JPS6130181B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas liquefaction or low temperature apparatus.

Conventionally, in liquefiers and refrigerators that use low-boiling point gases such as nitrogen, oxygen, and hydrogen, and rare gases such as helium and argon, a portion of the high-pressure gas is cooled to below the reversal temperature. The remaining high-pressure gas is cooled by the obtained low-pressure low-temperature gas through a heat exchanger, and then the high-pressure gas is isenthalpically expanded using a Joel-Thomson valve (hereinafter referred to as "JT valve"). , a method of liquefying or lowering the temperature of the gas is used.

In such devices, all of the expansion motive power obtained by expanding the high pressure gas is wasted to the outside in the form of heat. That is, a turbo blower is directly connected to a turbo expander, the work done by the expansion drives the turbo blower, and the blower compresses gas. The compressed gas is water-cooled to remove the heat of compression, expands through an expansion valve, and is sucked into the turbo blower again and circulated within the blower system. Alternatively, if a reciprocating expander is used, its output drives an oil pump and similarly discards the heat in the form of heat.

Turbo expanders and blowers cost tens of thousands to hundreds of thousands
Because they require high-speed rotation (rpm) and are in contact with cryogenic gas at temperatures of several tens of degrees Celsius, oil-lubricated bearings cannot be used; instead, gas bearings are used instead. There are both hydrodynamic and hydrostatic types of gas bearings, but the hydrostatic type is superior in terms of reliability, controllability, and maintainability. However, the static pressure type requires a portion of the compressed gas to be supplied to the bearings, which reduces the amount of high-pressure gas that can be used effectively, resulting in lower equipment efficiency compared to the dynamic pressure type. Ta.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned problems with expander output and bearings in the prior art.

This will be explained below using figures.

FIG. 1 schematically shows a conventionally used helium liquefaction refrigerator.

The gas compressed by the main compressor 1 is water-cooled by an aftercooler 2 and enters a cold box 3. The cold box 3 is a high-vacuum container that prevents convection heat transfer between the low-temperature equipment inside and the room-temperature outside. 4 to 10 are heat exchangers for exchanging heat between high-pressure gas and low-pressure low-temperature gas in countercurrent flow. The heat exchangers 4 and 5 are capable of exchanging heat with liquid nitrogen flowing inside a tube 13 having an inlet 11 and an outlet 12, and cool the high-pressure gas to approximately the nitrogen temperature.
A part of the high pressure gas leaving the heat exchanger 6 enters the first stage turbo expander 14, undergoes adiabatic expansion within the machine, becomes low pressure low temperature gas, and exchanges heat with the remaining high pressure gas in the heat exchanger 7. A portion of the gas leaving the heat exchanger 8 enters the second stage expander 15, and heat exchanges with the remaining high pressure gas in the heat exchanger 9.

The high-pressure gas leaving the heat exchanger 10 undergoes isenthalpic expansion in the JT valve 16, etc., and then partially liquefies in the liquid reservoir 17, and the remaining saturated gas is transferred to the heat exchangers 10 to 4.
After the high pressure gas undergoes heat exchange in sequence, it exits the cold box 3 and returns to the main compressor 1. The liquid liquefied in the liquid reservoir 17 may be taken out from the middle of the pipe 18, or it may be evaporated by removing heat from the load 20 in the external evaporator 19, and the entire amount of the liquid taken out becomes saturated gas and is taken out from the pipe 21. There are two cases: returning to cold box 3;

A turbo blower 22 is directly connected to the turbo expander 14, and the same type of working gas as in the turbo expander 14 is circulated within the blower system. The gas compressed by the blower is transferred to an aftercooler 23.
After being cooled with water, it is sucked into the blower 22 again through the expansion valve 24. The same applies to the blower 25. Note that 28 and 29 are aftercooler 2
The water inlet and outlet 3, 26 and 27 are the aftercooler and expansion valve of the turbo blower 25 system, respectively, and 30 and 31 are the aftercooler 26.
water inlet and outlet.

As is clear from the above explanation, the work done by the turbo expanders 14 and 15 is wasted as heat to the outside. Turbo expander 14
The rotating shafts connecting the turbo blower 22 or 25 to the turbo blower 22 or 25 are supported by gas bearings 32 and 33, respectively. This conventional example uses a hydrostatic gas bearing, in which a portion of high-pressure gas is supplied to the bearing section, and the rotating shaft is supported in a non-contact state by the static pressure of the gas.

