KR101609624B1 - Storage tank of liquefied natural gas - Google Patents

Abstract

A liquefied natural gas storage tank capable of suppressing pressure rise due to evaporation gas is provided. A liquefied natural gas (LNG) storage tank comprises: a tank body for storing LNG; An LNG injecting part connected to a pump for pumping LNG by a connecting pipe and having a first nozzle for injecting LNG into an evaporation gas area in an upper portion of the tank main body; And an LNG circulation unit connected to the branch pipe and having a second nozzle positioned below the LNG to circulate the LNG through the connection pipe and the branch pipe.

Description

{STORAGE TANK OF LIQUEFIED NATURAL GAS}

The present invention relates to a liquefied natural gas storage tank of a liquefied natural gas carrier, and more particularly to a liquefied natural gas storage tank capable of suppressing a pressure rise due to evaporative gas.

In general, natural gas is liquefied at extremely low temperatures in drilling facilities and becomes liquefied natural gas (hereinafter referred to as "LNG"), which is transported to the destination in the LNG storage tank of the carrier. LNG storage tanks are usually constructed with double insulation structure, but LNG is vaporized by boiling-off gas due to constantly shaking marine environment and heat input from the outside. Evaporation gas is a risk factor for increasing the pressure of the LNG storage tank.

A method of restricting the pressure rise of the LNG storage tank due to the evaporation gas, a method of re-liquefying the evaporated gas and returning it to the LNG storage tank, and a method of restricting the evaporation gas in the LNG storage tank to 200 And a method of maintaining the high pressure of about atmospheric pressure or less to suppress further generation of evaporative gas in the LNG storage tank.

However, the first method requires a complicated liquefaction facility and consumes a lot of power for liquefaction of evaporation gas. The second method is to increase the LNG storage tank to a considerably large thickness in order to accommodate the high-pressure evaporation gas at about 200 atmospheres. Therefore, the manufacturing cost of the LNG storage tank is increased and additional devices such as a high- need.

The present invention provides a LNG storage tank capable of suppressing an increase in the pressure of the LNG storage tank by slowing the generation rate of the evaporation gas by a simple device configuration and a control method.

A liquefied natural gas (LNG) storage tank according to an embodiment of the present invention includes a tank main body for storing LNG; An LNG injecting part connected to a pump for pumping LNG by a connecting pipe and having a first nozzle for injecting LNG into an evaporation gas area in an upper portion of the tank main body; And an LNG circulation unit connected to the branch pipe and having a second nozzle positioned below the LNG to circulate the LNG through the connection pipe and the branch pipe.

The LNG circulation section can operate when the pressure in the tank body is equal to or higher than the set pressure. When the temperature in the tank body reaches the saturation temperature, the LNG injection part can operate.

The connecting pipe can be located inside and outside the tank body, and the branch pipe can be located inside the tank body. The connection pipe may be divided into a front end connected to the pump with respect to one point and a rear end connected with the first nozzle, and a portion of the front end may be located outside the tank main body.

The LNG injection unit may include a first control valve provided at the front end portion and a second control valve provided at the rear end portion. The LNG circulation portion may include a third control valve installed in the branch pipe.

The LNG storage tank includes: a temperature sensor for measuring the LNG temperature inside the front end; The control unit may further include a control unit that receives a measurement signal from the temperature sensor and is electrically connected to the first to third control valves to control operations of the first to third control valves. The temperature sensor is installed close to the branch in the front end and can measure the LNG temperature immediately before entering the branch from the front end.

The LNG circulation part may operate before the LNG injection part operates to cool the connection pipe, and the LNG injection part may operate when the temperature of the LNG flowing through the connection pipe reaches the saturation temperature to inject the LNG into the evaporation gas area.

According to this embodiment, the temperature of the evaporation gas region can be lowered by spraying low-temperature LNG in the evaporation gas region, which is relatively higher in temperature than the LNG, so that the generation rate of the evaporation gas can be reduced. Also, by operating the LNG circulation unit before the LNG injection unit is operated to cool the connection pipe, it is possible to prevent an abrupt pressure increase that may occur at the beginning of operation of the LNG injection unit.

1 is a schematic view of a liquefied natural gas storage tank according to one embodiment of the present invention.
FIG. 2 is a flowchart showing a method of suppressing evaporation gas according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

1 is a schematic view of a liquefied natural gas storage tank according to one embodiment of the present invention.

Referring to FIG. 1, a liquefied natural gas (hereinafter referred to as LNG) storage tank 100 includes a tank main body 10 for storing LNG, a tank 10 for pumping LNG and injecting LNG into an evaporation gas area A10 above the LNG And an LNG circulation unit 30 for returning the pumped LNG back to the LNG. At this time, the LNG circulation unit 30 and the LNG injection unit 20 selectively operate.

