WO2015178634A1

WO2015178634A1 - Liquefied gas treatment system

Info

Publication number: WO2015178634A1
Application number: PCT/KR2015/004930
Authority: WO
Inventors: 이진광; 이상봉
Original assignee: 현대중공업 주식회사
Priority date: 2014-05-19
Filing date: 2015-05-15
Publication date: 2015-11-26

Abstract

The present invention relates to a liquefied gas treatment system in which a nitrogen control unit controls the content of nitrogen in a boil-off gas or a flash gas when nitrogen components of the flash gas are greater than or equal to a preset value. The efficiency of a boil-off gas compressor can be improved and the system can be stabilized by means of the nitrogen control unit.

Description

Liquefied gas treatment system

The present invention relates to a liquefied gas treatment system.

Recently, liquefied gas such as liquefied natural gas and liquefied petroleum gas has been widely used in place of gasoline or diesel according to technology development.

Liquefied natural gas is liquefied by cooling methane obtained by refining natural gas collected from a gas field. It is a colorless and transparent liquid. Liquefied petroleum gas, on the other hand, is a liquid fuel made by compressing a gas mainly composed of propane (C3H8) and butane (C4H10), which come with oil from an oil field, at room temperature. Liquefied petroleum gas, like liquefied natural gas, is colorless and odorless and is widely used as a fuel for household, business, industrial, and automobile use.

Such liquefied gas is stored in a liquefied gas storage tank installed on the ground or in a liquefied gas storage tank provided in a ship which is a means of transporting the ocean, and liquefied natural gas is liquefied to a volume of 1/600. The liquefied petroleum gas is reduced by the liquefied propane is 1/260, butane is reduced to a volume of 1/230 has the advantage of high storage efficiency.

Such liquefied gas is supplied and used to various demand sources. Recently, an LNG fuel supply method for driving an engine using LNG as fuel in LNG carriers carrying liquefied natural gas has been developed. The method used is being applied to other vessels other than LNG carriers.

However, the temperature and pressure of the liquefied gas required by the customer such as the engine may be different from the state of the liquefied gas stored in the liquefied gas storage tank. Therefore, in recent years, continuous research and development has been made regarding a technology for controlling the temperature and pressure of a liquefied gas stored in a liquid state and supplying it to a demand destination.

The present invention was created to solve the problems of the prior art as described above, an object of the present invention is to pressurize the evaporated gas to supply to the demand, and to expand or re-liquefy some evaporated gas, whereby re-liquefied evaporated gas An object of the present invention is to provide a liquefied gas treatment system capable of improving the re-liquefaction efficiency of re-liquefied boil-off gas by exchanging heat with boil-off gas.

In addition, an object of the present invention, when the flow rate of the boil-off gas for driving the boil-off gas compressor is insufficient, at least a portion of the flash gas generated during the re-liquefaction of the boil-off gas is used to join the boil-off gas, nitrogen contained in the flash gas It is to provide a liquefied gas treatment system that can improve the efficiency of the boil-off gas compressor by controlling so that the ratio is equal to or less than a set value, and can also stabilize the system.

In addition, an object of the present invention, if the ratio of nitrogen contained in the flash gas is more than the set value, in order to maintain at least a portion of the flash gas to the set value or less, liquefied gas storage tank, Gas Combustion Unit (GCU) Or to control the supply to the nitrogen storage tank, to provide a liquefied gas treatment system that can prevent the environmental pollution due to the discharge of flash gas to the atmosphere.

Liquefied gas processing system according to an aspect of the present invention, the boil-off gas compressor for pressurizing the boil-off gas discharged from the liquefied gas storage tank; An boil-off gas liquefier for liquefying at least a portion of the boil-off gas compressed in the boil-off gas compressor; A gas-liquid separator for separating a flash gas from the boil-off gas liquefied by the boil-off gas liquefier and mixing at least a portion of the flash gas with the boil-off gas; And a nitrogen controller for controlling the nitrogen content in the evaporated gas or the flash gas when the nitrogen component of the flash gas is equal to or greater than a preset value.

Specifically, the method may further include an boil-off gas heat exchanger for heat-exchanging the boil-off gas pressurized by the boil-off gas compressor and the boil-off gas supplied from the liquefied gas storage tank.

Specifically, the flash gas heat exchanger for heat-exchanging the boil-off gas and the flash gas compressed by the boil-off gas compressor further, the nitrogen control unit, the detector for analyzing and detecting the components of the flash gas generated in the gas-liquid separator; A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And a nitrogen composition controller for controlling the operation of the distributor by checking whether the ratio of the nitrogen component in the component of the flash gas received from the detector is equal to or less than a preset ratio value.

In detail, the nitrogen composition controller compares a current ratio value of a nitrogen component in the component of the flash gas received from the detector with the preset ratio value, and when the current ratio value is equal to or less than the preset ratio value. The flash gas controls the operation of the distributor so that all or at least a portion of the flash gas joins, and when the current ratio value is greater than or equal to the preset ratio value, the nitrogen component separated from the flash gas is transferred to the flash gas heat exchanger. The operation of the distributor is controlled to be supplied, wherein the distributor separates nitrogen according to a control signal of the nitrogen composition controller when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator is greater than or equal to a preset ratio value. Nitrogen-reduced flash gas is combined with the boil-off gas Rock, and it is possible to supply the separated nitrogen group wherein the flash gas heat exchanger.

Specifically, the flash gas heat exchanger for heat-exchanging the boil-off gas and the flash gas compressed by the boil-off gas compressor further, the nitrogen control unit, the detector for measuring and detecting the internal pressure of the gas-liquid separator; A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And a nitrogen composition controller for controlling the operation of the distributor by checking whether the internal pressure of the gas-liquid separator received from the detector is equal to or less than a predetermined pressure value.

In detail, the nitrogen composition controller compares a present pressure value of the gas-liquid separator internal pressure received from the detector with the preset pressure value, and when the present pressure value is equal to or less than the preset pressure value, the flash gas is Controlling the operation of the distributor to allow all or at least a portion of the evaporation gas to join, and when the current pressure value is greater than or equal to the preset pressure value, the distributor such that the nitrogen component separated from the flash gas is supplied to the flash gas heat exchanger. Wherein the distributor separates nitrogen according to a control signal of the nitrogen composition controller when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator is greater than or equal to a preset pressure value, thereby reducing nitrogen. A flash gas is combined with the boil-off gas and separated It can be supplied to a group flash gas heat the cattle.

Specifically, the nitrogen control unit may discharge the remaining part of the flash gas to the gas combustion device.

Specifically, the flash gas heater further heats the flash gas discharged to the gas combustion device by using the waste heat generated by the gas combustion device, wherein the nitrogen control unit, the component of the flash gas generated in the gas-liquid separator A detector that detects the analysis; A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And a nitrogen composition controller for controlling the operation of the distributor by checking whether the ratio of the nitrogen component in the component of the flash gas received from the detector is equal to or less than a preset ratio value.

Specifically, the apparatus further includes a flash gas heater for heating the flash gas discharged to the gas combustion apparatus using waste heat generated by the gas combustion apparatus, wherein the nitrogen controller measures and detects the internal pressure of the gas-liquid separator. sensor; A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And a nitrogen composition controller for controlling the operation of the distributor by checking whether the internal pressure of the gas-liquid separator received from the detector is equal to or less than a predetermined pressure value.

Specifically, the mixture further provided upstream of the boil-off gas heat exchanger, and mixes the boil-off gas supplied from the liquefied gas storage tank and the flash gas recovered from the gas-liquid separator to supply the boil-off gas to the boil-off gas heat exchanger. Can be.

In the liquefied gas treatment system according to the present invention, the liquefied gas is pressurized and supplied to the demand, and the liquefied gas is expanded or decompressed to liquefy, but at this time, the liquefied boil-off gas is heat-exchanged with the boil-off gas due to the cold heat of the boil-off gas. The reliquefaction efficiency of the reliquefaction evaporation gas can be improved, and fuel can be saved by preventing the evaporation gas from being discarded.

