KR101722604B1 - Boil Off Gas Treatment System And Method - Google Patents

Abstract

A vapor gas treatment system and method are disclosed. The evaporation gas processing system of the present invention comprises a BOG re-liquefaction line for re-liquefaction by compressing and cooling BOG (Boil-Off Gas) generated in an LNG storage tank provided in a ship or an offshore structure; A first expander provided in the BOG re-liquefaction line for expanding and thermally expanding refrigerant and a first compressor for compressing the BOG by rotational movement of a rotary shaft connected to the first expander, 1 compander; A second expander provided in the BOG re-liquefaction line for receiving and thermally expanding the refrigerant discharged from the first expander; a motor connected to the second expander for switching the expansion force of the refrigerant to a rotational force; And a second compressor connected to the rotation axis of the BOG re-liquefaction line and further compressing the BOG compressed from the first compressor by a rotational force, a second compressor disposed on the BOG re-liquefaction line to compress the BOG compressed by the second compressor A main heat exchanger for cooling by heat exchange with the refrigerant in the downstream of the second expander; And a fuel supply line for branching the BOG compressed from the downstream of the second compressor of the second compander in the BOG liquefaction line and supplying the branched BOG to the gas consuming place provided in the ship.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boil-

The present invention relates to a system and a method for treating an evaporative gas, and more particularly, to a system and a method for treating an evaporative gas, and more particularly, to a system and a method for treating an evaporative gas by supplying BOG generated from an LNG storage tank of a ship or a marine structure to a first and a second compander, The present invention relates to an evaporative gas treatment system and method capable of compressing BOG and cooling it by heat exchange with a refrigerant which has been thermally expanded, and re-liquefying it.

In recent years, consumption of liquefied gas such as LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas) has been rapidly increasing worldwide. The liquefied gas obtained by liquefying the gas at a low temperature has an advantage of being able to increase the storage and transport efficiency because the volume becomes very small as compared with the gas. In addition, liquefied natural gas (Liquefied Natural Gas) (hereinafter referred to as "LNG") can be used as an eco-friendly fuel which can remove or reduce air pollutants during the liquefaction process,

For example, liquefied natural gas is a colorless transparent liquid which can be obtained by cooling natural gas containing methane as a main component to about -162 ° C and liquefying it, and has a volume of about 1/600 as compared with natural gas. Therefore, it can be transported very efficiently when liquefied by LNG for transporting natural gas.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -162 ° C at normal pressure, LNG is sensitive to temperature change and is easily evaporated. As a result, the LNG storage tank of the LNG carrier is insulated. However, since the external heat is continuously transferred to the LNG storage tank, the LNG is continuously vaporized in the LNG storage tank during the LNG transportation, BOG) occurs. This also applies to other low temperature liquefied gases such as ethane.

BOG is a kind of loss and an important issue in transportation efficiency. Further, when the evaporation gas accumulates in the storage tank, the internal pressure of the tank may rise excessively, and there is a risk that the tank may be damaged. Therefore, various methods for treating BOG occurring in the storage tank have been studied. Recently, a method of re-liquefying BOG to return to a storage tank for processing BOG, a method of returning BOG to a storage tank, And the like are used.

The present applicant has proposed a re-liquefying apparatus which utilizes the cooling heat of the evaporation gas itself by using the evaporation gas as the cooling fluid on Jul. 10, 2013, No. 10-2013-0081029. The Partial Re-liquefaction System (PRS) proposed in the patent of No. 10-2013-0081029 is a device for re-liquefying the evaporated gas discharged outside the storage tank by using the evaporation gas itself as a refrigerant, It is possible to re-liquefy the evaporated gas without separately installing the re-liquefier, and it is evaluated as an epoch-making technology that can effectively reduce the overall natural evacuation rate (BOR) of the liquefied natural gas storage tank.

1 is a schematic configuration diagram of the redispersion apparatus of the present invention, No. 10-2013-0081029. Referring to FIG. 1, the process of re-liquefying the evaporation gas in the re-liquefier will be briefly described below.

The evaporated gas discharged from the storage tank 10 can be compressed through a multi-stage compressor including a plurality of compressors 30 and an intercooler (not shown). In the compressor shown in FIG. 1, five stages of compression and cooling are alternately performed while passing through five compressors 30, and are compressed. Some of the evaporated gas that has undergone the compression process is sent to a high-pressure fuel consuming station E1 requiring high-pressure fuel, for example, a high-pressure engine such as an ME-GI engine, Lt; / RTI > The evaporation gas (A line) supplied to the heat exchanger 20 through the multi-stage compression process is heat-exchanged in the heat exchanger 20 with the evaporation gas (B line) discharged from the storage tank 10 and introduced into the compressor. The temperature of the evaporation gas is increased through the compression process, so that the evaporation gas before compression discharged from the storage tank 10 is used as the refrigerant for cooling the compressed evaporation gas.

