JPH07138584A - Method and apparatus for treating bog vaporized in lng storage equipment - Google Patents

Abstract

PURPOSE:To reduce the equipment cost and operating cost by dispensing with the use of a compressor which is expensive and consumes much electric power. CONSTITUTION:The apparatus consists of an absorption tower 2 in which BOG 81 led through a BOG discharge line L2 is absorbed by an absorbent 9 to form a BOG absorbent solution 91, a stripping tower 3 in which the BOG absorbent solution 91 led through an absorbent solution discharge line L3 is externally heated to strip the BOG to form a stripped BOG 81a, an absorbent feedback line L5 through which the absorbent 9 regenerated by stripping BOG 81 in the tower 3 is fed back to the absorption tower 2, and a heat exchanger 12 in which heat exchange between LNG 8 led through an LNG discharge line L1 from an LNG tank 1 and the absorbent 9 flowing through the absorbent feedback line L5 is effected and which is installed in the absorbent feedback line L5.

Description

Detailed Description of the Invention

[0001]

The present invention relates to liquefied natural gas (LN
The present invention relates to a BOG processing device for processing so-called boil-off gas (BOG) generated by vaporization of LNG in a storage facility of G).

[0002]

2. Description of the Related Art LNG such as LNG tanks storing LNG
From the liquid surface of the G storage facility, BOG generated by vaporization of LNG is generated due to heat input from the outside or fluctuation of the liquid surface. If such generation of BOG is left unattended, the pressure in the storage facility rises, which is inconvenient for facility maintenance. Therefore, various measures have been taken to keep the pressure in the storage device constant.

As a facility for keeping the pressure inside the LNG storage facility constant, a facility as shown in FIG. 5 is generally used. That is, as shown in this figure, LNG8
The LNG tank 1 storing the LNG is provided with an LNG derivation path L1 ′ in which a withdrawal pump 11 is interposed, and the LNG derivation path L1 ′ is connected to the carburetor 5. This vaporizer 5 is a kind of heat exchanger, and seawater 98 is introduced from outside the system, and LNG8 derived from the LNG tank 1 by heat exchange with this seawater 98 is NG82.
And is led out of the system through the route L8. In the path L8, the NG 82 is at the pressure of the supply pipeline outside the system (for example, about 10 kg / cm ² Abs).

On the other hand, B generated inside the LNG tank 1
The OG81 is a BOG provided on the top of the LNG tank 1.
The gas is discharged through the discharge path L20, the pressure of the pipeline is increased by the compressor P interposed in the discharge path L20, the pressure of the pipeline is combined with the NG 82, and the pressure is sent to the customer.

That is, in order to match the pressure of the NG 82 which has been conventionally obtained by vaporizing the LNG 8 and which is adjusted to the pressure demanded by the customer, a compressor P is provided for the BOG 81, and the compressor P is provided. The BOG 81 is boosted by operating the.

In addition to directly pumping the BOG 81 in a pressurized gas state as described above, the BOG 81 is once boosted, and the BOG 81 in the boosted state is liquefied again to LN.
The method of returning to G is also applied. Regarding the treatment of BOG generated in such an LNG tank 1, for example, JP-A-4-309783 and JP-A-5-106793 can be cited.

[0007]

However, in any of the conventional methods for treating BOG, the BOG must be kept at a considerably high pressure regardless of which method is used. Is indispensable, the power consumption for that is very large, and there is a problem that the operating cost increases.

A BOG compressor, which is used for compressing a low temperature gas of about -130 ° C. such as BOG, and which plays a role of maintaining the internal pressure of the LNG storage facility, is important in a BOG processing device. Since the compressor occupies a large position, the compressor sufficiently satisfies the conditions on the process side, is easy to operate and maintain, and requires high reliability at the same time, special attention is paid to the structural design and manufacturing. There is. For example, the components of the low temperature part of the compressor are subjected to deep cooling treatment with liquid nitrogen in order to prevent deformation at ultra low temperatures, and measures are taken to avoid concentration of thermal stress due to ultra low temperatures in various places. Therefore, it is much more expensive than an ordinary compressor, and if such a BOG compressor is adopted, there is a problem that the equipment cost becomes extremely large.

The present invention has been made in order to solve the above-mentioned problems, paying attention to the fact that the composition of BOG is mostly methane, and methane is well absorbed by low-temperature hydrocarbons. The present invention has been reached by utilizing the property that It is an object of the present invention to provide a BOG processing apparatus that vaporizes in an LNG storage facility, which can reduce the facility cost and the operating cost without using an expensive and power-consuming compressor at all. I am trying.

