. However, such pressures and temperatures typically fall within certain ranges that are, for example, ±10% around a mean value. In this case, pressure and temperature levels can be in disjointed ranges or in ranges that overlap one another. In particular, pressure levels include unavoidable or expected pressure losses. The same applies to temperature levels.
The term “saturation” is used below to describe the increase in the degree of saturation of a working medium in a heat pump circuit that is initially not yet in a saturated state, i.e., is superheated. In embodiments of the invention, this is achieved in particular by withdrawing a vapor phase from a container, cooling it and at least partially or completely liquefying it, and subsequently at least partially feeding it back into the same container.
In the following, an “injection” refers to the introduction of a liquid medium into one or between multiple compressor stages of a multi-stage centrifugal compressor. One or more nozzles are used to finely atomize (nebulize) the liquid medium in order to ensure that it is converted into the gaseous state as quickly as possible.
By appropriately saturating the compressed working medium, in embodiments of the present invention, the superheating caused by the compression can be reduced. This can prevent the heat sink from being exposed to an undesirably high temperature, at least in part. This is particularly advantageous, for example, when boiling loaded amine in the regeneration column in amine scrubbing.
Amine scrubbing is a commonly used chemical process to separate carbon dioxide, hydrogen sulfide and other acidic gases from gas mixtures. Amine scrubbing is based on the principle of chemisorption. With amine scrubbing, comparatively high purities can be achieved even at relatively low pressures. The selectivity is also typically higher than with physisorption. In amine scrubbing, slightly alkaline aqueous solutions of amines (mostly ethanolamine derivatives) are typically used as scrubbing agents, which reversibly chemically absorb acid gases while releasing reaction heat. To regenerate the loaded scrubbing agent, the chemical equilibrium is reversed at high temperature (use of thermal energy) and low pressure, thus removing the bound acid gases from the scrubbing agent. Embodiments of the present invention can use the loaded scrubbing agent in particular as a heat sink, which can be heated in this way, but which is already at a comparatively high temperature before heating. The temperature at the bottom of the regeneration column is determined by substantially vaporizing water in a mixture with amines. At a minimum atmospheric pressure, the bottom temperature is more than 120° C. Therefore, a high-temperature heat pump is advantageously used for heating. Embodiments of the present invention thus relate to a method which comprises corresponding amine scrubbing.
Overall, the present invention provides a (high-temperature) heat pump method with an upper temperature level To of typically more than 120° C. and a COP value of typically more than 2.5. The heat is released largely isothermally at the upper temperature level To in embodiments of the present invention, so that excessive heating of the heat sink can be avoided. Excessive heating must be avoided because the amines used degrade at higher temperatures, i.e., change their chemical properties by changing the molecular structure. It can cause local damage to the amines, even if the bottom temperature remains at the boiling point.
The present invention proposes a heat pump method, in which a working medium is vaporized at a lower temperature level Tu using a heat source and subsequently compressed and liquefied at an upper temperature level To, using a heat sink, wherein: after being vaporized and before being compressed, the working medium is superheated; a temperature increase caused by the compression is restricted by means of injection into the compression; and after being compressed and before being liquefied, the working medium is saturated at the upper temperature level To. In the context of the present invention, the vaporized working medium is superheated in particular in a countercurrent heat exchanger against working medium liquefied at high pressure, wherein the suction temperature of a compressor used for compression is in particular at most 10 K, preferably at most 5 K, below the upper temperature level To.
The advantages of the measures proposed in accordance with the invention have already been explained above and include in particular increased efficiency while at the same time avoiding excessive heating of the heat sink.
In one embodiment of the present invention, the lower temperature level is in particular 10 to 60° C. The upper temperature level To is in particular at least 115° C., in particular at least 120° C. The method proposed in a corresponding embodiment of the present invention is a high-temperature heat pump method as mentioned at the outset, which is particularly advantageous for certain purposes, such as the amine scrubbing mentioned. The upper temperature level To can, for example, be up to 140° C., in particular up to 130° C. An inlet temperature level into the compression, i.e., a compressor used here, is in particular at most 10 K, more particularly at most 5 K below the upper temperature level To.
Within the scope of the present invention, an inlet pressure level of the compressor used can be in particular 1.5 to 5 bar, and an outlet pressure level can be in particular 20 to 50 bar.
