JPH0248827B2 - GOKUTEIONEKIKASOCHIOYOBISONONTENHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a cryogenic liquefaction device and a method of operating the same, and particularly to a cryogenic liquefaction device suitable for operation during precooling and a method of operating the same.

[Background of the invention]

FIG. 1 shows the operating procedure during precooling in a conventional cryogenic liquefaction device, such as a helium liquefaction machine. FIG. 1 shows a gas helium liquefaction machine. The liquefaction machine 1 basically consists of a first heat exchanger 2, a second heat exchanger 3, a third heat exchanger 4, and a fourth heat exchanger 5. , a fifth heat exchanger 6, and a first expansion turbine 7 for cold generation.
Second expansion turbine 8 and Joel-Thomson valve 9
Consists of. The high pressure gas helium at room temperature compressed by the compressor 10 flows into the high temperature end of the first heat exchanger 2 . The high pressure gas helium flowing out from the cold end of the first heat exchanger 2 is transferred to the flow rate or pressure regulating valve 11.
A part of the gas is distributed to the first expansion turbine 7 through the first expansion turbine 7, and after generating cold in the first expansion turbine 7, the cold is given to high-pressure gas helium in the third heat exchanger 4, and then again to the second expansion turbine. After generating cold in the fourth heat exchanger 8, the cold is introduced into the low-pressure inlet on the low temperature end side of the fourth heat exchanger 5, and the cold is provided to the fourth heat exchanger 5. here,
The Joel-Thomson valve 9 cannot practically utilize the cooling after expansion unless the temperature of the high-pressure gas helium on the valve inlet side drops to about 20K or less. When the inlet temperature of the Joel-Thomson valve 9 becomes 20K or less, the expanded low-temperature gas helium at the outlet of the Joel-Thomson valve 9 flows into the heat exchanger 6 from the low-temperature end inlet of the fifth heat exchanger 6.
〜2 sequentially, and the cold temperature cools each heat exchanger 6〜2.
Cool the high pressure gas helium inside. In this way, the temperature of the gas helium at the inlet of the Joel-Thomson valve 9 gradually decreases, and at the outlet of the Joel-Thomson valve 9, a part of the expanded low-pressure gas helium is liquefied and transferred to the gas-liquid separator 9'. Liquefied helium is produced.
The time it takes for the entire liquefier to start liquefying from room temperature is called a cool-down time, and when using a liquefier, the shorter the cool-down time, the more advantageous it is. As one method of shortening the cool down time, the low temperature end inlet of the fifth heat exchanger 6,
The low temperature end inlet of the first heat exchanger 2 and the bypass valve 12
The low-temperature, low-pressure gas at the outlet of the second expansion turbine 8 and a portion of the gas expanded by the Joel-Thomson valve 9 are passed through the bypass valve 12 to the low-temperature end inlet of the first heat exchanger 2. There is a way to get it back.
By this method, the temperature of the fifth heat exchanger 6 is cooled down to the expansion outlet temperature of the second expansion turbine 8 of about 15 K or less in a short time. That is, the heat exchanger on the low temperature side, for example, the fourth heat exchanger 5 and the fifth heat exchanger 6
, if the temperature of the low-pressure return gas is high, the pressure drop when passing through the heat exchanger becomes large, making it impossible to supply the high-pressure gas at a predetermined flow rate.However, this high-temperature low-pressure return gas is passed through the conduit 13 and bypassed to the high-temperature part. By doing so, pressure loss can be eliminated, and a predetermined flow rate of high-pressure gas can be supplied to the expansion turbine, etc., and cold generation can be increased, resulting in faster cooling. Also, the temperature of the high pressure helium gas on the inlet side of the Joel-Thomson valve 9 is approximately
In the case of a high temperature of 20K or more, practically usable cold is not generated, so the high temperature gas flows to the low pressure gas return side of the fifth heat exchanger 6, and the high pressure gas of the fifth heat exchanger 6 However, by bypassing this high temperature gas to the conduit 13, the fifth heat exchanger 6 is gradually cooled by the high pressure gas cooled by the fourth heat exchanger 5. Thereafter, the bypass valve 12 is throttled, the bypass flow rate is stopped, and the Joel-Thompson valve 9 is cooled to reach a liquefaction start state. FIG. 2 shows the relationship between the temperature θ of the thermometer 14 at the outlet of the Joel-Thomson valve 9 and the time T from the start of cool-down, and the relationship between the temperature θ of the thermometer 14 at the outlet of the Joel-Thomson valve 9 and the bypass valve 12 at the same time.
The relationship between the opening degree of the Joel-Thomson valve 9 and the opening degree of the Joel-Thomson valve 9 is shown. Each valve has a characteristic that the flow rate of gas passing through the valve increases as the degree of opening increases. The conventional setting value change of this valve opening and its switching timing are as follows.
When the temperature drop rate at the outlet of the Joel-Thomson valve 9 begins to decrease, for example, point A where the temperature drop rate decreases from the start of liquefaction operation, that is, the cool-down start point S in Figure 2, the temperature drop rate after switching decreases. point B, then points C and D, and point E, which reached the liquefaction temperature. In the prior art, this operation uses the value of the thermometer 14 as an input value, and the set temperature values at each point A to E as the judgment value for the switching condition to the set valve opening. This was done using sequence control.

