JPH0114480B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for moving a pig in a fluid transfer pipe, and in particular, to a method for moving a pig in a fluid transfer pipe, and in particular to a method for moving a pig in a branch pipe after oil has been transferred from an offshore tanker to an onshore tank. A method for moving pigs when the inside of a fluid transfer pipe is alternately partitioned into liquid and gas by multiple pigs, such as when replacing oil accumulated in a fluid transfer pipe with a gas such as inert gas or air. related to.

[Conventional technology]

For example, a fluid transfer pipe such as an oil pipe that imports and ships petroleum between a tanker and a land base tank has a branch such as a sub-oil pipe in the middle of the fluid transport pipe so that different types of petroleum can be received and shipped. A pipe and a valve (herein referred to as a pig stop valve) for stopping the pig downstream of the branch pipe are often provided.

In addition, this fluid transfer pipe is designed to prevent the fluid stagnant in the pipe from leaking or flowing out in the event of an unexpected impact such as an earthquake or a tanker collision. Once this is completed, the remaining fluid in the pipes will be replaced with other safe substances. This replacement includes a water replacement method, an air replacement method, an inert gas replacement method, and the like.

By the way, the above-mentioned water replacement method replaces the oil accumulated in the pipe with water such as fresh water, industrial water, seawater, etc., so it requires a large-scale wastewater treatment facility for the replacement water, and in the case of cold regions. In the case of seawater, heating and insulation equipment is required to prevent freezing, and in the case of seawater, corrosion prevention measures are required, and in the case of product oil transfer, etc., where water is mixed into the transferred fluid during replacement, the quality may be affected. There are various problems such as worsening of

On the other hand, the air replacement method and the inert gas replacement method do not have the above-mentioned problems such as the water replacement method.

[Problem that the invention seeks to solve]

However, in the case of a fluid transfer device that employs an air replacement method or an inert gas replacement method that has such advantages and is equipped with a branch pipe such as a sub-oil pipe and a pig stop valve, the pig stop valve There were frequent accidents where the pigs malfunctioned or the pigs were damaged.

A detailed investigation of the above cause shows that the upstream liquid A causes the pig _G1 to move from upstream to downstream in the fluid transfer pipe by pushing the downstream gas A in the fluid transfer pipe, and the pig _G1 transfers the fluid. After passing through the branch between the pipe and the branch pipe provided in the middle of the fluid transfer pipe, the pig _G1 is closed by closing the pig stop valve provided on the downstream side of the branch. Then, the liquid A is continuously transferred through the branch pipe to carry out import/shipping work, and then the pig G on the upstream side of the pig stop valve is closed by the upstream gas B. ₁ , the liquid in the fluid transfer pipe is pushed out to the branch pipe and moved from upstream to downstream. In a state where another pig G ₂ is stopped near the branch part, that is, the inside of the fluid transfer pipe is on the upstream side. From gas B, pig G ₂ , liquid A,
Pig G ₁ , Gas A, Pig stop valve closed, Gas A
It has been found that the accident occurs when the pig stop valve is opened and both pigs are moved downstream along the fluid transfer pipe by the upstream gas B.

This is because there is gas, which is a compressible fluid, on both sides of the closed pig stop valve, so the pressure on both sides will be different during the fluid transfer operation, and when the pig stop valve is opened, the upstream and downstream sides will be different. Due to the difference in pressure, the pig may move on its own and collide with the operating valve body (disc, ball) of the pig stop valve, deforming or damaging the valve body or pig, or the pig may press strongly against the valve body. It was discovered that this was due to the pig stop valve malfunctioning.

Also, when stopping the other pig G ₂ mentioned above,
Since the gas A existing between the pig stop valve in the closed state and the pig _G1 is a compressible fluid, and the gas B pushing the other pig _G2 is also a compressible fluid,
There was also a problem in that the stopping position of the above-mentioned different pig _G2 was different each time, and the above-mentioned pig _G1 also moved.

Therefore, in order to stop the pig G1 that has passed through the branching section, the pig _G1 is caused to pass through the pig stop valve provided in the middle of the fluid transfer pipe, and then the pig G1 is closed by closing the pig stop valve. ₁ on the downstream side of the pig stop valve, or after passing through the pig stop valve provided in the middle of the fluid transfer pipe, stop it by closing another pig stop valve, and then The method was changed to closing the pig stop valve that passed above.

When another pig G ₂ is stopped by these methods, the inside of the fluid transfer pipe is filled from the upstream side with gas B, pig G ₂ , liquid A, the closed pig stop valve, liquid A,
Pig G ₁ enters the state of gas A, and there is no compressible fluid gas between the stop valve and both pigs G ₁ and G ₂ , improving the accuracy of the stop position of the other pig G ₂ . At the same time, the problem that the Pig G ₁ mentioned above also worked was resolved.

However, when the pig stop valve is opened and both the pigs are moved downstream along the fluid transfer pipe by the upstream gas B, both sides of the pig stop valve are turned outward from the pig stop valve to cause liquid A and the pig G. ₁ or G ₂ and gas A or B, and when the pig stop valve is opened, the pig moves automatically due to the difference in pressure between the upstream and downstream sides, and the valve body of the pig stop valve is activated. The problem of deformation or damage of the valve body and pig due to collision with the valve body, or of the pig stopping valve being inoperable due to strong pressure contact with the valve body, remained unresolved.

[Means for solving problems]

In order to solve the above conventional problems, the present invention provides a pig that moves from upstream to downstream in a fluid transfer pipe by pushing the downstream fluid and passes through a pig stop valve provided in the fluid transfer pipe. is stopped downstream of the pig stop valve, and the pig stop valve is in a closed state, and then the liquid is pushed out to a branch pipe provided upstream of the pig stop valve to maintain the closed state. The pig, which has been moved from upstream to downstream in the fluid transfer pipe toward the pig stop valve by the upstream gas, is stopped upstream of the closed pig stop valve, and then both pigs are moved along the fluid transfer pipe. When moving, the upstream gas and the downstream gas of the pig stop valve are made to communicate with each other through a bypass pipe provided in the fluid transfer pipe to equalize the pressure, and then the communication between the upstream gas and the downstream gas is cut off. At the same time, the pig stop valve is opened.

[Effect]

In this method, first, the upstream gas and the downstream gas, which are compressible fluids, are communicated, and the gas flows from the high pressure side to the low pressure side, so that the pressure on both sides of the pig stop valve is equalized (equal pressure). Therefore, due to the incompressible liquid between the pig stop valve and the pig, both pigs do not move or come into contact with the pig stop valve during the pressure equalization work, and the pressure on both sides of the pig stop valve is reduced. become equal.

