KR101536394B1 - Liquefaction method, liquefaction device, and floating liquefied gas production equipment comprising same - Google Patents

Abstract

A liquefying method, a liquefying device, and a flue gas liquefied gas producing equipment having the liquefying gas capable of suppressing deterioration of liquefaction efficiency when liquefied gas is liquefied, being excellent in safety, and capable of making the equipment compact can be provided. Characterized in that the reduced liquefied gas is heat-exchanged with the low-temperature side heat medium of the same kind and lower in temperature than the high-pressure heat medium, after the reduced-pressure liquefied gas having undergone heat exchange with the single-component high-pressure heat medium is decompressed.

Description

TECHNICAL FIELD [0001] The present invention relates to a liquefaction method, a liquefaction device, and a liquefied gas production facility having the same. [0002] LIQUEFACTION METHOD, LIQUEFACTION DEVICE, AND FLOATING LIQUEFIED GAS PRODUCTION EQUIPMENT COMPRISING SAME [0003]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquefaction method, a liquefaction device and a flue gas liquefied gas production facility equipped with the liquefaction device, and more particularly to liquefaction of natural gas.

Generally, as a liquefaction facility onshore, liquefied gas is liquefied using a cascade refrigeration cycle or a refrigeration cycle using a mixed refrigerant of several kinds of refrigerants (for example, Patent Document 1). In recent years, marine deposits have been studied at installation sites of this liquefaction facility. In the case where a liquefaction facility identical to that on the land is installed on a marine vessel, there is a requirement for the use of marine vessels in consideration of performance against fluctuation, ease of liquefaction, and safety of installation space. Therefore, although it is used for re-liquefaction of the boil-off gas of the LNG, there is a room for application to the nitrogen expansion cycle of the nitrogen refrigerant whose liquefaction efficiency is poor as the liquefaction facility.

Japanese Patent Publication No. 2006-504928 Japanese Patent Publication No. 2006-503252

The heat exchange between natural gas and nitrogen in the nitrogen refrigeration cycle will be described with reference to Fig. In Fig. 5, the vertical axis represents the temperature (占 폚) and the horizontal axis represents the thermal load (kW). In Fig. 5, the solid line represents the natural gas raised to 4 MPa, and the dotted line represents the natural gas which is increased to 15 MPa. 5 indicate nitrogen in the case of heat exchange with natural gas raised to 4 MPa, and the two-dot chain line indicates nitrogen which is heat exchanged with natural gas raised to 15 MPa.

As shown in FIG. 5, when the natural gas (solid line) is stepped up to 4 MPa, a stepped phase in which the temperature change of the natural gas with respect to the thermal load decreases in the course of the temperature change. This step phase occurs because the temperature becomes constant while phase transition occurs between the liquid phase and the phase during the heat exchange of nitrogen as the refrigerant. Therefore, when nitrogen (one-dot chain line) is set to match the pinch point at which the temperature difference between natural gas and nitrogen increased to 4 MPa, the temperature difference between natural gas and nitrogen And the liquefaction efficiency is lowered in comparison with the case where the temperature difference is generally small.

Since the compression cycle of the heating medium nitrogen is driven by a gas turbine because it is a nitrogen compressor having a large required power as in the invention described in Patent Document 2, as a fuel consumed by the gas turbine, a part of the raw material gas to be liquefied is assumed . Since the off gas generated in the liquefaction process is low in pressure as the fuel of the gas turbine, repressurization is required and it is difficult to use. In order to maximize the liquefied gas as a product, there has been a problem of fuel conversion with a good efficiency of process off-gas.

Further, there is a problem that it is difficult to use the off-gas generated in the liquefaction process for the fuel of the gas turbine that drives the nitrogen compressor because the pressure thereof is almost at atmospheric pressure and the nitrogen component is large.

Further, when the nitrogen compressor is driven by a gas turbine and a steam turbine or a hybrid of a steam turbine and an electric motor as in the invention described in Patent Document 2, it is difficult to perform the ship repair, (Redundancy) due to the necessity of electrophoresis.

On the other hand, as shown by the dotted line in Fig. 5, when the natural gas is boosted to 15 MPa, the stepped phase generated in the natural gas stepped up to 4 MPa indicated by the solid line disappears and becomes a substantially straight line. Therefore, the temperature difference between the high-pressure natural gas and the nitrogen (double-dot chain line) raised to 15 MPa can be reduced over the whole, and heat exchange can be carried out. However, in order to heat exchange the high-pressure natural gas with nitrogen, it is necessary to use a shell-and-tube type heat exchanger, so that the heat exchanger becomes large and the installation space of the liquefier can not be reduced.

The present invention has been made in view of the above circumstances and provides a liquefaction method, a liquefying device, and an apparatus for producing a liquefied gas containing such liquefied gas, which are excellent in safety while suppressing a decrease in liquefaction efficiency and capable of making the equipment compact .

In order to solve the above problems, the liquefaction method, the liquefaction device, and the flue gas liquefied gas production facility having the liquefaction device of the present invention employ the following means.

In the first aspect of the present invention, after the pressure of the liquefied gas having undergone heat exchange with the single-component high-pressure heating medium is reduced to a predetermined pressure, the reduced-pressure liquefied gas is heat-exchanged with the low- And liquefying the liquid.

The liquefied gas is liquefied by heat exchange with the heating medium. The liquefaction efficiency of the liquefied gas is preferably such that the temperature difference between the liquefied gas and the heating medium is uniformly small during the heat exchange process. However, when the liquefied gas is at a high pressure, the temperature difference with the heating medium is substantially uniformly small during the heat exchange process, but the heat exchanger performing the heat exchange with the heat medium becomes large. When the liquefied gas is at a low pressure, the liquefied gas becomes stepped in the heat exchange process. Therefore, when the pressure of the heating medium is set in accordance with the point at which the temperature difference between the liquefied gas and the heating medium becomes the smallest (pinch point), the temperature difference between the liquefied gas and the heating medium becomes large in the process other than the pinch point, It falls off.

