JP4296616B2 - BOG liquefier for liquefied gas tank - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for liquefying BOG (boil-off gas) generated in a liquefied gas tank, and more particularly, to a BOG of a liquefied gas tank that can maintain its condensation pressure (temperature) at a predetermined value even if the amount of generated BOG varies. The present invention relates to a liquefaction device.
[0002]
[Prior art]
As a device for liquefying BOG generated in a liquefied gas tank such as an LNG tank, the BOG taken out from the liquefied gas tank is boosted to a predetermined pressure by a compressor, and the boosted BOG is guided into a condensation container. A BOG is known that is cooled by a heat exchange tube in a condensing container and liquefied (condensed).
[0003]
[Problems to be solved by the invention]
However, in the conventional BOG liquefaction apparatus, the heat exchange tube for cooling and liquefying BOG is always exposed to the BOG in the condensing container, and the heat transfer area to the BOG is always constant. When the flow rate of the water fluctuated, it was inevitable that the condensing pressure (temperature) fluctuated.
[0004]
That is, when the flow rate of the BOG introduced into the condensing container is reduced from the set value, the excessive amount of BOG is cooled by the heat exchange tube having a constant heat transfer area, and the condensation pressure is lowered. On the contrary, when the flow rate of the BOG increases from the set value, the BOG becomes insufficiently cooled and the condensation pressure increases.
[0005]
Thus, when the condensation pressure fluctuates due to fluctuations in the flow rate of the BOG, the suction pressure of the liquid extraction pump (centrifugal type) connected downstream of the condensing container fluctuates. For example, when the suction pressure falls However, there is a problem that the operation of the pump is not stable, such as cavitation occurs and liquefied BOG is gasified.
[0006]
The object of the present invention created in view of the above circumstances is to provide a BOG liquefaction apparatus for a liquefied gas tank that can maintain the condensation pressure (temperature) at a predetermined value even if the amount of BOG generated in the liquefied gas tank varies. There is to do.
[0007]
[Means for Solving the Problems]
To achieve the above object, a BOG liquefying apparatus for a liquefied gas tank according to the present invention includes a compressor for boosting a BOG taken out from the liquefied gas tank to a predetermined pressure, and an airtight condensing container into which the BOG boosted by the compressor is guided. And a heat exchange tube in which the BOG contained in the condensing container is cooled and liquefied and partly immersed in the liquefied BOG, and the liquefied BOG in the container connected to the lower part of the condensing container A siphon tube that leads to a gas tank, a liquid receiving vessel that covers the lower part of the siphon tube and that stores the liquefied BOG at a higher liquid level than the outlet of the siphon tube, and a liquefied BOG connected to the lower part of the liquid receiving vessel And a take-out pipe for taking out.
[0008]
According to the present invention, for example, when the amount of BOG generated in the liquefied gas tank is reduced more than before, the heat transfer area of the heat exchange tube in the condensing container becomes relatively larger than before. The amount of condensation in the container increases and the pressure in the condensation container drops. Then, the liquefied BOG in the liquid receiving container is sucked into the condensing container through the siphon tube, the liquid level of the liquefied BOG in the condensing container rises, and part of the heat exchange tube that has been exposed in the condensing container until then. Sinks below the liquid surface of the liquefied BOG, and its heat transfer area decreases. As a result, the heat transfer area of the heat exchange tube in the condensation container is automatically reduced to an area suitable for the reduced BOG amount, and the condensation pressure (temperature) is maintained at a predetermined value.
[0009]
On the contrary, when the amount of BOG generated in the liquefied gas tank increases more than before, the heat transfer area of the heat exchange tube in the condensing container becomes relatively smaller than before, so the condensation in the condensing container The volume decreases and the pressure in the condensation vessel increases. Then, the liquefied BOG in the condensing container is discharged to the lower receiving container through the siphon tube, the liquid level of the liquefied BOG in the condensing container is lowered, and the heat exchange that has been immersed in the liquefied BOG in the condensing container until then. A part of the tube is exposed and its heat transfer area increases. As a result, the heat transfer area of the heat exchange tube in the condensing container automatically expands to an area suitable for the increased BOG amount, and the condensing pressure (temperature) is maintained at a predetermined value.
