JPH06147667A - Method and apparatus for controlling operation of liquified freezer device - Google Patents

Abstract

PURPOSE:To enable the control of the degree of opening of an expansion valve accompanying liquifying operation of refrigerant and the control of pressure at the outlet of a supercritical expansion turbine along with its operation to be carried out concurrently and in a well-adapted manner. CONSTITUTION:The degree of opening of an expansion valve 6 is controlled in response to a storing condition of refrigerant liquid in a refrigerant liquid storing tank 1 and concurrently the degree of opening of an outlet valve 15 arranged on the upstream side of the expansion valve 6 is adjusted, thereby the pressure at an outlet port of a super critical expansion turbine 12 is controlled. In the case where both controls are carried out, the control of the degree of opening of a pre-cooling valve 24 arranged in a pre-cooling bypass line 23 bypassing a refrigerant liquid storing tank 1 and the expansion valve 6 and the control of the degree of opening of a bypass valve 26 arraanged in a turbine bypass line 25 bypassing the outlet port valve 15 are carried out and thereby the pressure at the inlet port of the expansion carried out and thereby the pressure at the inlet port of the expansion valve 6 is always kept at a lower pressure than the pressure at the outlet port of the supercritical expansion turbine 12 irrespective of the degree of opening of the expansion valve 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation control method and apparatus for a liquefaction refrigeration system in which a supercritical turbine expander is provided upstream of an expansion valve for liquefying a refrigerant.

[0002]

2. Description of the Related Art In recent years, in a cryogenic liquefaction refrigeration system such as a helium liquefaction refrigeration system, especially in a large liquefaction refrigeration system, its refrigerating capacity is increased and the liquefaction rate of an expansion valve (JT valve) is improved. Therefore, a supercritical turbine expander (hereinafter referred to as a supercritical expansion turbine) is often provided upstream of the expansion valve. In such a device, when helium is liquefied in the supercritical expansion turbine, a so-called drain attack phenomenon occurs in the turbine blade due to the droplets, which causes a great damage to the expansion turbine. It is necessary to provide the means of.

Therefore, in JP-A-60-164182, the expansion valve provided on the downstream side of the supercritical expansion turbine is also used as a pressure regulating valve, and the opening of the supercritical expansion turbine is adjusted by adjusting the opening thereof. A method of keeping the pressure always above the critical pressure of helium is shown.

[0004]

In the above method, originally,
The outlet pressure of the supercritical turbine type expander is controlled by using an expansion valve for controlling the degree of liquefaction of the refrigerant, and this expansion valve opening affects both the operation of the supercritical expansion turbine and the liquefaction operation. Since it is given, the following problems will occur.

A) When a dynamic pressure gas bearing is used in the supercritical expansion turbine, this bearing cannot fully exhibit its ability in the low rotation speed region, so when starting this supercritical expansion turbine. Needs to open the expansion valve located on the outlet side quite rapidly to raise the turbine speed to an appropriate speed as quickly as possible.

However, at the time when the expansion valve starts to open, the temperature of the refrigerant gas leaving the expansion valve is still high because the piping around the expansion valve and the expansion valve itself are not completely cooled. When the expansion valve is rapidly opened as described above, a large amount of high-temperature refrigerant gas will flow into the refrigerant liquid storage tank. Due to such an operation, the refrigerant liquid in the refrigerant liquid storage tank may vaporize rapidly and in large quantities, and the pressure in the refrigerant liquid storage tank may rise rapidly. In the worst case, the low pressure line connected to the compressor The pressure in the (refrigerant return line) is also adversely affected, and smooth operation of the liquefaction refrigeration system cannot be expected. Such a problem becomes particularly serious when a large-capacity refrigerant liquid storage tank is used.

B) During the precooling operation, when the refrigerant liquid in the refrigerant liquid storage tank has increased to a predetermined amount, there is a case where the expansion valve is closed to interrupt the liquefaction and, for example, only the precooling of the refrigeration load is continued. Even when the liquefaction is interrupted, it is necessary to continue the operation of the supercritical expansion turbine for the following reasons.

Reason: Precooling of the refrigeration load requires coldness generated in the supercritical expansion turbine.

Reason: When the supercritical expansion turbine is stopped, the temperature distribution inside the turbine becomes abnormal, and there is a risk that the clearance of the bearing and the like will deviate from an appropriate value and restart will be impossible.

However, in the above method, the operation of the supercritical expansion turbine becomes impossible when the expansion valve is closed, so that it is impossible to continue the operation of the supercritical expansion turbine while interrupting only the liquefaction operation.

As in the cases A) and B) described above, in the above conventional method, it is possible to simultaneously satisfy both the control conditions required for the liquefaction operation and the conditions required for the operation of the supercritical expansion turbine. There are cases where you cannot.

In view of such circumstances, the present invention can perform both the control of the outlet pressure of the supercritical expansion turbine and the liquefaction operation control by operating the expansion valve simultaneously and satisfactorily, especially during precooling. An object of the present invention is to provide an operation control method and device for a liquefaction refrigeration system.

