KR20210059155A - Liquefied nitrogen providing system used for testing liquefied natural gas cargo tank of floating type structure - Google Patents

Abstract

A liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure is disclosed. The liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure according to an embodiment of the present invention comprises: a buffer tank that supplies liquid nitrogen to an LNG cargo hold for testing of an LNG cargo hold of an offshore structure located on shore; and a control unit for controlling the amount of liquid nitrogen injected into the LNG cargo hold so that the internal temperature of the LNG cargo hold is maintained within a set temperature range for a set time.

Description

LIQUEFIED NITROGEN PROVIDING SYSTEM USED FOR TESTING LIQUEFIED NATURAL GAS CARGO TANK OF FLOATING TYPE STRUCTURE}

The present invention relates to a liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure.

After the LNG cargo hold of the offshore structure is built, the first integrity test for the secondary barrier is carried out on land. Thereafter, the offshore structure is moved offshore, and LNG received through LNG bunkering or produced directly from the offshore is injected into the LNG cargo hold to perform a cool down operation. After the cold shock is generated by the cooldown operation, a second integrity test is performed on the secondary barrier of the LNG cargo hold.

In this way, after performing the first integrity test on the secondary barrier on land, the offshore structure must be moved to offshore in order to perform the secondary integrity test on the secondary barrier.

However, in order to perform the LNG cargo hold test work offshore, the work approval process is complicated and expensive. In addition, there is a problem in that it is difficult to quickly respond to an emergency situation in offshore.

An embodiment of the present invention is to provide a liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure that supplies liquefied nitrogen from a yard to an LNG cargo hold so that the LNG cargo hold test work of an offshore structure is performed on shore.

According to an aspect of the present invention, a buffer tank for supplying liquefied nitrogen to the LNG cargo holds for testing an LNG cargo hold of an offshore structure located on shore; And a control unit for controlling the amount of liquefied nitrogen injected into the LNG hold so that the internal temperature of the LNG hold is maintained within a set temperature range for a set time. I can.

It may further include a tank lorry that receives the liquid nitrogen from the liquid nitrogen production unit and moves to a yard where the buffer tank is provided to supply the liquid nitrogen to the buffer tank.

A liquid nitrogen injection pipe connecting the buffer tank and the LNG cargo hold, an injection part for cooling down the LNG cargo hold by injecting the liquid nitrogen supplied through the liquid nitrogen injection pipe into the LNG cargo hold, and the liquid nitrogen A control valve disposed in the injection pipe and a temperature sensor for measuring a temperature inside the LNG cargo hold, wherein the control unit controls the degree of opening/closing of the control valve based on the measured temperature value, and The amount of liquid nitrogen injected into the LNG cargo hold can be adjusted.

The control unit may adjust the amount of liquid nitrogen injected into the LNG cargo hold so that the internal temperature of the LNG cargo holds -158°C±5°C.

The liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure according to an embodiment of the present invention may supply liquid nitrogen from a yard to the LNG cargo hold so that the LNG cargo hold test of the offshore structure is performed on shore.

The effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

1 is a flow chart of an LNG cargo hold test process of an offshore structure performed on shore according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating a process of testing an LNG cargo hold of an offshore structure performed on offshore following the LNG cargo hold test of FIG. 1.
3 is a block diagram showing a liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments introduced below are provided as examples in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments described below and may be embodied in other forms. In order to clearly describe the present invention, parts irrelevant to the description are omitted from the drawings, and in the drawings, the width, length, thickness, etc. of components may be exaggerated and expressed for convenience. The same reference numerals represent the same elements throughout the specification.

1 is a flow chart of an LNG cargo hold test process of an offshore structure performed on shore according to an embodiment of the present invention.

The LNG cargo hold test processes shown in FIG. 1 are performed on the LNG cargo hold of an offshore structure in a state in which the offshore structure is placed on shore.

Offshore structures according to an embodiment of the present invention include structures such as Floating Liquefied Natural Gas (FLNG), Floating Storage Regastification Unit (FSRU), and Floating Storage Unit (FSU) that do not have self-navigation capability, as well as LNG carriers with self-navigation capability. It may also include ships.

The term onshore used in an embodiment of the present invention means land and includes a yard that means a shipyard. In other words, onshore is used in a broader sense than yards. When the LNG cargo hold test is performed at the yard, it means that the LNG cargo hold test is performed in the shipyard where the offshore structure is built. Includes what is being done.

