KR100777136B1 - Boil off gas reliquefaction apparatus using line mixer - Google Patents

Abstract

The present invention relates to a reliquefaction apparatus for BOG generated from a storage tank of LNG, in which a BOG supplied to a BOG compressor is mixed with LNG in a line mixer to cool the BOG by latent heat of evaporation generated when the LNG evaporates, and the BOG and In order to mix LNG, a line mixer and a mist elimination drum are installed between the storage tank and the BOG compression unit to shorten the cooling time, thereby providing a BOG reliquefaction apparatus using a line mixer that is easy to control the temperature of the BOG and has a simple structure.

BOG, Reliquefaction, Line Mixer, Precooling

Description

BOIL OFF GAS RELIQUEFACTION APPARATUS USING LINE MIXER}

1A is a system schematic diagram of a reliquefaction apparatus for temperature control of a conventional BOG;

1B is a schematic cross-sectional view of the heat exchanger shown in FIG. 1A,

2 is a system schematic diagram of a BOG reliquefaction apparatus according to a first embodiment of the present invention;

3 is a schematic cross-sectional view of the line mixer shown in FIG.

4 is a system schematic diagram of a BOG reliquefaction apparatus according to a second embodiment of the present invention;

5 is a system schematic diagram of a BOG reliquefaction apparatus according to a third embodiment of the present invention;

6 shows a system schematic diagram of a BOG reliquefaction apparatus according to a fourth embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

1: BOG compression section 2, 2a, 2b, 2c: cold box unit

3: flow control means 4: working fluid compression

10: storage tank 11: the first BOG compressor

12: second BOG compressor 13: safety valve

14: recirculation valve 15: gas-liquid separator

16: Line Mixer 17: Mist Elimination Drum

20: condenser

21, 21a: first heat exchanger 22: second heat exchanger

23: third heat exchanger 24, 26: expansion turbine

25: expansion valve 30: buffer tank

31: first valve 32: second valve

41: first working fluid compressor 42: second working fluid compressor

43: third working fluid compressor 44: first cooler

45: second cooler 46: third cooler

The present invention relates to a BOG reliquefaction apparatus, and in particular, boil off gas (BOG) generated by evaporation of liquefied natural gas in a storage tank of a carrier transporting cryogenic liquefied natural gas (LNG). In the reliquefaction of the " BOG ", a BOG reliquefaction apparatus using a line mixer for pre-cooling the BOG by mixing the BOG and LNG before the condensation step of the BOG.

In general, not only storage tanks of liquefied natural gas (LNG) installed on land, but also storage tanks of carrier ships transporting LNG, regardless of the shape of the storage tank such as moss type or membrane type, it is generally about 0.1 for a day. As much as 3% to 3% of LNG is evaporated as a result of the inflow of external heat through the insulator that encloses the storage tank. If the amount of LNG BOG increases, the pressure inside the storage tank increases, which is a dangerous situation such as an explosion of the storage tank. Will result.

As described above, LNG boil-off gas generated inside the LNG storage tank has been typically used as an auxiliary fuel source for powering a boiler or generator of a carrier, but in recent years, the design of an LNG carrier has a turbine according to steam driving. Since diesel engines are used rather than engines, the necessity of using BOG as an auxiliary fuel source generated inside LNG storage tanks is rapidly decreasing.

Therefore, recently, a BOG reliquefaction apparatus has been introduced to recover such LNG BOG, reliquefy it to LNG, and send it back to the LNG storage tank. As an example, BOG reliquefaction as described in Korean Patent Laid-Open No. 2001-89142 has been introduced. A device is mentioned.

The BOG reliquefaction apparatus compresses the working fluid in one or more compressors, cools the compressed working fluid by indirect heat exchange in a first heat exchanger, cryogenically expands the cooled working fluid in one or more expansion turbines, and expands. A cryogenic refrigeration cycle configured to warm the cryogenic working fluid by indirect heat exchange with compressed steam (BOG) in a second heat exchanger, and return the heated expansion working fluid to the compressor through a first heat exchanger; It consists of a BOG cycle configured to compress the BOG generated in the tank in a compressor and to condense the compressed BOG at least partially through heat exchange with the expanded working fluid in the second heat exchanger and return it to the storage tank.

The BOG reliquefaction apparatus has a problem in that the BOG evaporated from the storage tank is compressed into the compressor without being cooled and is compressed in an increased state of the specific volume, which consumes a lot of power. In addition, since the BOG is compressed in the compressor and the temperature is increased to flow into the condenser, the load of the cryogenic refrigeration cycle must be increased in order to condense the heated BOG, resulting in an increase in the operating cost of the entire system.

The BOG reliquefaction apparatus, which was devised to solve this problem, is disclosed in WO2005 / 047761. FIG. 1A is a system schematic diagram of a reliquefaction apparatus for temperature control of BOG, and FIG. 1B is a cooling of BOG. For the sake of illustration, schematic cross-sectional views of heat exchangers installed in the BOG feed pipe are shown.

In the reliquefaction apparatus for temperature control of the BOG shown in Figure 1a is a BOG generated in the storage tank is compressed in the compressor 110, the compressed BOG with a cryogenic working fluid in the cold box (130) In the reliquefaction apparatus at least partially condensed through heat exchange to be returned to the storage tank, prior to the compression step of the BOG, the BOG is cooled by indirect heat exchange with LNG to control the temperature of the BOG. In order to cool the BOG supplied to the compressor 110, the heat exchanger 120 shown in FIG. 1B is connected to the BOG supply line at the inlet side of the compressor 110, and the heat exchanger 120 has a drum-shaped separation. It is composed of a separation chamber (129) and a pipe cooler (124) in the form of a fin tube heat exchanger installed in the interior space of the separation chamber (129). The inlet of the pipe cooler 124 is connected to the condensed BOG, that is, a first conduit 122 which is a pipe connected to the LNG to be returned to the heat exchanger 120 and the storage tank, the pipe cooler 124 The second conduit 126 is connected to the outlet of the pipe which is connected to allow the completely evaporated LNG to be mixed into the BOG supply line while passing through the heat exchanger 120.

In order to maintain the temperature of the BOG supplied to the compressor 110 and the cold box 130 in a set temperature range, the outlet temperature of the heat exchanger 120 and the outlet temperature of the compressor 110 are measured, and the first temperature is measured. The opening of the control valve 125 installed in the conduit 122 is controlled by the temperature control unit 160. Therefore, the flow rate flowing into the heat exchanger 120 through the first conduit 122 is controlled.

