JP2002143799A - Pig station and its cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the cleaning properties of a pig and a station and to prevent contamination when fluid is replaced. SOLUTION: A pig station is connected to a circulating passage (8) in which the pig (1) is moved and has a station housing (7) having an inlet (2) and an outlet (3), a holder part (6) for temporarily holding the pig (1) which is conveyed from the circulating passage (8) into the housing (7) through the inlet (2), and a discharge opening (4) for discharging waste liquid supplied from the circulating passage (8). The inside of the housing (7) and the pig (1) are cleaned by a cleaning solution which is supplied from the outlet (3) into the housing (7), liquid pressure is applied to the pig (1) held by the holder part (6), and the pig (1) is shot from the housing (7) into the circulating passage (8).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pig station for emitting and stopping a pig to be wiped by moving inside a pipe by applying a fluid pressure, and a cleaning method therefor.

[0002]

2. Description of the Related Art Solution or slurry-like raw materials such as paints, inks, chemicals, foods and drinks, algae, microorganisms, and other scales adhered to the inner wall of pipes reduce the ability to transport fluids, and reduce bacteria and mold. It causes unfavorable hygiene. In addition, when replacing the fluid to be transferred in the pipe with a different substance, or when changing the paint and ink to another color, cleaning by merely passing the liquid through the pipe removes residual substances on the pipe inner wall. It will not be possible to dissolve in the fluid after the change. In order to solve this problem, pigs are known which move in a pipe by applying a fluid pressure to scrape off residues and deposits. The pig is generally integrally formed of an elastic material such as rubber.

In a system that moves inside a pipe using a pig, a pig firing device is provided at the beginning of the pipe through which a fluid such as paint is transferred, and a pig stop device is provided at the end of the pipe. The fluid that gives the pig running pressure is air, nitrogen,
A compressible fluid (such as gas) such as steam or an incompressible fluid (such as liquid) such as tap water or a cleaning solution is used. By applying a fluid pressure, the pig loaded in the pig launching device is pressure-fed into the pipe, and the pig runs in close contact with the inner wall of the pipe to scrape the viscous substance attached to the pipe wall. When the pumped pig reaches the end of the pipe, the pig is stopped by the pig stopping device and is washed by the connected pig washing device. JP-A-9-
Japanese Patent Application Publication No. 192620 discloses a cleaning device that provides a station for firing and stopping a pig at both ends of a pipe, moves a pig arranged in the station to a cleaning room when cleaning is required, and cleans the pig and the station. .

[0004] Pig stations are also known in which the function of firing and stopping the pig is integrated. The pig station is disposed in a loop-shaped pipe including a transfer pipe for a fluid such as paint, and has a housing in which the inlet and outlet of the pig are connected to the pipe, and a sleeve for storing and firing the pig in the housing. Formed in a double structure. The pig that has been pressure-fed while wiping the inner wall of the pipe is housed in a sleeve, and is cleaned together with the pig station by supplying a cleaning solution to the pig station. The washed pigs
When changing the fluid such as paint, it is fired from the pig station and wipes the inside of the pipeline.

[0005]

However, if the station for firing and stopping the pig is different from the pig cleaning room, a mechanism for moving the pig from the stop position to the cleaning room and moving from the cleaning room to the firing station is required. At the same time, a new cleaning mechanism is required to prevent contamination of the piping from the pig stop position to the launch station. This increases the installation space and complicates the structure and control system.

In the pig station in which the pig launching and stopping mechanism is integrated and formed in a double structure, the pig cannot be sufficiently cleaned because the pig is housed closely in the sleeve. The pig is launched into the pipeline from the station in a contaminated state. In addition, there is a dead space where the cleaning liquid does not reach the station. Therefore, when changing the fluid to be transferred in the pipe, the amount of contamination of the fluid increases, and the changed fluid must be discarded in a large amount. In order to enhance the cleanability of the pig, a flow hole for the cleaning liquid can be provided in the sleeve in which the pig in the housing is housed, but in this method, when the pig is fired, a part of the fluid pressure escapes from the flow hole and the pig May not be launched from the pig station into the pipeline.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pig station and a method for cleaning the pig and the station, which enhance the cleaning performance of the pig and the station and prevent contamination at the time of fluid exchange.
It is another object of the present invention to provide a pig station that can reliably stop and fire a pig with a simple structure, and a method of cleaning the pig station.

