JP3836037B2 - BOG acceptance control method and apparatus for LNG ship at LNG acceptance base - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a BOG acceptance control method and apparatus for an LNG ship at an LNG acceptance base.
[0002]
[Prior art]
Natural gas is liquefied in LNG (Liquefied Natural Gas) liquefaction bases around the world, and the liquefied gas (LNG) is transported to an LNG receiving terminal by an LNG ship. BOG (Boil Off Gas) is generated when LNG is vaporized during transportation. At the LNG receiving terminal, the LNG ship accumulates BOG in the tank until the front scale is completed after the LNG ship arrives, and then the BOG receiving line formed separately from the LNG receiving line. When the (return gas piping) is connected to the LNG ship tank and the LNG ship tank pressure is higher than the land tank pressure, the BOG in the LNG ship tank is received by the land LNG tank. This is intended to protect the tank by lowering the cargo tank pressure of the LNG ship.
[0003]
When the land-side BOG pipe is initially connected to the LNG tank, the BOG pressure in the LNG tank (for example, about 15 to 16 kPa) may be higher than the pressure in the land-side LNG tank. The pressure is balanced by automatically flowing into the land side LNG tank via the return gas pipe.
[0004]
After that, when LNG cargo handling is started, LNG is received by the land side tank through the LNG receiving line, and the pressure in the LNG ship tank decreases, so the land side pressure feeder provided in the return gas piping is operated. The BOG in the land side LNG tank is returned to the LNG ship tank to secure the LNG ship tank pressure. This land-side pressure feeder is for returning the above-mentioned land-side tank BOG to the ship side, and is stopped when the BOG in the LNG ship tank flows into the land-side LNG tank before receiving the LNG. .
[0005]
[Problems to be solved by the invention]
When the distance between the receiving pier and the land side LNG tank is short as in the conventional LNG receiving base, and the design pressure of the land side LNG tank is lower than the design pressure of the LNG ship tank, The operation method and apparatus of this work without any trouble.
[0006]
In recent years, along with the advancement of LNG receiving tank construction technology, an LNG receiving base having a high-pressure land-side tank with a high design pressure (for example, 20 kPa or more) is being built. Just connecting to the ship tank can make it difficult to receive the ship-side BOG. Further, the BOG in the high-pressure land-side LNG tank may flow into the LNG ship tank and damage the LNG ship tank.
[0007]
Furthermore, considering the future situation of securing the LNG base site, the distance from the receiving pier to the land side LNG tank may be longer, especially in the case of a sea berth type where the receiving pier is on the sea, the receiving piping is It can be long and as long as several kilometers. In such a case, it becomes difficult to stably take the BOG into the land-side LNG tank only by the accumulated pressure of the BOG in the LNG ship tank.
[0008]
The present invention has been made in view of the circumstances as described above, and the BOG in the LNG ship tank is placed in the land-side LNG tank without being influenced by the length of the receiving pipe line or the design pressure of the land-side LNG tank. It is an object of the present invention to provide a BOG acceptance control method and apparatus for an LNG ship at an LNG acceptance base that can be stably taken over.
[0009]
[Means for Solving the Problems]
BOG acceptance control method of an LNG carrier in LNG receiving terminal according to the present invention, the LNG receiving terminals, there a way to accept the landside LNG tank through the return gas pipe by land lateral pressure feed machines for the return gas back to LNG ship tank BOG And
In the BOG acceptance control, control is performed so that the suction pressure of the land-side pressure feeder becomes constant.
[0010]
An apparatus for carrying out the above-described BOG acceptance control method according to the present invention includes a pipeline switching means capable of switching between the suction side and the delivery side of the land-side pressure feeder, and the pipeline switching means selectively. A line for returning the BOG in the land-side LNG tank to the LNG ship tank, a line for pumping the BOG in the LNG ship tank into the land-side LNG tank, and a return connected in the line A land-side pump for gas return, and pressure regulating means for maintaining a constant suction pressure of the land-side pump in a state where a line for pumping the BOG in the LNG ship tank into the land-side LNG tank is formed It is characterized by providing.