[0013]

The present invention is directed to a compressor for pumping a refrigerant, a liquid storage section for storing a liquefied refrigerant, and a high pressure for supplying the refrigerant pumped from the compressor to the liquid storage section. A liquefaction in which a line and a low-pressure line that returns the refrigerant from the liquid storage unit to the compressor are provided, an expansion valve whose opening can be adjusted is provided in the high-pressure line, and a supercritical turbine expander is provided on the upstream side of the expansion valve. In the refrigeration system, the storage state of the refrigerant liquid in the liquid storage section is detected, and the opening degree of the expansion valve is controlled based on the storage state, while the expansion is performed on the outlet side of the supercritical turbine expander. An outlet valve is provided at a position upstream of the valve, the turbine outlet pressure that is the outlet side of the supercritical turbine expander and is the upstream side of the outlet valve is detected, and at least this turbine outlet pressure is a factor. Captured as While controlling the turbine outlet pressure by adjusting the opening of the outlet valve, the expansion valve inlet pressure, which is the pressure on the inlet side of the expansion valve and on the downstream side of the outlet valve, is detected. At a flow rate such that is within a predetermined pressure range lower than the turbine outlet pressure,
In the high-pressure line, the supercritical turbine expander and the outlet valve are bypassed to flow the refrigerant, and in the high-pressure line, the expansion valve and the liquid reservoir are bypassed from a portion between the outlet valve and the expansion valve to reduce the low pressure. The refrigerant flows through the line (Claim 1). As a device therefor, an outlet valve is provided at a position on the outlet side of the supercritical turbine expander and upstream of the expansion valve, and a high pressure line is provided. A turbine bypass line that bypasses the supercritical turbine expander and the outlet valve, turbine bypass flow rate adjusting means that changes the refrigerant flow rate in the turbine bypass line, and a high pressure line that bypasses the expansion valve and the refrigerant liquid storage tank. A precooling bypass line connecting the low pressure line and the refrigerant flow rate in this precooling bypass line are changed. Cold bypass flow rate adjusting means, outlet pressure detecting means for detecting the turbine outlet pressure which is the outlet side of the supercritical turbine expander and is the upstream side pressure of the outlet valve, and at least this turbine outlet pressure as a factor Supercritical expansion turbine control means that takes in and controls the turbine outlet pressure by adjusting the opening of the outlet valve, storage state detection means that detects the storage state of the refrigerant liquid in the liquid storage section, and the detected storage state Expansion valve control means for controlling the opening degree of the expansion valve based on the above, and inlet pressure detection for detecting the expansion valve inlet pressure which is the pressure on the inlet side of the expansion valve in the high pressure line and on the downstream side of the outlet valve. Means and the expansion valve inlet pressure detected by the inlet pressure detecting means after the expansion valve is opened during precooling Those having a bypass flow control means for operating the turbine bypass flow rate adjusting means and the pre-cooling the bypass flow rate control means so as to be within a lower predetermined pressure range than the mouth pressure (claim 3).

Further, according to the present invention, when controlling the outlet pressure of the supercritical turbine type expander, a value relating to the rotation speed of the supercritical turbine type expander is detected, and the detected turbine outlet pressure is higher than the critical pressure of the refrigerant. The value related to the rotation speed of the turbine type expander was preset while the inlet pressure of the turbine type expander was at a pressure substantially equal to the discharge pressure of the compressor until it dropped to a high predetermined set pressure. The opening of the outlet valve is adjusted so that it falls within the range, and after the detected turbine outlet pressure reaches the set pressure, the inlet pressure of the turbine expander is approximately equal to the discharge pressure of the compressor. In this state, the opening of the outlet valve is adjusted so that the detected pressure falls within a preset pressure range near the set pressure (Claim 2). The supercritical expansion turbine control means is provided with rotation detection means for detecting a value related to the rotation speed of the critical turbine expander, and the turbine outlet pressure detected by the outlet pressure detection means is higher than the critical pressure of the refrigerant. Until the inlet pressure of the turbine type expander is substantially equal to the discharge pressure of the compressor until the pressure falls to a predetermined set pressure, the value related to the rotational speed of the turbine type expander is set in a preset range. After adjusting the opening of the outlet valve so that the pressure falls within the range and the turbine outlet pressure to be detected reaches the set pressure, the inlet pressure of the turbine expander is approximately equal to the discharge pressure of the compressor. Then, the opening degree of the outlet valve is adjusted so that the detected pressure falls within a preset pressure range near the set pressure (claim 4).

[0015]

According to the method and apparatus of claims 1 and 3, the expansion valve opening control is performed based on the storage state in the liquid storage portion, and independently of this, the outlet valve opening adjustment is performed. The turbine outlet pressure of the critical expansion turbine is controlled. Here, when the inlet pressure of the expansion valve approaches the turbine outlet pressure, the turbine outlet pressure cannot be lowered even when the outlet valve is fully opened, and the operation control of the supercritical expansion turbine becomes impossible. In the method and the apparatus, the expansion valve inlet pressure is constantly adjusted to the turbine outlet by adjusting the refrigerant flow rate that bypasses the supercritical turbine expander and the outlet valve, and the refrigerant flow rate that bypasses the expansion valve and the liquid reservoir. Since the control is performed so that the pressure falls within a predetermined pressure range lower than the pressure, good control of the turbine outlet pressure by opening and closing the outlet valve can be ensured regardless of the opening of the expansion valve.