In addition, the liquefied gas treatment system according to the present invention, when the flow rate of the boil-off gas for driving the boil-off gas compressor is insufficient to use at least a portion of the flash gas generated during the re-liquefaction of the boil-off gas to the boil-off gas, flash gas By controlling the nitrogen control unit so that the ratio of nitrogen contained in the gas is less than or equal to the set value, a certain flow rate or more is supplied to the boil-off gas compressor, thereby minimizing the recycling control to improve driving efficiency and appropriately adjusting the ratio of nitrogen in the system. It can be controlled to improve the efficiency of the boil-off gas compressor and to stabilize the system.

In addition, the liquefied gas treatment system according to the present invention, when the ratio of nitrogen contained in the flash gas is more than the set value, controlled by the nitrogen control unit so that at least a portion of the flash gas to be supplied to the liquefied gas storage tank to maintain the set value or less As a result, the flash gas can be stored and stored in the liquefied gas storage tank, thereby preventing environmental pollution due to the discharge of the flash gas into the atmosphere, and the internal pressure of the liquefied gas storage tank can be increased so that the boil-off gas can be well supplied. have.

In addition, the liquefied gas treatment system according to the present invention, when the flow rate of the boil-off gas for driving the boil-off gas compressor is insufficient, at least a portion of the flash gas generated during the re-liquefaction of the boil-off gas to join the boil-off gas, the flash gas In the case where the ratio of nitrogen contained in the gas is greater than or equal to the set value, the nitrogen control unit controls the nitrogen control unit to supply at least a part of the flash gas to the consumer in order to keep it below the set value, by heat-exchanging the flash gas with the evaporation gas for reliquefaction in the flash gas heat exchanger. In addition, the reliquefaction efficiency of the reliquefaction evaporation gas can be improved, and the flash gas can be treated at the consumer, thereby preventing environmental pollution due to the discharge of the flash gas into the atmosphere.

In addition, the liquefied gas treatment system according to the present invention, when the flow rate of the boil-off gas for driving the boil-off gas compressor is insufficient, at least a portion of the flash gas generated during the re-liquefaction of the boil-off gas to join the boil-off gas, the flash gas In the case where the ratio of nitrogen contained in the gas is greater than or equal to the set value, the nitrogen control unit controls the nitrogen gas to supply at least a part of the flash gas to the gas combustion device so as to maintain the set value or less. By using the waste heat generated in the combustion apparatus, the combustion efficiency of the flash gas and the energy efficiency due to the utilization of waste heat can be improved, and the flash gas can be burned in the gas combustion apparatus, resulting in the discharge of the flash gas into the atmosphere. Environmental pollution can be prevented.

In addition, the liquefied gas treatment system according to the present invention, by measuring the internal pressure of the gas-liquid separator to grasp the nitrogen content by the change in pressure and accordingly discharge the nitrogen to prevent the accumulation of nitrogen in the system, re-liquefaction efficiency is improved, The driving power of the boil-off gas compressor is optimized.

1 is a conceptual diagram of a liquefied gas treatment system according to a first embodiment of the present invention.

2 is a graph showing the power consumption of the flow rate of the boil-off gas compressor in a typical liquefied gas treatment system.

3 is a conceptual diagram of a liquefied gas treatment system according to a second embodiment of the present invention.

4 is a conceptual diagram of a liquefied gas treatment system according to a third embodiment of the present invention.

5 is a conceptual diagram of a liquefied gas treatment system according to a fourth embodiment of the present invention.

6 is a conceptual diagram of a liquefied gas treatment system according to a fifth embodiment of the present invention.

7 is a conceptual diagram of a liquefied gas treatment system according to a sixth embodiment of the present invention.

The objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and the preferred embodiments associated with the accompanying drawings. In the present specification, in adding reference numerals to the components of each drawing, it should be noted that the same components as possible, even if displayed on different drawings have the same number as possible. In addition, in describing the present invention, if it is determined that the detailed description of the related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual diagram of a liquefied gas treatment system according to a first embodiment of the present invention, Figure 2 is a graph showing the power consumption with respect to the flow rate of the evaporative gas compressor in a typical liquefied gas treatment system.

As shown in FIG. 1, the liquefied gas processing system 1 according to the first embodiment of the present invention includes a liquefied gas storage tank 10, a customer 20, an evaporative gas compressor 30, and an evaporated gas heat exchanger. 40, the boil-off gas liquefier 50, the gas-liquid separator 60, and the nitrogen control unit 70.

Hereinafter, in the present specification, liquefied gas may be used to encompass all gaseous fuels which are generally stored in a liquid state, such as LNG or LPG, ethylene, ammonia, and the like. Can be expressed as This can be applied to the boil-off gas as well. In addition, LNG may be used for the purpose of encompassing not only liquid NG (Natural Gas) but also supercritical NG for convenience, and evaporation gas may be used to include not only gaseous evaporation gas but also liquefied evaporation gas. Can be.

The liquefied gas storage tank 10 stores the liquefied gas to be supplied to the demand destination 20. The liquefied gas storage tank 10 should store the liquefied gas in a liquid state, where the liquefied gas storage tank 10 may have a pressure tank form.

In this embodiment, the boil-off gas generated in the liquefied gas storage tank 10 is supplied to the boil-off gas compressor 30 to be used for heating the boil-off gas, or the boil-off gas is vaporized and pressurized to be used as fuel of the demand destination 20. By utilizing it, boil-off gas can be utilized efficiently.

Here, the downstream of the liquefied gas storage tank 10 may be provided with a forced vaporizer (Forcing vaporizer, not shown), the forced vaporizer is operated when the flow rate of the boil-off gas is insufficient, the evaporated gas supplied to the demand destination 20 Can increase the flow rate. That is, the forced vaporizer is provided upstream of the point where the gas recovery line 17 is joined on the boil-off gas supply line 16 to vaporize the liquefied gas in the liquefied gas storage tank 10 to the boil-off gas compressor 30. Liquefied gas can be supplied. At the point where the boil-off gas supply line 16 and the gas recovery line 17 are joined, a mixer (not shown) for mixing the boil-off gas and the flash gas may be provided.

The mixer is provided upstream of the boil-off gas heat exchanger 40 on the boil-off gas supply line 16 so that the boil-off gas supplied from the liquefied gas storage tank 10 flows in and is recovered from the gas-liquid separator 60 to be described later. Can be introduced. Such a mixer may be in the form of a pressure tank forming a space for storing the boil-off gas and the flash gas. Here, the boil-off gas and the flash gas mixed in the mixer are supplied to the boil-off gas heat exchanger 40 which will be described later.

The demand destination 20 is driven through the boil-off gas and the flash gas supplied from the liquefied gas storage tank 10 to generate power. In this case, the demand source 20 may be a high-pressure engine and a gas fuel engine (eg, MEGI).

As the customer 20 reciprocates the piston (not shown) inside the cylinder (not shown) by the combustion of the liquefied gas, a crank shaft (not shown) connected to the piston is rotated and connected to the crank shaft. A shaft (not shown) can be rotated. Therefore, as the propeller (not shown) connected to the shaft rotates when the customer 20 drives, the hull may move forward or backward.

Of course, in the present embodiment, the demand source 20 may be an engine for driving the propeller, but may be an engine for power generation or an engine for generating other power. In other words, the present embodiment does not particularly limit the type of the demand destination 20. However, the demand source 20 may be an internal combustion engine that generates a driving force by the combustion of the boil-off gas and the flash gas.

The demand destination 20 may receive the boil-off gas and the flash gas pressurized by the boil-off gas compressor 30 to obtain a driving force. The states of the boil-off gas and the flash gas supplied to the customer 20 may vary depending on the condition required by the customer 20.

In addition, the demand source 20 may be a dual fuel engine in which the boil-off gas or oil is selectively supplied without being supplied by mixing the boil-off gas and oil. The dual fuel engine is selectively supplied with the boil-off gas or oil in this way to prevent the supply of two materials having different combustion temperatures from being mixed and prevent the efficiency of the demand source 20 from dropping.