[0010]

A method for treating BOG vaporized in an LNG storage facility according to claim 1 of the present invention is LN.
Absorb the BOG vaporized in the G storage facility with the absorbent to B
An OG absorbing liquid, and by supplying heat to the BOG absorbing liquid, BOG having a higher pressure than BOG vaporized in the LNG storage facility is taken out and the BOG absorbing liquid is regenerated as an absorbent. .

The method for treating BOG vaporized in the LNG storage equipment according to claim 2 of the present invention is an absorption tower in which the BOG vaporized in the LNG storage equipment is absorbed by an absorbent to form a BOG absorbing liquid. It is characterized in that it is provided with a diffusion tower for taking out BOG having a pressure higher than that of the BOG vaporized in the LNG storage facility by supplying heat to the absorbing solution and regenerating the BOG absorbing solution as an absorbent. is there.

According to a third aspect of the present invention, the apparatus for processing BOG vaporized in the LNG storage facility is provided with an LNG derivation path for deriving the LNG stored in the LNG storage facility, and the inside of the LNG storage facility is disposed. A BOG discharge path for discharging the BOG vaporized in step 2 is provided, and an absorption tower is provided to absorb the BOG drawn out through this discharge path into an absorbent to form a BOG absorbing liquid. The absorption liquid discharge path for discharging the BOG absorption liquid is provided by
A diffusion tower is provided in which heat is supplied from outside the system to the BOG absorption liquid led out through this absorption liquid discharge path to obtain the diffusion BOG, and the diffusion BOG diffused in the diffusion tower is provided. A BOG take-out path for taking out is arranged, and an absorbent feedback path for feeding back the regenerated absorbent regenerated by the diffusion of BOG in the desorption tower to the absorption tower is arranged, and the LNG storage facility is provided in the absorbent feedback path. Is provided with a heat exchanger for exchanging heat between the LNG led out through the LNG lead-out path and the regenerated absorbent flowing in the absorbent feedback path.

According to a fourth aspect of the present invention, an apparatus for processing BOG vaporized in the LNG storage facility is the LNG according to the first aspect.
In a BOG processing device that vaporizes in a storage facility, the BOG extraction path is connected to an LNG derivation path on the downstream side of the heat exchanger, and the BOG extraction path is cooled by the LNG derivation via the LNG derivation path. And a condenser for condensing the emitted BOG, and a condenser BOG downstream of this condenser.
Is provided to the LNG derivation path.

According to a fifth aspect of the present invention, the apparatus for processing BOG vaporized in the LNG storage facility is the third, third or fourth aspect.
In the apparatus for processing BOG vaporized in the LNG storage facility described above, the absorbent is propane or ethane.

[0015]

According to the present invention described in claim 1 or 2,
The BOG vaporized in the LNG storage facility is once absorbed by the absorbent and converted into the BOG absorbing liquid to be removed.
It becomes possible to maintain a predetermined pressure in the storage tank. After the pressure of the absorption liquid is increased by operating a pump, the BOG and the absorption liquid are rectified and separated in a stripping tower, so that the BOG in the absorption liquid once absorbed by the absorbent is diffused from the liquid. Due to the vapor-liquid equilibrium relationship, the released BOG can be converted into a BOG having a higher pressure than the vaporized BOG in the LNG storage facility.

That is, B vaporized in the LNG storage facility
The above-mentioned emission of BOG is achieved without operating the compressor, which consumes an extremely large amount of energy as in the past, to raise the pressure.
Vaporized LN extracted from LNG storage facility
It can be approximately the same as the pressure of G. Therefore, it becomes possible to combine the desorption BOG with the vaporized LNG and supply it to the outside of the system while energy saving is achieved.

According to the present invention as set forth in claim 3, the BOG vaporized inside the LNG storage facility is BOG.
It is introduced into the absorption tower via the discharge path. Then, since the BOG is absorbed and removed by the absorbent in the absorption tower, the high pressure inside the LNG storage facility is effectively suppressed.

BO formed by absorbing BOG by an absorbent
The G absorption liquid is supplied to the desorption column via the absorption liquid derivation route by the operation of the pump, and heat is supplied from the outside of the system in this desorption column, and BOG is diffused by rectification and separation, and the BOG extraction route is set. Taken out through,
The BOG absorbent becomes regenerated regenerated absorbent.

