JPH0250382B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for precooling a cryogenic liquefaction refrigeration system, and in particular to a method for precooling a cryogenic liquefaction refrigeration system that is a good enemy to a helium liquefaction refrigeration system that has a high cool-down frequency. It is about the method.

[Prior art]

A conventional method for pre-cooling working gas will be explained with reference to FIG. 1, taking a helium liquefaction refrigeration system as an example.

In FIG. 1, heat exchangers 11a to 11e and expansion turbines 12a and 12b are installed inside a cold box 10 that is maintained in a vacuum, and a compressor 13 and a dewar 14 are installed outside the cold box 10. has been done.

The outlet of the compressor 13 and the inlet of the JT valve 20a are
In the JT circuit 30, the outlet of the JT valve 20a and the compressor 13
The inlet is connected to the inlet by a low temperature return circuit 31. The heat exchangers 11a to 11e include a JT circuit 30 and a low temperature return circuit 31, and are connected from the compressor 13 side.
They are arranged sequentially toward the JT valve 20a side.

A turbine circuit 32 branches off from the JT circuit 30 between the heat exchangers 11a and 11b.
passes through the heat exchanger 11c, and then passes through the heat exchanger 11c.
It is merged and connected to the low temperature return circuit 31 between d and 11e. The turbine circuit 32 includes a heat exchanger 11c.
On the upstream side of the turbine inlet valve 21, the expansion turbine 1
2a is provided, and an expansion turbine 12b is provided on the downstream side.

A rapid cool circuit 33 branches off from the JT circuit 30 in the heat exchanger 11a, and the rapid cool circuit 33 is connected to a low temperature return circuit 31 between the JT valve 20a and the heat exchanger 11e. The rapid cool circuit 33 is provided with a precooling valve 22 .

A bypass circuit 34 branches from the low temperature return circuit 31 between the JT valve 20a and the heat exchanger 11e on the downstream side of the confluence point of the rapid cool circuit 33, and the bypass circuit 34 is a low temperature return circuit 31 between the JT valve 20a and the heat exchanger 11e. It is connected to the circuit 31. Bypass circuit 3
4 is provided with a bypass valve 23.

A liquefied gas circuit 35 branches from the JT circuit 30 between the JT valve 20a and the heat exchanger 11e on the upstream side of the JT valve 20a, and the liquefied gas circuit 35 is connected to the dewar 14 via a transfer tube 36. has been done. The liquefied gas circuit 35 is provided with a JT valve 20b.

A vaporized gas circuit 37 is connected to the top of the dewar 14, and the vaporized gas circuit 37 is connected to the low temperature return circuit 31 between the JT valve 20a and the heat exchanger 11e.
They are connected on the downstream side of the valve 20a. The vaporized gas circuit 37 is provided with a vaporized gas valve 24 .

Further, a pre-cooling circuit 38 runs through the heat exchanger 11a.

In this case, the working gas is precooled to its liquefaction temperature by the following operation.

(1) Precooling from room temperature to 100℃ (primary precooling) Precooling is mainly performed using a refrigerant flowing through the precooling circuit 38, such as liquid nitrogen (hereinafter abbreviated as LN ₂ ). In this case, the JT valve 20a, the turbine inlet valve 21, and the precooling valve 22 are opened, and the JT
Valve 20b, bypass valve 23, and vaporized gas valve 24 are closed. Note that the turbine inlet valve 21 may be closed.

A working gas at room temperature that has been pressurized to a predetermined pressure by the compressor 13, in this case helium gas (hereinafter referred to as
(abbreviated as GH _e ) flows through the JT circuit 30 and reaches the heat exchanger 11a, where a portion is diverted to the rapid cool circuit 33. diverted
GH _e is cooled to the LN ₂ temperature by LN ₂ flowing through the precooling circuit 38 while flowing through the rapid cool circuit 33 in the heat exchanger 11a. The thus cooled GH _e is introduced into the low temperature return circuit 31 via the rapid cool circuit 33 by opening the precooling valve 22, and is returned to the compressor 13 after flowing through the low temperature return circuit 31. On the other hand, the remaining
While the GH _e passes through the heat exchangers 11a to 11e and flows through the JT circuit 30, it sequentially exchanges heat with the GH _e that has been cooled to the LN ₂ temperature and flows through the low temperature return circuit 31, and is sequentially cooled. By repeating these operations, the pressure was increased by the compressor 13.
GH _e is cooled to 100ⓓ to complete the primary precooling.

