KR101122549B1 - Boil off gas control apparatus of lng carriers - Google Patents

Abstract

The present invention relates to a device for suppressing evaporation gas of a LNG carrier, comprising: a nitrogen supply device supplying nitrogen through a nitrogen line connected to an insulation space of a cargo hold, and supercooling nitrogen supplied from the nitrogen supply device to cool the entire cargo hold. And a heat exchange part for introducing nitrogen of the supercooled heat exchanged through a cooling line connected to the adiabatic space of the cargo hold so as to suppress generation of boil-off gas. Therefore, according to the present invention, by supplying the supercooled nitrogen to the insulation space of the cargo hold to give the effect of cooling the entire cargo hold has the effect of suppressing the generation of evaporated gas.

LNG carriers, evaporative gases, containment, nitrogen, cooling, heat exchange

Description

BOIL OFF GAS CONTROL APPARATUS OF LNG CARRIERS}

The present invention relates to a boil-off gas suppression apparatus for a liquefied natural gas carrier, and more specifically, a ship such as a gas carrier carrying a liquefied natural gas, or a synthesis for mining, storing, liquefying and vaporizing a gas in a floating state at sea. The present invention relates to a device for suppressing boil off gas (BOG) generated in a floating or stationary gas treatment plant equipped with a plant.

In general, liquefied natural gas (Liquefied Natural Gas (LNG)) is known to be a clean fuel and abundant reserves than petroleum, and its use is rapidly increasing with the development of mining and transport technology.

LNG is a liquid that is produced when the temperature of methane, the main component of natural gas, is lowered below -163 degrees Celsius under 1 atm.The volume of liquefied LNG is about 600% of the volume of gaseous LNG in the standard state. Is about 0.47, which is about one half of the crude oil share.

Because of this, LNG has the advantage of being easy to transport and store, while having a very low temperature and very dangerous in case of leakage, a separate gas storage tank made of insulation (insulation material) in ships or floating or fixed gas treatment facilities. Will be transported or stored.

In particular, LNG ships are different from crude oil carriers in a cryogenic liquid state at -163 ° C. Since the vaporization point of LNG is extremely low at -163 ° C, thorough insulation is required to prevent vaporization.

However, complete insulation is practically impossible and the LNG in liquefied state is changing to gaseous evaporated gas at a rate of about 0.15% per day while the ship is in operation.

For this reason, in ships, boil-off gas is naturally treated as a fuel of a propulsion engine, or by simply burning excess boil-off gas through a gas compression unit (GCU).

For example, the propulsion engine generates high pressure steam from a boiler by using boil-off gas as a fuel, and the steam drives a steam turbine to obtain propulsion force.

Referring to the specific example of the prior art of such an LNG ship as follows.

As shown in FIG. 1, the vessel's boil-off gas treatment system includes a fuel gas compressor 3, a gas turbine, and a dual fuel engine connected to a bog vent pipe 2 at the top of the gas storage tank 1. It consists of a propulsion means 10 and the like.

Here, a separate combustion device 9 is connected to and installed in the gas storage tank 1, and the vaporized gas is supplied to either the combustion device 9 or the propulsion means 10 by a predetermined pipe changing means (not shown). It is coupled to be transported.

During operation of the vessel, the boil-off gas is sent to the propulsion means 10 of the vessel to be used for propulsion, while surplus generated in the gas storage tank 1 when the vessel is not propelled by the propulsion means 10. The boil-off gas is sent to the combustion device 9 so that it can be burned directly.

However, for example, when a ship enters a terminal from a mountainous area, the operating speed should be lowered to less than 7 knots, and the waiting time for unloading at the terminal is about 10 hours. In this process, there is a problem in dealing with the continuous boil-off gas. Moreover, there is no way to send excess boil-off gas or to use boil-off gas to energize ships on standby.

Therefore, the method of suppressing the generation of boil-off gas rather than the treatment of boil-off gas is the best, for this purpose, the following method was conventionally used.

In FIG. 2, a conventional boil-off gas suppression apparatus is shown, and the high-temperature boil-off gas BOG naturally generated in the gas storage tank 1 is forced by a compressor 23 for the bottom of the gas storage tank 1. Existing hot gas that is injected into the cryogenic liquefied natural gas through the negative nozzle 21 and evaporated to the upper portion of the gas storage tank 1 is moved to the upper layer by using a pump 11 installed at the bottom of the gas storage tank 1. By lowering the temperature of the gas portion of the upper layer by the injection through the injection nozzle 13 of the introduced cryogenic liquefied gas is made of a structure to reduce the evaporation gas generation rate.

However, in the conventional boil-off gas reducing device, by directly injecting the vaporized high-temperature boiled gas into a relatively low temperature liquefied natural gas, it can cause the overall flow disturbance of the liquefied natural gas, which is the kinetic energy of the liquefied natural gas As a result of the increase, the vaporization is further promoted, which has the potential to accelerate the pressure rise inside the gas storage tank.