However, the conventional reliquefaction apparatus for controlling the temperature of the BOG, although the heat exchanger 120 is connected to the BOG supply line to cool the BOG supplied to the compressor 110 and the cold box 130, Since the heat exchanger 120 has a complicated structure in which the pipe cooler 124 is installed inside the chamber 129, the heat exchanger 120 is not easy to manufacture, and BOG and LNG are indirectly heat-exchanged through the pipe cooler 124 to cool the BOG. It takes a long time to cool down, so temperature control is not easy.

In addition, although the mesh screen 128 is installed on the upper portion of the chamber 129 to prevent the BOG condensed when the BOG is cooled, the mesh screen 128 is provided only. Since it is not easy to remove the mist (mist), when the BOG in the mist state is introduced, the compressor 110 may be damaged.

In addition, when a small amount of LNG flows into the pipe cooler 124 of the heat exchanger 120, since the heat exchange is performed only at the lower portion of the pipe cooler 124, the cooling of the BOG is not performed smoothly, thereby controlling the temperature of the BOG. There is a problem that is not easy.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, the object of the present invention is maintenance-free, easy to manufacture, simple structure, can quickly control the temperature of the BOG from the storage tank It is to provide a BOG reliquefaction device.

As a result of in-depth research to achieve the object of the present invention, the present inventors mix BOG supplied to a compressor with LNG in a line mixer to cool the BOG by latent heat of evaporation generated during evaporation of LNG, and the BOG. Line Mixer and mist elimination drum are installed between storage tank and BOG compression section to mix LNG with LNG. BOG reliquefaction apparatus has been developed to shorten the cooling time and to easily control temperature, remove mist and have simple structure. .

That is, according to one embodiment of the present invention, the BOG compression unit for pressurizing and supplying the natural gas (BOG) evaporated in the storage tank LNG is stored; A working fluid compressor connected to a plurality of working fluid compressors and a cooler such that the pressurizing and cooling processes are repeated to pressurize and supply the working fluid in the cryogenic refrigeration cycle for liquefying the BOG; And a cold box unit for liquefying the BOG by heat-exchanging with the BOG in a condenser after cryogenic expansion of the working fluid compression unit, and the BOG liquefied by the cold box unit to the storage tank. A BOG reliquefaction apparatus that is returned, a line mixer in which BOG evaporated in the storage tank and LNG supplied from outside is mixed between the BOG compression unit and the storage tank, and mist present in the BOG mixed in the line mixer. A mist removal drum for removing is provided, and the line mixer is provided with a BOG reliquefaction apparatus using a line mixer, wherein the BOG is cooled by latent heat of evaporation of LNG.

The mist elimination drum is preferably a drain pipe is formed at the lower end of the drum to recover the LNG collected from the drum to the storage tank.

In addition, the LNG supplied from the outside is preferably supplied from the storage tank or the liquefied BOG.

In addition, it is preferable that a gas-liquid separator is installed at the outlet of the cold box unit so that the liquefied BOG is returned to the storage tank by a pump, and the gaseous BOG is re-injected or discharged into the line mixer.

In addition, a gas-liquid separator is installed at the outlet of the cold box unit so that the liquefied BOG is returned to the storage tank by a pump or re-introduced to the line mixer through a recirculation valve, and the gaseous BOG is re-introduced or discharged into the line mixer. It is desirable to be.

The cold box unit may further include: a first heat exchanger connected to an outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid passing through the condenser; An expansion turbine connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And a condenser connected to an outlet of the expansion turbine to allow the cryogenic working fluid passing through the expansion turbine and the BOG flowing from the BOG compression unit to liquefy the BOG. In addition, other embodiments of the cold box unit described in the following specific embodiments may be applied.

In addition, a bypass pipe is formed in the working fluid inlet / outlet pipe of the cold box unit, and a part of the working fluid is recycled to the working fluid compression unit through the bypass pipe to control the flow rate of the working fluid supplied to the cold box unit. It is preferably configured to include a flow control means for, the bypass pipe of the flow control means is preferably provided with a buffer tank of the working fluid for adjusting the supply amount of the working fluid in accordance with the load fluctuation of the BOG.

Hereinafter, with reference to the accompanying drawings, a specific embodiment according to the present invention will be described in detail as follows. The temperature and pressure described below show one example, and the present invention is not limited to these numerical values.

As shown in FIG. 2, the BOG compression unit 1 pressurizing and supplying natural gas (BOG) evaporated in the storage tank 10 in which LNG is stored; A working fluid compressor (4) connected with a plurality of working fluid compressors and coolers to repeat the pressurizing and cooling processes to pressurize and supply the working fluid in the cryogenic refrigeration cycle for liquefying the BOG; And a cold box unit (2) for liquefying the BOG by heat-exchanging with the BOG in the condenser 20 after the cryogenic expansion of the working fluid of the working fluid compression unit 4 in the BOG reliquefaction apparatus. On the BOG line between the BOG compression section 1 and the storage tank 10, a line mixer 16 and a mist removal drum 17 are continuously installed.

The line mixer 16 according to the invention is shown in FIG. 3. In the line mixer 16 used in the present invention, several elements are fixed in a pipe in a lateral direction to convert the laminar flow into a turbulent fluid while causing continuous stirring during the passage, thereby effectively causing two or more fluids, It is a device that mixes gas and liquid, and it divides the fluid flow, reverses and changes the direction of the flow, and plays three roles of splitting, redirection, and mixing in the course of conveying in the pipe to achieve fine mixing.

In the present invention, the line mixer 16 has a path length through which the two fluids are mixed as the inlet 201 through which the BOG from the storage tank 10 flows and the inlet 202 through which the LNG flows from the outside are closer. It is preferable because it becomes long. BOG introduced into BOG inlet 201 is mixed with LNG introduced into LNG inlet 202. LNG introduced from the outside is applied to the surface 160a on the inner path of the line mixer 16, and the coated LNG flows along the path surface of the line mixer 16 and evaporates by a somewhat hot BOG. At this time, the temperature of the BOG is lowered by the latent heat of evaporation of LNG. The mixed gas of vaporized LNG and BOG is supplied to the BOG compression unit 1 via a mist removal drum 17 such as a knock-out drum.

In the mist elimination drum 17, droplets or mist are collected in the lower portion of the drum by gravity and only the mixed-cooled BOG is supplied to the BOG compression unit 1 at the outlet of the upper portion. It is desirable to install additional screens.

The LNG and BOG mixed in the line mixer 16 are moved to the BOG compression unit 1 after the mist or droplets are removed from the mist removal drum 17.