This regenerated absorbent is stored in the heat exchanger provided in the absorbent feedback path from the storage facility and then the L
It is cooled by heat exchange with LNG led out via the NG lead-out path, fed back to the absorption tower and used for recycling.

Thus, the BO absorbed in the absorption tower
By dispersing G in the stripping tower, the absorbent can be effectively regenerated, and BOG having a higher pressure than the pressure of BOG at the time of generation can be taken out from the vapor-liquid equilibrium relationship of the BOG absorbing liquid in the stripping tower. It will be possible.

Further, according to the invention of claim 4,
The BOG extraction path is connected to the LNG derivation path on the downstream side of the heat exchanger, the BOG extraction path obtains cold heat from the LNG derivable via the LNG derivation path, and a condenser for condensing the diffused BOG. Condensing BOG on the downstream side of the condenser
Is provided in the LNG derivation route, the BOG diffused in the desorption tower is liquefied in the condenser to be condensed BOG, and the BOG merges with the LNG in the LNG derivation route by the pressure pump. After that, it is led out of the system as LNG.

In addition, according to the present invention of claim 5,
Propane or ethane is applied as the absorbent. Therefore, when propane is used as the absorbent, the propane evaporation temperature is 10 kg / cm ² Abs.
Is normal temperature, and if the pressure of the BOG released in the stripping tower is adjusted to 10 kg / cm ² Abs, a large amount of air or seawater is used as a heat source for the evaporation of propane to diffuse the BOG. Can be supplied as is economical.

When ethane is used as the absorbent, the ethane vaporization temperature is 30-40 kg / pressure.
When it is cm ² Abs, it is normal temperature. Therefore, if the pressure of BOG released in the stripping tower is adjusted to 30 to 40 kg / cm ² Abs, a large amount is present in the evaporation of ethane for releasing BOG. It is economical because it can supply air, seawater, etc. as a heat source.

[0024]

EXAMPLE A BOG processing apparatus according to the present invention is a method in which a BOG vaporized in an LNG storage facility is once absorbed by an absorbent.
It is basically configured as an absorbing liquid, and by supplying heat to the BOG absorbing liquid, BOG having a higher pressure than the vaporized BOG in the LNG storage facility is taken out.

FIG. 1 is a system diagram showing an example of a BOG processing apparatus according to the present invention. As shown in this figure, LNG
The LNG tank 1, which is a storage facility, stores LNG supplied from an unillustrated dedicated ship or the like. At the bottom of the LNG tank 1, an LN for leading out the LNG 8 in the LNG tank 1 is provided.
A G lead-out path L1 is provided, and the tip of this LNG lead-out path L1 is connected to a vaporizer 5 that vaporizes LNG8. A withdrawal pump 11 is provided in the middle of the LNG derivation path L1. By operating the withdrawal pump 11, LNG8 stored in the LNG tank 1 is supplied to the carburetor 5. There is.

In this embodiment, an open rack type carburetor 5 is used. This open rack type carburetor 5 has a LNG 8
Is supplied, and seawater is supplied to the outer peripheral surface of the heat transfer tube via a path L9 as a heat source for vaporizing LNG8. The NG 82 obtained by vaporizing LNG 8 in the vaporizer 5 is led to the next step via the route L 8.

On the other hand, in the space above the liquid level of the LNG tank 1, the BOG 81 in which LNG 8 is vaporized by receiving external heat.
Is full. The pressure of the BOG 81 is approximately atmospheric pressure (about 1 kg / cm ² Abs). Then, the BOG discharge path L2 for discharging the BOG 81 filled in the space
Is disposed from the top of the LNG tank 1, and the discharge route L
The tip of 2 is connected to the lower part of the absorption tower 2.

From the upper part of the absorption tower 2, the absorbent 9 supplied into the absorption tower 2 through the absorbent feedback path L5 flows down, and the BOG discharge path L2.
BOG81 introduced from the bottom through this absorbent 9
Is brought into countercurrent contact with and is absorbed therein, and as a result, the absorbent 9 becomes a BOG absorbent 91 rich in methane and is temporarily stored in the bottom of the absorption tower 2. Further, an emergency path L30 is connected to the top of the absorption tower 2 and is brought into a circulation state with the outside of the system only when the pressure in the LNG tank 1 provided with a valve 24 which is normally closed is abnormally increased. There is.

