JP2020060103A - Cryogenic liquefied gas pump, and operation control method for cryogenic liquefied gas pump - Google Patents

Abstract

To provide a cryogenic liquefied gas pump capable of stably operating with liquid level variation suppressed, and an operation control method therefor.SOLUTION: A cryogenic liquefied gas pump 1 according to the present invention is a non-immersion type cryogenic liquefied gas pump 1 comprising an electric motor 3, an impeller 5, a shaft 7 connecting the electric motor 3 and the impeller 5, a magnetic bearing 9 supporting the shaft 7, and a housing 11 consisting of a motor housing 11m, an impeller housing 11i, and a shaft housing 11s covering those constituent devices. The cryogenic liquefied gas pump comprises: a temperature detection part 13 which is provided on an outer surface of the shaft housing 11s and detects temperature variation of the shaft housing 11s with the internal liquid level; a gas injection/discharge part 15 which injects/discharges a gas for liquid level adjustment into and from an internal space of the housing 11; and a gas injection/discharge mechanism part 17 which inputs a temperature detection signal of the temperature detection part 13 and injects/discharges the gas into and from the gas injection/discharge part 15 according to the temperature detection signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a low temperature liquefied gas pump used for transferring a low temperature liquefied gas, and an operation control method for the low temperature liquefied gas pump.

  In recent years, many systems using superconducting cables have been studied, and are approaching practical use. This superconducting cable needs to be maintained in an ultralow temperature state in order to secure its characteristics, and a superconducting cable cooling system has been developed. In such a superconducting cable cooling system, in many cases, a low-temperature liquefied gas such as liquid nitrogen is used to circulate the liquid nitrogen in the system. Therefore, a pump for circulating the liquid nitrogen ( Hereinafter, "low temperature liquefied gas pump") is indispensable.

  In the following description, the liquid transferred by the low-temperature liquefied gas pump will be described by taking liquid nitrogen as an example. A liquefied gas (for example, liquid oxygen, liquid argon), liquid hydrogen, liquid helium, liquid carbon dioxide, or the like of the gas to be used may be used as the transfer fluid.

  As the types of the low temperature liquefied gas pump, there are, for example, an immersion type liquid pump, a non-immersion type liquid pump, and a long axis type liquid pump. Hereinafter, each pump will be described.

(Immersion type liquid pump)
Immersion-type liquid pumps are often used, for example, for pressure-feeding liquefied natural gas. This liquid pump is a type of liquid pump that is installed in the liquefied gas to be processed and pressure-feeds the low-temperature liquefied gas. However, this immersion-type liquid pump uses heat generated from the liquid pump motor as heat that penetrates into the low-temperature liquefied gas that is pumped.Therefore, when it is used in a superconducting cable cooling system that must minimize the heat entering, It is not appropriate because it reduces the efficiency.

(Non-immersion type liquid pump)
As a liquid pump of a type different from the immersion type, there is a non-immersion type liquid pump in which a motor portion of the liquid pump is used at room temperature, which is disclosed in Patent Document 1, for example. The impeller portion of this liquid pump is operated at the temperature of the low temperature liquefied gas to be transferred, but the motor portion that drives the impeller is used at room temperature. In this type of liquid pump, a heating means is used between the impeller portion and the motor portion so that the motor is not cooled due to the liquid level trouble. With this heating means, there is room for improvement in that the heat penetration into the impeller portion cannot be ignored.

(Long-axis liquid pump)
There is a non-immersion type liquid pump that employs a long shaft to suppress heat entering (hereinafter referred to as "long shaft liquid pump"). As the long-axis liquid pump, for example, many types of long-axis liquid pumps are sold by Barber Nichols.