The pressure regulating valve 35 maintains the suction pressure of the main compressor 1 at a set pressure. During liquefaction operation, when a part of the compressed gas liquefies, the valve 3 is removed from the gas tank 36 to compensate for the liquefaction.
Gas is replenished into the system through 5. Valve 37 maintains the discharge pressure of main compressor 1 at a set value. During refrigeration operation, if the discharge pressure increases due to load fluctuation, the valve 37
Gas bypasses the gas tank 36 and maintains the discharge pressure constant. 38 is a bypass valve.

The principle of FIG. 2 is exactly the same as that of FIG. 1, except that a reciprocating expander is used instead of a turbo expander.

14a, 15a are reciprocating expanders, which include suction valves 22, 27, discharge valves 23, 26, cylinder 24,
28, pistons 25, 29, etc. are housed in the cold box 3 in order to come into contact with the cryogenic gas. Since the pistons 25 and 29 and the cylinders 24 and 28 come into contact with cryogenic gas, oil lubrication is impossible and they have an oil-free structure. Bearings and other parts that require oil lubrication are all installed externally.
The reciprocating expanders 14a and 15a are coupled to the coupling 3
0 and 31 are connected to oil pumps 32 and 33. The oil whose pressure has been increased by the pumps 32 and 33 is cooled by the water coolers 34 and 39, and the oil is cooled by the water coolers 34 and 39.
It reaches oil tanks 42 and 43 via 0 and 41. Therefore, all the output of the expander is wasted as heat.
At present, most expanders are turbo type, and reciprocating type is only used in some small scale machines.

The reason is that 1. Difficult to maintain airtightness.

That is, since the piston and cylinder are oil-free, it is difficult to maintain airtightness. In addition, seals are required for the piston rod, valve operating rod, etc. to separate the inside of the system from the atmosphere, but it is difficult to maintain airtightness because of the reciprocating movement.

2. It is larger than the turbo type, and there is a large amount of heat intrusion from the exposed part into the cold box.

3. There is noise and vibration.

Examples include.

However, the turbo type also has problems. In other words, there are two types of gas bearings used in turbo systems: static pressure type and dynamic pressure type.The former requires some compressed gas to be supplied to the bearing, but the latter does not, so the coefficient of performance of the device is The latter wins. On the other hand, the latter becomes unstable when starting and stopping, and is likely to cause a seizure accident due to contact between the shaft and the bearing. Originally, the latter has a weak shaft support force, so accidents are likely to occur during operational fluctuations and during so-called cooling down, in which the equipment is cooled from room temperature to an extremely low temperature. On the other hand, the former has a large shaft support force and is always stable, and is superior to the latter in terms of reliability, operability, and maintainability.

Next, the reason why the output of the expander is not effectively utilized in conventional devices will be explained.

Generally, it is not appropriate to use the expander output outside the system, because when operating the device, the expander output is not necessarily required outside the system at the same time. Therefore, it is desirable to utilize the expander output within the system. In this case, the first thing to consider is to use it as a driving force for the main compressor, but this is extremely difficult in a cryogenic liquefaction refrigerator due to its structure. The next possible method is to drive a blower. The problem in this case is how to effectively utilize the gas compressed by the blower.

A first method is to use a blower on the lower stage side of the compressor.

Figure 3 shows this method. The entire amount of suction gas from the main compressor 1 is guided to blowers 22 and 25, and the gas compressed here is sucked into the main compressor 1. However, this method is difficult to implement using cryogenic equipment. This is because the expander output decreases as the expander suction temperature decreases, and in the case of a helium refrigerator, it may be less than a few percent of the compressor required power. As described above, this method is not used in cryogenic equipment because the expected results cannot be obtained even if the entire amount of gas taken into the compressor is compressed using a blower.

As a second method, a blower may be used to compress part of the intake gas that reaches the main compressor, and the outlet gas may be sent to the second stage of multistage compression.

Figure 4 shows this method. Generally, in refrigerators that liquefy hydrogen or helium, it is common to perform multistage compression as shown in the figure. In this case, if a reciprocating main compressor is used, the discharge pressure of the first stage compressor 1 is generally higher than the discharge pressure of the turbo blowers 22 and 25, so the turbo blowers must be multi-staged. , the structure of the turbo blower becomes complicated. To eliminate this inconvenience, if a reciprocating blower is used, the blower discharge pressure can be kept high. However, driving with the turbo expanders 14 and 15 requires a reduction gear with a large reduction ratio. Therefore, it is not desirable to connect a reciprocating blower to the turbo expander 1, but it is more convenient if the reciprocating blower is driven by the reciprocating expander. In the end, it is optimal to combine reciprocating multi-stage compression with a reciprocating expander and a reciprocating blower.