(2) Precooling from 100〓 to the working gas liquefaction temperature (secondary precooling) Expansion turbines 12a, 12b and JT valve 2
Pre-cool by freezing at 0a. After the primary precooling is completed, the bypass valve 23 is opened, and the precooling valve 22 is closed. As a result, JT circuit 30
Some of the primary precooled GH _e that is distributed in
The current is shunted to a turbine circuit 32 . The GH _e shunted to the turbine circuit 32 is connected to the expansion turbine 12
It is cooled by adiabatic expansion in a, and the heat exchanger 1
After further cooling in 1c, the expansion turbine 12
It is further cooled by adiabatic expansion again at b.
The GH _e cooled in this way is sent to the turbine circuit 3.
2 is introduced into the low temperature return circuit 31, and after passing through the low temperature return circuit 31, it is introduced into the compressor 1.
Returned to 3. On the other hand, while the remaining GH _e passes through the heat exchangers 11b to 11d and flows through the JT circuit 30, it sequentially exchanges heat with the cooled GH _e flowing through the low temperature return circuit 31 and is sequentially cooled. In addition, after passing through the heat exchanger 11e, the JT circuit 30
is passed through the JT valve 20a to the low temperature return circuit 31.
A part of the GH _e introduced into the turbine circuit 34 is diverted to the bypass circuit 34, and then passed through the heat exchanger 11e and combined with the GH _e that has passed through the turbine circuit 32. During this time, in the heat exchanger 11e, the GH _e flowing through the low temperature return circuit 31 is further cooled by the GH _e flowing through the JT circuit 30 due to the difference in flow rate.

After that, the temperature of GH _e at the JT valve 0a inlet is
When the temperature reaches 50 to 60〓, the bypass valve 23 starts to be gradually closed, so that the GH _e that is cooled while flowing through the turbine circuit 32 and then merged with the GH _e flowing through the warm return circuit 31 is as follows. eventually
It is cooled at 11〓. Also, when the temperature of GH _e at the inlet of JT valve 20a reaches 15〓, JT valve 20a
The Jurth-Thomson effect begins to occur at 0, and JT
When the temperature at the inlet of the valve 20a reaches 6 to 7〓, the temperature of GH _e at the outlet of the JT valve 20a becomes the liquefaction temperature 4〓. In this way, when the temperature at the inlet of the JT valve 20a reaches 6~7〓, the bypass valve 20a
3 is fully closed, thereby completing the secondary precooling operation.

Note that after the secondary precooling operation is completed, the JT valve 20b and the vaporized gas valve 24 are opened, and
The JT valve 20a is closed, and the helium liquefaction refrigeration system shifts to steady operation. In other words, JT valve 2
A part of the GH _e is liquefied at 0b, and the liquefied helium (hereinafter abbreviated as LH _e ) and GH _e are supplied to the dewar 14 after flowing in a gas-liquid mixed phase through the liquefied gas circuit 35 and the transfer tube 36. LH _e is stored in dewar 14. Also, GH _e is
After flowing from the dewar 14 through the vaporized gas circuit 37 and the low temperature return circuit 31, it is returned to the compressor 13.

This method of precooling working gas has the following drawbacks.

(1) If the timing of gradual closing of the bypass valve 23 is delayed, the amount of chilled coolant discarded through the bypass circuit will increase, resulting in a longer secondary precooling time; The amount of GH _e flowing through the return circuit increases, and the high temperature on the return side of the heat exchanger 11e prevents the temperature on the JT circuit side from decreasing.
In order to prevent pre-cooling or to compensate for heat loss in the bypass circuit, the expansion turbine used to generate a large amount of cold, but now the flow rate in the bypass circuit has decreased and the heat loss has decreased, so the expansion turbine has changed. The amount of refrigeration generated at the outlet becomes so high that the temperature at the outlet of the expansion turbine decreases and liquefies, damaging the expansion turbine. Therefore, the gradual closing timing of the bypass valve is extremely difficult, and the secondary precooling operation becomes complicated.

(2) Even if the gradual opening timing of the bypass valve is good, the secondary precooling speed is limited by the amount of cooling in the expansion turbine, so the secondary precooling time cannot be further shortened.

