阅读说明：本技术 用于处理液化气再气化系统中的蒸发气体的装置和方法 (Apparatus and method for treating boil-off gas in liquefied gas regasification system ) 是由 曹斗现 安守敬 金泳铉 于 2018-12-28 设计创作，主要内容包括：本发明涉及一种用于处理液化气再气化系统中的蒸发气体的装置和方法,且更特定来说,涉及一种用于处理液化气再气化系统中的蒸发气体的装置和方法,其中,即使液化气再气化系统中没有或有少量再气化气体待发送,也可再液化和重新收集蒸发气体。根据本发明的用于处理液化气再气化系统中的蒸发气体的装置是用于处理在液化气再气化系统中产生的蒸发气体的蒸发气体处理装置,蒸发气体处理装置包括：低压压缩机,用于在燃料消耗者所需的压力下压缩蒸发气体；高压压缩机,安设在低压压缩机的后端,与低压压缩机串联,以便在再气化气体消耗者所需的压力下压缩已由低压压缩机压缩的低压蒸发气体；低温热交换器,用于冷却由高压压缩机压缩的高压蒸发气体；减压装置,用于将已由低温热交换器冷却的高压蒸发气体的压力减小到用于存储液化气的液化气储罐的内压；以及液化气滚筒,用于分离由减压装置在减压过程中产生的闪蒸气体,其中将与液化气滚筒分离的液态再液化蒸发气体重新收集到液化气储罐中。(The present invention relates to an apparatus and method for treating boil-off gas in a liquefied gas regasification system, and more particularly, to an apparatus and method for treating boil-off gas in a liquefied gas regasification system, in which boil-off gas can be reliquefied and recollected even if no or a small amount of regasified gas is to be sent in the liquefied gas regasification system. An apparatus for treating boil-off gas in a liquefied gas regasification system according to the present invention is a boil-off gas treatment apparatus for treating boil-off gas generated in a liquefied gas regasification system, the boil-off gas treatment apparatus including: a low pressure compressor for compressing the boil-off gas at a pressure required by a fuel consumer; a high pressure compressor installed at a rear end of the low pressure compressor, connected in series with the low pressure compressor, so as to compress the low pressure evaporation gas compressed by the low pressure compressor at a pressure required by a regasified gas consumer; a low temperature heat exchanger for cooling the high pressure boil-off gas compressed by the high pressure compressor; a pressure reducing device for reducing the pressure of the high-pressure boil-off gas, which has been cooled by the cryogenic heat exchanger, to an internal pressure of a liquefied gas storage tank for storing liquefied gas; and a liquefied gas drum for separating flash gas generated by the pressure reducing device during the pressure reduction, wherein the liquefied reliquefied boil-off gas separated from the liquefied gas drum is recollected into the liquefied gas storage tank.)

1. An apparatus for treating boil-off gas in a liquefied gas regasification system, the apparatus comprising:

a fuel compressor for compressing the boil-off gas to a pressure required by a fuel demand site;

a high pressure compressor disposed downstream of the fuel compressor in series with the fuel compressor and compressing low pressure boil-off gas compressed by the fuel compressor to a pressure required by a regasification gas demand site;

a low temperature heat exchanger cooling the high pressure boil-off gas compressed by the high pressure compressor;

a decompression unit decompressing the high-pressure boil-off gas cooled by the cryogenic heat exchanger to an internal pressure of a liquefied gas storage tank; and

a liquefied gas drum separating flash gas generated during the decompression by the decompression unit,

wherein the reliquefied boil-off gas separated by the liquefied gas drum is returned to the liquefied gas storage tank.

2. The apparatus of claim 1, further comprising:

an expander that expands and cools some of the high-pressure boil-off gas to be supplied to the cryogenic heat exchanger,

wherein the low temperature heat exchanger cools the high pressure boil-off gas by heat exchange with the boil-off gas expanded and cooled by the expander.

3. The apparatus of claim 2, further comprising:

a high temperature heat exchanger pre-cooling the high pressure evaporation gas to be supplied to the low temperature heat exchanger to an inlet temperature of the expander,

wherein some of the high pressure boil-off gas to be supplied from the high temperature heat exchanger to the low temperature heat exchanger is sent to the expander.

4. The apparatus according to claim 3, wherein the high temperature heat exchanger cools the high pressure boil-off gas to be supplied to the low temperature heat exchanger and the expander by heat exchange with expanded boil-off gas, which is heated by heat exchange in the low temperature heat exchanger and discharged from the low temperature heat exchanger.

5. The apparatus of claim 3, further comprising:

a gas compressor compressing the expanded boil-off gas that has undergone heat exchange in the cryogenic heat exchanger and is discharged from the cryogenic heat exchanger to a pressure of a flow of the boil-off gas compressed by the fuel compressor,

wherein the boil-off gas compressed by the gas compressor is merged with the flow of the boil-off gas compressed by the fuel compressor.

6. The apparatus of claim 5, wherein the gas compressor is connected to the expander via a common shaft.

7. The apparatus of claim 5, further comprising:

a gas cooler that adjusts a temperature of the evaporation gas compressed and heated by the gas compressor.