Between the liquefied gas storage tank 10 and the demand destination 20, an evaporated gas supply line 16 for transmitting an evaporated gas may be installed, and an evaporated gas heat exchanger 40 and an evaporated gas may be installed in the evaporated gas supply line 16. The compressor 30 may be installed to supply the boil-off gas to the demand source 20, and the boil-off gas return line 16a may be provided between the boil-off gas compressor 30 and the demand source 20 in the boil-off gas supply line 16. Branching may be provided. The boil-off gas return line 16a may be provided with an boil-off gas heat exchanger 40, an boil-off gas liquefier 50, and the like to be supplied to the gas-liquid separator 60. Although not shown, the boil-off gas supply line 16 may be further provided with a forced vaporizer, a mixer, and the like.

At this time, a fuel supply valve (not shown) is installed in the boil-off gas supply line 16 and the boil-off gas return line 16a, so that the amount of boil-off gas may be adjusted according to the opening degree of the fuel supply valve.

The boil-off gas compressor 30 pressurizes the boil-off gas generated in the liquefied gas storage tank 10. The boil-off gas compressor 30 may pressurize the boil-off gas generated and discharged from the liquefied gas storage tank 10 and supply the boil-off gas to the boil-off gas heat exchanger 40 or the customer 20.

The boil-off gas compressor 30 may be provided in plural to pressurize the boil-off gas in multiple stages. For example, the evaporation gas compressor 30 may be provided with five to allow the evaporation gas to be pressurized five times. The five-stage pressurized boil-off gas may be pressurized to 200 bar to 400 bar and supplied to the customer 20 through the high-pressure boil-off gas supply line 24.

Here, the boil-off gas return line 16a may be branched between the boil-off gas compressor 30 on the boil-off gas supply line 16 and the demand source 20 and connected to the boil-off gas heat exchanger 40. At this time, a valve (not shown) may be provided on the boil-off gas supply line 16 at the branch point to the boil-off gas heat exchanger 40, and the valve may be a flow rate or boil-off gas of the boil-off gas supplied to the customer 20. It is possible to control the flow rate of the boil-off gas supplied to the boil-off gas heat exchanger 40 through the compressor 30, it may be a three-way valve.

An evaporative gas cooler (not shown) may be provided between the plurality of evaporative gas compressors 30. When the boil-off gas is pressurized by the boil-off gas compressor 30, the temperature may also increase as the pressure increases, so the present embodiment may lower the temperature of the boil-off gas using the boil-off gas cooler. The boil-off gas cooler may be installed in the same number as the boil-off gas compressor 30, and each boil-off gas cooler may be provided downstream of each boil-off gas compressor 30.

As the boil-off gas compressor 30 pressurizes the boil-off gas, the boil-off gas may be in a state in which the pressure rises and the boiling point rises to be liquefied even at a relatively high temperature. Therefore, in the present embodiment, by increasing the pressure of the boil-off gas with the boil-off gas compressor 30, the boil-off gas can be easily liquefied.

The boil-off gas heat exchanger 40 is provided between the liquefied gas storage tank 10 and the boil-off gas compressor 30 on the boil-off gas supply line 16, and the boil-off gas pressurized by the boil-off gas compressor 30 (evaporation for reliquefaction). Gas) and the boil-off gas supplied from the liquefied gas storage tank 10 may be heat-exchanged. The boil-off gas exchanged in the boil-off gas heat exchanger 40 may be supplied to the boil-off gas liquefier 50 or the boil-off gas compressor 30 to be described later. That is, the re-liquefaction evaporated gas and the evaporated gas newly supplied from the liquefied gas storage tank 10 after being pressurized in the multistage by the evaporative gas compressor 30 and recovered by the evaporated gas liquefier 50 are the evaporated gas heat exchanger 40. Heat exchanger

The boil-off gas liquefier 50 is provided on the boil-off gas return line 16a and pressurizes the boil-off gas for re-liquefaction that is pressurized by the boil-off gas compressor 30 and heat-exchanged in the boil-off gas heat exchanger 40 to at least depressurize or expand. Liquefy some. For example, the boil-off gas liquefier 50 may depressurize the boil-off gas for reliquefaction to 1 bar to 10 bar, and the boil-off gas for re-liquefaction is liquefied and transported to the gas-liquid separator 60 or the liquefied gas storage tank 10 to 1 bar. The pressure can be reduced even, the evaporation gas for re-liquefaction at reduced pressure can be achieved by the cooling effect.

Here, the boil-off gas pressurized by the boil-off gas compressor 30 is cooled by heat-exchanging with the boil-off gas supplied from the boil-off gas storage tank 10 in the boil-off gas heat exchanger 40, but the pressure is reduced by the boil-off gas compressor 30. It is possible to maintain the discharge pressure discharged from. In this embodiment, the reliquefaction evaporation gas is cooled by reducing the reliquefaction evaporation gas using the evaporation gas liquefier 50 to liquefy the reliquefaction evaporation gas. In this case, as the pressure range under reduced pressure is wider, the cooling effect of the reliquefaction evaporation gas may be increased. For example, the evaporation gas liquefier 50 may supply the reliquefaction evaporation gas pressurized to 300 bar by the evaporation gas compressor 30 to 1 bar. Can be depressurized.

The boil-off gas liquefier 50 may consist of a Joule Thompson valve. Alternatively, the boil-off gas liquefier 50 may be made up of an expander (not shown). In the case of the Joule Thompson valve, it is possible to effectively cool the reliquefaction evaporation gas by reducing the pressure so that at least a part of the reliquefaction evaporation gas is liquefied. In addition, the expander may also be made of an expander (not shown).

On the other hand, the expander can be driven without using a separate power, in particular, by utilizing the generated power as the power for driving the boil-off gas compressor 30, it is possible to improve the efficiency of the liquefied gas treatment system (1). . Power transmission may be achieved, for example, by gear connection or after electric conversion.

The gas-liquid separator (separator) 60 separates gas from the boil-off gas for reliquefaction which is reduced or expanded in the boil-off gas liquefier 50. In the gas-liquid separator 60, the re-liquefaction evaporated gas is separated into a liquid and a gas, and the liquid is supplied to the liquefied gas storage tank 10 through the liquid recovery line 18, and the gas is a flash gas, which will be described later as a nitrogen control unit 70. ), All or most of the liquid is recovered upstream of the boil-off gas compressor 30 through the gas recovery line 17, or a portion of the liquefied gas through the gas treatment line 17a branched from the gas recovery line 17. Supply to the storage tank 10 may be stored. The case where the flash gas is stored in the liquefied gas storage tank 10 through the gas treatment line 17a will be described later.

Here, the re-liquefaction evaporated gas supplied to the gas-liquid separator 60 may be in a reduced pressure and cooled state in the evaporative gas liquefier 50. For example, in the boil-off gas compressor 30, the boil-off gas may be pressurized in multiple stages to have a pressure of 200 bar to 400 bar, and the temperature may be about 45 ° C. The boil-off gas (re-liquefaction boil-off gas) raised to a temperature of about 45 ° C. is recovered by the boil-off gas heat exchanger 40 and heat-exchanged with the boil-off gas around -100 ° C. supplied from the liquefied gas storage tank 10. It is supplied to the boil-off gas liquefier 50 in a state of cooling to a temperature of about ℃. At this time, the boil-off gas for re-liquefaction in the boil-off gas liquefier 50 may be cooled by a reduced pressure to have a pressure of about 1bar and a temperature of about -162.3 ℃.

As such, in the present embodiment, since the reliquefaction evaporation gas supplied to the gas-liquid separator 60 is decompressed in the evaporation gas liquefier 50 to have a temperature lower than −162 ° C., the reliquefaction evaporation gas of about 30 to 40% is used. Can be liquefied.

In addition, in the present embodiment, the vaporized gas liquefied in the gas-liquid separator 60 is recovered to the liquefied gas storage tank 10, and the flash gas generated in the gas-liquid separator 60 is recovered by the vaporized gas compressor 30 without discarding it. In addition, the boil-off gas and the flash gas may be pressurized through the boil-off gas compressor 30 and then supplied to the demand destination 20.