Hereinafter, in an embodiment of the present invention, it is described that the LNG cargo hold test process of an offshore structure is performed on shore, but it may be performed in a yard (shipyard) among on shores.

Referring to FIG. 1, first, a primary barrier global test (PBGT) of an LNG cargo hold of an offshore structure is performed on shore (S201). In this process (S201), an ammonia reactant is applied to the welding part of the primary barrier, ammonia gas is filled in the space between the primary and secondary barriers, and the integrity of the primary barrier is based on whether or not the ammonia reactant is discolored. It can be made in the process of judging. For example, if a groove is formed in the welding part of the primary barrier and the ammonia reactant applied to the welding part of the primary barrier reacts with the ammonia gas filled between the primary and secondary barriers and discolors, the primary barrier is judged to be defective. I can.

Next, the first secondary barrier tightening test (SBTT) of the LNG cargo hold of the offshore structure is performed on the shore (S202). In this process (S202), a different pressure is applied by filling with nitrogen gas to the lower insulating layer (IS) of the secondary barrier and the upper insulating layer (IBS; Inter Barrier Space) of the secondary barrier. It may consist of a process of measuring a pressure change value between the lower insulating layer of the barrier and the upper insulating layer of the secondary barrier, and determining whether the secondary barrier is sound based on the measured pressure change value. In this case, the pressures of the lower insulating layer of the secondary barrier and the upper insulating layer of the secondary barrier may be measured by a pressure gauge (not shown) installed in the corresponding space, respectively. For example, when the pressures of the lower insulating layer of the secondary barrier and the upper insulating layer of the secondary barrier are measured equal to each other, the secondary barrier may be determined to be defective.

Next, a pipe cold test is performed on a pipe that is connected to an LNG cargo hold of an offshore structure on the shore to perform LNG loading or unloading (S203). This process (S203) may consist of a process of passing the refrigerant through the pipe and measuring the amount of contraction and expansion of the pipe by a displacement measuring device (not shown). Here, the refrigerant may include liquid nitrogen. The pipe may be a pipe connected to the filling pipe and the discharge pipe of the pump tower to perform LNG loading or unloading, and a pipe cold test may be performed while the pipe is installed on a ship deck. If the amount of contraction and expansion of the pipe measured by the displacement meter is within the allowable range, it can be determined as normal.

Next, a cool-down operation for the interior of the LNG cargo hold of the offshore structure is performed on the shore (S204). This process (S204) may be performed using a refrigerant other than LNG, and liquefied nitrogen may be used as in the above-described pipe cold test. When liquefied nitrogen comes into contact with the LNG cargo hold at room temperature, most of it vaporizes immediately and can cause convection inside the LNG cargo hold. This process (S204) may include a process of controlling the internal temperature of the LNG cargo container to maintain -158°C±5°C while spraying liquid nitrogen into the LNG cargo container at room temperature.

Next, a warm-up operation for raising the internal temperature of the LNG cargo hold of the offshore structure to room temperature is performed on the shore (S205). This process (S205) may consist of a process of raising the temperature inside the LNG cargo hold by the heater 180 (see FIG. 3), but heating the fluid inside the LNG cargo hold by the heater 180 and injecting it back into the LNG cargo hold. .

Next, the fluid inside the LNG cargo hold of the offshore structure is discharged from the onshore, dry air is injected into the LNG cargo hold, and then visual inspection of the inside of the LNG cargo hold is performed (S206). When the temperature inside the LNG cargo container is raised to room temperature by the above-described heater 180, most of the gaseous nitrogen is present inside the LNG cargo container. Therefore, since the operator must enter the LNG cargo hold for visual inspection, nitrogen inside the LNG cargo hold is discharged and dry air at room temperature (20% oxygen concentration) is injected into the LNG cargo hold.

Next, a second secondary barrier integrity test of the LNG cargo hold of the offshore structure is performed on the shore (S207). In this process (S207), a different pressure is applied by filling the lower insulating layer of the secondary barrier and the upper insulating layer of the secondary barrier with nitrogen gas, and a pressure change value between the lower insulating layer and the upper insulating layer is measured after a set time, It may be performed as a process of determining whether or not the secondary barrier is sound based on the measured pressure change value.