The advantage of the long axis liquid pump is that the heat load / heat intrusion into the cooling system is small, but ball bearings are used as the bearings of the long axis shaft, so periodic maintenance is required, and the maintenance interval is There is a problem that maintenance is complicated because it is short. That is, it is necessary to heat the entire long-axis liquid pump to room temperature at every maintenance, and to cool the long-axis liquid pump again after the maintenance.
On the other hand, when a ball bearing is adopted as the bearing of the long shaft, the long shaft and the ball bearing are physically held in contact with each other and firmly held. Even if there is a change in the liquid level, the effect is small and the operation of the liquid pump itself is relatively stable.

JP2012-92813A

Of the above-mentioned types, long-axis liquid pumps are preferable except for maintenance problems. Therefore, in order to solve the maintenance problem of the long shaft liquid pump, it is conceivable to use a magnetic bearing instead of the ball bearing as the bearing of the long shaft.
However, when a magnetic bearing is used as the bearing of the long shaft, there is concern about the stability of the pump. This point will be described in detail with reference to FIG.

In FIG. 3, reference numeral 45 is a long-axis non-immersion type liquid pump (hereinafter, sometimes simply referred to as “liquid pump 45”), 3 is an electric motor, 5 is an impeller, and a long shaft 7 for connecting the electric motor 3 and the impeller 5 is used. Reference numeral 9 denotes a magnetic bearing that supports the shaft 7, and 11 denotes a housing (motor housing 11m, shaft housing 11s, impeller housing 11i) that covers these components.
In the non-immersion type liquid pump 45, usually, the shaft 7 connecting the electric motor 3 and the impeller 5 is arranged vertically downward.

  When the liquid pump 45 shown in FIG. 3 is operated, liquid nitrogen is introduced into the liquid pump 45 from the inlet 21, pressurized by the impeller 5, and then discharged from the discharge port 23. The liquid pump 45 is provided with a slight clearance (clearance 27) between the back surface 25 of the impeller 5 which is a moving part and the impeller housing 11i.

A part of the liquid nitrogen pressurized by the impeller 5 passes through the clearance 27, enters the shaft housing 11s, and forms a liquid surface 29 in a steady operation state. The liquid surface 29 has a large gas pressure in the housing 11, a discharge pressure Pd of the liquid nitrogen, a resistance of the liquid nitrogen to pass through the clearance (clearance 27), a head pressure of the liquid nitrogen liquid level, and a heat entering the liquid pump 45. It depends on the size. That is, the amount of the low temperature liquefied gas existing in the shaft 7 portion, that is, the liquid surface 29 of the low temperature liquefied gas is a natural condition, and it is difficult to control this.
The discharge pressure Pd of the liquid nitrogen of the liquid pump 45 usually has a constant fluctuation range, and the heat entering the liquid pump 45 also changes, so the liquid level 29 changes.

When the liquid surface 29 of the liquefied gas fluctuates, the discharge pressure of the liquid pump 45 also fluctuates, and the load acting on the magnetic bearing 9 also fluctuates. Since the magnetic bearing 9 supports the long shaft 7 in a non-contact manner in a cantilever state, there is a problem that the operation tends to become unstable if there is a load change.
Further, when the liquid level 29 rises, the electric motor 3 is cooled, which causes a problem in operation. On the contrary, when the liquid nitrogen liquid level is extremely lowered, there is a problem that gas is mixed into the pump discharge fluid.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a low-temperature liquefied gas pump that can suppress fluctuations in the liquid level and can perform stable operation, and an operation control method thereof.

(1) A cryogenic liquefied gas pump according to the present invention comprises an electric motor, an impeller, a shaft connecting the electric motor and the impeller, a magnetic bearing supporting the shaft, and a motor housing, an impeller housing, and a shaft housing that cover these components. A non-immersion type low temperature liquefied gas pump having a housing
A temperature detection unit provided on the outer surface of the shaft housing, the temperature detection unit detecting a temperature change of the shaft housing due to a change in the internal liquid level;
A gas injection / exhaust portion for injecting and exhausting a liquid level adjusting gas into the internal space of the housing;
A gas injection / exhaust mechanism section for inputting a temperature detection signal of the temperature detection section and injecting / exhausting gas from the gas injection / exhaust section based on the temperature detection signal. Is.