[0008]

SUMMARY OF THE INVENTION A pig station according to the present invention has an inlet (2) for receiving a pig (1) from a circuit (8).
And an outlet for applying hydraulic pressure to the pig (1) and firing into the circulation path (8)
Station housing (7) with (3) and circulation path (8)
Holder (6) for temporarily holding the pig (1) conveyed into the station housing (7) through the inlet (2) until it is fired through the outlet (3), and upstream from the holder (6) And a drain port (4) for discharging waste liquid pumped from the circulation path (8).

When the type or color of the liquid in the pipeline is switched, the pig (1) disposed in the holder (6) is fired.
The interior of the station housing (7) is pressurized, and the pig (1) is pumped from the outlet (3) into the circulation path (8), and the pig (1) pushes forward the liquid and the inner wall of the circulation path (8). Scraping off the deposits. At this time, the pig containing the deposits scraped off by the pig (1)
(1) The waste liquid at the front is removed from the drain port (4) through the inlet (2). The pig (1) passes from the circuit (8) through the entrance (2) and returns to the pig station again, where the station housing (7)
Stops at the holder (6) formed in the inside, so that a part of the liquid such as the cleaning liquid pumped from behind the pig (1) also drains (4)
Removed from Thereafter, the washing liquid is caused to flow back into the station housing (7) from the outlet (3) to wash the inside of the station housing (7) and the pig (1), and the washing waste liquid is discharged from the drain port (4). After washing of the pig station, the pig (1) waits in the holder (6) and is fired again at the time of washing the pipeline. As described above, since the inside of the station housing (7) can be sufficiently washed by the pig station having a simple structure, contamination by the residue in the pig station can be prevented when the type and color of the liquid are switched. Also, supply the cleaning liquid into the pig
Since (1) can be washed, there is no need to separately provide a pig station for stopping and firing the pig and a washing device for the pig (1), thereby saving space.

In the embodiment according to the present invention, the station housing (7) is vertically arranged with the outlet (3) facing downward, and a holder portion (6) is formed at a lower portion of the station housing (7). When the station housing (7) is arranged vertically with the outlet (3) facing downward, the waste liquid containing the liquid sent along with the pig (1) and the scraped off deposits is discharged from the drain port (4). Since the pressure in the circulation path (8) is partially released,
The pig (1) conveyed from the upper entrance (2) into the station housing (7) sinks to a lower portion of the station housing (7) with an appropriate pressure or its own weight, and stops at the holder (6). Even after the washing is completed, when the specific gravity of the pig (1) is larger than the specific gravity of the liquid, the pig (1) is surely seated at the firing position of the holder (6) by its own weight.

The holder part (6) is formed in a tapered shape whose diameter decreases toward the outlet (3). Accordingly, the station housing (7) has a simple shape with no irregularities, so that it can be completely washed to every corner in the station housing (7), and adherents hardly remain on the station housing (7). In addition, since the outer peripheral portion of the pig (1) is securely in contact with the tapered holder (6),
(1) The rear pressure can be prevented from being released, and the pig (1) can be reliably fired by the liquid pressure without providing a complicated pig firing structure.