The LNG storage tank 100 may be a storage tank installed in an LNG carrier, and the tank body 10 may be constructed in a conventional double insulation structure. Even if the tank body 10 is made of a double heat insulating structure, the LNG is vaporized by boiling-off gas due to the operating environment of the sea where the shaking is severe and the heat continuously flowing from the outside.

In the case of the LNG carrier, the evaporative gas of the LNG storage tank 100 is sent to the propulsion engine and used as propellant. When the propulsion engine is not in operation, it is sent to the combustion device and burned. However, it is best to suppress the generation of evaporative gas if the LNG carrier needs to lower the speed of entry, such as entering the terminal of the customer or passing through the canal.

The LNG injector 20 injects low-temperature LNG into the evaporation gas region A10 having a relatively higher temperature than the LNG to lower the temperature of the evaporation gas region A10, thereby slowing the generation rate of the evaporation gas. The LNG injector 20 includes a pump 21 for pumping the LNG, a first nozzle 22 for injecting the pumped LNG, a connecting pipe for connecting the pump 21 and the first nozzle 22 23).

The pump 21 is positioned below the tank main body 10 so as to be submerged in the LNG and the first nozzle 22 is located in the evaporation gas area A10 higher than the LNG water level. The first nozzles 22 are provided in a plurality of spaces with a distance therebetween, so that low-temperature LNG can be uniformly sprayed to various portions of the evaporation gas region A10.

The connection pipe 23 is positioned over the inside and the outside of the tank body 10. For example, the connection pipe 23 is composed of two vertical pipes extending vertically upward from the pump 21 and the first nozzle 22, and a horizontal pipe connecting the two vertical pipes from the outside of the tank body 10 Lt; / RTI >

The LNG circulation unit 30 includes a branch pipe 31 branched from the connecting pipe 23 and a second nozzle 32 installed at an end of the branch pipe 31. [ The branch pipe 31 branches from one point P1 of the vertical pipe connected to the first nozzle 22 and vertically extends toward the lower portion of the tank main body 10 so that most of the branch pipe 31 is submerged in the LNG. The second nozzle 32 is located at the end of the branch pipe 31 which is locked to the LNG.

The connection pipe 23 is divided into a front end portion 231 located between the pump 21 and the branch point P1 and a rear end portion 232 located between the branch point P1 and the first nozzle 22 . The LNG circulation unit 30 circulates the low temperature LNG through the front end portion 231 of the connection pipe 23 and the branch pipe 31 before the LNG injection unit 20 operates, Thereby cooling the portion 231.

A part of the connecting pipe 23 is located outside the tank body 10 and therefore has a higher temperature than the inside of the tank body 10. [ It is assumed that the heat energy of the connection pipe 23 and the mechanical energy of the pump 21 in the initial operation process of pumping the LNG and injecting the LNG into the evaporation gas area A10 Thermal energy due to the loss is transferred to the LNG and a part of the LNG is vaporized. This leads to a problem that the pressure of the tank main body 10 suddenly rises at the beginning of the LNG injection.

The LNG storage tank 100 according to the present embodiment includes the LNG injection unit 20 and the LNG circulation unit 30 to operate the LNG circulation unit 30 before the LNG injection unit 20 operates, The low temperature LNG is circulated to the inside of the pipe 23 for a predetermined time. Accordingly, since the LNG is injected after sufficiently cooling the connecting pipe 23, the problem of pressure increase due to the LNG vaporization can be solved at the initial stage of LNG injection.

The LNG injector 20 is connected to the first control valve 24 provided at the front end portion 231 of the connection pipe 23 and the second control valve 25 provided at the rear end portion 232 of the connection pipe 23 . The first control valve 24 may be located in a horizontal tube outside the tank body 10. [ The LNG circulation unit 30 includes a third control valve 33 installed in the branch pipe 31. The third control valve 33 is located in the evaporation gas area A10 higher than the LNG level.

The LNG storage tank 100 includes a temperature sensor 41 for measuring the LNG temperature inside the connection pipe 23, a pressure sensor 42 for measuring the pressure of the tank body 10, a temperature sensor 41, And a control unit 50 electrically connected to the sensor 42 and the first to third control valves 24, 25 and 33. The control unit 50 controls the operation of the first to third control valves 24, 25 and 33 according to the measurement signals of the temperature sensor 41 and the pressure sensor 42. [

The temperature sensor 41 measures the LNG temperature just before the branch pipe P1 of the front end portion 231 of the connecting pipe 23 and flows into the branch pipe 31 through the front end portion 231. [ The temperature sensor 41 outputs a temperature sensing signal to the control unit 50 and the pressure sensor 42 outputs a pressure sensing signal to the control unit 50.

The control unit 50 opens the first control valve 24 and the third control valve 33 to circulate the LNG when the pressure of the tank main body 10 rises due to the evaporated gas, When the LNG temperature reaches the saturation temperature of the LNG, the third control valve 33 is closed and the second control valve 25 is opened to inject the LNG into the evaporation gas area A10. The operation of the LNG storage tank 100 will be described in detail with reference to FIG.