In order to reduce the temperature difference between the liquefied gas and the heating medium, a cascade method is used in which a mixed heating medium such as hydrogen gas or nitrogen or a plurality of single-component heating medium is heat-exchanged by a plurality of heat exchangers. However, in the case of the cascade method, there is a problem that equipment such as a heat exchanger increases. In the case of using a mixed heating medium, since a plurality of components are used, a plurality of heating mediums are used in accordance with the characteristics of the liquid to be liquefied. However, since a combustible heating medium is used for a part thereof, there is a problem in stability.

Thus, in the present invention, the liquefied gas is heat-exchanged with the single-component high-temperature side heating medium, and thereafter, the pressure is reduced to a predetermined pressure. Further, the decompressed liquefied gas is heat-exchanged with a low-temperature side heat medium of the same kind as the high temperature side heat medium and lower in temperature than the high temperature side heat medium. Thereby, the liquefied gas heat-exchanged with the high-temperature heat medium can be decompressed so as to approximate the temperature change of the low-temperature heat medium medium, and then heat-exchanged with the low temperature side heat medium. Therefore, the temperature difference between the liquefied gas and the high-temperature side heat medium and the low temperature side heat medium can be kept substantially constant. Therefore, the liquefied gas can be efficiently liquefied by using a single-component heating medium.

The predetermined pressure refers to the pressure corresponding to the critical point of the liquefied gas that is heat-exchanged with the heating medium.

The liquefied gas is a raw material gas before liquefaction, and includes natural gas (LNG), liquefied petroleum gas (LPG), and the like.

A second aspect of the present invention is a heat exchanger comprising a heat exchanger for a high temperature side heating medium in which a liquefied gas and a high temperature side heating medium are heat-exchanged, a decompression valve for decompressing the liquefied gas derived from the heat exchanger for high temperature side heating medium, And a heat exchanger for a low temperature side heat medium in which a liquefied gas and a low temperature side heat medium are heat-exchanged, wherein the high temperature side heat medium and the low temperature side heat medium are single components and are of the same type, And the pressure of the liquefied gas led to the heat exchanger is reduced to a predetermined pressure.

Temperature side heating medium is introduced into a heat exchanger for a high temperature side heating medium and a low temperature side heating medium of the same kind as the high temperature side heating medium is introduced into a heat exchanger for a low temperature side heating medium, The pressure reducing valve for reducing the pressure of the liquefied gas to a predetermined pressure is formed. Thereby, the liquefied gas passing through the heat exchanger for the high temperature side heat medium body can be approximated to the temperature change of the low temperature side heat medium body by the pressure reducing valve, and can be guided to the heat exchanger for the low temperature side heat medium body. Therefore, the temperature difference between the liquefied gas and the high-temperature side heat medium and the low temperature side heat medium can be kept substantially constant. Therefore, the liquefied gas can be efficiently liquefied by using a single-component heating medium.

According to a third aspect of the present invention, there is provided a high-pressure turbine comprising a high-pressure turbine in which steam is induced and driven, a high-pressure turbine side shaft connected to the high-pressure turbine, a low pressure turbine in which steam derived from the high- And a low-temperature side heat medium-side heat medium-side heat medium-side heat medium-side heat medium-side heat medium-side heat medium-side heat medium-side heat medium-side heat medium- And a steam generating means for generating steam induced in the high pressure turbine, wherein the high temperature side heating medium compressor is connected to the high pressure turbine side shaft, the low temperature side heating medium compressor is connected to the low pressure side turbine side shaft To the liquefying device.

Pressure turbine is connected to the high-temperature side heat medium compressor and the low-pressure turbine side shaft is connected to the low-temperature side heat medium compressor. The high-pressure turbine shaft and the low-pressure turbine shaft constituting the cross-compound turbine are separated from each other. Therefore, by controlling each of the high-pressure turbine connected to the shaft of the high-pressure turbine and the low-pressure turbine connected to the shaft of the low- The compressor for the heat medium medium and the compressor for the low temperature heat medium medium can be independently controlled. Therefore, the high temperature side heating medium and the low temperature side heating medium can be independently compressed, and the freezing load of the high temperature side heating medium and the low temperature side heating medium can be independently controlled.

In any of the above-described liquefaction apparatuses according to the present invention, the heat exchanger for high temperature side heat medium may be plate type.

According to this constitution, plate type heat exchanger is used for the heat exchanger for high temperature side heat medium in which the liquefied gas and the high temperature side heat medium are heat-exchanged. Therefore, the heat exchanger for high temperature heat medium can be miniaturized. Therefore, it is possible to make the liquefaction apparatus compact.

In any of the above-described liquefaction apparatuses according to the present invention, the steam generating means may be configured to generate steam by using off-gas in the liquefied gas as fuel.

According to this structure, the steam generating means for generating steam by burning off gas in the liquefied gas as fuel is used. Therefore, the steam for driving the cross-compound turbine can be driven by using the off-gas at the atmospheric pressure generated in the liquefier. Therefore, off gas generated from the liquefier can be effectively used.

A fourth aspect of the present invention is a substructure liquefied gas production facility comprising any of the above-described liquefaction devices.

A liquefaction device constituted by a steam-driven cross-compound turbine is used in a flue gas liquefied gas production facility. Therefore, as a cross-compound turbine, a steam turbine used in a conventional marine cycle can be applied. Therefore, a new development of a cross-compound turbine for driving the compressor for the high temperature side heating medium and the compressor for the low temperature side heating medium becomes unnecessary, and the existing device can be effectively used.

In the above-described flue gas liquefied gas production equipment according to the present invention, nitrogen may be used for the high temperature side heating medium and the low temperature side heating medium.

A liquefaction device composed of a compressor for a high temperature side heating medium and a heat exchanger for a low temperature side heating medium using a non-combustible nitrogen as a heat source, a compressor for a low temperature side heating medium, a heat exchanger for a high temperature side heating medium and a heat exchanger for a low temperature side heating medium, . The steam turbine is used for driving the compressor for the high temperature side heating medium and the compressor for the low temperature side heating medium. By these means, it is possible to prevent the risk of explosion by leakage of the combustible gas from the heating medium or the like. Therefore, a device such as a compressor for a high temperature side heating medium, a compressor for a low temperature side heating medium, or a steam turbine can be disposed under the deck. Therefore, the space for disposing the liquefier on the deck can be reduced.