When the reliquefaction evaporated gas is separated into liquid and gas in the gas-liquid separator 60, the liquefied evaporated gas and the generated flash gas are respectively liquefied gas storage tanks through the liquid recovery line 18 and the gas recovery line 17. 10) and the boil-off gas compressor 30 may be recovered.

The liquid recovery line 18 is connected to the liquefied gas storage tank 10 from the gas-liquid separator 60 to serve as a passage for recovering the liquid evaporated gas to the liquefied gas storage tank 10.

The gas recovery line 17 is connected to the boil-off gas supply line 16 upstream of the boil-off gas compressor 30 in the gas-liquid separator 60 to recover the flash gas upstream of the boil-off gas compressor 30 so that the flash gas It can be prevented from being thrown away and wasted. When a mixer is provided upstream of the boil-off gas heat exchanger 40 on the boil-off gas supply line 16, the gas recovery line 17 may be connected to the mixer.

In this case, as described above, the flash gas may be cooled by being decompressed by the boil-off gas liquefier 50 to be -162.3 ° C. The boil-off gas of about -100 ° C. generated in the flash gas and the liquefied gas storage tank 10 may be At the point where the boil-off gas supply line 16 and the gas recovery line 17 meet, the mixture is introduced into the boil-off gas heat exchanger 40 as the boil-off gas of -110 ° C to -120 ° C (about -114 ° C).

Therefore, the evaporation gas (evaporation gas for reliquefaction) at 45 ° C., which is branched between the evaporation gas compressor 30 and the customer 20, and recovered along the evaporation gas return line 16a connected to the evaporation gas heat exchanger 40, is evaporated. It can be cooled by heat exchange with the boil-off gas of -110 to -120 ℃ in the gas heat exchanger (40). This can be achieved by additional cooling of the reliquefaction evaporation gas as compared with the absence of flash gas recovery (45 ° C reliquefaction evaporation gas heat exchanged with -100 ° C evaporation gas).

Accordingly, the reliquefaction evaporation gas discharged from the evaporation gas heat exchanger 40 and introduced into the evaporation gas liquefier 50 may be about −112 ° C., which is lower than that of the flash gas (about −97 ° C.). When the pressure is reduced by the boil-off gas liquefier 50, the temperature may be cooled to about −163.7 ° C. In this case, more re-liquefaction evaporated gas may be liquefied by the evaporative gas liquefier 50 and recovered to the liquefied gas storage tank 10 than there is no flash gas circulation.

Therefore, the present embodiment, by separating the evaporated gas in the gas state of the re-liquefied evaporation gas cooled through the evaporation gas liquefier 50 as a flash gas in the gas-liquid separator 60 to supply to the evaporation gas heat exchanger 40, By lowering the temperature of the boil-off gas recovered from the boil-off gas compressor 30 to the boil-off gas heat exchanger 40 and the boil-off gas liquefier 50 sufficiently, the liquefaction efficiency of the boil-off gas for reliquefaction can be raised to 60% or more. have.

In addition, in this embodiment, not only the boil-off gas from the liquefied gas storage tank 10 but also the flash gas is mixed with the boil-off gas and flows into the boil-off gas compressor 30, so that a predetermined flow rate or more is supplied to the boil-off gas compressor 30. Supplied, the driving efficiency can be improved.

As shown in the graph of Figure 2, in the case of a typical boil-off gas compressor, the power consumption (Shaft Power) increases when the flow rate (Mass Flow) increases. This means that a lot of power consumption is required to compress a large flow rate of boil-off gas. In this case, the section B may be a section having a larger flow rate than a predetermined value (a reference value for determining sections A and B) determined according to specifications of the boil-off gas compressor, driving conditions, and the like.

On the other hand, in the A section where the flow rate of the boil-off gas flowing into the boil-off compressor is less than the preset value, the power consumption does not decrease even if the flow rate decreases. This may cause surging when a certain volume of boil-off gas does not flow into the boil-off gas compressor, and recycle some of the boil-off gas when the boil-off gas flow into the boil-off gas compressor is lower than the preset value. This is because the evaporation gas inlet volume of the evaporative gas compressor must be maintained at a predetermined value or more, so that power consumption for recycling is generated.

However, in the boil-off gas compressor 30 of the present embodiment, since the flash gas may flow into the boil-off gas compressor 30 together with the boil-off gas, even if the flow rate of the boil-off gas decreases in the section A where the boil-off gas flow rate is less than or equal to a predetermined value. Since the flash gas can satisfy the volume required by the boil-off gas compressor 30, power consumption can be reduced as the boil-off gas flow rate decreases. That is, in the boil-off gas compressor 30 of the present embodiment, power consumption may be proportionally reduced when the flow rate is reduced in the A section.

Therefore, in the present embodiment, when the amount of the boil-off gas is small, by controlling the amount of flash gas to reduce the recycling control of the boil-off gas compressor 30, the required power according to the low load operation of the boil-off gas compressor 30 Can be saved.

In the boil-off gas compressor 30 of the present embodiment, power consumption increases as the flow rate increases. This is because a large amount of power consumption is required to compress a larger amount of boil-off gas. However, since the present embodiment includes a configuration for circulating the flash gas, the efficiency of reliquefaction of the boil-off gas is greatly improved regardless of whether the power consumption of the boil-off gas compressor 30 increases with the flow rate of the boil-off gas. You can.

As described above, the present embodiment pressurizes the boil-off gas generated in the liquefied gas storage tank 10 by external heat penetration and supplies it to the demand destination 20, or circulates the flash gas to the boil-off gas compressor 30 to Pressurized together and supplied to the demand destination 20 to prevent the evaporated gas from being discarded, thereby saving fuel, and further cooling the evaporated gas with flash gas to maximize the liquefaction efficiency. By using the mixture, a predetermined flow rate or more may be supplied to the boil-off gas compressor 30 to minimize the recycle control, thereby improving driving efficiency.

However, since the flash gas joined to the boil-off gas contains a large amount of nitrogen, the load of the boil-off gas compressor 30 may be increased when the boil-off gas into which the flash gas is introduced flows into the boil-off gas compressor 30. As the ratio of nitrogen to the boil-off gas supplied toward (20) increases, the efficiency of the demand source 20 may decrease, and when the nitrogen continues to accumulate, the entire system 1 may become unstable. In this embodiment, through the nitrogen control unit 70 to be described later to properly control the ratio of nitrogen in the system to improve the efficiency of the boil-off gas compressor as well as to stabilize the system.

The nitrogen controller 70 may be installed on the gas recovery line 17, and when the flow rate of the boil-off gas for driving the boil-off gas compressor 30 is insufficient, at least part of the flash gas generated in the gas-liquid separator 60. When the gas is joined to the boil-off gas of the boil-off gas supply line 16 through the gas recovery line 17, the flow rate of the flash gas to be controlled so that the ratio of nitrogen contained in the flash gas is below the set value, or joined to the boil-off gas Control to reduce the amount of gas, and prevents nitrogen from accumulating in the liquefied gas treatment system 1, and includes a detector 71, a nitrogen composition controller 72, and a distributor 73. Can be configured.

The sensor 71 may be provided in the gas-liquid separator 60 and directly determine a gas chromatography or a ratio of nitrogen in the flash gas, which may directly analyze a component of the flash gas generated in the gas-liquid separator 60. It may be a nitrogen sensor that can be measured by.

The detector 71 is provided in the gas-liquid separator 60 and may be provided in the gas recovery line 17 upstream or downstream of the distributor 73 to be described later.

The detector 71 may be provided with a wired or wireless transmitter, and may transmit the components of the flash gas analyzed as described above to the nitrogen composition controller 72 to be described later through wired or wireless methods.

The nitrogen composition controller 72 may include a wired / wireless transceiver between the detector 71 and the distributor 73 to be described later, and the nitrogen component ratio is preset in the component of the flash gas received from the detector 71. It is possible to control the operation of the distributor 73 to be described later through a wired or wireless method by checking whether the ratio is equal to or less than the ratio value.

