JPH0380990B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a reciprocating pump for low-temperature liquefied gases such as liquid oxygen and liquid nitrogen (hereinafter referred to as liquid pump), which has a low NPSH (net effective suction head). This invention relates to a liquid pump.

[Conventional technology]

Generally, low-temperature liquefied gases such as liquid oxygen and liquid nitrogen are often stored in a state close to that of a saturated liquid.
Moreover, even if it is in a supercooled state, it is likely to boil due to external heat and resistance while being sent from the storage tank through pipes and valves. Therefore, a liquid pump that sucks in and pumps such a liquid is required to have a low NPSH, but conventional liquid pumps are not satisfactory due to the following reasons.

Hereinafter, this will be explained with reference to the central vertical sectional view of a conventional liquid pump shown in FIG.
A gas-liquid separation chamber 4 is provided on the suction side of a compression chamber 3, which is defined by the tip of a piston 2 that reciprocates within the cylinder 1, and has an inlet 5 at the bottom and a vaporized gas outlet 6 at the top. have. Further, the suction port of the compression chamber 3 is provided with a suction valve element 7 that closes and opens as the piston 2 moves back and forth, and the discharge port is provided with a discharge valve element 8 that opens and closes as the piston 2 moves back and forth. 9 is a rider ring, and 10 is a piston ring.

In such a configuration, a tank (not shown)
The low-temperature liquefied gas extracted from the bottom is passed through the suction port 5.
The vaporized gas is introduced into the gas-liquid separation chamber 4 through the gas-liquid separation chamber 4, and bubbles generated during the introduction in the gas-liquid separation chamber 4 are separated by buoyancy and returned to the vaporization section of the tank via the vaporized gas outlet 6.

The liquid from which the vaporized gas has been separated is introduced into the compression chamber 3 by pushing open the suction valve 7 as the piston 2 moves backward, and is then compressed by the forward movement of the piston 2 and pushing the discharge valve 8 open. It flows as shown by the arrow and is sent to the user.

[Problems to be Solved by the Invention] However, in such a conventional liquid pump, (1) the suction valve 7 of the liquid pump is of the check valve type, and therefore inevitably requires a pressure difference for valve operation; Therefore, the resistance around the suction valve is large and the pressure inside the compression chamber 3 decreases, so that part of the liquid introduced into the compression chamber 3 vaporizes, preventing the introduction of new liquid.

(2) Since the compression ratio in the discharge process is high, the temperature of the residual liquid in the compression chamber 3 becomes high, which tends to vaporize in the suction process and prevents the introduction of new liquid.

(3) The inside of the compression chamber 3 is heated by frictional heat caused by the sliding of the piston ring 10 provided on the piston 2, promoting vaporization of the liquid.

As described above, the present invention provides a liquid pump that solves the problem of a part of low-temperature liquefied gas being vaporized and worsening NPSH in order to increase the pressure to a predetermined discharge pressure by one-stage compression. .

[Means to solve the problem]

The present invention provides a reciprocating pump for low-temperature liquefied gas in which a piston is inserted into a cylinder so as to be movable back and forth, and a compression chamber is formed in the cylinder in front of the tip of the piston. An annular gas-liquid separation chamber is formed on the outer periphery of the cylinder in which the large-diameter portion moves back and forth, with an inner tube portion and an outer tube portion having a low-temperature liquefied gas inlet and a vaporized gas outlet. A chamber formed in the cylinder behind the large-diameter section is communicated with the chamber through an opening formed in the inner pipe section, and the opening is closed by the large-diameter section when the piston retreats. The chamber behind the large-diameter portion is defined as a first-stage compression chamber, and the first-stage compression chamber and the compression chamber in front of the tip of the piston are communicated with each other by a passage passing through the inside of the piston. The present invention is characterized in that the compression chamber is used as a second stage compression chamber.

[Effect]

Therefore, the low-temperature liquefied gas extracted from the bottom of the tank (not shown) is introduced into the gas-liquid separation chamber through the low-temperature liquefied gas inlet by the advancement of the piston, and is generated in the pipe from the tank. The gas is separated, the separated gas returns to the tank through the vaporized gas outlet, and the liquid is introduced into the first stage compression chamber through the opening.

Then, when the piston moves back, the opening is closed by the large diameter part of the piston, and the liquid in the first stage compression chamber is pressurized by the first stage compression, and the pressurized liquid passes through the passage inside the piston. It is introduced into the second stage compression chamber.

As the piston moves forward again, the liquid in the second-stage compression chamber is further pressurized by second-stage compression and sent to the user.

