KR20160129100A - Natural gas liquefying system and liquefying method - Google Patents

Abstract

[PROBLEMS] To increase the discharge pressure of a compressor by using a power generated in an expander by expansion of a raw material gas, and to reduce a cooling performance required for a cooler. [MEANS FOR SOLVING PROBLEMS] A natural gas liquefaction system (1) comprises a first inflator (3) for generating a power by inflating natural gas obtained under a pressurized state as a raw material gas, a first inflator (3) A distillation device (15) for reducing or removing heavy materials in the raw material gas by distilling the raw material gas cooled by the first cooler; A first compressor 4 for compressing the raw material gas in which the heavy components are reduced or eliminated in the distillation apparatus and a liquefier 21 for liquefying the raw material gas compressed by the first compressor by heat exchange with the refrigerant .

Description

Technical Field [0001] The present invention relates to a natural gas liquefying system and a liquefying method,

The present invention relates to a liquefaction system and a liquefaction method of natural gas for cooling natural gas to produce liquefied natural gas.

Natural gas collected from a gas field or the like is liquefied in a liquefaction station or the like, and is stored or transported as LNG (liquefied natural gas). The LNG cooled to about -162 占 폚 has an advantage that the volume thereof is drastically reduced as compared with the natural gas (gas), and there is no need to store it at a high pressure. Generally, in the liquefaction treatment of natural gas, moisture, acid gas components and impurities such as mercury contained in the raw material gas are removed in advance, and heavy materials (benzene, C5 + hydrocarbons and the like having a relatively high solidification point) The raw material gas is liquefied.

As a means for liquefying natural gas in the past, a number of techniques have been developed using expansion by an expansion valve or a turbine, or heat exchange by a refrigerant having a low boiling point (including light hydrocarbon such as methane, ethane, and propane). For example, it is possible to use a cooler for cooling a raw material gas in which impurities have been removed in advance, an expander for isentropically expanding the raw material gas cooled by the cooler, and a raw material gas decompressed by the expander, A compressor for compressing the outflow gas from the distillation apparatus using a force of expansion generated in the inflator as a power source by providing a shaft common to the inflator and a distillation device for separating the outflow gas compressed by the compressor from the mixed refrigerant There is known a liquefaction system of a natural gas having a liquefier (main heat exchanger) liquefied by heat exchange (see Patent Document 1).

Patent Document 1: U.S. Patent No. 4065278

However, in the conventional natural gas liquefaction system as described in Patent Document 1, in order to reduce the load of the liquefier (main heat exchanger) and increase the efficiency of the liquefaction process, the discharge pressure of the compressor is increased To increase the pressure of the raw material gas introduced into the reaction chamber).

On the other hand, in order to increase the discharge pressure of the compressor, a larger power is required. In the conventional technology, the raw material gas cooled by the cooler is expanded by the expander. There is a problem in that it is difficult to increase the discharge pressure of the discharge gas.

In addition, in the above-mentioned prior art, since the cooling of the raw material gas by the cooler is performed before expanding the raw material gas in the inflator, the cooling capacity required for the cooler is relatively large, which leads to a problem that the cooling facility cost and operation cost are increased.

Further, in the above-mentioned prior art, since a condensation component is generated in the raw material gas by cooling the raw material gas by the cooler, a gas-liquid separating tank for separating (removing) the condensed component in the raw material gas before introducing the raw material gas from the cooler into the expander it may be necessary to provide a gas-liquid separation vassel. In addition, since the temperature of the raw material gas from the compressor rises, the temperature difference between the middle inlet of the liquefier and the refrigerant increases, thereby increasing the cooling capability required of the cooler.

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art, and it is an object of the present invention to provide a compressor capable of increasing the discharge pressure of a compressor by using a power generated by an expander by expansion of a raw material gas, And to provide a liquefaction system and a liquefaction method of natural gas.

In a first aspect of the present invention, there is provided a natural gas liquefaction system (1) for cooling natural gas to produce liquefied natural gas, comprising: a first inflator (1) for generating power by expanding natural gas obtained under a pressurized state as a raw material gas A first cooler (11, 12) for cooling the raw material gas decompressed by the expansion in the first inflator, and a second cooler for cooling the raw material gas cooled by the first cooler, A first compressor (4) for compressing the raw material gas in which the heavy component is reduced or removed by using the power generated by the first inflator, a distillation device (15) for reducing or removing the heavy component, A second heat exchanger for heat exchange between the raw material gas introduced into the first compressor and the raw material gas compressed by the first compressor, and a second heat exchanger for exchanging the raw material gas compressed by the first compressor In that it includes a liquefier (21) for liquefied by heat exchange with a coolant characterized.

In the natural gas liquefaction system according to the first aspect, the discharge pressure of the first compressor is increased by using the power generated by the first expander by the expansion of the raw material gas before being cooled by the first cooler, It is possible to reduce the cooling performance required for the cooler.

According to a second aspect of the present invention, there is further provided a heat exchanger (69) for performing heat exchange between the raw material gas introduced into the distillation apparatus and the overhead effluent (overhead distillate) from the distillation apparatus .