[Object of the Invention] An object of the present invention is to provide a precooling method for a cryogenic liquefaction refrigeration apparatus that can simplify the precooling operation and shorten the precooling operation time.

[Summary of the invention]

In the present invention, pre-cooling is performed by a heat exchanger on the high temperature side,
In the precooling of a cryogenic liquefaction refrigeration system in which the cooled working gas is sequentially circulated through a group of heat exchangers to generate a cryogenic refrigerant and the cryogenic refrigerant is stored, the high-temperature side of the group of heat exchangers is used. The working gas is mainly cooled by cooling the refrigerant used for pre-cooling, and the working gas is circulated by bypassing the cryogenic container side to pre-cool the circuit. After the primary pre-cooling is completed, a portion of the working gas is adiabatically expanded. In addition to the process of further cooling the working gas and pre-cooling the inside of the circuit, part of the circulating working gas is passed to the cryogenic container side, and the gasified cryogenic refrigerant from inside the cryogenic container is bypassed and added to the circulating working gas. By adding a process to pre-cool the inside of the circuit by merging them together and performing secondary pre-cooling, pre-cooling operation can be easily performed.
Furthermore, the precooling operation time can be shortened.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIG. Note that in FIG. 2, the same equipment as in FIG. 1 is indicated by the same reference numerals, and the explanation thereof will be omitted.

In FIG. 2, in this case, the dewar 14 is installed inside the cold box 10, and the dewar 14 is connected to a liquefied gas circuit 35. Further, the vaporized gas circuit 37 is connected to a low temperature return circuit 31 between the JT valve 20a and the heat exchanger 11e.

In this case, the primary precooling operation of the working gas, for example, GH _e, is performed by opening the JT valve 20b and the precooling valve 22, opening the turbine inlet valve 21, and opening the JT valve 22, as in the conventional case.
0a, the bypass valve 23 and the vaporized gas valve 24 are closed, and precooling is performed mainly using liquid nitrogen. Note that in this case, the turbine inlet valve 21 may be open.

In addition, in the secondary precooling operation, after the primary precooling is completed, that is, after the temperature has cooled to the liquid nitrogen temperature level in this case, the bypass valve 23 is first opened as in the conventional case, and the precooling valve is opened. 22 is closed. As a result, a portion of the primary precooled GH _e flowing through the JT circuit 30 is diverted to the turbine circuit 32. shunted to the turbine circuit 32
GH _e is cooled to below the primary precooling temperature by adiabatically expanding in the expansion turbine 12a, and is then cooled to below the primary precooling temperature.
After being further cooled in step c, it is adiabatically expanded again in the expansion turbine 12b, thereby being further cooled. The thus cooled GH _e is introduced into the low temperature return circuit 31 after passing through the turbine circuit 32, and is returned to the compressor 13 after passing through the low temperature return circuit 31. On the other hand, the remaining GH _e is from the heat exchangers 11b to 1
1d and flowing through the JT circuit 30, it sequentially exchanges heat with the cooled GH _e flowing through the low temperature return circuit 31 and is sequentially cooled. In addition, the heat exchanger 11e
After passing through the JT circuit 30, the GH _e was introduced into the low temperature return circuit 31 via the JT valve 20a, a part of which was diverted to the bypass circuit 34, and then passed through the heat exchanger 11e and distributed into the turbine circuit 32.
It will be merged with GH _e . During this time, in the heat exchanger 11e,
The GH _e flowing through the low temperature return circuit 31 is further cooled by the GH _e flowing through the JT circuit 30 due to the difference in flow rate.