Further, regarding the operation control of the supercritical expansion turbine, according to the method and the apparatus of claims 2 and 4, until the turbine outlet pressure reaches a predetermined set pressure, a value relating to the turbine rotation speed is set. Based on this, the outlet pressure control (in other words, the expansion ratio control of the turbine) is performed by adjusting the opening degree of the expansion valve, whereby turbine over-rotation during precooling is prevented. On the other hand, after the detected turbine outlet pressure reaches the set pressure, the outlet pressure control is performed so that the detected pressure falls within the pressure range near the set pressure, so that the refrigerant is liquefied in the turbine. It is prevented and the turbine outlet pressure is automatically adjusted to the rated pressure during normal operation. At this time, since the turbine inlet temperature has already dropped sufficiently, there is no possibility that turbine over-rotation will occur even if the turbine rotation speed is not particularly taken into consideration.

In such control, the turbine inlet pressure is always maintained at a pressure substantially equal to the compressor discharge pressure, and the turbine expansion ratio is adjusted only by changing the turbine outlet pressure, so the turbine operating pressure is liquefied. The maximum pressure is set within the operable range of the refrigeration system, and as a result, the amount of cold generation of the turbine increases, as will be described later.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.

In the figure, 1 is a refrigerant liquid storage tank (liquid storage part) for storing a liquefied refrigerant (here, helium), 2 is a cold insulation box, and a compressor 10 is provided outside the cold insulation box 2. The discharge side of the compressor 10 is connected to the refrigerant liquid storage tank 1 via the high pressure line 3, and the refrigerant liquid storage tank 1 is connected to the suction side of the compressor 10 via the low pressure line 4.

Inside the cool box 2, heat exchangers 5a, 5b, 5c, 5d and 5e are installed in order from the high temperature side as heat exchangers through which both the high pressure line 3 and the low pressure line 4 pass. A portion of the high pressure line 3 located between the heat exchangers 5b and 5c, and a heat exchanger 5 in the low pressure line 4
The portion located between c and 5d is connected via a turbine line 7, and an expansion turbine 8 for generating cold is provided in the middle of the turbine line 7.

In the high-pressure line 3, an expansion valve (JT valve) 6 is provided at a position on the outlet side of the heat exchanger 5e on the lowest temperature side, and a position upstream thereof, specifically, the heat exchanger 5 is provided.
The supercritical expansion turbine 12 is provided at a position between d and 5e. An inlet valve 14 that is switched between an open state and a closed state is provided on the inlet side of the supercritical expansion turbine 12, and an outlet whose outlet opening is adjustable upstream of the heat exchanger 5e. A valve 15 is provided. Further, a tachometer (rotation detecting means) 16 for detecting the number of revolutions per unit time (hereinafter, simply referred to as turbine revolution number) N of the supercritical expansion turbine 12 and an outlet pressure P of the supercritical expansion turbine 12 are detected. Outlet pressure gauges (outlet pressure detection means) 18 are provided at appropriate places, and detection signals of both are input to a turbine control device (supercritical expansion turbine control means) 20. The turbine control device 20 opens the inlet valve 14 and rotates at the rotation speed N from the time when the temperature in the vicinity of the supercritical expansion turbine 12 decreases to some extent during precooling of the liquefaction refrigeration system.
And the opening degree of the outlet valve 15 is controlled based on the outlet pressure P. The control contents are as follows.

I) Rotational speed control mode: The detected rotational speed N is reached until the detection outlet pressure P reaches a preset upper limit pressure P ₂ , more specifically, a pressure P ₂ slightly higher than the critical pressure of helium. Is a predetermined rotation speed range N ₁ ~
N _2, and more specifically to fit the maximum rotational speed (allowable maximum rotational speed) slightly lower rotational speed range N ₁ to N in ₂ than the supercritical expansion turbine 12 does not become over-rotation, the outlet valve 15
Turbine outlet pressure is controlled by opening and closing.

Ii) Pressure control mode: the above detection outlet pressure P
After reaching the lower limit pressure P ₂ , the opening / closing control of the outlet valve 15 is performed so that the outlet pressure P falls within the pressure range between the upper limit pressure P ₂ and the set pressure P ₁ slightly lower than the upper limit pressure P _2. I do.

In the low pressure line 4, the heat exchanger 5e
A return valve 22 is provided at a position on the upstream side (lower side in FIG. 1). The heat exchanger 5 in the high pressure line 3
The part located between e and the expansion valve 6 and the part located between the return valve 22 and the heat exchanger 5e in the low pressure line 4 are directly connected via the pre-cooling bypass line 23 and opened in the middle thereof. A precooling valve (precooling bypass flow rate adjusting means) 24 whose degree can be adjusted is provided. Further, in the high-pressure line 3, the portion located between the heat exchanger 5d and the inlet valve 14 and the portion located between the outlet valve 15 and the heat exchanger 5e are directly connected via the turbine bypass line 25. A bypass valve (turbine bypass flow rate adjusting means) 26 whose opening can be adjusted is provided in the middle thereof.

Further, in this apparatus, an inlet pressure gauge (inlet pressure detecting means) for detecting the inlet pressure of the expansion valve 6 (more specifically, the pressure between the heat exchanger 5e and the end of the precooling bypass line 23). 27, an in-tank pressure gauge (storage state detecting means) 28 for detecting the gas pressure in the refrigerant liquid storage tank 1, and a liquid level gauge 29 for detecting the liquid level in the storage tank 1 are arranged at appropriate positions. . These detection signals are sent to the valve control device 3
0, and the valve control device 30 controls the openings of the expansion valve 6, the precooling valve 24, and the bypass valve 26.

The valve control device 30 includes an expansion valve control section (expansion valve control means) 31, a pre-cooling valve control section (bypass flow rate control means) 32, and a bypass valve control section (bypass flow rate control means) as shown in FIG. ) 33.