8. The apparatus of claim 3, wherein the flash gas separated by the liquefied gas drum is merged with a stream of expanded boil-off gas to be supplied to the cryogenic heat exchanger.

9. A method for treating boil-off gas in a liquefied gas regasification system, comprising:

the boil-off gas is compressed to the low pressure required at the fuel demand site,

the low pressure boil-off gas is compressed to the high pressure required by the regasification demand site,

the high-pressure evaporation gas is cooled down,

decompressing the cooled high-pressure boil-off gas to an internal pressure of the liquefied gas storage tank; and

separating flash gas generated during the depressurization of the cooled high pressure boil-off gas and returning re-liquefied boil-off gas to the liquefied gas storage tank.

10. The method of claim 9, wherein cooling the high pressure boil-off gas comprises:

expanding and cooling some of the high pressure boil-off gas prior to cooling the high pressure boil-off gas; and

liquefying at least a portion of the high pressure boil-off gas by heat exchange between the expanded and cooled boil-off gas and the high pressure boil-off gas.

11. The method of claim 10, further comprising:

pre-cooling the high pressure boil-off gas by heat exchange with the expanded boil-off gas heated while cooling the high pressure boil-off gas before heat exchange between the expanded and cooled boil-off gas and the high pressure boil-off gas.

12. The method of claim 11, wherein pre-cooling the high pressure boil-off gas comprises:

cooling the high pressure boil-off gas to an inlet temperature of an expander that expands the high pressure boil-off gas.

13. The method of claim 11, wherein the expanded boil-off gas heated while cooling the high pressure boil-off gas is compressed to a pressure of a stream of boil-off gas to be compressed by a fuel compressor before merging with the stream of boil-off gas.

14. The method of claim 13, wherein the work of expansion in expanding the high pressure boil-off gas is recovered as the work of compression in compressing the expanded boil-off gas.

15. The method of claim 11, wherein the separated flash gas is combined with a flow of the expanded boil-off gas that exchanges heat with the high pressure boil-off gas.

Technical Field

The present invention relates to an apparatus and method for treating boil-off gas in a liquefied gas regasification system, and more particularly, to an apparatus and method for treating boil-off gas in a liquefied gas regasification system, which allows for reliquefaction and recovery of boil-off gas even when there is little or no regasified gas to be delivered in the liquefied gas regasification system.

Background

Typically, natural gas is transported in liquid form by LNG carriers to remote destinations after being converted to Liquefied Natural Gas (LNG) by liquefaction at extremely low temperatures at the production site. LNG is obtained by cooling natural gas to a very low temperature of about-163 ℃, and has a volume of about 1/600 that is the volume of gaseous natural gas, and thus is suitable for long-distance marine transportation.

LNG transported by LNG carriers may be regasified onshore or offshore before being supplied to onshore gas consumers. Examples of vessels suitable for regasifying LNG received from an offshore LNG carrier and supplying the regasified LNG to gas consumers include LNG regasification vessels and floating offshore structures (hereinafter collectively referred to as "LNG regasification vessels"), such as LNG RVs (LNG harvesting vehicles), which are LNG carrier vessels and LNG FSRUs (floating storage and regasification units).

Generally, a regasification facility provided to an LNG regasification vessel includes: a high pressure pump (high pressure) compressing the low pressure LNG stored in the LNG storage tank to a pressure required by a gas consumer; and a vaporizer (high pressure vaporizer) for vaporizing the compressed LNG by heating to a temperature required for a gas pipeline network (regas network) using a heating medium (heating medium) such as seawater (sea water). The regasified gas obtained by the high-pressure pump and the vaporizer is conveyed to a gas consumer (consumer) via a gas piping network.

Disclosure of Invention

Technical problem

An LNG storage tank provided to an LNG regasification vessel stores LNG in a liquid state at an extremely low temperature of about-163 ℃. Therefore, it is preferred that the LNG storage tank is thermally insulated so that the LNG can be maintained in a liquid state. However, even when the LNG storage tank is thermally insulated, LNG is naturally vaporized due to intrusion of external heat and the like. The pressure of the LNG storage tank rises as boil-off gas (BOG) continues to be generated due to natural vaporization of the LNG.

If the pressure of the LNG storage tank rises excessively, there is a risk of explosion and the like. Therefore, if the pressure of the LNG tank exceeds a preset value, the safety valve is opened to discharge the boil-off gas from the LNG tank.

In an LNG regasification vessel, the cold heat of LNG is used to recondense boil-off gas discharged from an LNG storage tank, and then supplied to a high-pressure pump and a vaporizer together with LNG to be regasified before being supplied to a gas consumer.

Here, since the boil-off gas is recondensed using the cold heat of the LNG to be regasified, the amount of the boil-off gas that can be recondensed is proportional to the amount of the LNG to be regasified. That is, boil-off gas can be treated by recondensation only if the amount of LNG to be regasified is sufficient to allow recondensation of boil-off gas discharged from the LNG storage tank.

In the LNG regasification vessel, the uncondensed boil-off gas that does not receive sufficient cold heat from the LNG due to the boil-off gas generated during the interruption of the regasification or the reduction in the amount to be regasified may be returned to the LNG storage tank. Further, boil-off gas that exceeds the capacity of the LNG storage tank to receive boil-off gas (as determined by the allowable pressure level of the LNG storage tank) may be supplied as fuel to the engine.