[0011]
In the present invention, the BOG in the LNG ship tank is taken up by the land-side LNG tank after passing through the land-side pressure transmitter for return gas return, and is boosted when passing through the land-side pressure transmitter. The BOG in the LNG ship tank can be fed into the land-side LNG tank in a stable state without being influenced by the length of the receiving pipe line or the design pressure of the land-side LNG tank. When the LNG is received into the land side tank, in order to keep the pressure in the LNG ship tank constant, the conduit switching means is operated to return the BOG in the land side LNG tank to the LNG ship tank. Switch to line. Thereby, the return gas return line similar to the conventional one is formed.
[0012]
In the line from the ship to the land-side pump, the pressure at the suction point of the land-side pump is set lower than the LNG ship tank pressure and the pressure that the ship-side tank should reach, so that In order to prevent natural BOG inflow to the side and stop receiving the land-side tank and avoid unnecessary BOG reception when the land-side tank reaches a pressure that should be reached, Is received, pressure control is performed so that the suction pressure on the suction side of the land-side pressure feeder is constant. Thereby, the acceptance of the BOG to the land side tank is further stabilized. In addition, as the pressure adjusting means for that purpose, a means for controlling the opening degree of the regulating valve provided with the inlet line to the land side LNG tank by the suction side pressure of the land side pressure feeder is preferable.
[0013]
In the present invention, the existing land-side pressure pump for returning the return gas is used to pressure-feed the BOG in the LNG ship tank into the land-side LNG tank, and the existing facilities of the LNG receiving base are used as they are. Thus, there is an advantage that the present invention can be implemented.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of a BOG acceptance control method and apparatus for an LNG ship at an LNG acceptance base according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a flowchart showing a BOG acceptance control method according to the present invention. In the figure, ST is an LNG ship tank, B is a berth, LT is a land side LNG tank, and RGB is a land side pressure feeder. A first pipeline 31 connected to the LNG ship tank ST at the berth B is connected to the suction side port 11 of RGB10, and a second pipe connected to the land side LNG tank LT is connected to the delivery side port 21 of RGB10. The pipe 41 is connected. Note that RGB is conventionally used only for returning return gas, but in the present invention, it is also used for receiving BOG.
[0015]
The first pipeline 31 includes a first branch pipeline 33 that branches at a branch point 32, and the first branch pipeline 33 is connected to the second pipeline 41 at a branch point 42. The second pipe 41 includes a second branch pipe 44 that branches at a branch point 43 that is on the RGB 10 side from the branch point 42, and the second branch pipe 44 is a branch that is on the berth B side from the branch point 32. The point 34 is connected to the first pipeline 31.
[0016]
The first branch pipe 33 is provided with a first on-off valve 35, and the second branch pipe 44 is provided with a control valve 45. This control valve 45 functions as a surging prevention control valve for RGB 10 when BOG is received. A discharge valve 46 is provided at the branch point 43 and the delivery-side port 21 in the second pipeline 41, and is opened during operation. Further, a second on-off valve 50 is provided between the branch point 32 and the branch point 34 in the first pipeline 31.
[0017]
A control valve 51 and a first flow meter 61 are provided in this order between the branch point 43 and the branch point 42 in the second pipeline 41, and the branch point 34 in the first pipeline 31. A second flow meter 62 is provided on the berth B side. In addition, when it is installed between the sending-out port 21 and the branch point 43, the flow meters 61 and 62 are one. Reference numeral 60 denotes a flow rate / pressure controller which takes in a total flow rate signal from the first flow meter 61 and the second flow meter 62 and outputs an opening signal corresponding to the total flow rate signal to the control valve 51. Furthermore, a pressure signal from a pressure gauge 63 provided immediately before the RGB 10 suction side port 11 of the first pipe line 31 is taken in, and an opening signal corresponding to the pressure signal is output to the control valve 51. The flow control and pressure control described above are performed by switching. As a result, the control valve 51 used as a surging prevention control valve when returning the return gas is used for suction pressure control when receiving the BOG.
[0018]
When receiving the BOG, the RGB 10 is operated, and the first on-off valve 35 is closed and the second on-off valve 50 is opened as shown in FIG. The flow rate / pressure controller 60 is on the pressure control side, and the opening degree of the control valve 51 is controlled according to the pressure. The opening of the control valve 45 is also controlled as appropriate for the purpose of preventing surging. The BOG in the LNG ship tank ST passes through the first pipeline 31 and flows into the RGB 10 from the suction side port 11 of the RGB 10, and after being boosted there, the second pipeline 41 from the delivery side port 21 of the RGB 10. Through the land side LNG tank LT.