The expansion valve control section 31 fully opens the return valve 22 and slightly opens the expansion valve 6 to start the liquefaction operation when the temperature in the vicinity of the expansion valve 6 has dropped to some extent, and thereafter, in the tank. The opening degree of the expansion valve 6 is controlled based on the liquid storage state in the tank detected by the pressure gauge 28 and the liquid level gauge 29. More specifically, the following control is performed during precooling.

When the tank pressure and the liquid level are within the normal range, the opening degree of the expansion valve 6 is gradually increased. When the liquid level decreases at a speed equal to or higher than a preset value and the tank pressure increases (for example, when the initial opening of the expansion valve 6 is too large and a large amount of refrigerant gas flows into the refrigerant liquid storage tank 1, ,
This occurs when the refrigerant gas temperature is higher than a predetermined temperature. )
First, the opening degree of the expansion valve 6 is reduced. In this case, it is further checked whether or not there is an abnormal change after the set time has elapsed.

As described above, the opening degree of the expansion valve 6 is increased to the set maximum opening degree, but when the liquid level in the refrigerant liquid storage tank 1 exceeds the set value, the expansion valve 6 is closed and the precooling valve is opened. A signal is output to the control unit 32 to open the precooling valve 24.

The pre-cooling valve control unit 32 opens the pre-cooling valve 24 when the pre-cooling operation of the cold insulation box 2 is started, and then the pre-cooling operation proceeds to open the expansion valve 6 and start the liquefaction operation. The precooling valve 24 is gradually throttled.

At the same time when the expansion valve 6 is opened, the precooling valve 24 is slightly throttled. Expansion valve inlet pressure detected by the inlet pressure gauge 27 and a preset set pressure (specifically, the turbine control device 2 described above).
(A little lower than the lower limit pressure P ₁ set at 0)
When the former pressure is lower than the latter pressure, the pre-cooling valve 24 is further throttled to increase the actual inlet pressure, and when the former pressure is higher than the latter pressure, the pre-cooling valve 24 is slightly opened to reduce the actual inlet pressure. This actual pressure approaches the set pressure by lowering. By repeating the above operation, the precooling valve 24 is fully closed before the expansion valve 6 opens to the set maximum opening.

The bypass valve control unit 33 includes the precooling valve 24.
Similarly to the above, the bypass valve 26 is opened from the start of precooling of the cold insulation box 2, and then the bypass valve 26 is gradually throttled in the following manner.

After the turbine control device 20 starts the operation of the supercritical expansion turbine 12, the bypass valve 2
Squeeze 6 a little. When the expansion valve inlet pressure detected by the inlet pressure gauge 27 is compared with a preset set pressure (pressure equivalent to the pressure set by the precooling valve control unit 32), and the former pressure exceeds the latter pressure. The bypass valve 26 is further throttled to lower the actual inlet pressure, and when the former pressure is lower than the latter pressure, the bypass valve 26 is slightly opened to increase the actual inlet pressure, so that the pre-cooling valve control section 32 can be operated. Perform the operation to bring the actual inlet pressure close to the set pressure. The outlet pressure of the supercritical expansion turbine 12 detected by the outlet pressure gauge 18 has dropped to a preset pressure (specifically, a pressure substantially equal to the set pressure P ₂ set by the turbine control device 20). From the time point, that is, the time when the turbine outlet pressure enters a substantially stable state, the bypass valve 26
Slowly squeeze until fully closed.

Returning to FIG. 1, a refrigerating load 34 is installed near the refrigerant liquid storage tank 1. This refrigeration load 34
Is connected to the refrigerant liquid storage tank 1 via a refrigerant liquid supply line 35, and is connected to the outlet side of the return valve 22 in the low pressure line 4 via a refrigerant return line 36. Supply valve 37 and return valve 3
8 are provided respectively.

Further, the outlet side portion of the supply valve 37 in the refrigerant liquid supply line 35 is connected to the high pressure line 3 via the precooling supply line 40, and the inlet side portion of the return valve 38 in the refrigerant return line 36 is the precooling return line. The low pressure line 4 is connected via 42 to a position between the heat exchangers 5a and 5b. The upstream end (upper end in the figure) of the pre-cooling supply line 40 is branched into lines 43 and 44, the line 43 being in the high pressure line 3 upstream of the heat exchanger 5a, and the line 44 being high pressure line 3 in the heat exchanger 5a. ，
5b are respectively connected to the portions located between them, and the lines 43, 44 and both lines 43, 44 are connected.
Temperature control valves 46, 47, 48 are provided at the confluent portions of the above, and a line switching valve 49 is provided in the middle of the precooling return line 42.

Next, the operation of this liquefaction refrigeration system will be described.

First, the cold storage box 2 and the refrigerating load 34 are precooled before the liquefaction operation.
Only 6,47,48,49 are open. When the compressor 10 operates in this state, the refrigerant passes through the high pressure line 3 and is auxiliary cooled by heat exchange with liquid nitrogen in the heat exchanger 5a, and then the turbine bypass line 25 that bypasses the supercritical expansion turbine 12. Through the pre-cooling bypass line 23 and the low pressure line 4 to the suction side of the compressor 10. Precooling in the cool box 2 is promoted by such circulation of the refrigerant. Further, a part of the auxiliary cooled refrigerant is supplied from the line 44 through the pre-cooling supply line 40 to the refrigeration load 3
4, the refrigerant is pre-cooled, and the refrigerant branched to the turbine line 7 performs cold work by performing work in the expansion turbine 8.