According to the present invention, the liquefied gas is heat-exchanged with the single-component high-temperature side heat medium, and thereafter, the pressure is reduced to a predetermined pressure. Further, the decompressed liquefied gas is heat-exchanged with a low-temperature side heat medium of the same kind as the high temperature side heat medium and lower in temperature than the high temperature side heat medium. Thereby, the pressure of the liquefied gas heat-exchanged with the high temperature heat medium is reduced to approximate the temperature change of the low temperature heat medium, and then heat exchange with the low temperature side heat medium can be performed. Therefore, the temperature difference between the liquefied gas and the high-temperature side heat medium and the low temperature side heat medium can be kept substantially constant. Therefore, the liquefied gas can be efficiently liquefied by using a single-component heating medium.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram of a liquid-fed-gas liquefaction plant equipped with a liquefier according to an embodiment of the present invention; FIG.
Fig. 2 is an enlarged right side view of the liquefier shown in Fig. 1. Fig.
3 is an enlarged view of the left side of the liquefier shown in Fig.
4 is a T-H diagram showing the relationship between natural gas and nitrogen in the liquefier shown in Figs. 2 and 3. Fig.
5 is a T-H diagram showing the relationship between natural gas and nitrogen at a plurality of pressures.

Fig. 1 is a schematic block diagram of a flue gas liquefied gas production facility provided with a liquefaction device according to an embodiment of the present invention. Fig.

A floating LNG (FLNG) 1 comprises a plurality of cargo tanks 2 for storing liquefied natural gas (liquefied gas), a front processing unit 3 and a liquefying unit And a power supply device (not shown) for supplying electric power to the main body type liquefied natural gas manufacturing facility 1.

The liquefied natural gas production facility (liquefied natural gas production facility) (1) is a refinery liquefied natural gas (liquefied gas), which is a raw material gas that is ejected from under the ground or under the seabed at a high pressure, Liquefied natural gas (LNG), which is installed on the sea.

The cargo tank (only three in this figure) 2 stores liquefied natural gas. Cargo tank 2 is a moss-independent spherical tank.

The pretreatment device 3 removes impurities such as carbon dioxide, hydrogen sulfide, moisture and heavy impurities contained in the natural gas which is a raw material gas.

The liquefier apparatus liquefies natural gas by heat exchange with a refrigerant (a heating medium for cooling). The liquefaction apparatus includes a cold box 5 in which a high-pressure nitrogen heat exchanger (not shown) and a low-pressure nitrogen heat exchanger (not shown) to be described later are stored, and a power supply device for supplying power to the inside of the ship. A power unit compartment 6 for a liquefier device in which a compartment 4, a high-pressure nitrogen compressor (not shown), a low-pressure nitrogen compressor (not shown), a compressor-driving steam turbine (not shown) And a storage compartment 7 in which an end flash tank (not shown) and the like are formed.

The cold box 5 is formed on the deck. A high-pressure nitrogen heat exchanger (a heat exchanger for a high-temperature side heat medium) and a low-pressure nitrogen heat exchanger (a heat exchanger for a low temperature side heat medium), which are a part of the liquefier, are formed in the cold box 5. The cold box (5) is subjected to thermal insulation measures to prevent heat from entering and leaving the outside.

The power unit section (6) for the liquefier is formed below the deck. In the power unit section 6 for the liquefier, a high-pressure nitrogen compressor (high temperature side heat medium compressor), a low pressure nitrogen compressor (low temperature side heat medium compressor), and a compressor driving steam turbine A cross-compound turbine) is formed.

The storage compartment 7 is formed under the deck, and an end flash tank is formed.

The in-ship power installation section 4 is formed below the deck, and includes a boiler (not shown), a gas-combustion diesel engine (not shown), and a gas-combustion diesel engine driven generator (not shown). The required power in the primary liquefied natural gas production facility 1 is supplied by these devices formed in the in-ship power installation section 4. [

Next, the configuration of the liquefaction apparatus of the present embodiment will be described with reference to Figs. 2 and 3. Fig.

Fig. 2 is a right-side enlarged view of the liquefier shown in Fig. 1, and Fig. 3 is a left enlarged view of the liquefier.

The liquefier 10 includes a high pressure nitrogen heat exchanger 11, a low pressure nitrogen heat exchanger 12, a high pressure nitrogen compressor 13, a low pressure nitrogen compressor 14, a compressor driving steam turbine 15, (Pressure reducing valve) 16, a boiler (not shown), and an end flash tank 30. The liquefier 10 is divided into a refrigeration cycle and a driving unit for driving the liquefier 10.

The refrigeration cycle includes a high pressure nitrogen loop 17 in which a high pressure natural gas (for example, 15 MPa to 20 MPa) and a refrigerant nitrogen are heat-exchanged, a relatively low pressure natural gas (for example, 6 MPa or less) Pressure nitrogen loop 18 in which heat exchange is performed. These two refrigeration cycles are independent loops.

The driving unit includes a compressor-driven steam turbine (15).

The high-pressure nitrogen loop 17 mainly includes a high-pressure nitrogen heat exchanger 11, a high-pressure nitrogen compressor 13, and a high-pressure nitrogen expander 19. [

The high-pressure nitrogen heat exchanger 11 is heat exchanged between high-pressure natural gas and nitrogen (hereinafter referred to as " high-pressure nitrogen "). As the high-pressure nitrogen heat exchanger 11, for example, plate-type stainless steel plate diffusion-bonded heat exchangers manufactured by Heatric Co., Ltd. are preferably used.

The high-pressure nitrogen compressor (13) compresses high-pressure nitrogen (high-temperature-side heating medium). The high-pressure nitrogen compressor (13) is connected to a high-pressure turbine-side reduction gear (20) connected to a compressor driving steam turbine (15) to be described later. The high-pressure nitrogen compressor (13) compresses high-pressure nitrogen by driving the high-pressure turbine-side reduction gear (20).