Since the station housing (7) has an inner diameter that is 1.1 to 3 times larger than the maximum diameter of the pig (1), the washing liquid flowing from the outlet (3) at the time of washing is released from the outer periphery of the pig (1). The pig (1) is floated while giving an appropriate buoyancy to the pig (1). As a result, the pig (1) does not come into contact with the inner wall of the station housing (7), and the entire pig (1) and the inner surface of the station housing (7) can be completely washed, thereby preventing contamination due to mixing with unnecessary liquid. It can be reliably prevented.
If the inner diameter of the station housing (7) is smaller than 1.1 times the maximum diameter of the pig (1), the outer periphery of the pig (1) frequently collides with the inner wall of the station housing (7), and the pig (1) ) May float excessively and collide with the upper part of the station housing (7), possibly damaging the pig (1). If it is more than three times, at an appropriate flow rate of the cleaning liquid, the cleaning liquid leaks too much from the outer periphery of the pig (1), so that the pig (1) does not float so much.
(1) cannot be sufficiently washed.

In the embodiment according to the present invention, a supply port (5) for supplying a cleaning liquid is further provided in the station housing (7). For this reason, the pig (1) arranged in the holder (6) can be pressure-fed from the outlet (3) toward the circulation path (8). In addition, since the cleaning liquid is supplied from the supply port (5) in addition to the outlet (3) at the time of cleaning, the inside of the supply nozzle (5a) of the supply port (5) can be cleaned, and the flow of the cleaning liquid is formed from various directions. Therefore, the cleaning property in the station housing (7) can be improved.

Pigment between the inlet (2) and the drain (4)
The pig (1) conveyed from the inlet (2) into the station housing (7) by making it shorter than the total length of (1) and by providing the locking portion (9) at the drain port (4), Drainage port with waste liquid (4)
To prevent it from leaking outside.

The method for cleaning a pig station according to the present invention comprises the steps of introducing a pig (1) moving in a circulation path (8) to scrape off deposits from an inlet (2) into a station housing (7); Removing the waste liquid of the adhered substances from the drain port (4), stopping the pig (1) settling in the station housing (7) with the holder (6), and removing the station housing (7). The washing liquid is supplied into the station housing (7) from the outlet (3) formed at the bottom, the pig (1) is floated from the holder (6), and the inside of the station housing (7) and the pig (1) are removed. Washing process and drain for washing waste liquid
Removing from (4).

The embodiment according to the present invention relates to a pig.
After floating (1) to wash the inside of the station housing (7) and the pig (1), the pig (1) is stopped on the holder (6) and formed on the side of the station housing (7). Supplying the cleaning liquid from the supply port (5), and cleaning the inside of the station housing (7) .After cleaning the inside of the station housing (7) and the pig (1), the holder section (6)
And firing the pig (1) arranged at the outlet from the outlet (3) to the circulation path (8) by hydraulic pressure.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pig station according to the present invention and a method for cleaning the same will be described below with reference to FIGS. As shown in FIG. 1, the pig station according to the present embodiment includes a circulation path (8) including a pipe through which a fluid is transferred.
A station housing (7) connected to the The station housing (7) is an inlet for introducing the pig (1) that scrapes off deposits while pressing the liquid remaining in the circulation path (8).
(2) and a holder that temporarily holds the introduced pig (1)
(6) and an outlet (3) through which the pig (1) passes when the pig (1) is fired from the holder (6) to the circulation path (8). The circulation path (8) connected to the station housing (7) can be formed into a single loop as shown in FIG. 2 (a) or a plurality of loops as shown in FIG. 2 (b). The pig (1) may be formed integrally with an elastic material such as rubber, but it must be sure that any bent or deformed parts in the piping are also scraped off and the liquid in front of the pig is pushed out without leaving behind. The pig (1) provided with the shaft (1a) and the skirt (1b) shown in FIG. Pig (1)
Is formed slightly larger than the inner diameter of the conduit of the circulation path (8) and smaller than the inner diameter of the station housing (7). Pig the inner diameter of the station housing (7)
It is formed 1.1 to 3 times larger than the maximum diameter of (1). For this reason, the washing liquid supplied from the outlet (3) escapes from the outer periphery of the pig (1) to give the pig (1) an appropriate buoyancy, and the pig (1) can be washed well. The holder part (6) is formed in a tapered shape having a diameter reduced toward the outlet (3), and is hydraulically or, alternatively, the station housing (7) is vertically arranged as shown in FIG. 1 and the specific gravity of the pig (1). When is larger than the liquid specific gravity, the pig (1) is held by the holder (6) due to gravity.