The evaporated gas (C line) cooled through heat exchange in the heat exchanger 20 after the compression is decompressed in the decompressor 40. At least a part of the evaporated gas compressed while passing through the heat exchanger (20) and the pressure reducing device (40) is re-liquefied. In the gas-liquid separator 50, the re-liquefied liquefied natural gas is separated from the evaporated gas remaining in the gaseous state, and the re-liquefied evaporated gas is returned to the storage tank 10, and the evaporated gas (D line) (B line) discharged from the storage tank 10 to the heat exchanger 20 again.

In the case where there is a low-pressure fuel consuming place which is supplied with a gas of lower pressure than the gas which has passed through all the multi-stage compressors in a ship, for example, three of the five compressors 30, And can be supplied as fuel to the fuel consumption destination E2. Further, when the amount of evaporative gas generated from the storage tank 10 is large and is supplied as fuel for the high-pressure and low-pressure fuel consuming destination and remains after liquefaction by the partial re-liquefier, venting or gas- ; Gas Combustion Unit) to incinerate.

The prior art of the applicant of the present invention is an apparatus capable of effectively treating the evaporative gas generated in the storage tank. In order to constitute such a device, an expensive compressor is constituted, so that the facility cost is high. Operating costs were high due to high power consumption while compressing. In particular, even when the evaporation gas is not supplied as fuel, it is necessary to install and operate a compressor capable of compressing the gas at an ultra-high pressure in order to process the BOG. It is difficult to design the compressor to satisfy the redundancy due to high cost. There is a problem in that the energy efficiency is not high considering the energy consumption due to the power consumption.

An object of the present invention is to propose a vaporized gas processing system which solves this problem and which can compress and re-liquefy BOG more economically.

According to an aspect of the present invention, there is provided a BOG re-liquefaction line for re-liquefaction by compressing and cooling BOG (Boil-Off Gas) generated in an LNG storage tank provided in a ship or an offshore structure;

A first expander provided in the BOG re-liquefaction line for expanding and thermally expanding refrigerant and a first compressor for compressing the BOG by rotational movement of a rotary shaft connected to the first expander, 1 compander;

A second expander provided in the BOG re-liquefaction line for receiving and thermally expanding the refrigerant discharged from the first expander; a motor connected to the second expander for switching the expansion force of the refrigerant to a rotational force; And a second compressor connected to the rotational axis of the first compressor and further compressing the BOG compressed from the first compressor by a rotational force;

A main heat exchanger provided in the BOG re-liquefaction line for cooling the BOG compressed by the second compressor by heat exchange with the refrigerant downstream of the second expander; And

And a fuel supply line for branching the BOG compressed from the downstream of the second compressor of the second compander in the BOG re-liquefaction line and supplying the branched BOG to the gas consuming place provided in the ship.

Preferably, an expansion means for monotonically expanding the BOG cooled by the main heat exchanger, and a flash drum for separating the LOG and the flash gas supplied from the BOG, which is thermally expanded in the expansion means, .

Preferably, a refrigerant circulation line in which the refrigerant for cooling the BOG is circulated and in which the first and second expanders are provided, and a refrigerant circulation line provided between the first and second expanders in the refrigerant circulation line, A first refrigerant compressor for receiving and compressing the discharged refrigerant, and a first compressor cooler for cooling the refrigerant compressed by the first refrigerant compressor.

Preferably, a precooler provided in the refrigerant circulation line for cooling the refrigerant by heat exchange with the BOG to be introduced into the first compressor of the first compander from the LNG storage tank and supplying the refrigerant to the first expander And an after-cooler provided in the coolant circulation line for cooling the coolant cooled by the first compressor cooler by heat exchange with the coolant to be supplied from the first expander to the first coolant compressor and supplying the cooled coolant to the second expander And an aftercooler.

Preferably, the second refrigerant compressor is provided in the refrigerant circulation line and receives and compresses the refrigerant heat-exchanged with the BOG in the main heat exchanger, and a second refrigerant compressor provided in the refrigerant circulation line, And a second compressor cooler for cooling the refrigerant, wherein the refrigerant cooled in the second compressor cooler can be supplied to the precooler.

Preferably, the liquid separated from the flash drum is re-stored in the LNG storage tank, and the gas may be supplied from the LNG storage tank to the BOG stream introduced into the precooler.