In the system for liquefying natural gas according to the second aspect, even when the temperature level of the raw material gas introduced into the liquefier can be lower than an appropriate range, it is possible to prevent the overflow from the distillation apparatus by heat exchange with the raw material gas introduced into the distillation apparatus. The temperature of the raw material gas can be brought close to the temperature at the introduction position in the liquefier by raising the temperature of the effluent.

According to a third aspect of the present invention, there is further provided a second heat exchanger (79) for performing heat exchange between the raw material gas introduced into the first compressor and the raw material gas after being compressed by the first compressor.

In the natural gas liquefaction system according to the third aspect, even when the temperature level of the raw material gas introduced into the liquefier after the compression by the first compressor can be raised to an appropriate range, By cooling the raw material gas from the first compressor by heat exchange, the temperature of the raw material gas can be brought close to the temperature at the introduction position in the liquefier.

As described above, according to the present invention, it is possible to increase the discharge pressure of the compressor by using the power generated in the expander by the expansion of the raw material gas in the liquefaction system of the natural gas, and reduce the cooling performance required for the cooler.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a configuration diagram showing a flow of a liquefaction process in a natural gas liquefaction system according to a first embodiment; FIG.
Fig. 2 is a first reference example corresponding to the first embodiment. Fig. 2 is a configuration diagram showing a flow of a liquefaction process in a conventional natural gas liquefaction system
3 is a second reference example corresponding to the first embodiment, and is a diagram showing a flow of a liquefaction process in a conventional liquefaction system of natural gas
4 is a configuration diagram showing the flow of liquefaction processing in the natural gas liquefaction system according to the first modified example of the first embodiment
5 is a configuration diagram showing the flow of liquefaction processing in the natural gas liquefaction system according to the second modification of the first embodiment
6 is a configuration diagram showing the flow of liquefaction processing in the natural gas liquefaction system according to the third modified example of the first embodiment
7 is a configuration diagram showing the flow of liquefaction processing in the natural gas liquefaction system according to the fourth modification of the first embodiment
8 is a configuration diagram showing the flow of liquefaction processing in the natural gas liquefaction system according to the second embodiment
Fig. 9 is a configuration diagram showing the flow of the liquefaction process in the natural gas liquefaction system according to the first modified example of the second embodiment
10 is a configuration diagram showing the flow of liquefaction processing in the natural gas liquefaction system according to the fifth modification of the first embodiment

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment)

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a configuration diagram showing a flow of a liquefaction process in a natural gas liquefaction system according to a first embodiment of the present invention; FIG. Table 1 shown later is the simulation results (the same applies to Tables 2 to 12) relating to the liquefaction treatment in the natural gas liquefaction system according to the first embodiment. Table 1 shows an example of the temperature, the pressure, the flow rate, and the molar fraction of each component of the liquefied natural gas (hereinafter referred to as raw material gas) in the liquefaction system 1 according to the first embodiment. The columns (i) - (ix) in Table 1 show numerical values at respective positions of the liquefaction system 1 to which the same numbers (i) - (ix) are given in FIG. 1, respectively.

In the present embodiment, natural gas containing about 80 to 98 mol% of methane is used as a raw material gas. The raw material gas contains at least one of 0.1 mol% or more of C5 + hydrocarbons and 1 ppm or more of BTX (benzene, toluene, xylene) as a middle fraction. Details of components other than methane in the raw material gas are shown in Table 1 (column (i)). The term " raw material gas " in this specification does not mean that it is strictly in a gaseous state, but refers to an object to be liquefied (including during processing) in the liquefaction system 1.

In the liquefaction system 1, the raw material gas is supplied to the water removal device 2 through the line L1, where moisture in the raw material gas is removed in order to prevent troubles due to icing or the like. Here, the raw material gas supplied to the water removal device 2 has a temperature of about 20 占 폚, a pressure of about 5,830 kPaA, and a flow rate of about 720,000 kg / hr. The water removal device 2 is composed of a dehydration tower filled with a moisture absorbent (molecular sieve or the like), and dehydration treatment is performed so that water content in the raw material gas is preferably less than 0.1 ppm mol. As the moisture removal device 2, other known devices may be employed as long as moisture in the raw material gas can be removed at a desired rate or less.

Although not described in detail here, the liquefaction system 1 is provided with a separation facility for separating the natural gas condensate as a pre-process of the water removal device 2, an acid gas removal facility for removing acid gas components such as carbon dioxide gas and hydrogen sulfide , A mercury removal facility for removing mercury, and the like can be provided. In the water removal device 2, a raw material gas from which impurities have been removed is usually supplied by each of these facilities. The raw material gas supplied to the water removal device 2 preferably contains less than 50 ppm mol of carbon dioxide (CO ₂ ), less than 4 ppm mol of hydrogen sulfide (H ₂ S), less than 20 mg / Nm 3 of sulfur, Of mercury. ≪ / RTI >

The supply source of the source gas is not particularly limited. In the liquefaction system 1, for example, a gas obtained under a pressurized condition, which is taken from, for example, a shale gas, a tight sand gas, or a colbbed methane, can be used as a source gas. As a method of supplying the source gas to the liquefaction system 1, a gas temporarily stored in a storage tank or the like may be supplied not only through piping from a gas field or the like.