Specifically, when the nitrogen composition controller 72 receives an analysis value of a component of the flash gas from the detector 71, the efficiency or system 1 of the evaporation gas compressor 30 depends on the ratio of nitrogen contained in the flash gas. On the basis of the preset ratio value obtained by creating a table by experiment of the influence on the stability of the), the current ratio value of the nitrogen component in the component of the flash gas received from the detector 71 is compared with the preset ratio value. When the ratio of nitrogen contained in the flash gas, which is the current value, is equal to or less than the preset ratio value, the distributor 73 to be described later so that the flash gas is joined to the boil-off gas of the boil-off gas supply line 16 through the gas recovery line 17. ), And when the ratio is equal to or greater than the preset ratio value, at least a portion of the flash gas is diverted from the gas recovery line 17 through the gas treatment line 17a. A storage tank 10 or the gas combustion device (not shown), may control the operation of the nitrogen storage tank (not shown) to be described later is supplied to the dispenser such as (73).

The distributor 73 may be provided on the gas recovery line 17, may be connected to the liquefied gas storage tank 10 by the gas processing line 17a, and according to a control signal of the nitrogen composition controller 72. The operation is controlled. The distributor 73 may distribute the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas flowing into the boil-off gas compressor 30.

The distributor 73 may include a wired or wireless receiver for receiving a control signal from the nitrogen composition controller 72 and may be a three-way valve or a nitrogen separator.

The three-way valve increases the opening degree to the liquefied gas storage tank 10 when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator 60 is greater than or equal to the preset ratio value according to the control signal of the nitrogen composition controller 72. It is operated so that the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 1 can be kept below the set value.

The three-way valve may allow the entire amount or at least a portion of the flash gas to join the boil-off gas when the ratio of nitrogen contained in the flash gas is equal to or less than the preset ratio value.

The nitrogen separator separates nitrogen when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator 60 is greater than or equal to the preset ratio value according to the control signal of the nitrogen composition controller 72, thereby reducing the nitrogen gas. To be combined with the boil-off gas of the boil-off gas supply line 16 through the gas recovery line 17, and the separated nitrogen through the gas treatment line 17a to the liquefied gas storage tank 10 or gas combustion device, nitrogen storage By being operated to be supplied to a tank or the like, the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 1 can be kept below the set value.

The nitrogen separator may not allow the nitrogen gas contained in the flash gas to separate when the ratio of the nitrogen contained in the flash gas is less than or equal to the set value, and may allow the entire amount or at least a portion of the flash gas to be combined with the boil-off gas. .

Here, the predetermined ratio value of the nitrogen ratio refers to a case where the cumulative ratio of nitrogen in the boil-off gas becomes 20 to 40% (preset value), and the cumulative ratio of nitrogen in the boil-off gas is 20 to 40% (preset value). In this case, the distributor 73 may separate nitrogen from the flash gas and supply nitrogen to the liquefied gas storage tank 10, a gas combustion device (not shown), a nitrogen storage tank (not shown), or the like. .

In the embodiment of the present invention, the ratio of nitrogen accumulated in the boil-off gas is not converged to 40 to 60%, so that the methane (CH 4) in the boil-off gas is chemically entangled by nitrogen and cannot be re-liquefied, but the gas together with the nitrogen By circulating in the liquefied gas treatment system 1 in a state, it is possible to prevent the reliquefaction efficiency of the boil-off gas from dropping rapidly.

In addition, in the embodiment of the present invention, by preventing the proportion of nitrogen accumulated in the boil-off gas to converge to 40 to 60%, it is possible to prevent the compression work of the boil-off gas compressor 30 from increasing, and thus the boil-off gas It is possible to prevent the power consumption of the compressor 30 from increasing.

As described above, according to the present embodiment, by controlling the ratio of nitrogen contained in the flash gas to be equal to or less than the preset ratio value, a predetermined flow rate or more is supplied to the boil-off gas compressor 30 to minimize the recycling control to improve driving efficiency. In addition, the ratio of nitrogen in the system 1 can be properly controlled to improve the efficiency of the boil-off gas compressor 30, and to stabilize the system 1. When the ratio of nitrogen is equal to or greater than the preset ratio value, the flash gas is controlled by the liquefied gas storage tank 10 by controlling at least a portion of the flash gas to be supplied to the liquefied gas storage tank 10 so as to maintain the preset ratio value or less. It can be stored and can prevent the environmental pollution due to the discharge of flash gas to the atmosphere, the internal pressure of the liquefied gas storage tank 10 to increase the internal pressure of the evaporated gas It may be supplied.

As shown in FIG. 3, the liquefied gas treatment system 2 according to the second embodiment of the present invention includes a liquefied gas storage tank 10, a customer 20, an evaporative gas compressor 30, and an evaporative gas heat exchanger. 40, an evaporative gas liquefier 50, a gas-liquid separator 60, a nitrogen control unit 70, a consumer 410, and a flash gas heat exchanger 420. Compared to the first embodiment of the present invention, the second embodiment of the present invention has a different configuration of the consumer 410 and the flash gas heat exchanger 420, and the gas treatment line 17a of the second embodiment of the present invention has a different configuration. The connection is different. The same or corresponding components as those of the first embodiment of the present invention are denoted by the same reference numerals for convenience, and redundant description thereof will be omitted.

The consumer 410 may be a gas combustion device or a nitrogen storage tank, and when the ratio of nitrogen contained in the flash gas is greater than or equal to the preset ratio value, the consumer 410 may be maintained at or below the preset ratio value through the gas treatment line 17a. The flash gas supplied from the gas-liquid separator 60 may be processed. In this case, the gas treatment line 17a may be connected to the consumer 410 such as a gas combustion device or a nitrogen storage tank from the distributor 73 of the nitrogen control unit 70.

The flash gas heat exchanger 420 may be provided on the gas treatment line 17a and the boil-off gas return line 16a, specifically, on the gas treatment line 17a between the distributor 73 and the consumer 410. It may be provided in, between the boil-off gas compressor 30 and the boil-off gas liquefier 50, between boil-off gas heat exchanger 40 and boil-off gas liquefier 50 or boil-off gas heat exchanger 40 and boil-off gas compressor It may be provided between the boil-off gas return line (16a) between (30).

In the flash gas heat exchanger 420, a relatively high temperature evaporation gas for reliquefaction evaporation is cooled by obtaining a cooling heat from a relatively low temperature flash gas, thereby improving the cooling efficiency of the evaporation gas liquefier 50. Here, the boil-off gas heat exchanger 40 and the flash gas heat-exchanger 420 are provided on the boil-off gas return line 16a upstream of the boil-off gas liquefier 50 to further increase the liquefaction efficiency of the boil-off gas for reliquefaction. have.

In the above, when the consumer 410 is a gas combustion device, a flash gas containing nitrogen (if the distributor is a three-way valve) supplied from the distributor 73 or a flash gas containing a large amount of nitrogen (the distributor is a nitrogen separator). ), The flash gas generated in the gas-liquid separator 60 may be cooled by being decompressed by the boil-off gas liquefier 50 to be in a low temperature state (eg, −162.3 ° C.) as mentioned above. And considering that the temperature for burning in the gas combustion apparatus is 40 ° C., for example, it is necessary to raise the temperature of the flash gas before the flash gas is supplied to the gas combustion apparatus.

In the present embodiment, the flash gas heat exchanger 420 may heat the flash gas to a temperature for burning in the gas combustion apparatus before the flash gas is supplied to the gas combustion apparatus. At this time, in the flash gas heat exchanger 420, the flash gas having a relatively low temperature is heated by obtaining heat from a relatively high temperature evaporation gas for reliquefaction, thereby improving the combustion efficiency of the gas combustion device.

The distributor 73 of the nitrogen control unit 70 may be a three-way valve or a nitrogen separator. Since the configuration of the second embodiment of the present invention has a configuration different from that of the first embodiment of the present invention, the respective functions are different. This may be different.

That is, in the three-way valve of the second embodiment, when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator 60 is greater than or equal to the preset ratio value according to the control signal of the nitrogen composition controller 72, the consumer 410 Operated to increase the opening degree to the flash gas heat exchanger 420 provided upstream, the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 2 is kept below a predetermined ratio value. Not only that, but also to improve the liquefaction efficiency of the reliquefaction evaporated gas. At this time, the consumer 410 is preferably a gas combustion device.

