JP2001056096A - Prevention method and device against forming liquid in lng tank into heavy gravity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form light gravity the liquefied natural gas in LNG tank to reduce its heating value. SOLUTION: This device is provided with an LNG tank 1 for storing a liquefied natural gas, a heater 9 for heating one part of the liquefied natural gas sent from LNG tank 1 to a carburetor 8, a decompressor 10 for decompressing the heated liquefied natural gas, a flash drum 11 for separating a light gravity gas with a low heating value from the liquefied natural gas to the vaporized light gas and the heavy gravity gas with a high heating value of a liquid by heating and decompressing, a condenser 7 for returning the light gravity gas to LNG tank 1 after liquefying by the cool heat of the other liquefied natural gas sent from LNG tank 1 to the carburetor 8, and lines 5, 6 for sending out the heavy gravity gas to the carburetor 8 after mixing to the other liquefied natural gas liquefied the light gravity gas so as to be in an allowable heating value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LNG for preventing the heat generation of liquefied natural gas in an LNG tank from increasing.
The present invention relates to a method and apparatus for preventing heavy liquid in a tank.

[0002]

2. Description of the Related Art Generally, ethane is mainly composed of methane,
Natural gas containing propane and butane is cooled to −162 ° C. or lower and stored in a LNG tank as a natural liquid gas (LNG) as a liquefied fuel.

[0003] When liquefied natural gas in an LNG tank is stored for a long period of time or when stored in a small LNG tank, methane in the liquefied natural gas is gradually vaporized by external heat (BOG). ), The vaporized gas is constantly discharged out of the system of the LNG tank.

[0004] Therefore, the liquefied natural gas in the LNG tank evaporates a light component having a low calorific value and a heavy component having a high calorific value remains. Nevertheless, there has been a problem that the total heat generation of the liquefied natural gas in the LNG tank increases, that is, the liquid in the LNG tank becomes heavier.

For this reason, measures have been taken such that the vaporized gas vaporized by external heat is again liquefied and returned to the LNG tank.

[0006]

However, when the vaporized gas is returned to the liquefied LNG tank again, the calorific value can be maintained substantially constant so as to prevent the liquefied natural gas from becoming heavier. There has been a problem that it is not possible to reduce the calorific value of liquefied natural gas to a lighter state so as to prevent the heavierization of natural gas in advance.

An object of the present invention is to provide a method and apparatus for preventing the liquid in an LNG tank from being heavier in order to reduce the calorific value of the liquefied natural gas in the LNG tank to a lighter state.

[0008]

According to the method of the present invention for preventing the liquid in the LNG tank from becoming heavier, a part of the liquefied natural gas sent from the LNG tank to the vaporizer is heated and reduced in pressure to reduce the calorific value. The low light components are vaporized and separated, and the light components are
The liquefied natural gas sent from the LNG tank to the vaporizer is liquefied by the cold heat and returned to the LNG tank, and the heavy component having a high calorific value from which the light component is removed is reduced to within the allowable calorific value. The mixture is mixed with other liquefied natural gas and sent to a vaporizer.

Further, in the method for preventing the liquid in the LNG tank from being heavier according to the present invention, the separation ratio of the light components may be adjusted by changing the temperature of the temperature rise and the pressure of the reduced pressure.

An apparatus for preventing heavy liquid in an LNG tank according to the present invention comprises: an LNG tank for storing liquefied natural gas;
A heater that raises the temperature of a portion of the liquefied natural gas sent from the G tank to the vaporizer, a decompressor that depressurizes the liquefied natural gas that has been heated, and a lighter that has a lower calorific value from the liquefied natural gas by raising and lowering the temperature A flash drum which separates the light component into a light component that has been vaporized and a heavy component having a high calorific value of the liquid;
A condenser that is liquefied by the cold heat of another liquefied natural gas sent from the NG tank to the vaporizer and returned to the LNG tank; and another liquefied natural gas that liquefies the light fraction so that the heavy fraction falls within the allowable calorific value. And a line for mixing the gas with the gas and sending it to the vaporizer.

When the liquefied natural gas in the LNG tank is sent out to the vaporizer, a part of the liquefied natural gas to be sent out is heated by a heater and then decompressed by a decompressor, and then is discharged from the liquefied natural gas by a flash drum. Separating the light component that has vaporized the light component with low calorific value and the heavy component with high calorific value at an appropriate ratio,
The light component is liquefied by the cold heat of other liquefied natural gas sent from the LNG tank to the vaporizer and returned to the LNG tank, and the heavy component having a high calorific value from which the light component has been removed is within the allowable calorific value. The light components are mixed with other liquefied natural gas and sent to a vaporizer.

