JPH0770575A - Method and apparatus for treating boil-off gas produced in storage tank of liquefied natural gas - Google Patents

Abstract

PURPOSE:To improve the unit requirement for liquefying a boil-off gas generated in a storage tank of a liquefied natural gas by mixing the boil-off gas with an LPG in a heat exchanger equipped with a precooler and installed in a discharge line of the liquefied natural gas, thereby cooling and liquefying the boil-off gas, and discharging it with the liquefied natural gas. CONSTITUTION:The figure shows an example wherein a boil-off gas(BOG) generated in a liquefied natural gas(LNG) tank 1 is pressurized and conveyed through a line 2 and a compressor 3 to a precooling heat exchanger 5; a liquefied petroleum gas(LPG) is conveyed through a line 4 to a precooling heat exchanger 6; an LNG from the tank 1 is conveyed through a line 8, a heat exchanger 7, and the precooling heat exchangers 5 and 6 to the evaporator side; and the BOG and LPG, both after precooled, are mixed with each other in the heat exchanger 7, are liquefied again by exchanging heat with the LNG from the tank 1, and are conveyed through a drum 10 to a pump 11 which sends and mixes them into LNG being discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating evaporated gas generated in a liquefied natural gas storage tank.

[0002]

Liquefied natural gas (hereinafter referred to as "LNG")
Evaporative gas (hereinafter referred to as "BOG") is generated in the tank that stores
Will need to be processed.

FIG. 5 shows a conventional BOG processing apparatus, in which the BOG generated in the LNG tank 20 is
After being collected outside the tank 20 by the BOG line 21 and boosted to a required pressure by the compressor 22, it is mixed with LPG sent from the liquefied petroleum gas (hereinafter referred to as “LPG”) line 24 in the gas-liquid separator 23. Then, the gas-liquid separated product is guided to the heat exchanger 25, where the gas-liquid is mixed and at the same time heat-exchanged with the LNG discharged from the discharge line 26 for reliquefaction, which is then introduced to the drum 27 and temporarily For,
Then, it is mixed with the payout line 26 via the pump 28 and sent out to the vaporizer side. In the case of the above conventional apparatus, a plate fin type heat exchanger is used as the heat exchanger 25, and in the case of this plate fin type heat exchanger, the temperature difference between BOG and LNG is 50 ° C. due to restrictions on strength.
Must be kept within. Therefore, a method is used in which a part of the dispensed LNG is branched by a pre-cooling line 29 and put into the gas-liquid separator 23 to pre-cool BOG and LPG, thereby suppressing the temperature difference from LNG to within 50 ° C.

Next, in the above-mentioned conventional example, B before reliquefaction
The reason for mixing LPG with OG is that mixing LPG with BOG improves the liquefaction efficiency (liquefaction basic unit).

[0005]

However, according to the above-mentioned conventional example, there are the following problems.

A. LNG for the purpose of lowering the temperature of BOG
When directly mixed with, this LNG gasifies,
The amount of reliquefaction in the heat exchanger 25 increases. As a result, the liquefaction unit consumption becomes worse.

[0007] An object of the present invention is to improve the liquefaction unit in a BOG treatment method and apparatus.

[0008]

The constitution of the present invention is as follows.

1. Evaporated gas and liquefied petroleum gas are discharged by using a pre-cooling heat exchanger, each is indirectly pre-cooled by liquefied natural gas, and this pre-cooled evaporative gas and liquefied petroleum gas are introduced to a heat exchanger and mixed, and at the same time evaporated by this heat exchanger. A method for treating evaporative gas generated in a liquefied natural gas storage tank that mixes with liquefied liquefied natural gas discharged to a vaporizer and cooled by liquefied natural gas.

2. A mixture of evaporative gas and liquefied petroleum gas is discharged in advance using a pre-cooling heat exchanger and indirectly pre-cooled by liquefied natural gas, and then guided to a gas-liquid separator for gas-liquid separation, which is then a heat exchanger. At the same time as mixing the gas and liquid, it is cooled and reliquefied by liquefied natural gas.
A method for treating evaporative gas generated in a liquefied natural gas storage tank mixed with liquefied natural gas discharged to a vaporizer.

3. The evaporative gas is discharged using a precooling heat exchanger and indirectly precooled by liquefied natural gas, and then this precooled evaporative gas and liquefied petroleum gas are introduced to a mixer for mixing and gas-liquid separation, which is then heated. At the same time as introducing the gas and liquid to the exchanger, it is cooled by blown out liquefied natural gas and re-liquefied, and this is the treatment of the evaporative gas generated in the liquefied natural gas storage tank that mixes with the blown out liquefied natural gas to the vaporizer. Method.

