DK2225501T3

DK2225501T3 - METHOD AND DEVICE FOR CRYOGEN COOLING

Info

Publication number: DK2225501T3
Application number: DK08852903.7T
Authority: DK
Inventors: Fabien Durand; Alain Ravex
Original assignee: Air Liquide
Priority date: 2007-11-23
Filing date: 2008-10-23
Publication date: 2018-11-19
Also published as: WO2009066044A4; PL2225501T3; PL2225501T5; EP2225501A2; EP3410035A1; EP2225501B2; WO2009066044A3; DK2225501T4; JP2011504574A; FR2924205A1; EP2225501B1; FR2924205B1; US20100263405A1; KR20100099129A; FI2225501T4; WO2009066044A2; CN101868677A; ES2693066T3; ES2693066T5; EP3561411A1

Description

The present invention relates to a cryogenic refrigeration device and method.

The invention relates more specifically to a cryogenic refrigeration device configured to transfer heat from a cold source to a hot source via a working fluid circulating in a closed working circuit, the working circuit comprising in series: a compression portion, a cooling portion, an expansion portion and a heating portion.

The cold source can, for example, be liquid nitrogen to be cooled and the hot source, water or air.

Refrigerators known for cooling superconducting elements generally use a reverse Brayton cycle. These known refrigerators use a lubricated screw compressor, a plate-type reverse-flow exchanger and an expansion turbine.

These known refrigerators have numerous disadvantages, from among: - low energy efficiency of the cycle and consequently of the refrigerator, - the use of oil for cooling and lubricating the compressor, this requires an operation of de-oiling the working gas after compression, - the use of rotary seals between the electric motor and the compressor, - low isothermal compression efficiency of the compressor, - periodicity of the maintenance operations.

Document US-3,494,145 describes a refrigeration system using couplings via gears requiring oil bearings. This type of device uses rotary seals such as mechanical packings between the working gas and the gear and the oil-bearing casing. This architecture increases the risk of leakage of the working gas and possible contamination of the working gas by the oil. This system moreover relates to a motor of the low-speed type.

Document US-4,984,432 describes a refrigeration system using compressors or turbines of the liquid ring type functioning with a low-speed motor using conventional bearings such as ball bearings. This technology relates to volumetric compressors and turbines.

One aim of the present invention is to overcome all or some of the disadvantages of the prior art noted above.

To this end, the invention proposes a cryogenic refrigeration device configured to transfer heat from a cold source to a hot source via a working fluid circulating in a closed working circuit, the working circuit comprising in series: a portion for the substantially isothermal compression of the fluid, a portion for the substantially isobaric cooling of the fluid, a portion for the substantially isothermal expansion of the fluid and a portion for the substantially isobaric heating of the fluid, the compression portion of the working circuit comprising at least two compressors arranged in series and at least one exchanger for cooling the compressed fluid arranged at the outlet of each compressor, the expansion portion of the working circuit comprising at least one expansion turbine and at least one exchanger for heating the expanded fluid, the compressors and the expansion turbine(s) being driven by at least one so-called high-speed motor comprising an output shaft, one of the ends of which carries and rotates by direct coupling a first compressor and the other end of which carries and rotates by direct coupling an expansion turbine.

The embodiments make it possible to obtain a system without oil contamination and without contact. This is because the combination of centrifugal compressors, centripetal turbines and bearings according to the invention reduces or eliminates any contact with the fixed parts and rotating parts. This makes it possible to avoid any risk of leakage. The whole of the system is in fact hermetic and comprises no rotary seal vis-å-vis the atmosphere (such as mechanical packings or dry face seals).

Moreover, the invention further comprises the following characteristics: - the compressors are of the centrifugal compression type, - the expansion turbine(s) is/are of the centripetal expansion type, - the output shafts of the motors are mounted on bearings of the magnetic type or of the dynamic gas type, said bearings being used for supporting the compressors and the turbines, - the cooling portion and the heating portion comprise a common heat exchanger wherein the working fluid passes in reverse flow depending on whether it is being cooled or heated.

Furthermore, specific embodiments can also comprise the following characteristics: - the working circuit comprises a volume forming a buffer storage for the working fluid, - the working fluid is in gaseous phase and constituted of a pure gas or a mixture of pure gases from among: helium, neon, nitrogen, oxygen, argon, carbon monoxide or methane, or any other fluid having a gaseous phase at the temperature of the cold source.

