JPH07117311B2 - Control method for cryogenic liquefaction refrigeration system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method for a cryogenic liquefaction refrigeration system, and more particularly to a cooled object having various load specifications such as refrigeration load, liquefaction load, refrigeration load + liquefaction load. The present invention relates to a control method suitable for a cryogenic liquefaction refrigeration system that cools a liquid.

[Conventional technology]

The cryogenic liquefaction refrigeration system, especially the helium liquefaction refrigeration system, has the theoretical power (minimum power) required to obtain the refrigeration capacity at cryogenic temperatures, which is about 70 times the refrigeration capacity. Further, in consideration of the efficiency of the equipment, the loss due to heat invasion from the outside, etc., 500 times to 1000 times the refrigerating capacity is practically required. Therefore, it is important not only to improve the efficiency of the device, but to operate the device smoothly and efficiently is also important.
This is an important issue.

In general, a cryogenic liquefaction refrigeration system expands a compressor that compresses gas, a heat exchanger that cools the compressed high-pressure gas below a reverse temperature, and a high-pressure gas that cools below the reverse temperature. From the Joule-Thomson valve that produces liquefied gas, the expander that produces the cold required to cool the high-pressure gas that flows through the Joule-Thomson valve, and the expander inlet valve that controls the amount of gas that flows into the expander. Composed.

The operation control of the cryogenic liquefaction refrigeration system including these components is performed by operating the Joule-Thomson valve and the expander inlet valve.

Further, JP-A-57-108557 discloses a method of controlling a cryogenic liquefaction refrigeration system. In this control method, the capacity of the compressor is controlled by the liquid level in the liquid reservoir or the temperature in the gas line, but the expander inlet valve and the Joule-Thomson valve are not operated.

[Problems to be solved by the invention]

The former of the above-mentioned prior art is performed by operating the Joule-Thomson valve and the expander inlet valve, but the appropriate opening degree of each valve greatly varies depending on the load condition of the cooled object, and is smaller than the maximum device capacity. For a constant load, automatic combinations were difficult because of infinite combinations of valve opening degrees, large time constants, slow response, and temporary reverse response. For this reason, in the conventional cryogenic refrigeration system, the operator operates by trial and error, or the operation is performed without any valve operation corresponding to the load condition.

Therefore, the conventional cryogenic liquefaction refrigerating apparatus has a complicated operation, and it is difficult to perform an appropriate operation corresponding to the load condition.

The latter is effective when the load condition exists only in one mode (for example, refrigeration load), but it is difficult to control efficiently when various load conditions exist.

An object of the present invention is to provide a cryogenic liquefaction refrigeration system capable of properly maintaining the valve opening degrees of the expander inlet valve and the Joule-Thomson valve in accordance with the load condition of the object to be cooled and operating the device smoothly and efficiently. It is to provide a control method.

[Means for solving problems]

The purpose is to control the valve opening of one of the expander inlet valve and the Joule-Thomson valve according to the load condition of the object to be cooled, and to introduce the valve opening of the other valve into the cryogenic liquefier. It is achieved by controlling the flow rate of the above to be constant.

[Action]

The valve opening of one of the expander inlet valve and the Joule-Thomson valve is controlled by the load condition of the object to be cooled, and the valve opening of the other valve is set to the flow rate of high-pressure gas to be introduced into the cryogenic liquefaction refrigeration system. Since the control is performed so as to be constant, the valve openings of the expander inlet valve and the Joule-Thomson valve are appropriately maintained in accordance with the load condition of the object to be cooled, and the device can be operated smoothly and efficiently.

〔Example〕

In the cryogenic liquefaction refrigeration system, by appropriately controlling the distribution of high-pressure gas compressed by the compressor with the Joule-Thomson valve and the expander inlet valve, it is possible to exhibit the proper device capacity corresponding to the load condition of the cooled object. it can. As the load condition of the cooled object, there are cases of only the polarization load, only the refrigeration load, and the case of the liquefaction load + the refrigeration load. Each of them is equipped with a Joule-Thomson valve for maximizing the capacity of the device. The proper opening of the expander inlet valve is different.
The above relationship will be described with reference to FIG.

