KR20030073975A - Boil off gas management method and system assembly of Liquefied Natural Gas Carrier - Google Patents

Abstract

PURPOSE: A method and system apparatus for processing an evaporation gas of an LNG ship are provided to make maintenance and repair easy and improve the functions from a viewpoint of operation and efficiency. CONSTITUTION: The system apparatus comprises: a gas dome(30) formed on the upper end of a storage tank(20): a first low efficiency compressor(50); a gas heater(60); a check valve(170); a second low efficiency compressor(180); a constant speed motor(40); a boiler(90) connected to the gas heater(60) for burning an evaporation gas; a main valve(70) disposed between the gas heater(60) and an engine room(80) where the boiler(90) is disposed; a strip spray pump(100); a flow control valve(120) in which parts of LNG are fed through a pressure control valve(110); a recovery line(130); a temperature control valve(140); a carburetor(150); a mixer(160); and a boiler(90) connected to the mixer(160) for burning LNG of gaseous state.

Description

Boil off gas management method and system assembly of Liquefied Natural Gas Carrier

The present invention relates to a method and system for treating boil-off gas generated in a storage tank due to the amount of heat transferred from the outside during operation of a natural gas carrier, and more particularly, a compressor for raising the temperature and pressure of the boil-off gas. Is estimated based on the maximum fuel consumption of the boiler, but since the price of LNG is higher than that of ship oil in actual vessel operation, only the evaporated gas generated from the storage tank is used as a low-efficiency compressor. The present invention relates to a method and a system apparatus for treating boil-off gas of an LNG carrier, which is easy to operate and maintain by reducing the system to be treated, thereby reducing manufacturing costs.

Generally, natural gas carriers (hereinafter referred to as LNG carriers) store liquefied natural gas (LNG, Liquefied Natural Gas, hereinafter referred to as LNG) by liquefying gaseous natural gas at -163 ° C. It is a ship to transport.

The storage tank of the LNG carrier is made of aluminum only because of the property of maintaining rigidity even at extremely low temperatures.

There are two types of storage tank formation methods of the LNG carrier, a spherical independent tank type and a membrane type (aka diaphragm type), and a spherical independent tank type is named Moss after the developer's name, and the membrane type is Technigas. It's called Technigas and Gas Transport.

The spherical independent tank method is a method of manufacturing a ball-shaped tank having a diameter of 40 m and then fixing it to the ship by making a ball-shaped tank having a diameter of 40 m with aluminum. It has the advantage of low stress concentration point in manufacturing or use.

However, since the ground height of the vessel is increased and receives a lot of wind during the operation of the vessel, the steering and mooring mooring device has to be strengthened.

The membrane method is a good way to keep warm on the inner wall of the cargo hold of the ship without making a separate tank, and the heat insulating surface is sealed with a thin metal plate, while the hull is reduced to an optimized size and the installation of special equipment is unnecessary It has the disadvantages that many stress concentration points are used during fabrication or use, and damage factors such as stranding in case of collision outside the hull are to be avoided.

The difference between the membrane type technigas formula and the gas transport formula lies in the construction and construction method of the insulation.

In the LNG carrier, external heat such as direct sunlight of the sun is transmitted to the storage tank during operation, and at this time, a boil off gas (BOG) in which a part of LNG is vaporized is generated in the storage tank.

The amount of evaporated gas evaporated in the storage tank varies depending on winter and summer, but on average, about 0.15% of the total amount of stored gas is generated in one day.

The boil-off gas is discharged from the storage tank through a safety valve when the set pressure is higher than the set safety pressure (0.25 bar). The discharged boil-off gas is used as a fuel of a boiler for the operation of the vessel, thereby keeping the pressure in the gas storage tank stable. do.

1 is a piping diagram showing an apparatus for treating an evaporative gas treatment system of an existing LNG carrier, and as shown in the drawing, the gas dome 2 formed on the upper side of the storage tank 1 is generated by the evaporated gas generated in the storage tank 1. Is discharged through).

The boil-off gas discharged through the gas dome 2 is transferred to the demister 3 along the transfer pipe.

The boil-off gas passing through the demister 3 is transferred to the first compressor 5 to which the variable speed motor 4 is attached.

The low temperature and high pressure evaporated gas passing through the first compressor 5 is transferred to the gas heater 6 to raise the temperature suitable for combustion.

In the middle of the pipe connected from the first compressor 5 to the gas heater 6, a check valve 17 is installed to prevent the reverse conveyance to the first compressor 5.