When the LNG cargo hold is of the Mark-III type, unlike the primary barrier, the secondary barrier is not constructed by welding, but is constructed by adhesive. As described above, the reason that the secondary barrier integrity test is performed twice in the first and second phases is that after the first secondary barrier integrity test when drying the LNG cargo, the inside of the LNG cargo holds When liquefied nitrogen is injected, the LNG cargo container undergoes a rapid temperature change (hereinafter referred to as cold shock). At this time, since the secondary barrier materials in the LNG cargo hold cause shrinkage and relaxation, it is necessary to check the integrity of the secondary barrier through a secondary barrier integrity test once more.

That is, the above-described first secondary barrier integrity test process (S202) is performed under the condition that the LNG cargo hold drying process is finished, and the second secondary barrier integrity test process (S207) is performed under the condition that the LNG cargo holds cold shock. do. In an embodiment of the present invention, the inside of the LNG cargo hold is cooled down by spraying liquid nitrogen in the process S204 as described above, but a cold shock is applied while maintaining the internal temperature at -158°C±5°C for a set period of time (for example, 22 hours). I can.

As described above, according to the exemplary embodiment of the present invention, cost reduction and work efficiency may be improved by performing the LNG cargo hold test process of an offshore structure on shore. In particular, it is possible to increase the simplicity, stability, and efficiency of work, and to speed up the work schedule by performing large-scale test tasks that had to be performed offshore in the past.

In addition, the LNG cargo hold test process (S201 to S207) of the offshore structure described above may be performed in a yard (shipyard). That is, the above-described process (S201 to S207) may be performed in a shipyard in which offshore structures are built during onshore, and in this case, the movement of offshore structures is minimized, thereby reducing cost and increasing the efficiency of test work.

As described in Fig. 1, after performing the test work on the LNG cargo hold at the onshore, offshore structures without self-navigation capability (e.g., FLNG) are offshore, and offshore structures with self-navigation capability (e.g., LNG carriers) are at the onshore terminal. The remaining LNG cargo hold tests can be performed. Hereinafter, a description will be given by taking FLNG as an offshore structure without self-navigation capability and an LNG carrier as an offshore structure with self-navigation capability.

FIG. 2 is a flowchart illustrating a process of testing an LNG cargo hold of an offshore structure performed on an offshore following the LNG cargo hold test of FIG. 1.

Referring to FIG. 2, for example, in the case of FLNG, in a state in which FLNG is placed on the offshore, LNG is filled in the LNG cargo hold and a pumping test is performed on the pump inside the LNG cargo hold (S208). At this time, the pump may be a pump for offloading LNG installed in the pump tower, and the test may be performed while the LNG is filled inside the LNG cargo hold.

In the case of FLNG, after producing LNG offshore, the produced LNG is filled inside the LNG cargo hold, and a pumping test for a pump (not shown) provided inside the LNG cargo hold can be performed immediately. In addition, as another example, after receiving LNG by the LNG bunkering method, the FLNG may perform a pumping test on a pump provided inside the LNG cargo hold.

Next, a test of offloading the LNG inside the LNG cargo hold to another LNG vessel using the loading arm on the offshore is performed (S209).

In the case of FLNG without the above-described self-portability, the processes S208 and S209 were performed offshore, but in the case of LNG carriers, after placing the LNG carrier at the onshore terminal, LNG was filled in the LNG cargo hold, and a pumping test for the pump inside the LNG cargo was carried out. You can do it.

Then, a test of offloading the LNG inside the LNG cargo hold to another LNG vessel using the loading arm at the terminal may be performed.

3 is a block diagram showing a liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure according to an embodiment of the present invention.

Referring to FIG. 3, a liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure according to an embodiment of the present invention is a liquid nitrogen used for testing the LNG cargo hold 101 of an offshore structure 100 located on the shore of FIG. Is supplied by onshore.

Such a liquid nitrogen supply system receives liquid nitrogen from the liquid nitrogen production unit 105 that produces liquid nitrogen, and is moved to the buffer tank 120 to supply liquid nitrogen to the buffer tank 120, and the LNG cargo tank The buffer tank 120 for supplying liquid nitrogen to 101 and the amount of liquid nitrogen injected into the LNG container 101 so that the internal temperature of the LNG container 101 is maintained within the set temperature range for a set time. It includes a control unit 130.

In addition, the liquefied nitrogen supply system includes a liquid nitrogen injection pipe 140 connecting the buffer tank 120 and the LNG cargo container 101, and the liquefied nitrogen supplied through the liquefied nitrogen injection pipe 140 into the LNG cargo storage 101. It may include an injection unit 150 to inject to, a control valve 160 disposed in the liquid nitrogen injection pipe 140, and a temperature sensor 170 that measures a temperature in the LNG cargo hold 101.