(2) Further, in the apparatus described in (1) above, the gas injection / exhaust mechanism is configured to inject a gas obtained by gasifying the low temperature liquefied gas discharged from the low temperature liquefied gas pump. It is characterized by.

(3) Further, in the device described in (1) or (2), the gas injecting / exhausting portion has a gas injecting portion and a gas exhausting portion separated from each other, and the gas injecting portion is provided in the motor housing. The gas discharge part is provided in the shaft housing.

(4) An operation control method for a low temperature liquefied gas pump according to the present invention is the operation control method for a low temperature liquefied gas pump according to any one of (1) to (3),
During steady operation of the low temperature liquefied gas pump,
When the temperature detecting unit detects a temperature higher than a preset temperature, the gas injecting / exhausting mechanism unit discharges gas, and the temperature detecting unit detects a temperature lower than the preset temperature. In addition, the gas injecting / exhausting mechanism injects gas.

(5) An operation control method for a low temperature liquefied gas pump according to the present invention is the operation control method for a low temperature liquefied gas pump according to any one of (1) to (3),
At the time of starting the low temperature liquefied gas pump,
The gas injection / exhaust mechanism is configured to discharge the gas from the gas injection / exhaust unit until the temperature detected by the temperature detection unit falls below a predetermined temperature.

According to the present invention, a temperature detecting portion which is provided on the outer surface of the shaft housing and detects a temperature change of the shaft housing due to a change of the inner liquid level, and a gas for adjusting the liquid level are injected into and discharged from the inner space of the housing. A gas injection / exhaust unit and a gas injection / exhaust mechanism unit for inputting a temperature detection signal from the temperature detection unit and injecting / exhausting gas from the gas injection / exhaust unit based on the temperature detection signal are provided. As a result, the following effects can be achieved.
During steady operation, the liquid level in the shaft housing can be controlled within a certain range, preventing unstable operation due to load fluctuations due to liquid level fluctuations, and ensuring stable operation of the low temperature liquefied gas pump. realizable.
In addition, since the liquid level can be controlled within a predetermined range, there is a problem that the motor is cooled due to the liquid level rising too much in the shaft housing, or the liquid level in the shaft housing drops below a predetermined position. It is possible to avoid the trouble that the gas fluid is mixed in the low temperature liquefied gas discharged from the outlet.

It is explanatory drawing of the low temperature liquefied gas pump concerning one embodiment of this invention. It is explanatory drawing explaining the relationship between the liquid level height in a housing and the temperature in a housing in the low temperature liquefied gas pump shown in FIG. It is a figure explaining the subject which an invention tends to solve.

As shown in FIG. 1, the low temperature liquefied gas pump 1 according to the present embodiment includes an electric motor 3, an impeller 5, a long shaft 7 connecting the electric motor 3 and the impeller 5, and a magnetic bearing 9 supporting the shaft 7. A housing 11 including a motor housing 11m, an impeller housing 11i, and a shaft housing 11s that cover these components, a temperature detection unit 13 provided in the shaft housing 11s, and a gas for adjusting the liquid level are injected into the internal space of the housing 11. A gas injection / exhaust mechanism for inputting the gas injection / exhaust part 15 to be exhausted and the temperature detection signal of the temperature detection part 13 and injecting / exhausting gas from the gas injection / exhaust part 15 based on the temperature detection signal. And a part 17 are provided.
Hereinafter, each configuration will be described in detail.

<Electric motor>
As the electric motor 3, for example, a common one such as a DC motor or a three-phase induction motor can be applied.
The electric motor 3 is housed in a portion of the housing 11 that houses the electric motor 3 (motor housing 11m). The motor housing 11m has an airtight structure, and the electric motor 3 is arranged in the motor housing 11m with the tip of the rotating shaft facing downward.