After that, as the next operation of secondary precooling, JT valve 2
When the temperature of GH _e at the inlet of 0a reaches 50 to 60, the JT valve 20b and the vaporized gas valve 24 are opened. In this case, the valve opening degree of JT valve 20b is
The amount of GH _e that has enough refrigeration to further cool down the GH _e at the inlet of 0a to 6-7〓 is adjusted to such an extent that it evaporates from the LH _e stored in the dewar 14. Some of them are distributed through JT circuit 30,
During secondary precooling, which is diverted to the liquefied gas circuit 35,
A part of the LH _e stored in the dewar 14 is evaporated and vaporized by the GH _e . The temperature of this GH _e is
Near the liquefaction temperature, in this case the liquefaction temperature is 4〓,
After flowing through the vaporized gas circuit 37, this GH _e is merged with the GH _e flowing through the low temperature return circuit 31 on the side of the heat exchanger 11e. As a result, the GH _e that is cooled while flowing through the turbine circuit 32 and then merged with the GH _e flowing through the warm return circuit 31 is as follows:
It was finally cooled down to 11〓, and JT valve 20
The temperature of GH _e at the inlet of a is 6 to 7〓. At these times, the JT valve 20a and the bypass valve 23 are closed, thereby completing the secondary precooling operation, and then the helium liquefaction refrigeration system shifts to steady operation. In other words, part of the GH _e is liquefied at the JT valve 20b,
LH _e and GH _e are supplied to the dewar 14 after flowing through the liquefied gas circuit 35 in a gas phase mixed phase, and the LH _e is stored in the dewar 14 . In addition, the GH _e is connected from the dewar 14 to the vaporized gas circuit 37 and the low temperature return circuit 31.
After being distributed, it is returned to the compressor 13.

The working gas precooling method as in this embodiment provides the following effects.

(1) During the secondary precooling operation, the GH _e of the low temperature return circuit is cooled by the extremely low temperature vaporized gas from the dewar, so the GH _e of the low temperature return circuit is cooled as before.
Depending on the temperature, there is no need to gradually close the bypass valve, and the precooling movement can be performed easily.

(2) In addition to the cooling generated by the expansion turbine, secondary precooling can be performed by cooling the extremely low temperature vaporized gas from the dewar, so the secondary precooling speed can be improved, and therefore the secondary precooling time can be increased. can be further shortened.

Note that, in addition to the method described in this embodiment, the secondary precooling may be performed in the following manner.

(1) After removing the bypass circuit and bypass valve and completing the primary precooling, a portion of the LH _e stored in the dewar is immediately evaporated and vaporized, and the cold contained in this GH _e is used for the secondary precooling. in this case,
The structure of the refrigeration system is simplified, and the operation of opening and closing the bypass valve is no longer necessary, so the secondary precooling operation can be further simplified.

Further, the operating temperature of each valve is not limited to only the temperature described in this embodiment, but can be set as appropriate.

〔Effect of the invention〕

According to the present invention, there is an effect that the precooling operation can be performed easily and the precooling operation time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a conventional helium liquefaction refrigeration system, and FIG. 2 is a system diagram showing an example of a helium liquefaction refrigeration system according to the present invention. 10...Cold box, 11a-11e...
...heat exchanger, 12a, 12b...expansion turbine,
13... Compressor, 14... Dewar, 20a, 2
0b...JT valve, 21...Turbine inlet valve, 22
... Precooling valve, 23 ... Bypass valve, 24 ... Vaporized gas valve, 30 ... JT circuit, 31 ... Low temperature return circuit, 32 ... Turbine circuit, 33 ... Rapid cool circuit, 34 ... Bypass circuit, 35 . . . Liquefied gas circuit, 37 . . . Vaporized gas circuit, 38 . . . Precooling circuit.

Claims (1)

[Scope of Claims] 1 Pressurizing the working gas with a compressor and circulating the working gas sequentially through a group of heat exchangers, and pre-cooling the high temperature side of the group of heat exchangers with a refrigerant to remove the heat. A part of the working gas is branched from the middle of the exchanger group, adiabatically expanded, and merged with the return of the circulating working gas to cool the working gas, and the working gas is cooled on the low-temperature side of the heat exchanger group. In a pre-cooling method for a cryogenic liquefaction refrigeration apparatus, the cryogenic refrigerant is generated, the cryogenic refrigerant is stored in a cryogenic container, and the cryogenic refrigerant gasified in the cryogenic container is used as the return working gas for the circulation, After the primary precooling is completed, the working gas is mainly cooled by cooling a refrigerant for precooling the high temperature side of the heat exchanger group, and the cryogenic container side is bypassed to circulate the working gas and precool the inside of the circuit. , In addition to the step of adiabatically expanding a portion of the working gas to further cool the working gas and precooling the inside of the circuit, a portion of the circulating working gas is flowed to the cryogenic container side, and the circulating working gas is bypassed. A method for precooling a cryogenic liquefaction refrigeration apparatus, characterized in that secondary precooling is performed by adding a step of precooling the inside of the circuit by combining the working gas with the gasified cryogenic refrigerant from the cryogenic container.