Further, the nitrogen separator of the second embodiment separates nitrogen when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator 60 is equal to or greater than the preset ratio value according to the control signal of the nitrogen composition controller 72. The flash gas having reduced nitrogen is joined with the boil-off gas of the boil-off gas supply line 16 through the gas recovery line 17, and the separated nitrogen is provided upstream of the consumer 410 through the gas treatment line 17a. By being operated to be supplied to the flash gas heat exchanger 420, the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 2 can be maintained not only below the set value, but also for reliquefaction. It is possible to improve the liquefaction efficiency of the boil-off gas. At this time, the consumer 410 is preferably a nitrogen storage tank.

Here, the predetermined ratio value of the nitrogen ratio refers to a case where the cumulative ratio of nitrogen in the boil-off gas becomes 20 to 40% (preset value), and the cumulative ratio of nitrogen in the boil-off gas is 20 to 40% (preset value). In this case, the distributor 73 may separate nitrogen from the flash gas and supply nitrogen to the consumer 410.

In the embodiment of the present invention, the ratio of nitrogen accumulated in the boil-off gas is not converged to 40 to 60%, so that the methane (CH 4) in the boil-off gas is chemically entangled by nitrogen and cannot be re-liquefied, but the gas together with the nitrogen By circulating in the liquefied gas treatment system 2 in a state, it is possible to prevent the reliquefaction efficiency of the boil-off gas from dropping rapidly.

As shown in FIG. 4, the liquefied gas treatment system 3 according to the third embodiment of the present invention includes a liquefied gas storage tank 10, a customer 20, an evaporative gas compressor 30, and an evaporative gas heat exchanger. 40, an evaporative gas liquefier 50, a gas-liquid separator 60, a nitrogen control unit 70, a gas combustion device 510, and

flash gas heaters

520a and 520b. The third embodiment of the present invention is different from the above-described first embodiment of the present invention in the configuration of the gas combustion device 510 and the

flash gas heaters

520a and 520b, and the gas processing line 17a related to this configuration. The connection relationship between is different. The same or corresponding components as those of the first embodiment of the present invention are denoted by the same reference numerals for convenience, and redundant description thereof will be omitted.

The gas combustion device 510 is a flash supplied from the gas-liquid separator 60 through the gas treatment line 17a to maintain the ratio of nitrogen contained in the flash gas at or below the preset ratio value. The gas can be combusted. In this case, the gas treatment line 17a may be connected to the gas combustion device 510 from the distributor 73 of the nitrogen control unit 70.

Here, the gas combustion device 510 needs to raise the temperature of the flash gas before the flash gas is supplied to the gas combustion device 510 similarly to the case where the consumer 410 of the second embodiment is the gas combustion device. have.

The

flash gas heaters

520a and 520b may be provided upstream of the gas combustion device 510, specifically, on the gas treatment line 17a between the distributor 73 and the gas combustion device 510. The flash gas may be heated to a temperature for burning in the gas combustion device 510 before being supplied to the gas combustion device 510. Here, the

flash gas heaters

520a and 520b may be configured by arranging the main heater 520a and the auxiliary heater 520b in series, and by further providing the auxiliary heater 520b in the main heater 520a, In the combustion device 510, the combustion treatment efficiency may be further increased.

The

flash gas heaters

520a and 520b may heat the flash gas by using electrical energy as a heat source or using a heat transfer medium. In this case, the heat transfer medium may be glycol water or steam, and glycol water is a fluid mixed with ethylene glycol and water, and is heated in a medium heater (not shown) and cooled by flash gas to circulate. Can be. In addition, the flash gas heater 520 can heat the flash gas using waste heat generated from a generator or other equipment provided in the ship.

In the present embodiment, the gas combustion device 510 and the heat transfer medium circulation line 19 passing through the

flash gas heaters

520a and 520b are provided to provide the gas combustion device as a heat source of the

flash gas heaters

520a and 520b. Waste heat generated at 510 may be used. The heat transfer medium flowing through the heat transfer medium circulation line 19 may be glycol water or steam.

The distributor 73 of the nitrogen control unit 70 may be a three-way valve or a nitrogen separator. Since the configuration of the third embodiment of the present invention has a configuration different from that of the first embodiment of the present invention, the respective functions are different. This may be different.

That is, the three-way valve of the third embodiment, when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator is greater than or equal to the preset ratio value in accordance with the control signal of the nitrogen composition controller 72, the gas combustion device 510 By operating to increase the opening degree, it is possible to keep the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 3 below the preset ratio value.

Further, the nitrogen separator of the third embodiment separates nitrogen when the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator 60 is equal to or greater than the preset ratio value according to the control signal of the nitrogen composition controller 72. The flash gas having reduced nitrogen is joined with the boil-off gas of the boil-off gas supply line 16 through the gas recovery line 17, and the separated nitrogen is sent to the gas-combustion apparatus 510 through the gas treatment line 17a. By being operated to be supplied, the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 3 can be kept below a predetermined ratio value.

Here, the predetermined ratio value of the nitrogen ratio refers to a case where the cumulative ratio of nitrogen in the boil-off gas becomes 20 to 40% (preset value), and the cumulative ratio of nitrogen in the boil-off gas is 20 to 40% (preset value). In this case, the distributor 73 may separate nitrogen from the flash gas and supply nitrogen to the gas combustion device 510.

In the embodiment of the present invention, the ratio of nitrogen accumulated in the boil-off gas is not converged to 40 to 60%, so that the methane (CH 4) in the boil-off gas is chemically entangled by nitrogen and cannot be re-liquefied, but the gas together with the nitrogen By circulating in the liquefied gas processing system 3 in a state, it is possible to prevent the reliquefaction efficiency of the boil-off gas from dropping rapidly.

As shown in FIG. 5, the liquefied gas processing system 4 according to the first embodiment of the present invention includes a liquefied gas storage tank 10, a customer 20, an evaporative gas compressor 30, and an evaporative gas heat exchanger. 40, the boil-off gas liquefier 50, the gas-liquid separator 60, and the nitrogen control unit 70.

The fourth embodiment of the present invention excludes the configuration of the detector 71 and the nitrogen composition controller 72 from the configuration of the nitrogen control unit 70 in comparison with the first embodiment of the present invention described above, and the pressure sensor 74. The pressure control unit 75 is added, and the driving relationship of the distributor 73 related to the added configuration is different. The same or corresponding components as those of the first embodiment of the present invention are denoted by the same reference numerals for convenience, and redundant description thereof will be omitted.

The pressure sensor 74 may be provided in the gas-liquid separator 60, and may measure the internal pressure of the gas-liquid separator 60 to detect an increase or a decrease in the internal pressure.

The pressure sensor 74 may indirectly measure the nitrogen component of the flash gas, and the nitrogen component of the flash gas is contained in the internal pressure of the gas-liquid separator 60 and the flash gas corresponding thereto in the pressure controller 75 to be described later. The proportion of components of nitrogen can be measured indirectly by means of a converted table.

The pressure sensor 74 may include a wired or wireless transmitter and transmit the internal pressure of the gas-liquid separator 60 analyzed as described above to the pressure controller 75 to be described later through wired or wireless methods. .

The pressure controller 75 may include a wired or wireless transceiver between the pressure sensor 74 and the distributor 73 to be described later, and the internal pressure of the gas-liquid separator 60 received from the pressure sensor 74 is preset. It is possible to control the operation of the distributor 73 to be described later through a wired or wireless method by checking whether or not the pressure value or less.

