JPH06123505A - Method and apparatus for controlling operation of liquefying refrigerating plant - Google Patents

Abstract

PURPOSE:To provide a positive prevention of liquefying of helium within a supercritical expansion turbine and an excessive rotation of the turbine and shorten a precooling time under an easy operation control and a low cost. CONSTITUTION:Each of the number of rotation N and an outlet pressure P of a supercritical expansion turbine 12 is detected by a rotary meter 16 and an outlet pressure gauge 18, respectively, and then the detected signals are inputted to a control device 50. A turbine inlet pressure is always substantially equal to a discharging pressure of a compressor 10. At a stage in which the detected outlet pressure P is sufficiently high, the valve travel of an expansion valve 6 is controlled in such a manner that the detected number of rotations N may be set within a predetermined range. After the detected outlet pressure P reaches a set pressure higher than the critical pressure of helium, the valve travel of the expansion valve 6 is controlled in such a manner that the detected outlet pressure P is set within a specified range less than the set pressure.

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 an outlet valve such as an expansion valve is provided on the downstream side of a supercritical turbine expander.

[0002]

2. Description of the Related Art In recent years, in a cryogenic liquefaction refrigeration system such as a helium liquefaction refrigeration system, particularly a large liquefaction refrigeration system, its refrigerating capacity is increased and the liquefaction rate at an outlet valve (JT valve) is improved. Therefore, a supercritical turbine expander (hereinafter referred to as a supercritical expansion turbine) is often provided upstream of the outlet 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.

As such means, for example, Japanese Patent Laid-Open No. Sho 60
In JP-A-164182, an outlet valve provided on the downstream side of the supercritical expansion turbine is also used as a pressure regulating valve,
A method is disclosed in which the outlet pressure of the supercritical expansion turbine is always maintained at a pressure equal to or higher than the critical pressure of helium by adjusting the opening degree. However, in this method, since no consideration is given to over-rotation of the supercritical expansion turbine that is expected to occur during precooling, the occurrence of such over-rotation causes damage such as seizure to the supercritical expansion turbine. There is a risk.

As a control method in consideration of such turbine over-rotation, for example, in Japanese Patent Laid-Open No. 1-269875, the outlet temperature and outlet pressure of the supercritical expansion turbine are detected, and the detected outlet temperature is the critical temperature of helium. Above
In addition, by increasing the opening of the outlet valve as much as possible within the range where the detected pressure is equal to or higher than the suction pressure of the compressor, the turbine outlet pressure is reduced as much as possible while preventing liquefaction of helium in the supercritical expansion turbine, which is high. While ensuring an expansion ratio and a larger amount of cold generation, an inlet valve whose opening can be adjusted is provided on the inlet side of the supercritical expansion turbine, and the inlet pressure of the turbine is appropriately reduced by restricting the inlet valve. , That in which the rotation speed of the supercritical expansion turbine is always kept below a preset rotation speed is shown.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The device of Japanese Patent No. 875 has the following problems to be solved.

A) In the above method, the turbine outlet pressure is made as small as possible, and then the turbine inlet pressure is appropriately lowered by the inlet valve in order to prevent over-rotation in the supercritical expansion turbine. Even if a high expansion ratio is obtained by lowering the pressure, the operating pressure of the supercritical expansion turbine during precooling is low (lower than the operating pressure during normal operation), and as a result, a large increase in the amount of cold generation occurs, as described later. Consequently, it is difficult to effectively reduce the precooling time.

B) In the above method, helium liquefaction is prevented by controlling the opening of the outlet valve based on the comparison between the turbine outlet temperature and the helium critical temperature.
In the extremely low temperature region (the region where the turbine inlet temperature is 9K or less), the rate of change of the turbine outlet temperature is very small compared to the rate of change of the turbine inlet temperature. In other words, the inlet condition of the supercritical expansion turbine is somewhat different. Even if it changes, the turbine outlet temperature changes only slightly. Therefore, in order to properly control the supercritical expansion turbine by using the turbine outlet temperature as a factor, extremely accurate temperature measuring means must be used. Therefore, there are drawbacks that the cost of the apparatus is increased and the reliability of control accuracy is poor.

In view of such circumstances, the present invention can reliably prevent helium liquefaction and turbine over-rotation in the supercritical expansion turbine and shorten the precooling time by a simple and low-cost means. An object of the present invention is to provide an operation control method and device for a liquefaction refrigeration system.