<Impeller>
The impeller 5 is installed at the tip of the shaft 7, is arranged in a portion of the housing 11 that houses the impeller 5 (impeller housing 11i), and is rotationally driven by the electric motor 3. The impeller housing 11i is provided with an inlet 21 for introducing the low temperature liquefied gas into the housing 11 at a lower portion thereof and a discharge port 23 for discharging the low temperature liquefied gas at a side portion thereof.
As described in FIG. 3, a slight gap (clearance 27) is provided between the back surface 25 of the impeller 5 and the impeller housing 11i.
The impeller 5 rotates in the impeller housing 11i to introduce the low temperature liquefied gas from the introduction port 21, pressurizes it to a predetermined pressure, and discharges it from the discharge port 23.

<Shaft>
The shaft 7 has one end connected to the three axes of the electric motor and the other end to which the impeller 5 is attached. The shaft 7 is a long shaft, and the length thereof is approximately 1.5 times or more the axial distance between the two bearings 9 (L in FIG. 1) or more.
The shaft 7 is disposed in a portion of the housing 11 that houses the shaft 7 (shaft housing 11s).
A magnetic bearing 9 is provided on one end side of the shaft 7 and is rotatably supported in a cantilever state.

<Magnetic bearing>
The magnetic bearing 9 is a magnetic bearing utilizing the attractive force of a normal electroconductive magnet, and stably supports the shaft 7 by a displacement sensor and a control system.
Since the magnetic bearing 9 is a non-contact type bearing, it does not require maintenance in a short period of time like a ball bearing, and can solve the above-mentioned problems in the ball bearing.

<Housing>
The housing 11 is for accommodating components such as the electric motor 3, the impeller 5, and the shaft 7, and is composed of the motor housing 11m, the impeller housing 11i, and the shaft housing 11s as described above.
As shown in FIG. 1, the impeller housing 11i, the shaft housing 11s, and the motor housing 11m are in communication with each other. Therefore, the low temperature liquefied gas introduced into the impeller housing 11i enters into the shaft housing 11s, and the liquid surface 29 is formed in the shaft housing 11s. The evaporated gas of the low temperature liquefied gas reaches the inside of the motor housing 11m from the inside of the shaft housing 11s. Therefore, in the shaft housing 11s, as shown in FIG. 2, the temperature near the liquid surface 29 is low and the temperature is gradually increasing.

<Temperature detector>
The temperature detection unit 13 is provided on the outer wall of the shaft housing 11s and detects a temperature change of the shaft housing 11s due to a change of the liquid level inside. In other words, the temperature detection unit 13 estimates a change in the liquid level inside the shaft 7 by detecting a change in the temperature of the shaft housing 11s.

As shown in FIG. 2, there is a liquid surface 29 in the lower part inside the shaft housing 11s, and the inside of the shaft housing 11s is filled with the vapor of the low temperature liquefied gas. For this reason, the temperature of the portion of the shaft housing 11s near the liquid surface 29 is low, and the temperature of the portion far from the liquid surface 29 (the portion near the electric motor 3) is high. For example, the upper end of the shaft housing 11s is at room temperature (for example, 300K) and the lower end is at 80K, and a temperature gradient exists in the axial direction of the shaft housing 11s.
Therefore, for example, when the liquid surface 29 rises from the position A in FIG. 2 and moves to the position B indicated by the chain double-dashed line, the temperature curve appears to have moved parallel to the upper part of the figure as shown in FIG. Therefore, the temperature detected by the temperature detection unit 13 decreases. In this way, by detecting the change in the temperature detected by the temperature detector 13, it is possible to know the rise and fall of the liquid surface 29.

  The temperature detecting unit 13 needs to be installed at the same position as or above the position where the liquid surface 29 in the shaft housing 11s is at the uppermost position. This is because, if the temperature is constantly detected at a position lower than the liquid surface position, even if the liquid surface 29 changes, the detected temperature does not change and the change in the liquid surface 29 cannot be detected.