Next, in order to move both pigs, even if the communication between the upstream gas and the downstream gas is cut off and the pig stop valve is opened, both pigs will not move because the pressure on both sides of the pig stop valve is equalized. The pig stop valve operates smoothly and opens without touching the pig stop valve, allowing both pigs to move along the fluid transfer pipe.

In addition, the pig that pushes the downstream gas and moves from upstream to downstream in the fluid transfer pipe by the upstream gas and passes through the pig stop valve provided in the fluid transfer pipe stops downstream of the pig stop valve, and , as mentioned above, the case where the pig stop valve is closed is as follows.
A case where the pig is stopped downstream of the pig stop valve by passing through the pig stop valve provided in the middle of the fluid transfer pipe and closing the pig stop valve, or a case where the pig is stopped on the downstream side of the pig stop valve, or in the middle of the fluid transfer pipe. A case in which the pig is passed through the pig stop valve provided at the top of the pipe, and then stopped by the closing operation of another pig stop valve, preferably an upstream pig stop valve, and then the pig stop valve that has passed is closed. There is.

In addition, the liquid is pushed out to a branch pipe provided upstream of the pig stop valve, and the pig that has moved from upstream to downstream in the fluid transfer pipe is closed by the upstream gas toward the closed pig stop valve. In order to stop the pig on the upstream side of the pig stop valve, it is desirable to stop the gas supply to the upstream side of the pig and close the valve of the branch pipe, but if the branch pipe is thin, such an operation is not recommended. The pig can also close the branch pipe by itself and stop the pig.

Furthermore, during the pressure equalization operation, the liquid is pushed out to a branch pipe provided upstream of the pig stop valve and moved from upstream to downstream in the fluid transfer pipe by the upstream gas toward the closed pig stop valve. It is desirable that the state in which the pig stopped upstream of the pig stop valve in the closed state is a state in which the supply of gas upstream of the pig is stopped and the gas upstream of the pig is sealed. For example, if the gas on the downstream side of the pig stop valve in the closed state is in a sealed state, the pressure on both sides of the pig stop valve will be equal even if the supply of gas on the upstream side of the pig is not stopped. I have no problem with that. In addition, the gas on the upstream side of the closed pig stop valve is in a sealed state, and the gas on the downstream side of the pig stop valve is not in a sealed state, but is usually in a vent tank or the like installed downstream of the fluid transfer pipe. If the pig stop valve is in communication with the atmosphere through the mist separator, the gas on the upstream side of the pig stop valve will flow to the atmosphere through the bypass pipe, the fluid transfer pipe downstream of the pig stop valve, and the mist separator. The pressure on both sides can be equalized. In this case, unlike the case where, for example, the vent of the fluid transfer pipe is simply opened to bring the pressure to atmospheric pressure, resulting in equal pressure on the upstream and downstream sides of the pig stop valve, a mist of the transferred liquid may be released into the atmosphere. In addition, there is an advantage that piping for sending gas to the mist separation device is not necessary because the fluid transfer pipe downstream of the pig stop valve can be used. In short, it is sufficient that the pressure on both sides of the pig stop valve be equalized.

〔Example〕

An embodiment of the present invention will be described in detail below based on the drawings.

FIG. 1 shows an embodiment of the overall configuration of an oil feeding device for carrying out the method for moving a pig in a fluid transfer pipe according to the present invention.

In the figure, numeral 1 is an offshore tanker, and 2 and 2a are the first and second tankers installed at an onshore oil receiving base, respectively.
It is a base tank. A is the oil feed line of this oil feed device,
B is an inert gas (hereinafter referred to as N ₂ gas) line.

Oil feed line A is the main oil feed pipe (fluid transfer pipe) a ₁
, a tip oil feed pipe _A2 that supplies oil from the tanker ₁ to the main oil feed pipe A1, and a terminal oil feed pipe _A3 that receives the oil transferred by the main oil feed pipe A1 to the first base tank 2 _.
and a sub oil transmission pipe (branch pipe) A ₄ that receives oil from the onshore part of the main oil transmission pipe A ₁ into the second base tank 2a.
, oil pipe A ₅ for launching pigs, and oil pipe A ₆ for collecting pigs.
and the first, second, and third bypass oil pipes a ₇ , a ₈ ,
It consists of a ₉ and a pressure equalizing pipe (bypass pipe) a ₁₀ .

The main oil transmission pipe _A1 is installed between the offshore cargo handling pier S and the onshore oil receiving base, and a pig launcher 3 is attached to the end on the pier side, and a pig receiver 4 is attached to the end on the onshore side. ing. moreover,
In the main oil pipe _A1 , there is a first electric valve MV-1 near the pig launcher 3, a second electric valve MV-2 near the boundary between the sea area and the land area, and a third electric valve near the pig receiver 4. A fourth electric valve (pig stop valve) MV-4 is provided between the second electric valve MV-2 and the third electric valve MV-3.

The tip oil feed pipe _A2 has the same diameter as the main oil feed pipe _A1 , and one end is connected to the fifth electric valve MV-5.
It is connected to the loading arm 5 installed on the offshore cargo handling pier S, and the other end is connected to the sixth electric valve MV-6.
Through the main oil pipe A ₁ first electric valve MV
-1 and the second electric valve MV-2.
It is connected to branch point A near electric valve MV-1.

The terminal oil pipe _A3 has the same diameter as the main oil pipe _A1 , and one end is connected to the third electric valve MV of the main oil pipe _A1 .
-3 and the fourth electric valve MV-4, it is connected to the branch point RO near the third electric valve MV-3, and the other end is connected to the first base tank 2, and on the way, from the branch point RO side A seventh electric valve MV-7, an air separator 6, and a flow meter 7 are installed.

The sub oil pipe _A4 is branched from the branch point C of the main oil pipe _A1 between the second electric valve MV-2 and the fourth electric valve MV-4, and is connected to the second base tank 2a. Flow control valve CV-1, air separator 6a,
A flow meter 7a is provided. In addition, the pig launching oil pipe _A5 has a smaller diameter than the main oil pipe _A1 ,
A fifth electric valve MV-- whose one end is connected to the approximate center of the pig launcher 3, and whose other end is connected to the tip oil feed pipe _a2
It is connected to a branch point near the fifth electric valve MV-5 between the fifth electric valve MV-5 and the sixth electric valve MV-6,
Flow control valves are installed sequentially from the pig launcher side on the way.
CV-2 and air separator 8 are installed.
The pig recovery oil pipe _A6 has a smaller diameter than the main oil pipe _A1 , and has a flow rate adjustment valve CV-3 in the middle.
One end is connected to the pig receiver 4, and the other end is connected between the seventh electric valve MV-7 of the terminal oil feed pipe _a3 and the air separator 6.