The high-pressure nitrogen expander 19 is for expanding high-pressure nitrogen. To the high-pressure nitrogen inflator 19, a high-pressure nitrogen booster 21 is connected. The high-pressure nitrogen booster (21) is driven by the high-pressure nitrogen inflator (19) being rotated and driven by expanding high-pressure nitrogen. The high-pressure nitrogen booster 21 is driven to boost the high-pressure nitrogen.

The low pressure nitrogen loop 18 mainly includes a low pressure nitrogen heat exchanger 12, a low pressure nitrogen compressor 14, and a low pressure nitrogen inflator 22.

The low-pressure nitrogen heat exchanger 12 is heat exchanged between natural gas and nitrogen (hereinafter referred to as " low-pressure nitrogen "). For the low-pressure nitrogen heat exchanger 12, a heat exchanger of an aluminum brazing plate fin type is used.

The low-pressure nitrogen compressor (14) compresses low-pressure nitrogen (low-temperature side heating medium). To the low-pressure nitrogen compressor 14, a low-pressure turbine-side reduction gear 23 connected to a compressor-driving steam turbine 15 to be described later is connected. The low-pressure nitrogen compressor (14) compresses the low-pressure nitrogen by driving the low-pressure turbine-side reduction gear (23).

The low-pressure nitrogen expander (22) expands the low-pressure nitrogen. To the low-pressure nitrogen expander 22, a low-pressure nitrogen booster 24 is connected. The low-pressure nitrogen booster 24 is driven by the low-pressure nitrogen inflator 22 being rotationally driven by expanding the low-pressure nitrogen. The low-pressure nitrogen booster 24 is driven to boost the low-pressure nitrogen.

The compressor-driven steam turbine 15 is a large-scale cross-compound steam turbine used in the ship's cycle. As the compressor-driven steam turbine 15, UST (Ultra Steam Turbine) manufactured by Mitsubishi Heavy Industries, Ltd. is preferably used.

The compressor driving steam turbine 15 includes a high pressure turbine 15a, a medium pressure turbine 15b, a first low pressure turbine 15c and a second low pressure turbine 15d. The high pressure turbine 15a and the intermediate pressure turbine 15b are formed on the primary shaft 15e (high pressure turbine side shaft). The first low pressure turbine (low pressure turbine) 15c and the second low pressure turbine (low pressure turbine) 15d are formed on a secondary shaft (low pressure turbine shaft) 15f.

A high-pressure turbine-side reduction gear 20 is connected to an end of the primary shaft 15e and a low-pressure turbine-side reduction gear 23 is connected to an end of the secondary shaft 15f.

The high-pressure turbine side speed reducer 20 transfers the output from the primary shaft 15e to the high-pressure nitrogen compressor 13. As a result, the high-pressure nitrogen compressor 13 is driven by rotating the high-pressure turbine 15a or the intermediate-pressure turbine 15b.

The low-pressure turbine-side reduction gear 23 transfers the output from the secondary shaft 15f to the low-pressure nitrogen compressor 14. Thereby, the low-pressure nitrogen compressor 14 is driven by the first low-pressure turbine 15c or the second low-pressure turbine 15d being rotationally driven.

The boiler (steam generating means) is a burning boiler that uses liquefied natural gas such as off-gas and boil-off gas, which will be described later, and heavy oil as fuel.

The end flash tank 30 inflates and lowers the temperature of the liquefied natural gas that has passed through the high-pressure nitrogen cycle 17 and the low-pressure nitrogen cycle 18. In the end flash tank 30, the nitrogen component contained in the liquefied natural gas is removed. Further, instead of the end flash tank 30, a pressure reducing valve may be used.

The Row Thompson expansion valve 16 is formed between the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18. The Row Thompson expansion valve 16 inflates the natural gas passed through the high-pressure nitrogen loop 17 by the drawing mechanism.

Next, a method of liquefying natural gas will be described.

Natural gas, which is a raw material gas ejected from below the ground or below the seabed, is led to the pretreatment device 3 formed on the deck of the substructure LNG production facility 1 (see FIG. 1). In the pretreatment device 3, the natural gas contains carbon dioxide, hydrogen sulfide, moisture, heavy components, and the like.

The natural gas purified by the pretreatment device 3 is led to the cold box 5. Natural gas introduced into the cold box 5 is boosted to 15 MPa or more, for example, by the pressure-increasing compressor 31 (see Fig. 2) or the like. It is preferable that the pressure increase is not less than 10 MPa.

The natural gas that has become high in pressure by the pressure-increasing compressor (31) is led to the first heat exchanger (32). The natural gas introduced into the first heat exchanger 32 is heat-exchanged with seawater and the temperature is lowered to, for example, 30 占 폚. The natural gas whose temperature has been lowered by the first heat exchanger (32) is again introduced into the second heat exchanger (33). The natural gas introduced into the second heat exchanger (33) is heat-exchanged with fresh water which is chiller water, and the temperature is lowered to, for example, -20 ° C. Thus, the heat exchange efficiency with the high-pressure nitrogen in the high-pressure nitrogen loop 17 can be improved by performing the heat exchange with the chiller water to perform the quenching.

The natural gas which is turbulent by the second heat exchanger (33) is led to the high pressure nitrogen loop (17). The natural gas introduced into the high-pressure nitrogen loop 17 is led to the high-pressure nitrogen heat exchanger 11 constituting the high-pressure nitrogen loop 17. The natural gas introduced into the high-pressure nitrogen heat exchanger 11 is heat-exchanged with the high-pressure nitrogen in the first subcooling portion K1 formed in the high-pressure nitrogen heat exchanger 11. [ By the heat exchange with the high-pressure nitrogen in the first subcooling portion K1, the natural gas is lowered to, for example, -80 占 폚.

The natural gas whose temperature has been lowered is led to the Row Thompson expansion valve 16. Natural gas introduced into the Row Thompson valve 16 is expanded (decompressed) to, for example, 10 MPa by passing through the Row Thompson expansion valve 16. As a result, the temperature of the natural gas passing through the Row Thompson expansion valve 16 is reduced to, for example, -90 캜.