In addition, as shown in Figures 4 to 6, at the outlet of the cold box units (2, 2a, 2b, 2c) is a gas-liquid separator 15 is installed to liquefy BOG by the pump (P) storage tank Returned to (10), the gaseous BOG can be re-introduced or discharged to the line mixer 16. In addition, a gas-liquid separator 15 is installed at the outlet of the cold box units 2, 2a, 2b, and 2c so that the liquefied (condensed) BOG is returned to the storage tank by a pump or the recirculation valve 14 is removed. Through the line mixer 16 is re-introduced, the gaseous BOG may be re-introduced or discharged to the line mixer 16.

Hereinafter, the entire system of the present invention will be described by dividing each specific embodiment.

(First embodiment)

2 is a system schematic diagram of a BOG reliquefaction apparatus according to a first embodiment of the present invention.

In the BOG reliquefaction apparatus according to the first embodiment of the present invention, the line mixer 16 supplies the BOG supplied to the BOG compression section 1 in the configuration described in the patent application No. 2005-65501 filed by the applicant of the present invention. Is a device configured to cool BOG by mixing with LNG.

In the BOG reliquefaction apparatus according to the first embodiment of the present invention, the gaseous natural gas (evaporated natural gas, BOG) generated in the storage tank 10 is liquefied by heat exchange with a cryogenic refrigeration cycle, and then stored again. It is a device for returning to the tank (10) for storage.

In the BOG reliquefaction apparatus according to the first to fourth embodiments of the present invention, the cryogenic refrigeration cycle consists of a closed system, the working fluid (refrigerant) circulating inside the closed system of the BOG liquefaction point Nitrogen, helium, argon, and the like may be used as materials that can be cooled below (−162 ° C.), but the operation using nitrogen as a working fluid will be described in the present invention.

BOG reliquefaction apparatus according to the first embodiment of the present invention shown in Figure 2 includes a BOG compression unit (1) for pressurizing the BOG generated in the storage tank 10 in which LNG is stored; Working fluids connected with a plurality of working fluid compressors (41, 42, 43) and coolers (44, 45, 46) to repeat the pressurizing and cooling processes to pressurize and cool the working fluid in the cryogenic refrigeration cycle for liquefying the BOG A compression section 4; A cold box unit (2) for liquefying the BOG by heat-exchanging with the BOG in the condenser 20 after cryogenic expansion of the working fluid of the working fluid compression unit 4; And forming a bypass pipe in the working fluid inlet / outlet pipe of the cold box unit 2, and recycling a part of the working fluid to the working fluid compression unit 4 through the bypass pipe to the cold box unit 2. It is configured to include a flow rate control means for adjusting the flow rate of the working fluid supplied to the, and is configured to return the BOG liquefied by the cold box unit (2) to the storage tank (10). A line mixer 16 and a mist elimination drum 17 are installed on the BOG line between the BOG compression unit 1 and the storage tank 10.

Here, the buffer pipe 30 of the working fluid for adjusting the supply amount of the working fluid in accordance with the load fluctuation of the BOG is installed in the bypass pipe of the flow control means (3).

Referring to Figure 2 described in more detail with reference to the above, first, the system for supplying and reclaiming the BOG evaporated in the LNG stored in the storage tank 10, the storage tank 10, BOG compression unit (1), the condenser 20 and the pump P are comprised.

A discharge port is formed in the upper portion of the storage tank 10 so that the BOG can be discharged and connected to the BOG supply pipe, and the BOG inside the storage tank 10 has a predetermined pressure (about 1.03 bar) or more. When opened, the safety valve 13 is formed to open and close to lower the pressure of the storage tank 10 below a predetermined pressure.

The BOG compression unit (1) is composed of a motor (M), a plurality of BOG compressors (11, 12) and pipes that interconnect them, and the BOG compressors (11, 12) to be driven by the motor (M) It is connected.

The first and second BOG compressors 11 and 12 are sequentially connected by pipes so that the BOG supplied from the storage tank 10 may be compressed and transferred step by step by the BOG compressors 11 and 12. Here, since the BOG compression unit 1 according to the present invention compresses and transfers BOG in two stages, the first and second BOG compressors 11 and 12 are connected in series by pipes.

The condenser 20 is a device for liquefying heat by compressing the compressed BOG with the cryogenic expanded working fluid. The condenser 20 is installed inside the cold box unit 2 so that the compressed BOG and the cryogenic expanded working fluid pass therethrough. The flow path is formed in. The pump P for returning the condensed BOG to the storage tank 10 is connected to the BOG outlet pipe of the condenser 20, and the return pipe formed at the outlet of the pump P is the storage tank 10. )

In addition, in order to control the supply temperature of the BOG supplied to the BOG compression unit (1) by branching the outlet side return pipe of the cold box unit 2, one pipe is connected to the storage tank 10, the other One pipe is connected to a supply pipe connecting the outlet of the storage tank 10 and the inlet of the BOG compression unit 1 to form a bypass pipe, the temperature of the BOG supplied to the BOG compression unit 1 When is increased, the BOG is pre-cooled by controlling the temperature by recycling a part of the BOG condensed through the bypass pipe and mixing the BOG and the condensed BOG. Of course, it is also possible to pre-cool using the LNG stored in the storage tank 10 instead of the condensed BOG.

At this time, the line mixer 16 and the mist elimination drum 17 is installed on the BOG line between the BOG compression unit 1 and the storage tank 10 to facilitate temperature control.

Here, the bypass pipe is formed with a recirculation valve 14 to adjust the recycle amount of the condensed BOG, the control method of the recirculation valve 14 is to manually open or close the valve or the outlet of the storage tank 10 Alternatively, a temperature sensor (not shown) may be formed at the inlet of the BOG compression unit 1 to automatically control the opening and closing degree of the recirculation valve 14 according to the supply temperature of the BOG. Automatic control of the recirculation valve 14 by the temperature sensor is controlled only until the temperature supplied to the BOG compression unit 1 reaches a steady state, after which the recirculation valve 14 is closed and the condensed BOG is stored. It is returned to the tank (10).

The cold box unit 2 is connected to the outlet of the flow control means 3 (may be connected directly from the working fluid compression section 4 without passing through the flow control means) from the flow control means (3) A first heat exchanger 21 for precooling the introduced working fluid to the low temperature part working fluid that has passed through the condenser 20; An expansion turbine 24 connected to the outlet of the first heat exchanger 21 to expand the working fluid to cryogenic temperature; And a condenser 20 connected to the outlet of the expansion turbine 24 to allow the cryogenic working fluid passed through the expansion turbine 24 and the BOG flowing from the BOG compression unit 1 to liquefy the BOG. It is configured to include).