An absorption liquid outlet path L3 is arranged at the bottom of the absorption tower 2, and its tip is connected to the upper part of the diffusion tower 3 for regenerating the BOG absorption liquid 91 and returning it to the original absorbent 9. Has been done. The absorption liquid pump 21 is provided in the middle of the absorption liquid discharge path L3.
B stored in the bottom of the absorption tower 2 by operating
The OG absorbing liquid 91 is pressurized and introduced into the upper part of the stripping tower 3 via the absorbing liquid outlet path L3.

BOG absorbing liquid 9 introduced into the stripping tower 3
When heat is supplied from outside the system to 1 and rectified, the BOG 81 absorbed by it is diffused, and as a result, BOG 81 is absorbed.
A high-pressure release BOG81a separated from the absorption liquid 91 at a high pressure of about −60 ° C. is led out from the BOG extraction route L4 provided at the top of the diffusion tower 3, and the concentration of BOG81 in the BOG absorption liquid 91 is significantly reduced. Then, the so-called regenerated absorbent 9 is returned and stored in the bottom portion of the stripping tower 3.

Since the emission BOG81a led to the BOG extraction path L4 is still at a low temperature of about -60 ° C,
The warmer 4 that warms this to room temperature is the BOG extraction path L.
It is provided in the middle of 4. Then, the BOG extraction route L
Since the tip of 4 is connected to the path L8 provided in the vaporizer 5, the diffusion BOG8 extracted from the diffusion tower 3
1a passes through the BOG extraction path L4, is heated to room temperature by the warmer 4 on the way, and then merges with the NG 82 exiting the vaporizer 5 in the path L8 and is led out of the system.

A condenser 6 using the cold heat of the LNG introduction path L1 shown by the two-dot chain line in FIG. 1 may be provided on the BOG extraction path L4 and upstream of the warmer 4. . Then, the return path L4a may be branched from the condenser 6, and the tip thereof may be connected to the upper part of the diffusion tower 3. By doing so, a part of the diffused BOG 81a taken out from the top of the stripping tower 3 is led out in a gaseous state via the BOG taking-out path L4, and the rest is fed back to the stripping tower 3 in a liquid state. It is possible to adjust the concentration of the absorbing liquid contained in the diffused BOG 81a led out of the system by appropriately setting the flow rate ratio of.

BOG absorbing liquid 91 in the stripping tower 3
Regarding the supply of heat to, the following measures are taken in this embodiment. That is, the diffusion tower 3
A circulation path L6 is disposed between the bottom of the absorbent 9 and the liquid surface position of the absorbent 9, and a reboiler that heats the absorbent 9 by heat exchange with air or seawater supplied from outside the system in the middle of the path L6. 31 is provided. Therefore, the absorbent 9 stored at the bottom of the stripping tower 3 is heated to about room temperature in the reboiler 31 while being circulated through the circulation path L6, and is returned to the stripping tower 3 in a gaseous state. Is heated as an upward flow, the BOG absorbing liquid 91 introduced from the upper part of the stripping tower 3 is heated by this heat, and the BOG in it is diffused to regenerate the absorbent 9. ing.

A replenishment path L7 is connected to the lower part of the desorption tower 3, and the exhausted absorbent 9 is newly replenished through the replenishment path L7.

The circulation path L is provided at the bottom of the stripping tower 3.
In addition to 6, the absorbent feedback path L5 for feeding back the absorbent 9 regenerated by the diffusion of BOG in the diffusion tower 3 to the upper part of the absorption tower 2 is provided.
Then, in the absorbent feedback path L5, the L
A heat exchanger 12 is provided for exchanging heat between the LNG 8 derived from the NG tank 1 via the LNG derivation path L1 and the regenerated absorbent 9 flowing in the absorbent feedback path L5.

Therefore, the absorbent 9 heated to about room temperature in the stripping tower 3 is about -160 in the heat exchanger 12.
The heat is exchanged with the LNG8 at a temperature of ℃ and cooled to about −150 ° C. By this cooling, the amount of absorption of the BOG81 can be increased, which is fed back to the upper part of the absorption tower 2. .

Further, the absorption liquid outlet path L near the absorption tower 2
3 is provided with a control valve 22, detects the pressure in the emergency path L30 below the valve 24, and opens and closes the control valve 22 so that the detected pressure becomes a preset pressure. A pressure controller 23 for issuing a command is provided. The above pressure setting value is almost the same as atmospheric pressure 1
Since the pressure is kg / cm ² Abs, the pressure in the absorption tower 2 is almost the same as the atmospheric pressure.