On the upstream side of the holder section (6), a drain port (4) for discharging waste liquid pumped into the station housing (7) together with the pig (1) from the circulation path (8) through the inlet (2). ). So that the pig (1) does not flow out from the drain (4)
The drainage nozzle (4a) of the drainage port (4) is provided with a locking part (9), and the interval (L) from the inlet (2) to the drainage port (4) is set longer than the entire length of the pig (1). Form short. The locking portion (9) is provided with a rod-like body near the axis of the drain nozzle (4a) so that resistance does not hinder the outflow of the waste liquid. The drain port (4) discharges the washing waste liquid supplied from the outlet (3) to wash the inner wall of the station housing (7) and the pig (1).

As shown in FIG. 1, between the outlet (3) and the drain port (4), when the station housing (7) is washed, the outlet is provided.
A supply port (5) capable of supplying a cleaning liquid from other than (3) is provided.
The cleaning liquid supplied from the supply port (5) gives a different flow from that supplied from the outlet (3), cleans the supply nozzle (5a) and the inside of the station housing (7), and drains the liquid (4). Is discharged to the outside.

An embodiment of the pig station cleaning method will be described with reference to FIG. In the present embodiment, first, a pig (1) that moves in the circulation path (8) and scrapes off deposits on the inner wall of the pipe is introduced into the station housing (7) from the inlet (2).
The scraped off deposits are moved into the station housing (7) together with the liquid in front of the pig (1) and a part of the washing waste liquid behind the pig (1), which has been pushed to the pig (1) through the circulation path (8). Introduced,
As shown in FIG. 3A, the liquid is removed from the drain port (4). The pig (1) naturally sinks in the vertically arranged station housing (7) with the outlet (3) facing downward, and FIG.
The skirt portion (1b) is locked and stopped by the tapered holder portion (6) as shown in FIG.

Next, as shown in FIG.
Supply the cleaning liquid into the station housing (7) from
The pig (1) is floated from the holder (6) to wash the inside of the station housing (7) and the pig (1). The cleaning solution is
Use the same organic solvent, alkali solution, and the like as the cleaning liquid for pumping the inside of the circulation path (8), and change the type according to the liquid transferred in the pipe. By floating the pig (1) from the holder (6), not only the wall surface inside the station housing (7) but also the pig (1) and the holder (6) can be reliably washed. The washing waste liquid is discharged to the outside through the drain port (4).

After the pig (1) is floated to clean the inside of the station housing (7) and the pig (1), the supply of the cleaning liquid from the outlet (3) is stopped, and the pig (1) is moved to the holder ( Place it again in 6). With the pig (1) placed in the holder (6),
As shown in FIG. 3D, the station housing (7)
The cleaning liquid is supplied from a supply port (5) formed on the side of the supply port (5) to remove waste liquid containing adhering matter remaining in the supply nozzle (5a) of the supply port (5), and to remove the cleaning liquid from the station housing (7). Wash again. Thereafter, the cleaning liquid may be supplied again from the outlet (3) according to the degree of contamination in the pig (1) and the station housing (7).

Station housing (7) inside and pig
After completely removing the contaminants attached to (1),
The pig (1) arranged in (6) is fired from the outlet (3) to the circulation path (8) by the hydraulic pressure from the supply port (5) or the inlet (2).