The first bypass oil pipe _a7 has an eighth electric valve MV-8 on the way, and is installed as a bypass for the second electric valve MV- ₂ of the main oil pipe a1. The diameter of this first bypass oil pipe a ₇ (or the 8th
The diameter of the electric valve MV-8) is set to be extremely small compared to the diameter of the main oil pipe _A1 (or the diameter of the second electric valve MV-2), and is normally the diameter of the first bypass oil pipe _A7 . is set to about 0.5 to 5% in area ratio with respect to the diameter of the main oil pipe _A1 .

The second bypass oil pipe _a8 has a ninth electric valve MV-9 in the middle, and one end is connected to the fourth valve of the main oil pipe _a1 .
It is connected between the electric valve MV-4 and the branch point C of the sub-oil feed pipe _A4 , and the other end is connected between the flow rate control valve CV-1 of the sub-oil feed pipe A- ₄ and the air separator 6a. There is.

In addition, the third bypass oil pipe _a9 has a tenth electric valve MV-10 in the middle, and one end is connected to the main oil pipe _a1.
4th electric valve MV-4 and 3rd electric valve MV
-3 near the fourth electric valve MV-4, and the other end is connected between the flow rate control valve CV-1 of the sub oil pipe _a4 and the air separator 6a.

The diameters of the second and third bypass oil pipes a ₈ and a ₉ (or the diameters of the ninth electric valve MV-9 and the tenth electric valve MV-10) are the same as those of the main oil transmission pipe a ₁ and the sub oil Diameter of feed pipe a ₄ (or 4th electric valve MV
-4 and the diameter of the flow rate control valve CV-1), and is usually set at about 0.5 to 5% in terms of area ratio. The pressure equalizing pipe _a10 has a small diameter like the above-mentioned bypass pipes _a7 , _a8 , and _a9 , and there is a 11th pipe in the middle.
It has an electric valve MV-11, and is piped as a bypass of the fourth electric valve MV-4 of the main oil pipe _a1 . In addition, in the figure, 9, 10, 10a are vent tanks, 11, 12, 13, 13a, 14,
14a is a drain pump.

On the other hand, the N ₂ gas system line B is composed of a gas supply pipe b ₁ , first and second gas recovery pipes b ₂ and b ₃ , and a pig back-pushing pipe b ₄ around the N ₂ gas tank 15. There is.

Gas supply pipe B ₁ has a gas pressure control valve CV in the middle.
-4, and is piped between the N ₂ gas tank 15 and the pig launcher 3. The first gas recovery pipe b ₂ is equipped with an N ₂ gas compressor 16, first and second mist separators 17 and 18, and a gas pressure adjustment valve CV-5 in sequence from the N ₂ gas tank 15 side, and the N ₂ gas tank 15 and the pig launcher 4. 2nd gas recovery pipe b ₃
Attach pressure control valve CV-6 in the middle,
One end is connected between both mist separators 17 and 18 in the first gas recovery pipe _b2 , and the other end is connected to the upstream side of the second electric valve MV-2 (hereinafter referred to as equipment, etc.) in the main oil pipe _a1 . Pig launcher 3 in the center
The side where the pig receiver 4 is located is referred to as the "upstream side" and the side where the pig receiver ₄ is located is referred to as the "downstream side". There is. Pig reverse push tube b ₄ is
A gas pressure regulating valve CV-7 and a twelfth electric valve MV-12 are provided in the middle, one end of which is connected to the _N2 gas tank 15, and the other end is connected to the third part of the main oil feed pipe _a1 .
Connection pipes are respectively connected to the branch point G between the electric valve MV-3 and the branch point E of the third bypass oil pipe _A9 . In addition, 14b in the figure is a drain pump that collects drain from the first mist separator 17.

By the way, the main oil pipe _A1 has a first pig detector near the downstream side of the first electric valve MV-1.
PD ₁ has second and third pig detectors PD 2 and PD ₃ near the upstream side of the second electric valve MV-2, and a fourth pig detector PD 2 and PD ₃ near the upstream side and downstream side of the fourth electric valve MV-4. , 5th, 6th, 7th Pig Detector
PD ₄ , PD ₅ , PD ₆ , PD ₇ are the third electric valve MV
8th Pig Detector PD ₈ is located near the upstream side of the branch point B of terminal oil pipe a ₃ on the upstream side of 3.
A ninth pig detector PD ₉ is provided between the electric valve MV-3 and the pig receiver 4, respectively.

The second pig detector PD ₂ is installed near the upstream side of the main oil pipe a ₁ to the branch point of the second gas recovery pipe b ₃ , and the second electric valve MV
-2 (or to the branch point of the second gas recovery pipe b ₃ , the first
The installation distance from the branch point d) of the bypass oil pipe _A7 is the pig movement speed in the main oil pipe _A1 , the second electric valve MV-2, and the third electric valve MV-3.
and the time required to open or close pressure regulating valve CV-6, these valves MV-2, MV-3,
It is set taking into consideration the flow rate characteristics when CV-6 is opened or closed.

In other words, the installation position of the Pig Detector PD ₂ is the offshore oil transmission pipe _A1 where the pig moves with _N2 gas on the upstream side and oil on the downstream side, as described below.
In the case of gas replacement, the speed of deceleration of the pig due to the closing operation of the second electric valve MV- ₂ by the pig passage detection signal of the second pig detector PD 2 is changed between the main oil feed pipe a ₁ and the second At the branching point with the collection pipe _b3 , when the predetermined set speed Vmin is reached and the pig passes the installation position of the third pig detector _PD3 , the second electric valve MV-2 is completely closed. This is the position calculated from the first condition such that (see Figure 5), and
In the case of gas recovery from offshore oil transmission pipe _A1 , where the pig moves with oil on the upstream side and _N2 gas on the downstream side, the pig passage detection signal from the second pig detector PD ₂ causes the closure. Pressure regulating valve starts to
Third electric valve MV-3 begins to open with CV-6
When the pig passes the branch point between the main oil supply pipe _A1 and the second gas recovery pipe _B3 , the pressure regulating valve CV-6 has just completed closing, and the third electric valve
It is required that MV-3 be at a position calculated from the second condition (see Fig. 5) that provides the timing to obtain the opening degree Qmin that allows a flow rate greater than the minimum flow rate of the tanker 1 pump. However, in reality, the position calculated from the first condition and the position calculated from the second condition do not match, so the position calculated from the one condition, which has a larger distance from the second electric valve MV-2, 2. Determine the installation position of Pig Detector PD ₂ , and use a timer to determine the difference in the closing timing of pressure regulating valve CV-6 and third electric valve MV-3 based on the difference between this position and the position calculated from the other condition. (See Fig. 5 - In the case of Fig. 5, the first condition is when the distance from the second electric valve MV-2 is determined to be large.)