<Gas injection / exhaust section>
The gas injection / exhaust part 15 is a part for injecting and exhausting a liquid level adjusting gas into the internal space of the housing 11, and is provided in the gas injection part 31 provided in the motor housing 11m and the shaft housing 11s. The gas exhaust unit 33 is provided.
The liquid level adjusting gas may be a gas obtained by gasifying a low temperature liquefied gas having a predetermined pressure, for example, nitrogen gas when the low temperature liquefied gas is liquid nitrogen. In this case, part of the pressurized liquid nitrogen discharged from the discharge port 23 may be vaporized and then injected.
Moreover, the gas to be injected is not limited to the low temperature liquefied gas to be transferred, and for example, helium gas may be injected. Helium gas generally has a lower dew point than low-temperature liquefied gas such as liquid nitrogen to be transferred, and there is no problem even if it contacts the liquid nitrogen in the housing 11.

The gas injection part 31 and the gas discharge part 33 may be at the same position or at different positions.
In the present embodiment, the gas injection part 31 is provided on the upper surface of the motor housing 11m and the gas discharge part 33 is provided on the shaft housing 11s. The reason for doing this is as follows.
Since the temperature of the upper portion of the motor housing 11m is close to room temperature and there is no difference from the temperature of the injected gas, the gas injection does not affect the detection temperature. If a gas at room temperature is injected near the liquid surface 29, the liquid surface 29 will evaporate rapidly and temperature detection will become unstable.
Further, injecting the room temperature gas is more efficient than injecting the low temperature gas because the absolute amount of injection can be reduced and the pressure in the housing 11 can be increased.

This is because the gas discharge part 33 is provided in the shaft housing 11s, but since the inside of the shaft housing 11s is at a relatively low temperature, the pressure inside the housing 11 is likely to drop even if the absolute amount of discharge is small.
When the gas is discharged, the temperature changes above the position due to the movement of the gas having a temperature higher than that position. Therefore, the gas discharge unit 33 is provided above the temperature detection unit 13, and the temperature change due to the discharge of the gas It is preferable to suppress the occurrence.

  Regarding the installation positions of the gas discharge part 33 and the temperature detection part 13 in the shaft housing 11s, the following is a tentative guide. In the shaft housing 11s, assuming that the portion corresponding to the back surface 25 of the impeller 5 is 0% and the room temperature portion of the shaft housing 11s is 100%, it is assumed that the gas discharge portion 33 is above the temperature detection portion 13. The temperature detection unit 13 can be installed at a position of 20 to 80%, and the gas discharge unit 33 can be installed at a position of 30 to 80%.

<Gas injection / discharge mechanism>
The gas injection / exhaust mechanism section 17 inputs the temperature detection signal of the temperature detection section 13 and injects / exhausts gas from the gas injection / exhaust section 15 based on the temperature detection signal. Gas injection pipe 35 connected to 31, gas injection on-off valve 37 provided in gas injection pipe 35, gas exhaust pipe 39 connected to gas exhaust portion 33, and gas exhaust pipe 39 The discharge on-off valve 41, a valve control unit 43 that inputs a detection signal of the temperature detection unit 13 and controls the opening and closing of the gas injection on-off valve 37 and the gas discharge on-off valve 41 are configured.

When it is estimated that the liquid level 29 has risen due to the signal from the temperature detection unit 13, the valve control unit 43 opens the gas injection on-off valve 37 to lower the liquid level 29 and opens the gas. Inject from 31 into the housing 11. By injecting the gas, the pressure inside the housing 11 rises, and the liquid level 29 drops.
On the contrary, when it is estimated that the liquid level 29 is lowered by the signal from the temperature detection unit 13, the valve control unit 43 opens the gas discharge on-off valve 41 to raise the liquid level 29 and discharges the gas. The gas in the housing 11 is discharged from the portion 33. As the gas is discharged, the pressure inside the housing 11 drops, and the liquid level 29 rises.