〔Example〕

Embodiments of the liquid pump according to the present invention will be described below with reference to FIGS. 2 and 3.

Figure 2 is a central vertical sectional view of a horizontal liquid pump;
The figure is a - sectional view of FIG.

A piston 12 is fitted into the cylinder 11 so as to be movable back and forth. A large diameter portion 12A is provided at the intermediate portion of the piston 12, and an inner tube portion 1 is provided on the outer circumference of the cylinder 11 in which the large diameter portion 12A moves back and forth.
1A and the outer tube part 11B form an annular gas-liquid separation chamber 1.
6 is formed. A low-temperature liquefied gas inlet 17 formed below the outer tube section 11B and a vaporized gas outlet 18 formed above the outer tube section 11B communicate with the gas-liquid separation chamber 16, respectively.

A chamber formed in the cylinder 11 behind the large diameter portion 12A communicates with the gas-liquid separation chamber 16 through a plurality of openings 19 formed in the inner tube portion 11A, and when the piston 12 retreats, the large diameter The portion 12A is the opening 19
is closed to form the first stage compression chamber 13.

Cylinder 11 in front of the tip of the piston 12
The compression chamber formed therein communicates with the first stage compression chamber 13 through a passage 15 passing through the piston 12 to become a second stage compression chamber 14 .

A discharge space 20 is formed in the cylinder 11 between the front of the large diameter portion 12A of the piston 12 and the second stage compression chamber 14, and the end of the discharge space 20 communicates with the gas-liquid separation chamber 16. There is.

In addition, 21 is a rider ring, 22 is a piston ring provided on the second stage compression chamber 14 side of the piston 12, and 23 is a passage 15 provided by the piston 12 moving back and forth.
24 is a discharge valve that opens and closes the discharge port of the second stage compression chamber 14 as the piston 12 moves back and forth; 25 is a shaft seal for the first stage compression chamber 13.

Next, the operation of the liquid pump according to the present invention configured as described above will be explained.

The low-temperature liquefied gas extracted from the lower part of the tank (not shown) moves the piston 12 forward (in the direction of arrow a).
The gas is introduced into the gas-liquid separation chamber 16 through the low-temperature liquefied gas inlet 17, and in the gas-liquid separation chamber 16, the gas generated in the pipe from the tank is separated and rises, and is discharged from the vaporized gas outlet 18 into the tank. The liquid is returned to the upper gas phase and introduced into the first stage compression chamber 13 through the opening 19.

Then, when the piston 12 moves backward (in the direction of arrow b), the opening 19 is closed by the outer periphery of the large diameter portion 12A of the piston 12, and the liquid in the first stage compression chamber 13 is pressurized by the first stage compression. The pressurized liquid passes through the passage 15 in the piston 12, pushes open the suction valve 23, and is introduced into the second stage compression chamber 14.

When the piston 12 moves forward again (in the direction of arrow a), the liquid in the second stage compression chamber 14 is further pressurized by the second stage compression, and the pressurized liquid pushes the discharge valve 24 open. Derived to the destination of use.

In this way, when the first stage compression chamber 13 takes in liquid, the second stage compression chamber 14 performs the second stage compression and discharge, and conversely, when the first stage compression chamber 13 performs the first stage compression and discharge, the second stage compression chamber 14 performs the second stage compression and discharge.
Liquid suction is performed in the stage compression chamber 14, and at this time, leaked liquid due to compression in the first stage compression chamber 13 passes between the outer periphery of the large diameter portion 12A and flows from the opening 19 into the gas-liquid separation chamber 16, Otherwise, it flows into the discharge space 20 and then returns to the gas phase part of the tank via the vaporized gas discharge port 18, and the leakage liquid in the second stage compression chamber 14 is also drained between the piston ring 22 and the cylinder 11. It enters the discharge space 20 and, after being vaporized, is returned to the gas phase of the tank in the same manner as described above.

In this embodiment, as described above, by performing the compression process in two stages, the compression ratio in the first stage can be made small, so there is no need to provide a sealing member in the large diameter portion 12A of the piston 12. It is possible to minimize the generation of frictional heat due to sliding.

Additionally, a gas-liquid separation chamber 1 is provided around the first stage compression chamber 13.
6, the liquid stored in the gas-liquid separation chamber 16 acts as a heat insulating layer, and the temperature of the outside air is not directly transmitted to the liquid in the first stage compression chamber 13. The rate of vaporization of the liquid decreases.