The third pig detector PD ₃ is located between the branch point d of the first bypass oil pipe a ₇ and the branch point of the second gas recovery pipe b ₃ in the main oil pipe a ₁ and is very close to said branch point d. located at the location. Further, the fourth pig detector PD ₄ is provided near the upstream side of the branch point C of the sub oil pipe A ₄ in the main oil pipe A ₁ , The installation distance from the branch point C of oil pipe _A4 and the branch point H of second bypass oil pipe _A8 is determined by the pig movement speed in the main oil pipe _A1 and the required closing of the flow control valve CV-1. It is calculated and set based on the same conditions as the first condition when determining the installation position of the second pig detector PD ₂ , taking into consideration the time and flow rate characteristics when closed.

The fifth pig day detector PD ₅ is the main oil pipe A ₁
It is provided at a position close to the branch point H between the branch point H of the second bypass oil feed pipe _A8 and the branch point C of the sub oil feed pipe _A4 . The 6th pig detector PD ₆ is located between the 4th electric valve MV-4 and the branch point H of the 3rd bypass oil pipe _A9 in the main oil pipe _A1 .
The seventh pig detector PD 7 is installed near the electric valve MV-4, and the seventh pig detector PD ₇ is connected to the branch point H of the third bypass oil pipe A ₉ in the main oil pipe A ₁ and the pig reverse push pipe B ₄ . It is located near the branch point E between the branch point G and the branch point E.

Next, a control system for each part of the recovery and replacement apparatus will be explained with reference to FIGS. 2 to 4.

FIG. 2 is a flow sheet showing a fully automatic operation system for the N ₂ gas compressor 16.

Since the N ₂ gas compressor 16 in this recovery and displacement apparatus is operated before and after receiving oil, its operation is not continuous operation but batch operation. Therefore N ₂
Automatic operation of the gas compressor 16 is desirable in terms of saving labor for the operator, and in this embodiment, it is operated as shown in the figure. Note that the arrows drawn between each block in the figure indicate the order of operation. Only the operation of turning on (ON) the start switch is performed manually by the operator, and the other blocks surrounded by two-dot chain lines are operated by an automatic sequence. Note that PS ₁ and PS ₂ in the figure are pressure switches provided on the mist separators 17 and 18, respectively, and PS ₃ and PS ₄ are pressure switches provided on the main oil feed pipe _a1 .

FIG. 3 shows the pig launcher 3, respectively.
1 is a system diagram and flow sheet showing a pig launch system according to the present invention.

Hydraulic cylinders 21 and 22 operated by a hydraulic unit 20 are attached to the pig launcher 3, and the pins 21 and 22 of each cylinder 21 and 22 are
a, 22a are faced into the pig launcher 3. In the figure, 23 is a sequence control device, PD ₁₀ is a pig detector for detecting the seating of the pig before launching, a ₅ is the oil pipe for launching the pig, b ₁ is the gas supply pipe, MV
-1 is the first electric valve, and G ₁ , G ₂ , and G ₃ are pigs stored in the pig launcher 3. The pig launcher 3 is configured in this way, and this operation is sequentially controlled as shown in the flow sheet, and each pig
G ₁ , G ₂ , and G ₃ are fired. The pig is stored in the pig launcher 3 manually by the operator.

Figure 4 is a flow sheet for pressure and flow rate control using the electric valve adopted in this oil feeding device. 3 in the diagram
0 is the sub oil pipe a ₄ of the oil transport line A, the pig launching oil pipe a ₅ , the pig recovery oil pipe a ₆ , the _N2 gas line B
gas supply pipe b ₁ , first and second gas recovery pipes b ₂ , b ₃ ,
Oil or _N2 gas flow path showing pig backpush tube b ₄ etc.
Reference numeral 31 denotes a flow rate or pressure transmitter attached to the flow path 30, and transmitters _FIC1 , _FIC2 , _FIC3 , PIC1, PIC attached to each of the pipes _a4 , _a5 , _a6 , _{b1 to b4 . 2} , PIC ₃ ,
Showing PIC ₄ . Reference numeral 32 designates an electric valve provided in the flow path 30, which includes flow rate control valves CV- ₁ to CV-3 and pressure control valve CV- ₄ provided in each of the pipes _a4 , _a5 , _a6 , b1 to b4. ~CV-7 is shown. 33 is a controller, 34 is a positioner, 35 is a start forced closing circuit, 36 is a contactor, 37 is a sequence circuit, and each of the above parts is installed on a panel. The dotted line arrows in the figure indicate the condition signal paths of each part.

Temperature, pressure, flow rate in normal process industries,
When controlling industrial quantities such as liquid level, the control end, that is, the various control valves, may adopt a continuous control system using a diaphragm or air cylinder operator powered by air pressure, but for practical use, a dryer A control valve powered by pneumatic pressure is used to control systems that require an air source with an attached air source and are planned to be installed over long distances with a small number of control loops, such as this oil delivery system. Adopting this would not only require large-scale equipment but also be extremely uneconomical, so in this example, we adopted a method of controlling the fluid in the pipeline using an electric valve to simplify the ancillary equipment. It's on.

Next, the operation of the oil feeding device constructed as described above will be explained.

(1) Replacement with _N2 gas up to the offshore branch point and
How to recover _N2 gas.

How to replace gas in the oil pipe (when replacing oil in the oil pipe with _N2 gas) The opening/closing status of _each valve before gas replacement is as follows. There is.

(MV valve opening/closing status) MV-1 “closed”, MV-2 “open”, MV-3
“Open”, MV-4 “Open”, MV-5 “Closed”, MV
-6 “closed”, MV-7 “closed”, MV-8 “open”,
MV-9 “closed”, MV-10 “closed”, MV-1
1 “closed”, MV-12 “closed” (CV valve opening/closing status) CV-1 “closed”, CV-2 “closed”, CV-3
“Open”, CV-4 “Closed”, CV-5 “Closed”, CV-
6 “Closed”, CV-7 “Closed” To replace the N ₂ gas in the main oil pipe a ₁ , first insert the pig G ₁ into the pig launcher 3 and open the first electric valve MV-1. Next, by opening the pressure control valve CV-4, the gas pressure accumulated in the _N2 gas tank 15 is
Pig G ₁ joins G ₁ and moves inside main oil pipe A ₁ while pushing the oil inside main oil pipe A ₁ .
It is replaced with _N2 gas. At this time, the pressure of the _N2 gas supplied from the _N2 gas tank 15 is controlled by the pressure control valve CV-4, and the flow rate on the oil side is controlled by the flow rate control valve CV-3, so that the difference between before and after the pig _G1 is controlled. The pressure is kept constant and the pig _G1 moves through the pipe at a constant speed.
In addition, in order to prevent wear of pig G ₁ and to switch each electric valve within a fixed time, in this embodiment, the moving speed of pig G ₁ is constant at approximately 1.0.
Flow control valve CV-3 so that m/sec
controlled by.