As described above, the light portion of the liquefied natural gas sent out from the LNG tank to the vaporizer is returned to the LNG tank, so that the entire composition of the liquefied natural gas in the LNG tank can be changed to be lightened. , Resulting in LNG
The liquefied natural gas in the tank can be prevented from being heavier in advance. In addition, the liquefied natural gas from which the light components are separated at an appropriate ratio is mixed with other liquefied natural gas obtained by liquefying the light components and generates an allowable calorific value. Liquefied natural gas can be used normally without sending natural gas to the vaporizer.

[0013] If the separation ratio of the light components is adjusted by changing the temperature for raising the temperature and the pressure for reducing the pressure, the amount of the light components to be returned to the LNG tank can be changed, so that the overall composition of the liquefied natural gas is changed to an appropriate state. can do.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an embodiment of a heavy-duty preventing device used in the method for preventing heavy-duty liquid in an LNG tank according to the present invention.

LN in which liquefied natural gas is stored as internal liquid
The G tank 1 discharges vaporized gas (BOG) out of the system.
It has an OG line 2 and a delivery line 4 for delivering natural liquid gas via an LNG pump 3.

The delivery line 4 is branched at an intermediate position into two, a first delivery line 5 of a main line and a second delivery line 6 of a sub line. The first delivery line 5 is connected via a condenser 7 to a vaporizer. The second delivery line 6 is connected to a flash drum 11 via a heater 9 using a heat medium and a pressure reducing device 10 of a pressure reducing valve.

The second delivery line 6 includes a heater 9 and a condenser 7
The temperature controller 12 is connected to a flow control valve 13 that controls the flow rate of the heat medium flowing in the heater 9.

The flash drum 11 has a structure for separating liquefied natural gas into a gas phase and a liquid phase. The flash drum 11 has a gas line 14 on the gas phase side and a liquid line 15 on the liquid phase side.

The gas line 14 of the flash drum 11
Is connected to a condenser 7 through which the first delivery line 5 passes, where the first delivery line 5 is connected to the cooling side 16 of the condenser 7 and the gas line 14 is connected to the condensation side 17 of the condenser 7. Connected to each other.

A connection line 18 is provided on the condensation side 17 of the condenser 7.
And a return line 21 connected to the LNG tank 1 via a pressure-reducing valve 20.

On the other hand, the liquid line 15 of the flash drum 11 is connected via a heavy liquid pump 22 to the first delivery line 5 between the condenser 7 and the vaporizer 8. Is provided in the city as a city gas or the like.

The BOG line 2 for discharging the vaporized gas from the LNG tank 1 may be connected to a delivery line 4 on the discharge side of the vaporizer 8 via a compressor (not shown).
You may make it emit to outside air as it is, and burn it.

The operation of the embodiment of the present invention will be described below.

The liquefied natural gas in the LNG tank 1 is supplied to the vaporizer 8
Liquefied natural gas is delivered to the delivery line 4 by the LNG pump 3 and sent to the first delivery line 5 of the main line.
And to the second delivery line 6 of the sub line. Here, most of the liquefied natural gas is delivered to the first delivery line 5, and part of the liquefied natural gas is delivered to the second delivery line 6.

The liquefied natural gas in the first delivery line 5 is delivered to the vaporizer 8 through the cooling side 16 of the condenser 7, and the liquefied natural gas in the second delivery line 6 is heated to a predetermined temperature by the heater 9. You.

Here, the temperature of the liquefied natural gas heated by the heater 9 is measured by a temperature controller 12 provided in the second delivery line 6, and the temperature controller 12 controls the temperature of the liquefied natural gas. The temperature of the heater 9 is appropriately changed by adjusting the flow rate control valve 13 of the heat medium in the heater 9 so as to be in an appropriate range.

The liquefied natural gas whose temperature has been increased is then supplied to the decompressor 1
The pressure of the flash drum 11 is reduced to a predetermined pressure by 0.
The flash drum 11 vaporizes light-weight low-calorific methane from the liquefied natural gas as methane gas, and converts the liquefied natural gas into methane gas and the remaining heavy liquid with a high calorific value. The methane gas is sent out to the gas line 14 and the heavy liquid is sent out to the liquid line 15, respectively.

