KR102260415B1 - method and Apparatus for transferring liquid cargo - Google Patents

Abstract

The present invention provides a liquid cargo transport device. The liquid cargo transfer device of the present invention includes: a liquid cargo transfer line connected to a liquid cargo storage tank; a drum connected to the liquid cargo transfer line and providing a space for storing liquid cargo; a pressing unit for pressing the liquid cargo storage tank so that the liquid cargo stored in the liquid cargo storage tank is supplied to the drum through the liquid cargo transfer line; a discharge line connected to the lower part of the drum for unloading the liquid cargo stored in the drum and provided with a main pump for providing conveying pressure to the liquid cargo; And it may include a drum pressure adjusting unit for adjusting the pressure of the drum to maintain a constant flow rate of the liquid cargo discharged through the discharge line.

Description

Pressurized liquid cargo transfer device and method { method and Apparatus for transferring liquid cargo}

The present invention relates to a pressurized liquid cargo transport apparatus and method.

In a conventional LNG carrier to which a GTT membrane type cargo hold is applied, a pump tower, which is a pipe structure, is formed inside the cargo hold to load or discharge LNG. The pump tower is also used as a pipe for discharging LNG through a pipe while supporting various types of piping and an LNG cargo pump.

1 is a view showing a pump tower installed in a conventional cargo hold.

Referring to FIG. 1 , when conventional LNG is shipped and discharged, LNG is transported outside the cargo hold through the same liquid line, but inside the cargo hold, through a filling pipe (2) at the time of shipment and discharge. LNG is loaded and unloaded through a discharge pipe (4). This is because the LNG cargo pump (5) is attached to the lowermost end of the discharge pipe (4) as a submerged type, so when the discharge pipe (4) is used for filling (Filling), the cargo pump (5) This is because it can be damaged by reverse rotation, and when cooled LNG flows in through the discharge pipe for supporting the structure, it generates stress in the entire structure by thermal contraction.

In particular, in case of failure of the LNG cargo pump (5), it cannot be repaired immediately, so two units must be configured for each cargo hold (1). economic costs are borne.

In addition, in order to solve the above problem by configuring a separate branch line, a remote controllable valve is required, but this method is also impossible because it is difficult to develop an actuator that can be operated in a cryogenic environment. Therefore, in the conventional LNG inflow and discharge system in the tank of a ship, the filling pipe 2 is formed separately from the discharge pipe 4 to load LNG.

However, in the case of a fluid inflow and discharge structure in a tank of a conventional ship, the structure is complicated because a separate filling pipe 2 is required, and the member required to support the filling pipe 2 in addition to the filling pipe 2 is As it is required, a lot of economic cost is borne in the construction of the facility. Therefore, it is required to develop a structure for inflow and discharge of fluid in a tank that minimizes the use of related piping and improves economic efficiency.

In order for the fluid inflow and outflow structures in the tank to satisfy these requirements, it is required to develop a technology that enables filling of the fluid through the discharge pipe 4 .

One object of the present invention is to provide a pressurized liquid cargo transport apparatus and method that can simplify the structure of inflow and discharge of liquid cargo in a cargo hold by unifying a filling pipe and a discharge pipe.

The problems to be solved by the present invention are not limited thereto, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, a liquid cargo transfer line connected to the liquid cargo storage tank; a drum connected to the liquid cargo transfer line and providing a space for storing liquid cargo; a pressing unit for pressing the liquid cargo storage tank so that the liquid cargo stored in the liquid cargo storage tank is supplied to the drum through the liquid cargo transfer line; a discharge line connected to the lower part of the drum for unloading the liquid cargo stored in the drum and provided with a main pump for providing conveying pressure to the liquid cargo; and a drum pressure adjusting unit for adjusting the pressure of the drum in order to maintain a constant flow rate of the liquid cargo discharged through the discharge line may be provided.

In addition, the drum pressure control unit includes a water level sensing member for measuring the level of the liquid cargo in the drum; a pressure measuring member for measuring the boil-off gas pressure in the drum; and a control unit configured to receive measurement values from the water level sensing member and the pressure measuring member to control the amount of BOG in the drum.

In addition, the control unit may include: a vapor control valve installed on a gas transfer line through which the boil-off gas in the drum is exhausted; and a control valve installed in the main pump and the discharge line.