When the temperature in the vicinity of the expansion valve 6 drops to a predetermined temperature while the precooling proceeds in this way, the return valve 22 is fully opened and the expansion valve 6 is slightly opened by the control signal from the expansion valve control unit 31. The pre-cooling valve 24 is slightly throttled at the same time as the liquefaction operation is started by opening. After that, the opening degree of the expansion valve 6 is controlled based on the tank liquid storage state detected by the tank pressure gauge 28 and the liquid level gauge 29. In parallel with this, the opening degree of the precooling valve 24 is controlled. As a result, the inlet pressure of the expansion valve 6 is always maintained at a pressure near a constant pressure lower than the lower limit pressure P ₁ set by the turbine control device 20, regardless of the opening degree of the expansion valve 6.

When the precooling further progresses and the temperature in the vicinity of the supercritical expansion turbine 12 drops to a predetermined temperature (that is, the temperature at which the supercritical expansion turbine 12 can operate), the supercritical expansion turbine 12 as shown in the flowchart of FIG. The operation control operation of is started.

First, the inlet valve 14 is fully opened and the outlet valve 15 is gradually opened, whereby a part of the refrigerant gas circulating in the high pressure line 3 and the low pressure line 4 passes through the supercritical expansion turbine 12 and By supercritical expansion turbine 12
The pre-cooling operation is started (step S1).

At this time, the turbine control device 20 sets the outlet pressure P currently detected by the outlet pressure gauge 18 to a preset set pressure P ₂ , more specifically, the critical pressure of helium (about 2.2 atm). ) Pressure P set to a value slightly higher than
₂ is compared, and when the former exceeds the latter (YES in step S2), the outlet valve 15 of the outlet valve 15 is adjusted so that the detected rotation speed N falls within a preset range between the rotation speeds N ₁ and N ₂ . The opening is set (step S3).

Actually, at the beginning of precooling, the turbine outlet pressure (outlet valve inlet pressure) is sufficiently higher than the set pressure P ₂ as shown in FIG. It will be exclusively controlled. Specifically, when the detected rotation speed N drops to the lower limit rotation speed N ₁ ,
As shown at points B-B ', C-C', and D-D 'in FIG. 4, the opening of the outlet valve 15 is increased to reduce the turbine outlet pressure (that is, increase the expansion ratio). As a result, the actual turbine rotation speed is increased, and when the detected rotation speed N rises to the upper limit rotation speed N _2, control is performed to stop the increase of the outlet valve opening and suppress the rotation speed increase. Here, the lower limit rotation speed N ₁ is set to the minimum rotation speed at which the supercritical expansion turbine 12 can effectively perform work, and the upper limit rotation speed N ₂ is the maximum rotation speed at which the turbine does not become over-rotation. Therefore, the actual rotational speed N is controlled between the rotational speeds N ₁ and N ₂ so that the supercritical expansion turbine 1 is prevented while preventing turbine over-rotation.
The operation control that maximizes the function of No. 2 will be executed.

By such control, the outlet valve 15 is gradually opened and the turbine outlet pressure P is gradually decreased.
From the time when the outlet pressure P drops to the upper limit pressure P ₂ (NO in step S2), the turbine control device 20 sets the outlet pressure P to the lower limit pressure P ₁ and the upper limit pressure P ₂ which is a constant value higher than the lower limit pressure P _1. The pressure control is performed exclusively so that the pressure falls within the range (step S4). More specifically, when the detected pressure P decreases to the lower limit pressure P ₁ , the point E in FIG.
The outlet pressure P is increased by throttling the outlet valve 15 as shown at points E ′ and F−F ′, and when the outlet pressure P reaches the upper limit pressure P ₂ , the throttling of the outlet valve 15 is stopped. Therefore, control is performed to suppress the rise of the outlet pressure P.
By performing such control, the turbine outlet pressure P
It is possible to shift to the normal operation state as it is, while maintaining

In the control based on the outlet pressure, the turbine speed N is not taken into consideration. However, when the turbine outlet pressure P actually reaches the set pressure P ₁ , the turbine inlet temperature has already dropped sufficiently. Therefore, even if the turbine speed N is not taken into consideration, there is no possibility of causing turbine over-rotation. The control based on the outlet pressure is performed even after shifting to the normal operation.

During such turbine operation control, the opening degree control of the expansion valve 6 is performed independently of the control operation. For example, when the refrigerant liquid storage tank 1 is full, the expansion valve 6 is controlled even during turbine operation.
May be closed completely, and liquefaction may be interrupted. Here, conventionally, since the opening degree of the expansion valve 6 directly affects the turbine outlet pressure, it is impossible to operate the supercritical expansion turbine 12 when the expansion valve 6 is fully closed as described above. However, in this device, by controlling the opening degrees of the precooling valve 24 and the bypass valve 26, the expansion valve inlet pressure (that is, the outlet pressure of the outlet valve 15) is always lower than the lower limit pressure P ₁ regardless of the opening degree of the expansion valve 6. Since it is maintained at an appropriate low pressure, the turbine outlet pressure can be appropriately adjusted from beginning to end by opening / closing the outlet valve 15. Therefore, it is possible to precool the refrigeration load 34 by utilizing the cold generated by the supercritical expansion turbine 12 while stopping the liquefaction operation.