The invention further proposes a cryogenic refrigeration method configured to transfer heat from a cold source to a hot source via a working fluid circulating in a closed working circuit, the working circuit comprising in series: a compression portion comprising at least two compressors arranged in series, a portion for cooling the fluid, an expansion portion comprising at least one expansion turbine, and a heating portion, the method comprising a working cycle comprising a first step of substantially isothermal compression of the fluid in the compression portion by cooling the compressed fluid at the outlet of the compressors, a second step of substantially isobaric cooling of the fluid in the cooling portion, a third step of substantially isothermal expansion of the fluid in the expansion portion by heating the expanded fluid at the outlet from the turbine, and a fourth step of substantially isobaric cooling of the fluid that has exchanged thermally with the cold source, the working cycle of the fluid (temperature T, entropy S) being of the reverse Ericsson type according to claim 6.

Moreover: - during the first substantially isothermal compression step, the compressed fluid is cooled at the outlet of each compressor to maintain the temperatures of the fluid at the inlet and outlet of each compression substantially equal and preferably in a range of around 10K, - during the third substantially isothermal expansion step the expanded fluid is cooled at the outlet of each turbine to maintain the temperatures of the fluid at the inlet and outlet of each turbine substantially equal and preferably in a range of around 5K, - the compressors and the expansion turbine(s) are driven by at least one so-called high-speed motor comprising an output shaft, one of the ends of which carries and rotates by direct coupling a first compressor and the other end of which carries and rotates by direct coupling an expansion turbine, and in that the method comprises a step of transferring part of the mechanical work from the turbine(s) to the compressor(s) via the output shaft(s).

Furthermore, embodiments of the invention can comprise one or more of the following characteristics: - at the end of the second cooling step, the working fluid is brought to a low temperature of around 60K and in that the working circuit comprises a number of compressors around three times greater than the number of expansion turbines, - the working fluid is used for cooling or keeping cold superconducting elements at a temperature of around 65K, - the drop in temperature of the fluid constituting the cold source is substantially identical to the increase in temperature of the gas in the exchangers.

The invention can have one or more of the following advantages: - the cycle of the working fluid (reverse Ericsson type) makes it possible to obtain a greater efficiency than the known systems without creating or increasing other disadvantages, - the expansion work in the turbines can advantageously be improved, - it is possible to dispense with the use of oil for lubrication or cooling, this makes it possible to remove the de-oiling installation downstream of the compressor, as well as the operations of processing and recycling the waste oil, - the system only requires a small number of moving parts, which increases the simplicity and reliability thereof. It is possible, by virtue of the invention, for the compressor, to dispense with a mechanical power transmission of the speed multiplier type, universal joints, etc, - the maintenance operations are reduced or even practically non-existent, - the system makes it possible to avoid rotary seals and to use a system that is completely hermetic vis-å-vis the outside. This prevents any loss or contamination of the working cycle gas, - the volume of the refrigerator can be reduced compared with the known systems.

Other particularities and advantages will emerge upon reading the following description, made in reference to the figures, wherein: - figure 1 shows a schematic view illustrating the structure and functioning of a first example embodiment of a refrigeration device according to the invention, - figure 2 shows schematically a detail of figure 1 illustrating an arrangement of a motor driving a compressor-compressor or compressor-turbine assembly, - figure 3 shows schematically an example of a working cycle of the working fluid of the refrigerator of figure 1, - figure 4 shows a schematic view illustrating the structure and functioning of a second example embodiment of a refrigerator according to the invention, - figure 5 shows schematically a second example of a working cycle of the working fluid of the refrigerator according to figure 3.

Referring to the example embodiment in figure 1, the refrigerator according to the invention is provided to transfer heat from a cold source 15 at a cryogenic temperature to a hot source at ambient temperature 1, for example.

The cold source 15 can, for example, be liquid nitrogen to be cooled and the hot source 1, water or air. To achieve this transfer of heat, the refrigerator illustrated in figure 1 uses a working circuit 200 of a working gas comprising the components listed below.

The circuit 200 comprises a plurality of centrifugal compressors 3, 5, 7 arranged in series and functioning at ambient temperature.

The circuit 200 comprises a plurality of heat exchangers 2, 4, 6 functioning at ambient temperature, arranged respectively at the outlet of the compressors 3, 5, 7. The temperatures of the working gas at the inlet and outlet of each compression stage (i.e. at the inlet and outlet of each compressor 3, 5, 7) are maintained by heat exchangers at a substantially identical level (see zone A in figure 3, which represents a working cycle of the gas: temperature in K as a function of the entropy S in J/kg). In figure 3, the rising parts of the zone A in saw teeth each correspond to a compression stage, while the descending parts of this zone A each correspond to cooling by exchanger.

This arrangement makes it possible to approach isothermic compression. The inlet and outlet temperatures of each compression stage are substantially the same.