Further, it is preferable that the natural gas is 10 MPa or less due to expansion by the Row Thompson expansion valve 16.

Natural gas that has been expanded and lowered in temperature by passing through the Row Thompson expansion valve 16 is led to the low pressure nitrogen loop 18. The natural gas induced in the low pressure nitrogen loop 18 is led to the low pressure nitrogen heat exchanger 12 constituting the low pressure nitrogen loop 18. [ The natural gas introduced into the low-pressure nitrogen heat exchanger 12 is heat-exchanged with the low-pressure nitrogen in two stages. That is, after the temperature of the natural gas is reduced to, for example, -135 占 폚 in the second subcooling portion K2 formed in the low-pressure nitrogen heat exchanger 12, For example, -160 DEG C at the subcooling portion K3 to be liquefied.

The liquefied natural gas liquefied in this way is led to the end flash tank 30. The liquefied natural gas led to the end flash tank 30 is expanded in the end flash tank 30, so that the temperature thereof is lowered and nitrogen content in the liquefied natural gas is released. The liquefied natural gas in which the temperature is further lowered and the nitrogen component is released is led to and stored in the cargo tank 2 shown in Fig.

A part of the liquefied natural gas led to the end flash tank 30 is gasified. The amount of gasified liquefied natural gas (hereinafter referred to as "off-gas") is controlled by controlling the temperature of the liquefied natural gas which is led to the end flash tank 30 so that the flash rate is, for example, 10% or less.

Off-gas (for example, -140 占 폚) is led from the end flash tank 30 to the low-pressure nitrogen heat exchanger 12. The off-gas introduced into the low-pressure nitrogen heat exchanger 12 is heat-exchanged with the aforementioned natural gas in the second subcooling portion K2 formed in the low-pressure nitrogen heat exchanger 12. [ As a result, the off-gas has a temperature of, for example, -100 ° C. Further, the off-gas is led to the second condensing section G2 formed in the low-pressure nitrogen heat exchanger 12. [ The off-gas led to the second condensing section G2 is heat-exchanged with the low-pressure nitrogen to be described later. The off-gas heat-exchanged in the second condensing section G2 is heated to, for example, 30 占 폚 and is led out from the low-pressure nitrogen heat exchanger 12.

The boil-off gas in which a part of the liquefied natural gas is vaporized in the cargo tank 2 (see Fig. 1) is also introduced into the low-pressure nitrogen heat exchanger 12 in the same manner as the offgas. The boiling off gas led to the low-pressure nitrogen heat exchanger 12 is heat-exchanged in the second subcooling portion K2 and the second condensing portion G2 formed in the low-pressure nitrogen heat exchanger 12, Is heated to 30 DEG C and is drawn out from the low-pressure nitrogen heat exchanger (12).

Next, the flow of the high-pressure nitrogen will be described.

The high pressure nitrogen circulating in the high pressure nitrogen loop 17 is compressed to, for example, 12 MPa and 120 deg. C by the high pressure nitrogen compressor 13 driven by the high pressure turbine side speed reducer 20. The high-pressure nitrogen that has become high-pressure is led to the third heat exchanger (34). The high-pressure nitrogen introduced into the third heat exchanger 34 is heat-exchanged with the feed water derived from a water supply system (not shown), and the temperature is lowered to 85 캜.

The high-pressure nitrogen having passed through the third heat exchanger (34) is again introduced into the fourth heat exchanger (35). The high-pressure nitrogen introduced into the fourth heat exchanger 35 is heat-exchanged with fresh water derived from a fresh water system (not shown), and the temperature is lowered to 40 캜. High-pressure nitrogen whose temperature has dropped to 40 캜 is led to the high-pressure nitrogen heat exchanger (11). The high-pressure nitrogen introduced into the high-pressure nitrogen heat exchanger (11) is led to the first condensing portion (G1) formed in the high-pressure nitrogen heat exchanger (11).

The high-pressure nitrogen introduced into the first condensing section G1 undergoes heat exchange with the expanded high-pressure nitrogen passing through the first subcooling section K1. As a result, the high-pressure nitrogen that has passed through the first condensing section G1 is lowered to, for example, -25 캜. High-pressure nitrogen whose temperature has been lowered by heat exchange in the first condensing section (G1) is led to the high-temperature nitrogen inflator (19). The high-pressure nitrogen introduced into the high-temperature nitrogen expander 19 is expanded to, for example, 2 MPa and -85 캜. The high-pressure nitrogen whose temperature has been reduced by the expansion is led to the first subcooling portion K1 formed in the high-pressure nitrogen heat exchanger 11. [

The expanded high-pressure nitrogen introduced into the first subcooling portion K1 is heat-exchanged with the aforementioned natural gas and heated to, for example, -30 占 폚. The high-pressure nitrogen heated in the first subcooling portion K1 is heat-exchanged with the high-pressure nitrogen derived from the fourth heat exchanger 35 in the first condensing portion G1 and heated to, for example, 35 占 폚.

The expanded high-pressure nitrogen heated through the first subcooling portion K1 and the first condensing portion G1 formed in the high-pressure nitrogen heat exchanger 11 is led to the high-pressure nitrogen booster 21. [ The expanded high-pressure nitrogen introduced into the high-pressure nitrogen booster 21 is increased in pressure by the high-pressure nitrogen booster 21 and is led to the fifth heat exchanger 36, for example, at 3 MPa and 85 캜.

The pressurized high-pressure nitrogen introduced into the fifth heat exchanger 36 is heat-exchanged with fresh water derived from the fresh water system, and the temperature is lowered to, for example, 40 占 폚. The high-pressure nitrogen that has passed through the fifth heat exchanger (36) and has dropped in temperature is led to the high-pressure nitrogen compressor (13).

As described above, the high-pressure nitrogen is circulated in the high-pressure nitrogen loop 17.

Next, the flow of the low-pressure nitrogen will be described.

The low pressure nitrogen circulating in the low pressure nitrogen loop 18 is compressed to, for example, 5 MPa by the low pressure nitrogen compressor 14 driven by the low pressure turbine side speed reducer 23. The compressed low-pressure nitrogen is led to the sixth heat exchanger (37). The low-pressure nitrogen introduced into the sixth heat exchanger (37) is heat-exchanged with the water supplied from the water supply system, and the temperature is lowered to, for example, 85 ° C.