A recondenser provided in the fuel supply line and supplied with the BOG branched from the downstream of the second compressor to mix and cool the LNG supplied from the LNG storage tank; A high pressure pump that is supplied with LNG from the re-condenser and compresses the LNG at a supply pressure of the gas consuming place; and a vaporizer provided in the fuel supply line for forcibly vaporizing the LNG compressed by the high pressure pump.

Preferably, the BOG expander may be provided in the fuel supply line to swell the BOG branched from the downstream of the second compressor to supply the expanded BOG to the re-condenser.

Preferably, in the re-condenser, the BOG and the LNG are mixed and the gas-liquid separated to supply the liquid to the high-pressure pump, and the gas may be supplied from the LNG storage tank to the BOG flow introduced into the precooler.

Preferably, the apparatus further includes a low-pressure gas supply line branched from the BOG re-liquefaction line and supplying the compressed BOG as fuel to a low-pressure gas consuming place provided in the ship or the offshore structure.

According to another aspect of the present invention, there is provided a method for controlling a boil-off gas (BOG) generated in an LNG storage tank provided on a ship or an offshore structure by a first compressor, including a first expander and a first compressor, to a compander;

2) compressing the BOG in the first compressor by rotational movement of a rotary shaft connected to the first expander while receiving the refrigerant in the first expander to thermally expand;

3) supplying the compressed BOG to a second compander including a second expander, a motor, and a second compressor to supply the refrigerant discharged from the first expander to the second expander while thermally expanding the refrigerant, Switching the expansion force of the refrigerant to a rotational force in a motor connected to the second expander and further compressing the BOG compressed from the first compressor by a rotational force in the second compressor connected to the rotation axis of the motor;

4) The BOG compressed at the downstream of the second compressor is branched, mixed with LNG supplied from the LNG storage tank, recycled, compressed and forcedly vaporized, and supplied to the high pressure gas consuming place as fuel; And

5) Cooling the BOG compressed by the second compressor by heat exchange with the refrigerant which is thermally expanded in the second expander to re-liquefy.

The BOG generated in the LNG storage tank can be effectively re-liquefied and stored through the evaporative gas treatment system and method of the present invention, thereby securing the safety of the tank and the ship, and improving the transportation efficiency of the LNG. Also, the BOG is compressed in the first and second compander using the energy generated when the BOG is circulated in the refrigerant, and the energy generated when the refrigerant is thermally expanded, and the refrigerant cooled through the thermal expansion in the first and second compander It is possible to realize a highly efficient and compact system.

Fig. 1 schematically shows a partial redistribution device capable of treating an evaporative gas according to the applicant's prior patent.
2 schematically shows a vaporized gas processing system according to a first embodiment of the present invention.
3 schematically shows a vaporized gas processing system according to a second embodiment of the present invention.
4 schematically shows a vaporized gas processing system according to a third embodiment of the present invention.
5 schematically shows a vaporized gas processing system according to a fourth embodiment of the present invention.
Fig. 6 schematically shows an evaporative gas treatment system according to a fifth embodiment of the present invention.
7 schematically shows a vaporized gas processing system according to a sixth embodiment of the present invention.
8 schematically shows a vaporized gas processing system according to a seventh embodiment of the present invention.
9 schematically shows an evaporative gas treatment system according to an eighth embodiment of the present invention.

In order to fully understand the present invention, operational advantages of the present invention, and objects achieved by the practice of the present invention, reference should be made to the accompanying drawings and the accompanying drawings which illustrate preferred embodiments of the present invention.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

FIG. 2 schematically shows an evaporative gas treatment system according to an embodiment of the present invention.

First, the evaporation gas processing system described below of the present invention is a system for processing all kinds of ships and marine structures such as LNG carriers, Liquefied Ethane Gas (LEG) carriers, LNG RVs and LNG carriers equipped with storage tanks capable of storing low- It can be applied for evaporative gas treatment in marine structures such as LNG FPSO, LNG FSRU, including the same vessel.

LNG, which is a typical low-temperature liquid cargo, will be described as an example for convenience of explanation in the following embodiments, but the present invention is not limited thereto. The liquefied gas stored in such a storage tank may be any liquid cargo that can be liquefied and transported at a low temperature. For example, in addition to LNG, LEG, LPG, liquefied nitrogen, liquefied gas such as ethylene, acetylene, propylene, and the like may be applicable.

As shown in FIG. 2, the evaporative gas processing system of the present embodiment is a system for processing BOG (Boil-Off Gas) generated in an LNG storage tank (not shown) provided in a ship or a sea structure, A BOG re-liquefaction line BLa for re-liquefaction by compressing and cooling the generated boil-off gas (BOG), and a refrigerant circulation line CLa for circulating the refrigerant for cooling the BOG.