A linear hydrocarbon is applied as the absorbent 9. The reason why such a hydrocarbon is used as the absorbent 9 is that the composition of BOG81 is almost entirely composed of methane gas, and that methane gas is inherently easily absorbed by a straight-chain hydrocarbon of the same series in a low temperature state. Because it has. Then, in this embodiment, propane or ethane is applied as the absorbent 9.

In FIG. 2, the pressure is atmospheric pressure (about 1 kg / cm ² Abs).
4 is a graph illustrating the relationship between the amount of dissolved BOG in propane and temperature at the time, and FIG. 3 is a graph illustrating the relationship between the amount of dissolved BOG in ethane and temperature under the same conditions as described above. First, as can be seen from the graph shown in FIG. 2, propane is about 1 at −140 ° C. under atmospheric pressure.
It is possible to absorb 8 mol% of methane, -1
At 50 ° C, it can absorb as much as 36 mol% of methane. Further, as shown in the graph of FIG. 3, ethane can absorb 19 ml% of methane at 180 ° C. and 37 ml% of methane at −150 ° C. under atmospheric pressure.

As shown in FIGS. 2 and 3, the lower the temperature of the absorbent, the more the absorption amount of methane increases. However, as shown in FIG. 1, the cold heat for cooling the absorbent 9 is used. Since the source is LNG8 of about -160 ° C drawn out from the LNG tank 1 in the heat exchanger 12, the temperature of the absorbent 9 is about -150 ° C even if heat exchange is effectively performed between the two. It is the limit.

When the amount of the absorbent 9 cooled to about −150 ° C. as described above is smaller than the amount of BOG81 introduced from the LNG tank 1 to the absorption tower 2 in terms of heat balance, the absorption is Absorbent 9 flowing down from above in the tower 2
Temperature is too high than expected and BOG
Since the absorption amount of 81 with respect to the absorbent 9 becomes small, it is necessary to secure a predetermined flow rate of the absorbent 9 in order to avoid such an inconvenience.

BO vaporized in the LNG storage facility of the present invention
Since the G processing apparatus is configured as described above, first, about −130 generated in the space above the liquid surface of the LNG tank 1 is generated.
The BOG 81 at ℃ is introduced through the BOG discharge path L2 into the absorption tower 2 which is set to a pressure slightly lower than the pressure in this space (about 1 kg / cm ² Abs). Then, while being countercurrently contacted with the absorbent 9 at about −150 ° C. flowing down from above in the absorption tower 2, it is absorbed by this absorbent 9, and as a result, the methane-rich BOG absorbent 91 is absorbed at the bottom of the absorption tower 2. Is stored.

Then, the BOG absorbing liquid 91 of about -130 to -140 ° C stored in the bottom portion of the absorption tower 2 is withdrawn by the operation of the absorbing liquid pump 21, introduced into the upper portion of the diffusion tower 3, and the diffusion tower 3 is discharged. Reboiler 3 introduced from the bottom of 3
It is heated by the vapor of the absorbent 9 at room temperature heated by 1. As a result, B once absorbed in the absorption tower 2
OG81 is diffused from the BOG absorbing liquid 91 and the temperature is about −
Dissipating BOG81a at 60 ° C and pressure of about 10 kg / cm ² Abs
And is led out of the system via the BOG extraction route L4.

On the other hand, the room temperature absorbent 9 regenerated by the dispersion of the dispersion BOG 81a in the dispersion tower 3 is withdrawn through the absorbent feedback path L5 connected to the bottom of the dispersion tower 3 and the heat exchanger 12 At LNG derivation route L1
It is heat-exchanged with LNG8 of about -160 ° C which is led out of the LNG tank 1 through
It is supplied again to the upper part of the absorption tower 2 for absorbing OG81.

The present invention, as described in detail above, uses BOG8.
By properly utilizing the thermal equilibrium relations such as temperature and pressure for 1 and the absorbent 9, the low pressure BOG 81 of about atmospheric pressure is stored in the LNG tank 1 without using a compressor as in the conventional case. It is capable of raising the pressure to a high pressure of about ² Abs, and as a power, the BOG absorbing liquid 91 staying at the bottom of the absorption tower 2 is diffused into the diffusion tower 3
Since only the absorption liquid pump 21 for pumping into the pump is required, the electric power required for operating this pump 21 is significantly smaller than the electric power required for compression of the conventional BOG 81.
It is possible to significantly improve the operating cost required for processing the vaporized BOG 81 in the NG tank 1.