The moisture-removed raw material gas in the moisture removal device 2 is sent to the first inflator 3 through the line L2. The first inflator (3) comprises a turbine device for reducing the pressure of the raw material gas by expanding the flowing source gas isentropically so as to extract the power (or energy) based on the expansion force. In the expansion process (first expansion process) by the first expander 3, the pressure and the temperature of the material gas are lowered. The first inflator 3 has a shaft 5 coaxial with the first compressor 4 which will be described later in detail so that the power generated by the first inflator 3 is transmitted as the power of the first compressor 4 So that it can be used. When the number of revolutions of the first inflator 3 is lower than the number of revolutions of the first compressor 4, a booster or the like can be provided between the first inflator 3 and the first compressor 4. The temperature of the raw material gas discharged from the first inflator 3 is lowered to about 8.3 캜 and the pressure is lowered to about 4,850 kPaA. The pressure of the raw material gas discharged from the first inflator 3 is usually in the range of 3,000 kPaA-5,500 kPaA (30 bara-55 bara), and more preferably in the range of 3,500 kPaA-5,000 kPaA (35 bara-50 bara).

The raw gas from the first inflator 3 is sent to the cooler 11 through a line L3. On the downstream side of the cooler 11, a cooler 12 is connected to constitute a cooler group (first cooler). The raw material gas is sequentially cooled by heat exchange (first cooling step) with the refrigerant in the first coolers 11, 12. The temperature of the raw material gas cooled by the first coolers 11 and 12 is usually in the range of -20 DEG C to 50 DEG C, and more preferably in the range of -25 DEG C to 35 DEG C. When the raw material gas introduced into the liquefaction system 1 is relatively high in pressure (for example, 100 bara or more), the outlet temperature of the raw material gas in the first inflator 3 is relatively low (for example, -30 ° C), so that the first coolers 11 and 12 may be omitted. The omission of the cooler on the upstream side of the distillation apparatus 15 is also applicable to the structures shown in Figs. 5 to 7 and the like which will be described later.

In the present embodiment, the C3-MR (C3-MR: pre-cooled mixed refrigerant) system is adopted. In the first coolers 11 and 12, propane is used as refrigerant to precool the raw material gas, , Liquefying the raw material gas and performing supercooling to a cryogenic temperature with a refrigeration cycle using a mixed refrigerant described later in detail. Propane refrigerant C3R having a medium pressure (MP) and a low pressure (LP) is used as the first coolers 11 and 12 and the raw material gas is introduced into the first coolers 11 and 12 stepwise And cooled. Although not shown, the first coolers 11 and 12 constitute a part of a known refrigeration cycle including a compressor for a propane refrigerant, a condenser, and the like.

The liquefaction system 1 is not limited to the C3-MR system, and may be a cascade system constituting individual refrigeration cycles by a plurality of refrigerants (methane, ethane, propane, etc.) having different boiling points, a mixed refrigerant such as ethane, The DMR (Double Mixed Refrigerant) system used in the pre-cooling process and the MFC (Mixed Fluid Cascade) system in which heat exchange is performed stepwise using mixed refrigerants of different series for each cycle of pre-cooling, liquefaction and supercooling can do.

The raw material gas from the cooler 12 is sent to the distillation unit 15 via line L4. At this time, the pressure of the raw material gas may be made to be equal to or lower than the critical pressure of methane and heavy matter by expansion or the like in the first inflator (3). The distillation apparatus 15 is composed of a distillation tower having a plurality of shelf stages therein, and removes heavy components contained in the raw material gas (distillation step). The liquid containing the heavy component is discharged through a line L5 connected to the tower bottom of the distillation apparatus 15. [ The liquid containing the heavy component discharged from the line L5 to the outside is a temperature of about 177 DEG C and a flow rate of about 20,000 kg / hr. Here, the " heavy component " refers to a high boiling point component such as benzene or C5 + hydrocarbon having relatively high freezing point, and may include C2 + hydrocarbons other than methane. The line L5 is provided with a circulation section having a reboiler 16 so that a part of the liquid discharged from the bottom of the tower of the distillation apparatus 15 is supplied to the reboiler 16 from the outside Oil) and then circulated to the distillation unit 15 again.

On the other hand, in the distillation apparatus 15, the raw material gas (light component) containing methane as the main component as the low boiling point component is separated as the overhead effluent, and this raw material gas is once introduced into the liquefier 21 through the line L6) And cooled in the tube circuits 22a and 22b. Here, the raw material gas delivered to the line L6 is at a temperature of about -45.6 占 폚 and a pressure of about 4,700 kPaA. In addition, the raw material gas from which the heavy matters are removed by the distillation apparatus 15 becomes C5 + of less than 0.1 mol%, and BTX (benzene, toluene, xylene) of less than 1 ppm mol. The raw material gas is cooled to a temperature of about -65.2 占 폚 by flowing through the pipe circuits 22a and 22b and then sent from the liquefier 21 to the first gas-liquid separation tank 23 through the line L7.