The BOG re-liquefaction line BLa is provided with a first expander 121a for receiving and expanding the refrigerant and a first compressor 122a for compressing the BOG by rotating the rotary shaft connected to the first expander, A second expander 141a for receiving the refrigerant discharged from the first expander and thermally expanding the refrigerant, and a second expander 141b for compressing the compressed BOG from the first compressor to a rotary shaft connected to the second expander A second compander 140a including a second compressor 142a for further compression by rotational motion is provided.

That is, in the first and second compander 120a and 140a, the energy generated during the thermal expansion of the refrigerant is transferred to the first and second compressors by the rotation axis while the refrigerant is cooled by being thermally expanded. . The first and second expanders 121a and 141a may be, for example, a turbine type expander.

The BOG generated in the LNG storage tank (not shown) is compressed to a pressure of at least 1 bar g, preferably at least 1.3 bar g at the first compressor and at least 3 bar g, preferably at least 5 bar g It is compressed by internal and external pressure.

In order to effectively re-liquefy the BOG compressed through the first and second compander 120a and 140a, the BOG re-liquefaction line BLa is further compressed by the first and second compressors 120a and 140a. And a booster compressor 160a for receiving and compressing the BOG.

A main heat exchanger 180a for cooling the compressed BOG by heat exchange with the refrigerant downstream of the second expander 141a is provided downstream of the booster compressor 160a of the BOG re-liquefaction line BLa, Through heat exchange with the refrigerant cooled by the monotonic expansion, the compressed BOG is cooled. The BOG cooled in the main heat exchanger 180a is subjected to the thermal expansion through the expansion means 190a such as a J-T valve or an expander and then introduced into the flash drum 195a. In the flash drum 195a, the LOG which has been liquid-phase is re-stored in the LNG storage tank by separating the re-liquefied LNG and the flash gas by receiving the BOG which is subjected to the mono-expansion while passing through the expansion means.

That is, the BOG compressed through the first and second compander 120a and 140a and the booster compressor 160a is supplied to the main heat exchanger 180a through the first and second expanders 121a and 121b of the first and second compander, And 141a, and is cooled through heat exchange with the refrigerant cooled. In the case of methane, the critical pressure is about 55 bar. The BOG is further compressed to a pressure of about 50 bar g, which is close to the critical pressure, through each of the compressors of the first and second compander and the booster compressor and then introduced into the main heat exchanger . When the BOG is introduced into the main heat exchanger when compressed to a high pressure of about the critical pressure, an effective phase change can be achieved through heat exchange with the refrigerant. The BOG cooled at a low temperature of about -150 ° C. through the main heat exchanger is decompressed and further cooled through the expansion means through the thermal expansion and introduced into the flash drum, and the gaseous flash gas and the LNG are separated from the saturated state in the flash drum .

The LNG separated through the flash drum 195a is re-stored in an LNG storage tank (not shown), and the flash gas can be supplied upstream of the BOG re-liquefaction line so that it can be re-liquefied together with the BOG generated from the LNG storage tank.

In the present embodiment, the refrigerant is a means for compressing the BOG in the first and second compander, and the refrigerant cooled by the single thermal expansion through the first and second compander is supplied to the main heat exchanger again, Circulates the refrigerant circulation line (CLa) while being utilized as a heat medium for cooling heat for cooling the BOG.

The first and second expanders 121a and 141a are provided in the refrigerant circulation line CLa so that the refrigerant discharged after the short expansion in the first expander can be further cooled before being supplied to the second expander, A first refrigerant compressor (240a) for receiving and compressing the refrigerant discharged from the first expander is disposed between the first and second expanders of the refrigerant circulation line (CLa). The first refrigerant compressor (240a) for cooling the refrigerant compressed by the first refrigerant compressor A cooler 250a is provided. The refrigerant cooled by the first compressor cooler 250a is subjected to heat exchange with the refrigerant to be supplied from the first expander 121a to the first refrigerant compressor 240a in an aftercooler 230 provided in the refrigerant circulation line Lt; / RTI > Since the refrigerant is compressed by the first refrigerant compressor and becomes higher in temperature, it can be cooled through heat exchange with the refrigerant before compression. The refrigerant compressed and cooled through the first refrigerant compressor, the coolers 240a and 250a and the aftercooler 230a is supplied to the second expander 141a at a temperature of -40 ° C or lower, preferably -50 ° C or lower, Cooled further through thermal expansion, and then supplied to the main heat exchanger 180a at a cryogenic temperature of about -150 ° C.