The control of the liquid surface 29 will be described more specifically.
If, in FIG. 2, it is desired to control the liquid surface 29 to the A position, the temperature (target temperature) detected by the temperature detection unit 13 when the liquid surface 29 is at the A position, and the liquid surface 29 has an allowable value. A temperature when the liquid level 29 has risen to the limit (liquid level upper limit temperature) and a temperature when the liquid level 29 has dropped to the limit of the allowable value (liquid level lower limit temperature) are set in the valve control unit 43.

  The valve control unit 43 constantly inputs the temperature detected by the temperature detection unit 13, and when the input temperature drops to the liquid level upper limit temperature, the gas injection opening / closing valve 37 is opened to lower the liquid level 29. Is injected from the gas injection part 31 into the housing 11. The gas injection rate can be adjusted by appropriately adjusting the opening degree of the gas injection on-off valve 37. When the temperature detected by the temperature detection unit 13 reaches the target temperature, the valve control unit 43 closes the gas injection opening / closing valve 37 to stop gas injection.

On the contrary, when the input temperature from the temperature detection unit 13 rises to the liquid level lower limit temperature, the valve control unit 43 opens the gas discharge on-off valve 41 to raise the liquid level 29 and opens the gas discharge unit 33 to the housing. The gas in 11 is discharged. The gas discharge rate can be adjusted by appropriately adjusting the opening degree of the gas discharge on-off valve 41. When the temperature detected by the temperature detection unit 13 reaches the target temperature, the control unit closes the gas discharge on-off valve 41 to stop gas discharge.
By repeating such an operation, the liquid surface 29 can be controlled within a predetermined range, and the change of the moment to the magnetic bearing 9 due to the liquid surface change can be suppressed.
That is, in the present invention, not by measuring the exact position (height) of the liquid surface 29 of the low temperature liquefied gas in the shaft housing 11s, only by measuring the temperature of the wall surface in the shaft housing 11s, The change of the liquid surface 29 of the low temperature liquefied gas inside can be suppressed.

  Since the temperature of the low temperature liquefied gas changes depending on its pressure, the above-mentioned target temperature, liquid level upper limit temperature, and liquid level lower limit temperature must be set for each operating pressure of the pump. However, since it is complicated to change the set value every time the operating pressure changes, the set value of the target temperature may be determined based on the physical properties (boiling point, dew point, etc.) of the fluid to be transferred. For example, when the fluid to be transferred is liquid nitrogen, the boiling points thereof are 103.8K and 115.6K, respectively, when the operating pressure is 1 MPa (A) and 2 MPa (A). Therefore, the set value of the target temperature in the valve control unit is set to the boiling point + α of the operating pressure of the liquid nitrogen that is the transfer target fluid, and the valve control unit inputs the operating pressure and automatically sets the target temperature. Thus, smooth operation is possible without changing the target temperature for control each time.

Next, an operation control method of the low temperature liquefied gas pump 1 according to the present embodiment configured as described above will be described.
The main purpose of the present invention is to suppress the change of the liquid level 29 in the shaft housing 11s during the steady operation, but by having the configuration of the present invention, the conventional problem at the time of starting the pump can also be solved. Therefore, first of all, conventional problems and their effects will be described when the pump is started.

<At pump startup>
(Conventional issue at startup)
In the conventional non-immersion type liquid pump 45 (see FIG. 3), when the liquid pump 45 is started after maintenance, it is necessary to cool it to the temperature during steady operation, but it is difficult to shorten the time required for this cooling. It was
The reason for this will be described below.
When the liquid pump 45 at room temperature is cooled, a low temperature liquefied gas (for example, liquid nitrogen) to be transferred is introduced into the liquid pump 45 for cooling, but the liquid nitrogen introduced from the inlet to the liquid pump 45 is stored in the liquid pump 45. The impeller part is cooled and liquid nitrogen is vaporized. The vaporized nitrogen gas is discharged from the discharge port 23 of the liquid pump 45. The piping around the liquid pump is usually designed assuming that liquid nitrogen flows, and when vaporized nitrogen gas flows through that piping, a large amount of gas is added to the piping that is designed assuming that liquid flows. As a result, the pressure loss increases and it is difficult to cool the liquid pump 45 in a short period of time.