The liquefaction device 21 constituting the main heat exchanger of the liquefaction system 1 is constructed in such a manner that the heat transfer pipe (tube bundle) for flowing the raw material gas and the refrigerant is wound in a coil shape, Wound type heat exchanger. The liquefaction device 21 is provided with a low temperature region Z1 located at the bottom (bottom portion) where the mixed refrigerant is introduced and having the highest temperature (here, temperature region) and a low temperature region Z2 located at the middle portion, A zone Z2 and a cold zone Z3 located at an upper portion where the liquefied raw material gas is discharged and the lowest temperature is provided. Further, in the first embodiment, the low temperature side tempered region Z1b and the high temperature side low temperature side region Z1b are formed in the low temperature side region Z1. The tube circuits 22a and 22b together with the tube circuits 42a and 42b and the tube circuits 51a and 51b through which the mixed refrigerant flows and which will be described in detail later constitute a tube bundle arranged in the heat-source zones Z1a and Z1b, respectively. In the present embodiment, the high temperature side heat zone Z1a is about -35 DEG C at the upstream (inlet) side of the raw material gas to be cooled and about -50 DEG C at the downstream (outlet) side of the raw material gas, The zone Z1b is about -50 DEG C on the upstream side of the raw material gas and about -65 DEG C on the downstream side of the raw material gas while the middle zone Z2 is about -65 DEG C on the upstream side of the raw material gas, And the cold zone Z3 is set to about -135 DEG C at the upstream side of the raw material gas and about -155 DEG C at the downstream side of the raw material gas. However, the temperatures on the upstream side and the downstream side in each region are not necessarily limited to those shown here. Further, the value of each temperature may fluctuate within a predetermined range (for example, in a range of about +/- 5 DEG C).

The first gas-liquid separation tank 23 separates the liquid component (condensed component) in the raw material gas, and liquid such as hydrocarbon constituting the liquid component is distilled again by the reflux pump 24 provided in the line L8 To the device (15). On the other hand, in the first gas-liquid separation tank 23, the raw material gas containing methane as a main component constituting the gaseous component is sent to the first compressor 4 through the line L9. Here, the raw material gas delivered to the line L8 has a flow rate of approximately 83,500 kg / hr, and the raw material gas delivered to the line L6 has a flow rate of approximately 780,000 kg / hr. The first gas-liquid separation tank 23 can be cooled using a mixed refrigerant or an ethylene refrigerant to be described later.

The first compressor (4) is a single-stage centrifugal compressor in which a wing wheel for compressing gas is mounted on a shaft (5) coaxial with the first inflator (3). The raw material gas compressed by the compression process (first compression process) by the first compressor 4 is introduced into the liquefier 21 through the line L10. The raw material gas discharged from the first compressor (4) to the line (L10) has a pressure of about 5,500 kPaA at a temperature of about -51 캜. The raw material gas introduced into the liquefaction device 21 is preferably compressed by the first compressor 4 to a pressure of at least 5,171 kPaA.

The line L10 is connected to the tube circuit 30 disposed in the heat-up region Z1b in the liquefier 21 and the upper end of the tube circuit 30 is connected to the tube circuit 31 and the tube circuit 32 arranged in the cold zone Z3. The raw material gas passes through the pipe circuit 31 and the pipe circuit 32 and is liquefied and supercooled. The raw gas then passes through an expansion valve 33 provided in the line L11 and is sent to a storage LNG tank (not shown). In the liquefaction step by the liquefaction device 21, the raw material gas after finally passing through the expansion valve 33 has a pressure of about -162 占 폚 and a pressure of about 120 kPaA.

The raw material gas flowing in the liquefier 21 is cooled using a refrigeration cycle using a mixed refrigerant. In the present embodiment, nitrogen is added to a hydrocarbon mixture containing methane, ethane and propane as a mixed refrigerant, but not limited thereto, and other known components can be used as long as the desired cooling ability can be ensured.

In the liquefaction device 21, the high-pressure (HP) mixed refrigerant MR is supplied to the refrigerant separator 41 through the line L12. The mixed refrigerant constituting the liquid phase component of the refrigerant separator 41 is introduced into the liquefier 21 through the line L13 and then placed in the warming zones Z1a and Z1b upward in the liquefier 21 And the tube circuit 43 disposed in the middle area Z2 and then expanded through the expansion valve 44 provided in the line L14 and partly expanded by flash evaporation do.