However, boil-off gas exceeding both the capacity of the LNG storage tank and the fuel requirement of the engine needs to be sent to the GCU (gas combustion unit) to be combusted or needs to be vented (venting) to the air.

However, since the boil-off gas mainly contains methane having the highest boiling point among the components constituting the LNG, burning or discharging the boil-off gas is a great economic loss.

Embodiments of the present invention have been conceived to solve such problems in the art, and it is an aspect of the present invention to provide an apparatus and method for treating boil-off gas in a liquefied gas regasification system, which allows for reliquefaction and recovery of the boil-off gas without waste even when the amount to be regasified is insufficient to allow recondensation of the boil-off gas.

Technical solution

According to an aspect of the present invention, there is provided an apparatus for treating boil-off gas in a liquefied gas regasification system, the apparatus comprising: a fuel compressor for compressing the boil-off gas to a pressure required by a fuel demand site; a high pressure compressor disposed downstream of the fuel compressor in series with the fuel compressor and compressing low pressure boil-off gas compressed by the fuel compressor to a pressure required by a regasification gas demand site; a low temperature heat exchanger cooling the high pressure boil-off gas compressed by the high pressure compressor; a decompression unit decompressing the high-pressure boil-off gas cooled by the cryogenic heat exchanger to an internal pressure of a liquefied gas storage tank; and a liquefied gas drum separating flash gas generated during the decompression by the decompression unit, wherein re-liquefied boil-off gas separated by the liquefied gas drum is returned to the liquefied gas storage tank.

The device may further include: an expander expanding and cooling some of the high-pressure boil-off gas to be supplied to the cryogenic heat exchanger, wherein the cryogenic heat exchanger can cool the high-pressure boil-off gas by heat exchange with the boil-off gas expanded and cooled by the expander.

The device may further include: a high temperature heat exchanger pre-cooling the high pressure boil-off gas to be supplied to the low temperature heat exchanger to an inlet temperature of the expander, wherein some of the high pressure boil-off gas to be supplied from the high temperature heat exchanger to the low temperature heat exchanger may be sent to the expander.

The high temperature heat exchanger may cool the high pressure boil-off gas to be supplied to the low temperature heat exchanger and the expander through heat exchange with expanded boil-off gas, which is heated by heat exchange in the low temperature heat exchanger and discharged from the low temperature heat exchanger.

The device may further include: a gas compressor compressing the expanded boil-off gas that has undergone heat exchange in the cryogenic heat exchanger and is discharged from the cryogenic heat exchanger to a pressure of a flow of the boil-off gas compressed by the fuel compressor, wherein the boil-off gas compressed by the gas compressor may be merged with the flow of the boil-off gas compressed by the fuel compressor.

The gas compressor may be connected to the expander via a common shaft.

The device may further include: a gas cooler that adjusts a temperature of the evaporation gas compressed and heated by the gas compressor.

The flash gas separated by the liquefied gas drum may be joined with a flow of the expanded boil-off gas to be supplied to the cryogenic heat exchanger.

According to another aspect of the present invention, there is provided a method for treating boil-off gas in a liquefied gas regasification system, the method comprising: compressing the boil-off gas to a low pressure required by the fuel demand site; compressing the low-pressure boil-off gas to a high pressure required by a regasification gas demand site; cooling the high pressure boil-off gas; decompressing the cooled high-pressure boil-off gas to an internal pressure of the liquefied gas storage tank; and separating flash gas generated during the depressurization of the cooled high pressure boil-off gas and returning re-liquefied boil-off gas to the liquefied gas storage tank.

Cooling the high pressure boil-off gas may comprise: expanding and cooling some of the high pressure boil-off gas prior to cooling the high pressure boil-off gas; and liquefying at least a portion of the high pressure boil-off gas by heat exchange between the expanded and cooled boil-off gas and the high pressure boil-off gas.

The method may further comprise: pre-cooling the high pressure boil-off gas by heat exchange with the expanded boil-off gas heated while cooling the high pressure boil-off gas before heat exchange between the expanded and cooled boil-off gas and the high pressure boil-off gas.

Pre-cooling the high pressure boil-off gas may comprise: cooling the high pressure boil-off gas to an inlet temperature of an expander that expands the high pressure boil-off gas.

The expanded boil-off gas heated upon cooling the high pressure boil-off gas may be compressed to a pressure of a stream of boil-off gas to be compressed by a fuel compressor before merging with the stream of the boil-off gas.

The work of expansion in expanding the high-pressure boil-off gas can be recovered as the work of compression in compressing the expanded boil-off gas.

The separated flash gas may be combined with a flow of the expanded boil-off gas that exchanges heat with the high pressure boil-off gas.

Advantageous effects

In the apparatus and method for treating boil-off gas in a liquefied gas regasification system according to the present invention, even when the amount of liquefied gas to be regasified or fuel consumption is insufficient to recondense the boil-off gas, the boil-off gas can be recondensed and recovered without waste, thereby allowing the boil-off gas to be efficiently recovered without waste.