In order to prepare for an emergency in which maintenance or repair of the first compressor 5 is required, a second compressor 18 driven by the transmission motor 4 is installed.

The high temperature and high pressure evaporated gas passing through the gas heater 6 is transferred to the boiler 9 installed in the engine room 8 through the main valve 7 and combusted.

The lower side of the storage tank 1 is equipped with a strip spray pump 10 for supplying LNG to meet gas shortages that may occur during combustion of the boiler 9.

Part of the LNG discharged by the strip spray pump 10 is transferred to the flow control valve 12 through the pressure control valve 11, and the rest is recovered back to the storage tank 1 along the recovery line 14 do.

Part of the LNG transferred to the flow control valve 12 is transferred to the temperature control valve 13, the remainder is transferred to the vaporizer 15 is phase-changed from the liquid state to the gas state.

The gaseous LNG passing through the vaporizer 15 and the liquid LNG transferred through the temperature regulating valve 13 are mixed with each other in the mixer 16.

The LNG passing through the mixer 16 is transferred to the demister 3 along the transfer pipe in a state where the liquid component and the gas component are mixed due to the difference in the liquefaction temperature.

In the demister 3, a liquefied component is separated from LNG in a state in which a liquid component and a gas component are mixed, and a gaseous LNG component and an evaporated gas discharged directly from the storage tank 1 are mixed to form the first component. Conveyed to a low efficiency compressor (5).

The conventional LNG carrier's boil-off gas treatment system has the wider operating range of the low-efficiency compressor that compresses the boil-off gas, but commercial operation is operated at a low speed, so the utility value is low. Since it is formed in a complex structure required, it is difficult to maintain and repair.

An object of the present invention devised to solve the problems as described above is to facilitate the maintenance and operation by treating only the evaporated gas generated in the storage tank with a low efficiency compressor and simplifying the system to eliminate the demister when using the vaporizer. And in terms of efficiency.

In order to achieve the object of the present invention as described above, the evaporated gas discharged from the storage tank is used as a fuel of the vessel by transferring to the boiler by using a low efficiency compressor and gas heater with a constant speed motor, and during combustion of the boiler Provided is a method and system for treating boil-off gas of an LNG carrier, which supplies vaporized LNG from a storage tank to a boiler by using a strip spray pump, a vaporizer, and a mixer to supply a fuel shortage.

1 is a piping diagram showing a boil-off gas treatment system apparatus of an existing LNG carrier.

2 is a piping diagram showing a boil-off gas treatment system apparatus of the LNG carrier according to an embodiment of the present invention.

Figure 3 is a flow chart showing the procedure of the boil-off gas treatment method of the LNG carrier according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

20: storage tank 30: gas dome

40: constant speed motor 50: first low efficiency compressor

60 gas heater 70 main valve

80: engine room 90: boiler

100: strip spray pump 110: pressure control valve

120: flow control valve 130: recovery line

140: temperature control valve 150: carburetor

160: mixer 170: check valve

180: second low efficiency compressor

Hereinafter, a method and a system apparatus for treating boil-off gas of an LNG carrier according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a piping diagram illustrating an apparatus for treating boil-off gas in an LNG carrier according to an embodiment of the present invention, and FIG. 3 is a flowchart illustrating a method of treating boil-off gas in an LNG carrier according to an embodiment of the present invention. .

As shown in the figure, the evaporated gas generated in the storage tank 20 is discharged through the gas dome 30 formed on the upper side of the storage tank 20. (ST 10)

The boil-off gas discharged through the gas dome 30 is transferred to the first low efficiency compressor 50 to which the constant speed motor 40 is attached along the transfer pipe to increase the pressure. (ST 20)

The low temperature and high pressure evaporated gas passing through the first low efficiency compressor 50 is transferred to the gas heater 60 to raise the temperature suitable for combustion. (ST 30)

In the middle of the pipe connected from the first low efficiency compressor 50 to the gas heater 60 is provided a check valve 170 to prevent the reverse transfer to the first low efficiency compressor 50.

The pipe for transferring the boil-off gas to the first low efficiency compressor 50 is also connected to the second low efficiency compressor 180 to which the constant speed motor 40 is attached to prepare for an emergency in which the first low efficiency compressor 50 is not used. do.

The high temperature and high pressure evaporated gas passing through the gas heater 60 is transferred to the boiler 90 installed in the engine room 80 through the main valve 70 and combusted. (ST 40)

The lower side of the storage tank 20 is equipped with a strip spray pump 100 for supplying LNG to meet the gas shortage that may occur during combustion of the boiler (90).