Subsequently, the mixed refrigerant that has passed through the expansion valve 44 flows downward from the spray header 45 disposed at the upper portion of the middle region Z2 (i.e., flows countercurrently to the flow of the raw material gas in the liquefier 21) ). The mixed refrigerant discharged from the spray header 45 flows through the intermediate tube bundle constituted by the tube circuit 31 disposed in the middle region Z2, the tube circuit 43 and the tube circuit 52 described later, And flows downward while exchanging heat with the lower tube bundle composed of the tube circuits 22a and 22b disposed in the first tube circuit Z1 and the tube circuit 30 and the tube circuits 42a and 42b and tube circuits 51a and 51b described later.

On the other hand, the mixed refrigerant constituting the gaseous component of the refrigerant separator 41 is introduced into the liquefier 21 through the line L15 and thereafter flows upward in the liquefaction device 21 into the warmed regions Z1a and Z1b The tube circuit 52 arranged in the middle region Z2 and the tube circuit 53 arranged in the cold region Z3 are sequentially passed through the tube circuits 51a and 51b arranged in the line L16, Passes through the expansion valve 54 and expands, and a part thereof flash evaporates.

The mixed refrigerant that has passed through the expansion valve 54 is cooled down to a temperature below the boiling point of methane (about -167 ° C in this case) and flows downward from the spray header 55 disposed at the upper part of the cold zone Z3 So as to be countercurrent to the flow of the raw material gas in the liquefier 21). The mixed refrigerant discharged from the spray header 55 flows downward while exchanging heat with the upper tube bundle constituted by the tube circuit 32 and the tube circuit 53 disposed in the cold zone Z3 and further flows downwardly, The mixed refrigerant discharged from the header 45 and then mixed with the mixed refrigerant discharged from the mixed refrigerant discharged from the intermediate region Z2 and the mixed refrigerant discharged from the intermediate region Z2, Flows downward while exchanging heat with the lower tubes constituted by the tube circuits 22a and 22b, the tube circuit 30, the tube circuits 42a and 42b and the tube circuits 51a and 51b .

The mixed refrigerant discharged from the spray header 45 and the spray header 55 flows through the line L17 connected to the bottom of the liquefier 21 as a gas of the mixed refrigerant MP of low pressure LP . The facility (the refrigerant separator 41, etc.) relating to the mixed refrigerant provided in the liquefaction device 21 described above constitutes a part of a refrigerant cycle for mixed refrigerant having a known configuration not shown here, The mixed refrigerant is circulated to the refrigerant separator 41 through the compressor L12, the condenser, and the like.

As described above, the raw material gas introduced into the liquefaction system 1 is effectively liquefied through the expansion process, the cooling process, the distillation process, the compression process, and the liquefaction process. The liquefaction system 1 can be applied to a base-rod liquefying base for producing liquefied natural gas (LNG) containing methane as a main component, for example, from a raw gas collected from a gas field or the like.

(First and second reference examples)

2 and 3 show the flow of liquefaction treatment in a conventional liquefaction system of natural gas as first and second reference examples corresponding to the first embodiment of the present invention, respectively. In the liquefaction systems 101 and 201 shown in Figs. 2 and 3, the same reference numerals are given to the components corresponding to the liquefaction system 1 according to the first embodiment. Table 2 and Table 3 show an example of the temperature, pressure, flow rate and molar fraction of each component in the liquefaction systems 101 and 201 as the first and second reference examples, respectively, as in Table 1. The liquefaction system 201 of the second reference example is configured based on the conventional art of the above-described Patent Document 1 (US Pat. No. 4,065,278).

2, in the liquefaction system 101 of the first reference example, the first inflator 3 and the first compressor 4 in the liquefaction system 1 of the first embodiment described above are not provided , And the raw material gas from the moisture removal device 2 is sent to the cooler 110 through the line L101. The cooler 11 and the cooler 12 are sequentially connected to the downstream side of the cooler 110 to constitute a cooler group. The raw material gas is sequentially introduced into the three coolers 110, 11, 12 by heat exchange with the coolant . Propane refrigerant of a high pressure (HP), a medium pressure (MP) and a low pressure (LP) is used for the coolers 110, 11 and 12 and a raw material gas is introduced into the coolers 110, . The raw material gas discharged from the cooler 12 at the downstream most is a temperature of about -34.5 DEG C and a pressure of about 5,680 kPaA. This raw material gas is decompressed by the expansion in the expansion valve 113 provided in the line L4 and then introduced into the distillation apparatus 15. [

In the liquefaction system 101, the raw gas containing methane as a main component constituting the gaseous component in the first gas-liquid separation tank 23 is placed in the middle area Z2 in the liquefier 21 through the line L102 Is introduced into the tube circuit (31). Here, the raw material gas discharged from the first gas-liquid separation tank 23 to the line L102 is at a temperature of about -65.3 DEG C and a pressure of about 4,400 kPaA.