In addition, the liquid nitrogen supply system is one of a safety valve (193, Safety Valve) and a safety device (195, Safety System) for emergency situations and abnormal conditions in the liquid nitrogen injection pipe 140. The ideal can be prepared.

Hereinafter, each component will be described in detail.

The liquefied nitrogen production unit 105 may be manufactured by a gas specialized company. The liquid nitrogen produced by the liquid nitrogen production unit 105 is transported to the location where the offshore structure 100 of the onshore is located while being stored in the tank lorry 110.

The buffer tank 120 may be provided in a movable trailer type, and may receive liquefied nitrogen from the tank lorry 110 and stably supply liquefied nitrogen to the LNG cargo hold 101 of the offshore structure 100. Like the tank lorry 110, the buffer tank 120 may be transported to a location where the onshore offshore structure 100 is located. Although not shown, facilities such as a cryogenic pump, a vaporizer, and a mixer are provided in the buffer tank 120 to discharge liquefied nitrogen toward the LNG cargo hold 101.

The control unit 130 controls the degree of opening and closing of the control valve 160 based on the temperature value measured by the temperature sensor 170 to determine the amount of liquefied nitrogen injected by the injection unit 150 into the LNG cargo hold 101. Adjust. For example, the control unit 130 may control the degree of opening/closing of the control valve 160 so that the temperature inside the LNG cargo window 101 is adjusted in the range of -158°C±5°C. Through this, the internal temperature of the LNG cargo container 101 may be maintained at an approximately LNG temperature level (approximately -163°C), and a test operation using liquid nitrogen instead of LNG may be performed on shore when testing the LNG cargo container. In other words, since the liquid nitrogen is maintained at the LNG temperature level, the same effect as the cargo hold test performed using LNG can be achieved.

Specifically, when cooling down the inside of the LNG cargo container 101, when liquid nitrogen having approximately -195°C is injected into the LNG cargo container 101 at room temperature, the temperature of the LNG cargo container 101 is gradually lowered. When the liquid nitrogen comes into contact with the LNG cargo hold 101 at room temperature, most of the liquid nitrogen is vaporized immediately and may cause a convection phenomenon inside the LNG cargo hold 101. At this time, when adjusting the speed of lowering the temperature of the LNG cargo container 101 according to the amount of liquid nitrogen injected, if the temperature of the LNG cargo container 101 decreases too rapidly, a great deal of pressure may be applied to the components of the LNG cargo container 101. Therefore, it is possible to control the injection amount of liquid nitrogen at a preset speed.

Liquefied nitrogen is injected toward the inner wall of the LNG cargo hold 101 at room temperature, and then the temperature rises and can be converted into a gaseous state immediately. When the cooling down operation for the inside of the LNG cargo hold 101 is continued, it reaches approximately -158°C, and the injection unit 150 may stop spraying of liquid nitrogen from this point. At this time, the controller 130 closes the control valve 160 based on the temperature value measured by the temperature sensor 170, so that the injection of liquid nitrogen by the injection unit 150 may be stopped.

In addition, the control unit 130 may maintain the temperature fluctuation range of the inside of the LNG cargo hold 101 for 22 hours according to the preset cooldown condition of the cargo hold to be -158 °C ± 5 °C. That is, after the injection of liquid nitrogen into the LNG cargo hold 101 is stopped, the temperature inside the LNG cargo hold 101 gradually increases as time passes, and the control unit 130 is measured by the temperature sensor 170. Based on the set temperature value, the control valve 160 is opened so that liquefied nitrogen is injected into the LNG cargo hold 101 by the injection unit 150 little by little, for 22 hours according to the preset cooldown condition of the cargo hold. The temperature fluctuation range can be maintained at -158℃±5℃.

The liquefied nitrogen injection pipe 140 supplies liquefied nitrogen supplied from the buffer tank 120 to the LNG cargo hold 101 and is provided to withstand cryogenic liquefied gas. The liquid nitrogen injection pipe 140 may be transported together with the buffer tank 120 to a location where the offshore structure 100 of the onshore is located. As described above, the tank lorry 110, the buffer tank 120, and the liquid nitrogen injection pipe 140 may be provided to be movable, so that the test work of the LNG cargo hold 101 of the offshore structure 100 is performed anywhere on the shore, In other words, it can be performed not only at the shipyard, but also at other berthing places outside it.