In addition, the control unit controls the vapor control valve to reduce the amount of BOG exhausted through the gas transfer line when the liquid cargo level in the drum rises above a preset water level and the BOG pressure in the drum is low, and the When the level of the liquid cargo in the drum is higher than the preset water level and the BOG pressure in the drum is high, the vapor control valve may be controlled to increase the amount of BOG exhausted through the gas transfer line.

In addition, it may further include a filling line connected to the liquid cargo transfer line, receiving the liquid cargo from the outside.

In addition, the pressurizing unit may further include a compressor receiving the boil-off gas from the drum and compressing it, and the boil-off gas compressed in the compressor may be provided to the liquid cargo storage tank through the gas transfer line.

In addition, the pressurizing unit may further include a terminal gas line connected to the compressor and providing boil-off gas from the liquid cargo storage terminal.

In addition, further comprising a cooling unit for preventing the temperature rise of the liquid cargo storage tank when the compressed boil-off gas is supplied to the liquid cargo storage tank; The cooling unit is installed in the liquid cargo storage tank injection nozzle for spraying the liquid cargo; and a supply line for cooling that connects the spray nozzle and the drum and supplies a portion of the liquid cargo stored in the drum to the spray nozzle by an auxiliary pump.

In addition, the pressurizing unit further includes a bypass line connected to the gas transfer line by bypassing the compressor to pressurize the boil-off gas generated in the liquid cargo storage tank, and the boil-off gas generated in the liquid cargo storage tank is the After being compressed in the compressor through a bypass line, the gas may be supplied to a consumer.

In addition, the compressor may further include a recovery line provided to store excess BOG remaining after being supplied to the gas demander among the BOG compressed in the compressor in the drum.

According to another aspect of the present invention, the step of pressurizing the liquid cargo storage tank using boil-off gas so that the liquid cargo stored in the liquid cargo storage tank is transferred to the drum;

and discharging the liquid cargo stored in the drum to a liquid cargo storage terminal through pumping of a main pump, wherein the boil-off gas used to pressurize the liquid cargo storage tank is the boil-off gas generated in the drum in the compressor. Using the compressed compressed boil-off gas, the discharging step may be provided with a liquid cargo transport method of adjusting the pressure of the drum to maintain a constant flow rate of the liquid cargo discharged from the drum.

In addition, the pressure control of the drum reduces the amount of BOG exhausted from the drum when the liquid cargo level in the drum is higher than a preset water level, and the BOG pressure in the drum is low, and the liquid cargo level in the drum is lowered. When the boil-off gas pressure in the drum is higher than the set water level, the amount of boil-off gas exhausted from the drum may be increased.

In addition, when the boil-off gas used to pressurize the liquid cargo storage tank in the pressurization step is insufficient, the boil-off gas generated from the gas storage terminal is provided and used, and the compressed boil-off gas is pressurized into the liquid cargo storage tank. At the same time, it is possible to prevent the temperature rise of the liquid cargo storage tank by spraying the liquid cargo.

In addition, the liquid cargo sprayed into the liquid cargo storage tank may be provided from the drum.

In addition, when the liquid cargo is unloaded into the liquid cargo storage tank, a portion of the liquid cargo is stored in the drum, and the pump cooldown that proceeds before using the main pump is performed using the liquid cargo stored in the drum, , BOG generated in the pump cool-down process may be provided to the liquid cargo storage tank.

According to the embodiment of the present invention, the flow rate discharged through the pressure control of the drum can always be maintained constant.

According to the embodiment of the present invention, it is possible to fill and discharge liquid cargo through the liquid cargo transfer line, so there is no need to implement a separate pump tower inside the storage tank, thereby simplifying the configuration and increasing price competitiveness. .

According to an embodiment of the present invention, the liquid cargo stored in the drum has a special effect that can be utilized for multiple purposes.

Effects of the present invention are not limited to the above-described effects, and effects not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the present specification and accompanying drawings.

1 is a view showing a pump tower installed in a conventional cargo hold.
2 is a view showing a floating offshore structure to which a liquid cargo transport device is applied.
3 is a view for explaining a process of loading (filling) the liquid cargo in the storage tank.
4 is a view showing a movement path of boil-off gas during a full sail.
5 is a view showing another movement path of the boil-off gas.
6 is a view for explaining a cool-down process of the main pump.
7 is a view for explaining a process of unloading a liquid cargo from the storage tank.
8 is a view showing a movement path of boil-off gas during a ballistic voyage.
9 is a view showing a configuration for adjusting the pressure of the drum in the liquid cargo transport device.
10 is a table showing a pressure curve of the water level and boil-off gas in the drum.