Therefore. The method of suppressing evaporated gas by pressurizing the gas storage tank is also used, but this also increases the manufacturing cost since the thickness of the gas storage tank must be considerably thick, and also when unloading when the pressure inside the gas storage tank is higher than the pressure of the terminal. There was a problem.

The present invention has been invented to solve the above problems, the object is that the heat of the outside is moved along the wall surface of the cargo hold is gathered at the upper end of the cargo hold, the heat of the cargo hold in view that the generated evaporation gas due to this heat It is to provide a boil-off gas suppression apparatus of a liquefied natural gas carrier to supply the super-cooled nitrogen to the space to cool the entire cargo hold to suppress the generation of boil-off gas.

In order to achieve the above object, according to the present invention, the nitrogen supply device for supplying nitrogen through a nitrogen line connected to the insulating space of the cargo hold, and the cooling of the cargo hold by supercooling the nitrogen supplied from the nitrogen supply device of the evaporation gas Provided is an evaporative gas suppression apparatus for a liquefied natural gas carrier including a heat exchanger for introducing nitrogen of the supercooled heat exchanged through a cooling line connected to an insulation space of a cargo hold so as to suppress the occurrence.

And the nitrogen line, through the dome structure of the cargo hold can be installed nitrogen inlet and nitrogen discharge unit in the insulation space of each of the I and I.

In addition, the cooling line is connected to the insulation space of the IBS through the dome structure of the cargo hold can be made of the supply of supercooled nitrogen only to the IBS.

Furthermore, a three-way valve is installed at the intersection of the nitrogen line and the cooling line to recycle the elevated temperature nitrogen to the heat exchanger to heat exchange or discharge it to the outside.

According to the boil-off gas suppression apparatus of the liquefied natural gas carrier of the present invention, by supplying the supercooled nitrogen to the heat insulation space of the cargo hold to cool the whole cargo hold has the effect of suppressing the generation of the boil-off gas.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention. It is not limited.

3 is a block diagram of a boil-off gas suppression apparatus of a liquefied natural gas carrier according to an embodiment of the present invention.

As shown in FIG. 3, the apparatus for suppressing evaporation gas of a liquefied natural gas carrier of the present embodiment includes a nitrogen supply device 110 for supplying nitrogen to an insulation space of the cargo hold 100, and an insulation space of the cargo hold 100. It may include a heat exchange unit 120 for introducing the supercooled nitrogen.

In this case, the cargo hold 100 may be a marine structure such as a liquefied natural gas carrier (LNGC) or a floating liquefied natural gas storage evaporation unit (FSRU) that is anchored and operated in one place.

The cargo hold 100 shows a membrane type in a basic form, but it may be applicable to a cargo hold or a modified cargo hold.

Here, the membrane-shaped cargo hold 100 is described as an example. The cargo hold 100 is insulated by the primary barrier 104 of the membrane and the secondary barrier 106 made of a heat insulator so that the cold heat of the liquefied natural gas is hull ( 140 is designed so as not to affect. The interval between the primary barrier 104 and the secondary barrier 106 is referred to as IBS (Inter Barrier Space) 105, and the interval between the secondary barrier 106 and the inner wall of the hull 140 is (IS: Insulation Space) 107.

In addition, a dome 102 may be formed at the center of the upper end of the cargo hold 100 to install various pipe lines.

Nitrogen supply device 110 is installed to supply nitrogen to the cargo hold 100, by supplying nitrogen, which is an inert gas to the cargo hold 100 to prevent explosion risk and the space on the IBS (105) and the Is (107) Moisture can be removed or a constant pressure can be maintained.

A nitrogen line 112 may be installed to extend from the nitrogen supply device 110 to the cargo hold 100, and the nitrogen line 112 may be connected to the nitrogen supply device 110 through the dome 102. 107 and the nitrogen inlet 112a may be installed so as to be located in the respective spaces of the IBs 105, and nitrogen circulated through the IS 107 and the IBS 105 through the nitrogen inlet 112a. Nitrogen discharge portion 112b may be installed in each of the IES 107 and the IBS 105 to be discharged.

In addition, the heat exchanger 120 which supercools the nitrogen supplied from the nitrogen supply device 110 and cools the entire cargo hold 100 to suppress the generation of boil-off gas, has a cooling line 122 connected from the heat exchanger 120 to the cargo hold. The dome 102 of the (100) is installed in the IBs 105 to supply the supercooled nitrogen only to the IBs 105 side.

The reason why the supercooled nitrogen flows only into the IBs 105 is because when the supercooled nitrogen also flows into the IS 107, the hull 140 directly contacting the ISU 105 may be affected.

In addition, the heat exchanger 120 may be a cooler, an evaporator, or a condenser as it is capable of supercooling nitrogen by being brought into contact with a low temperature fluid supplied to the outside by receiving nitrogen having an elevated temperature.

