JPH065143B2 - Control method for cryogenic liquefaction refrigeration system - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a cryogenic liquefaction refrigeration system, and more particularly to a control method suitable for a cryogenic liquefaction refrigeration system that requires various operating conditions such as reduction operation. is there.

[Background of the Invention]

Cryogenic liquefier, especially helium liquefier,
The theoretical power required to obtain refrigeration capacity at extremely low temperatures is about 70 times the refrigeration capacity. Furthermore, considering the efficiency of the equipment and the loss due to heat intrusion, the refrigeration capacity is actually about 50%.
It requires a capacity of 0 to 1000 times. Therefore, it is important not only to improve the efficiency of the device, but also to efficiently operate the device is an important issue.

In order to operate the device efficiently, optimum control of the compressor is required together with optimum adjustment in the cold box.

The conventional helium liquefaction refrigeration system is small in size, has a relatively small compressor power of several hundred KW, and does not operate continuously for a long time. The optimum control of was not performed.

Previously proposed compressor control methods include a method for controlling the capacity of the compressor (controlling the output flow rate) so as to keep the temperature at an appropriate position in the cold box constant, and a liquid in a liquid helium tank. There is a method of controlling the capacity of the compressor so as to keep the helium liquid level constant. (See JP-A-57-108557) However, these conventionally proposed control methods are methods for directly controlling the capacity of the compressor without adjusting the inside of the cold box, so that the optimum operation of the apparatus is performed. The situation could not be realized and was not practical.

[Object of the Invention]

An object of the present invention is to provide a control method for realizing optimum operation of a cryogenic liquefaction refrigeration system.

[Outline of Invention]

In a cryogenic liquefaction refrigeration system, an intermediate pressure tank that is generally used at an intermediate pressure between the suction pressure and the discharge pressure of a compressor is provided to control the suction pressure and the discharge pressure. On the other hand, the high-pressure refrigerant gas required in the cold box varies greatly depending on the load conditions, etc. Therefore, of the high-pressure refrigerant gas compressed by the compressor, the remainder not used in the cold box bypasses the medium pressure tank. It will be. That is, the bypass amount bypassed to the medium-pressure tank side is minimum when the load amount of the cooled object to which the refrigerant gas is supplied from the cold box is maximum, and the bypass amount is maximum when the load amount is minimum. The present invention suppresses the bypass amount, which unnecessarily increases when the load amount is small, to a constant value by performing control such that the output flow rate of the compressor also decreases when the load amount of the cooled object is small. It was done.
That is, since the bypass amount is suppressed to a constant value regardless of the magnitude of the load amount, the compressor can operate at the minimum necessary operating point according to the load amount, and highly efficient device operation can be realized.

Example of Invention

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 discharge pressure control valve, 4 is a suction pressure control valve, 5 is a high pressure bypass pipe,
6 is a low pressure bypass pipe, 7 is a high pressure line, 8 is a low pressure line, 10 is a cold box, 11a to 11e are heat exchangers, 12 is an expander inlet valve, 13 is a Joule-Thomson expansion valve (hereinafter,
(Abbreviated as JT valve), 14a and 14b are expanders, 15 is a liquid nitrogen introduction pipe as an auxiliary cold source, 16 is a liquefaction line, 17 is an expander line, 18 and 19 are conduits, 20 is a cooled object, and 25 is This is a controller that detects the flow rate in the low-pressure bypass pipe 6 and controls the output flow rate of the compressor 1 so that the flow rate in the low-pressure bypass pipe 6 becomes constant.

In the above configuration, most of the high pressure refrigerant gas compressed by the compressor 1 passes through the high pressure line 7 and the cold box.
After being introduced into the first heat exchanger 11 and cooled by exchanging heat with the liquid nitrogen and the low-pressure refrigerant gas in the first heat exchanger 11a, the liquefaction line 16
And branch to expander line 17. The high-pressure refrigerant gas branched to the expander line 17 passes through the expander inlet valve 12 and adiabatically expands in the first expander 14a to generate cold, and then the third heat exchanger 11c heats the low-pressure refrigerant gas and heat. After exchanging and further lowering the temperature, the second expander 14b again adiabatically expands to generate cold and join the low pressure line 8. On the other hand, the first heat exchanger 11a
After being cooled by, the high-pressure refrigerant gas branched to the liquefaction line 16 exchanges heat with the low-pressure refrigerant gas in the second to fifth heat exchangers 11b to 11e and is finally cooled to the reversal temperature or lower. , JT
The valve 13 adiabatically expands to a cryogenic refrigerant, which is sent to the cooled object 20 through the conduit 18. The refrigerant that has absorbed the heat load in the cooled object 20 returns to the cold box 10 again through the conduit 19,
After being refrigerated by exchanging heat with the heat exchangers 11e to 11a, it is circulated to the suction side of the compressor 1 through the low pressure line 8.