When the pig G ₁ passes through the second pig detector PD ₂ and is detected, the second pig detector PD 2 is detected as shown in FIG.
The second detection signal is detected by Pig Detector PD ₂ .
The electric valve MV-2 begins to close, the flow rate is gradually narrowed down, and the speed of the pig _G1 is reduced.
When the second electric valve MV-2 is completely closed, oil flows only from the first bypass oil pipe _a7 , the pig _G1 becomes even slower, and the upstream branch of the first bypass oil pipe _a7 flows. When it reaches near the point D, the third pig detector PD ₃ detects it, and this detection signal triggers the second gas recovery pipe.
It is confirmed that Pig G ₁ has passed the branch point of b ₃ . 3rd pig detector PD ₃ is pig
After detecting the passage of the pig G ₁ , a timer is used to set a time difference corresponding to the time it takes the pig G ₁ to reach the branch point _N of the first bypass oil pipe _A7 from the installation position of the pig detector PD 3. 3 Pig detector PD ₃ sends a gas replacement end signal, so the 8th electric valve MV-8
and the third electric valve MV-3 is closed,
As shown in FIG. 5, the pig _G1 stops at the branch point N, and the inside of the main oil pipe _a1 located above the sea is replaced with _N2 gas.

At the same time as the replacement is completed, the pressure control valve CV-4
is closed, and the pressure control valve CV-6 is closed.
is opened and depressurization of the replacement gas is performed. This depressurization work is carried out when it would be a safety hazard to store the replacement gas, which has reached a high pressure state during the replacement work, in the main oil transmission pipe _A1 for a long period of time after the replacement is completed. This can be omitted if there is no problem with security. During this depressurization work, the displacement gas in the sea part of the main oil pipe _A1 is replaced by the pressure control valve CV.
-6, via mist separator 17
_N2 gas tank 1 by _N2 gas compressor 16
5 will be collected. That is, when the pig G ₁ passes through the second pig detector PD ₂ and is detected, the N ₂ gas compressor 16 is in a no-load operation with the electric motor started, and the pressure regulating valve CV- 6 opens and starts pressure control of the mist separator 17, load operation is started by a signal from the first pressure switch PS ₁ installed in the mist separator 17, and the displacement gas in the main oil feed pipe A ₁ is sucked. do. When the pressure of the replacement gas in the sea part of the main oil pipe _a1 is reduced to the set pressure of the third pressure switch _PS3 installed in the sea part of the main oil pipe _a1 , the pressure from the pressure switch _PS3 is reduced. N ₂ by signal
The gas compressor 16 is automatically stopped, the pressure control valve CV-6 is closed, and the pressure reduction work is completed.

In the oil feeding work associated with N ₂ gas replacement in the above, the movement to accurately stop the pig G ₁ at a fixed position upstream of the second electric valve MV-2 in the main oil feeding pipe A ₁ (this oil feeding device Replacement of _N2 gas in the offshore part of main oil pipe _A1 and the second
The branch part N2 to the base tank _2a (in gas replacement, etc.) is used to ascertain the accurate amount of residual oil in the pipe for bonded processing, for example, and to the second electric valve MV-2 which is operating in the closing direction. This operation is required to prevent pig G ₁ from being bitten. As mentioned above, in this embodiment, the diameter of the eighth electric valve MV-8 is 0.5 to 5 in area ratio to the second electric valve MV-2.
%, but this is because when the pig G 1 approaches the branch part of the second gas recovery pipe b ₃ in the main oil transmission pipe a ₁ , the corner part between _{the pig G 1 and} the branch part When the amount of displacement gas leaking from 〓 to the main oil transmission pipe A _{1 in front of the pig G 1 and} the amount of oil sent from the first bypass oil transmission pipe A ₇ are balanced, the pig G ₁ is connected to the branch part. Therefore, if the flow rate that does not stop the pig G ₁ midway flows to the first bypass oil feed pipe a ₇ , and the pig G ₁ stops at the branch part d of the first bypass oil feed pipe a ₇ , , Pig G ₁ completely seals the branch part 2 and prevents the replacement gas from leaking into the first bypass oil pipe A ₇ . It will change if other conditions are different.

Method for recovering _N2 gas in oil pipes (when transporting oil through gas-replaced oil pipes) The opening/closing status of each valve after _N2 gas replacement is as follows.

(MV valve opening/closing status) MV-1 “closed”, MV-2 “closed”, MV-3
“Closed”, MV-4 “Open”, MV-5 “Closed”, MV
-6 “closed”, MV-7 “closed”, MV-8 “closed”,
MV-9 “closed”, MV-10 “closed”, MV-1
1 “closed”, MV-12 “closed” (CV valve opening/closing status) CV-1 “closed”, CV-2 “closed”, CV-3
“Open”, CV-4 “Closed”, CV-5 “Closed”, CV-
6 “Closed”, CV-7 “Closed” N ₂ The status of the main oil pipe a ₁ after gas replacement is determined by the pig on the upstream side of the second electric valve MV-2.
G ₁ is stopped and the upstream of pig G ₁ is N ₂
replaced with gas. To recover the gas in the main oil pipe _A1 , first, insert the previously used pig _G1 and another pig _G2 into the pig launcher 3. Next, the original fifth electric valve MV-5 of the loading arm 5, the first electric valve MV-1 and the second electric valve MV-2 at the outlet of the pig launcher 3, the flow rate adjustment valve CV-2, and the pressure adjustment valve CV- Open 6. When oil is started to be received by the oil pump (not shown) of the tanker 1 in this state, the oil passes through the air separator 8 and is sent into the pig launcher 3 while the flow rate is controlled by the flow control valve CV-2. When pressure is applied to the pig G ₂ in the pig launcher 3, the pig G ₂ enters the main oil pipe A ₁ and moves. At the same time, the first pig detector PD ₁ detects the movement of the pig G ₂ and detects N. ₂ The gas compressor 16 automatically starts and the pressure regulating valve
The replacement gas in the main oil pipe _a1 via the CV-6 and the mist separator 17 is recovered into the N2 gas tank 15 by _{the N2} gas compressor 16.