And a three-way valve 124 is installed at the intersection of the nitrogen line 112 and the cooling line 122 from the nitrogen discharge portion 112b to recycle heat exchanged nitrogen to the heat exchanger 120 side to heat exchange or Can be discharged to the outside.

The three-way valve 124 may be a solenoid valve.

In addition, valves 130 may be installed on the nitrogen line 112 and the cooling line 122, respectively, to block or release the supply.

The action of the boil-off gas suppression device of the LNG carrier having such a structure is made as follows.

Referring to FIG. 3 again, natural gas in a gaseous state is liquefied to cryogenic temperature and stored in the cargo hold 100 at atmospheric pressure (1.013 bar). However, the heat from the outside during transportation of the liquefied natural gas is moved along the wall surface of the cargo hold 100 is collected at the upper end of the cargo hold 100, the heat generated by the evaporation gas due to the pressure rise factor of the cargo hold 100 Works.

Therefore, in the present invention, by cooling the adiabatic space that is the wall surface of the cargo hold 100 to suppress the generation of evaporated gas as much as possible.

That is, nitrogen, which is an inert gas supplied from the nitrogen supply device 110, opens nitrogen inlets 112a positioned at the IBS 105 and the IS 107 of the cargo hold 100 along the nitrogen line 112, respectively. The nitrogen is supplied to each of the IBs 105 and the IS 107 through. The nitrogen supplied at this time may be to prevent the explosion risk and to remove moisture or maintain a constant pressure on the IBs 105 and the IS 107 space.

In addition, the heat exchange part 120 allows the supercooled nitrogen to be introduced into the IBS 105 along the cooling line 122 by the heat exchange, thereby cooling the entire cargo hold 100, thereby blocking external heat and evaporating. Generation of gas can be suppressed.

In addition, the nitrogen which is elevated in temperature by circulating the IBs 105 and the IS 107 is discharged through the nitrogen discharge part 112b connected to the dome 102 and is immediately discharged or exchanged through the control of the three-way valve 124. Re-introduced into the unit 120 to perform a heat exchange can be introduced through the cooling line 122 as described above.

In addition, the valve 130 installed in the nitrogen inlet 112a and the nitrogen outlet 112b can control the amount of nitrogen inlet or the amount of discharge, and in some cases can be blocked. In addition, the valve 130 installed on the cooling line 122 may control or temporarily block the supply of cold air according to the degree of supercooling of nitrogen, and control the inflow into the heat exchanger 120 for heat exchange of the heated nitrogen. .

Therefore, according to the above, by supplying the supercooled nitrogen to the insulation space of the cargo hold to give the effect of cooling the entire cargo hold to suppress the generation of evaporated gas can be improved the loading efficiency of liquefied natural gas.

As described above as a specific embodiment of the boil-off gas suppression apparatus of a liquefied natural gas carrier according to the present invention, this is only an example, the present invention is not limited to this, and has the broadest range in accordance with the basic idea disclosed herein Should be interpreted as Those skilled in the art can easily change the material, size, etc. of each component according to the application field, and can be combined / substituted the disclosed embodiments to implement a pattern of a timeless shape, but this also does not depart from the scope of the present invention will be. It will be apparent to those skilled in the art that various changes and modifications may be readily made without departing from the spirit and scope of the invention as defined by the appended claims.

1 is a schematic diagram showing an evaporative gas treatment system of a LNG carrier according to the prior art;

Figure 2 shows a boil-off gas suppression apparatus according to the prior art,

3 is a block diagram of a boil-off gas suppression apparatus of a liquefied natural gas carrier according to an embodiment of the present invention.

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

100: cargo hold 102: dome

104: primary barrier 105: Ivy

106: secondary barrier 107: ice

110: nitrogen supply device 112: nitrogen line

112a: nitrogen inlet 112b: nitrogen outlet

120: heat exchanger 122: cooling line

124: three-way valve 130: valve

140: hull

Claims (4)

A nitrogen supply device for supplying nitrogen through a nitrogen line connected to the insulation space of the cargo hold, It includes a heat exchanger for introducing the nitrogen of the supercooled heat exchanged through the cooling line connected to the insulating space of the cargo hold so as to suppress the generation of the evaporation gas by supercooling the nitrogen supplied from the nitrogen supply device to cool the entire cargo hold, The nitrogen line, Nitrogen inlet and nitrogen outlet are installed in the insulation space of each I and IB through the dome structure of the cargo hold. Evaporative gas suppression apparatus of LNG carrier. delete The method of claim 1, The cooling line, Evaporative gas suppression apparatus of the LNG carrier which is connected to the insulation space of the IB through the dome structure of the cargo hold to supply the supercooled nitrogen only to the IB. The method according to claim 1 or 3, A three-way valve is installed at the intersection of the nitrogen line and the cooling line to recirculate the elevated temperature nitrogen to the heat exchanger to heat exchange or discharge to the outside of the LNG carrier.

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