Further, there are few reliable compressors for compressing a low-temperature gas in the market, and as a result, they are very expensive, but the present invention applies such an expensive compressor. Since this is not the case, it is possible to reduce the equipment cost of the entire apparatus, and this is also excellent.

Particularly, when propane is used as the absorbent 9, since the evaporation temperature of propane is room temperature at 10 kg / cm ² Abs, air or steam is not used as a heat source for evaporation of the absorbent 9 in the reboiler 31. It is possible to apply seawater as it is, and energy saving is realized.

It is required that the pressure of the desorption BOG 81a taken out of the system via the BOG take-out path L4 is high, and therefore the pressure in the desorption tower 3 is 30-40 kg /
When it is necessary to set cm ² Abs, ethane may be used as the absorbent 9. This is because the evaporation temperature of ethane is about room temperature in the range of 30 to 40 kg / cm ² Abs, and thus air, seawater, etc. can be directly applied as a heat source for heat exchange in the reboiler 31.

Table 1 below shows actual examples of the operating conditions of the absorption tower 2 and the diffusion tower 3 for the embodiment shown in FIG.

[0050]

[Table 1]

In the operation shown in Table 1 above, the power required is only for the absorbent pump 21 which is operated to feed the BOG absorbent 91 stored in the bottom of the absorber 2 to the stripper 3. The power consumption is about 100 kW. On the other hand, if the compressor is applied as in the conventional case, the power consumption of the compressor is required to be about 900 kW, and it can be seen how the present invention is effective in reducing the operating cost.

Under the above conditions, the absorbent 9 is propane, and the evaporation temperature at 10 kg / cm ² Abs is room temperature. Therefore, the absorbent 9 in the reboiler 31 is
It is possible to use the atmosphere or seawater as a heat source for the evaporation heat of, which is convenient for energy saving.

Further, since most of the components of BOG81 are methane and the calorific value thereof is low and it cannot be delivered as it is as city gas, in the conventional method of boosting BOG81 with a compressor, the BOG after boosting is converted to BOG. Although it was done to add butane and propane for heating,
When the device of the present invention is applied as a facility for producing city gas, it is not necessary to separately add the butane and propane for heating as described above, and the temperature and pressure conditions in the stripping tower 3 are appropriately set and released. It can be sufficiently dealt with by adjusting the concentration of propane in BOG81a.

In addition, when the demand for the pressure of the desorbing BOG 81a derived from the BOG extraction path L4 is higher than the above conditions, for example, 30 kg / cm ² Abs, when propane is used as the absorbent 9, the reboiler 31 In order to evaporate propane, a heat source at room temperature or higher is required, and steam or the like must be used. Therefore, in such a case, ethane may be applied as the absorbent 9. Then, the evaporation temperature of ethane is 30 kg.
Since the temperature is room temperature / cm ² Abs, it is possible to use the atmosphere or seawater as a heat source in the reboiler 31.

FIG. 4 is a system diagram showing another example of the BOG processing apparatus according to the present invention. In the case of this example, the diffusion tower 3
The desorption BOG 81a derived from the above is condensed and fed back to the desorption column 3 partially, and the remaining part is introduced into the LNG derivation path L1 on the downstream side of the heat exchanger 12. Therefore, the same condenser 6 as described above is provided at the tip of the BOG extraction path L4 extending from the top of the stripping tower 3, and the downstream side of this condenser 6 is the return path L4a.
1 and is not connected to the path L8 by further extending the BOG extraction path L4 downstream of the condenser 6 as in the previous example shown in FIG.

Instead, the return path L4a branches into a connecting path L4b on the way, and the connecting path L4b is connected to the heat exchanger 1.
2 is connected to the LNG derivation route L1 on the downstream side. A pressurizing pump 32 is provided in the communication path L4b, and by operating the pressurizing pump 32, the liquid BOG 81b condensed in the condenser 6 joins the LNG derivation path L1.

By doing so, even if the pressure of the NG 82 sent out of the system is as high as 70 kg / cm ² Abs, the compressor consumes a very large amount of power as in the conventional case and dissipates it. It is not necessary to pressurize the BOG 81a, but it can be covered by the operation of the pressurizing pump 32 that consumes significantly less power, which is extremely useful in reducing the operating cost.