A second refrigerant compressor 210a for receiving and compressing the refrigerant discharged from the main heat exchanger for re-cooling and circulating the heated refrigerant while transmitting cold heat to the BOG compressed by the main heat exchanger 180a, A second compressor cooler 220 for cooling the compressed refrigerant in the compressor is provided in the refrigerant circulation line CLa. The refrigerant compressed through the second refrigerant compressor to a pressure of about 50 barg is cooled to about 30 ° C through heat exchange with fresh water in the second compressor cooler, and then flows into the precooler 110a along the refrigerant circulation line. . In the pre-cooler 110a, the refrigerant that is primarily cooled in the second compressor cooler 220a is added through the heat exchange with the BOG to be introduced into the first compressor 122a of the first compander from the LNG storage tank (not shown) And is supplied to the first expander 121a at a temperature of 0 ° C or lower, preferably about -20 ° C or lower.

As such a refrigerant, for example, BOG, methane, N ₂ , or a mixed gas including such a gas may be used. For example, the refrigerant may be a mixed gas of 90% methane and 10% nitrogen. A refrigerant supply line (not shown) branched from the BOG re-liquefaction line at the rear end of the main heat exchanger and connected to the refrigerant circulation line at the front end of the second refrigerant compressor may be additionally provided for circulating the BOG through the refrigerant .

Through such a system, the BOG generated in the LNG storage tank can be efficiently re-liquefied and stored, thereby securing the safety of the tank and the ship, and improving the transportation efficiency of the LNG. In addition, by circulating the BOG through the refrigerant, the BOG is compressed using the energy generated when the refrigerant is thermally expanded, and the BOG is cooled by the refrigerant cooled through the thermal expansion, thereby realizing a highly efficient and compact system. It is possible to reduce the cost of circulating the refrigerant by supplying a separate refrigerant.

FIG. 3 schematically shows an evaporative gas treatment system according to a second embodiment of the present invention.

The second embodiment shown in Fig. 3 is a system in which, in the evaporative gas treatment system of the above-described first embodiment, a fuel supply system is added so that BOG can be supplied as fuel to the in-vessel gas consuming place of a ship or an offshore structure.

To this end, the BOG compressed from the front end or the rear end of the booster compressor 160b is branched downstream of the second compressor 142b of the second compander in the BOG re-liquefaction line BLb and supplied to the in- A fuel supply line FLb is further provided. In the fuel supply line FLb, the BOG is branched and mixed with the LNG supplied from the LNG storage tank, recycled, compressed and forcedly vaporized, and supplied as fuel to the high-pressure gas consumption point HCb.

The high-pressure gas consuming place (HCb) may be a propulsion engine or a power generation engine such as a ship. More specific examples may include ME-GI engine, DF generator, gas turbine, DFDE and the like. The high-pressure gas is compressed according to the fuel supply conditions of the gas consuming place. For example, if the gas consuming place is the ME-GI engine, high pressure gas of about 150 to 400 bara can be supplied.

The fuel supply line FLb includes a recondenser 310b that receives BOG branched from the downstream of the second compressor and mixes LNG supplied from the LNG storage tank to cool the LNG, A high pressure pump 320b for compressing at the supply pressure of the consumer and a vaporizer 330b for forcibly vaporizing the LNG compressed in the high pressure pump are provided. The fuel supply line FLb can be branched from the BOG resupply line at the front end or the rear end of the booster compressor 160b and is compressed through the first and second compressors 122b and 142b, The BOG branched to the fuel supply line FLb can be condensed at least partially while being mixed with the cryogenic LNG pumped from the feed pump 340b in the recondenser 310b have. When the LNG is separated from the bottom of the condenser and supplied to the high-pressure pump 320b, the high-pressure pump compresses the LNG to meet the supply conditions of the high-pressure gas consuming area. Pressure to a supercritical pressure of about 300 bara.

The vaporizer 330b forcibly vaporizes the compressed LNG in the supercritical state. However, since the gas and liquid can not be distinguished from each other in the supercritical state, the expression 'the compressed LNG is vaporized' means that the compressed LNG is supplied with thermal energy to increase the temperature (or, in the case of a supercritical state with a high density, State) can be meaningful.

On the other hand, the LNG, which is a liquid through the gas-liquid separation in the condenser 310b, is supplied to the high-pressure gas consumption unit HCb as fuel as described above, and the gas is supplied from the LNG storage tank to the pre- Can be supplied as a stream of BOG to be introduced into the reactor and re-liquefied.