The methane gas in the gas line 14 is sent to the condensation side 17 of the condenser 7 and is cooled by the liquefied natural gas in the first delivery line 5 to become methane liquid. The methane liquid flows into the receiver 19 and returns. It is returned from the line 21 into the LNG tank 1 via the pressure reducing valve 20.

On the other hand, the heavy liquid in the liquid line 15 is sent out via the heavy liquid pump 22 to the first delivery line 5 between the condenser 7 and the vaporizer 8 and mixed.

The mixed natural liquid gas is sent to the vaporizer 8 and becomes natural gas, which is used as city gas or the like.

As described above, methane gas, which is a light portion of liquefied natural gas sent from the LNG tank 1 to the vaporizer 8, is returned to the LNG tank 1, so that the overall composition of the liquefied natural gas in the LNG tank 1 is reduced. Alternatively, the liquefied natural gas in the LNG tank 1 can be prevented from becoming heavier as a result. or,
The heavy liquefied natural gas from which the light methane gas is separated at an appropriate ratio is mixed with the liquefied natural gas in the first delivery line 5 to have an allowable calorific value. Liquefied natural gas can be used normally without sending natural gas to the vaporizer 8. Further, the vaporized gas vaporized by the external heat is liquefied again and the LNG tank 1
Compared with the case of returning to the inside, various facilities can be downsized, and the design of the condenser 7 and the like can be facilitated, and the cost can be reduced.

If the temperature of the heater 9 and the pressure of the pressure reducer 10 are changed to adjust the separation ratio of the light components, the amount of the methane liquid returned to the LNG tank 1 can be changed. The composition can be changed to an appropriate state.

The method and apparatus for preventing heavy gas in an LNG tank according to the present invention are not limited to the above-described embodiment, but may be applied to a case where natural gas vaporized by a vaporizer is lightened. It is needless to say that liquid propane gas may be appropriately added to the above, and that various changes may be made without departing from the scope of the present invention.

[0035]

According to the method and apparatus for preventing the liquid in the LNG tank from being heavier according to the present invention, the following various excellent effects can be obtained.

I) Since the light portion of the liquefied natural gas sent from the LNG tank to the vaporizer is returned to the LNG tank, the entire composition of the liquefied natural gas in the LNG tank can be changed to be lightened. As a result, the liquefied natural gas in the LNG tank can be prevented from becoming heavier in advance. In addition, the liquefied natural gas from which the light components are separated at an appropriate ratio is mixed with other liquefied natural gas obtained by liquefying the light components and generates an allowable calorific value. Liquefied natural gas can be used normally without sending natural gas to the vaporizer.

II) If the separation ratio of the light components is adjusted by changing the temperature for raising the temperature and the pressure for reducing the pressure, the amount of the light components to be returned to the LNG tank can be changed. Can be changed to

[Brief description of the drawings]

FIG. 1 is an overall system diagram showing an example of an embodiment of a heavy-duty preventing device used in a method for preventing heavy-duty liquid in an LNG tank according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tank 5 First delivery line (line) 6 Second delivery line (line) 7 Condenser 8 Vaporizer 9 Heater 10 Decompressor 11 Flash drum

Claims (3)

[Claims] 1. A part of liquefied natural gas delivered from a LNG tank to a vaporizer is heated and decompressed to vaporize and separate light components having a low calorific value, and the light components are vaporized from the LNG tank. The other liquefied natural gas sent to the vessel was liquefied by the cold heat and returned to the LNG tank, and the heavy component having a high calorific value from which the light component was removed was liquefied so as to be within the allowable calorific value. A method for preventing the liquid in an LNG tank from becoming heavier, comprising mixing with another liquefied natural gas and sending it to a vaporizer. 2. The method according to claim 1, wherein the separation ratio of the light components is adjusted by changing the temperature of the temperature rise and the pressure of the reduced pressure. 3. An LNG tank for storing liquefied natural gas, a heater for raising the temperature of a portion of the liquefied natural gas sent from the LNG tank to a vaporizer, and a decompressor for decompressing the heated liquefied natural gas. A flash drum that separates a light component having a low calorific value from the liquefied natural gas into a light component having a low calorific value and a heavy component having a high calorific value of the liquid by raising and reducing the temperature; A condenser that is liquefied by the cold heat of the other liquefied natural gas sent to the LNG tank and returned to the LNG tank; and the heavy component is mixed with another liquefied natural gas obtained by liquefying the light component so as to be within the allowable calorific value. A device for preventing the liquid in the LNG tank from being heavier, comprising: a line for sending out to a vaporizer.