The exchangers 2, 4, 6 can be separate or be constituted of separate portions of the same exchanger in thermal exchange with the hot source 1.

The refrigerator comprises a plurality of so-called high-speed motors (70 see figure 2). High-speed motor normally means motors where the rotation speed makes it possible for direct coupling with a centrifugal compression stage or a centripetal expansion stage. The high-speed motors 70 preferably use magnetic or dynamic gas bearings 171 (figure 2). A high-speed motor typically rotates at a rotation speed of 10000 revolutions per minute or several tens of thousands of revolutions per minute. A low-speed motor rather rotates with a speed of a few thousand revolutions per minute.

Downstream of the compression portion comprising the compressors in series, the refrigerator comprises a heat exchanger 8, preferably of the reverse-flow plate type separating the elements at ambient temperature (at the top part of the circuit 200 shown in figure 1) from the cryogenic temperature elements (at the bottom part of the circuit 200). The fluid is cooled (corresponding to zone D in figure 3). The cooling of the gas from ambient temperature to cryogenic temperature takes place by reverse-flow exchange with the same working gas at cryogenic temperature that returns from the expansion portion after heat exchange with the cold source 15.

Downstream of this cooling portion constituted by the plate exchanger 8, the circuit comprises one or more expansion turbines 9, 11, 13, preferably of the centripetal type, arranged in series. The turbines 9, 11, 13 operate at cryogenic temperature, the inlet and outlet temperatures of each expansion stage (turbine inlet and outlet) are maintained substantially identical by one or more cryogenic heat exchangers 10, 12, 14 arranged at the outlet of the turbine or turbines. This corresponds to zone C in figure 3, the descending portions of zone C each corresponding to an expansion stage, while the rising portions of this zone correspond to the heating in the exchangers 10, 12, 14. This arrangement makes it possible to approach isothermic expansion. The inlet and outlet temperatures of each expansion stage are substantially the same. In addition, and in order to increase the efficiency of the refrigerator, the increase in the temperature of the working gas in the exchanger or exchangers (10, 12, 14) can be substantially identical (in absolute value) to the reduction in the temperature of the fluid to be cooled (15) (cold source).

These heat exchangers 10, 12, 14 can be separate or be constituted of separate portions of the same exchanger in thermal exchange with the cold source 15.

Downstream of the expansion portion and of the thermal exchange with the cold source 15, the working fluid once again exchanges thermally with the plate-type heat exchanger 8 (zone B in figure 3). The fluid exchanges thermally in the exchanger 8 in reverse flow with respect to the passing thereof after the compression portion. After heating, the fluid returns to the compression portion and can restart the cycle.

The circuit can further comprise a working-gas storage at ambient temperature (not shown for reasons of simplification) in order to limit the pressure in the circuits, when the refrigerator is stopped, for example.

The refrigerator preferably uses a fluid in gaseous phase circulating in closed circuit as a working fluid. It is constituted, for example, of a pure gas or a mixture of pure gases. The gases best suited to this technology are in particular: helium, neon, nitrogen, oxygen and argon. Carbon monoxide and methane can also be used.

The refrigerator is designed and controlled in this way so as to obtain a working cycle of the fluid similar to the reverse Ericsson cycle, i.e. isothermal compression, isobaric cooling, isothermal expansion and isobaric heating.

According to an advantageous particularity, the refrigerator uses, for driving at least compressors 3, 5, 7 (i.e. for driving the impellers of the compressors), a plurality of so-called high-speed motors 70.

As shown schematically in figure 2, each high-speed motor 70 receives, on one of the ends of the output shaft thereof, a compressor impeller 31 and, on the other end of the shaft thereof, another compressor impeller or turbine impeller 9. This arrangement provides numerous advantages. This configuration makes it possible, in the refrigerator, for direct coupling between the motor 70 and the compressor impellers 3, 5, 7 or between the motor 70 and the turbine impellers 9, 11, 13. This makes it possible to dispense with a speed multiplier or reducer (which limits the number of moving parts required). This configuration also makes it possible for improvement in the mechanical work of the turbine or turbines 9, 11, 13 and consequently an increase in the overall energy efficiency of the refrigerator. According to this configuration, the refrigerator functions without oil, which guarantees the purity of the working gas and eliminates the need for a de-oiling operation.

The number of high-speed motors is mainly dependent on the energy efficiency required for the refrigerator. The greater this efficiency, the greater the number of highspeed motors required.