In this case, the flow rate of oil received from the tanker 1 is controlled by the flow rate control valve CV-2, but if the set value of the flow rate is equal to or lower than the suction capacity of the _N2 gas compressor 16 The N ₂ gas compressor 16 repeats loaded operation and no-load operation depending on the difference between the received oil flow rate and the suction capacity of the N ₂ gas compressor 16. This load operation and no-load operation are performed by detecting the pressure inside the mist separator 17 by the first pressure switch PS ₁ installed in the mist separator 17. Note that if the received oil flow rate is higher than the suction capacity of the _N2 gas compressor 16, the _N2 gas pressure in the main oil pipe _a1 will gradually increase as the pig _G2 moves, but the N2 gas pressure will increase gradually as the pig _G2 moves. The suction pressure of the compressor 16 is controlled by the pressure control valve CV- ₆ , and the load is kept constant _.
Oil can be accepted if the oil pump discharge pressure of the tanker 1 has a capacity higher than the N ₂ gas pressure that has risen at the branch point of the tanker 1.

Next, Pig G ₂ is the second Pig Detector PD ₂
When detected, the pressure control valve CV is automatically operated as shown in Figure 5.
-6 is closed, the third electric valve MV-3 is opened, and N ₂ gas recovery is completed. In addition, Pig G ₂ , which is pushed by oil and moves, is the second gas recovery pipe.
When passing through the branch point b ₃ , the pressure control valve CV-6 is completely closed at the same time, so a large amount of oil flows through the second gas recovery pipe b ₃ to the mist separator 17. It does not flow into. Even after N ₂ gas recovery is completed, the movement of pig G ₂ does not stop, and the oil received last time, pigs G ₁ and G ₂ , and the oil received this time move inside the main oil pipe A ₁ to the pig receiver 4 side. move towards. The 9th pig detector PD ₉ at the entrance of pig receiver 4 is the upstream pig.
When the passage of G ₂ is detected, the third electric valve MV
-3 is closed, the seventh electric valve MV-7 is opened, and the two pigs G ₁ and G ₂ are stored in the pig receiver 4.

Next, the sixth electric valve MV-6 opens, and the flow rate adjustment valve CV-2 and the first electric valve MV open.
-1 is closed and normal oil reception begins.

(2) Gas recovery and replacement methods for all oil pipelines.

Method for recovering gas in oil pipes (when replacing gas in oil pipes is recovered and transporting oil) The opening/closing status of each valve after gas replacement is as follows.

(MV valve opening/closing status) MV-1 “closed”, MV-2 “open”, MV-3
“Closed”, MV-4 “Open”, MV-5 “Closed”, MV
-6 “closed”, MV-7 “closed”, MV-8 “closed”,
MV-9 “closed”, MV-10 “closed”, MV-1
1 “closed”, MV-12 “closed” (CV valve opening/closing status) CV-1 “closed”, CV-2 “closed”, CV-3
“Closed”, CV-4 “Closed”, CV-5 “Closed”, CV-
6 “Closed”, CV-7 “Closed” Insert pig G ₁ into pig launcher 3.
Next, the original fifth electric valve MV-5 of loading arm 5, and the first electric valve MV-5 of the pig launcher 3 outlet.
Outlet valve MV-1, third electric valve MV-
3. Open flow control valve CV-2 and pressure control valve CV-5. Tanker 1 in this state
When the pump starts receiving oil, the oil flows through the air separator 8 and is sent to the pig launcher 3 while the flow rate is controlled by the flow rate control valve CV- ₂ . G ₁ moves, and when the first pig detector PD ₁ detects the passage of pig G ₁ , the N ₂ gas compressor 16 is started and the displacement gas in the main oil feeder a ₁ is transferred to the pressure regulating valve CV -
5. The _N2 gas is recovered into the gas tank 15 by the N2 gas compressor 16 via the mist separators 18 and 17, similar to the _N2 gas in the sea part of the main oil pipe _a1 .

When Pig G ₁ is detected passing by the 8th Pig Detector PD ₈ , the 7th electric valve MV-7
is opened, and the oil that has pushed the pig _G1 passes through the air separator 6 and the flow meter 7, and is sent to the base tank 2. Next, when the passage of pig G ₁ is detected by the ninth pig detector PD ₉ , the third electric valve MV-3 closes, and the pressure regulating valve
CV-5 is closed, pig G ₁ is stored in pig receiver 4, and the recovery of N ₂ gas is completed.

Next, the sixth electric valve MV-6 opens, and the flow rate adjustment valve CV-2 and the first electric valve MV open.
-1 is closed and normal oil reception is started. In addition, when recovering N ₂ gas, the mist separators 17 and 18 separate oil from the N ₂ gas, but the mist separators 17 and 18
The oil stagnant in each drain pump 14b,
14 and sent into the oil pipe. The oil remaining in the vent tanks 9, 10 is similarly recovered by each drain pump 12, 13. Further, oil remaining in the pig launcher 3 and the pig receiver 4 is similarly recovered by drain pumps 11 and 14, respectively.

Method for replacing _N2 gas in oil pipes The opening and closing status of each valve before replacing _N2 gas is as follows.

(MV valve opening/closing status) MV-1 “closed”, MV-2 “open”, MV-3
“Closed”, MV-4 “Open”, MV-5 “Closed”, MV
-6 “closed”, MV-7 “closed”, MV-8 “closed”,
MV-9 “closed”, MV-10 “closed”, MV-1
1 “closed”, MV-12 “closed” (CV valve opening/closing status) CV-1 “closed”, CV-2 “closed”, CV-3
“Open”, CV-4 “Closed”, CV-5 “Closed”, CV-
6 “Closed”, CV-7 “Closed” To replace the entire length of the main oil pipe A ₁ with N ₂ gas, first insert the pig G ₁ into the pig launcher 3, and then open the first electric valve MV-1 and the third electric valve. Open valve MV-3. Pressure regulating valve CV
- When 4 is opened, the gas pressure accumulated in the N ₂ gas tank 15 is applied to the pig G ₂ , pushing the oil in the main oil pipe A ₁ while the pig G ₂ pumps N ₂ gas inside the main oil pipe A ₁ . The oil in the main oil pipe _A1 flows through the pig recovery oil pipe _A6 , and is controlled by the flow rate control valve CV-3.
Sent to base tank 2. When the passage of the pig G ₂ is detected by the ninth pig detector PD ₉ at the inlet of the pig receiver 4, the flow rate adjustment valve CV-3 and the pressure adjustment valve CV-4 are activated.
is closed, the total length of main oil pipe _A1 is _N2
It will be in a state where it is replaced with gas. After that, the pressure control valve CV-5 is opened, and in the same way as in the N ₂ gas replacement method in the sea part of the main oil transmission pipe, the N ₂ in the main oil transmission pipe a ₁ is removed.
After the gas pressure reduction work is performed, the first electric valve MV-1, the third electric valve MV-3, and the pressure control valve CV-5 are closed, and the N ₂ gas replacement of the entire length of the pipe is completed.

(3) Oil supply and N ₂ gas replacement method for the second base tank 2a.