As shown in Fig. 3, the liquefaction system 201 of the second reference example is an improvement of the liquefaction system 101 of the first reference example, and includes an inflator 3 and a compressor 4. However, unlike the first inflator 3 of the liquefaction system 1 in the first embodiment described above, in the liquefaction system 201, the inflator 3 is provided with a cooler group (here, three coolers 110, 11 and 12) As shown in Fig. In the liquefaction system 201, the raw material gas sent out from the cooler 12 is sent to the separator 213 through the line L202 to be subjected to gas-liquid separation. The raw material gas constituting the vapor phase component in the separator 213 is sent to the expander 3 via the line L203 and expanded in the expander 3 and then sent to the distillation unit 15 via the line L204. On the other hand, the liquid constituting the liquid component in the separator 213 is sent to the line L205 provided with the expansion valve 214. [ The liquid is expanded in the expansion valve 214 and then sent to the distillation unit 15 via the line L204 together with the raw gas from the inflator 3. [

In the liquefaction system 201, the constitution on the downstream side from the distillation apparatus 15 is almost the same as that in the first embodiment, but the raw material gas sent out from the compressor 4 to the line L10) Lt; 0 > C and a pressure of about 5,120 kPaA.

Comparing the first and second reference examples with the present invention described above, in the liquefaction system 1 according to the present invention, since the first inflator 3 is arranged on the upstream side of the first coolers 11, 12 The expansion of the raw material gas at a higher temperature and the higher pressure than in the case where the inflator 3 is disposed at the downstream side of the coolers 110, 11 and 12 as in the liquefaction system 201 of the second reference example, Lt; / RTI > As a result, the first compressor 4 can be driven more efficiently (i.e., the discharge pressure of the first compressor 4 can be increased), the pressure of the raw material gas introduced into the liquefier 21 becomes higher, 21) can be increased.

In the liquefaction system 1, since the first inflator 3 is disposed on the upstream side of the cooler group (first coolers 11 and 12), the temperature of the raw material gas is increased by expansion in the first inflator 3 It is possible to reduce the cooling ability of the cooler group (that is, to omit the cooler 110 in the second reference example). Furthermore, in the liquefaction system 1, it is possible to omit a gas-liquid separator (separator 213) for separating (removing) condensation components in the raw material gas between the cooler group and the inflator 3.

(First, Second, and Third Modifications of the First Embodiment)

Figs. 4, 5, and 6 are diagrams showing the flow of the liquefaction process in the natural gas liquefaction system according to the first, second, and third modifications of the first embodiment of the present invention, respectively. In the liquefaction system 1 shown in Figs. 4, 5 and 6, the same constituent elements as those of the liquefaction system 1 related to the first embodiment (including other modified examples) are denoted by the same reference numerals And detailed description thereof will be omitted except for the matters mentioned below.

As shown in Fig. 4, in the liquefaction system 1 according to the first modification, a heat exchanger 69 is provided between the line L4 and the line L9. The raw material gas flowing through the line L9 separated as the gaseous component in the first gas-liquid separation tank 23 is supplied to the raw gas flowing in the line L4 introduced from the cooler 12 into the distillation apparatus 15, Is introduced into the first compressor (4) after being heated by heat exchange. The raw material gas compressed by the first compressor 4 is introduced into the liquefier 21 through the line L10. Line L10 is connected to the pipe circuit 30 disposed in the low temperature region Z1 having the highest temperature in the liquefaction device 21. [ The tube circuit 30 is disposed in the heat-resistant region Z1 together with the tube circuit 22 into which the overflow of the distillation apparatus 15 is introduced, the tube circuit 42 through which the mixed refrigerant flows, and the tube circuit 51 Thereby constituting the vascular system.

With this configuration, even when the temperature level of the raw material gas introduced into the liquefier 21 through the line L10 in the first modification can be lower than an appropriate range, the heat exchange in the heat exchanger 69 The temperature of the raw material gas can be suitably increased. That is, in the first modification, the temperature of the raw material gas in the compressed line L10 is set to be close to the temperature of the introduction position (the tube circuit 30) in the liquefier 21 As a result, the thermal load of the liquefier 21 can be reduced (suppressing the generation of thermal stress, etc.).

The arrangement of the heat exchanger 69 in the first modification (that is, the object to be heat-exchanged with the raw material gas flowing through the line L4 introduced into the distillation apparatus 15) So that the temperature of the raw material gas of the liquefier 21 can be made close to the temperature at the introduction position of the liquefier 21. For example, in the liquefaction system 1 according to the second modification shown in Fig. 5, a heat exchanger 69 is provided between the line L4 and the line L10). Thus, the raw material gas flowing through the line L10 compressed by the first compressor 4 is introduced into the liquefier 21 after being heated by heat exchange with the raw gas flowing through the line L4. The raw material gas heated in the heat exchanger 69 is introduced into the liquefier 21 without passing through the first compressor 4 and the like so that the raw material gas at the time of introduction into the liquefier 21 There is an advantage that it is easy to control the temperature of the gas.

6, a heat exchanger 69 is provided between the line L4 and the line L6 in the liquefaction system 1 according to the third modification. The raw material gas flowing through the line L6 separated as the overhead effluent from the distillation apparatus 15 is heated by heat exchange with the raw material gas flowing through the line L4 and is then supplied to the liquefier 21 (22). In this third modified example, particularly, a natural gas (an empty gas) having a relatively low heavy content (high hydrocarbon content) as shown in Table 1 is used as the raw material gas and the temperature of the raw material gas flowing through the line L6 after distillation The temperature of the raw material gas can be suitably increased by heat exchange in the heat exchanger 69 even when the level can be lowered than the proper range.