[0009]

The present invention is directed to a compressor for pumping a refrigerant, a high pressure line for supplying the refrigerant pumped from the compressor to a refrigeration load, and a low pressure for returning the refrigerant from the refrigeration load to the compressor. Line, the supercritical turbine type expander is provided in the high pressure line, in a liquefaction refrigeration apparatus provided with an outlet valve on the outlet side thereof, a value relating to the rotational speed of the supercritical turbine type expander and a turbine outlet pressure. The turbine outlet pressure to be detected is reduced to a preset pressure higher than the critical pressure of the refrigerant until the inlet pressure of the turbine expander becomes substantially equal to the discharge pressure of the compressor. The opening of the outlet valve is controlled so that the value related to the rotational speed of the turbine expander is kept within a preset range while keeping it, and the turbine outlet pressure to be detected becomes the set pressure. After that, while maintaining the inlet pressure of the turbine type expander at a pressure substantially equal to the discharge pressure of the compressor, the opening degree of the outlet valve is set so that the detected pressure falls within a preset pressure range near the set pressure. Is controlled (Claim 1). As a device therefor, rotation detecting means for detecting a value relating to the rotation speed of the supercritical turbine expander, outlet pressure detecting means for detecting a turbine outlet pressure of the supercritical turbine expander, and the detected turbine outlet Until the pressure drops to a predetermined set pressure that is higher than the critical pressure of the refrigerant, the inlet pressure of the turbine type expander is approximately equal to the discharge pressure of the compressor, and the turbine type expander The opening of the outlet valve is controlled so that the value related to the rotation speed falls within a preset range,
After the turbine outlet pressure to be detected reaches the preset pressure, the inlet pressure of the turbine expander is kept at a pressure substantially equal to the discharge pressure of the compressor within a preset pressure range near the preset pressure. An outlet valve control means for controlling the opening of the outlet valve so as to contain the detected pressure is provided (claim 3).

Further, according to the present invention, the amount of cold generation of the supercritical expansion turbine is adjusted by changing the set pressure and the pressure range (Claim 2). As a device therefor, the outlet valve control means is used. A set pressure changing means for changing the set pressure and the pressure range to be set is provided (Claim 4).

[0011]

According to the method and the apparatus of claims 1 and 3, until the turbine outlet pressure reaches a predetermined set pressure, the outlet pressure control is performed by adjusting the opening of the outlet valve on the basis of the value relating to the turbine rotation speed. By performing (in other words, controlling the expansion ratio of the turbine), turbine over-rotation during precooling can be 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.

Further, since the turbine inlet pressure is constant, by changing the set pressure and pressure range of the turbine outlet pressure as in the method and apparatus according to claims 2 and 4, the turbine expansion ratio and therefore the cold generation thereof can be generated. The amount can be adjusted.

[0014]

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 refrigerating load, 2 is a cool box, a compressor 10 is provided outside the cool box 2, and the discharge side of this compressor 10 is connected to a refrigerating load 1 via a high pressure line 3.
And the refrigeration load 1 is connected to
It is connected to the suction side of the compressor 10 via. The refrigeration load 1 may be of any type, and may be, for example, a refrigerant liquid storage tank that stores a liquefied refrigerant (here, helium).

Inside the cool box 2, heat exchangers 5a, 5b, 5c and 5d 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.
The portion of the high-pressure line 3 located between the heat exchangers 5a and 5b, and the heat exchangers 5b and 5c in the low-pressure line 4.
The portions located between are 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 (also serving as an outlet valve in the present invention) 6 is provided at a position on the outlet side of the heat exchanger 5d on the lowest temperature side, and a position on the upstream side of this, specifically, The supercritical expansion turbine 12 is provided at a position between the heat exchangers 5c and 5d. The structure of the main part is shown in FIG.

In the figure, 20 is a rotary shaft and 30
Is a casing that houses the rotary shaft 20, and a turbine impeller 21 is fixed to one end (the left end in FIG. 2) of the rotary shaft 20, and a braking fan 22 is fixed to the other end. An inlet nozzle 31 for introducing adiabatic expansion helium into the turbine is provided in a portion of the casing 30 corresponding to the turbine impeller 21, and a front chamber 32 is formed further downstream thereof.
Downstream of the front chamber 32, the turbine impeller 2
A jet nozzle 33 is provided at a position on the upstream side of 1. Further, the rear chamber 34 is provided on the downstream side of the turbine impeller 21.
Are formed.