Further, according to the present invention, by efficiently processing boil-off gas, the internal pressure of the liquefied gas storage tank can be kept constant within a safe operation range while reducing the amount of LNG discarded.

Drawings

Fig. 1 is a schematic view of an apparatus for treating boil-off gas in a liquefied gas regasification system according to an embodiment of the present invention.

Detailed Description

The above and other aspects, features and advantages of the present invention will become apparent from the following detailed description of the embodiments, which is to be read in connection with the accompanying drawings.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that throughout the specification and drawings, like components will be identified by like reference numerals. It is to be understood that the present invention may be embodied in various forms and is not limited to the following embodiments.

As used herein, "Liquefied Gas" may refer to gases that may be transported in liquid form by liquefaction at cryogenic temperatures, such as Liquefied petrochemical gases, e.g., lng (Liquefied Natural Gas), leg (Liquefied ethane Gas), lpg (Liquefied petroleum Gas), Liquefied Ethylene Gas (Liquefied Ethylene Gas), and Liquefied Propylene Gas (Liquefied Propylene Gas). Further, "liquefied gas" may also refer to a gas in a liquid state, such as liquefied carbon dioxide, liquefied hydrogen, and liquefied ammonia. However, in the following embodiments, the present invention will be described using a typical liquefied gas LNG as an example.

Although LNG contains primarily methane and further contains ethane, propane, butane, and the like, its composition may vary depending on the production site.

Furthermore, in one embodiment of the present invention, the LNG Regasification vessel may include any vessel having an LNG Regasification facility to regasify LNG and supply it to gas consumers, including self-propelled vessels (such as LNG RV (Regasification vessel)) and Floating offshore structures (such as LNG FSRU (Floating Storage Regasification Unit)). In addition, the LNG regasification vessel may include a Floating Storage Power Plant (FSPP) that generates electricity using regasified gas as a fuel and supplies the generated electricity to onshore Power consumers while regasifying and supplying it to gas consumers.

However, the apparatus and method for processing boil-off gas in a liquefied gas regasification system according to the following embodiments will be described as being applied to, for example, an LNG FSRU having a regasification system or a ship having LNGFSPP having both a regasification system and a power generation system.

Further, the ship according to one embodiment of the present invention regasifies LNG at sea to supply regasified (regas) gas to an onshore gas consumer via a piping network, and also generates electricity using the LNG as fuel to supply the generated electricity to an onshore power consumer.

Although the apparatus and method for processing boil-off gas in an LNG system according to one embodiment of the present invention will be described as being applied to a ship, it is to be understood that the apparatus and method for processing boil-off gas may also be applied to an onshore facility.

Fig. 1 is a schematic diagram of an LNG regasification system according to an embodiment of the present invention. An apparatus and method for processing boil-off gas in an LNG regasification system according to an embodiment of the present invention will now be described with reference to fig. 1.

Referring to fig. 1, the apparatus for processing boil-off gas in an LNG regasification system according to this embodiment includes: a fuel compressor (600) for compressing the boil-off gas to a pressure required by a fuel demand site; a high pressure compressor (700) for compressing the boil-off gas to a pressure required by the regasification demand site; an expander (420) that expands the high-pressure boil-off gas compressed by the high-pressure compressor (700); and a low-temperature heat exchanger (200) for liquefying the high-pressure boil-off gas by using the cold heat of the boil-off gas cooled by expansion in the expander (420).

Although not shown in fig. 1, the LNG FSRU or LNG FSPP to which this embodiment is applied includes an LNG regasification system. The LNG regasification system may include: LNG storage tanks (not shown); a high pressure pump (not shown) that compresses the LNG to be regasified to the pressure required at the regasification gas demand site; and a vaporizer (not shown) vaporizing the compressed LNG and supplying the vaporized LNG to the regasification gas demand site.

LNG stored in an LNG storage tank is compressed by a high-pressure pump to a pressure required for a regasification gas demand site, vaporized by a vaporizer, and supplied to the regasification gas demand site.

LNG storage tanks store LNG at very low temperatures of about-163 ℃ and pressures of about 0.5 to 1.1 bar. That is, the LNG storage tank is preferably thermally insulated so that LNG can be stored in a constant liquid state.

However, even when the LNG storage tank is adiabatic, LNG is naturally vaporized due to intrusion of external heat into the LNG storage tank, thereby generating Boil-Off Gas (BOG). Accordingly, the LNG storage tank may be designed to withstand a pressure rise caused by boil-off gas generated in the LNG storage tank until a preset pressure is reached. Further, the LNG storage tank may be designed such that when the internal pressure of the storage tank exceeds a preset pressure, the safety valve is opened to discharge boil-off gas from the LNG storage tank.

The boil-off gas line (BL) according to this embodiment connects the LNG storage tank to the fuel compressor (600) such that the boil-off gas discharged from the LNG storage tank is supplied to the fuel compressor (600) through the boil-off gas line (BL).

The fuel compressor (600) compresses the boil-off gas delivered through the boil-off gas line (BL) to a low pressure required by the fuel demand site.