Hereinafter, the cold box unit 2 of the BOG reliquefaction apparatus according to the present invention is provided with an expansion turbine 24 for cryogenic expansion of the working fluid, but the present invention is not limited thereto, and the expansion turbine 24 is replaced with an expansion valve. It is also possible to use.

Here, the low temperature operating fluid is cryogenic expansion by the expansion turbine 24 of the cold box unit 2 and the heat exchange with the BOG in the condenser 20 after the operation is returned to the working fluid compression unit (4) The fluid is defined as the fluid, and the high temperature working fluid is defined as the working fluid from the working fluid compression section 4 to the expansion turbine 24.

A generator (G) is connected to the rotary shaft of the expansion turbine (24) to use electrical energy generated by the expansion turbine (24) as driving energy of the working fluid compression unit (4) or the BOG compression unit (1). It is possible.

The cold box unit 2 is formed as a single module, which shortens the pipe between the components by condensing the first heat exchanger 21, the expansion turbine 24, and the condenser 20 in a limited space. The heat loss through the pipe can be minimized. That is, the length of the pipe connecting the expansion turbine 24 and the condenser 20 is shortened so that the cryogenic state of the working fluid at the outlet of the expansion turbine 24 can be stably maintained.

In addition, as the cold box unit 2 is modularized, the cold box unit 2 and the BOG reliquefaction apparatus can be miniaturized and can be easily mounted on a ship.

In addition, the cold box unit 2 is preferably insulated with a generally known heat insulator.

The working fluid compression unit 4 compresses the working fluid (nitrogen) to a high pressure (about 58 bar) so that the working fluid (nitrogen) can be sufficiently cryogenically expanded in the expansion turbine 24 and through the flow control means 3, the cold box unit. Heated operation by the compression operation of the plurality of working fluid compressors 41, 42, 43 and the working fluid compressors 41, 42, 43 for compressing the working fluid in multiple stages as means for supplying pressure to (2). It consists of a plurality of coolers (44, 45, 46) provided between each working fluid compressor (41, 42, 43) to cool the fluid.

Here, when the pressure of the working fluid is rapidly increased or the flow rate is rapidly increased during the compression operation of the working fluid compressor (41, 42, 43), if the whole system, that is, the BOG reliquefaction device is abnormally operated, it is bypassed again. It is also possible to add a surge pipe for introducing into the working fluid compressors 41, 42, 43.

The first to third working fluid compressors 41, 42, and 43 are sequentially connected to the working fluid compression unit 4 of the BOG reliquefaction apparatus according to the present invention in order to compress the working fluid in three stages. The outlets of the working fluid compressors 41, 42, and 43 are connected to the first to third coolers 44, 45, and 46 for heat exchange with seawater. Here, the first to third working fluid compressors (41, 42, 43) are aligned to rotate in engagement with one rotation shaft, the rotation shaft is connected to be driven by a motor (M).

In addition, the first to third coolers 44, 45 and 46 operate and cool only when the working fluid is raised above a predetermined temperature by the first to third working fluid compressors 41, 42 and 43. When the thermal stress is applied to the working fluid compression unit 4 because the temperature of the working fluid recovered from the cold box unit 2 is low, the first to third coolers 44, 45, and 46 are applied. It is desirable to control the operation of the.

The flow control means (3) is a means for adjusting the supply amount of the working fluid in accordance with the load fluctuation of the BOG to form a bypass pipe in the working fluid inlet and outlet pipe of the cold box unit (2), the bypass pipe is operated A fluid buffer tank 30 is provided, and first and second valves 31 and 32 for adjusting the flow rate are provided at the front and rear sides of the buffer tank 30, respectively.

When the load of the BOG is maximized, the first and second valves 31 and 32 are all closed, and 100% of the working fluid circulating in the cryogenic refrigeration cycle includes the working fluid compression unit 4 and the cold box unit ( Allow circulation to 2).

On the other hand, when the load of the BOG decreases, the opening degree of the first valve 31 is adjusted and opened, and the second valve 32 is closed to close a part of the working fluid discharged from the working fluid compression unit 4. It is to be introduced into the buffer tank (30).

On the other hand, when the load of the BOG decreases and then increases again, a part of the working fluid stored in the buffer tank 30 by closing the first valve 31 and opening part or all of the second valve 32. Is circulated to the cryogenic refrigeration cycle.

Since the buffer tank 30 is filled with a predetermined amount of nitrogen, it is also possible to replenish or adjust the working fluid (nitrogen) that is increased or decreased during the operation of the cryogenic refrigeration cycle.

The operating method of the BOG reliquefaction apparatus according to the first embodiment of the present invention will be described by dividing the BOG circulation process and the refrigeration cycle for the working fluid (nitrogen).

First, the circulation process of the BOG, when the LNG stored in the storage tank 10 is evaporated by the external temperature difference and the internal pressure rises above the set pressure, the safety valve 13 formed at the outlet of the storage tank 10 ) Is opened and the evaporated BOG is discharged. At this time, when the temperature of the BOG is a set temperature, that is, -120 ℃ or more, the LNG stored in the storage tank 10 or a part of the liquefied BOG flowing from the condenser 20 is the BOG and the line mixer 16 The BOG to be mixed and supplied to the BOG compression unit 1 is maintained at 1.03 bar, -120 ° C. Here, in order to recycle the liquefied BOG, a part of the liquefied BOG is introduced by mixing the BOG by opening a recirculation valve 14 installed in the bypass pipe of the return pipe. In addition, in order to inject the LNG stored in the storage tank 10 it is preferable to form a pipe so that the pipe (not shown) formed in the lower portion of the storage tank 10 is connected to the supply pipe of the BOG.

The BOG introduced into the BOG compression unit 1 is compressed to 3.2 bar and −50.83 ° C. in two stages of the BOG compressors 11 and 12 to become a superheated state of high temperature and high pressure.

The compressed BOG is heat-exchanged with a cryogenic expanded working fluid (nitrogen) by a nitrogen refrigeration cycle in the condenser 20 of the cold box unit 2 is liquefied into a 3.0bar, -154.7 ℃ subcooled liquid.