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a pig station according to the present invention is disposed in a coating pipe will be described with reference to FIGS. The pipe diagrams shown in FIGS. 4 to 8 show a station housing (7) for firing and stopping the pig (1), and a station housing (7).
Loop (8) where pigs (1) fired from move
And a color change valve (16) that can switch a plurality of connections with the circulation path (8) according to the paint to be used;
Detects passage of a paint gun (15) that sprays paint supplied from a color change valve (16) and a pig (1) traveling in a circulation path (8), and sends control signals such as valve switching. Sensor
(11, 12, 13). In FIG. 4, the paint A tank (32)
The paint A stored in the tank is filled in the circulation path (8),
This shows the state of being injected from (15).

After the use of the paint A is finished, the paint B tank (3
In order to switch to the paint B stored in 3), the paint A in the circulation path (8) was collected and washed. The process of collecting and cleaning the paint A is performed by firstly using a paint pump A (22) for supplying the paint A.
Is turned off, the valve (42) on the discharge side of the paint pump A (22) is closed, the valve (46) connected to the outlet (3) of the station housing (7) and the valve connected to the supply port (5). (47) opened. A first port (41a) connected to the outlet (3) of the station housing (7) with respect to the color change valve (16).
Port connected to the paint pump A (22) and B (23) side
(41b), the three-way valve (41) is switched to the first port (41a) side, the cleaning pump (21) for supplying the cleaning liquid is turned on,
The pig (1) was fired from the station housing (7) into the circuit (8). At this time, since the valves (48) and (49) connected to the drain port (4) and the inlet (2) are closed, the hydraulic pressure from the washing pump (21) is supplied to the station housing (7). Everything is transmitted to the pig (1) through the mouth (5), and the pig (1) can be fired from the holder (6) of the station housing (7). The fired pig (1) passes through the first port (41a) of the three-way valve (41) and, as shown in FIG. 5, in the circulation path (8) together with the cleaning liquid supplied from the cleaning tank (31). It moved while pushing forward paint A. The paint A filled in the circulation path (8)
For the color change valve (16), a first port (52a) connected to the cleaning tank (31) side and a second port (52b) connected to the paint A tank (32) and the paint B tank (33). Paint tank A (3) through the second port (52b) of the three-way valve (52)
Returned to 2). Further, the pig (1) proceeds in the circulation path (8). When the pig (1) reaches the sensor (13), the washing pump (21) is turned off, the pig (1) also stops, and the valves (46, 47) and the circulation path ( The valve (53) for returning the paint A to the paint A tank from 8) is closed, the valves (48, 49) and the valve (50) for supplying the cleaning liquid directly to the circulation path (8) are opened, and the cleaning pump (21) is opened. It turns ON again. Pig which was stopped (1)
Is pushed by the washing liquid flowing into the circulation path (8) through the valve (50), and as shown in FIG.
Moved towards. Since the paint A immediately before the pig is mixed with the cleaning liquid, the paint A is not collected and is collected in the station housing (7).
And, it was sent to the drainage tank (34) through the drainage port (4).

The pig (1) further proceeds along the circulation path (8) and the sensor (1)
After passing through 1), it was transported into the station housing (7). When the pig (1) passes through the sensor (11) for a certain period of time, the washing pump (21) is turned off, the valves (49, 50) are closed, and the pig (1) in the station housing (7) is 3
As in (a) and (b), the user seated on the tapered holder (6). Thereafter, the valve (46) and the valve (55) for connecting the valve (46) and the cleaning pump (21) are opened, the cleaning pump (21) is turned on, and the cleaning liquid flows from the outlet (3) into the station housing (7). Supplied to As a result, the pig (1) floats in the station housing (7) as shown in FIGS. 3C and 7, the pig (1) and the inner wall of the station housing (7) are washed, and the washing waste liquid is discharged. The liquid was sent from the liquid outlet (4) to the drainage tank (34). Subsequently, the washing pump (21) is turned off and the pig (1)
To the holder (6), close the valves (46, 55), and close the valve (47).
Was opened, the cleaning pump (21) was turned on, and the cleaning liquid was supplied from the supply port (5) to clean the inside of the station housing (7). Finally, the valves (46, 47, 55) were switched so that the cleaning liquid could be supplied from the outlet (3) as described above, and the cleaning liquid was supplied again from the outlet (3) to float the pig (1) for cleaning. Pig
In this embodiment, the cleaning step (1) and the cleaning step of cleaning the inside of the station housing (7) were performed for about 20 seconds.