FIG. 2 is an example of a characteristic diagram of a cryogenic liquefaction refrigeration system. In FIG. 2, A ₀ is the device capacity when the Joule-Thomson valve and the expander inlet valve are properly adjusted, and A ₁ is the Joule-Thomson valve opening that allows the maximum refrigerating capacity to be exhibited when there is no liquefaction load. Is a characteristic curve when the valve and the expander inlet valve are fixed, where A ₂ is the case where the Joule Thomson valve and the expander inlet valve are fixed to a valve opening that can generate the maximum liquefaction capacity when there is no refrigeration load Is a characteristic curve of. Characteristic curve A
₀ indicates the maximum capacity of the device when the maximum capacity of the compressor is used, and the opening degrees of the Joule-Thomson valve and the expander inlet valve correspond to each point and only one set exists. On the other hand, with respect to the capacity condition inside the characteristic curve A ₀ , there are an infinite number of combinations of opening degrees of the Joule-Thomson valve and the expander inlet valve.

Depending on the load condition (refrigeration load or liquefaction load) of the object to be cooled, the expander inlet valve and the joule may be operated in order to smoothly and efficiently operate the device corresponding to the characteristics of the cryogenic liquefaction refrigeration device described above. One valve opening degree of the Thomson valve may be controlled, and the other valve may be controlled to control the flow rate of the high pressure gas corresponding to the characteristic curve A _{0 of} FIG. Further, in order to operate the apparatus efficiently, it is possible to change the flow rate control set value of the high-pressure gas introduced into the cryogenic liquefaction refrigeration apparatus in accordance with the load condition. Further, when the adjustment is performed by using the heater, it is also a good method to change the high pressure gas flow rate control set value according to the heater input value.

An embodiment of the present invention will be described below with reference to FIG. First
In the figure, 1 is a compressor, 2 is a medium pressure tank, 3 is a high pressure gas pressure control valve, 4 is a low pressure gas pressure control valve, 10 is a cold box, 11a to 11e are heat exchangers, 12 is an expander inlet valve, 13 Is a Joule-Thomson valve (hereinafter abbreviated as JT valve), 14a and 14b are expanders, 15 is a gas-liquid separator, 16 is a liquefied gas transfer pipe, 17 is a low temperature gas return pipe, and 18 is a liquid that is an auxiliary cold source. Nitrogen supply pipe, 31 is JT valve 13 controller, 32 is refrigeration load signal, 33
Is a control signal for JT valve 13, 35 is a controller for expander inlet valve 12, 36
Is the high-pressure gas flow signal introduced into the cold box 10, 37
Is a control signal for the expander inlet valve 12.

Next, the operation of the cryogenic liquefaction refrigeration system configured as described above will be described. Most of the high-pressure gas compressed by the compressor 1 is introduced into the cold box 10, and is cooled by exchanging heat with the liquid nitrogen and the low temperature gas in the first heat exchanger 11a, and then liquefied and expanded. Branch to. The high-pressure gas branched to the expander line passes through the expander inlet valve 12
After the cold is generated by performing adiabatic expansion work in the expander 14a, the third heat exchanger 11c exchanges heat with the low-pressure gas to further reduce the temperature, and the second expander 14b performs adiabatic expansion work again to perform the cold. Is generated and joins the low pressure gas line. on the other hand,
After being cooled in the first heat exchanger 11a, the high-pressure gas branched to the liquefaction line exchanges heat with the low-pressure gas in the second to fifth heat exchangers 11b to 11e, and finally cooled to the reversal temperature or lower. JT
After being expanded by the valve 13 to partially generate liquefied gas and gas-liquid separated by the gas-liquid separator 15, the liquefied gas is supplied to the cooled objects 20a to 20n by the liquefied gas transfer pipe 16 and absorbs the heat load. Gasified to return to the cold box 10 through the low-temperature gas return pipe 17, merge with the low-temperature gas separated by the gas-liquid separator 15, and heat exchangers 11e-1
After cold recovery by heat exchange in 1a, it returns to the suction side of the compressor 1. On the other hand, part of the low-temperature gas gasified in the cooled objects 20a-20n cools the cooled objects 20a-20n by sensible heat, and returns to the suction side of the compressor 1 through the room temperature gas return pipe 21.