Oil supply to the second base tank 2a (all lines are
(When replacing with _N2 gas) Collect the replacement gas on the upstream side of the fourth electric valve MV-4 and send it to the second base tank _2a via the recovered main oil pipe _A1 and sub oil pipe A4. carry out oil transport to The opening/closing status of each valve when all lines are replaced with _N2 gas is as follows.

(MV valve opening/closing status) MV-1 “closed”, MV-2 “open”, MV-3
“Closed”, MV-4 “Open”, MV-5 “Closed”, MV
-6 “closed”, MV-7 “closed”, MV-8 “closed”,
MV-9 “closed”, MV-10 “closed”, MV-1
1 “closed”, MV-12 “closed” (CV valve opening/closing status) CV-1 “closed”, CV-2 “closed”, CV-3
“Closed”, CV-4 “Closed”, CV-5 “Closed”, CV-
6 “Closed”, CV-7 “Closed” Insert pig G ₁ into pig launcher 3.
Next, the original fifth electric valve MV-5 of the loading arm 5, the first electric valve MV-1 at the outlet of the pig launcher 3, and the third electric valve
MV-3, flow rate control valve CV-2 and pressure control valve CV-5 are opened. In this state, when the tanker 1's oil feed pump starts receiving oil, oil flows into the pig launch oil feed pipe _A5 ,
Passes through air separator 8 to flow control valve CV-2
It is fed into the pig launcher 3 while its flow rate is controlled by . When the oil feed pressure is applied to the pig G ₁ in the pig launcher 3, the pig G ₁ enters the main oil feed pipe a ₁ and moves toward the downstream side within the oil feed pipe a ₁ . At this time, move pig G ₁ first.
The Pig Detector PD ₁ detects this and starts the N ₂ gas compressor 16, and the replacement gas in the main oil pipe a ₁ is compressed into N ₂ gas via the pressure control valve CV-5 and the mist separators 18 and 17. The gas is collected by machine 16 into the _N2 gas tank.
When Pig G ₁ pushed by oil is detected passing by the 6th Pig Detector PD ₆ ,
This detection signal causes the fourth electric valve MV-4 to
is closed, the flow rate control valve CV-1 is opened, and the oil is sent to the second base tank 2a through the oil feed pipe _A4 . Pig G ₁ , which has been traveling inside main oil transmission pipe A ₁ , travels inside main oil transmission pipe A ₁ until the fourth electric valve MV-4 is completely closed, and when it is completely closed, the main oil flue pipe a ₁
It stops between the seventh pig detector PD ₇ and the branch point of the pig backpush tube _b4 , and the replacement gas recovery is completed. When replacement gas recovery is completed,
The N ₂ gas compressor 16 is stopped, and the third electric valve MV-3 and pressure control valve CV-5 are closed.

Next, insert _the pig G ₁ stopped between the seventh pig detector PD ₇ in the main oil pipe A 1 and the branch point of the pig reverse push pipe B ₄ into the main oil pipe
In order to return A ₁ to the branching point H with the 3rd bypass oil pipe A ₉ , as shown in Fig. 6, first the 10th electric valve MV of the 3rd bypass oil pipe A ₉ is
-10 will be held. Next, the 12th electric valve MV-12 and pressure control valve CV-7 of the pig back-pushing pipe b ₄ are opened, and the displacement gas stored in the N ₂ gas tank 15 is transferred to the pig back-pushing pipe b ₄
through the main oil pipe _A1 , and the oil pipe
When you press the pig G ₁ that is stopped inside a ₁ ,
Pig _G1 moves to the upstream side, and the oil on the upstream side of the pig _G1 passes through the third bypass oil pipe _A9 ,
The oil is sent to the second base tank 2a via the sub-oil pipe _A4 .

When the passage of the pig G ₁ is detected by the seventh pig detector PD ₇ , the pig G ₁
A time difference is set by the timer for the time required to reach the branching point E from the installation position of Pig Detector PD ₇ , and the 7th Pig Detector PD ₇ sends a pig back push end signal, and the 10th electric valve MV-10 No. 12 electric valve MV-1
2 and pressure control valve CV-7 are closed,
The pig _G1 stops at the branch point E, and the pig reverse push operation is completed.

As mentioned above, the purpose of _the operation to push back the pig _G1 and stop it at a certain position (branch point H) is to
This is similar to the case where the pig is stopped at the branch point N of the first bypass oil pipe _A7 during _N2 gas replacement.

Note that during the pig reverse push operation, the first electric valve MV-1 closes and the sixth electric valve MV-6 closes.
opens, the flow control valve CV-2 closes, and the oil from the tanker 1 enters the main oil supply pipe _A1 from the tip oil supply pipe _A2 , and flows into the second base tank 2a.
Regular oil intake will be carried out.

_N2 gas replacement for the second base tank 2a.

The oil on the upstream side of the fourth electric valve MV-4 (the downstream side of the fourth electric valve MV-4 has been replaced with N ₂ gas) is recovered into the second base tank 2a, and after recovery, the oil is transferred to the main oil transmission pipe a ₁ Collect the two pigs inserted into the pig receiver 4.

The opening/closing status of each valve before _N2 gas replacement is as follows.

(MV valve opening/closing status) MV-1 “closed”, MV-2 “open”, MV-3
“Closed”, MV-4 “Closed”, MV-5 “Closed”, MV
-6 “closed”, MV-7 “closed”, MV-8 “closed”,
MV-9 “open”, MV-10 “closed”, MV-1
1 “closed”, MV-12 “closed” (CV valve opening/closing status) CV-1 “open”, CV-2 “closed”, CV-3
“Closed”, CV-4 “Closed”, CV-5 “Closed”, CV-
6 “closed”, CV-7 “closed” To replace the _N2 gas upstream of the fourth electric valve MV-4, first insert a pig into the pig launcher 3.
When G ₂ is inserted and the first electric valve MV-1 and pressure control valve CV-4 are opened, the gas pressure accumulated in the N ₂ gas tank 15 is
Join _G2 . Pig _G2 moves while pushing the oil in main oil pipe _A1 , and moves inside main oil pipe _A1 .
It is replaced with _N2 gas. The oil on the upstream side of the _fourth electric valve MV-4 of the main oil feed pipe A1 flows through the sub oil feed pipe _A4 and the second bypass oil feed pipe _A8 , and the flow rate is controlled by the flow rate control valve CV-1. Meanwhile, it is sent to the second base tank 2a.

When the passage of Pig G ₂ is detected by the 4th Pig Detector PD ₄ , the flow control valve CV-
1 starts to close, the flow rate is gradually narrowed down, and the moving speed of pig G ₂ is slowed down. When the flow rate control valve CV-1 is completely closed, oil flows only from the second bypass oil feed pipe _a8 , and the pig
G ₂ becomes even slower and the second bypass oil pipe
When it reaches near the branch point H of A ₈ , the fifth pig detector PD ₅ detects this and uses this detection signal to pig the branch point H of the sub oil pipe A ₄ .
It is confirmed that G ₂ has passed.