The low-pressure nitrogen having passed through the sixth heat exchanger (37) is again introduced into the seventh heat exchanger (38). The low-pressure nitrogen introduced into the seventh heat exchanger 38 is heat-exchanged with the water supplied from the water supply system, and the temperature is lowered to, for example, 40 占 폚. The low-pressure nitrogen having passed through the sixth heat exchanger (37) and the seventh heat exchanger (38) and having a reduced temperature is led to the low-pressure nitrogen heat exchanger (12). The low-pressure nitrogen introduced into the low-pressure nitrogen heat exchanger (12) is led to the second condenser (G2) formed in the low-pressure nitrogen heat exchanger (12).

The low-pressure nitrogen introduced into the second condensing section G2 is heat-exchanged with the expanded low-pressure nitrogen passing through the second subcooling section K2. Thus, the low-pressure nitrogen that has passed through the second condensing section G2 is lowered to, for example, -90 占 폚. The low-pressure nitrogen heat-exchanged in the second condensing section (G2) is led from the low-pressure nitrogen heat exchanger (12) to the low-pressure nitrogen expander (22). The low-pressure nitrogen whose temperature is lowered by the low-pressure nitrogen expander 22 is expanded to, for example, 3 MPa and -164 캜. The low-pressure nitrogen whose expansion is further lowered is led to the third subcooling portion K3 formed in the low-pressure nitrogen heat exchanger 12. [

The expanded low-pressure nitrogen introduced into the third subcooling portion K3 is heat-exchanged with the natural gas passed through the second subcooling portion K2 described above, and is heated to -140 DEG C, for example. The expanded low-pressure nitrogen that has passed through the third subcooling portion K3 is again heat-exchanged in the second subcooling portion K2 with the natural gas introduced from the row Thomson expansion valve 16 to the low-pressure nitrogen heat exchanger 12. [ The low pressure nitrogen expanded by heat exchange with the natural gas is heated to, for example, -100 ° C.

The low-pressure nitrogen expanded through the second cooler (K2) is again introduced to the second condenser (G2) formed in the low-pressure nitrogen heat exchanger (12). The expanded low-pressure nitrogen introduced into the second condenser G2 is heat-exchanged with the low-pressure nitrogen derived from the seventh heat exchanger 38. Thereby, the expanded low-pressure nitrogen becomes, for example, 36 DEG C and is led out from the low-pressure nitrogen heat exchanger 12. [

The low-pressure nitrogen heated through the third subcooling portion K3, the second subcooling portion K2 and the second condensing portion G2 formed in the low-pressure nitrogen heat exchanger 12 is supplied to the low-pressure nitrogen booster 24 . The expanded low-pressure nitrogen introduced into the low-pressure nitrogen booster 24 is boosted by the low-pressure nitrogen booster 24 to become, for example, 1 MPa and 85 캜. The boosted low-pressure nitrogen is directed to the eighth heat exchanger 39.

The pressurized low-pressure nitrogen introduced into the eighth heat exchanger 39 is heat-exchanged with the water supplied from the water supply system, and the temperature is lowered to, for example, 40 占 폚. The low-pressure nitrogen whose temperature has passed through the eighth heat exchanger (39) is led to the low-pressure nitrogen compressor (14).

As described above, the low-pressure nitrogen is circulated in the low-pressure nitrogen loop 18.

Next, the flow of the steam will be described.

The off-gas and the boil-off gas, which are led out from the second condensing section G2 formed in the low-pressure nitrogen heat exchanger 12 and heated to, for example, 30 DEG C, are led to the boiler. The off-gas and the boil-off gas led to the boiler are burned as the fuel of the boiler and generate steam of high temperature and high pressure (for example, 555 DEG C, 11 MPa). The steam generated in the boiler is led to the high-pressure turbine 15a of the compressor-driven steam turbine 15. The steam introduced into the high-pressure turbine 15a is converted into the rotational energy of the high-pressure turbine 15a so as to rotate the high-pressure turbine 15a. The primary shaft 15e rotates as the high-pressure turbine 15a is rotationally driven. As the primary shaft 15e rotates, the intermediate-pressure turbine 15b and the high-pressure turbine side speed reducer 20 formed on the primary shaft 15e are driven.

On the other hand, the steam in which the high-pressure turbine 15a is rotationally driven becomes, for example, 2 MPa and is led out from the high-pressure turbine 15a. The steam derived from the high-pressure turbine 15a is guided to a reheater (not shown). The reheat-induced steam is reheated to, for example, a reheating steam at 555 ° C. This reheated steam is directed to the intermediate-pressure turbine 15b of the compressor-driven steam turbine 15.

The reheated steam guided to the intermediate pressure turbine 15b converts the thermal energy into the rotational energy of the intermediate pressure turbine 15b to rotationally drive the intermediate pressure turbine 15b. The primary-side shaft 15e is rotated again by the rotation of the intermediate-pressure turbine 15b. As the primary shaft 15e rotates again, the high-pressure turbine speed reducer 20 formed on the primary shaft 15e is driven again.

In the intermediate pressure turbine 15b, a part of steam is drawn from the middle stage thereof. The additional steam of 1 MPa, for example, is used for the high pressure steam for use in the feed liquefied natural gas production facility 1 (see Fig. 1).

The steam passing through the entire end of the intermediate-pressure turbine 15b is, for example, 110 DEG C and is led to the first low-pressure turbine 15c of the compressor-driven steam turbine 15. [

The steam introduced into the first low-pressure turbine 15c converts the heat energy into rotational energy of the first low-pressure turbine 15c to rotationally drive the first low-pressure turbine 15c. The second low-pressure turbine 15c is rotationally driven to rotate the secondary shaft 15f. The second low-pressure turbine 15d and the low-pressure turbine-side reduction gear 23 formed in the secondary shaft 15f are driven by the rotation of the secondary shaft 15f.