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings, and in the description with reference to the accompanying drawings, the same or corresponding components are given the same reference numbers regardless of the reference numerals, and duplicates thereof A description will be omitted.

2 is a view showing a floating offshore structure to which a liquid cargo transport device is applied.

As can be seen in FIG. 2 , the floating offshore structure 10 has a hull 30 comprising liquid cargo storage tanks 20 . The liquid cargo unloading in the liquid cargo storage tank 20 is made by the liquid cargo transfer device 100 installed in the hull 30 .

Here, the floating offshore structure 10 is an offshore floating production, storage and offloading (FPSO) and natural gas production and storage facility for temporarily storing or processing natural gas or crude oil when drilling is performed at sea. It may be a Floating Liquefied Natural Gas (FLNG), or a Floating Storage and Regasification Unit (FSRU), but is not limited thereto and may be a structure in which a storage tank for storing liquefied cargo is installed.

The liquid cargo transport apparatus 100 of the present invention can perform loading and unloading of liquid cargo by unifying a filling pipe and a discharge pipe, and applying a transport pressure to the liquid cargo during the unloading operation It is a device that can be transferred by pressurizing the liquid cargo stored in the liquid cargo storage tank (hereinafter referred to as the storage tank; 20) using the boil-off gas stored in the drum 120 without the configuration of an underwater transfer pump for the purpose.

The liquid cargo transfer device 10 of the present invention may be suitable for application in a case where the head pressure is low, such as a small LNG tank or a storage tank of a liquid cargo (eg, liquefied hydrogen) having a remarkably low density.

The liquid cargo transfer device 100 includes a liquid cargo transfer line 110 , a drum 120 , a filling line 130 , a pressurizing unit 200 , a cooling unit 300 , a discharge line 140 , and a main pump 150 . may include.

The liquid cargo transfer line 110 is connected to the drum 120 installed on the deck of the hull 30 through the upper part from the lower part of the storage tank 20 . A filling line 130 is connected to the liquid cargo transfer line 110 .

The drum 120 has a storage space in which the liquid cargo is stored, and has a smaller capacity than the storage tank 20 .

The pressurizing unit 200 is provided to pressurize the liquid cargo storage tank 20 so that the liquid cargo stored in the liquid cargo storage tank is supplied to the drum 120 through the liquid cargo transfer line 110 .

For example, the pressurizing unit 200 may include a compressor 220 , a gas transfer line 210 , a terminal gas line 230 , a pump gas line 240 , and a bypass line 250 . The compressor 220 is installed on the gas transfer line 210 . The compressor 220 receives BOG from the drum 120 and compresses it, and the BOG compressed by the compressor 220 (hereinafter, compressed BOG) is supplied to each storage tank 20 through a gas transfer line 210 . is provided as

The gas transfer line 210 is connected to the upper end of the storage tank 20 . The gas transfer line 210 may be used as a path for supplying compressed BOG to the storage tank 20 and a path for discharging BOG from the storage tank. A demand source supply line 212 for supplying boil-off gas to a demand source may be connected to the gas transfer line 210 . A first drum gas line 214 may be connected to the demand source supply line 212 . The first drum gas line 214 is branched from the gas transfer line 210 corresponding to the section between the compressor 220 and the drum 120 and is connected to the demand supply line 212 . The first drum gas line 214 may be connected to a first point P1 on the gas transfer line 210 corresponding to a section between the compressor and the storage tank.

A second drum gas line 216 is branched from the first drum gas line 214 , and the second drum gas line 216 is at a second point P2 where the bypass line 250 and the gas transfer line 210 join. ) can be connected to

The bypass line 250 may be connected to the gas transfer line 210 to bypass the compressor 220 in order to pressurize the boil-off gas generated in the storage tank 20 . One end of the bypass line is connected to the first point P2 on the gas transfer line in the section between the compressor and the storage tank, and the other end of the gas transfer line 210 corresponds to the section between the compressor 220 and the drum 120. It can be connected to the three points (P3). Meanwhile, the surplus BOG remaining after being supplied to a gas demander among the BOG compressed by the compressor 220 may be moved from the compressor 220 to the drum 120 through the first drum gas line 214 . As such, the first drum gas line 214 may be used as a recovery line for recovering boil-off gas, if necessary.