Specifically, when the pressure controller 75 receives the internal pressure value of the gas-liquid separator 60 from the pressure sensor 74, the pressure controller 75 measures the ratio of nitrogen contained in the flash gas according to the internal pressure of the gas-liquid separator 60 by experiment. By converting through a table, a preset ratio value obtained by creating a table by experiments on the effect of the efficiency of the boil-off gas compressor 30 or the stability of the system 1 according to the ratio of nitrogen contained in the flash gas is calculated. Based on a predetermined pressure value derived through the above or obtained by creating an experimental table of the effects on the efficiency of the boil-off gas compressor 30 or the stability of the system 1 according to the internal pressure of the gas-liquid separator 60. On the basis of the preset pressure value, the present pressure value of the gas-liquid separator 60 received from the detector 71 is compared with the preset pressure value, and when the present pressure value is equal to or less than the preset pressure value, Control the operation of the distributor 73 to be described later so that the flash gas is joined to the boil-off gas of the boil-off gas supply line 16 through the water line 17, and if at least a portion of the flash gas is at least a predetermined pressure value to recover the gas Distributor 73 to be described later to be supplied to the liquefied gas storage tank 10 or a gas combustion device (not shown), nitrogen storage tank (not shown), etc. through the gas treatment line 17a branching from the line 17. Can control the operation.

The distributor 73 may be provided on the gas recovery line 17, may be connected to the liquefied gas storage tank 10 by the gas treatment line 17a, and may operate according to a control signal of the pressure controller 75. This is controlled. The distributor 73 may distribute the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas flowing into the boil-off gas compressor 30.

The distributor 73 may include a wired or wireless receiver for receiving a control signal from the pressure controller 75, and may be a three-way valve or a nitrogen separator.

The three-way valve is operated to increase the opening degree to the liquefied gas storage tank 10 when the internal pressure of the gas-liquid separator 60 is equal to or greater than the predetermined pressure value according to the control signal of the pressure control unit 75, thereby The ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside can be kept below the set value.

The three-way valve may allow the entire amount or at least a part of the flash gas to join the boil-off gas when the internal pressure of the gas-liquid separator 60 is equal to or less than the predetermined pressure value.

The nitrogen separator separates nitrogen when the internal pressure of the gas-liquid separator 60 is greater than or equal to a preset pressure value according to a control signal of the pressure controller 75 to evaporate the flash gas having reduced nitrogen through the gas recovery line 17. The gas supply line 16 is combined with the boil-off gas, and the separated nitrogen is operated to be supplied to the liquefied gas storage tank 10 or the gas combustion device, the nitrogen storage tank, etc. through the gas treatment line 17a. The ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside 1) can be kept below the set value.

The nitrogen separator may not allow the nitrogen gas contained in the flash gas to separate when the internal pressure of the gas-liquid separator 60 is less than or equal to a predetermined pressure value, and may allow the entire amount or at least a portion of the flash gas to join the evaporation gas. to be.

In the embodiment of the present invention, the ratio of nitrogen accumulated in the boil-off gas is not converged to 40 to 60%, so that the methane (CH 4) in the boil-off gas is chemically entangled by nitrogen and cannot be re-liquefied, but the gas together with the nitrogen By circulating in the liquefied gas treatment system 4 in a state, it is possible to prevent the reliquefaction efficiency of the boil-off gas from dropping rapidly.

As shown in FIG. 6, the liquefied gas treatment system 5 according to the fifth embodiment of the present invention includes a liquefied gas storage tank 10, a demand destination 20, an evaporative gas compressor 30, and an evaporated gas heat exchanger ( 40, an evaporative gas liquefier 50, a gas-liquid separator 60, a nitrogen control unit 70, a consumer 410, and a flash gas heat exchanger 420. The fifth embodiment of the present invention excludes the configuration of the detector 71 and the nitrogen composition controller 72 from the configuration of the nitrogen control unit 70 in comparison with the second embodiment of the present invention described above, and the pressure sensor 74. The pressure control unit 75 is added, and the driving relationship of the distributor 73 and the consumer 410 related to the added configuration is different. The same or corresponding components as those of the first embodiment of the present invention are denoted by the same reference numerals for convenience, and redundant description thereof will be omitted.

The consumer 410 may be a gas combustion device or a nitrogen storage tank, and when the internal pressure of the gas-liquid separator 60 is equal to or greater than the preset pressure value, the gas-liquid through the gas treatment line 17a to maintain the equal pressure or less. The flash gas supplied from the separator 60 may be processed. In this case, the gas treatment line 17a may be connected to the consumer 410 such as a gas combustion device or a nitrogen storage tank from the distributor 73 of the nitrogen control unit 70.

The distributor 73 of the nitrogen control unit 70 may be a three-way valve or a nitrogen separator. Since the configuration of the fifth embodiment of the present invention has a configuration different from that of the above-described second embodiment of the present invention, each function This may be different.

That is, the three-way valve of the fifth embodiment is a flash gas heat exchanger 420 provided upstream of the consumer 410 when the internal pressure of the gas-liquid separator 60 is equal to or higher than the preset pressure value according to the control signal of the pressure controller 75. By operating to increase the opening degree to), not only can the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 5 be kept below the preset ratio value, but also the evaporation gas for reliquefaction It is possible to improve the liquefaction efficiency of the. At this time, the consumer 410 is preferably a gas combustion device.

Further, the nitrogen separator of the fifth embodiment separates nitrogen when the internal pressure of the gas-liquid separator 60 is equal to or greater than the preset pressure value according to the control signal of the pressure controller 75, thereby recovering the flash gas in which nitrogen is reduced. Through the line 17 to be combined with the boil-off gas of the boil-off gas supply line 16, the separated nitrogen is supplied to the flash gas heat exchanger 420 provided upstream of the consumer 410 through the gas treatment line (17a) In this way, the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 5 can be maintained below a set value, and the liquefaction efficiency of the reliquefaction evaporation gas can be improved. do. At this time, the consumer 410 is preferably a nitrogen storage tank.

In the embodiment of the present invention, the ratio of nitrogen accumulated in the boil-off gas is not converged to 40 to 60%, so that the methane (CH 4) in the boil-off gas is chemically entangled by nitrogen and cannot be re-liquefied, but the gas together with the nitrogen By circulating in the liquefied gas treatment system 5 in a state, it is possible to prevent the reliquefaction efficiency of the boil-off gas from dropping rapidly.

As shown in FIG. 7, the liquefied gas processing system 6 according to the sixth embodiment of the present invention includes a liquefied gas storage tank 10, a customer 20, an evaporative gas compressor 30, and an evaporated gas heat exchanger. 40, an evaporative gas liquefier 50, a gas-liquid separator 60, a nitrogen control unit 70, a gas combustion device 510, and

flash gas heaters

520a and 520b. The sixth embodiment of the present invention excludes the configuration of the detector 71 and the nitrogen composition controller 72 among the above-described third embodiment of the present invention and the nitrogen control unit 70, and the pressure sensor 74, the pressure. The control unit 75 is added, and the driving relationship between the distributor 73 and the gas combustion device 510 related to the added configuration is different. The same or corresponding components as those of the first embodiment of the present invention are denoted by the same reference numerals for convenience, and redundant description thereof will be omitted.

When the internal pressure of the gas-liquid separator 60 is equal to or greater than the preset pressure value, the gas combustion device 510 supplies the flash gas supplied from the gas-liquid separator 60 through the gas processing line 17a to maintain the pressure equal to or less than the predetermined pressure value. Can be burned. In this case, the gas treatment line 17a may be connected to the gas combustion device 510 from the distributor 73 of the nitrogen control unit 70.

The distributor 73 of the nitrogen control unit 70 may be a three-way valve or a nitrogen separator. Since the configuration of the sixth embodiment of the present invention has a configuration different from that of the third embodiment of the present invention, each of the functions This may be different.

That is, the three-way valve of the sixth embodiment is operated to increase the opening degree to the gas combustion device 510 when the internal pressure of the gas-liquid separator 60 is equal to or higher than the preset pressure value according to the control signal of the pressure control unit 75. In addition, the ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside the system 6 can be maintained below a predetermined ratio value.

In addition, according to the control signal of the pressure control unit 75, the nitrogen separator of the sixth embodiment separates nitrogen when the internal pressure of the gas-liquid separator 60 is equal to or higher than the preset pressure value, thereby recovering the flash gas having reduced nitrogen. By joining the boil-off gas of the boil-off gas supply line 16 through line 17 and supplying the separated nitrogen to the gas-combustion apparatus 510 through the gas treatment line 17a, thereby The ratio of nitrogen in the mixed gas (evaporation gas and flash gas) circulating inside can be kept below the preset ratio value.