18, 19, and 20 are the second and third rows, respectively.
This is the fourth stage compressor.

In this case, as mentioned above, the reciprocating type has several drawbacks, and furthermore, the expander output is very small in cryogenic equipment, so if the blower discharge pressure is increased as much as necessary, the flow rate will be very small, making it impractical. becomes scarce. Another possible combination is to combine a turbo-type multi-stage compressor with a turbo-type expander and a turbo-type blower. In this case, turbo-type multi-stage compressors have a large number of stages for light gases such as helium and hydrogen, are more expensive than reciprocating types, and are also limited in response to fluctuations in operating conditions. is not used.

For the above reasons, the output of the expander is not effectively utilized in cryogenic liquefaction refrigerators.

The present invention eliminates the various disadvantages mentioned above,
The purpose is to effectively utilize the output of the expander and to improve the reliability and performance of the device.

Next, examples of the present invention will be described.

Fig. 5 shows one embodiment, and the principle is exactly the same as Fig. 1, but a screw type compressor is used as the main compressor, and the blower outlet gas is transferred to the confined space of the screw type compressor or compressed. It is distinctive in that it guides people through the process.

In the figure, reference numeral 1a denotes a screw compressor, which is driven by a prime mover 24 via a coupling 23. Oil separator 2 for oil injection screw type compressors
It is necessary to provide 6. The suction gas line and the discharge gas line are exactly the same as in FIG. 1.
The expanders 14 and 15 and the blowers 22 and 25 as gas pressurizers are both turbo type and are integrated by a directly connected shaft, and the directly connected shaft is supported by gas bearings 32 and 33. The gas bearing may be either a hydrodynamic type or a static pressure type, but as described above, the latter is superior to the former in terms of reliability, controllability, and maintainability. Further, according to the embodiment, it is possible to prevent a decrease in the efficiency of the device due to the bearing supply gas, which is a disadvantage of the static pressure type.

A part of the low pressure gas exiting the heat exchanger 4 is guided to the suction side of the turbo blowers 22 and 25, and the gas compressed by the blowers passes through the constant pressure valve 27 to the confined space or compression stroke of the screw compressor 1a. It is fed into the machine through a suction hole 28 provided at one point. The position of the suction hole 28 is determined from the discharge hole 33 after the tooth-shaped space formed by both the male and female rotors is completely sealed by the rotor casing 29, the rotor suction end surface 30, the rotor discharge end surface 31, and the rotor meshing contact line. It may be provided at any position immediately before being discharged (this is referred to as a confined space), that is, during a stroke in which the intake gas is compressed (this is referred to as a compression stroke). That is, the suction hole 28 may be provided in a confined space having an internal pressure equal to or slightly lower than the outlet pressure of the blower or in a compression stroke position.

The features of feeding the discharge gas of the blower into the confined space of the screw compressor or into an appropriate position in the compression stroke are as follows.

1. Effective use of expander output becomes possible.

The entire amount of gas compressed by the blower directly connected to the expander is used as part of the compressed gas of the compressor. Therefore, the expander output is effectively used as part of the compression power of the main compressor.

2. The volumetric efficiency of the compressor is improved.

Since the gas from the blower is fed into the compression stroke (confined space) of the screw compressor, the amount of gas processed by the compressor increases by that amount even though the amount of gas sucked into the compressor remains the same. In other words, performance efficiency can be increased.

3. The liquefaction efficiency or coefficient of performance of the device is improved compared to the conventional method using hydrostatic gas bearings.
In other words, in addition to effectively utilizing the expander output and increasing the volumetric efficiency of the compressor, by feeding gas into the confined space of the screw compressor.
With the addition of the feature of improved KW/m ² /h (the required shaft power in KW to compress 1 cubic meter of gas in 0 hours), the liquefaction efficiency or coefficient of performance of the device is significantly improved.

Conventional equipment using hydrostatic gas bearings has the disadvantage that a portion of the compressed gas is supplied to the bearings, which reduces the amount of compressed gas that can be used effectively compared to hydrodynamic gas bearings. Ta. According to the method of the present invention, as mentioned in 1 and 2 above, the disadvantage of reducing the amount of high pressure gas that can be effectively used is eliminated by utilizing the output of the expander and improving the volumetric efficiency of the main compressor, compared to the conventional method. The efficiency of the device is significantly improved.