The liquefied BOG is returned to and stored in the storage tank 10 through a pump (P) installed in the return pipe, during the initial operation of the BOG reliquefaction apparatus or the BOG discharged from the storage tank 10 is discharged to a high temperature If so, part of the LNG is re-injected to mix with the BOG through the recirculation valve (14). Here, the method of returning the condensed BOG to the storage tank 10 has a method of spraying through the spray head from the top of the storage tank 10 or supply to the bottom of the storage tank 10. When introduced into the bottom of the storage tank 10, the nitrogen component of the uncondensed gas contained in the liquefied BOG is dissolved in the LNG to maintain a low nitrogen ratio in the gas phase. Since nitrogen has a lower liquefaction point than methane, which is a main component of LNG, preventing an increase in nitrogen content in the BOG can reduce the load of the two stage BOG compressors 11 and 12 or the condenser 20.

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14.2bar, 35.46 ℃ three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through, the pressure is increased to 58 bar, 43 ° C., and the compressed working fluid (nitrogen) is supplied to the cold box unit 2 by a predetermined amount through the operation of the flow regulating means 3.

The nitrogen gas supplied to the cold box unit 2 is cooled to 58 bar and −105 ° C. by heat exchange with a low temperature operating fluid that has passed through the condenser 20 in the first heat exchanger 21, and the high pressure working fluid. While passing through the expansion turbine 24 is expanded to a cryogenic, low-pressure gas of 10.5 bar, -167 ℃ is further cooled.

The cryogenic working fluid is heat-exchanged with the BOG supplied from the BOG compression unit 1 in the condenser 20 to liquefy the BOG to 3.0 bar, -154.7 ° C. supercooled liquid, and at the same time the cryogenic working fluid is The temperature is raised to 10.3 bar, -134 ° C.

The working fluid is heated to 10 bar, 40 ° C. by heat exchange with the high temperature part working fluid supplied from the working fluid compression part 4 in the first heat exchanger 21, and then the flow rate adjusting means 3 through a return pipe. Re-inserted into the working fluid compression section 4 to complete the cryogenic refrigeration cycle.

Second Embodiment

4 is a system schematic diagram of a BOG reliquefaction apparatus using a line mixer according to a second embodiment of the present invention.

In the BOG reliquefaction apparatus according to the second embodiment of the present invention, BOG is added by adding a line mixer 16 and a mist removing drum 17 to the configuration described in Patent Application No. 2005-78588 filed by the applicant of the present invention. It is a device configured to cool the BOG by mixing the BOG supplied to the compression unit 1 with the LNG in the line mixer 16.

In the BOG reliquefaction apparatus according to the second embodiment of the present invention, only the gas-liquid separator 15 is added to the configuration of the cold box unit 2a and the outlet of the cold box unit 2a with respect to the first embodiment. The differences are different, and the rest of the configuration and the connection relationship between the respective configurations are the same as in the first embodiment. In addition, the second embodiment of the present invention differs only in the operation method of the refrigeration cycle through the cold box unit (2a), the operation method for the remaining configuration is the same as the first embodiment described above.

Therefore, in the second embodiment of the present invention, a description of portions overlapping with the first embodiment will be omitted, and a different configuration from the first embodiment will be described.

The cold box unit 2a is connected to the outlet of the flow regulating means 3 so as to precool the working fluid flowing from the flow regulating means 3 to the low temperature working fluid which has undergone heat exchange. 22); A first heat exchanger (21) connected to the outlet of the second heat exchanger (22) for cooling the precooled working fluid to the low temperature operating fluid passing through the condenser (20); By bypassing a portion of the working fluid flowing into the first heat exchanger 21 and expanding at a low temperature, it is mixed with the low temperature operating fluid passed through the condenser 20 and re-introduced into the first heat exchanger 21. An expansion turbine 26 for further cooling the precooled working fluid passing through the first heat exchanger 21; An expansion valve 25 connected to the outlet of the first heat exchanger 21 to expand the working fluid to cryogenic temperature; And a condenser 20 connected to the outlet of the expansion valve 25 so that the cryogenic working fluid passing through the expansion valve 25 and the BOG flowing from the BOG compression unit 1 exchange with each other to liquefy the BOG. It is configured to include).

A gas-liquid separator 15 is installed at the outlet of the cold box unit 2a so that the BOG in the liquid state is returned to the storage tank 10 by a pump P, or a portion of the BOG in the liquid state is the storage tank 10. In order to precool the BOG generated in the) to the line mixer 16 through the bypass pipe is mixed with the BOG and re-introduced to the BOG compression unit 1 through the mist removal drum 17, BOG condensed in the gas-liquid separator 15 is re-injected or discharged into the BOG compression unit (1).

As described above, the working fluid is pre-cooled by the second heat exchanger 22, and the working fluid, which has been low-temperature expanded by the expansion turbine 26, is re-introduced into the first heat exchanger 21 to provide the expansion valve 25. By further cooling the working fluid supplied to the) it is possible to stably maintain the temperature of the working fluid supplied to the expansion valve (25).

The cold box unit 2a is formed as a single module, which connects the first and second heat exchangers 21 and 22, the expansion valve 25, the expansion turbine 26, and the condenser 20 in a limited space. By compacting, pipes between components can be shortened to minimize heat loss through the pipes.

A generator is connected to the rotary shaft of the expansion turbine 26 so that the electrical energy generated by the expansion turbine 26 can be used as driving energy of the working fluid compression unit 4 or the BOG compression unit 1.

The operating method of the BOG reliquefaction apparatus according to the second embodiment of the present invention will be briefly described by dividing the BOG circulation process and the refrigeration cycle for the working fluid (nitrogen).

First, the circulation process of the BOG, when the LNG stored in the storage tank 10 is evaporated by the external temperature difference and the internal pressure rises above the set pressure, the safety valve 13 formed at the outlet of the storage tank 10 ) Is opened and BOG is discharged. At this time, the BOG is properly mixed in the liquefied BOG and the line mixer 16 to be maintained at 1.03bar, -120 ℃.

The BOG introduced into the BOG compression unit 1 is compressed at 2.5 bar and −73 ° C. in two stages of the BOG compressors 11 and 12 to be in a superheated state at high temperature and high pressure.

The compressed BOG is heat-exchanged with a cryogenic expanded working fluid (nitrogen) by a nitrogen refrigeration cycle in the condenser 20 of the cold box unit 2a and liquefied into a supercooled liquid of 2.3 bar and -155 ° C.

The liquefied BOG is returned to the storage tank 10 through the pump (P) installed in the return pipe after the gas and liquid is separated from the gas-liquid separator 15 is stored, the BOG reliquefaction apparatus During the initial operation of the or when the BOG discharged from the storage tank 10 is discharged to a high temperature, a portion of the LNG is re-introduced to be mixed with the BOG through the recirculation valve (14).