In the cryogenic liquefaction refrigeration apparatus as described above, the low temperature gas returning to the low temperature gas return pipe 17 corresponds to the refrigerating load of the cooled objects 20a to 20n, and the normal temperature gas returning to the normal temperature gas return tube 21 is the cooled object 20.
Supports liquefaction load of a to 20n.

Next, a control method of the cryogenic liquefaction refrigerating apparatus having the above-described configuration and operation will be described. As a method of detecting the refrigeration load of the cooled objects 20a to 20n, for example, it is possible by multiplying the low-temperature gas flow rate returned from the cooled objects 20a to 20n by the latent heat of liquefied gas, and taken into the controller 31 as a refrigeration load signal 32. , The JT valve 13 is adjusted by the control signal 33 to the valve opening degree corresponding to the refrigeration load. On the other hand, the flow rate of high-pressure gas introduced into the cold box 10 is taken into the controller 35 as a signal 36, and the control signal is sent.
It is kept constant by controlling the expander inlet valve 12 at 37. The above control method will be described with reference to FIG. 2. For example, when a refrigeration load corresponding to a is received, the opening of the JT valve 13 is set and the high pressure is set so that the liquefaction capacity corresponding to b can be exerted. The gas flow rate control is performed by the expander inlet valve 12.

Further, when it is not necessary to exert the maximum liquefaction capacity for a certain refrigeration load due to the relationship between the load conditions of the objects to be cooled 20a-20n and the capacity of the cryogenic liquefaction refrigeration system, in FIG. Instead, changing the high-pressure gas flow rate control set value to the condition of b'is desirable in order to reduce power consumption and perform efficient operation. Furthermore, when the load is adjusted by the heater, changing the high pressure gas flow rate control set value according to the heater input value is a simple and highly reliable method for performing efficient operation control of the device. .

In the above description, the case of controlling by the refrigeration load has been described, but it is clear that direct control can also be performed by the low temperature return gas flow rate. It is also possible to control by the liquefaction load. Furthermore, in the above description, the case where the JT valve is controlled by the load and the high pressure gas flow rate is controlled by the expander inlet valve has been described, but the expander inlet valve is controlled by the load and the high pressure gas flow rate is controlled by the JT valve. It is obvious that control may be performed with.

As described above in detail, according to the present embodiment, the cryogenic liquefaction refrigeration system can be easily maintained in an appropriate operating state in response to various load conditions, and satisfactory and efficient operation control can be performed. Furthermore, by controlling the flow rate of the high-pressure gas, the pressure rise of the low-pressure line due to the excessive flow of the high-pressure gas can be prevented, the refrigeration temperature can be stably maintained, and the flow rate of the low-temperature return gas from the cooled object increased in a pulsed manner. Occasionally, it is possible to prevent overcooling of the expander, which has the effect of improving the reliability and stability of equipment operation.

〔The invention's effect〕

The present invention, as explained above, controls the valve opening of one of the expander inlet valve and the JT valve under the load condition of the cooled object, and the valve opening of the other valve to the cryogenic liquefaction refrigeration system. By controlling the flow rate of the high-pressure gas to be introduced at a constant level, the opening degrees of the expander inlet valve and JT valve can be properly maintained according to the load conditions of the cooled object, and the device can operate smoothly and efficiently. There is an effect that you can drive to.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a cryogenic liquefier refrigerating apparatus embodying the present invention, and FIG. 2 is a characteristic diagram showing an example of characteristics of the cryogenic refrigerating apparatus. 1 ... Compressor, 12 ... Expander inlet valve, 13 ... JT valve, 31,3
5 ... Controller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Kajiwara 794, Higashitoyoi, Kudamatsu City, Yamaguchi Prefecture Inside the Kasado Plant, Hitachi Ltd. (56) Reference JP-A-55-49664 (JP, A) Sho-60-50354 (JP, A)

Claims (1)

[Claims] 1. A cryogenic liquefaction refrigeration system comprising a compressor, an expander, a heat exchanger, an expander inlet valve for adjusting the flow rate of high-pressure gas introduced into the expander, and a Joule-Thomson valve. The flow rate of high-pressure gas introduced into the cryogenic liquefaction refrigeration system is controlled by controlling the load condition of the object to be cooled, which is the valve opening of one of the expander inlet valve and the Joule-Thomson valve. A method for controlling a cryogenic liquefaction refrigerating apparatus, which is characterized by controlling the temperature to be constant.