The exhaust line 260 is connected to the bypass line 250 . The exhaust line 260 may be connected to another demand (additional demand) that requires the boil-off gas.

A terminal gas line 230 that receives boil-off gas from a liquid cargo storage terminal (not shown) is connected to the compressor 200 . When the compressed BOG to be provided to the storage tank 20 is insufficient, the pressurizing unit 200 may receive BOG from the liquid cargo storage terminal through the terminal gas line 230 . In addition, a pump gas line 240 receiving the boil-off gas from the main pump 150 may be connected to the compressor 220 .

The discharge line 140 is connected to the bottom of the drum 120 . A main pump 150 is installed on the discharge line 140 . The main pump 150 is provided to apply a conveying pressure to the liquid cargo stored in the drum 120 .

The cooling unit 300 is provided to prevent the temperature rise of the storage tank 20 when the compressed BOG is supplied to the storage tank 20 . For example, the cooling unit 300 may include a spray nozzle 310 , a cooling supply line 320 , and an auxiliary pump 330 .

The spray nozzle 310 is installed in the upper part of the inside of the storage tank 20 to spray the liquid cargo.

The cooling supply line 320 connects the spray nozzle 310 and the drum 120 . The auxiliary pump 330 applies a conveying pressure for supplying a portion of the liquid cargo stored in the drum 120 to the spray nozzle 310 .

3 is a view for explaining a process of loading (filling) the liquid cargo in the storage tank. For reference, for convenience of explanation, the transport path of the liquid cargo is indicated by a dotted line, and the transport path of the boil-off gas is indicated by a thick solid line. And, among the valves installed in each line in FIGS. 3 to 8 , a valve with a black inside indicates a closed state, and other valves indicate an open state.

3 , the liquid cargo is stored in the storage tank 20 through the liquid cargo transfer line 110 through the filling line 130 . At this time, a portion of the liquid cargo is stored in the storage space of the drum 120 . The liquid cargo stored in the storage space of the drum 120 may be used to cool down the main pump 150 . BOG generated in the storage space of the drum 120 and BOG generated in the storage tank 20 may be provided to additional demand through the exhaust line 260 connected to the bypass line 250 .

Here, an additional consumer requires boil-off gas and can be driven using it as a raw material. For example, the additional demand may be a generator (eg, DFDG), a gas combustion unit (GCU), or a boiler (eg, a boiler generating steam), but is not limited thereto.

4 is a view showing a movement path of boil-off gas during a full sail.

For reference, for convenience of explanation, the transport path of the liquid cargo is indicated by a dotted line, and the transport path of the boil-off gas is indicated by a thick solid line.

Referring to FIG. 4 , the boil-off gas generated from the storage tank 20 during a laden voyage in which the storage tank is filled with liquid cargo passes through the gas transfer line 210 and the bypass line 250 , and the compressor 220 ) after being compressed in the consumer through the supply line 212 may be supplied to the consumer. In addition, when the amount of boil-off gas generated in the storage tank 20 is insufficient, the boil-off gas in the drum 120 may be provided. As another method, the liquid cargo may be supplied to the demand by utilizing the auxiliary pump 330 installed in the cooling supply line 320 .

For reference, the consumer may use boil-off gas (or liquefied gas) pressurized and vaporized to about 200 to 400 bar by a compressor, and may be a high-pressure engine using high-pressure boil-off gas of about 300 bar, driving a propeller It may be an engine that directly rotates the propeller shaft to do so, or an engine for generating other power.

5 is a view showing another movement path of the boil-off gas.

For reference, for convenience of explanation, the transfer path of the boil-off gas is indicated by a thick solid line.

Referring to FIG. 5 , when the amount of BOG used in the consumer is reduced due to slow operation, the surplus BOG is compressed through the compressor 220 and then through the first drum gas line 214 at the first point P1. It may be stored in the drum 120 .

6 is a view for explaining a cool-down process of the main pump.

For reference, for convenience of explanation, the transfer path of the boil-off gas is indicated by a thick solid line.