Thereafter, the valves (46, 48) are closed, and the valve (50) and the valve (44) disposed between the three-way valve (41) and the drainage tank (34) are opened, as shown in FIG. So that the cleaning liquid flows from the valve (50)
(8), and flows through the pipe (6) on the supply side of the paints A and B to the drainage tank (34) through the second port (41b) of the three-way valve (41).
1) was washed. Subsequently, the valve (44) is closed, the valve (51) disposed between the three-way valve (52) and the drainage tank (34) is opened, and the valve (5
The washing liquid sent from (0) to the circulation path (8) is the second port of the valve (52).
The pipe (62) on the collecting side of the paints A and B was washed through (52b).

Next, the valves (50, 51) are closed, the three-way valve (52) is switched to the first port (52a), and the valve (55) is opened. It was sent to 8) and returned to the washing liquid tank (31) for circulating washing. The circulation cleaning can be omitted depending on the state of the paint A remaining in the circulation path (8). Thereafter, the pig (1) was moved again in the circulation path (8) in the same manner as in the above step, and the components of the paint A remaining in the circulation path (8) were completely removed. The pig (1) returns into the station housing (7), the washing pump (21) is turned off, and washing of the circulation path (8) is completed.

After the washing is completed, the valves (46, 47) are opened to supply the paint B in the paint B tank (33), and the first ports (41a, 52a) of the three-way valves (41, 52) are opened. The pig (1) in the station housing (7) was pushed out by the pump (21) in the same manner as described above. The fired pig (1) moves in the pipe and the three-way valve (41)
When passing through the sensor (12), the cleaning pump (21)
Turned off and pig (1) also stopped. Subsequently, the valve (46, 4
7) is closed, the valve (43) on the discharge side of the paint pump B (23) is opened,
The three-way valve (41) was switched to the second port (41b), the paint pump B (23) was turned on, and the paint B was supplied to the circulation path (8). The cleaning liquid filled in the circulation path (8) was returned to the cleaning liquid tank (31) together with the pig (1).

After passing through the sensor (13), the pig (1) travels along the circulation path (8) in the same manner as described above, and the station housing (7)
The cleaning liquid was supplied from the outlet (3) and the supply port (5) into the station housing (7), and the step of cleaning the pig (1) and the inner wall of the station housing (7) was performed again.
Unlike the cleaning step of removing the paint A, the front of the pig (1) is filled with the cleaning liquid and the back is filled with the paint B, but the same cleaning step as described above was performed.

Although not shown, the circulation path (8) is filled with the paint B, and when the paint B is used by spraying it from the coating gun (15), the components of the paint A are completely removed. The amount of paint B to be applied can be greatly reduced, and a product coated with a constant color can always be provided.

[0032]

According to the present invention, the cleaning liquid is supplied to clean the inside of the pig station and the pig can be surely cleaned, so that the dirt adhering to the pig station and the pig dissolves in the fluid after the transfer which is transferred in the pipe. And the amount of waste liquid can be reduced. In addition, since the launching, stopping, and cleaning of the pig are all performed in the pig station and the internal structure is simple, the space is reduced, and dirt hardly adheres to the inside of the pig station.

[Brief description of the drawings]

FIG. 1 is a sectional view of a pig station according to the present invention.

FIG. 2 is a conceptual diagram showing a circulation path.

FIG. 3 is a cross-sectional view illustrating a cleaning process of a pig and a pig station according to the present invention.