[0058]

As described in detail above, in the method for treating BOG according to claim 1 of the present invention, the BOG vaporized in the LNG storage facility is absorbed by the absorbent to obtain a BOG absorbing liquid, and
The BOG absorbent is regenerated into an absorbent by taking out BOG having a pressure higher than that of the BOG vaporized in the LNG storage facility by supplying heat to the OG absorbent. BOG processing equipment
An absorption tower for absorbing BOG vaporized in the LNG storage facility into a BOG absorption liquid by an absorbent, and supplying heat to the BOG absorption liquid to generate BOG having a higher pressure than the BOG vaporized in the LNG storage facility. Take out and BOG
And a diffusion tower for regenerating the absorbent into an absorbent.

Therefore, the vaporized BO in the LNG storage facility
By once absorbing G into the absorbent and converting it into a BOG absorbent, it is possible to maintain the inside of the LNG storage tank at a predetermined pressure. Then, by applying external heat to the absorbing liquid, the BOG in the absorbing liquid once absorbed by the absorbent is diffused from the liquid, and the BOG thus diffused is absorbed.
Is vaporized in the LNG storage facility due to the vapor-liquid equilibrium relationship.
It becomes easier to make the BOG at a higher pressure than the OG.

That is, B vaporized in the LNG storage facility
The above-mentioned emission of BOG is achieved without operating the compressor, which consumes an extremely large amount of energy as in the past, to raise the pressure.
Vaporized LN extracted from LNG storage facility
It can be approximately the same as the pressure of G. Therefore, it becomes possible to combine the desorption BOG with the vaporized LNG and supply it to the outside of the system while energy saving is achieved.

Further, the apparatus for treating BOG according to the third aspect of the present invention is provided with an absorption tower in which the absorbent absorbs the BOG derived from the LNG storage facility to form the BOG absorbing liquid. A diffusion tower is provided in which BOG is diffused by supplying heat from outside the system to the BOG absorbing liquid introduced from this absorption tower, and a regenerated absorbent regenerated by the diffusion of BOG in this diffusion tower. And above L
A heat exchanger for exchanging heat with LNG led out from the NG storage facility via the LNG lead-out path is provided.

Therefore, the BOG vaporized inside the LNG storage facility is introduced into the absorption tower through the BOG discharge route,
As it is absorbed and removed by the absorbent in this absorption tower,
High pressure in the LNG storage facility is effectively suppressed.

BO formed by absorption of BOG by an absorbent
The G absorption liquid is supplied to the desorption column via the absorption liquid derivation path by the operation of the pump, and heat is supplied from the outside of the system in the desorption tower, and BOG is diffused to become a regenerated absorbent.

This regenerated absorbent is stored in the heat exchanger provided in the absorbent feedback path from the storage facility to the above L
It is cooled by heat exchange with LNG led out via the NG lead-out path, fed back to the absorption tower and used for recycling.

As described above, by circulating and moving the absorbent between the absorption tower and the diffusion tower, the BOG absorbed in the absorption tower is diffused in the diffusion tower,
From the vapor-liquid equilibrium relationship of the BOG absorbing liquid in the stripping tower, it becomes possible to take out BOG having a pressure higher than the pressure of BOG at the time of generation. Therefore, LNG is vaporized and NG in a high pressure state
In the case where the above is supplied to a predetermined equipment outside the system, the high pressure BOG can be directly joined to the NG without providing a booster, which is convenient in terms of equipment simplification.

Further, in the BOG processing apparatus according to claim 4 of the present invention, the BOG extraction path is connected to the LNG derivation path on the downstream side of the heat exchanger, and the BOG extraction path is L-shaped.
Since a condenser that obtains cold heat from the LNG led out via the NG derivation path to condense the diffused BOG and a pressurizing pump that guides the condensed BOG to the LNG derivation path on the downstream side of the condenser are provided. The BOG diffused in the stripping tower is liquefied by the condenser to become LNG, merged with LNG led out from the LNG storage facility in the LNG lead-out path, and thereafter led out of the system as LNG. Therefore, dissipate BO
Even if the BOG separated from the G absorbing solution is not separately processed and matched with LNG, the normal LNG processing may be performed thereafter, which is convenient for simplifying the equipment.