Similarly, in the portion of the casing 30 corresponding to the braking fan 22, a tip end portion of an annular guide cylinder 36 serving as a partition wall is provided so as to face the rotating peripheral surface of the braking fan 22. The outer side surface of the guide cylinder 36 and the inner side surface of the casing 30 surround the annular first chamber 35, and the inner side surface of the guide cylinder 36 and the casing 30.
The second chamber 37 is surrounded by the inner surface of the
Helium gas is enclosed in 7. Both rooms 35, 37
Are connected via a circulation path 40, and a speed control valve 41 and a heat exchanger 42 are provided on the way.

In such a turbine, the helium introduced into the turbine through the inlet nozzle 31 is
Through the front chamber 32, expansion work is performed in the turbine portion including the ejection nozzle 33 and the turbine impeller 21, and the refrigerant flows out of the turbine through the rear chamber 34 in a state where the temperature and the pressure are reduced. The expansion work is transmitted as rotational energy from the turbine impeller 21 to the braking fan 22 via the rotary shaft 20. This energy is transmitted to the helium gas that circulates in the order of the first chamber 35, the circulation path 40, and the second chamber 37. Then, this helium gas is used as the heat exchanger 4
The energy is released to the outside of the system by exchanging heat with the cooling water or the like in 2, and the rotation suppression of the turbine impeller 21 is controlled by adjusting the opening degree of the speed control valve 41.

Returning to FIG. 1, the above-mentioned supercritical expansion turbine 1
An inlet valve 14 that is switched between an open state and a closed state is provided on the upstream side of 2. Further, in this device, a tachometer (rotation detecting means) 16 for detecting the number of revolutions (hereinafter, simply referred to as turbine revolution number) N of the supercritical expansion turbine 12 and the supercritical expansion turbine 12 are detected.
An outlet pressure gauge (outlet pressure detection means) 18 for detecting the outlet pressure P of the above is provided, and detection signals of both are input to a control device (outlet valve control means) 50. The control device 50 is configured to control the opening degree of the expansion valve 6 based on the rotational speed N and the outlet pressure P as described below.

The contents of the control operation performed by the controller 50 and the operating procedure of the entire liquefaction refrigeration system will be described with reference to the flow chart of FIG. 3 and the graph of FIG.

The operation of the supercritical expansion turbine 12 is started when the precooling in the cold insulation box 2 progresses to a certain extent and the temperature drops to the extent that the turbine operation becomes possible. First, the control device 50 switches the inlet valve 14 to open while the compressor 10 is operating, and opens the expansion valve 6 a little, so that a part of the helium gas circulating in the high pressure line 3 and the low pressure line 4 is supercritically expanded. It is passed through the turbine 12 and its pre-cooling is started (step S1).

After that, the control device 50 controls the outlet pressure P currently detected by the outlet pressure gauge 18 and a preset set pressure P ₂ , more specifically, the critical pressure of helium (about 2.
2 atm) and the pressure P ₂ set to a value slightly higher than 2 atm), and if the former exceeds the latter (YE in step S2)
S), the opening degree of the expansion valve 6 is set so that the detected rotation speed N falls within the range between the preset rotation speeds N ₁ and N ₂ (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. 4, so the control device 50 controls the rotational speed as described above. Will be done exclusively. Specifically, when the detected rotation speed N drops to the lower limit rotation speed N ₁ , B in FIG.
As shown by the points -B ', C-C', and D-D ', the opening of the expansion valve 6 is increased to decrease the turbine outlet pressure (that is, increase the expansion ratio). The 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 in the outlet valve opening and suppress the increase in rotation speed. Here, the lower limit rotation speed N
₁ is set to the minimum number of revolutions that allows the supercritical expansion turbine 12 to effectively perform work, and the upper limit number of revolutions N
₂ is set to a rotational speed slightly lower than the maximum rotational speed (maximum permissible rotational speed) at which the turbine does not become over-rotated, and therefore the actual rotational speed is set between these rotational speeds N ₁ and N _2. By controlling the number N, the operation control that maximizes the function of the supercritical expansion turbine 12 while preventing turbine over-rotation is executed.

By such control, the expansion valve 6 is gradually opened and the turbine outlet pressure P is gradually decreased. From the time when the outlet pressure P is reduced to the set pressure P ₂ (NO in step S2). ), The control device 50 exclusively performs pressure control so that the outlet pressure P falls within the range between the set pressure P ₂ and the lower limit pressure P ₁ which is a fixed value lower than the set pressure P ₂ (step S4). More specifically, when the detected pressure P falls to the set pressure P _{1, the} outlet pressure P is increased by throttling the expansion valve 6 as shown at points E-E 'and F-F' in FIG. When the outlet pressure P reaches the upper limit pressure P ₂ , the expansion pressure of the expansion valve 6 is stopped so that the outlet pressure P
Control to suppress the rise of By performing such control, it is possible to directly shift to the normal operation state while maintaining the turbine outlet pressure P at a favorable value.