As described above, in this method and apparatus, the opening control of the precooling valve 24 and the bypass valve 26 is performed in parallel with the opening control of the expansion valve 6 based on the liquid storage state in the tank. Since the expansion valve inlet pressure is always maintained at an appropriate pressure lower than the turbine outlet pressure, the outlet valve 15 can be freely operated without being restricted by the opening degree of the expansion valve 6 to achieve an appropriate supercritical expansion. The operation control of the turbine 12 can be executed.

Further, in this embodiment, regarding the control of the supercritical expansion turbine 12, in the initial stage of the turbine precooling when the outlet pressure thereof is sufficiently high, the expansion valve opening control based on the turbine rotation speed N is performed to control the supercritical expansion turbine opening. Critical expansion turbine 1
Control that keeps the outlet pressure P within a certain pressure range higher than the helium critical pressure from the latter stage of pre-cooling when the turbine outlet pressure P drops and the turbine over-rotation does not occur while the 2 is effectively working. By performing the above, there is an advantage that the helium liquefaction in the supercritical expansion turbine 12 can be prevented and the normal operation state can be smoothly performed as it is.

Moreover, during the execution of the above control, the inlet pressure of the supercritical expansion turbine 12 is always set to a pressure substantially equal to the discharge pressure of the compressor 10, and the opening degree of the outlet valve 15 is adjusted, that is, the turbine outlet pressure is adjusted. Since the turbine expansion ratio is controlled only by this, the control content can be simplified, and the inlet valve 14 can be used only for opening / closing switching (that is, one whose opening cannot be adjusted). Cost can be reduced. Furthermore, unlike the conventional control that gradually opens the inlet valve while maintaining the turbine outlet pressure near the helium critical pressure as in the past, the turbine operating pressure during precooling operation is higher than the operating pressure during normal operation. The amount of cold generation of the supercritical expansion turbine 12 during the precooling operation can be significantly increased as compared with the conventional case, and thus the precooling time can be shortened.

The reason is as follows. For example, in a supercritical expansion turbine with a braking fan, if various operating conditions such as the turbine speed N, the temperature of the braking fan circulation path, and the opening of the speed control valve in this circulation path are constant,
The power of the braking fan is proportional to the pressure of the braking fan circulation passage. The power of the braking fan is almost equal to the amount of cold generated by the supercritical expansion turbine. On the other hand, in the supercritical expansion turbine with a braking fan, in order to reduce the load on the thrust bearing,
Generally, the pressure in the turbine section and the pressure in the brake fan circulation path are equalized. Therefore, if the turbine operating pressure is increased by maintaining the turbine inlet pressure at high pressure and gradually decreasing the turbine outlet pressure as in the above method and apparatus, the pressure in the braking fan circulation path is maintained higher than that in the conventional method. As a result, the amount of cold generated by the turbine can be significantly increased.

However, in the method and apparatus according to the first and third aspects of the present invention, regardless of the specific control content of the supercritical expansion turbine, at least the outlet pressure is taken as a factor to perform turbine operation control. The present invention can be effectively applied. Further, when performing the turbine operation control shown in this embodiment, it is sufficient to detect a value relating to the rotation speed of the turbine, and instead of taking in the rotation speed N per unit time as in the above embodiment, the rotation speed of the turbine is directly measured. You may make it take in.

Next, a second embodiment will be described with reference to FIGS.

In this embodiment, the apparatus shown in FIG. 1 is provided with a thermometer 50 for detecting the temperature of the refrigerant at a proper place in the low pressure line 4, and based on the detected temperature,
By changing the lower limit pressure P ₁ and the upper limit pressure P ₂ set by the turbine control device 20, the turbine cold generation amount is controlled. The reason why the amount of cold generation can be controlled by changing the set pressure value is as follows.

FIG. 6 is an hs diagram for the above device. In the figure, it is assumed that the turbine inlet pressure is 15 atm, the turbine outlet pressure is 6 atm, the turbine flow rate is Mc, and the specific enthalpy difference between the turbine inlet and outlet is Δhc (point A → C 'in the figure). From this state, the outlet pressure setting value P
₁ and P ₂ were changed to small values of 3.9 atm and 4.1 atm, respectively, so that the actual outlet pressure became lower (about 4 atm).
If the turbine flow rate at this time is Md and the specific enthalpy difference between the turbine inlet and outlet is Δhd, then the turbine flow rate is Md> Mc, and the specific enthalpy difference is also As shown in FIG.
hd> Δhc. Here, since the amount of cold generation is equal to the product of the turbine flow rate and the specific enthalpy difference between the turbine inlet and outlet, the amount of cold generated by the turbine increases as the outlet pressure setting value drops.

That is, according to the device of the second embodiment,
By increasing the outlet pressure setting value, the amount of cold generation can be reduced, and by decreasing the outlet pressure setting value, the amount of cold generation can be increased. Instead of such automatic temperature control, for example, the turbine control device 2
In addition to inputting several kinds of outlet pressure set values P ₁ and P ₂ into 0, a set value input device such as a keyboard is connected to this turbine control device 20 to select _one of the above input values by the operation. The user may be allowed to select a desired setting value, or the setting value may be changed in an analog manner by adjusting a knob or the like.

Next, a third embodiment will be described with reference to FIG.

In the first embodiment, when it is necessary to fully close the expansion valve 6 during the operation of the supercritical expansion turbine 12, the precooling valve 24 is opened (or its opening is increased) and the supercritical valve is opened. The gas flowing through the expansion turbine 12 is passed through the pre-cooling bypass line 23 and the low pressure line 4 to the compressor 10
However, if the cold of the gas can be used more effectively, the refrigerating capacity of the entire apparatus can be increased.