[0010]
The BOG liquefier is connected to the BOG gas phase portion in the condensing container and the BOG gas phase portion in the liquid receiving container, and the BOG gas phase in the condensing container is provided in the communication tube. You may further provide the pressure control valve in which the opening degree is adjusted in order to maintain the pressure of a part at a predetermined value. In this way, by appropriately adjusting the opening of the pressure control valve to keep the pressure of the BOG gas phase portion in the condensing container at a predetermined value, it is likely to fluctuate in the condensing container when the BOG amount varies as described above. The condensation pressure (temperature) of the BOG is quickly and accurately maintained at a predetermined value.
[0011]
In addition, the BOG liquefaction apparatus is connected to the inlet of the heat exchange tube and supplied with liquefied gas from the liquefied gas tank; and the exhaust connected to the outlet of the heat exchange tube and discharged after liquefied gas is exchanged You may further provide the collection pipe which collects a pipe | tube, this discharge pipe, and the extraction pipe | tube connected to the said liquid receiving container. Thus, by using the liquefied gas from the liquefied gas tank as the refrigerant of the heat exchange tube, the temperature change of the refrigerant is reduced and the condensation pressure (temperature) of the BOG is stabilized.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0013]
As shown in FIG. 1, a gas extraction pipe 2 for extracting BOG (boil-off gas: vaporized gas) generated in the tank 1 is connected to the top of the liquefied gas tank 1 (LNG tank). A compressor 3 (such as a piston type or a centrifugal type) that pressurizes the BOG taken out from the tank 1 to a predetermined pressure is interposed between the gas take-out pipes 2. Connected to the tip of the gas extraction pipe 2 is an airtight condensing container 4 through which the BOG boosted by the compressor 1 is guided.
[0014]
A heat exchange tube 5 that cools and liquefies the BOG in the container 4 is accommodated in the condensing container 4. As shown in FIG. 1, the heat exchange tube 5 is arranged in the vertical direction, and a part (lower part) of the heat exchange tube 5 is immersed in a liquefied BOG (shown by oblique lines) stored in the container 4. That is, the heat exchange tube 5 is partially covered with the liquefied BOG stored in the container 4 in accordance with the upper and lower levels of the liquefied BOG. The substantial heat transfer area (exposed portion above the liquid level of the liquefied BOG) is changed. In addition, the heat exchange tube 5 is not restricted to what was folded up and down like the example of a figure, For example, you may use what was shape | molded by the horizontal U shape.
[0015]
The heat exchange tube 5 has an inlet 5a at the lower part and an outlet 5b at the upper part. A supply pipe 6 to which liquefied gas (liquefied natural gas) in the liquefied gas tank 1 is supplied is connected to the inlet 5 a of the heat exchange tube 5. The supply pipe 6 is provided with a pump 7 (centrifugal type) that pumps the liquefied gas. A discharge pipe 8 through which the liquefied gas after heat exchange is discharged in a liquid phase state is connected to the outlet 5b of the heat exchange tube 5. That is, the liquefied gas in the liquefied gas tank 1 is used for the refrigerant flowing in the heat exchange tube 5.
[0016]
A siphon tube 9 that guides the liquefied BOG stored in the container 4 downward is connected substantially vertically to the lower part of the condensing container 4. A lower part of the siphon tube 9 is provided with a liquid receiving container 10 for storing liquefied BOG (shown by hatching) flowing out from the outlet 9 a of the siphon tube 9 so as to cover the lower part of the siphon tube 9 in an airtight manner. The outlet 9 a of the siphon tube 9 is positioned below the liquid level of the liquefied BOG stored in the liquid receiving container 10. Thus, the liquefied BOG in the liquid receiving container 10 and the liquefied BOG in the condensing container 4 are connected via the siphon tube 9.