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 ₂ , 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.

As described above, according to this method and apparatus, at the beginning of precooling when the turbine outlet pressure P is sufficiently high,
By controlling the outlet valve opening degree based on the turbine speed N, the supercritical expansion turbine 12 is effectively operated while preventing its over-rotation, and the turbine outlet pressure P is reduced to eliminate the risk of turbine over-rotation. From the above, by controlling the outlet pressure P within a certain pressure range above the helium critical pressure, the supercritical expansion turbine 12
It is possible to smoothly shift to the normal operation state while preventing helium liquefaction inside.

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 to adjust the opening degree of the expansion valve 6, that is, the turbine outlet pressure. 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 conventional case,
Since the turbine operating pressure during precooling operation is higher than the operating pressure during normal operation, the supercritical expansion turbine 12 during precooling operation is used.
There is an effect that the amount of cold generation of is significantly increased as compared with the conventional case, and thereby the precooling time can be shortened.

The reason is as follows. In the supercritical expansion turbine 12 with a braking fan as shown in FIG. 2, when various conditions such as the turbine speed N, the temperature of the braking fan circulation path 40, and the opening of the speed control valve 41 are constant, the braking fan 22 Is proportional to the pressure in the brake fan circulation passage. The power of the braking fan is almost equal to the amount of cold generated by the supercritical expansion turbine 12. On the other hand, in the supercritical expansion turbine with a braking fan, the pressure in the turbine section and the pressure in the braking fan circulation path 40 are generally equalized in order to reduce the load on the thrust bearing. Therefore, if the turbine operating pressure is increased by maintaining the turbine inlet pressure at a high pressure all the time and gradually decreasing the turbine outlet pressure as in the above method and apparatus, the pressure in the braking fan circulation path 40 will be higher than that in the conventional method. Can be maintained at a high level, which can significantly increase the amount of cold generated by the turbine.

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

In this embodiment, in the apparatus shown in FIG. 1, the control device 50 is previously provided with several kinds of outlet pressure set values P.
₁ and P ₂ are input, and this control device 5
A set value input device 52 as shown in FIG. 5 is connected to 0 so that a desired set value can be selected from the input values by its operation. According to such a device, as described below with reference to FIG. 6, there is an advantage that the amount of cold generated by the turbine can be easily adjusted by changing the set pressure.

FIG. 6 shows the h of the first embodiment device.
It is a -s diagram. In the figure, the turbine inlet pressure is set to 15
atm, turbine outlet pressure 6 atm, turbine flow rate Mc,
It is assumed that the turbine inlet / outlet is operated at a specific enthalpy difference of Δhc (point A → point C'in the figure). From this state, the outlet pressure set values P ₁ and P ₂ are changed to small values of 3.9 atm and 4.1 atm, respectively, so that the actual outlet pressure converges at a lower pressure (about 4 atm) (Fig. Point → D'point),
When the turbine flow rate at this time is Md and the specific enthalpy difference between the turbine inlet and outlet is Δhd, the turbine flow rate is Md> Mc, and the specific enthalpy difference is also Δhd> Δhc as shown in FIG. 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.

The present invention is not limited to the above embodiments, but the following modes can be adopted as examples.

(1) In the second embodiment, the outlet pressure set value is selected from a plurality of types as described above, and the set value can be changed in an analog manner by adjusting a knob or the like. You may Alternatively, the temperature of the return refrigerant gas at an appropriate place in the low-pressure line 4 may be detected, and the amount of cold generation may be automatically controlled based on this temperature.

(2) In the present invention, it suffices to detect the value relating to the rotational speed of the turbine, and the rotational speed per unit time may be taken in as in the above embodiment, or the rotational speed of the turbine may be taken directly. You may

(3) Supercritical expansion turbine 1 according to the present invention
Regardless of the specific structure of No. 2, in addition to the structure shown in FIG. 2 described above, various structures conventionally used in a liquefaction refrigeration system can be applied.

(4) The present invention can be applied to various liquefaction refrigeration systems in which the supercritical expansion turbine 12 is provided upstream of the expansion valve 6 in the high pressure line 3, and is shown in each of the above embodiments. As described above, the heat exchanger 5d does not have to be interposed between the supercritical expansion turbine 12 and the expansion valve 6.

(5) In the above embodiment, the expansion valve 6 is also used as the outlet valve in the present invention, but the present invention is not limited to this, and the expansion valve 6 is provided on the upstream side of the expansion valve 6 different from this. An outlet valve may be additionally provided and the turbine outlet pressure may be controlled by operating this outlet valve.