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14bar, 35.4 ℃ to the three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through, the pressure is raised to 58 bar and 43 ° C., and the compressed working fluid (nitrogen) is supplied to the cold box unit 2a by a predetermined amount through the operation of the flow regulating means 3.

The nitrogen gas supplied to the cold box unit 2a is precooled to 57.3 bar and −83.5 ° C. by heat exchange with the low temperature part working fluid in the second heat exchanger 22, and the condenser 20 in the first heat exchanger 21. Cooled to 57.5 bar, -137.9 ℃ by heat exchange with the low temperature working fluid passed through the), the high-pressure working fluid is expanded to cryogenic, low pressure gas of 14.6 bar, -163 ℃ while passing through the expansion valve (25) More cool. Here, the low temperature part working fluid flowing into the first heat exchanger 21 bypasses a part of the high temperature part working fluid supplied to the first heat exchanger 21 to allow 14.5 bar and −140 ° C. in the expansion turbine 26. It is a working fluid mixed with the low temperature working fluid passed through the condenser 20 after low temperature expansion.

The cryogenic working fluid is heat-exchanged with the BOG supplied from the BOG compression unit 1 in the condenser 20 to liquefy the BOG into a supercooled liquid of 2.3 bar and −155 ° C., while the cryogenic working fluid is The temperature is raised to 14.4 bar, -138.9 ° C.

The working fluid is heated to 14.2 bar, −106 ° C. by heat exchange with the hot part working fluid supplied from the working fluid compression part 4 in the first heat exchanger 21, and the second heat exchanger 22 is heated. After passing through 14bar, 35.4 ° C. while passing through the flow control means (3) through the return pipe to the working fluid compression unit (4) to complete the cryogenic refrigeration cycle.

(Third Embodiment)

5 is a system schematic diagram of a BOG reliquefaction apparatus using a line mixer according to a third embodiment of the present invention.

In the BOG reliquefaction apparatus according to the third embodiment of the present invention, BOG is added by adding a line mixer 16 and a mist removing drum 17 to the configuration described in Patent Application No. 2005-109931 filed by the applicant of the present invention. It is a device configured to cool the BOG by mixing the BOG supplied to the compression unit 1 with the LNG in the line mixer 16.

The BOG reliquefaction apparatus according to the third embodiment of the present invention has a different configuration of the cold box unit 2b with respect to the first and second embodiments described above, and the cold box unit 2b with respect to the first embodiment. Only that the gas-liquid separator 15 is added to the outlet of the gas is different, and the rest of the configuration and the connection relationship between the components are the same as in the first and second embodiments. In addition, the third embodiment of the present invention differs only in the operation method of the refrigeration cycle through the cold box unit (2b), the operation method for the remaining configuration is the same as the first embodiment described above.

Therefore, in the third embodiment of the present invention, a description of portions overlapping with those of the first embodiment will be omitted, and a configuration different from the first embodiment will be described.

The cold box unit 2b is connected to the outlet of the flow regulating means 3 to supply a second working heat exchanger for precooling the working fluid introduced from the flow regulating means 3 to the low temperature working fluid after the heat exchange process. 22); Connected to the outlet of the second heat exchanger 22 to form three paths through which the pre-cooled working fluid, the BOG flowing from the BOG compression unit 1, and the cold working fluid passing through the condenser 20 pass; A first heat exchanger (21a) for cooling the pre-cooled working fluid and BOG with the low temperature part working fluid; By bypassing a portion of the working fluid flowing into the first heat exchanger (21a) by low temperature expansion, it is mixed with the low temperature operating fluid passed through the condenser 20 and re-introduced into the first heat exchanger (21a) An expansion turbine 26 for further cooling the pre-cooled working fluid passing through the first heat exchanger 21a and the BOG; An expansion valve 25 connected to the outlet of the first heat exchanger 21a to expand the working fluid to cryogenic temperature; And a condenser connected to the outlet of the expansion valve 25 to allow the cryogenic working fluid passed through the expansion valve 25 and the BOG passing through the first heat exchanger 21a to liquefy the BOG. 20).

A gas-liquid separator 15 is installed at the outlet of the cold box unit 2b so that the BOG in the liquid state is returned to the storage tank 10 by a pump P, or a portion of the BOG in the liquid state is the storage tank 10. In order to pre-cool the BOG generated in the), it is introduced into the line mixer 16 through the bypass pipe, mixed with the BOG, and re-introduced into the BOG compression unit 1, and non-condensing in the gas-liquid separator 15. The BOG is re-injected or discharged into the BOG compression unit 1.

By pre-cooling the BOG compressed by the BOG compression unit 1 in the first heat exchanger 21a as described above, the BOG temperature at the inlet of the condenser 20 is set within the set range even if there is a change in the amount or temperature of the BOG. You can keep it constant. In addition, the working fluid is pre-cooled by the second heat exchanger 22, and the working fluid, which is expanded at a low temperature by the expansion turbine 26, is re-introduced into the first heat exchanger 21a to the expansion valve 25. By further cooling the supplied working fluid, the temperature of the working fluid supplied to the expansion valve 25 can be stably maintained.

The cold box unit 2b is formed as a single module, and an electric energy may be obtained by connecting a generator to the rotating shaft of the expansion turbine 26.

The operating method of the BOG reliquefaction apparatus according to the third embodiment of the present invention will be briefly described by dividing the BOG circulation process and the refrigeration cycle for the working fluid (nitrogen).

First, the circulation process of the BOG, when the LNG stored in the storage tank 10 is evaporated by the external temperature difference and the internal pressure rises above the set pressure, the safety valve 13 formed at the outlet of the storage tank 10 ) Is opened and BOG is discharged. At this time, the BOG is properly mixed in the liquefied BOG and the line mixer 16 to be maintained at 1.03bar, -120 ℃.

The BOG introduced into the BOG compression unit 1 is compressed to 3.6 bar and −41.98 ° C. in two stages of the BOG compressors 11 and 12 to be in a superheated state of high temperature and high pressure.

The compressed BOG is cooled to 3.3 bar and −134 ° C. by heat exchange with the low temperature part working fluid in the first heat exchanger 21 a having three paths formed therein, and then the condenser 20 of the cold box unit 2 b. Heat exchanged with the cryogenic expanded working fluid (nitrogen) by nitrogen refrigeration cycle and liquefied into 3.0bar, -154.7 ℃ supercooled liquid.