The embodiment shown in FIG. 5 is a combination of a turbo expander and a turbo blower, but as described above, a combination of a reciprocating expander and a reciprocating blower as a gas pressurizer is also possible.

This embodiment is shown in FIG. Since the reciprocating type can have a higher blower compression ratio than the turbo type, it can be used not as a blower but as a compressor. That is, as shown in the figure, reciprocating compressors 22a and 25a can be combined with reciprocating expanders 14a and 15a. 29 is a suction valve, 30 is a discharge valve, and 31 and 32 are couplings.

The reciprocating type has greater mechanical loss than the turbo type, and if the expander output is small, the blower may not be able to be driven. Therefore, when the suction temperature of the expander is high, the expander output increases, so a reciprocating type combination is effective. On the other hand, if the expander has a low suction temperature and the expander output is small, a turbo type combination with low mechanical loss is appropriate. In terms of gas types, a reciprocating type can be used for gases with comparatively high boiling points such as nitrogen and oxygen, but a turbo type combination is suitable for gases such as hydrogen and helium.

The cycle represented by FIG. 1 is called a Claude cycle and is widely put into practical use. Because turbo expanders rotate at high speeds using bearings while generating extremely low temperatures, they are extremely vulnerable to contamination by foreign substances such as foreign gases such as air (which condense and solidify) and dust from pipes. For this reason, the expander cycle is sometimes used as a separate cycle from the liquefaction cycle. This cycle is called the Preyton cycle, and FIG. 7 shows a conventionally used Preyton cycle.

Next, the flow of this Preyton cycle will be explained.

This cycle consists of two independent systems. One is a system including the JT valve 16 and the main compressor 1, and this is called the JT system. Others are expansion machines 14,1
5 and a compressor 39, and this is called an expander system. The principle is exactly the same as the Claude cycle shown in Figure 1, except that the JT system and expander system are provided independently. The gas compressed by the main compressor 1 of the JT system is cooled with water in the aftercooler 2 and enters the cold box 3. By heat exchangers 4 to 10,
The high-pressure gas, which has been cooled to below the inversion temperature by the return gas and the expander outlet gas, is isenthalpically expanded by the JT valve 16 and partially liquefied in the liquid reservoir 17. The remaining saturated gas becomes return gas and returns to the main compressor 1 after sequentially exchanging heat with the high pressure gas as a counterflow.

The gas compressed by the compressor 39 of the expander system enters the cold box 3 via the aftercooler 40, and sequentially exchanges heat with the expander outlet gas, and at the outlet of the heat exchanger 6, a part of the gas is transferred to the first stage expander 4. The remaining high pressure gas enters the second stage expander 15 at the exit of the heat exchanger 8, where it undergoes adiabatic expansion to generate the lowest temperature of the expander system. After exchanging heat with the high pressure gas of the system, the return gas exchanges heat with the high pressure gas of the JT system and the high pressure gas of the expander system in a counterflow and returns to the compressor 39. Pressure regulating valve 41, 43, 44
Each gas tank 42 has the same function as the JT system. When the gas bearings 32 and 33 are of the static pressure type, a portion of the high pressure gas is supplied from the inlet of the heat exchanger 4 through the pipe 34. The blower system is exactly the same as that shown in FIG. Even in this Playton cycle, the output of the expander is wasted as heat.

FIG. 8 shows an example of the present invention in which the output of the expander is effectively used to improve the efficiency of the device.

The JT system is exactly the same as Figure 7. A feature of the present invention is that a screw type compressor 39a is used in the expander system of the Preyton cycle, and the turbo type expanders 14, 15 and the turbo type blowers 22, 25 as gas pressurizers are rotated by gas bearings 32, 33. A part of the suction gas reaching the screw compressor 39a is sucked into the turbo blowers 22, 25, and the gas compressed here is transferred to the confined space of the screw compressor 39a or compressed. It is where it is fed into the machine through a suction hole 28 made in the stroke.

The effects of the present invention are as described in FIG. 5, and the output of the expander can be used effectively, and the volumetric efficiency of the compressor can be improved. Furthermore, the liquefaction efficiency or coefficient of performance is improved compared to conventional systems using hydrostatic gas bearings, and the drawbacks of hydrostatic bearings can be eliminated.