The ratio between the number of compression stages (compressors) and the number of expansion stages (turbines) depends on the target cold temperature. For example, a refrigerator where the cold source is at 273K, the number of compression stages is substantially equal to the number of expansion stages. For a refrigerator where the cold source is at 65K, the number of compression stages is approximately three times greater than the number of expansion stages.

Figure 4 illustrates another embodiment which can, for example, be used for cooling or maintaining the temperature of superconducting cables at a cryogenic temperature of approximately 65K. For this temperature level, the number of compression stages (compressors) must be around three times greater than the number of expansion stages (turbines). This can be achieved according to several possible configurations. For example, three compressors and one turbine or six compressors and two turbines, etc.

Choosing the number of members will depend on the energy efficiency required. Thus, a solution using three compressors and one turbine will have a lower energy efficiency than a solution using six compressors and two turbines.

In the example of figure 4, the refrigerator comprises six compressors 101, 102, 103, 104, 105, 106 and two turbines 116, 111 and four high-speed motors 107, 112, 114, 109. The first two compressors 101, 102 (i.e. the impellers of the compressors) are mounted respectively at both ends of a first high-speed motor 107. The following two compressors 103, 104 are mounted respectively at both ends of a second high-speed motor 112. The following compressor 105 and the turbine 116 (i.e. the turbine impeller) are mounted respectively at both ends of a third high-speed motor 114. Finally, the last turbine 111 and the sixth compressor 106 are mounted respectively at both ends of a fourth motor 109.

The transit of the working gas during a cycle in the closed loop circuit can be described as follows.

During a first step, the gas is compressed progressively, passing successively through the four compressors in series 101, 102,103, 104, 105, 106.

At the end of each compression stage (at the outlet of each compressor), the working gas is cooled in a respective heat exchanger 108 (by heat exchange with air or water, for example) to approach isothermal compression. After this compression portion, the gas is cooled isobarically through a reverse-flow plate exchanger 103. After this cooling portion, the cooling gas is expanded progressively in the two centripetal turbines in series 116, 111.

After each expansion stage, the working gas is heated by heat exchange in an exchanger 110 (for example, by heat exchange with the cold source), so as to achieve substantially isothermal expansion. At the end of this isothermal expansion, the working gas is heated in the exchanger 113 and can then restart a new cycle by a compression.

Figure 5 shows the cycle (temperature T and entropy S) of the working fluid of the refrigerator in figure 5. As above, for figure 3, there can be seen in the compression zone A, six saw teeth corresponding to the six successive compressions and coolings. In the expansion zone C, there can be seen two saw teeth corresponding to the two successive expansions and heating.

The invention improves cryogenic refrigerators in terms of energy efficiency, reliability and compactness. The invention makes it possible to reduce maintenance operations and to eliminate the use of oils.

Of course, one end or both ends of the output shafts of the motor or motors can directly drive more than one impeller (i.e. a plurality of compressors or a plurality of turbines).

Claims

A cryogenic cooling device intended to transfer heat from a cold source (15) to a hot source (1) via a working fluid circulating in a closed working circuit (200), comprising a working circuit (200) in series: a total a substantially isothermal fluid compression section, a substantially isobaric fluid cooling section, a substantially isothermal fluid expansion section, and a substantially isobaric fluid heating section, wherein the compression section of the working circuit (200) comprises at least two compressors (7, 5, 3, 101, 101, 101 , 105, 106) arranged in series and at least one compressed fluid cooling exchanger (6, 4, 2, 108) located at the outlet of each compressor (7, 5, 3, 101, 102, 103, 104, 105, 106), wherein the expansion section of the working circuit (200) comprises at least one expansion turbine (9, 11, 13, 116, 111) and at least one expanded fluid heat exchanger (10, 12, 14, 110), characterized in that the compressors (7, 5, 3, 101 , 102, 103, 104, 105, 106) and expansion tour the turbine (s) (9, 11, 13) are driven by several engines (70, 107, 112, 114, 109) called high-speed motors, that is, rotating at a speed of 10,000 rpm, or tens of thousands of rpm. at least one of the motors comprises an output shaft of which one of the ends carries and drives in rotation by direct coupling a first compressor (7, 5, 3,101, 102, 103, 104, 105, 106) and of which it the other end carries and drives by rotation a direct turbine (9, 11, 13, 116, 111) in which the number of decompression levels, that is, the compressors, is substantially equal to or higher than the number of expansion levels, that is, the turbines. and knowing that the compressors (7, 5, 3, 101, 102, 103, 104, 105, 106) are of the centrifugal compression type and that the expansion turbine (s) (9, 11, 13, 116, 111) are of the centripetal expansion type and know that the output shafts (71) of the motors (70, 107, 112, 114, 109) are mounted on bearings (171) of the magnetic or gas-activated type, wherein said bearings (171) are used to support the compressors (7, 5, 3, 101, 102, 103, 104, 105, 106) and the turbines (9, 11, 13, 116, 111), and in that the cooling section and the heating section comprise a common heat exchanger (8, 113) in which the working fluid passes through a countercurrent depending on whether it is cooled or heated.