In embodiments of the present invention, the temperature increase caused by the compression can be restricted by injection, in particular to a temperature level of at most 180° C. Such a restriction can prevent excessive heating, for example when using a loaded scrubbing agent in amine scrubbing as a temperature sink.
In one embodiment of the present invention, the injection can be carried out using a part of the working medium which is branched off from a remainder fed to superheating and then to compression before vaporization and before superheating, expanded, and fed to compression at one or more intermediate stages of compression. The corresponding working medium used for injection can be returned to the circuit and is used further in this way.
Injection can in particular be carried out in a multi-stage manner. In particular, an arrangement as described in EP 3 505 767 B1 can be used here. A particularly advantageous embodiment is described in the applicant's European patent application No. 20 176 585.6 in connection with surge control. As disclosed therein, the injection provided in an embodiment of the present invention can also be carried out using one or more nozzles. The nozzle or at least one of the plurality of nozzles may have an outlet arranged in a return bend between different compressor stages of a multi-stage centrifugal or turbo compressor. The nozzle or at least one of the plurality of nozzles or at least one line connected thereto may have thermal insulation. The nozzle or at least one of the plurality of nozzles or at least one line connected thereto may have a degassing device. The nozzle or at least one of the plurality of nozzles can be operated with a pressure difference of 2 to 10 bar, in particular 7 bar.
The embodiments just explained serve in particular to avoid vapor bubbles or a vapor lock. A vapor lock can result from the working medium to be injected outgassing in the supply line to the injection nozzle. The liquid working fluid passes through regions with higher temperatures as it approaches the hot return bend. Since this is not necessarily supercooled, corresponding outgassing can occur. Only a small part of the vapor formed can pass through the injection nozzle. If the vaporization rate becomes higher than the maximum possible vapor flow in the nozzle, no more liquid can pass through the nozzle. This can lead to insufficient atomization and vaporization.
Thermal insulation can be designed in particular in the form of a double-walled design of a line portion with an intermediate space, which can in particular be evacuated. In certain embodiments, the thermal insulation may extend as far as technically possible in the direction of the injection point in order to reduce the heat flow and thus the risk of vapor bubbles. Degassing can be carried out in particular using a line which is arranged, for example, coaxially inside or outside the line through which the working medium to be injected is passed. In this way, the cold gas formed by vaporization can be preferentially fed to the compressor. A further fundamentally possible alternative is to supercool the liquid to be injected so that vaporization and thus the formation of vapor bubbles can be avoided.
In one embodiment of the present invention, a compressor configured as a single-shaft turbo compressor or screw compressor can be used for compression. Screw compressors are particularly suitable for smaller arrangements, whereas (multi-stage) single-shaft turbo compressors, in particular of the type just described, are used in particular for larger arrangements.
In one embodiment of the present invention, a heat pump method comprises in particular that saturation is carried out using a container from which a vapor phase is taken at the head side, at least partially liquefied in a heat exchanger thermally coupled to the heat sink, and fed back into the container.
In one embodiment of the present invention, a heat pump method is proposed in which the container is empty or equipped with trays and/or packings. Empty containers have particular weight and cost advantages, while built-in components promote equilibrium.
In one embodiment of the present invention, the heat pump method comprises a start-up operating mode and a subsequent operating mode carried out after the start-up operating mode, wherein the working medium in the subsequent operating mode is saturated at the upper temperature level To and wherein the working medium in the start-up operating mode is cooled at least in part after compression using a further heat sink to an intermediate temperature level Tm between the lower temperature level Tu and the upper temperature level To. To simplify the start-up of the compressor, a cooler can be provided which can dissipate the heat generated during compression at an intermediate temperature level Tm below the upper temperature level To. In embodiments of the present invention, an associated container can be combined with the container previously explained in connection with saturation.
In one embodiment of the present invention, the further heat sink can be thermally coupled to a start-up cooler. In this case, an embodiment can be provided in which the lower temperature level Tu is at least partially lowered in the start-up operating mode by first passing a heating medium at the lower temperature level Tu through the start-up cooler and then through a heat exchanger used for the vaporization of the working medium. In other words, in a corresponding embodiment, it can be provided that the start-up cooler is also used to reduce the lower temperature level Tu at least temporarily.
In one embodiment of the present invention, the heat source can be a condensing cooling medium of a refrigeration circuit or comprise such a cooling medium whose condensation heat at the lower temperature level Tu is used at least in part for the vaporization of the working medium. In such cases in particular, the previously explained embodiment with temporary reduction of the lower temperature level Tu can be advantageous, since this can improve the condensation conditions of the cooling medium.