[0041]

As described above, according to the present invention, in the liquefaction refrigeration system in which the supercritical expansion turbine is provided on the upstream side of the expansion valve, the inlet pressure of the supercritical expansion turbine is substantially equal to the discharge pressure of the compressor. In the pre-cooling initial stage when the turbine outlet pressure is sufficiently high and the turbine outlet pressure is sufficiently high, the expansion valve opening control (that is, turbine outlet pressure control) is performed based on the value related to the turbine rotation speed. From the latter stage of precooling where 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, so supercritical expansion is simple and low cost. Chilling of the supercritical expansion turbine is ensured by reliably preventing turbine over-rotation and refrigerant liquefaction in the turbine, and maintaining the turbine operating pressure higher than before. It is possible to significantly increase the raw amount,
This has the effect of reducing the precooling time.

By changing the set pressure of the turbine outlet pressure and the set pressure range and changing the turbine expansion ratio, it is possible to adjust the amount of cold generation of the supercritical expansion turbine during steady operation.

[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 sectional front view showing a main part of a supercritical expansion turbine provided in the liquefaction refrigeration system.

FIG. 3 is a flowchart showing a control operation performed by a 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 expansion 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.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refrigeration load 3 High pressure line 4 Low pressure line 5a-5d Heat exchanger 6 Expansion valve (outlet valve) 10 Compressor 12 Supercritical expansion turbine 16 Tachometer (rotation speed detection means) 18 Outlet pressure gauge (outlet pressure detection means) 50 Control device (expansion valve control means) 52 Set value input device (set value changing means)

Claims (4)

[Claims] 1. A compressor for sending a refrigerant under pressure, and a high-pressure line for supplying the refrigerant sent under pressure from the compressor to a refrigeration load,
A low pressure line for returning the refrigerant from the refrigeration load to the compressor is provided, a supercritical turbine type expander is provided in the high pressure line, and in the liquefaction refrigeration apparatus provided with an outlet valve on the outlet side thereof, the supercritical turbine type The value related to the rotational speed of the expander and the turbine outlet pressure are detected, and the inlet pressure of the turbine expander is adjusted until the detected turbine outlet pressure drops to a predetermined set pressure higher than the critical pressure of the refrigerant. The opening of the outlet valve is controlled so that the value related to the rotational speed of the turbine expander is kept within a preset range while being kept at a pressure substantially equal to the discharge pressure of the compressor, and the turbine outlet pressure to be detected is After reaching the set pressure, a preset pressure range near the set pressure is maintained with the inlet pressure of the turbine expander kept at a pressure substantially equal to the discharge pressure of the compressor. Operation control method of liquefying refrigerating apparatus characterized by controlling the opening of the outlet valve to keep the detected pressure within. 2. The operation control method for a liquefaction refrigeration system according to claim 1, wherein the amount of cold generation of the supercritical expansion turbine is adjusted by changing the set pressure and the pressure range. Operation control method. 3. A compressor for sending refrigerant under pressure, and a high-pressure line for supplying the refrigerant sent under pressure from the compressor to a refrigeration load,
A low-pressure line that returns the refrigerant from the refrigeration load to the compressor, and a heat exchanger that performs heat exchange between the refrigerants flowing through both lines, the high-pressure line is provided with a supercritical turbine expander, In the liquefaction refrigeration apparatus provided with an outlet valve whose opening degree can be adjusted on the outlet side, a rotation detection unit that detects a value related to the rotation speed of the supercritical turbine expander,
Outlet pressure detection means for detecting the turbine outlet pressure of the supercritical turbine expander, and the turbine expansion until the detected turbine outlet pressure drops to a predetermined set pressure higher than the refrigerant critical pressure. Controls the opening of the outlet valve so that the value related to the rotational speed of the turbine type expander falls within a preset range while the inlet pressure of the machine is at a pressure substantially equal to the discharge pressure of the compressor, and the value is detected. After the turbine outlet pressure reaches the set pressure, the turbine expander inlet pressure is within a preset pressure range near the set pressure in a state where the inlet pressure of the turbine expander is substantially equal to the discharge pressure of the compressor. An operation control device for a liquefaction refrigeration system, comprising: an outlet valve control means for controlling the opening of the outlet valve so as to contain the detected pressure. 4. The liquefaction refrigeration system according to claim 3, further comprising set pressure changing means for changing the set pressure and the pressure range set by the outlet valve control means. Device operation control device.