(Fourth Modification of First Embodiment)

7 is a configuration diagram showing a flow of liquefaction processing in a natural gas liquefaction system according to a fourth modification of the first embodiment of the present invention. In the liquefaction system 1 shown in Fig. 7, the same constituent elements as those of the liquefaction system 1 relating to the first embodiment (including other modified examples) are given the same reference numerals, The detailed description thereof will be omitted.

The fourth modified example has a structure similar to that of the third modified example described above and is further provided with a heat exchanger 79 between the line L9 and the line L10, There is further provided a cooler 80 using low-pressure (LP) propane refrigerant (C3R). The raw material gas discharged from the first compressor 4 is cooled by the cooler 80 and further cooled by heat exchange with the raw material gas flowing in the line L9 toward the first compressor 4, (21). Here, the downstream side of the line L10 is connected to the pipe circuit 31 disposed in the middle region Z2.

Thus, in the fourth modified example, the raw material gas discharged from the first compressor 4 can be introduced into the middle region Z2. Thereby, the tube bundle of the hot zone Z1 is divided by the three tube circuits 22, the tube circuit 42 and the tube circuit 51 and the tube bundle of the middle zone Z2 by three tube circuits 31, It can be constituted by the tube circuit 43 and the tube circuit 52, respectively. As a result, in the fourth modified example, in the case where the liquefier 21 is constituted by a spool-winding type heat exchanger, the arrangement of the tube circuits in the heat-temperature zone Z1 and the heat- And the size of the liquefaction device 21 can be avoided. In the cooler 80, propane refrigerant used in the first coolers 11 and 12 is used. However, the present invention is not limited to this, and air-cooled or water-cooled coolers may be used.

(Fifth Modification of First Embodiment)

10 is a configuration diagram showing the flow of liquefaction processing in a natural gas liquefaction system according to a fifth modification of the first embodiment of the present invention. In the liquefaction system 1 shown in Fig. 10, the same constituent elements as those of the liquefaction system 1 relating to the first embodiment (including other modified examples) are given the same reference numerals, The detailed description thereof will be omitted.

The fifth modified example has a structure similar to that of the fourth modified example described above except that the cooler 80 in the fourth modified example is omitted and the line L6 from the distillation device 15 and the line A heat exchanger 100 is further provided between the line L10 from the heat exchanger 4 and the line L10. The raw material gas discharged from the first compressor 4 to the line L10 is supplied to the line L6 from the distillation unit 15 instead of being cooled by the cooler 80, And then introduced into the heat exchanger 79 as in the fourth modification. On the other hand, the raw material gas from the distillation apparatus 15 is once introduced into the liquefier 21 through the line L6 after heat exchange, and is cooled in the pipe circuit 22. With this configuration, in the fifth modified example, the cooling of the source gas by the cooler 80 in the fourth modified example is supplemented by heat exchange in the heat exchanger 100 (the cooler 80 is omitted) have. In the fifth modified example, the heat exchanger 69 in the fourth modified example is omitted, but in some cases, the heat exchanger 69 is provided in the same manner as in the fourth modified example, (L6) may be introduced into the heat exchanger (100) through the heat exchanger (69).

(Second Embodiment)

8 is a configuration diagram showing the flow of liquefaction processing in the liquefaction system for natural gas according to the second embodiment of the present invention. In the liquefaction system 1 shown in Fig. 8, the same constituent elements as those of the liquefaction system 1 according to the first embodiment are denoted by the same reference numerals, respectively. It is omitted.

In the liquefaction system 1 of the second embodiment, an impurity containing methane of about 88 mol% is used as a raw material gas. In this liquefaction system 1, the raw material gas separated as the overhead effluent of the distillation apparatus 15 is directly introduced into the first compressor 4 through the line L19 and is compressed. Thereafter, the raw material gas is sent from the first compressor 4 through the line L20 to the pipe circuit 22 disposed in the heat-up region Z1, and is preliminarily cooled. Thereafter, the raw gas is further cooled through the line L21 to the first Liquid separating tank 23 as shown in FIG.

The first gas-liquid separation tank 23 separates liquid components (condensed components) in the raw gas and supplies liquid such as hydrocarbons constituting the liquid component to the distillation device 89 via an expansion valve 89 provided in the line L22. (15). On the other hand, in the first gas-liquid separation tank 23, the raw material gas containing methane as a main component constituting the gaseous component is sent to the pipe circuit 31 in the liquefier 21 through the line L23.