In this embodiment, the fuel demand site may be a power generation engine (dual fuel diesel electric (DFDE) engine) that generates electricity using the evaporated gas compressed to a low pressure as fuel. The power generating engine may be, for example, a DFDG (dual fuel diesel generator). The DFDG is a generator connected to an engine shaft and uses a 4-stroke (4-stroke) cycle.

Furthermore, DFDE engines use an Otto cycle (Otto cycle) in which low pressure natural gas at a pressure of about 2bar to about 8bar or about 6.5bar is injected into the combustion air inlet and then compressed by an upwardly moving piston.

That is, the fuel compressor (600) according to this embodiment compresses the boil-off gas to a pressure of about 2 to 8bar or about 5to 6.5 bar. The boil-off gas compressed by the fuel compressor (600) will be hereinafter referred to as "low-pressure boil-off gas".

Referring to fig. 1, the fuel compressor (600) according to this embodiment may be a two-stage compressor including two compression units, e.g., a first fuel compression unit (610) and a second fuel compression unit (620), to compress the boil-off gas to a low pressure in two stages. While the fuel compressor (600) is described in this embodiment as a two-stage compressor, it should be understood that the invention is not so limited.

Furthermore, the first fuel compression unit (610) and the second fuel compression unit (620) may be connected to each other via a common shaft (draft).

The apparatus for processing boil-off gas according to this embodiment may further include: a first cooler (630) disposed downstream of the fuel compressor (600) to cool the low-pressure evaporation gas heated by being compressed by the first fuel compression unit (610) and the second fuel compression unit (620).

Although the first cooler (630) is depicted in fig. 1 as being disposed downstream of the second fuel compression unit (620), it should be understood that the present invention is not so limited and the first cooler may be disposed both downstream of the first fuel compression unit (610) and downstream of the second fuel compression unit (620).

The first cooler (630) according to this embodiment may be a seawater cooler that cools the low-pressure boil-off gas through heat exchange with cooling water, seawater, or the like, or may be an atmospheric cooler that cools the low-pressure boil-off gas through heat exchange with air.

The first cooler (630) may cool the low pressure boil-off gas to a temperature required by the fuel demand site or an inlet temperature of the high pressure compressor (700) described below.

The apparatus for processing boil-off gas according to this embodiment may further include: a fuel supply line (EL) disposed downstream of the first cooler (630) to connect to a fuel demand site; and a high-pressure gas line (HL) disposed downstream of the first cooler (630) to be connected to the high-pressure compressor (700).

That is, the low-pressure evaporation gas compressed by the fuel compressor (600) and cooled by the first cooler (630) is delivered to the fuel demand place through the fuel supply line (EL) or delivered to the high-pressure compressor (700) through the high-pressure gas line (HL).

The flow rate of the low-pressure evaporation gas sent to the fuel supply line (EL) or the high-pressure gas line (HL) may be controlled by a controller (not shown). For example, the controller may control such that some of the low-pressure boil-off gas corresponding to the fuel demand of the fuel demand site (i.e., the load-related fuel demand of the power generation engine) is first sent to the fuel supply line (EL), and the other low-pressure boil-off gas remaining after being supplied to the fuel demand site is sent to the high-pressure gas line (HL).

The high pressure gas line (HL) according to this embodiment may connect the fuel compressor (600) to the high pressure compressor (700), and the fuel compressor (600) and the high pressure compressor (700) according to this embodiment may be connected in series to each other via the high pressure gas line (HL). That is, all or a part of the low-pressure evaporation gas compressed by the fuel compressor (600) is supplied to the high-pressure compressor (700) through the high-pressure gas line (HL).

The high pressure compressor (700) compresses the low pressure boil-off gas to delivery pressure, i.e., the pressure required at the site of regasified gas demand. Here, the regasification gas demand site may be an onshore gas terminal, and in this embodiment, the pressure of regasification gas required by the regasification gas demand site may be in the range of about 50barg to about 100 barg.

That is, the high pressure compressor (700) compresses the low pressure boil-off gas to a pressure of about 50barg to 100 barg. The boil-off gas compressed by the high-pressure compressor (700) will be hereinafter referred to as "high-pressure boil-off gas".

The high-pressure compressor (700) is connected to the regasification gas demand site via a regasification gas delivery line (SL) so that high-pressure boil-off gas compressed by the high-pressure compressor (700) can be supplied to the onshore gas terminal through the regasification gas delivery line (SL) together with regasification gas vaporized by the vaporizer. The regasification gas transfer line (SL) may also be connected to the vaporizer of the LNG regasification system.

Referring to fig. 1, the high pressure compressor (700) according to this embodiment may be a three-stage compressor including three compression units, for example, a first high pressure compression unit (710), a second high pressure compression unit (730), and a third high pressure compression unit (750), to compress low-pressure evaporation gas in three stages. While the high pressure compressor (700) is described in this embodiment as a three stage compressor, it should be understood that the invention is not so limited.

Further, the first high pressure compression unit (710), the second high pressure compression unit (730), and the third high pressure compression unit (750) may be connected to each other via a common shaft (draft).