FIG. 4 is a pipe diagram showing a first embodiment of a pig station according to the present invention.

FIG. 5 is a pipe diagram showing a second embodiment of the pig station according to the present invention.

FIG. 6 is a pipe diagram showing a third embodiment of a pig station according to the present invention.

FIG. 7 is a pipe diagram showing a fourth embodiment of a pig station according to the present invention.

FIG. 8 is a pipe diagram showing a fifth embodiment of the pig station according to the present invention.

[Explanation of symbols]

(1)-pig, (1a)-shaft, (1b)-skirt, (2)-inlet, (3)-outlet, (4)-drain port, (4a)-・ Drain nozzle, (5) ・ ・ Supply port, (5a)
・ ・ Supply nozzle, (6) ・ ・ Holder part, (7) ・ ・ Station housing, (8) Circulation path, (9) ・ ・ Locking part,
(11, 12, 13) ・ ・ Sensor, (15) ・ ・ Coating gun, (16)
..Color change valves, (21).
(22) ・ ・ Paint pump A 、 (23) ・ ・ Paint pump B 、 (3
1) ・ ・ Cleaning liquid tank (32) ・ ・ Paint A tank, (33) ・
・ Paint B tank, (34) ・ ・ Drainage tank,

Continued on the front page (72) Inventor Takuo Nakamura 3-29-5 Takada, Toshima-ku, Tokyo Inside Soken Chemical Co., Ltd. (72) Inventor Takashi Hashizume 3-29-5 Takada, Toshima-ku, Tokyo Soken Kagaku (72) Inventor Seiji Miyamoto 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa F-term (reference) 3B116 AA13 AA47 AB51 BA02 BA03 BA08 BA24 BA38 BA39 BB01 CD22 CD41 3B201 AA13 AA47 AB51 BA02 BA03 BA08 BA24 BA38 BA39 BB01 BB92 CD22 CD41

Claims (10)

[Claims] 1. A station housing having an inlet for receiving a pig from the circuit and an outlet for applying hydraulic pressure to the pig and firing into the circuit, and a pig conveyed from the circuit through the inlet into the station housing through the outlet. A pig station comprising: a holder portion that temporarily holds the liquid until it is fired; and a drain port that is formed upstream of the holder portion and that discharges waste liquid pumped from a circulation path. 2. The pig station according to claim 1, wherein the station housing is vertically arranged with the outlet facing downward, and a holder portion is formed at a lower portion of the station housing. 3. The pig station according to claim 1, wherein the holder portion is formed in a tapered shape whose diameter decreases toward the outlet. 4. The pig station according to claim 1, wherein the station housing has an inner diameter that is 1.1 to 3 times larger than a maximum diameter of the pig. 5. The pig station according to claim 1, wherein a supply port for supplying a cleaning liquid is provided in the station housing. 6. The pig station according to claim 1, wherein the distance from the inlet to the liquid outlet is shorter than the entire length of the pig. 7. The pig station according to claim 1, wherein a locking portion for preventing the pig from flowing out is provided at the drain port. 8. A step of introducing a pig that moves in the circulation path and scrapes off deposits from the inlet into the station housing, removing waste liquid of the scraped-off deposits from the drain port, and removing the waste liquid from the drain port. A step of stopping the sinking pig at the holder, a step of supplying a cleaning liquid into the station housing from an outlet formed at the bottom of the station housing, and floating the pig from the holder to wash the inside of the station housing and the pig. And a step of removing a washing waste liquid from a drain port. 9. After the pig is floated to wash the inside of the station housing and the pig, the pig is stopped at the holder, and a cleaning liquid is supplied from a supply port formed at a side of the station housing. The method for cleaning a pig station according to claim 8, comprising a step of cleaning the inside. 10. The pig station cleaning method according to claim 8, further comprising the step of, after cleaning the inside of the station housing and the pig, firing the pig arranged in the holder portion from the outlet to the circulation path by hydraulic pressure.