In one embodiment of the present invention, a working medium is used which has a critical temperature that is at least 20° C. or 30° C. above the upper temperature level To. The working medium can in particular comprise one or more components selected from n-butane, i-pentane, n-pentane, cyclobutane and cyclopentane.
In one embodiment of the present invention, the heat source can be a condensing refrigerant and/or a regenerated amine from acid gas scrubbing or comprise a corresponding medium. In particular, when using a regenerated amine, an advantageous integration into corresponding amine scrubbing can be achieved because both a suitable heat source (in the form of the regenerated scrubbing agent) and a suitable heat sink (in the form of the loaded scrubbing agent) can be used.
A heat pump arrangement which is designed to vaporize a working medium at a lower temperature level Tu using a heat source and subsequently to compress and liquefy said working medium at an upper temperature level To using a heat sink is also the subject of the present invention.
A corresponding heat pump arrangement comprises means which are designed to superheat the working medium, after being vaporized and before being compressed, in order to restrict a temperature increase caused by the compression by means of injection into the compression, and to saturate the working medium, after being compressed and before being liquefied, at the upper temperature level To.
Reference is expressly made to the above statements with regard to features and advantages of a corresponding heat pump arrangement which in embodiments of the invention can in particular be designed to carry out a method as has been explained above. In particular, such a heat pump arrangement has a control device which is designed to switch between the start-up and the follow-up operating mode when required, for example according to a fixed switching pattern, on the basis of a sensor signal or on request.
The invention will be described in more detail hereafter with reference to the accompanying drawings, which illustrate one embodiment of the invention.
In the single FIGURE, a heat pump process is illustrated in the form of a highly simplified process flow diagram and is designated as 100. The figure also serves to explain a corresponding heat pump arrangement. If method steps are explained below, the corresponding explanations apply to components of the arrangement in the same way and vice versa. For additional information on the abbreviations and variables used below, please refer to the explanations given at the beginning.
In the process illustrated in the FIGURE, a liquid working medium fed to a heat exchanger E1 via a line L1 with a valve V1 is vaporized at a first (lower) pressure level against a heat source or a heating medium which is available at a lower temperature level Tu. The vaporized working fluid is fed via a line L2 to a countercurrent heat exchanger E3 and is superheated in the countercurrent heat exchanger against liquefied working fluid in a line L3 at a second (higher) pressure level. The superheated working medium is fed to a compressor C1 via a line L4 and removed from it via a line L5. Using a container D1, the compressed working medium is liquefied, whereby a vapor phase is withdrawn from the container D1 via a line L6 and at least partially liquefied in the heat exchanger E2 against a heat sink or a cooling medium which is available at an upper temperature level To and returned to the container D1 via a line L7. In other words, the container D1 serves to saturate the compressed working medium from the line L5 with the liquid from the condenser E2, which releases heat Qo at To to the heat sink. A liquid phase is taken from the container D1 via the already mentioned line L3 and further cooled in the countercurrent heat exchanger E3 while superheating the vaporized working medium in the line L2.
In the method 100, an inlet temperature level of the compressor C1 is at most 10 K, preferably at most 5 K below the upper temperature level To. The superheated working medium is compressed in the compressor C1 to an outlet pressure level which corresponds at least to the boiling pressure of the working medium at the temperature To of the heat sink.
By saturating the compressed working medium in the container D1, the superheating caused by the compression is reduced. This can prevent the heat sink from being exposed to an undesirably high temperature, at least in part.
This is an important criterion for process selection, for example when boiling loaded amine in the regeneration column of a carbon dioxide scrubber. Superheating the working medium before compression enables an efficient method with a COP value >2.5.
The temperature increase in the compressor C1 can be limited to <180° C. by injecting supercooled working medium via a line L8 with a valve V2. To simplify the start-up of the compressor C1, a cooler E4 can be provided which can dissipate the heat generated during compression at an intermediate temperature level Tm below the upper temperature level To. An associated container D2 can, if necessary, be combined with the container D1 or connected to the cooler E4 in the manner described, whereby the working medium can be fed to the container D2 via a line L9 with a valve V3 and can be removed from it via a line L10. The start-up cooler E4 can also be used to lower the upper temperature level (To) at least temporarily.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21020642.1 | Dec 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/025514 | 11/16/2022 | WO |