At the time of start-up, liquid nitrogen or vaporized low-temperature nitrogen gas does not come into direct contact with the back surface 25 of the impeller 5 or the lower portion of the shaft 7 that should be cooled to a low temperature. Was needed. Since FIG. 3 shows a steady state, the liquid surface 29 is at the position of the shaft housing 11s.
Further, the back surface 25 of the impeller 5 and the lower portion of the shaft 7 are basically cooled by heat conduction, but it was not possible to quantitatively grasp how many times they were cooled. Therefore, if the liquid pump 45 is started with insufficient cooling of the back surface 25 of the impeller 5 and the lower portion of the shaft 7, a part of the liquid nitrogen introduced from the inlet 21 of the liquid pump 45 is vaporized. As a result, the liquid nitrogen was pushed out, the liquid pump 45 could not be started normally, and the liquid pump 45 needed to be cooled again.

In order to solve the problems of the conventional liquid pump 45 as described above, by adopting the above-described structure in the present invention, smoother startup can be performed as compared with the conventional one. explain.
When the low temperature liquefied gas pump 1 is started, the gas discharge on-off valve 41 is opened until the temperature of the wall surface of the shaft housing 11s is cooled to a predetermined temperature. By opening the gas discharge on-off valve 41, the pressure inside the housing 11 can be lowered, so that a portion of the liquid nitrogen introduced into the impeller housing 11i passes through the clearance 27 and enters the shaft housing 11s. As a result, the low temperature liquefied gas is brought into direct contact with the impeller 5 and the shaft 7 to reduce the cooling time. Further, by measuring the temperature of the wall surface of the shaft housing 11s, the cooling state of the low temperature liquefied gas pump 1 can be quantitatively grasped, and it can be accurately known whether or not the cooling is completed to a predetermined temperature.
Further, by extracting the gas from the gas discharge on-off valve 41, it is possible to prevent the temperature of the electric motor 3 from becoming too low.

  Further, as described above, the cooling of the impeller 5 and the shaft 7 is promoted, so that the temperature of the discharged nitrogen gas decreases, and the pressure loss when the nitrogen gas passes through the pipe connected to the discharge port 23. Is small, the passage of the low temperature liquefied gas through the impeller 5 during the initial cooling of the pump can be promoted, and also in this respect, the initial cooling can be promoted.

  When the opening of the gas discharge on-off valve 41 is controlled by the temperature of the wall surface of the shaft housing 11s when the pump is started, the set value for temperature control may be different from the set value for steady operation. That is, when the pump is started, the set value for temperature control is set to a temperature lower than that during steady operation. That is, since the temperature of the entire pump is high, the cooling of the pump can be promoted by controlling the liquid level 29 of the low temperature liquefied gas, for example, liquid nitrogen in the shaft housing 11s to a position higher than that in the normal operation. In this case, for example, when the temperature of the wall surface of the shaft housing 11s reaches 80 (atmospheric pressure of liquid nitrogen saturated) to 100K, it can be determined that the pump has been sufficiently cooled, and the pump can be started.

<During steady operation>
During steady operation, when the temperature detection unit 13 detects a temperature higher than a preset temperature, it is estimated that the liquid level 29 is lowered, so the valve control unit 43 causes the gas discharge on-off valve 41. Is released to discharge the gas in the housing 11, and the pressure in the housing 11 is lowered to raise the liquid level 29.
On the contrary, when the temperature detection unit 13 detects a temperature lower than the preset temperature, it is estimated that the liquid level 29 is rising, so the valve control unit 43 opens the gas injection opening / closing valve 37. By doing so, gas is injected into the housing 11 and the pressure in the housing 11 is increased to lower the liquid surface 29.