According to this embodiment, a cooler may be disposed downstream of each of the compression units of the high pressure compressor (700). That is, the apparatus for processing a boil-off gas according to this embodiment may further include: a second cooler (720) disposed downstream of the first high pressure compression unit (710) to cool the evaporation gas to be supplied from the first high pressure compression unit (710) to the second high pressure compression unit (730); a third cooler (740) disposed downstream of the second high pressure compression unit (730) to cool the evaporation gas to be supplied from the second high pressure compression unit (730) to the third high pressure compression unit (750); and a fourth cooler (760) disposed downstream of the third high-pressure compression unit (750) to cool the evaporation gas discharged from the third high-pressure compression unit (750).

Each of the second cooler (720), the third cooler (740), and the fourth cooler (760) according to this embodiment may be a seawater cooler that cools the high-pressure evaporation gas through heat exchange with cooling water, seawater, or the like, or may be an atmospheric cooler that cools the high-pressure evaporation gas through heat exchange with air.

The apparatus for processing boil-off gas according to this embodiment may further include: a Reliquefaction Line (RL) branching from a regasification gas delivery line (SL) connecting the high-pressure compressor (700) to a regasification gas demand site, and connected to the low-temperature heat exchanger (200).

That is, among the high-pressure boil-off gas compressed by the high-pressure compressor (700), a part of the high-pressure boil-off gas remaining after being supplied to the regasification gas demand site is delivered to the cryogenic heat exchanger (200) through the Reliquefaction Line (RL) to be reliquefied and recovered.

Further, the apparatus for processing a boil-off gas according to this embodiment may further include: a pressure reducing valve (800) that reduces the pressure of the high-pressure boil-off gas cooled by the low-temperature heat exchanger (200); and a liquefied gas drum (100) that performs gas-liquid separation by separating flash gas generated during pressure reduction by the pressure reduction valve (800) from the depressurized boil-off gas.

The high-pressure boil-off gas cooled by the cryogenic heat exchanger (200) is decompressed by a decompression valve (800), and then undergoes gas-liquid separation by a liquefied gas drum (100) to allow re-liquefaction of the boil-off gas to be recovered in a liquid state.

The reliquefied boil-off gas from which the flash gas has been separated by the liquefied gas drum (100) may be returned to the LNG storage tank. Accordingly, the pressure reducing valve (800) may reduce the high-pressure boil-off gas to the internal pressure of the LNG storage tank, so that the reliquefied boil-off gas may be returned to the LNG storage tank.

The apparatus for processing boil-off gas according to this embodiment may further include: a flash gas line (FL) connecting the liquefied gas drum (100) to a low temperature inlet of the low temperature heat exchanger (200). The gaseous flash gas separated by the liquefied gas drum (100) is supplied to the cryogenic heat exchanger (200) through the flash gas line (FL).

The gaseous flash gas separated by the liquefied gas drum (100) may be used as a refrigerant for cooling the high-pressure boil-off gas introduced into the low-temperature heat exchanger (200) through the high-temperature inlet of the low-temperature heat exchanger (200).

The apparatus for processing boil-off gas according to this embodiment may further include: an expansion line (PL) branching from the Reliquefaction Line (RL) upstream of the cryogenic heat exchanger (200) and connected to the expander (420).

That is, some of the high-pressure evaporation gas to be supplied from the high-pressure compressor (700) to the cryogenic heat exchanger (200) through the Reliquefaction Line (RL) may be supplied to the expander (420) through the expansion line (PL).

Further, an expansion line (PL) may be connected between the outlet of the expander (420) and the flash gas line (FL). That is, the boil-off gas expanded by the expander (420) may be combined with the flow of the flash gas to be introduced into the cryogenic heat exchanger (200) through the flash gas line (FL).

The boil-off gas is cooled as it is expanded by the expander (420). Therefore, according to this embodiment, the expanded boil-off gas can be used as a refrigerant for cooling the high-pressure boil-off gas in the low-temperature heat exchanger (200).

As used herein, "cooling" includes liquefaction, condensation, and subcooling of the boil-off gas. For example, the high-pressure boil-off gas may be introduced into the cryogenic heat exchanger (200) in a liquid state, a gaseous state, or a gas-liquid mixed state, and may be liquefied or supercooled by heat exchange in the cryogenic heat exchanger (200).

In the cryogenic heat exchanger (200) according to this embodiment, the high pressure boil-off gas exchanges heat with the mixture of flash gas and expanded boil-off gas, so that the high pressure boil-off gas is cooled and the mixture is heated.

The apparatus for processing boil-off gas according to this embodiment may further include: a high temperature heat exchanger (300) disposed upstream of a point at which the expansion line (PL) branches off from the Reliquefaction Line (RL) and precools the high pressure boil-off gas to be introduced into the low temperature heat exchanger (200).

The high temperature heat exchanger (300) according to this embodiment may cool the high pressure boil-off gas to the inlet temperature of the expander (420).

Some of the high-pressure evaporation gas pre-cooled by the high-temperature heat exchanger (300) is supplied to the expander (420), and the other high-pressure evaporation gas remaining after being supplied to the expander (420) is supplied to the low-temperature heat exchanger (200) to be cooled.