[0017]
The BOG gas phase portion at the top of the condensing container 4 and the BOG gas phase portion at the top of the liquid receiving container 10 are communicated with each other via a communication pipe 11. The communication pipe 11 is provided with a pressure control valve 12 for maintaining the pressure of the BOG gas phase portion in the condensation container 4 at a predetermined value by adjusting the pipe cross-sectional area. The opening degree of the pressure control valve 12 is appropriately adjusted by the pressure controller 13. The pressure controller 13 detects the pressure of the BOG gas phase portion in the condensing container 4, and based on the detected value, the opening degree of the pressure control valve 12 in order to keep the BOG gas phase portion in the condensing container 4 at a predetermined pressure. Is to adjust.
[0018]
An extraction pipe 14 for taking out the internal liquefied BOG is connected to the lower part of the liquid receiving container 10. A pump 15 (centrifugal type) is provided in the middle of the take-out pipe 14 for discharging the liquefied BOG in the liquid receiving container 10. The distal end of the extraction pipe 14 and the distal end of the discharge pipe 8 connected to the outlet 5 b of the heat exchange tube 5 are gathered by a collecting pipe 16. Thereby, the liquefied BOG (liquefied natural gas) flowing in the extraction pipe 14 and the liquefied gas (liquefied natural gas) flowing in the discharge pipe 8 are collected and mixed in the liquid phase state by the collecting pipe 16.
[0019]
A mixed liquefied gas (liquefied natural gas) of liquefied BOG and liquefied gas flowing in the collecting pipe 16 is pumped by a pump 17 (centrifugal type) provided in the collecting pipe 16 and led to the vaporizer 18, where the vaporizer It is vaporized in 18 and becomes gas (natural gas). The gas (natural gas) generated in the vaporizer 18 is supplied to the downstream consumption system through the supply pipe 19.
[0020]
The operation of the present embodiment having the above configuration will be described.
[0021]
In FIG. 1, BOG generated in the liquefied gas tank 1 is boosted to a predetermined pressure by the compressor 3 and then guided into the condensation container 4, cooled by the heat exchange tube 5, and liquefied (condensed). In the condensing container 4. The liquefied BOG in the condensing container 4 is guided to the lower receiving container 10 through the siphon tube 9 and stored in the receiving container 10.
[0022]
At this time, the pressure control valve 12 adjusts the pipe cross-sectional area of the communication pipe 11 so as to keep the pressure of the BOG gas phase portion in the condensation container 4 at a predetermined value (0 to 100%). All of the liquefied BOG does not fall to the liquid receiving container 10 side, and a part of the liquefied BOG is stored in the condensing container 4. Therefore, a part (lower part) of the heat exchange tube 5 in the condensing container 4 is immersed in the liquefied BOG stored in the condensing container 4, and a substantial heat transfer area for the BOG introduced into the condensing container 4. Becomes a portion exposed above the liquid surface of the liquefied BOG.
[0023]
Here, if the amount of BOG generated in the liquefied gas tank 1 is reduced for some reason (the state shown in FIG. 1), the heat transfer area of the heat exchange tube 5 in the condensing container 4 is reduced. Therefore, the amount of condensation in the condensation container 4 increases, and the pressure in the condensation container 4 drops. Then, as shown in FIG. 2 (a), the liquefied BOG in the liquid receiving container 10 is sucked into the condensing container 4 through the siphon tube 9, and the liquid level of the liquefied BOG in the condensing container 4 rises and condenses until then. A part of the heat exchange tube 5 exposed in the container 4 sinks below the liquid level of the liquefied BOG.
[0024]
As a result, the heat transfer area of the heat exchange tube 5 to the BOG in the condensing container 4 (the area of the portion exposed above the liquid level of the liquefied BOG) is automatically reduced to an area suitable for the reduced BOG amount, The condensation pressure (temperature) is maintained at a predetermined value. At this time, the opening degree of the pressure control valve 12 is appropriately adjusted to maintain the pressure in the BOG gas phase portion in the condensation container 4 at a predetermined value, so that it is likely to change in the condensation container 4 when the BOG amount changes. The BOG condensation pressure (temperature) is maintained at a predetermined value quickly and accurately.