A portion of the LNG discharged by the strip spray pump 100 is transferred to the flow control valve 120 through the pressure control valve 110, and the rest is recovered back to the storage tank 20 along the recovery line 130. (ST 50)

A portion of the LNG transferred to the flow control valve 120 is transferred to the temperature control valve 140, the rest is transferred to the vaporizer 150 is phase-changed from the liquid state to the gas state. (ST 60)

The gaseous LNG passing through the vaporizer 150 and the liquid LNG transferred through the temperature control valve 140 are mixed with each other in the mixer 160. (ST 70)

The gaseous LNG passing through the mixer 160 is transferred to the boiler 90 through the main valve 70 and combusted. (ST 80)

Evaporation gas treatment system of the LNG carrier according to an embodiment of the present invention made of the above configuration is to use a low-efficiency compressor 50 is attached to the constant speed motor 40 and to separate the liquid components when using the vaporizer 150 The demister installed for the sake of the carburettor 150 is deleted due to the change in the operating temperature of the outlet side and the change in the connection position, thereby simplifying the system.

The present invention having the configuration as described above has the effect that the maintenance and operation is easy and the function is improved in terms of efficiency by simplifying the boil-off gas treatment system for supplying and burning the boil-off gas generated in the storage tank to the boiler.

Claims (2)

In the storage tank in which the boil-off gas vaporized by the LNG stored therein is generated due to the amount of heat transferred from the outside during the operation of the LNG carrier, the boil-off gas generated in the storage tank 20 is discharged through the gas dome 30. (ST 10), the step of transferring the boil-off gas discharged through the gas dome 30 to the first low efficiency compressor 50 to which the constant speed motor 40 is attached (ST 20), the first low efficiency compressor 50 The low temperature and high pressure evaporated gas passing through the gas heater 60 is transferred to the gas heater 60 (ST 30), and the high temperature and high pressure evaporated gas passed through the gas heater 60 is transferred to the boiler 90 through the main valve 70. Transported and combusted (ST 40), LNG is discharged through the strip spray pump 100 to meet the gas shortage during combustion of the boiler (90) (ST 50), the strip spray pump 100 Part of the LNG discharged through is transferred to the temperature control valve 140, and the rest The gas phase is transferred to the vaporizer 150 and the phase change from the liquid state to the gas state (ST 60), the gaseous LNG passed through the vaporizer 150 and the liquid state transferred through the temperature control valve 140 LNG is mixed with each other in the mixer 160 (ST 70), the gaseous LNG passing through the mixer 160 is transferred to the boiler 90 characterized in that the step (ST 80) Method of treating boil-off gas in LNG carriers. In a storage tank in which the boil-off gas vaporized by the LNG stored therein is generated due to the amount of heat transferred from the outside during the operation of the LNG carrier, a gas formed on the upper side of the storage tank 20 to discharge the boil-off gas vaporized therein. A first low efficiency compressor 50 connected to the dome 30 and the gas dome 30 to increase the pressure of the boil-off gas, a gas connected to the first low efficiency compressor 50 to increase the temperature of the boil-off gas Maintenance or inspection of the check valve 170 and the first low efficiency compressor 50 provided to prevent backflow of the evaporative gas between the heater 60, the first low efficiency compressor 50 and the gas heater 60. A boiler which is connected to the second low efficiency compressor 180, the first and second low efficiency compressors 50, 180 for driving the constant speed motor 40 and the gas heater 60 to burn the boil-off gas. 90, the gas heater (60) ) And a main valve 70 installed between the engine room 80 in which the boiler 90 is installed, and installed at the lower side of the storage tank 20 to satisfy the gas shortage during combustion of the boiler 90. Strip spray pump 100 for supplying a portion of the LNG discharged by the strip spray pump 100 to the flow rate control valve 120, the flow rate control valve 120 is transferred through the pressure control valve 110 A recovery line 130 connected to the pressure regulating valve 110, a temperature regulating valve 140 connected to the flow regulating valve 120, and the flow regulating valve for recovering the remaining amount of the transferred LNG to the storage tank. A vaporizer 150 connected to the 120 to phase-change the liquid LNG to a gaseous state, connected to the vaporizer 150 and the temperature control valve 140 is mixed with the liquid LNG and the gaseous LNG is mixed with each other A mixer 160, connected to the mixer 160 Boil-off gas treatment system unit of an LNG carrier, characterized in that consisting of a boiler 90 for combustion of LNG element state.