In the high temperature heat exchanger (300), the high pressure boil-off gas to be supplied to the low temperature heat exchanger (200) and the expander (420) exchanges heat with a flow of the mixture discharged from the low temperature heat exchanger (200) after being used to cool the high pressure boil-off gas, so that the high pressure boil-off gas is cooled and the mixture is heated.

The high-pressure boil-off gas cooled by the high-temperature heat exchanger (300) is separated and supplied to the low-temperature heat exchanger (200) and the expander (420).

According to this embodiment, the flash gas line (FL) is connected between the liquefied gas drum (100), the low temperature heat exchanger (200), the high temperature heat exchanger (300) and the fuel compressor (600).

The flow of mixture heated by the high temperature heat exchanger (300) is joined by a flash gas line (FL) with the flow of low pressure boil-off gas to be compressed by the fuel compressor (600).

That is, a flow of a mixture of refrigerants used to cool the high-pressure evaporation gas in the low-temperature heat exchanger (200) and the high-temperature heat exchanger (300) is returned to the fuel compressor (600) to be compressed to a low pressure.

In this way, according to this embodiment, the generated boil-off gas is completely recovered without any waste, thereby allowing efficient handling of the boil-off gas.

In fig. 1, the flash gas line (FL) is depicted as being coupled upstream of the second fuel compression unit (620) of the fuel compressor (600). That is, according to this embodiment, the flow of the mixture used as the refrigerant in the low temperature heat exchanger (200) and the high temperature heat exchanger (300) is joined with the flow of the boil-off gas to be introduced into the second fuel compression unit (620). However, it should be understood that the present invention is not limited thereto. For example, the flash gas line (FL) may be joined with the boil-off gas line (BL) at a point upstream of the fuel compressor (600) where the flow of compressed boil-off gas has the most similar pressure as the flow of the mixture through the flash gas line (FL).

In this embodiment, the flow of the mixture will be described as merging with the flow of boil-off gas upstream of the second fuel compression unit (620).

Further, the apparatus for processing a boil-off gas according to this embodiment may further include: a gas compressor (410) compressing a flow of the mixture to be introduced into the boil-off gas line (BL) through the flash gas line (FL) to a pressure of the boil-off gas to be introduced into the second fuel compression unit (620); and a gas cooler (500) that adjusts the temperature of the stream of the mixture compressed by the gas compressor (410).

The gas compressor (410) according to this embodiment may be connected to the expander (420) via a common shaft. That is, the expansion work in the expander (420) is recovered as the compression work in the gas compressor (410). In this embodiment, the gas compressor (410) and expander (420) are described as being used in conjunction with each other via a common shaft to form a compression expander (400), as depicted in fig. 1.

Next, the operation principle of the apparatus for processing boil-off gas in an LNG regasification system set forth above will be described with reference to fig. 1.

In this example, it is assumed that the boil-off gas introduced into the fuel compressor (600) via the boil-off gas line (BL) has a flow rate of about 2.3ton/hr, a pressure of about 0barg, and a temperature of about-120 ℃. However, it should be understood that the present invention is not limited thereto, and the process conditions (e.g., flow rate, pressure, and temperature of the fluid) described in this embodiment may vary depending on the pressure of the regasification gas delivery or the composition of the LNG.

First, the boil-off gas introduced into the fuel compressor (600) through the boil-off gas line (BL) is compressed to about 2.2barg by the first fuel compression unit (610) and heated to-27.1 ℃ while being compressed.

The evaporation gas compressed by the first fuel compression unit (610) is introduced into the second fuel compression unit (620) through the evaporation gas line (BL). Here, a flow of a mixture used as a refrigerant in the low temperature heat exchanger (200) and the high temperature heat exchanger (300) is joined with a flow of the evaporation gas compressed by the first fuel compression unit (610) through the flash gas line (FL). The stream of the mixture through the flash gas line (FL) can have a flow rate of about 6.9ton/hr, a pressure of about 2.2barg, and a temperature of about 43 ℃.

The net stream of boil-off gas entering the second fuel compression unit (620), i.e. the combined stream of boil-off gas compressed by the first fuel compression unit (610) and the mixture delivered via the flash gas line (FL), has a flow rate of about 9.5ton/hr, a pressure of about 2.2barg and a temperature of about 23.3 ℃.

In the second fuel compression unit (620), the stream of boil-off gas is compressed to about 5.5 barg. Some of the low-pressure boil-off gas compressed by the second fuel compression unit (620) is supplied to the fuel demand site, and the other low-pressure boil-off gas is introduced into the high-pressure compressor (700).

In this embodiment, it is assumed that the low pressure boil-off gas sent to the fuel supply line (EL) for supply to the fuel demand site has a flow rate of about 0.7ton/hr, and the low pressure boil-off gas sent to the high pressure gas line (HL) for introduction into the high pressure compressor (700) has a flow rate of about 8.8 ton/hr. The flow rate of the low pressure boil-off gas sent to the high pressure gas line (HL) for introduction into the high pressure compressor (700) corresponds to about 10mmscfd (million standing and cubic fe per day).

The boil-off gas introduced into the high pressure compressor is compressed to about 15.5barg by the first high pressure compression unit (710), to about 40barg by the second high pressure compression unit (730), and to about 100barg by the third high pressure compression unit (750).