Pressure gas supply line (LFLb) branched from the BOG re-liquefaction line upstream from the booster compressor is provided in the ship, if there is a gas consuming place using gas relatively low in addition to the high-pressure gas consuming place in the ship, the first and second compressors The BOG compressed through the heat exchangers 122b and 142b may be supplied as fuel to the low-pressure gas consuming location LCb. Examples of such gas consuming sources include engines such as DFDE (Dual Fuel Diesel Engine) or DFDG (Dual Fuel Diesel Generator).

In this system, the BOG generated from the LNG storage tank is effectively re-liquefied and stored, thereby securing the safety of the tank and the ship and enhancing the transport efficiency of the LNG. In addition to the advantage of improving the transportation efficiency of the LNG, Compressed through a dual-type compander, mixed with LNG in a condenser, liquefied, compressed through a high-pressure pump, and supplied to a high-pressure gas consumer such as the ME-GI engine to directly compress and supply the gaseous BOG The energy consumption required for fuel compression can be remarkably reduced. Further, the pressurized BOG can be turned to the fuel supply line, and the load on the re-liquefaction system can be dispersed.

Other configurations are similar to those of the first embodiment described above, so duplicate descriptions are omitted.

4 schematically shows the evaporative gas treatment system of the third embodiment of the present invention.

As shown in Fig. 4, the system of the present embodiment is characterized in that, in the system of the first embodiment, the second compander 140c is provided as a motor driven type compander. The second compander 140c includes a second expander 141c for receiving the refrigerant and thermally expanding the refrigerant, a motor (not shown) connected to the second expander for switching the expansion force of the refrigerant to a rotational force, And a second compressor 142c for compressing the BOG by a rotational force. Since the BOG can be compressed to a constant pressure by the second compressor by the motor, the boost compressor as in the first and second embodiments described above can be omitted and the system configuration can be simplified.

On the other hand, at the rear end of the main heat exchanger 180c in the BOG liquefaction line BLc, there can be provided a liquid expander 185c for expanding the BOG or LNG cooled by the main heat exchanger to reduce the pressure. The BOG or LNG cooled in the main heat exchanger 180c may be further roughened by expansion means 190c such as a J-T valve or an expander after passing through the liquid expander 185c. Liquid expanders can also be powered by other in-vessel devices through expansion forces during BOG or LNG expansion. Further, the liquid expander 185c and the expansion means 190c are repeatedly decompressed and cooled, whereby the re-liquefaction efficiency of BOG can be further increased.

A duplicate description of the configuration described in the above embodiments is omitted.

Fig. 5 schematically shows a vaporized gas processing system according to a fourth embodiment of the present invention.

As shown in Fig. 5, the system of the present embodiment has a system of a third embodiment in which a motor-driven second compander is provided. In the system of the third embodiment, similarly to the second embodiment, .

Since the motor-driven second compander 140d is provided in the present embodiment and the booster compressor is not provided, the fuel supply line FLd is connected to the second compressor 142d of the second compander and the main heat exchanger The BOG regeneration line BLd is branched from the BOG re-liquefaction line 180d to supply the compressed BOG to the re-condenser 310d.

The fuel supply line FLd may be provided with a BOG expander 305d that can be cooled by the thermal expansion prior to supplying the BOG branched from the downstream of the second compressor to the re-condenser. The BOG thus branched is thermally expanded prior to being introduced into the re-condenser 310d through the BOG expander 305d in the fuel supply line FLd and cooled by the isentropic motion, so that the BOG can be more effectively re-condensed in the re- have. Other devices such as an expansion valve may be configured to replace the BOG expander.

A duplicate description of the configuration described in the above embodiments is omitted.

Fig. 6 schematically shows the evaporative gas treatment system of the fifth embodiment of the present invention.

The system of the present embodiment is constructed so as to reduce the configuration cost of the system by deleting the precooler from the system of the first embodiment. The refrigerant circulating in the refrigerant circulation line (CLe) may be BOG, nitrogen or a mixed gas thereof as described above. In this embodiment, preferably, the cold energy of the refrigerant for re- A mixed gas of nitrogen (N ₂ ) and BOG, particularly preferably a mixed gas containing at least 50% nitrogen (N ₂ ), can be used as a refrigerant.

Further, if the composition ratio of nitrogen in the refrigerant is increased to sufficiently ensure the cooling of the refrigerant, the booster compressor can be also eliminated. Some of the compander, for example the second compander 140e, may be provided in a motor driven type compander as in the previous embodiments for compressing the BOG while removing the booster compressor.