In addition, the apparatus for treating BOG according to claim 5 of the present invention is such that propane or ethane is applied as the absorbent. Therefore, when propane is used as the absorbent, the evaporation temperature of this propane is room temperature when the pressure is 10 kg / cm ² Abs, and the pressure of the BOG released in the stripping tower is about 10 kg / cm ² Abs. If it is adjusted to, it is economical because a large amount of air, seawater, etc., can be supplied as a heat source for the evaporation of propane for releasing BOG.

When ethane is used as the absorbent, the ethane evaporation temperature is 30-40 kg / pressure.
When it is cm ² Abs, it is normal temperature. Therefore, if the pressure of BOG released in the stripping tower is adjusted to 30 to 40 kg / cm ² Abs, a large amount is present in the evaporation of ethane for releasing BOG. It is economical because it can supply air, seawater, etc. as a heat source.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a BOG processing apparatus according to the present invention.

FIG. 2 BO for propane used as an absorbent
It is a graph which illustrates the relationship between G dissolution amount and temperature.

FIG. 3 BOG for ethane used as an absorbent
It is a graph which illustrates the relationship between the amount of dissolution and temperature.

FIG. 4 is a system diagram showing another example of the BOG processing apparatus according to the present invention.

FIG. 5 is a system diagram showing an example of a conventional BOG processing device.

[Explanation of symbols]

 1 LNG tank 11 Extraction pump 12 Heat exchanger 2 Absorption tower 21 Absorption liquid pump 22 Control valve 23 Pressure controller 24 Valve 3 Dispersion tower 31 Reboiler 32 Pressurization pump 4 Warmer 5 Vaporizer 6 Condenser 8 LNG (liquefaction natural Gas 81 BOG (boil-off gas) 81a BOG (pressurized boil-off gas) 81b BOG (liquid boil-off gas) 82 NG (natural gas) 9 absorbent 91 BOG absorption liquid L1 LNG derivation route L2 BOG discharge route L3 absorption liquid derivation route L4 BOG extraction pathway L5 absorbent feedback pathway

Claims (5)

[Claims] 1. A BOG having a pressure higher than that of the BOG vaporized in the LNG storage facility by absorbing BOG vaporized in the LNG storage facility with an absorbent to form a BOG absorbent, and supplying heat to the BOG absorber. Take out B
LNG characterized by regenerating an OG absorbent into an absorbent
A method for treating BOG vaporized in a storage facility. 2. An absorption tower for absorbing BOG vaporized in an LNG storage facility into a BOG absorbing liquid by absorbing the BOG, and this B
An LNG characterized by being provided with a diffusion tower for taking out BOG having a higher pressure than BOG vaporized in the LNG storage facility by supplying heat to the OG absorbing solution and regenerating the BOG absorbing solution as an absorbent. BOG processing device that vaporizes in storage equipment. 3. LN stored in an LNG storage facility
An LNG derivation path for deriving G is arranged, a BOG discharge path for discharging BOG vaporized inside the LNG storage facility is arranged, and the BOG derived through the discharge path is absorbed by the absorbent to cause BOG. An absorption tower for converting the absorption liquid is provided, and an absorption liquid outlet path for deriving the BOG absorption liquid by operating a pump is arranged from the absorption tower. The BOG absorption liquid discharged through the absorption liquid outlet path is connected to the outside of the system. A diffusion tower for dissipating BOG by supplying heat from it to obtain diffused BOG is provided, and the dissipation B diffused in this diffusion tower
A BOG extraction path for extracting OG is provided, and an absorbent feedback path for feeding back the regenerated absorbent regenerated by the diffusion of BOG in the diffusion tower to the absorption tower is provided, and the LN is provided in the absorbent feedback path.
A vaporizer in the LNG storage facility, characterized in that a heat exchanger for exchanging heat between the LNG derived from the G storage facility via the LNG delivery route and the regenerated absorbent flowing in the absorbent feedback route is provided. BOG processing device. 4. The BOG extraction path is connected to an LNG derivation path on the downstream side of the heat exchanger, and the BOG extraction path obtains cold heat from the LNG derived through the LNG derivation path to condense the dissipated BOG. 4. The L according to claim 3, wherein a condenser for causing the condensed BOG and a pressurizing pump for guiding the condensed BOG to the LNG derivation path are provided on the downstream side of the condenser.
BOG processing device that vaporizes in NG storage facility. 5. The LNG according to claim 2, 3 or 4, wherein the absorbent is propane or ethane.
BOG processing device that vaporizes in storage equipment.