In the first low-pressure turbine 15c, a part of the steam is plumbed from the middle portion thereof. The additional steam of, for example, 0.1 MPa is used for the low-pressure steam steam used in the substation liquefied natural gas production facility 1 (see Fig. 1).

The steam having passed through the entire end of the first low-pressure turbine 15c is led to the second low-pressure turbine 15d formed in the secondary shaft 15f.

Further, the second low-pressure turbine 15d is supplied separately with assist steam of, for example, 0.6 MPa from an assist steam supply system (not shown). The second low-pressure turbine 15d is rotationally driven by the supplied assist steam. The second low-pressure turbine 15d is rotationally driven so that the low-pressure turbine-side reduction gear 23 connected to the secondary shaft 15f can be driven.

The steam passing through the entire end of the first low pressure turbine 15c and the assist steam driving the second low pressure turbine 15d are led to a main condenser (main condenser) not shown and heat exchanged with the seawater to be plural .

Thus, the compressor-driving steam turbine 15 can control the high-pressure turbine-side reduction gear 20 and the low-pressure turbine-side reduction gear 23 independently of each other by the primary shaft 15e and the secondary shaft 15f And the low-pressure turbine-side reduction gear 23 can also be independently controlled by driving the second low-pressure turbine 15d by the assist steam.

Here, a T-H diagram of the natural gas and the nitrogen refrigerant of this embodiment will be described with reference to Fig. 4 and Fig. 5 described above.

4 shows a T-H diagram of the natural gas and the nitrogen refrigerant of the present embodiment.

In Fig. 4, the horizontal axis represents the thermal load (kW), and the vertical axis represents the temperature (占 폚). The solid line in Fig. 4 represents the natural gas raised to 15 MPa or 4 MPa, and the one-dot chain line represents the nitrogen which is heat exchanged with the natural gas when the pressure is raised to 4 MPa.

5 shows a T-H diagram showing the relationship between natural gas and nitrogen at a plurality of pressures.

In Fig. 5, the horizontal axis represents the thermal load (kW), and the vertical axis represents the temperature (占 폚). The solid line in Fig. 5 represents natural gas boosted to 15 MPa, the dotted line represents natural gas boosted to 4 MPa, the one-dot chain line represents nitrogen with a small temperature difference to natural gas of relatively low pressure of 4 MPa, The two-dot chain line indicates nitrogen having a small temperature difference with respect to natural gas at a high pressure of 15 MPa.

As shown in Fig. 5, a natural gas of 4 MPa (solid line) has a stepped phase in which a temperature change hardly occurs in a process of heat exchange with nitrogen and the temperature is lowered. In the liquefaction of natural gas, since the liquefaction efficiency is good when the temperature difference from nitrogen is small, the pinch point where the temperature difference between nitrogen (dashed line) and natural gas becomes small becomes stepwise. Therefore, in the heat exchange process other than the step-by-step, the temperature difference between the natural gas and the nitrogen becomes large, and the liquefaction efficiency decreases as a whole.

When the natural gas is raised to a high pressure of, for example, 15 MPa (dotted line), the stepped phase generated in the natural gas of 4 MPa disappears, and the temperature change of the natural gas becomes substantially linear. As a result, the temperature difference between natural gas of 15 MPa and nitrogen (chain double-dashed line) is reduced, and liquefaction can be efficiently performed over the entire range.

Further, as shown in Fig. 5, at the low temperature portion of the natural gas, even when the natural gas pressure was 15 MPa or 4 MPa, the temperature difference between the natural gas and nitrogen was small.

In the present embodiment, as shown in Fig. 4, natural gas is boosted to a high pressure (for example, 15 MPa) at the high temperature portion of the natural gas and natural gas is compressed at a relatively low pressure ) So as to make the temperature difference almost uniform over the entire region of the heat exchange process by performing heat exchange with nitrogen.

That is, in the high-temperature section of the natural gas, high-pressure natural gas is heat-exchanged with high-pressure nitrogen in the high-pressure nitrogen loop 17, and low-temperature natural gas is heat-

The linear Thomson expansion valve 16 is formed between the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18 to expand the high-pressure natural gas of 15 MPa to a low-pressure natural gas of 4 MPa. As a result, as shown in Fig. 4, the temperature difference between the natural gas at the high-pressure portion and the low-pressure natural gas at 4 MPa can be reduced, and the temperature change over the entire region of the natural gas can be made substantially linear.

As described above, the liquefying apparatus 10 according to the present embodiment and the flue gas liquefied natural gas producing plant 1 equipped with the liquefier 10 exhibit the following operational effects.

(Low-temperature side heat medium) of the same kind as the high-pressure nitrogen is introduced into the low-pressure nitrogen heat exchanger (low-temperature side heat medium) through a high-pressure nitrogen heat exchanger (heat exchanger for high temperature side heat medium) A decompression valve (decompression valve) 12 for decompressing the natural gas (the liquefied gas) to a predetermined pressure is provided between the high-pressure nitrogen heat exchanger 11 and the low-pressure nitrogen heat exchanger 12, (16). Thus, the natural gas having passed through the high-pressure nitrogen heat exchanger 11 can be approximated to the temperature change of the low-pressure nitrogen by the low-pressure Thomson expansion valve 16 and can be guided to the low-pressure nitrogen heat exchanger 12. Therefore, the temperature difference due to the heat exchange between the natural gas and the high-pressure nitrogen and the temperature difference due to the heat exchange between the natural gas and the low-pressure nitrogen can be maintained almost constant in the heat exchange process. Therefore, natural gas can be efficiently liquefied by using a single component of nitrogen (heat medium).

A high-pressure nitrogen compressor (high-temperature side heating medium compressor) 13 is connected to a primary shaft (high-pressure turbine side shaft) 15e via a high-pressure turbine side speed reducer 20 and a secondary shaft Pressure nitrogen compressor (low-temperature-side heat medium compressor) 14 via a low-pressure turbine-side reduction gear 23. The low- Since the primary shaft 15e and the secondary shaft 15f constituting the compressor-driven steam turbine (cross-compound turbine) 15 are separated from each other, the high-pressure turbine (high-pressure turbine) (Low-pressure turbine) 15a and a second low-pressure turbine (low-pressure turbine) 15d respectively connected to the intermediate-pressure turbine (high-pressure turbine) 15b, The nitrogen compressor (13) and the low-pressure nitrogen compressor (14) can be independently controlled. Therefore, the high-pressure nitrogen and the low-pressure nitrogen can be independently compressed, and the refrigeration load of the low-pressure nitrogen circulating through the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18 can be controlled independently.