Further, the axial formation position of the inner tube portion 11A of the opening 19 is insulated from the gas-liquid separation chamber 16 when the piston 12 is retreating and pressurizing the first stage compression chamber 13, and conversely, when the piston 12 is retreating and pressurizing the first stage compression chamber 13, When moving forward and the first stage compression chamber 13 is inhaling, it is provided at a position communicating with the gas-liquid separation chamber 16. The inner tube portion 11A of the opening 19 may be formed at any position in the circumferential direction, but it should be taken into consideration that the liquid introduced into the gas-liquid separation chamber 16 may contain bubbles in the boiling state. ,
It is desirable to provide it only on the upper half side as shown in FIG.

Further, since the first and second stage compression chambers 13 and 14 are communicated with each other through the passage 15 passing through the piston 12 without using any external piping, the configuration becomes simple and compact. Furthermore, this passage 15
The openings 19 are branched into four parts near the large diameter part 12A of the piston 12, but this number may be set as appropriate, and the number of openings 19 is five in the drawing, but this number may also be set as appropriate. good.

Although the embodiment of the horizontal liquid pump has been described above, the same effect can be obtained even in the case of a vertical type. In this case, the piston moves up and down, and the low temperature liquefied gas inlet 17 and vaporized gas outlet 18 are closed. installed horizontally. In the case of a vertical type, the inflow liquid will flow into the first stage compression chamber 13 through the opening 19 while collecting at the bottom of the gas-liquid separator 16. It can be provided over the entire circumference of the inner tube portion 11A of the cylinder as long as it is at a position that is closed by the large diameter portion 12A when the cylinder is retracted.

〔Effect of the invention〕

As mentioned above, in the liquid pump according to the present invention, (1) the compression process is performed in two stages, so the first
The liquid compressed in the stage compression chamber is introduced into the second stage compression chamber in a supercooled state, so even if the liquid is compressed in the second stage compression chamber and the liquid temperature rises, it is already supercooled. By compressing the liquid in the state, the amount of vaporization is significantly reduced, and the NPSH is lower than before.
can be significantly improved.

(2) Since the compression process is carried out in two stages, the compression ratio in each stage can be reduced, and the rise in liquid temperature in the first and second stage compression chambers can be minimized. The amount of vaporized residual liquid in the compression chamber is reduced,
NPSH can be improved.

(3) Liquid is introduced into the first stage compression chamber through an opening provided in the inner tube forming the gas-liquid separation chamber, and this liquid does not experience any resistance when introduced, so it is not depressurized. It never evaporates. In addition, even if the liquid brown rises during compression in the first stage compression chamber and some of the residual liquid in the first stage compression chamber is vaporized, it is easily discharged through the opening, so the first stage compression The inflow of liquid subsequently introduced into the chamber is not obstructed, and this also makes it possible to improve NPSH.

[Brief explanation of drawings]

FIG. 1 is a central longitudinal sectional view of a conventional reciprocating pump for low-temperature liquefied gas, and FIGS. 2 and 3 are examples of the reciprocating pump for low-temperature liquefied gas according to the present invention, and FIG. The vertical sectional view, FIG. 3, is a - sectional view taken from FIG. 2. 11... Cylinder, 11A... Inner tube part of cylinder 11, 11B... Outer tube part of cylinder 11, 12
...Piston, 12A... Large diameter portion of piston 12, 13... First stage compression chamber, 14... Second stage compression chamber, 15... Passage, 16... Gas-liquid separation chamber, 17...
...low-temperature liquefied gas inlet, 18... vaporized gas outlet, 19... opening, 20... exhaust space, 21...
... Rider ring, 22 ... Piston ring, 2
3...Suction valve element, 24...Discharge valve element, 25...Shaft seal of first stage compression chamber 13.

Claims (1)

[Claims] 1. A reciprocating pump for low-temperature liquefied gas in which a piston is inserted into a cylinder so as to be movable back and forth, and a compression chamber is formed in the cylinder in front of the tip of the piston, wherein the piston is provided with a large diameter part, and the large diameter part An annular gas-liquid separation chamber is formed on the outer periphery of the cylinder in which the cylinder moves back and forth, with an inner tube section and an outer tube section having a low-temperature liquefied gas inlet and a vaporized gas outlet, and the gas-liquid separation chamber and the large diameter A chamber formed in a cylinder at the rear of the piston is communicated with a chamber formed in a cylinder at the rear of the piston through an opening formed in the inner pipe, and the opening is closed by the large diameter part when the piston retreats, and the large diameter part The rear chamber is a first-stage compression chamber, and the first-stage compression chamber and the compression chamber in front of the tip of the piston are communicated with each other by a passage passing through the inside of the piston. A reciprocating pump for low-temperature liquefied gas, characterized in that a second-stage compression chamber is a reciprocating pump for low-temperature liquefied gas.