After the fifth pig detector PD ₅ detects the passage of the pig G ₂ , the pig G ₂ moves from the installation position of the pig detector PD ₅ to the second bypass oil pipe a ₈
The 5th pig day detector PD ₅
A gas replacement end signal is sent from the 9th electric valve MV-9 and the pressure control valve CV-
4 is closed, the pig _G2 will definitely stop at the branch point of the second bypass oil pipe _A8 ,
The upstream side of the fourth electric valve MV-4 of the main oil pipe _a1 is replaced with _N2 gas.

As mentioned above, _the operation to decelerate pig _G2 and stop it at a certain position ₍ branch point This is the same as when stopping at the branch point d of the first bypass oil pipe _a7 .

Next, after Pig G ₂ stops at the branch point H on the upstream side of the fourth electric valve MV-4 of the main oil pipe _A1 , it opens the fourth electric valve MV-4 and stops at the branch point H. Pig G ₂ at the branch point E and pig G ₁ stopped at the branch point E are to be collected into the pig receiver 4, but if there is a difference in N ₂ gas pressure between the upstream side of pig G ₂ and the downstream side of pig G ₁ . , the two pigs G ₁ and G ₂ start moving during the opening operation of the fourth electric valve MV-4, and these pigs come into close contact with the fourth electric valve MV-4, causing the opening operation of the valve MV-4. The upstream side of pig G ₂ and the downstream side of pig G ₁ may be It is necessary to equalize the _N2 gas pressure on both sides. This pressure equalization operation is performed by
Open the 11th electric valve MV-11 of A ₁₀ , connect the main oil pipe A ₁ on the upstream side of Pig G ₂ and the downstream side of Pig G ₁ to each other, and connect N ₂ on the higher pressure side.
This is done by releasing the gas to the side with lower pressure.

After the pressure equalization operation is completed, turn on the 11th electric valve.
MV-11 is closed.

After doing this, the fourth electric valve MV-
4. When the third electric valve MV-3 and pressure control valves CV-4 and CV-5 are opened, the _N2 gas compressor 16 is started, and the pigs _G1 and _G2 move inside the main oil pipe _A1 . Start moving towards receiver 4. The _N2 gas on the downstream side of pig _G1 in main oil pipe _A1 is controlled by pressure control valve CV-5,
It passes through the mist separators 18 and 17 and is recovered to the N ₂ gas tank 15 by the N ₂ gas compressor 16 as described above. When the passage of the upstream pig G ₂ is detected by the ninth pig detector PD ₉ at the inlet of the pig receiver 4, the pressure regulating valve CV-4 is closed, and after further pressure reduction work, the pressure regulating valve CV-4 is closed. -5, the first electric valve MV-1, and the third electric valve MV-3 are closed, and the work of collecting the pigs G ₁ and G ₂ to the pig receiver 4 is completed. Note that a small amount of oil remaining between the pigs G ₁ and G ₂ is separated by the mist separator 18 and collected into the first base tank 2 by the drain pump 14 .

〔Effect of the invention〕

As described above, in the present invention, the pig moves from upstream to downstream in the fluid transfer pipe by pushing the downstream fluid and uses the upstream liquid, and passes through the pig stop valve provided in the fluid transfer pipe, and the pig moves downstream of the pig stop valve. stop on the side,
In addition, while the pig stop valve is in a closed state, the liquid is then pushed out to a branch pipe provided upstream of the pig stop valve, and the fluid is transferred by the upstream gas toward the closed pig stop valve. When moving both pigs along the fluid transfer pipe from a state in which the pig that has moved from upstream to downstream in the pipe is stopped upstream of the closed pig stop valve, the gas on the upstream side of the pig stop valve is moved. After the downstream gas is made to communicate with the downstream gas through a bypass pipe provided in the fluid transfer pipe to equalize the pressure, the communication between the upstream gas and the downstream gas is cut off and the pig stop valve is opened. During the above-mentioned pressure equalization work as well as while opening the pig stop valve, the pig will not move on its own and collide with the operating valve body of the pig stop valve, causing deformation or damage to the valve body or the pig. Alternatively, the pig can operate smoothly without causing abnormal torque to open the pig stop valve due to strong pressure contact with the valve body, or causing the pig stop valve to become inoperable. can be moved to

In addition, since the pressure is equalized by communicating with the bypass pipe, unlike simply opening the vent of the fluid transfer pipe to create atmospheric pressure, which results in equal pressure on the upstream and downstream sides of the pig stop valve, No mist of transfer liquid is released into the tank. Furthermore, even if it is an open type (disposable type) inert gas replacement method or air replacement method, the pipe that sends the gas to the mist separation device such as a vent tank that is usually installed at the downstream end of the fluid transfer pipe. However, since the fluid transfer pipe on the downstream side of the pig stop valve can be used, there is an advantage that this is not necessary.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing an embodiment of an oil transfer device implementing the method for moving a pig in a fluid transfer pipe according to the present invention; Fig. 2 is a sequence block diagram of a fully automatic system for an _N2 gas compressor; Figure 3 is an explanatory diagram of the automatic firing system for a large pig, Figure 4 is a block diagram showing the pressure and flow rate control situation using a large electric valve, and Figures 5 to 5 are explanations of the operation of stopping the pig on the upstream side of the electric valve. FIG. 6 is an explanatory diagram of the operation of the pig reverse push operation. a ₁ ...Main oil pipe (fluid transfer pipe), a ₄ ...Sub oil pipe (branch pipe), a ₁₀ ...Pressure equalization pipe (bypass pipe), MV-4...Electric valve (pig stop valve) ,
MV-11...Electric valve.

Claims (1)

[Claims] 1. A pig that pushes downstream fluid and moves from upstream to downstream in a fluid transfer pipe by the upstream liquid and passes through a pig stop valve provided in the fluid transfer pipe stops downstream of the pig stop valve, and While the pig stop valve is in a closed state, the liquid is then pushed out to a branch pipe provided upstream of the pig stop valve, and the upstream gas flows inside the fluid transfer pipe toward the closed pig stop valve. When a pig that has moved from upstream to downstream is stopped upstream of the closed pig stop valve and moves both pigs along the fluid transfer pipe, the gas on the upstream side of the pig stop valve and the gas downstream of the pig stop valve are moved. Fluid transfer characterized in that after the side gas is communicated with a bypass pipe provided in the fluid transfer pipe to equalize the pressure, communication between the upstream side gas and the downstream side gas is cut off and the pig stop valve is opened. How to move a pig in a pipe.