Further, a liquid expander 185e may be provided at the rear end of the main heat exchanger to expand the BOG or LNG cooled by the heat exchange with the refrigerant to reduce the pressure. The BOG or LNG cooled in the main heat exchanger 180e is further reduced in pressure and cooled through an expansion device 190e such as a JT valve or an expander after passing through the liquid expander 185e to further improve the re-liquefaction efficiency of the BOG have.

A duplicate description of the configuration described in the above embodiments is omitted.

Fig. 7 schematically shows the evaporative gas treatment system of the sixth embodiment of the present invention.

As shown in Fig. 7, this embodiment adds a fuel supply system capable of supplying BOG to the in-vessel gas consumption place similar to the second embodiment in the system of the fifth embodiment in which the precooler is eliminated.

The fuel supply line FLf is branched from the BOG re-liquefaction line BLf at the upstream of the main heat exchanger 180f in order to supply the BOG to the gas consuming place. The BOG expander 305f may be provided in the fuel supply line so that the branched BOG is thermally expanded prior to introduction into the re-condenser and cooled by isentropic motion, so that it can be more effectively recycled in the re-condenser. Other devices such as an expansion valve may be configured to replace the BOG expander.

In this embodiment as well, the pressurized BOG can be turned to the fuel supply line FLf, and the load on the re-liquefied system can be dispersed, and the on-board BOG can be effectively treated in accordance with the situation .

A duplicate description of the configuration described in the above embodiments is omitted.

8 schematically shows a vaporized gas processing system according to a seventh embodiment of the present invention.

As shown in FIG. 8, the system according to the present embodiment includes, in the system of the first embodiment, a de-superheater (not shown) for heating the compressed BOG through the first and second compressors 122g and 142g and the booster compressor 160g desuperheater (400 g) is provided upstream of the main heat exchanger 180g of the BOG re-liquefaction line (BLg).

In the de-superheater 400g, the BOG discharged after being compressed by the booster compressor 160g is thermally exchanged with the BOG introduced from the LNG storage tank (not shown) or the flash drum 195g to the first compressor 122g And can be supplied to the main heat exchanger 180g.

In the first embodiment described above, the BOG introduced into the first compressor from the LNG storage tank is used for cooling the refrigerant in the precooler. However, in the present embodiment, And is used for cooling.

The compressed BOG or LNG cooled through the main heat exchanger can be further cooled while being thermally expanded through the liquid expander 185g.

In the present embodiment, the precooler 110g of the refrigerant circulation line CLg differs from the previous embodiments in that the refrigerant compressed and cooled through the second refrigerant compressor 210g and the second refrigerant compressor cooler 220g , The refrigerant is cooled by heat exchange with uncompressed refrigerant to be supplied from the main heat exchanger 180g to the second refrigerant compressor 210g, and is supplied to the first expander 121g.

In the present embodiment, the compressed BOG is introduced into the main heat exchanger 180g after being cooled through the de-superheater 400g. Therefore, even if heat exchange is performed between the BOG and the main heat exchanger, the cooling loss of the refrigerant is not large, and the cooling of the refrigerant passing through the main heat exchanger can be utilized in the precooler 110g.

A duplicate description of the configuration described in the above embodiments is omitted.

9 schematically shows an evaporative gas treatment system of an eighth embodiment of the present invention.

As shown in Fig. 9, the system of the present embodiment is similar to the system of the seventh embodiment in that a de-superheater for warming compressed BOG upstream of the main heat exchanger of the BOG liquefaction line is provided, It has added a fuel supply system that can supply BOG to gas consumers in the ship.

Unlike the seventh embodiment in which the BOG compressed by cold heat of the BOG or flash gas introduced into the first compressor from the LNG storage tank or the flash drum is cooled, the de-superheater 400h of the present embodiment differs from the seventh embodiment in that, Heat the BOG using cold heat.

To this end, in this embodiment, a fuel heating line FHLh connected to the front end of the vaporizer 330h via the de-superheater 400h is provided at the rear end of the high-pressure pump 320h of the fuel supply line FLh. Thus, in the de-superheater, the BOG compressed through the first and second compressors 122h and 142h and the booster compressor 160h is heat-exchanged with the LNG compressed by the high-pressure pump 320h of the fuel supply line.

In this embodiment, since the compressed BOG is warmed through the de-superheater 400h and then supplied to the main heat exchanger 180h, the BOG re-liquefaction efficiency can be increased. Further, since the LNG that has passed through the high-pressure pump 320h in the fuel supply line FLh is heated through the de-superheater 400h, the heat energy required in the vaporizer 330h can be reduced for supplying the fuel to the high- , And energy efficiency can be increased.