Of the high-pressure refrigerant gas compressed by the compressor 1, the remaining high-pressure refrigerant gas that has not been introduced into the cold box 10 is the high-pressure bypass pipe 5, the discharge pressure control valve 3, the intermediate pressure tank 2, the suction pressure control valve 4, The low pressure line 8 is bypassed by a bypass mechanism including the low pressure bypass pipe 6. in this case,
The controller 25 controls the output flow rate of the compressor 1 so that the bypass flow rate is minimized. This output flow rate control is performed, for example, by controlling the rotation speed of the compressor motor and opening / closing control of the suction slide valve of the compressor.

Next, the characteristics and effects of the apparatus according to the embodiment of the present invention having the above-described configuration and operation will be described. It is necessary to adjust the cold box 10 in order to operate the cryogenic liquefier refrigeration apparatus under optimum conditions. Especially, it is important to control distribution of high-pressure refrigerant gas between the expander line 17 and the liquefaction line 16.
This control is performed by adjusting the expander inlet valve 12 and the JT valve 13, and in this case the refrigerating output and the cold box 10
FIG. 2 shows the relationship with the amount of high-pressure refrigerant gas required in. Second
In the figure, the curve groups a to c shown by solid lines are performance curves when the opening of the expander inlet valve 12 is kept constant and the opening of the JT valve 13 is changed. A curve shown by a dotted line obtained as an envelope curve is a characteristic curve showing the minimum high-pressure frozen gas amount corresponding to a predetermined refrigerating output.

As described above, the cold box 10 is adjusted by adjusting the cold box 10 according to the load condition.
Therefore, the amount of high pressure refrigerant gas required varies. Furthermore, the object to be cooled
During precooling of 20, the amount of high-pressure refrigerant gas required in the cold box 10 is greatly reduced as compared with the steady state.

According to this embodiment, the amount of bypass to be increased or decreased corresponding to the amount of high-pressure refrigerant gas required in the cold box 10 is kept to the minimum, that is, the value of the amount of bypass at the time of maximum load. Since the output flow rate can be controlled, the optimum capacity control of the compressor can be performed very easily and efficiently regardless of the adjustment method in the cold box 10.

〔The invention's effect〕

As described above, according to the present invention, the output flow rate of the compressor is controlled so that the amount of the refrigerant gas bypassed by the bypass mechanism is kept constant. Therefore, the amount of high pressure refrigerant gas required in the cold box is controlled. There is an effect that the compressor can be optimally controlled in accordance with the increase and decrease of the above, and the operating power can be reduced to the necessary minimum.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing an embodiment of a control method of a cryogenic liquefaction refrigeration system according to the present invention, and FIG. 2 is a curve diagram showing an example of characteristics of a cryogenic liquefaction refrigeration system. . 1 ... Compressor, 2 ... Medium pressure tank, 3 ... Discharge pressure control valve, 4 ... Suction pressure control valve, 5 ... High pressure bypass pipe, 6
...... Low pressure bypass pipe, 7 ...... High pressure line, 8 ...... Low pressure line, 10 ...... Cold box, 11a to 11e ...... Heat exchanger, 12 ...... Expander inlet valve, 13 ...... Joule Thomson expansion valve, 14a ， 14b …… Expansion machine ， 15 …… Liquid nitrogen introduction pipe ， 16…
… Liquefaction line, 17 …… Expansion line, 18,19 …… Conduit,
20 ... Cooled object, 25 ... Controller.

Claims (1)

[Claims] 1. A high-pressure refrigerant gas compressed by a compressor is sent to a cold box which produces a cryogenic refrigerant via a high-pressure line, and a low-pressure refrigerant gas from the cold box is circulated to a suction side of the compressor via a low-pressure line. In addition, in the cryogenic refrigeration system in which a part of the high-pressure refrigerant gas in the high-pressure line is bypassed to the low-pressure line via the bypass mechanism, regardless of the load amount of the cooled object connected to the cold box, A method for controlling a cryogenic liquefaction refrigeration apparatus, wherein the output flow rate of the compressor is controlled so that the amount of refrigerant gas bypassed by the bypass mechanism is kept constant.