FIG. 2 is a flowchart showing a method of suppressing evaporation gas according to an embodiment of the present invention.

1 and 2, the method for suppressing evaporation gas includes a first step (S10) of measuring the pressure of the tank main body 10 and an LNG circulation part 30 operating when the measured pressure is equal to or higher than the set pressure, A second step S20 for cooling the pipe 23, a third step S30 for measuring the LNG temperature in the connection pipe 23, and a third step S30 for measuring the temperature of the LNG circulation part 30 And a fourth step S40 in which the operation of the LNG injecting unit 20 is stopped and the LNG is injected into the evaporation gas area A10.

In the first step S10, the pressure sensor 42 measures the pressure of the tank main body 10 and outputs a measurement signal to the control unit 50. [

In the second step S20, when the pressure of the tank main body 10 exceeds the set pressure due to the generation of the evaporative gas, the pump 21 operates and the control unit 50 controls the first control valve 24 and the third control The valve 33 is opened to operate the LNG circulation unit 30. [

The LNG pumped by the pump 21 flows through the front end portion 231 of the connection pipe 23 and the inside of the branch pipe 31 and is again injected into the LNG through the second nozzle 32 and circulated. Due to the LNG circulation, the front end portion 231 outside the tank main body 10 is sufficiently cooled by the low temperature LNG.

In the third step S30, the temperature sensor 41 measures the temperature of the LNG flowing in the front end portion 231 of the connection pipe 23, and outputs a measurement signal to the control unit 50. [ The LNG temperature measurement using the temperature sensor 41 is performed simultaneously with the second step S20.

During the initial operation of the LNG circulation unit 30, the thermal energy of the front end 231 and the thermal energy due to the mechanical loss of the pump 21 are introduced into the LNG. Therefore, the measured temperature of the LNG is higher than the saturation temperature of the LNG I have. As the LNG circulation is repeated, the measured temperature of the LNG gradually becomes closer to the saturation temperature.

In the fourth step S40, when the sensed temperature of the LNG reaches the saturation temperature of the LNG, the control unit 50 closes the third control valve 33 and opens the second control valve 25 to supply the pumped LNG to the first nozzle (22). As a result, low-temperature LNG is injected into the evaporation gas region A10, which is relatively higher in temperature than the LNG, thereby lowering the temperature of the evaporation gas region A10 and relaxing the generation rate of the evaporation gas.

As described above, in the method of suppressing the evaporation gas according to the present embodiment, a predetermined amount of LNG is initially circulated without injecting the pumped LNG directly into the evaporation gas region A10, thereby reaching the saturation temperature of the LNG, It is possible to effectively suppress the rapid pressure rise that may occur at the beginning of the operation of the LNG jetting section 20 by injecting the LNG.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

100: LNG storage tank 10: tank body
A10: Evaporation gas area 20: LNG distributing part
21: pump 22: first nozzle
23: connectors 24, 25: first and second control valves
30: LNG circulation part 31: Branch engine
32: second nozzle 33: third control valve
41: Temperature sensor 42: Pressure sensor
50:

Claims (9)

A tank body for storing liquefied natural gas (LNG);
A pump for pumping LNG; a first nozzle for injecting the LNG pumped from the pump into an evaporation gas area above the LNG; and a connection unit for connecting the pump and the first nozzle, An LNG injection part having a pipe; And
A branch pipe branching toward the LNG from one point of a portion of the connection pipe that contacts the first nozzle in the tank main body and the whole branch is located inside the tank main body; And an LNG circulation unit for circulating the LNG pumped by the pump through the connection pipe and the branch pipe,
The LNG circulation unit operates before the operation of the LNG injection unit to cool a portion of the connection pipe located outside the tank body,
Wherein the LNG injection unit operates when the temperature of the LNG flowing through the connection pipe reaches a saturation temperature to inject LNG into the evaporation gas area. The method according to claim 1,
Wherein the LNG circulation section operates when the pressure in the tank body is equal to or higher than a set pressure. The method according to claim 1,
And an LNG storage tank in which the LNG injection unit operates when the temperature in the tank body reaches a saturation temperature. delete The method according to claim 1,
The connection pipe is divided into a front end connected to the pump and a rear end connected to the first nozzle with respect to the one point,
And a part of the front end portion is located outside the tank body. 6. The method of claim 5,
Wherein the LNG injector includes a first control valve installed at the front end and a second control valve installed at the rear end,
And the LNG circulation unit includes a third control valve installed in the branch pipe. The method according to claim 6,
A temperature sensor for measuring the LNG temperature inside the front end; And
Further comprising a control unit that is provided with a measurement signal from the temperature sensor and is electrically connected to the first to third control valves to control operations of the first to third control valves. 8. The method of claim 7,
Wherein the temperature sensor measures a temperature of the LNG immediately before the branch pipe is introduced into the branch pipe from the front end of the LNG storage tank. delete

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