The liquefied BOG is returned to the storage tank 10 through the pump (P) installed in the return pipe after the gas and liquid is separated from the gas-liquid separator 15 is stored, the BOG reliquefaction apparatus During the initial operation or when the BOG discharged from the storage tank 10 is discharged to a high temperature, a portion of the LNG is re-introduced to mix with the BOG evaporated in the line mixer 16 through the recirculation valve (14). .

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14.3bar, 36.08 ℃ three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through the pressure is raised to 58bar, 40 ℃ pressure, the compressed working fluid (nitrogen) is supplied to the cold box unit (2b) a predetermined amount through the operation of the flow rate adjusting means (3).

The nitrogen gas supplied to the cold box unit 2b is precooled to 57.7 bar and −70 ° C. by heat exchange with the low temperature working fluid in the second heat exchanger 22, and in the first heat exchanger 21 a of three paths. Cooled to 57.4 bar, -132 ° C by heat exchange with the low temperature working fluid and compressed BOG passing through the condenser 20, the high-pressure working fluid is passed through the expansion valve 25, 15.2 bar, -162.6 ° C , It is expanded to a low pressure gas and further cooled. Here, the low temperature part working fluid flowing into the first heat exchanger 21a bypasses a portion of the high temperature part working fluid supplied to the first heat exchanger 21a to allow 15.2 bar and −129.3 ° C. in the expansion turbine 26. It is a working fluid mixed with the low temperature working fluid passed through the condenser 20 after low temperature expansion.

The cryogenic working fluid is heat-exchanged with the BOG supplied from the BOG compression unit 1 in the condenser 20 to liquefy the BOG to 3.0 bar, -154.7 ° C. supercooled liquid, and at the same time the cryogenic working fluid is The temperature is raised to 14.9 bar, -145 ° C.

The working fluid is heated to 14.6 bar, −86.42 ° C. by heat exchange with the high temperature part working fluid supplied from the working fluid compression part 4 and the compressed BOG in the first heat exchanger 21a, and the second heat exchanger ( After passing through 22) and heated to 14.3 bar, 36.08 ℃ through the flow control means (3) through the return pipe to the working fluid compression unit (4) to complete the cryogenic refrigeration cycle.

(Example 4)

6 is a system schematic diagram of a BOG reliquefaction apparatus using a line mixer according to a fourth embodiment of the present invention.

In the BOG reliquefaction apparatus according to the fourth embodiment of the present invention, BOG is added by adding a line mixer 16 and a mist removal drum 17 to the configuration described in Patent Application No. 2006-1271 filed by the applicant of the present invention. It is a device configured to cool the BOG by mixing the BOG supplied to the compression unit 1 with the LNG in the line mixer 16.

In the BOG reliquefaction apparatus according to the fourth embodiment of the present invention, the configuration of the cold box unit 2c is different from that of the first to third embodiments, and the cold box unit 2c is different from that of the first embodiment. Only that the gas-liquid separator 15 is added to the outlet of the different, and the remaining configuration and the connection relationship of each configuration is the same as the first to third embodiments. In addition, the fourth embodiment of the present invention differs only in the operation method of the refrigeration cycle through the cold box unit (2c), the operation method for the remaining configuration is the same as the first embodiment described above.

Therefore, in the fourth embodiment of the present invention, a description of portions overlapping with those of the first embodiment will be omitted, and a configuration different from the first embodiment will be described.

The cold box unit (2c) is connected to the outlet of the flow rate control means 3, the second heat exchanger for pre-cooling the working fluid flowing from the flow rate control means (3) to the low-temperature operating fluid through a heat exchange process ( 22); Connected to the outlet of the second heat exchanger 22 to form three paths through which the pre-cooled working fluid, the BOG flowing from the BOG compression unit 1, and the cold working fluid passing through the condenser 20 pass; A first heat exchanger (21a) for cooling the pre-cooled working fluid and BOG with the low temperature part working fluid; A third heat exchanger 23 connected to the outlet of the first heat exchanger 21a to cool the high temperature part working fluid flowing from the first heat exchanger 21a to the low temperature part working fluid passing through the condenser 20. ); Bypassing a portion of the working fluid flowing into the first heat exchanger (21a) by low temperature expansion and mixing it with the low temperature operating fluid passed through the third heat exchanger (23) to the first heat exchanger (21a) An expansion turbine (26) for further cooling the pre-cooled working fluid and BOG passing through the first heat exchanger (21a) again; An expansion valve 25 connected to the outlet of the third heat exchanger 23 to expand the working fluid to cryogenic temperature; And a condenser connected to the outlet of the expansion valve 25 so that the cryogenic working fluid passing through the expansion valve 25 and the BOG passing through the first heat exchanger 21a exchange each other to liquefy the BOG. 20 is configured to include.

A gas-liquid separator 15 is installed at the outlet of the cold box unit 2c so that a liquid BOG is returned to the storage tank 10 by a pump P or a portion of the BOG in the liquid state is stored in the storage tank 10. In order to pre-cool the BOG generated in the), it is introduced into the line mixer 16 through the bypass pipe, mixed with the BOG, and re-introduced into the BOG compression unit 1, and non-condensing in the gas-liquid separator 15. The BOG is re-injected or discharged into the BOG compression unit 1.

By pre-cooling the BOG compressed by the BOG compression unit 1 in the first heat exchanger 21a as described above, the temperature of the BOG evaporated at the inlet of the condenser 20 is set even if there is a generation amount or temperature change of the BOG evaporated. It can be kept constant within the range. In addition, the working fluid is pre-cooled by the second heat exchanger 22, and the working fluid expanded at a low temperature by the expansion turbine 26 is re-injected into the first heat exchanger 21a to cool the high-temperature operating fluid. By further cooling the working fluid supplied from the third heat exchanger 23 to the expansion valve 25, the temperature of the working fluid supplied to the expansion valve 25 can be more stably maintained.

The cold box unit (2c) is formed as a module, it is possible to obtain electrical energy by connecting a generator to the rotary shaft of the expansion turbine (26).

The operating method of the BOG reliquefaction apparatus according to the fourth embodiment of the present invention will be briefly described by dividing the BOG circulation process and the refrigeration cycle for the working fluid (nitrogen).

First, when the circulation process of the BOG evaporated, when the LNG stored in the storage tank 10 is evaporated by the external temperature difference and the internal pressure rises above the set pressure, the safety valve formed at the outlet of the storage tank 10 (13) is opened and BOG is discharged. At this time, the BOG is properly mixed in the liquefied BOG and the line mixer 16 to be maintained at 1.03bar, -120 ℃.