[0019]
The RGB 10 is in operation, and even if a large pipeline loss due to the length of the first pipeline 31 or the like occurs, the BOG in the LNG ship tank is reliably drawn into the RGB 10. Further, since the pressure is increased by the RGB 10, even if the design pressure of the land-side LNG tank LT is as high as 20 kPa, it can be reliably pumped into the tank.
[0020]
In the line from the ship to the land-side pump, the pressure at the suction side port 11 of the RGB 10 is set lower than the pressure of the LNG ship tank ST and should be reached by the ship-side tank ST, so that from the ship side to the land side. When the natural BOG inflow is promoted and the pressure that the land-side LNG tank LT has reached is reached, the acceptance to the land-side LNG tank LT is stopped and unnecessary BOG acceptance is not performed. Desirably, therefore, pressure control is performed to make the suction pressure of the suction side port 11 of RGB 10 constant when receiving BOG. Specifically, pressure information from the pressure gauge 63 provided immediately before the suction side port 11 of RGB 10 is always sent to the flow rate / pressure controller 60, and an opening degree signal is output to the control valve 51 by the pressure signal. Thus, feedback control is performed.
[0021]
When the LNG is received into the land-side tank, the first on-off valve 35 and the adjustment valve 45 are fully opened and the adjustment valve 50 is closed so that the pressure in the LNG ship tank becomes constant. Thereby, a return gas return line similar to the conventional one is formed. In order to prevent surging, the flow / pressure controller 60 is switched to the flow adjustment side, and the total flow signal of the first flow meter 61 and the second flow meter 62 is sent to the flow / pressure controller 60. The required opening degree signal is output to the control valve 51 by the flow rate signal, and the necessary partial circulation flow is formed as in the conventional case.
[0022]
【The invention's effect】
As described above, according to the BOG reception control method and apparatus for an LNG ship at the LNG reception base according to the present invention, the LNG is not affected by the length of the BOG reception pipe line or the design pressure of the land side LNG tank. The BOG in the ship tank can be stably taken into the land side LNG tank, and as a result, the BOG receiving operation at the LNG receiving base can be greatly stabilized.
[Brief description of the drawings]
FIG. 1 is a flowchart showing BOG acceptance control of an LNG ship at an LNG acceptance base according to the present invention.
[Explanation of symbols]
ST ... LNG ship tank, B ... berth, LT ... Land side LNG tank, 10 ... Land side pressure feeder (Return Gas Blower: RGB), 11 ... Suction side port, 21 ... Sending side port, 31 ... First pipeline , 41 ... second pipe, 32, 34, 42, 43 ... branch point, 33 ... first branch pipe, 44 ... second branch pipe, 35 ... first on-off valve, 45 ... regulating valve 50 ... second on-off valve, 51 ... regulator valve, 61 ... first flow meter, 62 ... second flow meter, 60 ... flow rate / pressure controller, 63 ... pressure gauge

Claims (2)

In the LNG receiving terminal, a method of receiving the BOG in the LNG tank by the land-side LNG tank through the return gas pipe by the land-side pressure feeder for returning the return gas ,
In the BOG acceptance control, a BOG acceptance control method for an LNG ship at an LNG acceptance base , wherein control is performed so that the suction pressure of the land-side pressure feeder is constant . An apparatus for carrying out a BOG acceptance control method of an LNG ship at an LNG acceptance base according to claim 1,
Pipeline switching means capable of switching the pipeline between the suction side and the delivery side of the land-side pressure feeder;
A line that is selectively formed by the pipeline switching means, a line that returns the BOG in the land-side LNG tank into the LNG ship tank, and a line that pressure-feeds the BOG in the LNG ship tank into the land-side LNG tank;
A land-side pump for return gas return connected in the line;
Pressure regulating means for maintaining a constant suction pressure of the land-side pressure feeder in a state where a line for pumping the BOG in the LNG ship tank into the land-side LNG tank is formed.

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