Referring to FIG. 6 , since the main pump 150 is exposed to the external atmosphere unlike the existing submersible pump installed in the storage tank, it is necessary to cool-down before carrying out the unloading operation. Cool-down of the main pump 150 is performed in advance using the liquid cargo stored in the drum 120 .

In this process, BOG generated from the main pump 150 is provided to the compressor 220 through the pump gas line 240 . In addition, the boil-off gas in the drum 120 and the right storage tank may also be provided to the compressor 220 . BOG compressed by the compressor 220 (hereinafter, compressed BOG) is supplied to the left storage tank among the two storage tanks through the gas transfer line 210 . In the storage tank on the left, the liquid cargo is transferred to the drum 120 through the liquid cargo transfer line 110 by the pressing force of the compressed boil-off gas. Accordingly, the drum 120 is supplied with the liquid cargo used for the cooling down of the main pump 150 .

7 is a view for explaining a process of unloading a liquid cargo from the storage tank. For reference, for convenience of explanation, the transport path of liquid cargo is indicated by a dotted line, and the transport path of boil-off gas is indicated by a thick solid line.

As shown in FIG. 7 , in the unloading operation, the pressurizing unit 200 presses the two storage tanks 20 , and the liquid cargo stored in the storage tank 20 by the pressing force of the compressed boil-off gas is transferred to the liquid cargo transfer line 110 . is moved to the drum 120 through the

In this pressurization process, the compressed BOG passing through the compressor 220 has a temperature at room temperature, which is higher than the liquid cargo inside the storage tank 20, and thus may cause an increase in the temperature inside the storage tank 20. In order to minimize this problem, the temperature rise inside the storage tank 20 is suppressed through the cooling unit 300 during the pressurization process. That is, when the compressed BOG is pressurized into the storage tank 20 and at the same time liquid cargo is sprayed inside the storage tank 20, the low-temperature liquid cargo cools the compressed BOG, thereby reducing the temperature increase of the storage tank 20. prevention, and it is possible to reduce the required amount of compressed BOG discharged through the compressor 220 , thereby reducing the capacity of the compressor 220 . The liquid cargo sprayed into the storage tank 20 is provided from the drum 120 .

On the other hand, the liquid cargo moved from the storage tank 20 to the drum 120 is transferred to a liquid cargo storage terminal (eg, a carrier or a storage tank on the ground) (not shown) through the discharge line 140 , at this time The liquid cargo is transferred by the main pump 150 .

8 is a view showing a movement path of boil-off gas during ballistic sailing.

For reference, for convenience of explanation, the transfer path of the boil-off gas is indicated by a thick solid line.

Referring to FIG. 8 , since the amount of BOG generated from the storage tank 20 is reduced during the ballistic voyage, BOG required for navigation may be provided from the liquid cargo stored in the drum 120 . That is, the liquid cargo of the drum 120 may be provided to an evaporator (not shown) through the supply line 320 for cooling, and then provided to a consumer.

9 is a view showing a configuration for adjusting the pressure of the drum in the liquid cargo transport device.

9, the liquid cargo transport apparatus 100 has a drum pressure control unit 1220. The drum pressure control unit 122 is configured to maintain a constant flow rate of the liquid cargo discharged through the discharge line 142. The pressure of the drum 120 is adjusted.

For example, the drum pressure adjusting unit 122 includes a water level sensing member 124 for measuring the liquid cargo level in the drum 120 , a pressure measuring member 126 for measuring the boil-off gas pressure in the drum 120 , and a water level sensing member It may include a control unit 128 that receives the measurement value from the 124 and the pressure measuring member 126 to control the BOG emission in the drum 120 .

The control unit 128 controls the vapor control valve 211 installed on the gas transfer line 210 through which the boil-off gas in the drum 120 is exhausted, the main pump 150 and the control valve 142 installed on the discharge line 140 . Each can be controlled.

The control unit 128 controls the vapor control valve to reduce the amount of BOG exhausted through the gas transfer line 210 when the liquid cargo level in the drum 120 rises higher than the preset water level and the BOG pressure in the drum 120 is low. (211) is controlled. In addition, when the liquid cargo level in the drum 120 rises above a preset water level and the BOG pressure in the drum 120 is high, the control unit 128 controls the vapor so that the amount of BOG exhausted through the gas transfer line 210 is increased. Controls the valve 211 .