Therefore, in this embodiment, in the apparatus shown in FIG. 1, a cryogenic refrigerant supply line 51 branching from the high pressure line 3 on the upstream side of the expansion valve 6 is additionally provided, and this refrigerant supply line 51 has a temperature The temperature control valve 39 is provided on the downstream side of the control valve 48 and connected to the pre-cooling supply line 40.

According to this structure, the temperature control valve 39
And the whole or part of the gas flowing through the supercritical expansion turbine 12 is supplied to the refrigerating load 34 via the cryogenic refrigerant supply line 51, whereby the cold can be effectively used.

Although the first to third embodiments have been described above, the storage state detecting means in the present invention is not limited to the in-tank pressure gauge 28 and the liquid level gauge 29 as described above, and the opening degree of the expansion valve 6 can be used. Anything that detects a value that can be provided as a control factor may be used. For example, instead of the in-tank pressure gauge 28 in the above embodiment, as shown in FIG. 8, a return pressure detector 2 for detecting the pressure in the vicinity of the refrigerant liquid storage tank 1 in the low pressure line 4 is shown.
Even if 8'is provided, the storage state can be grasped in the same manner as above.

Further, the present invention can be applied to various liquefaction refrigerating apparatuses in which the supercritical expansion turbine 12 is provided on the high pressure line 3 upstream of the expansion valve 15, and as described in the above embodiments. The heat exchanger 5e may not be interposed between the expansion valve 6 and the outlet valve 15, and conversely, the heat exchanger may be interposed between the supercritical expansion turbine 12 and the outlet valve 15.

[0061]

As described above, according to the present invention, the outlet valve of the supercritical expansion turbine is provided on the upstream side of the expansion valve, the turbine outlet pressure is controlled by adjusting the opening degree of the outlet valve, and the supercritical expansion turbine is also provided. To bypass the expansion valve and the liquid storage part to bypass the expansion valve and the liquid storage part to flow the refrigerant from the high pressure line to the low pressure line, and adjust the bypass flow rate to adjust the bypass valve flow rate regardless of the opening degree of the expansion valve. Is always controlled to an appropriate pressure lower than the turbine outlet pressure, so that the expansion valve opening degree is controlled well based on the storage state of the refrigerant liquid in the liquid storage portion,
The operation of the supercritical expansion turbine can be well controlled by adjusting the opening of the outlet valve without being affected by the opening of the expansion valve. Therefore, for example, it becomes possible to continue the operation of the supercritical expansion turbine without any inconvenience even while the expansion valve is fully closed to interrupt the liquefaction.

Further, in the method and apparatus according to claims 2 and 4, regarding the operation control of the supercritical expansion turbine, in the liquefaction refrigeration system in which the supercritical expansion turbine is provided upstream of the expansion valve, the supercritical expansion is performed. The inlet pressure of the turbine is maintained at a pressure substantially equal to the discharge pressure of the compressor, and in the early stage of precooling when the turbine outlet pressure is sufficiently high, the expansion valve opening control (that is, turbine The outlet pressure is controlled), and from the latter stage of pre-cooling where the turbine outlet pressure is low and there is no risk of turbine over-rotation, the outlet pressure is controlled so that it falls within a predetermined range above the refrigerant critical pressure. And at low cost, it surely prevents over-rotation of the supercritical expansion turbine and liquefaction of the refrigerant in the turbine, and keeps the turbine operating pressure higher than before. The Rukoto, a cold generating of the supercritical expansion turbine can be greatly increased, thereby there is an effect that it is possible to shorten the pre-cooling time.

[Brief description of drawings]

FIG. 1 is a flow sheet of a helium liquefaction refrigeration system according to a first embodiment of the present invention.

FIG. 2 is a functional block diagram of a valve control device provided in the liquefaction refrigeration system.

FIG. 3 is a flowchart showing a control operation performed by a turbine control device provided in the liquefaction refrigeration system.

FIG. 4 is a graph showing changes over time in the rotational speed, inlet / outlet pressure, inlet valve opening, and outlet valve opening of the supercritical expansion turbine during operation of the liquefaction refrigeration system.

FIG. 5 is a flow sheet of a helium liquefaction refrigeration system according to a second embodiment of the present invention.

FIG. 6 is an hs diagram for the device.

FIG. 7 is a flow sheet of a helium liquefaction refrigerating apparatus according to a third embodiment of the present invention.

FIG. 8 is a flow sheet of a helium liquefier refrigerating apparatus according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Refrigeration load 3 High pressure line 4 Low pressure line 5a-5e Heat exchanger 6 Expansion valve 10 Compressor 12 Supercritical expansion turbine 16 Tachometer (rotation speed detection means) 18 Outlet pressure gauge (outlet pressure detection means) 20 Turbine control device ( Supercritical expansion turbine control means) 23 Pre-cooling bypass line 24 Pre-cooling valve (pre-cooling bypass flow rate adjusting means) 25 Turbine bypass line 26 Bypass valve (turbine bypass flow rate adjusting means) 27 Inlet pressure gauge (inlet pressure detecting means) 28 In-tank pressure gauge (Storage state detection means) 28 'Return pressure gauge (storage state detection means) 29 Liquid level gauge (storage state detection means) 30 Valve control device 31 Expansion valve control section (expansion valve control means) 32 Precooling valve control section (bypass flow rate) Control means) 33 Bypass valve control section (bypass flow rate control means)