In this control method, the following disadvantages occur in order to shorten the cool-down time. First, it is necessary to increase the number of times the sequence control is switched and to set the optimum valve opening degree at each switching point. In other words, the set values for the temperature and valve opening are determined by actually operating the liquefier and measuring the temperature and valve opening using the thermometer 14.
In consideration of the characteristics of the bypass valve 12 and the Joel-Thompson valve 9, values suitable for the liquefier must be determined. This requires a lot of time and operating costs. Second, in order to shorten the cool-down time, the number of sequence changes must be increased. This increases the amount of sequence programs and increases the cost of the controller. Thirdly, changes in the thermometer and valve characteristics over time, such as changes in absolute temperature values due to changes in the power supply and element characteristics of the thermometer, dirt on the valve, clogging due to dust, etc.
The problem is that erroneous control occurs due to changes in the actual opening degree due to changes in the output of the valve stem drive section.

[Object of the Invention] An object of the present invention is to provide a method for controlling cool-down of a liquefier, which can shorten the cool-down time and whose controllability is not impaired over time.

[Summary of the invention]

The present invention branches a part of refrigerant gas from a compressor and adiabatically expands it to generate cold, cools the refrigerant gas by exchanging heat with return gas containing the cold, and cools the cooled refrigerant gas. In a device that is adiabatically expanded and liquefied by an expansion valve, a flow path that branches from a return line downstream of the expansion valve and bypasses a heat exchanger, a valve that adjusts the flow rate of return gas in the flow path, and an expansion valve. A temperature detector detects the return gas temperature in the return line on the downstream side, and a second differential value of temperature with respect to time is calculated based on the temperature value detected by the temperature detector, and the valve is controlled based on the second differential value. During pre-cooling operation, a valve that branches from the return line downstream of the expansion valve, bypasses the heat exchanger, and returns the return gas to the compressor side, is installed on the downstream side of the expansion valve during precooling operation. By controlling the return gas temperature of the return line by detecting and calculating the temperature using the second-order differential value with respect to time, the cool-down time is shortened and controllability is not impaired.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 3 to 6.

FIG. 5 shows an example of a cryogenic liquefaction device. This figure shows the control mechanism of the bypass valve.
Only the fourth heat exchanger 5 and subsequent parts of the liquefier shown in the figure are shown. In this figure, the same reference numerals as in FIG. 1 indicate the same members, and the parts omitted from illustration are the same as in FIG. 1, and their explanation will be omitted. This figure differs from FIG. 1 in that the signal from the thermometer 14 is input to a computing unit 15, and the bypass valve 12 is controlled by the computing unit 15.

This control will be explained below.

First, FIG. 3 shows a temperature distribution model of temperature θ and time T during cool-down of the cryogenic liquefaction device as shown in FIG. When the temperature θ shows such a temperature distribution, the temperature drop rate, that is,
The temperature difference dθ (that is, the first-order differential value) before and after the elapse of time dT changes as time passes between each of A ₁ to A ₁₁ as shown in FIG. 4. The temperature distribution model in FIG. 3 occurs when the opening degree of the bypass valve 12 is significantly reduced at point _A4 in the figure. That is, the temperature from A ₆ to A ₈ is higher than the temperature at A ₆ . This is because the flow rate of the still-high-temperature gas that has exited the Joel-Thomson valve 9 flowing toward the fifth heat exchanger 6 increases, resulting in a large pressure drop in the fifth heat exchanger 6, which causes high pressure to flow into the liquefier. As the gas supply decreases,
Joel-Thomson valve 9 flowing to the fifth heat exchanger 6 side
As the flow rate of the still-hot gas increases,
This is because the high-pressure gas in the fifth heat exchanger 6 is temporarily deprived of cooling. After this, the supplied high-pressure gas is gradually cooled down, and the gas temperature on the high-pressure side and the low-pressure side becomes well balanced, and the temperature starts to drop again. At this point, additional bypass valve 1
If the opening degree of 2 is decreased, A ₆ due to the above reason
It takes time for the temperature to drop below , and the cool-down time becomes longer.

Therefore, in the relationship between the temperature drop rate dθ/dT and the time T shown in FIG. 4, if the curve of dθ/dT is downward to the right in the figure, the opening degree of the bypass valve 12 is increased and the curve is to the right in the figure. In the case of an increase, the opening degree of the bypass valve 12 is controlled to be decreased. Note that in this case, since the purpose is to lower the temperature, the direction in which θ falls is defined as positive, and the direction in which θ increases is defined as negative. In this case, in order to further simplify the control, calculate the differential of the temperature drop rate dθ/dT in Figure 4, that is, d ² θ/dT ² (secondary differential value), and calculate d ² θ/dT ²
When <0, the opening degree of the bypass valve 12 is increased, and when d ² θ/dT ² ≧0, the opening degree of the bypass valve 12 is controlled to be decreased.