The stainless steel plate diffusion type (plate type) is used for the high-pressure nitrogen heat exchanger 11 in which natural gas and high-pressure nitrogen are heat-exchanged. Therefore, the high-pressure nitrogen heat exchanger 11 can be downsized. Therefore, the cold box 5 in which the high-pressure nitrogen heat exchanger 11 constituting the liquefaction apparatus 10 is accommodated can be made compact.

Further, the pressure of the natural gas is lowered by passing through the Row Thompson expansion valve 16, so that an aluminum brazed plate fin type (plate type) is used for the low-pressure nitrogen heat exchanger 12. Therefore, the low-pressure nitrogen heat exchanger 12 can also be downsized. Therefore, the cold box 5 constituting the liquefaction apparatus 10 can be made more compact.

(Steam generating means) for generating steam by burning off gas and boil-off gas in the liquefied natural gas as fuel. Therefore, the steam for driving the compressor-driven steam turbine 15 can be driven using off-gas or boil-off gas generated in the liquefied gas device 10. [ Therefore, off gas or boiling off gas generated from the liquefier 10 can be effectively used.

The liquefier 10 constituted by the steam turbine 15 for driving a compressor driven by steam is used for a liquefied natural gas producing plant (a liquefied natural gas producing plant). For this reason, a cross-compound type steam turbine used for a conventional warming-up period can be applied to the compressor-driven steam turbine 15. Therefore, it is not necessary to newly develop the compressor-driven steam turbine 15 to drive the high-pressure nitrogen compressor 13 and the low-pressure nitrogen compressor 14, so that existing equipment can be effectively used.

Pressure nitrogen compressor (13) and a low-pressure nitrogen compressor (14) using a non-combustible nitrogen as a heating medium and a liquefaction device (10) constituted by a high-pressure nitrogen heat exchanger (11) And is used for the liquefied natural gas production facility (1). The high-pressure nitrogen compressor (13) and the low-pressure nitrogen compressor (14) are driven by using a compressor-driven steam turbine (15). Thus, it is possible to prevent the danger of explosion by leakage of a combustible gas such as a heating medium. Pressure nitrogen compressor (14), a compressor-driven steam turbine (15) and a compressor-driven steam turbine (15) are connected to a power unit section (6) for a liquefying apparatus below a deck of a liquefied natural gas producing plant (1) And the like can be arranged. Therefore, the space for disposing the liquefier 10 on the deck can be reduced.

In the present embodiment, nitrogen is used as the heating medium used in the liquefier 10, but a non-combustible heating medium may be used.

In the present embodiment, liquefied natural gas (LNG) is used as the liquefied gas, but it may be a liquefied petroleum gas (LPG) or the like.

In the present embodiment, natural gas introduced from the pressure-increasing compressor 31 to the high-pressure nitrogen heat exchanger 11 is first cooled by the first heat exchanger 32 and the second heat exchanger 33. However, And the second heat exchanger 33 may not be formed by the chiller water. Pressure nitrogen and low-pressure nitrogen introduced into the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18 can be increased by using the chiller water at a temperature of about -10 DEG C to -30 DEG C. However, It does not have to be frozen.

The high-temperature exhaust gas discharged from the gas-fired diesel engine provided in the in-ship power installation section (4) is led to an arrangement recovery device (not shown) such as an arrangement recovery boiler to generate steam, The generated steam may be guided to the compressor-driven steam turbine 15 and used for starting the compressor-driven steam turbine 15 or the like. As a result, the arrangement from the gas-fired diesel engine can be effectively utilized.

1: Substrate-type liquefied natural gas production facility (Subsidiary liquefied gas production facility)
10: Liquefaction facility
11: High-pressure nitrogen heat exchanger (heat exchanger for high-temperature side heating medium)
12: Low pressure nitrogen heat exchanger (heat exchanger for low temperature heat medium)
16: Row Thompson expansion valve (pressure reducing valve)

Claims (7)

delete A heat exchanger for a high temperature heat medium in which the liquefied gas and the high temperature heat medium are heat-exchanged,
A decompression valve for decompressing the liquefied gas derived from the heat exchanger for the high temperature heat medium,
And a heat exchanger for a low temperature side heat medium in which the liquefied gas passed through the pressure reducing valve and the low temperature side heat medium are heat-exchanged,
The high temperature side heating medium and the low temperature side heating medium are single components and are of the same kind,
Wherein the pressure reducing valve reduces pressure of the liquefied gas guided to the heat exchanger for the low temperature side heating medium to a predetermined pressure,
A high pressure turbine in which steam is induced and driven,
A high pressure turbine side shaft connected to the high pressure turbine,
A low pressure turbine in which steam derived from the high pressure turbine is guided and driven;
A cross-compound turbine having a low-pressure turbine side shaft connected to the low-pressure turbine,
A high-temperature heat medium compressor for compressing a high-temperature heat medium medium introduced into the heat exchanger for the high temperature heat medium medium;
A low temperature side heat medium compressor for compressing the low temperature side heat medium which is led to the low temperature side heat medium heat exchanger,
And a steam generating means for generating steam induced in the high-pressure turbine,
And the compressor for the high temperature side heating medium is connected to the shaft on the side of the high pressure turbine, and the compressor for the low temperature side heating medium is connected to the shaft on the low pressure side. delete 3. The method of claim 2,
The heat exchanger for high temperature side heating medium is plate type. 3. The method of claim 2,
Wherein the steam generating means generates steam by using off-gas in the liquefied gas as fuel. A liquid liquefied natural gas production facility equipped with the liquefaction device according to any one of claims 2, 4 and 5. The method according to claim 6,
And the nitrogen is used for the high temperature side heating medium and the low temperature side heating medium.

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