Claims (4)

[Claims] 1. A compressor for pumping a refrigerant, a liquid storage section for storing a liquefied refrigerant, a high-pressure line for supplying the refrigerant pumped from the compressor to the liquid storage section, and a liquid storage section for storing the refrigerant. A low pressure line for returning the refrigerant to the compressor, an expansion valve having an adjustable opening is provided in the high pressure line, and in the liquefaction refrigeration apparatus in which a supercritical turbine type expander is provided on the upstream side of the expansion valve, in the liquid storage section Detecting the storage state of the refrigerant liquid, while controlling the opening degree of the expansion valve based on this storage state, at the outlet side of the supercritical turbine type expander and upstream of the expansion valve An outlet valve is provided, the turbine outlet pressure, which is the outlet side of the supercritical turbine expander and the upstream side of the outlet valve, is detected, and at least this turbine outlet pressure is taken as a factor to open the outlet valve. Degree adjustment Control the turbine outlet pressure by detecting the expansion valve inlet pressure, which is the pressure on the inlet side of the expansion valve and on the downstream side of the outlet valve, and the expansion valve inlet pressure is lower than the turbine outlet pressure. At a flow rate such that the pressure is within the pressure range, the refrigerant flows in the high pressure line by bypassing the supercritical turbine expander and the outlet valve, and the expansion is performed from a portion between the outlet valve and the expansion valve in the high pressure line. A method for controlling the operation of a liquefaction refrigeration system, characterized in that a refrigerant is caused to flow through the low-pressure line by bypassing the valve and the liquid reservoir. 2. The operation control method for a liquefaction refrigeration system according to claim 1, wherein when controlling the outlet pressure of the supercritical turbine expander, a value relating to the rotational speed of the supercritical turbine expander is detected and detected. The turbine expansion is performed in a state where the inlet pressure of the turbine expander is substantially equal to the discharge pressure of the compressor until the turbine outlet pressure drops to a predetermined set pressure higher than the critical pressure of the refrigerant. After adjusting the opening of the outlet valve so that the value related to the rotation speed of the machine falls within a preset range and the turbine outlet pressure to be detected reaches the set pressure, the inlet pressure of the turbine expander is set to the above. It is characterized in that the opening degree of the outlet valve is adjusted so that the detected pressure falls within a preset pressure range near the set pressure in a state where the pressure is substantially equal to the discharge pressure of the compressor. Operation control method for liquefaction refrigeration system. 3. A compressor for pumping a refrigerant, a liquid storage section for storing a liquefied refrigerant, a high-pressure line for supplying the refrigerant pumped from the compressor to the liquid storage section, and a liquid storage section for storing the refrigerant. A low pressure line for returning the refrigerant to a compressor, an expansion valve having an adjustable opening degree is provided in the high pressure line, and in the liquefaction refrigeration apparatus in which a supercritical turbine type expander is provided on the upstream side thereof, the supercritical turbine A turbine bypass line that bypasses the supercritical turbine type expander and the outlet valve in the high-pressure line, while providing the outlet valve at a position upstream of the expansion valve on the outlet side of the expander.
Turbine bypass flow rate adjusting means for changing the refrigerant flow rate in this turbine bypass line, a precooling bypass line that bypasses the expansion valve and the refrigerant liquid storage tank and connects the high pressure line and the low pressure line, and the refrigerant flow rate in this precooling bypass line Precooling bypass flow rate adjusting means for changing, outlet pressure detecting means for detecting the turbine outlet pressure which is the outlet side of the supercritical turbine expander and is the upstream side pressure of the outlet valve, and at least this turbine outlet pressure Supercritical expansion turbine control means that takes in as a factor and controls the turbine outlet pressure by adjusting the opening of the outlet valve, storage state detection means that detects the storage state of the refrigerant liquid in the liquid storage portion, and this detected Expansion valve control means for controlling the opening degree of the expansion valve based on the storage state, and the high pressure line In the inlet side of the expansion valve, the inlet pressure detecting means for detecting the inlet pressure of the expansion valve, which is the pressure on the downstream side of the outlet valve, and the inlet pressure detecting means after the expansion valve is opened during precooling. A bypass flow rate control means for operating the turbine bypass flow rate adjusting means and the precooling bypass flow rate adjusting means so that the expansion valve inlet pressure is within a predetermined pressure range lower than the turbine outlet pressure based on the detected expansion valve inlet pressure. An operation control device for a liquefaction refrigeration system, comprising: 4. The operation control device for a liquefaction refrigeration system according to claim 3, further comprising rotation detection means for detecting a value related to the rotation speed of the supercritical turbine expander,
The inlet pressure of the turbine type expander until the turbine outlet pressure detected by the outlet pressure detecting means falls to a predetermined set pressure higher than the critical pressure of the refrigerant through the supercritical expansion turbine control means. The opening of the outlet valve is adjusted so that the value relating to the rotational speed of the turbine expander falls within a preset range in a state in which the discharge pressure of the compressor is approximately equal to the turbine outlet pressure to be detected. After reaching the set pressure, the detected pressure is kept within a preset pressure range near the set pressure with the inlet pressure of the turbine expander at a pressure substantially equal to the discharge pressure of the compressor. An operation control device for a liquefaction refrigeration system, characterized in that the opening degree of the outlet valve is adjusted.