In the embodiment of the present invention, the ratio of nitrogen accumulated in the boil-off gas is not converged to 40 to 60%, so that the methane (CH 4) in the boil-off gas is chemically entangled by nitrogen and cannot be re-liquefied, but the gas together with the nitrogen By circulating in the liquefied gas treatment system 6 in a state, it is possible to prevent the reliquefaction efficiency of the boil-off gas from dropping rapidly.

As described above, in the present embodiment, by controlling the internal pressure of the gas-liquid separator 60 to be equal to or less than a predetermined pressure value, a predetermined flow rate or more is supplied to the evaporative gas compressor 30, thereby minimizing recycling control, thereby improving driving efficiency. In addition, the ratio of nitrogen in the systems 1 to 6 can be properly controlled to improve the efficiency of the boil-off gas compressor 30 and to stabilize the systems 1 to 6, and the gas-liquid separator ( When the internal pressure of 60) is greater than or equal to the preset pressure value, the flash gas is controlled to be supplied to the liquefied gas storage tank 10 so as to maintain at least a portion of the flash gas to maintain the preset pressure value or less. It can be stored in the, can prevent the environmental pollution due to the discharge of flash gas to the atmosphere, it is possible to increase the internal pressure of the liquefied gas storage tank 10 to ensure that the boil-off gas is well supplied. .

Although the present invention has been described in detail through specific examples, it is intended to describe the present invention in detail, and the present invention is not limited thereto, and should be understood by those skilled in the art within the technical spirit of the present invention. It is obvious that the modifications and improvements are possible.

All simple modifications and variations of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be apparent from the appended claims.

Patent Literature

(Previous Document 1) Registered Patent Publication No. 10-1289212 (Notice Date: July 29, 2013)

(Previous Document 2) Publication No. 10-2011-0118604 (Published Date: October 31, 2011)

Claims

An evaporating gas compressor for pressurizing the evaporating gas discharged from the liquefied gas storage tank;

An boil-off gas liquefier for liquefying at least a portion of the boil-off gas compressed in the boil-off gas compressor;

A gas-liquid separator for separating a flash gas from the boil-off gas liquefied by the boil-off gas liquefier and mixing at least a portion of the flash gas with the boil-off gas; And

And a nitrogen controller for controlling the nitrogen content in the evaporated gas or the flash gas when the nitrogen component of the flash gas is equal to or greater than a preset value.
The method of claim 1,

And a boil-off gas heat exchanger for heat-exchanging the boil-off gas pressurized by the boil-off gas compressor and the boil-off gas supplied from the liquefied gas storage tank.
The method of claim 2,

Further comprising a flash gas heat exchanger for heat-exchanging the flash gas and the boil-off gas compressed in the boil-off gas compressor,

The nitrogen control unit,

A detector for analyzing and detecting a component of the flash gas generated in the gas-liquid separator;

A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And

And a nitrogen composition controller for controlling the operation of the distributor by checking whether the nitrogen component ratio is less than or equal to a preset ratio value in the component of the flash gas received from the detector.
The method of claim 3, wherein the nitrogen composition controller,

Comparing the current ratio value of the nitrogen component in the component of the flash gas received from the detector with the preset ratio value,

If the current ratio value is less than or equal to the preset ratio value, control the operation of the distributor to allow the flash gas to totally or at least partially join the boil-off gas,

When the current ratio value is greater than or equal to the preset ratio value, the operation of the distributor is controlled to supply the nitrogen component separated from the flash gas to the flash gas heat exchanger.

The distributor,

When the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator is greater than or equal to a preset ratio value, the nitrogen is separated according to a control signal of the nitrogen composition controller so that the nitrogen-reduced flash gas is combined with the boil-off gas. And supplying the separated nitrogen to the flash gas heat exchanger.
The method of claim 2,

Further comprising a flash gas heat exchanger for heat-exchanging the flash gas and the boil-off gas compressed in the boil-off gas compressor,

The nitrogen control unit,

A detector for measuring and detecting the internal pressure of the gas-liquid separator;

A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And

And a nitrogen composition controller for controlling the operation of the distributor by checking whether the internal pressure of the gas-liquid separator received from the detector is equal to or less than a predetermined pressure value.
The method of claim 5, wherein the nitrogen composition controller,

Comparing the current pressure value of the gas-liquid separator internal pressure received from the sensor with the preset pressure value,

When the current pressure value is less than or equal to the preset pressure value, controlling the operation of the distributor to allow the flash gas to totally or at least partially join the boil-off gas,

When the current pressure value is equal to or greater than the preset pressure value, the operation of the distributor is controlled to supply nitrogen component separated from the flash gas to the flash gas heat exchanger.

The distributor,

When the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator is greater than or equal to a predetermined pressure value, nitrogen is separated according to a control signal of the nitrogen composition controller to allow the nitrogen-reduced flash gas to merge with the boil-off gas. And supplying the separated nitrogen to the flash gas heat exchanger.
The method of claim 1, wherein the nitrogen control unit,

Liquefied gas processing system, characterized in that for discharging the remaining portion of the flash gas to the gas combustion device.
The method of claim 7, wherein

Further comprising a flash gas heater for heating the flash gas discharged to the gas combustion device by using the waste heat generated in the gas combustion device,

The nitrogen control unit,

A detector for analyzing and detecting a component of the flash gas generated in the gas-liquid separator;

A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And

And a nitrogen composition controller for controlling the operation of the distributor by checking whether the nitrogen component ratio is less than or equal to a preset ratio value in the component of the flash gas received from the detector.
The method of claim 8, wherein the nitrogen composition controller,

Comparing the current ratio value of the nitrogen component in the component of the flash gas received from the detector with the preset ratio value,

If the current ratio value is less than or equal to the preset ratio value, control the operation of the distributor to allow the flash gas to totally or at least partially join the boil-off gas,

When the current ratio value is greater than or equal to the preset ratio value, the operation of the distributor is controlled to supply the nitrogen component separated from the flash gas to the flash gas heat exchanger.

The distributor,

When the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator is greater than or equal to a preset ratio value, the nitrogen is separated according to a control signal of the nitrogen composition controller so that the nitrogen-reduced flash gas is combined with the boil-off gas. And supplying the separated nitrogen to the flash gas heat exchanger.
The method of claim 7, wherein

Further comprising a flash gas heater for heating the flash gas discharged to the gas combustion device by using the waste heat generated in the gas combustion device,

The nitrogen control unit,

A detector for measuring and detecting the internal pressure of the gas-liquid separator;

A distributor for distributing the flow of the flash gas to join at least a portion of the flash gas to the boil-off gas introduced into the boil-off gas compressor; And

And a nitrogen composition controller for controlling the operation of the distributor by checking whether the internal pressure of the gas-liquid separator received from the detector is equal to or less than a predetermined pressure value.
The method of claim 10, wherein the nitrogen composition controller,

Comparing the current pressure value of the gas-liquid separator internal pressure received from the sensor with the preset pressure value,

When the current pressure value is less than or equal to the preset pressure value, controlling the operation of the distributor to allow the flash gas to totally or at least partially join the boil-off gas,

When the current pressure value is equal to or greater than the preset pressure value, the operation of the distributor is controlled to supply nitrogen component separated from the flash gas to the flash gas heat exchanger.

The distributor,

When the ratio of nitrogen contained in the flash gas supplied from the gas-liquid separator is greater than or equal to a predetermined pressure value, nitrogen is separated according to a control signal of the nitrogen composition controller to allow the nitrogen-reduced flash gas to merge with the boil-off gas. And supplying the separated nitrogen to the flash gas heat exchanger.
The method of claim 2,

And a mixer provided upstream of the boil-off gas heat exchanger and mixing the boil-off gas supplied from the liquefied gas storage tank with the flash gas recovered from the gas-liquid separator to supply the boil-off gas to the boil-off gas heat exchanger. Liquefied gas treatment system.