Some of the high pressure boil-off gas compressed to 100barg by the high pressure compressor (700) is supplied to a regasification gas demand site through a regasification gas transfer line (SL), and the other high pressure boil-off gas is sent to a Reliquefaction Line (RL).

In the present embodiment, the boil-off gas treatment method will be described with reference to the case where the regasification gas demand of the regasification gas demand site can be satisfied by the regasification gas supplied from the vaporizer since regasification is not performed, that is, there is no regasification gas demand of the regasification gas demand site, or the regasification gas demand of the regasification gas demand site is low.

In other words, in this embodiment, it is assumed that the high-pressure boil-off gas compressed by the high-pressure compressor (700) is entirely sent to the Reliquefaction Line (RL) without being sent to the regasification gas transport line (SL).

High pressure boil-off gas compressed by high pressure compressor (700) and having a pressure of 100barg, about 43 ℃ and 8.8ton/hr (10MMSCFD) is supplied to high temperature heat exchanger (300) via Reliquefaction Line (RL). The high pressure boil-off gas is cooled to about 25 ℃ in a high temperature heat exchanger (300).

Some of the high-pressure boil-off gas cooled by the high-temperature heat exchanger (300) is sent to the expander (420) through the expansion line (PL), and the expander (420) supplies the remaining other high-pressure boil-off gas to the low-temperature heat exchanger (200) through the Reliquefaction Line (RL).

In this example, it is assumed that the high pressure boil-off gas cooled by the high temperature heat exchanger (300) and having a flow rate of about 8.8ton/hr is distributed to the expansion line (PL) at a flow rate of 6.5ton/hr and distributed to the low temperature heat exchanger (200) at a flow rate of about 2.3 ton/hr.

The high pressure boil-off gas, having a flow rate of about 2.3ton/hr and a temperature of-25 ℃, is cooled (liquefied) to about-157 ℃ in a cryogenic heat exchanger (200).

The high-pressure boil-off gas cooled by the cryogenic heat exchanger (200) is depressurized by a pressure reducing valve (800) to about 0.5barg and cooled to about-168.1 ℃ while being depressurized.

Re-liquefied boil-off gas passing through a pressure reducing valve (800) and having about 0.5barg, -168.1 ℃ and 2.3ton/hr is supplied to the liquefied gas drum (100) and then undergoes gas-liquid separation in the liquefied gas drum (100) before being returned to the LNG storage tank.

According to this embodiment, the reliquefied boil-off gas in liquid state from which flash gas having a flow rate of about 0.4ton/hr has been separated by the liquefied gas drum (100) is returned to the LNG storage tank at a flow rate of about 1.9 ton/hr.

The gaseous flash gas separated by the liquefied gas drum (100) and having about 0.4ton/hr, 0.5barg and-168.1 deg.c is supplied to the cryogenic heat exchanger (200) through the flash gas line (FL) to recover cold heat therefrom.

Here, the flow of the flash gas to be supplied to the cryogenic heat exchanger (200) is merged with the flow of the boil-off gas expanded by the expander (420).

The high pressure boil-off gas, having a temperature of about 6.5ton/hr, 100barg and-25 ℃, is introduced into the expander (420) as described above. The high pressure boil-off gas is expanded by an expander (420) to about 0.5barg and cooled to-158.6 ℃ while expanding.

A stream of a mixture of boil-off gas expanded by an expander (420) and having about 6.5ton/hr, 0.5barg and-158.6 ℃ and flash gas separated by a liquefied gas drum (100) and having 0.4ton/hr, 0.5barg and-168.1 ℃ is supplied as a refrigerant to the cryogenic heat exchanger (200), wherein the stream of the mixture has about 6.9ton/hr, 0.5barg and-159 ℃.

The stream of the mixture is heated to about-90.7 ℃ while cooling the high pressure boil-off gas in the cryogenic heat exchanger (200).

A flow of the mixture heated when cooling the high-pressure evaporation gas in the low-temperature heat exchanger (200) is supplied as a refrigerant to the high-temperature heat exchanger (300).

The stream of the mixture is heated to about 40.0 ℃ while cooling the high pressure boil-off gas in the high temperature heat exchanger (300).

The stream of the mixture heated while cooling the high pressure boil-off gas in the high temperature heat exchanger (300) is compressed to about 2.2barg by the gas compressor (410) and then adjusted to about 43 ℃ by the fifth cooler (500) before being merged with the stream of boil-off gas to be supplied to the second fuel compression unit (620).

As described above, according to the present invention, boil-off gas generated in an LNG regasification system is liquefied using cold heat recovered by expanding the boil-off gas itself, rather than being recovered by condensing the boil-off gas using cold heat of LNG to be regasified, whereby all of the boil-off gas can be reliquefied and recovered regardless of the flow rate or fuel consumption of the regasified gas.

Although some embodiments have been described herein, it should be understood that these embodiments are provided by way of illustration only and are not to be construed as limiting the invention in any way, and that various modifications, changes, alterations, and equivalent embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention. The scope of the invention should be defined by the appended claims and equivalents thereof.