As described above, according to the present embodiment, it is possible to shorten the cooling time when starting the pump.
Further, since the liquid surface 29 in the shaft housing 11s can be controlled within a certain range during steady operation, it is possible to prevent the operation from becoming unstable due to the fluctuation of the load due to the fluctuation of the liquid surface, and to perform the low temperature liquefied gas pump. 1 stable operation can be realized.
Further, since the liquid surface 29 can be controlled within a predetermined range, the liquid surface 29 in the shaft housing 11s rises too much, which causes the electric motor 3 to be cooled, and the liquid surface 29 in the shaft housing 11s falls below a predetermined position. By descending, it is possible to avoid the trouble that the gas fluid is mixed in the low temperature liquefied gas discharged from the discharge port 23.

In the present invention, it is not possible to accurately measure the position (height) of the liquid surface 29 of the low temperature liquefied gas in the shaft housing 11s.
However, the position (height) of the liquid surface 29 of the low temperature liquefied gas in the shaft housing 11s is a result determined by various conditions, and if the liquid surface height is constant, no matter where it exists in the shaft housing 11s, there is a problem. There is no. In the present invention, focusing on the problem that the liquid level 29 of the low temperature liquefied gas changes, by measuring the temperature of the wall surface of the shaft housing 11s, the liquid level 29 of the low temperature liquefied gas in the shaft housing 11s is measured. Is estimated and the liquid level height is controlled within a certain range.

1 Low-temperature liquefied gas pump 3 Electric motor 5 Impeller 7 Shaft 9 Magnetic bearing 11 Housing 11m Motor housing 11s Shaft housing 11i Impeller housing 13 Temperature detection part 15 Gas injection / exhaust part 17 Gas injection / exhaust mechanism part 21 Inlet port 23 Outlet port 25 Rear face 27 Clearance 29 Liquid level 31 Gas injection part 33 Gas discharge part 35 Gas injection pipe 37 Gas injection on-off valve 39 Gas discharge pipe 41 Gas discharge on-off valve 43 Valve control part 45 Non-immersed liquid pump

Claims (5)

Non-immersion type low temperature liquefaction provided with an electric motor, an impeller, a shaft connecting the electric motor and the impeller, a magnetic bearing supporting the shaft, and a housing made up of a motor housing, an impeller housing and a shaft housing for covering these components. A gas pump,
A temperature detection unit provided on the outer surface of the shaft housing, the temperature detection unit detecting a temperature change of the shaft housing due to a change in the internal liquid level;
A gas injection / exhaust portion for injecting and exhausting a liquid level adjusting gas into the internal space of the housing;
A low temperature characterized by comprising a gas injection / exhaust mechanism section for inputting a temperature detection signal of the temperature detection section and for injecting / exhausting gas from the gas injection / exhaust section based on the temperature detection signal. Liquefied gas pump.   The low temperature liquefied gas pump according to claim 1, wherein the gas injection / exhaust mechanism is configured to inject a gas obtained by gasifying the low temperature liquefied gas discharged from the low temperature liquefied gas pump.   The gas injecting / exhausting part is separated into a gas injecting part and a gas exhausting part, the gas injecting part is provided in the motor housing, and the gas exhausting part is provided in the shaft housing. The low temperature liquefied gas pump according to claim 1 or 2. The operation control method for a low temperature liquefied gas pump according to any one of claims 1 to 3,
During steady operation of the low temperature liquefied gas pump,
When the temperature detecting unit detects a temperature higher than a preset temperature, the gas injecting / exhausting mechanism unit discharges gas, and the temperature detecting unit detects a temperature lower than the preset temperature. In the method for controlling operation of a low temperature liquefied gas pump, the gas injection / exhaust mechanism section injects gas. The operation control method for a low temperature liquefied gas pump according to any one of claims 1 to 3,
At the time of starting the low temperature liquefied gas pump,
The operation control of the low temperature liquefied gas pump, wherein the gas injecting / exhausting mechanism is configured to discharge the gas from the gas injecting / exhausting section until the temperature detected by the temperature detecting section becomes equal to or lower than a predetermined temperature. Method.

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