The injection unit 150 may include a nozzle for injecting liquid nitrogen supplied through the liquid nitrogen injection pipe 140 into the LNG cargo hold 101.

In addition, the control valve 160 is disposed in the liquid nitrogen injection pipe 140 to adjust the flow rate of the liquid nitrogen supplied to the LNG cargo hold 101.

The temperature sensor 170 measures the temperature inside the LNG cargo container 101 that changes as liquefied nitrogen is injected into the interior of the LNG cargo container 101.

The safety valve 193 and the safety device 195 can protect the facility against an abnormal condition caused by an overpressure of a supply facility (liquid nitrogen supply system) due to an interruption in supply of liquid nitrogen or an emergency situation. have.

At least one of the safety valve 193 and the safety device 195 may be disposed at one or more of the front and rear ends of the control valve 160 of the liquid nitrogen injection pipe 140.

The safety valve 193 may include, for example, a Pressure Relief Valve (PRV) for facility overpressure and a Pressure Vacuum Valve (PVV) for low pressure (vacuum) phenomenon.

In addition, the safety device 195 may include one or more of means such as an alarm for an abnormal situation, automatic supply and stop.

For example, the above-described facility overpressure phenomenon may occur in piping and facilities that supply liquid nitrogen when liquid nitrogen is supplied to the cargo hold (main ship) by using a transport means such as a pump, and when supply and demand of the cargo hold (main ship) is impossible due to an emergency situation. . In addition, the overpressure phenomenon may be caused by a surge caused by sudden valve operation or operation change during normal operation. In addition, when the cargo hold (main ship) cannot be supplied for a long period of time, the overpressure may occur when the supply piping and the operating range of the corresponding facility are out of range due to vaporization of liquid nitrogen in the supply facility.

In addition, the above-described low pressure (vacuum) phenomenon may occur when the flow rate range that can be supplied from the liquid nitrogen supply facility to the ship is exceeded, or may occur when the transfer equipment such as a pump is operated in a situation where the liquid nitrogen is insufficient in the liquid nitrogen supply facility.

In an embodiment of the present invention, it is possible to effectively prepare for the above-described overpressure phenomenon and low pressure (vacuum) phenomenon through the safety valve 193 and the safety device 195.

In this way, by the liquid nitrogen supply system according to an embodiment of the present invention, liquid nitrogen instead of LNG can be injected into the LNG cargo hold 101 of the offshore structure 100 while maintaining the LNG temperature level, so that the offshore structure The test work on the LNG cargo hold of (100) can be carried out effectively.

In the above, specific embodiments have been illustrated and described. However, the present invention is not limited to the above-described embodiments, and those of ordinary skill in the art to which the invention pertains can perform various changes without departing from the gist of the technical idea of the invention described in the following claims. I will be able to.

100: ship 101: LNG cargo hold
105: liquid nitrogen production unit 110: tank lorry
120: buffer tank 130: control unit
140: liquid nitrogen injection pipe 150: injection part
160: control valve 170: temperature sensor
180: heater

Claims (3)

A buffer tank for supplying liquid nitrogen to the LNG hold for testing the LNG hold of offshore structures located on shore; And
A liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure comprising a; a control unit for controlling the amount of liquid nitrogen injected into the LNG hold so that the internal temperature of the LNG hold is maintained within a set temperature range for a set time. The method of claim 1,
A liquid nitrogen supply system for testing an LNG cargo hold of an offshore structure further comprising a tank lorry receiving the liquid nitrogen from the liquid nitrogen production unit and moving to a yard where the buffer tank is provided to supply the liquid nitrogen to the buffer tank. The method of claim 1,
A liquid nitrogen injection pipe connecting the buffer tank and the LNG cargo hold,
An injection unit for injecting the liquid nitrogen supplied through the liquid nitrogen injection pipe into the LNG cargo hold to cool down the LNG cargo hold;
A control valve disposed in the liquid nitrogen injection pipe,
Further comprising a temperature sensor for measuring the temperature inside the LNG cargo hold,
The control unit controls the degree of opening and closing of the control valve based on the measured temperature value to control the amount of liquefied nitrogen injected into the LNG cargo hold by the injection unit. .
[Claim 4]
The method of claim 3,
The control unit controls the amount of liquefied nitrogen injected into the LNG hold so that the internal temperature of the LNG hold is maintained at -158℃±5℃.

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