4. A BOG line for collecting evaporative gas generated in a liquefied natural gas storage tank, a compressor attached to the BOG line, and an LPG line for mixing liquefied petroleum gas with the recovered evaporative gas to improve the liquefaction unit. , B attached to the BOG line
OG pre-cooling heat exchanger, LPG pre-cooling heat exchanger attached to the LPG line, BOG re-liquefaction heat exchanger, LNG discharged from inside the liquefied natural gas storage tank, the heat exchanger and BOG pre-cooling heat L and LPG pre-cooling heat exchanger, which is sent to the vaporizer side via the heat exchanger
The NG payout line, the evaporative gas discharged from the BOG precooling heat exchanger and the liquefied petroleum gas discharged from the LPG precooling heat exchanger are mixed in the heat exchanger, and at the same time, reliquefaction is performed while passing through the heat exchanger. , The re-liquefied BOG is temporarily stored in the drum, and the re-liquefied evaporative gas is pumped by the LN.
L consisting of a reliquefaction line mixed with the G payout line
BOG treatment device generated in NG storage tank.

[0013]

The evaporative gas generated in the liquefied natural gas storage tank is recovered by the BOG line and is pressurized to a predetermined pressure by the compressor to reach the BOG preheat exchanger. On the other hand, the liquefied petroleum gas mixed in the BOG for the purpose of improving the liquefaction unit consumption reaches the LPG preheat exchanger via the LPG line.

The liquefied natural gas discharged from the liquefied natural gas storage tank passes from the LNG discharge line through the heat exchanger to the BOG precooling heat exchanger and the LPG precooling heat exchanger, where it is vaporized. The gas and liquefied petroleum gas are indirectly precooled and then sent to the vaporizer side.

The evaporative gas and the liquefied natural gas, which have been indirect precooled by the BOG precooling heat exchanger and the LPG precooling heat exchanger, and have sufficiently lowered in temperature, are mixed in the heat exchanger, where the liquefaction is carried out before the precooling. It is cooled by petroleum gas, reliquefied, and once enters the drum. The liquefied evaporative gas in the drum is mixed with the liquefied liquefied natural gas in the payout line after the pressure is raised by the pump, reaches the vaporizer, and is sent to the consumer side after the vaporization.

[0016]

Embodiments of the present invention will be described with reference to FIG.
1 is an LNG tank, 2 is a BOG line for collecting the BOG generated in the LNG tank 1, 3 is a compressor attached to the BOG line 2, 4 is LPG for improving the liquefaction unit of the collected BOG LPG line for mixing in, 5 is a BOG precooling heat exchanger attached to the BOG line 2, 6 is an LPG precooling heat exchanger attached to the LPG line 4, and 7 is a heat exchanger for BOG reliquefaction , 8 are LNs that guide the LNG discharged from the LNG tank 1 to the vaporizer via the heat exchanger 7, the BOG precooling heat exchanger 5 and the LPG precooling heat exchanger 6.
The G payout line, 9 mixes the BOG discharged from the BOG precooling heat exchanger 5 and the LPG discharged from the LPG precooling heat exchanger 6 in the heat exchanger 5, and then reliquefies the heat in the heat exchanger 5. , Lead it to the drum 10 and store it in this drum 10
It is a reliquefaction line for mixing with the LNG payout line 8 by the pump 11.

Next, the operation of the above embodiment will be described.

BOG generated in the LNG tank 1 is B
It is recovered by the OG line 2, is pressurized to a predetermined pressure by the compressor 3, and reaches the BOG preheat exchanger 5. On the other hand, LPG mixed in BOG for the purpose of improving the liquefaction unit
Reaches the LPG preheat exchanger 6 via the LPG line 4.

LNG dispensed from inside the LNG tank 1.
Passes through the BOG precooling heat exchanger 5 and the LPG precooling heat exchanger 6 from the LNG payout line 8 via the heat exchanger 7, where the BOG and LNG are indirectly precooled and then sent to the carburetor side. To be done.

BOG and LPG precooled by the BOG precooling heat exchanger 5 and the LPG precooling heat exchanger 6 and having a sufficiently lowered temperature
Are mixed in the heat exchanger 7 and, at the same time, cooled in the heat exchanger 7 by the delivery LNG before reaching the pre-cooling and reliquefied, and then once passed through the reliquefaction BOG line 9 to the drum 10 once.
Get in The liquefied BOG in the drum is mixed into the payout LNG in the payout line 8 after boosting by the pump 11, reaches a vaporizer (not shown), and is sent to the consumer side after vaporization.