Device according to claim 1, characterized in that the working circuit comprises a volume which forms a buffer capacity for storing the working fluid.

Device according to claim 1 or 2, characterized in that the working fluid is in the gaseous phase and consists of a pure gas or a mixture of pure gases including: helium, neon, nitrogen, oxygen, argon, carbon monoxide, methane or any of the following: preferably other fluid having a gaseous phase at the temperature of the cold source.

Device according to any one of claims 1 to 3, characterized in that it comprises at least one motor (70, 107, 112, 114, 109) with at least one of the ends of the output shaft rotating by direct coupling at least two wheels ( compressor wheels and / or turbine wheels).

Device according to claim 4, characterized in that it comprises at least one motor with which one end of the output shaft thereof rotates by direct coupling two compressor wheels, the other end of the output shaft by direct coupling rotates a turbine wheel.

A cryogenic cooling method intended to transfer heat from a cold source (15) to a hot source (1) via a working fluid circulating in a closed working circuit (200), the working circuit (200) comprising in series: a compression section comprising at least two compressors (7, 5, 3, 101, 102, 103, 104, 105, 106) arranged in series, a fluid cooling section, an expansion section comprising at least one expansion turbine (9, 11, 13, 116, 111), and a heating section the method comprising a duty cycle comprising a first substantially isothermal fluid compression step in the compression section upon cooling of the compressed fluid leaving the compressors (7, 5, 3, 101, 102, 103, 104, 105, 106), a second substantially isobaric fluid compression stage in the cooling section, a third substantially isothermal fluid expansion stage in the expansion section by heating the expanded fluid leaving the turbine, and a fourth substantially isobaric fluid heating step thermally alternated with the cold source (15), wherein the fluid operating cycle (temperature T, entropy S) is of the inverse Ericsson type, where, during the first substantially isothermal compression step, the compressed fluid leaving each compressor (7, 5, 3, 101, 102, 103, 104, 105, 106) are cooled to keep the fluid temperatures entering and leaving each compressor substantially the same, and preferably in a range of about 10 K, where below the third in total substantially isothermal expansion steps, the expanded fluid leaving each turbine (9, 11, 13, 116, 111), heated to maintain the fluid temperatures entering and leaving each turbine (9, 11, 13, 116, 111) substantially and preferably in a region of about 5 K, characterized in that the compressors (7, 5, 3, 101, 102, 103, 104, 105, 106) and the expansion turbine (s) (9, 11, 13, 116), 111) is driven by several engines (70, 107, 112, 114, 109) called high-speed motors, that is, say, rotating at a speed of 10000 rpm or tens of thousands of rpm, and at least one of the motors comprises an output shaft of which one of the ends carries and drives by direct coupling a first compressor (7, 5 , 3, 101, 102, 103, 104, 105, 106) and of which the other end carries and drives in rotation by direct coupling an expansion turbine (9, 11, 13, 116, 111), the number of compression steps it will say compressors, are substantially equal to or higher than the number of expansion stages, that is, turbines, and the method comprises a step of transferring part of the mechanical work of the turbine (s) (9, 11, 13, 116). , 111) to the compressor (s) (7, 5, 3, 101, 102, 103, 104, 105, 106) via the output shaft (s) (71) and knowing that the output shafts (71) of the motors (70, 107, 112, 114, 109) are mounted on the bearings (171) of the magnet or gas activating type, wherein said le you (171) are used to support the compressors and turbines, and know that the cooling section and the heating section comprise a common heat exchanger (8, 113) in which the working fluid passes through a countercurrent depending on whether it is cooled or heated.

Process according to claim 6, characterized in that from the second cooling step the working fluid is brought to a low temperature of about 60 K and in that the working circuit (200) comprises a number of compressors (7, 5, 3, 101, 102, 103 , 104, 105, 106), which is three times the number of expansion turbines (9, 11, 13, 116, 111).

Method according to any one of claims 6 or 7, characterized in that the working fluid is used to cool or hold the cold superconducting elements at a temperature of about 65 K.

Process according to any one of claims 6 to 8, characterized in that the temperature drop of the fluid constituting the cold source (15) is substantially identical to the temperature rise of the working gas in the heat exchangers (110, 10, 12, 14). the work cycle (200).