The BOG introduced into the BOG compression unit 1 is compressed to 3.2 bar and −50.83 ° C. in two stages of the BOG compressors 11 and 12 to become a superheated state of high temperature and high pressure.

The compressed BOG is cooled to 3.1 bar and −130 ° C. by heat exchange with the low temperature part working fluid in the first heat exchanger 21 a having three paths formed therein, and then the condenser 20 of the cold box unit 2 c. While passing through the heat exchange with the cryogenic expanded working fluid (nitrogen) by the nitrogen refrigeration cycle is liquefied to 3.0bar, -154.7 ℃ supercooled liquid.

The liquefied BOG is returned to the storage tank 10 through the pump (P) installed in the return pipe after the gas and liquid is separated from the gas-liquid separator 15 is stored, the BOG reliquefaction apparatus During the initial operation of the or when the BOG discharged from the storage tank 10 is discharged to a high temperature, a portion of the LNG is re-introduced to be mixed with the BOG through the recirculation valve (14).

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14.2bar, 35.46 ℃ three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through the pressure is raised to 58bar, 43 ℃ pressure, the compressed working fluid (nitrogen) is supplied to the cold box unit (2c) a predetermined amount through the operation of the flow control means (3).

The nitrogen gas supplied to the cold box unit 2c is precooled to 57.9 bar and -77 ° C by heat exchange with the low temperature part working fluid in the second heat exchanger 22, and in the first heat exchanger 21a of three paths. It is cooled to 57.8 bar, -134 ° C by heat exchange with the cold working fluid passed through the third heat exchanger 23 and the compressed BOG. The working fluid passing through the first heat exchanger 21a is further cooled to 57.7 bar and -137 ° C by heat exchange with the low temperature part working fluid passing through the condenser 20 in the third heat exchanger 23. The high pressure working fluid is expanded to cryogenic, low pressure gas of 14.6 bar, -163.3 ° C while passing through the expansion valve 25, and is further cooled. Here, the low temperature part working fluid flowing into the first heat exchanger 21a bypasses a part of the high temperature part working fluid supplied to the first heat exchanger 21a to allow 14.5 bar and −136.9 ° C. in the expansion turbine 26. It is a working fluid mixed with the low temperature operating fluid passed through the third heat exchanger 23 after low temperature expansion.

The cryogenic working fluid is heat-exchanged with the BOG supplied from the BOG compression unit 1 in the condenser 20 to liquefy the BOG to 3.0 bar, -154.7 ° C. supercooled liquid, and at the same time the cryogenic working fluid is The temperature is raised to 14.5 bar, -150.7 ° C.

The working fluid is heated to 14.4 bar and −140 ° C. by heat exchange with the high temperature part working fluid passing through the first heat exchanger 21a in the third heat exchanger 23, and in the first heat exchanger 21a. Heated to 14.3 bar, −98.88 ° C. by heat exchange with the hot part working fluid supplied from the working fluid compression unit 4 and the compressed BOG, and heated to 14.2 bar and 35.46 ° C. while passing through the second heat exchanger 22. After re-injection into the working fluid compression unit (4) through the flow rate adjusting means (3) through the recovery pipe to complete the cryogenic refrigeration cycle.

As described above, the BOG reliquefaction apparatus according to the present invention has the advantage that the cooling of the BOG is made faster because the LNG is vaporized while mixing with the BOG in the line mixer, it is possible to quickly control the temperature of the BOG. Compared with the conventional heat exchanger for BOG precooling, the structure of the system of the present invention is simple, and therefore, the manufacturing is easy and the apparatus cost is low.

In addition, by removing the mist contained in the vaporized mixed gas after mixing the BOG and LNG from the mist removal drum to prevent the droplets from flowing into the BOG compression unit.

Claims (7)

BOG compression unit for pressurizing and supplying natural gas (BOG) evaporated in the storage tank in which LNG is stored; A working fluid compressor connected to a plurality of working fluid compressors and a cooler such that the pressurizing and cooling processes are repeated to pressurize and supply the working fluid in the cryogenic refrigeration cycle for liquefying the BOG; And a cold box unit for liquefying the BOG by heat-exchanging with the BOG in a condenser after cryogenic expansion of the working fluid compression unit, and the BOG liquefied by the cold box unit to the storage tank. As a returning BOG reliquefaction device, Between the BOG compression unit and the storage tank is provided a line mixer is mixed with the BOG evaporated from the storage tank and LNG supplied from the outside, and a mist removal drum for removing the mist present in the BOG mixed in the line mixer In the line mixer, BOG reliquefaction apparatus using a line mixer, characterized in that the BOG is cooled by latent heat of evaporation of LNG. The method of claim 1, The mist elimination drum is a BOG reliquefaction apparatus using a line mixer, characterized in that the drain pipe is formed in the lower end of the drum to recover the LNG collected from the drum to the storage tank. The apparatus of claim 1, wherein the LNG supplied from the outside is supplied from the storage tank or the liquefied BOG. According to any one of claims 1 to 3, wherein the outlet of the cold box unit is a gas-liquid separator is installed, the liquefied BOG is returned to the storage tank by a pump, the gaseous BOG is re-introduced to the line mixer BOG reliquefaction apparatus using a line mixer, characterized in that the discharge or. According to any one of claims 1 to 3, wherein the outlet of the cold box unit is provided with a gas-liquid separator is liquefied BOG is returned to the storage tank by a pump or re-introduced to the line mixer through a recirculation valve, BOG reliquefaction apparatus using a line mixer, characterized in that the gaseous BOG is re-introduced or discharged to the line mixer. According to any one of claims 1 to 3, wherein the cold box unit, A first heat exchanger connected to an outlet of the working fluid compression unit for precooling the working fluid introduced from the working fluid compression unit to the low temperature part working fluid passing through the condenser; An expansion turbine connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And BOG using a line mixer comprising a condenser connected to the outlet of the expansion turbine and the cryogenic working fluid passing through the expansion turbine and the BOG flowing from the BOG compression unit to liquefy the BOG by mutual heat exchange Reliquefaction apparatus. According to any one of claims 1 to 3, wherein the working fluid inlet and outlet pipe of the cold box unit is formed by the bypass pipe, and through the bypass pipe a part of the working fluid to the working fluid compression unit by recirculating the cold And a flow rate adjusting means for adjusting the flow rate of the working fluid supplied to the box unit, and the bypass pipe of the flow rate adjusting means includes a buffer tank of the working fluid for adjusting the supply amount of the working fluid according to the load variation of the BOG. BOG reliquefaction apparatus using a line mixer, characterized in that the provided.

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