[0025]
On the contrary, when the amount of BOG generated in the liquefied gas tank 1 is increased from that (the state of FIG. 1), the heat transfer area of the heat exchange tube 5 in the condensing container 4 is relatively more than before. Therefore, the amount of condensation in the condensation container 4 decreases, and the pressure in the condensation container 4 increases. Then, as shown in FIG. 2 (b), the liquefied BOG in the condensing container 4 is discharged to the lower receiving container 10 through the siphon tube 9, and the liquid level of the liquefied BOG in the condensing container 4 is lowered. A part of the heat exchange tube 5 immersed in the liquefied BOG in the condensation container 4 is exposed.
[0026]
As a result, the heat transfer area of the heat exchange tube 5 to the BOG in the condensing container 4 (the area of the portion exposed above the liquid level of the liquefied BOG) is automatically expanded to an area suitable for the increased amount of BOG, The condensation pressure (temperature) is maintained at a predetermined value. At this time, the opening degree of the pressure control valve 12 is appropriately adjusted to maintain the pressure of the BOG gas phase portion in the condensation container 5 at a predetermined value. The BOG condensation pressure (temperature) is maintained at a predetermined value quickly and accurately.
[0027]
As described above, according to the present embodiment, even when the amount of BOG generated in the liquefied gas tank 1 is changed, the condensation pressure (temperature) can be kept substantially constant. 14 can be supplied to the 14 discharge pumps 15 to prevent instability such as cavitation. In the present embodiment, since the liquefied gas from the liquefied gas tank 1 is used as the refrigerant of the heat exchange tube 5 that condenses and liquefies BOG, the temperature change of the refrigerant is reduced, and this also causes the BOG condensation pressure to be reduced. (Temperature) is stabilized.
[0028]
In addition, the BOG liquefaction apparatus according to the present embodiment is compact because the condensing container 4 and the liquid receiving container 10 are stacked in two stages on the upper and lower sides via the siphon tube 9. The installation area is reduced.
[0029]
【The invention's effect】
As described above, according to the BOG liquefying apparatus for a liquefied gas tank according to the present invention, the condensation pressure (temperature) can be maintained at a predetermined value even when the amount of BOG generated in the liquefied gas tank varies. it can. Therefore, a stable liquefied gas can be supplied to the dispensing pump, and unstable phenomena such as cavitation can be avoided.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a BOG liquefying apparatus for a liquefied gas tank according to an embodiment of the present invention.
FIG. 2 is an explanatory view showing the operation of the BOG liquefying apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Liquefied gas tank 3 Compressor 4 Condensation container 5 Heat exchange tube 5a Heat exchange tube inlet 5b Heat exchange tube outlet 6 Supply pipe 8 Discharge pipe 9 Siphon pipe 10 Receiving container 11 Communication pipe 12 Pressure control valve 14 Extraction pipe 16 Assembly tube

Claims (3)

A compressor that boosts the BOG taken out from the liquefied gas tank to a predetermined pressure, an airtight condensing container to which the BOG boosted by the compressor is guided, and the BOG contained in the condensing container is cooled and liquefied. In addition, a heat exchange tube partially immersed in the liquefied BOG, a siphon tube connected to the lower part of the condensing container and guiding the liquefied BOG in the container downward, and a lower part of the siphon tube are hermetically covered. A BOG liquefaction of a liquefied gas tank, comprising: a liquid receiving container for storing the liquefied BOG at a liquid level higher than an outlet of the siphon pipe; and a take-out pipe connected to a lower portion of the liquid receiving container to take out the internal liquefied BOG. apparatus. A communication pipe that communicates the BOG gas phase portion in the condensing vessel and the BOG gas phase portion in the liquid receiving vessel, and the pressure of the BOG gas phase portion in the condensing vessel that is interposed in the communication tube is set to a predetermined value. The BOG liquefying apparatus for a liquefied gas tank according to claim 1, further comprising a pressure control valve whose opening degree is adjusted to maintain the pressure. A supply pipe connected to the inlet of the heat exchange tube and supplied with liquefied gas from a liquefied gas tank; a discharge pipe connected to the outlet of the heat exchange tube and discharged from the liquefied gas after heat exchange; and 2. The BOG liquefying apparatus for a liquefied gas tank according to claim 1, further comprising a collecting pipe that collects the take-out pipe connected to the liquid receiving container.

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