FIG. 6 shows a temperature drop curve when cool-down is performed according to the present invention. According to this control method, from the liquefaction machine cool-down start time S to the liquefaction start time E, the bypass valve opening degree is set at a time interval.
By gradually decreasing dT, the temperature θ after the Joel-Thompson valve can be rapidly lowered, and the cool-down time can be greatly shortened.

In addition, in this control method, since the difference between the temperature input values from the thermometer 14 is used as an indirect input value, the absolute value of the input value of the thermometer 14 does not have to match the actual temperature, and the thermometer 14 Controllability will not be impaired unless the characteristic, for example, that the output value decreases as the temperature decreases, is reversed or the output value becomes constant. This also applies to the characteristics of the valve opening and flow rate.
In other words, even if the actual valve opening changes due to dust or a change in the output of the valve stem drive unit, the CV value will not impair controllability as long as the flow rate increases as the opening increases.

In addition, since this control method does not require the actual temperature after the Joel-Thomson valve, the same control method can be used even for different types of liquefiers with different heat exchanger sizes. This eliminates the need for trial runs to select control judgment values.

Furthermore, in this control method, it is only necessary to judge whether to increase or decrease the opening degree of the bypass valve when (d ² θ/dT ² ) is ≦0 or >0, and the configuration of the controller and the amount of calculation program can be reduced. , the cost of the controller can be reduced.

〔Effect of the invention〕

As described above, according to the present invention, the control time pitch dT of the valve opening can be shortened to about 1 minute, so compared to the cool-down time of about 30 minutes in conventional sequence control, the control time pitch dT of the valve opening can be shortened to about 1 minute. Cooldown time can be reduced by 30%. In addition, since the temperature calculation for control is based on the temperature difference, the control function does not deteriorate due to aging of the thermometer, and the opening of the control valve is also controlled by adding and subtracting minute openings. In order to
This has the effect of preventing the control function from deteriorating due to changes in the CV value of the valve over time.

[Brief explanation of drawings]

Figure 1 is a system diagram of a liquefaction machine according to the prior art;
The figure is a diagram showing the temperature-time relationship during cool-down according to the prior art, Figures 3 and 4 are temperature-time relationship diagrams explaining the cool-down control method according to the present invention, and Figure 5 is a diagram showing the temperature-time relationship according to the present invention. FIG. 6 is a system diagram showing an example of a liquefier in which the method is implemented, and FIG. 6 is a diagram showing the relationship between temperature and time during cool-down according to the present invention. 1... Liquefier, 2... First heat exchanger, 3... Second heat exchanger, 4... Third heat exchanger, 5... Fourth heat exchanger, 6... Fifth heat exchanger , 7...first expansion turbine, 8...second expansion turbine, 9...joule-Thompson valve, 9'...gas-liquid separator, 10...compressor, 11...pressure regulating valve, 12... Bypass valve, 13... Conduit, 14... Thermometer, 15... Arithmetic unit.

Claims (1)

[Scope of Claims] 1. A compressor that boosts the pressure of refrigerant gas, an expander that branches off and adiabatically expands a part of the refrigerant gas from the compressor to generate cold and merges it with low-pressure return gas, and A cryogenic liquefaction device comprising: a heat exchanger that cools the refrigerant gas by exchanging heat with a low-pressure return gas having the refrigerant gas; and an expansion valve that adiabatically expands and liquefies the cooled refrigerant gas, the expansion valve being downstream of the expansion valve. a flow path that branches from the return line and bypasses the heat exchanger; a valve that adjusts the flow rate of return gas in the flow path; and a temperature detector that detects the temperature of the return gas in the return line downstream of the expansion valve; A cryogenic liquefaction device comprising: a control device that calculates a second-order differential value of temperature with respect to time based on the temperature value detected by the temperature detector, and controls the valve based on the second-order differential value. 2. A part of the refrigerant gas from the compressor is branched and adiabatically expanded to generate cold, and a heat exchanger exchanges heat with the return gas having the cold to cool the refrigerant gas, and the cooled gas is cooled. In a method of operating a cryogenic liquefaction device in which refrigerant gas is adiabatically expanded and liquefied by an expansion valve, the return gas is branched from a return line downstream of the expansion valve, bypasses the heat exchanger, and returns to the compressor side. A cryogenic liquefaction method characterized in that a valve that adjusts the flow rate of the expansion valve is controlled by a second-order differential value with respect to time of a temperature calculated by detecting a return gas temperature in a return line downstream of the expansion valve during precooling operation. How to operate the equipment.