As for the combination of the expander and the blower, in addition to the above-mentioned turbo type, a reciprocating type combination is also possible. FIG. 9 shows an embodiment of the present invention using a combination of a reciprocating expander and a reciprocating compressor as a gas pressurizer.

That is, reciprocating compressors 22a and 25a are operated by reciprocating expanders 14a and 15a, respectively.
A part of the suction gas is sucked into the screw compressor 39a of the expander system and compressed, and the discharged gas is sent into the machine through the suction hole 28 provided in the confined space of the screw compressor 39a. It's becoming like that.

In this way, in the Preyton cycle expander system, the turbo blower is driven by the turbo expander, or the reciprocating blower or reciprocating compressor is driven by the reciprocating expander, and the compressor of the expander system is A part of the suction gas is sucked into a blower or compressor driven by an expander, and the discharge gas compressed here is sent to the confined space or compression stroke of the screw compressor, which eliminates the conventional method. It becomes possible to eliminate drawbacks and significantly improve the efficiency of the device.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a gas liquefaction device using a conventionally used Claude cycle type turbo expander, and Fig. 2 is a system diagram of a gas liquefaction device using the expander shown in Fig. 1 as a reciprocating expander. Figure 3 is a system diagram of a gas liquefaction system that directs the entire amount of suction gas into the compressor to a blower, and Figure 4 shows a system diagram of a gas liquefaction system that leads a portion of the suction gas into the compressor to a blower. System diagram, FIG. 5 is a system diagram of the first embodiment of the gas liquefaction apparatus of the present invention using the Claude cycle system, and FIG. 6 is a system diagram of the second embodiment of the gas liquefaction system of the present invention using the Claude cycle system. , FIG. 7 is a system diagram of a gas liquefaction device using the conventionally used Preyton cycle, FIG. 8 is a system diagram of a third embodiment of the gas liquefaction device of the present invention using the Preyton cycle method, and FIG. 9 This is a system diagram of a fourth embodiment of the gas liquefaction apparatus of the present invention using the Preyton cycle system. 1... Main compressor, 1a... Screw type compressor, 4
10... Heat exchanger, 14, 15... Turbo expander as an expander, 14a, 15a... Reciprocating expander as an expander, 22, 25... Turbo blower as a gas pressurizer, 22a, 25a... Reciprocating blower or reciprocating compressor as gas pressurizer, 2
8... Suction hole, 39... Main compressor, 39a... Screw type compressor.

Claims (1)

[Claims] 1. A part of the high-pressure gas compressed by the screw compressor is adiabatically expanded through the expander, and the remaining high-pressure gas is expanded through the heat exchanger using the low-pressure low-temperature gas obtained by this expansion. In an apparatus that liquefies or lowers the temperature of gas by cooling and then reducing the pressure and expanding the high-pressure gas, the suction side is connected to the suction gas path leading to the suction side of the screw compressor, and the suction side is connected to the suction gas path leading to the suction side of the screw compressor. A gas liquefaction or low-temperature device comprising a gas pressurizer whose discharge side is connected to an inlet gas path leading to a confined space of the machine, and the gas pressurizer is connected to the expansion machine. . 2. The gas liquefaction or low-temperature device according to claim 1, wherein the expander is a turbo expander and the gas pressurizer is a turbo blower. 3. The gas liquefaction or low-temperature device according to claim 1, wherein the expander is a reciprocating expander and the gas pressurizer is a reciprocating compressor. 4 The high-pressure gas compressed by the screw compressor of the expansion machine system is adiabatically expanded through the expander, and the low-pressure low-temperature gas obtained by this expansion is used to transfer the high-pressure gas compressed by the Jordan compressor to the heat exchanger. In an expansion machine system of a device that liquefies or lowers the temperature of gas by cooling the high-pressure gas through the compressor, and then reducing the pressure and expanding the high-pressure gas, the suction side is connected to the suction gas path leading to the suction side of the screw compressor. and a gas pressurizer whose discharge side is connected to the feed gas path leading to the confined space of the compressor, and the gas pressurizer is connected to the expander. Liquefaction or cryogenic equipment. 5. The gas liquefaction or low-temperature device according to claim 4, wherein the expander is a turbo expander and the gas pressurizer is a turbo blower. 6. The gas liquefaction or low-temperature device according to claim 4, wherein the expander is a reciprocating expander, and the gas pressurizer is a reciprocating blower or a reciprocating compressor.