In this embodiment, since the de-superheater 400h uses the cold heat of the fuel supply system, unlike in the seventh embodiment, the cold heat of the BOG introduced from the BOG storage tank or the flash drum to the first compressor 122h, And can be used for cooling the refrigerant in the cooler 110h.

A duplicate description of the configuration described in the above embodiments is omitted.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. It is.

BL: BOG liquefaction line
CL: Refrigerant circulation line
FL: fuel supply line
FHL: Fuel heating line
110: pre-cooler
120: 1st compander
130, 150, 170: Heat exchanger
140: 2nd compander
160: Booster compressor
180: main heat exchanger
190: Expansion means
195: flash drum
210: second refrigerant compressor
220: Second compressor cooler
230: Aftercooler
240: first refrigerant compressor
250: First compressor cooler
310: Re-condenser
320: High pressure pump
330: vaporizer
340: Feed pump

Claims (11)

A BOG re-liquefaction line for compressing and cooling BOG (Boil-Off Gas) generated in an LNG storage tank provided in a ship or a marine structure to re-liquefy the same;
A first expander provided in the BOG re-liquefaction line for expanding and thermally expanding refrigerant and a first compressor for compressing the BOG by rotational movement of a rotary shaft connected to the first expander, 1 compander;
A second expander provided in the BOG re-liquefaction line for receiving and thermally expanding the refrigerant discharged from the first expander; a motor connected to the second expander for switching the expansion force of the refrigerant to a rotational force; And a second compressor connected to the rotational axis of the first compressor and further compressing the BOG compressed from the first compressor by a rotational force;
A main heat exchanger provided in the BOG re-liquefaction line for cooling the BOG compressed by the second compressor by heat exchange with the refrigerant downstream of the second expander;
A fuel supply line for branching the BOG compressed from the downstream of the second compressor of the second compander in the BOG re-liquefaction line and supplying the branched BOG to the gas consuming place provided in the ship;
A refrigerant circulation line in which the refrigerant for cooling the BOG is circulated and the first and second expanders are provided;
A first refrigerant compressor provided between the first and second expanders in the refrigerant circulation line for receiving and compressing the refrigerant discharged from the first expander; And
A first compressor cooler for cooling the refrigerant compressed in the first refrigerant compressor;
Wherein the evaporation gas processing system comprises: The method according to claim 1,
Expansion means for thermally expanding the BOG cooled in the main heat exchanger; And
Further comprising a flash drum for separating the LNG supplied from the BOG subjected to the thermal expansion in the expansion means and the re-liquefied LNG and the flash gas. delete 3. The method of claim 2,
A precooler provided in the refrigerant circulation line for cooling the refrigerant by heat exchange with the BOG to be introduced into the first compressor of the first compander from the LNG storage tank and supplying the refrigerant to the first expander; And
An aftercooler which is provided in the refrigerant circulation line and cools the refrigerant cooled in the first compressor cooler by heat exchange with the refrigerant to be supplied from the first expander to the first refrigerant compressor and supplies the cooled refrigerant to the second expander ); ≪ / RTI > 5. The method of claim 4,
A second refrigerant compressor provided in the refrigerant circulation line for receiving and compressing the refrigerant heat-exchanged with the BOG in the main heat exchanger; And
And a second compressor cooler provided in the refrigerant circulation line for cooling the refrigerant compressed by the second refrigerant compressor,
And the refrigerant cooled in the second compressor cooler is supplied to the precooler. 5. The method of claim 4,
Wherein the liquid separated from the flash drum is restored to the LNG storage tank and the gas is supplied from the LNG storage tank to the BOG stream introduced into the precooler. 5. The method of claim 4,
A recondenser provided in the fuel supply line and supplied with the BOG branched from the downstream of the second compressor to mix and cool the LNG supplied from the LNG storage tank;
A high pressure pump which is provided in the fuel supply line and receives LNG from the re-condenser and compresses the LNG at a supply pressure of the gas consuming place; And
Further comprising a vaporizer provided in the fuel supply line for forcibly vaporizing the LNG compressed in the high-pressure pump. 8. The method of claim 7,
Wherein the fuel supply line is provided with a BOG expander for thermally expanding the BOG branched from the downstream of the second compressor and supplying the expanded BOG to the re-condenser. 8. The method of claim 7,
Wherein the BOG and the LNG are mixed in the re-condenser and are subjected to vapor-liquid separation to supply the liquid to the high-pressure pump, and the gas is supplied from the LNG storage tank to the BOG flow introduced into the precooler. . 3. The method of claim 2,
And a low-pressure gas supply line branched from the BOG re-liquefaction line and supplying the compressed BOG as fuel to a low-pressure gas consuming place provided in the ship or an offshore structure. delete

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