As such, when the flow rate flowing into the drum 120 is greater than the flow rate going out to the discharge line 140 , the water level of the drum 120 rises, and accordingly, the pressure in the drum 120 also increases. This reduces the pressure difference between the storage tank 20 and the drum 120 , so that the flow rate flowing into the drum 120 naturally decreases. Conversely, when the water level of the drum 120 goes down, the pressure in the drum 120 is reduced and the flow rate flowing into the drum 120 increases, so that the flow rate flowing into the drum 120 and the flow rate going out can be constantly adjusted. However, the liquid cargo in the drum 120 is vaporized by the incoming heat, which is why it is pressurized in the drum 120. As shown in FIG. 10, this part applies the pressure in the drum to the water level and the pressure curve (P) of the boil-off gas. can be controlled with

The above description is merely illustrative of the technical idea of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

110: liquid cargo transfer line 120: drum
130: filling line 140: discharge line
150: main pump 200: pressurization unit
300: cooling unit

Claims (9)

a liquid cargo transfer line connected to the liquid cargo storage tank;
a drum connected to the liquid cargo transfer line and providing a space for storing liquid cargo;
a pressing unit for pressing the liquid cargo storage tank so that the liquid cargo stored in the liquid cargo storage tank is supplied to the drum through the liquid cargo transfer line; and
a discharge line connected to the lower part of the drum for unloading the liquid cargo stored in the drum and provided with a main pump for providing conveying pressure to the liquid cargo;
The pressurizing part
a compressor receiving the boil-off gas from the drum and compressing it;
a gas transfer line used as a path for supplying the boil-off gas compressed in the compressor to the liquid cargo storage tank or for discharging the boil-off gas from the liquid cargo storage tank;
and a bypass line connected to the gas transfer line by bypassing the compressor to pressurize the boil-off gas generated in the liquid cargo storage tank,
BOG generated in the liquid cargo storage tank is compressed in the compressor through the bypass line and then supplied to a gas demanding destination,
The liquid cargo transport apparatus further comprising a recovery line provided to store the remaining surplus BOG among the BOG compressed by the compressor to the gas demander in the drum. a liquid cargo transfer line connected to the liquid cargo storage tank;
a drum connected to the liquid cargo transfer line and providing a space for storing liquid cargo;
a pressing unit for pressing the liquid cargo storage tank so that the liquid cargo stored in the liquid cargo storage tank is supplied to the drum through the liquid cargo transfer line;
a discharge line connected to the lower part of the drum for unloading the liquid cargo stored in the drum and provided with a main pump for providing conveying pressure to the liquid cargo;
a drum pressure adjusting unit for adjusting the pressure of the drum to maintain a constant flow rate of the liquid cargo discharged through the discharge line;
the pressurizing part
and a compressor for receiving and compressing boil-off gas from the drum;
BOG compressed in the compressor is provided to the liquid cargo storage tank through a gas transfer line,
The drum pressure control unit
a water level sensing member for measuring the level of the liquid cargo in the drum;
a pressure measuring member for measuring the boil-off gas pressure in the drum; and
and a control unit configured to receive measurement values from the water level sensing member and the pressure measuring member to control the amount of BOG in the drum,
the control unit
a vapor control valve installed on a gas transfer line through which the boil-off gas in the drum is exhausted; and
A liquid cargo transport device for controlling the main pump and a control valve installed on the discharge line. 3. The method of claim 2,
the control unit
When the BOG pressure in the drum with respect to the liquid cargo level in the drum is lower than a preset ratio, the vapor control valve is controlled so that the amount of BOG exhausted through the gas transfer line is reduced,
When the BOG pressure in the drum with respect to the liquid cargo level in the drum is higher than a preset ratio, the vapor control valve is controlled to control the vapor control valve to increase the amount of BOG exhausted through the gas transfer line. 3. The method according to claim 1 or 2,
Further comprising a cooling unit for preventing the temperature rise of the liquid cargo storage tank when the compressed boil-off gas is supplied to the liquid cargo storage tank;
The cooling unit
a spray nozzle installed inside the liquid cargo storage tank to spray liquid cargo; and
and a supply line for cooling that connects the spray nozzle and the drum and supplies a portion of the liquid cargo stored in the drum to the spray nozzle by an auxiliary pump.
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