FIG. 2 shows the BOG line 2 and the LPG line 4
, BOG and LPG are mixed first, and the mixture is discharged by the pre-cooling heat exchanger 12 and indirectly pre-cooled by LNG, and then it is once introduced to the gas-liquid separator 13, where the gas-liquid is separated, and this is heat-exchanged. This is an embodiment of a method of introducing gas into a vessel 7 to mix gas and liquid and simultaneously reliquefying.

In FIG. 3, the pre-cooling heat exchanger 5 is attached only to the BOG line 2 side, and the pre-cooled BOG and LPG are mixed in the gas-liquid separator 13 and the gas-liquid separated is heat exchanger 7.
It is an embodiment of a method of introducing the above into a mixture and mixing and reliquefying at the same time.

FIG. 4 shows the BO executed in the embodiment shown in FIG.
In the case of the embodiment of the present invention shown by a dotted line as a comparative example of the liquefaction unit of the processing method of G and the conventional example shown in FIG. 5, the improvement of the liquefaction unit is obvious.

[0024]

As described above, the present invention provides payout LNG
BOG and LPG or BOG and LPG before reliquefaction
Indirect precooling of the mixture or BOG, then
Since the liquid is guided to the heat exchanger and is cooled by the LNG to be reliquefied, the following effects can be obtained.

A. LNG that was partially mixed to lower the temperature
The amount of heat for reliquefying the vaporized amount of is unnecessary. As a result, it is possible to improve the unit liquefaction unit.

B. Since the amount of reliquefaction is reduced, the heat exchanger can be downsized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an example of indirectly precooling a mixture of BOG and LPG mixed in advance.

FIG. 3 is an explanatory diagram of an embodiment in which BOG is indirectly precooled in advance.

FIG. 4 is a comparative explanatory diagram of a liquefaction unit.

FIG. 5 is an explanatory diagram of a conventional BOG processing method and apparatus.

[Explanation of symbols]

 1 LNG tank 2 BOG line 3 Compressor 4 LPG line 5 BOG precooling heat exchanger 6 LPG precooling heat exchanger 7 Heat exchanger 8 LNG delivery line 9 Reliquefaction line 10 Tank 11 Pump 12 Precooling heat exchanger 13 Gas-liquid separator

Claims (4)

[Claims] 1. Evaporated gas and liquefied petroleum gas are discharged by utilizing a precooling heat exchanger and indirectly precooled by liquefied natural gas,
This pre-cooled evaporative gas and liquefied petroleum gas are introduced into a heat exchanger to be mixed, and at the same time, the evaporative gas is discharged from this heat exchanger and cooled by liquefied natural gas for reliquefaction, which is delivered to the carburetor. Method for treating evaporative gas generated in a liquefied natural gas storage tank mixed in a tank. 2. A premixed mixture of vaporized gas and liquefied petroleum gas is discharged using a precooling heat exchanger and indirectly precooled by liquefied natural gas, and then led to a gas-liquid separator for gas-liquid separation, This is led to a heat exchanger to mix the gas and liquid and at the same time cooled by blown out liquefied natural gas to be re-liquefied, and then vaporized in the liquefied natural gas storage tank mixed with the blown out liquefied natural gas to the vaporizer. Gas treatment method. 3. The vaporized gas is discharged by using a precooling heat exchanger and indirectly precooled by liquefied natural gas, and then the precooled vaporized gas and liquefied petroleum gas are introduced into a mixer for mixing and gas-liquid separation. It is conducted to a heat exchanger to mix the gas and liquid and at the same time cooled by discharged liquefied natural gas to be re-liquefied, which is then generated in the liquefied natural gas storage tank that mixes with discharged liquefied natural gas to the vaporizer. Evaporative gas treatment method. 4. A BOG line for recovering evaporative gas generated in a liquefied natural gas storage tank, a compressor attached to the BOG line, and a liquefied petroleum gas mixed with the recovered evaporative gas for improving liquefaction unit. For LPG, BOG pre-cooling heat exchanger attached to the BOG line, LPG pre-cooling heat exchanger attached to the LPG line, heat exchanger for BOG reliquefaction, paying out from the liquefied natural gas storage tank The LNG
The heat exchanger, the BOG pre-cooling heat exchanger, and the LPG pre-cooling heat exchanger, and the LNG delivery line for sending out to the carburetor side via the heat exchanger, the evaporative gas and the LPG pre-cooling heat leaving the BOG pre-cooling heat exchanger The liquefied petroleum gas discharged from the exchanger is mixed in the heat exchanger, and at the same time, reliquefied while passing through the heat exchanger, the reliquefied BOG is temporarily stored in the drum, and the vaporized gas after the reliquefaction is stored. A re-liquefaction line that mixes the LNG with the LNG payout line by a pump, and a processing apparatus for BOG generated in the LNG storage tank.