In the liquefaction system 1 according to the second embodiment, the first gas-liquid separation tank 23 is provided downstream of the first compressor 4, and the raw gas from the first compressor 4 is supplied to the heat- Liquid separator 23 so that the temperature level of the source gas is brought close to the temperature level of the heat-up zone Z1 of the liquefier 21 And the gas phase component from the first gas-liquid separation tank 23 is supplied to the liquid-phase reforming device 21 after the raw-material gas is cooled in the heat-trapping zone Z1 (the pipe circuit 22) Is introduced into the intermediate region Z2 (the tube circuit 31), the temperature level of the raw material gas can be easily brought close to the temperature level of the middle region Z2 of the liquefier 21. Furthermore, since the raw material gas from the first gas-liquid separation tank 23 can be sent and fed by the first compressor 4, the circulation from the first gas-liquid separation tank 23 to the distillation apparatus 15 in the above- There is an advantage that the reflux pump 24 provided in the path (line L21) can be omitted.

It is advantageous to increase the discharge pressure of the compressor 4 (that is, increase the pressure of the raw material gas introduced into the liquefier 21) for liquefying the raw material gas in the liquefier 21. However, as in the first embodiment or the like, the top effluent of the distillation apparatus 15 is once cooled by the liquefier 21, and thereafter the gas-liquid separation is performed in the first gas-liquid separation tank 23, 4, and then introduced into the liquefaction device 21, the temperature of the raw material gas in the first compressor 4 before the liquefier 21 rises, so that the composition of the raw material gas, the pressure, There is a problem that the temperature level of the raw material gas deviates from an appropriate range for introduction into the liquefier 21 depending on the conditions, thereby increasing the thermal load of the liquefier 21. Such a problem can be solved by changing the introduction position of the raw material gas into the liquefier 21, but in the case of using a spool-winding type heat exchanger or the like which is not easy to change the introduction position of the raw material gas as a main heat exchanger, There is a case that it can not cope with the structure of. The raw material gas separated as the overhead effluent of the distillation apparatus 15 is directly introduced into the first compressor 4 through the line L19 and is compressed as in this embodiment. Liquid separation in the first gas-liquid separation tank 23 after cooling the raw material gas compressed in the warm region Z1 of the liquefier 21 and separating the gaseous component into an intermediate region Z2 (That is, the temperature level of the raw material gas is adjusted to be close to the temperature level of the introduction position in the liquefier 21) .

(First Modification of Second Embodiment)

9 is a configuration diagram showing the flow of liquefaction processing in the natural gas liquefaction system according to the first modification of the second embodiment of the present invention. In the liquefaction system 1 shown in Fig. 9, the same components as those of the liquefaction system 1 according to the first embodiment are denoted by the same reference numerals, It is omitted.

As shown in Fig. 9, in the liquefaction system 1 according to the first modification of the second embodiment, a heat exchanger 69 is provided between the line L4 and the line L20. The raw material gas flowing through the line L20 sent from the first compressor 4 is heated by heat exchange with the raw material gas flowing through the line L4 and then supplied to the heat- Is introduced into the arranged tube circuit (22). Since the raw material gas heated in the heat exchanger 69 is introduced into the liquefier 21 without passing through the first compressor 4 or the like in the first modification of the second embodiment, There is an advantage that it is easy to control the temperature of the raw material gas.

The arrangement of the heat exchanger 69 in the first modified example of the second embodiment described above is such that the temperature of the raw material gas in the compressed line L20 is close to the temperature at the introduction position of the liquefier 21 Various changes are possible as long as it is possible.

While the present invention has been described based on specific embodiments thereof, these embodiments are merely illustrative and the present invention is not limited to these embodiments. The components of the natural gas liquefaction system and the liquefaction method according to the present invention described in each of the above-described embodiments are not necessarily essential, and can be suitably selected from a variety of components as long as they do not deviate at least from the scope of the present invention. Note that the combination of the constituent elements shown in each embodiment is not necessarily essential, and the constituent elements of the plurality of embodiments can be appropriately selected and used as long as they do not deviate at least from the scope of the present invention.

1 liquefaction system
2 Moisture removal device
3, 3a First inflator
3b second expander
4, 4a first compressor
4b third compressor
5 Shaft
10, 11, 12 The first cooler
15 distillation unit
21 Liquefaction device
23 First gas-liquid separation tank
33 expansion valve
41 Refrigerant Separator
44 expansion valve
45 Spray Headers
54 expansion valve
55 Spray Headers
69 Heat exchanger
79 Heat Exchanger
80 cooler
Z1 heat zone
Z2 middle area
Z3 cold zone

Claims (34)

A method of cooling a natural gas feed,
(a) reducing the pressure of the natural gas feed to produce a depressurized feed gas;
(b) removing the heavy fraction from the depressurized feed gas to produce a top fraction and a bottom fraction;
(c) cooling said overhead effluent to produce a cooled top effluent;
(d) separating the cooled top effluent into a gaseous component and a liquid component;
(e) increasing the pressure of the gaseous component to produce a compressed feed gas; And
(f) heat-exchanging the gaseous component and the compressed feed gas to produce at least a cooled compressed feed gas. The method according to claim 1,
Further comprising the step of cooling the decompressed feed gas in step (a) before removing the heavy fraction in the step (b). The method according to claim 1,
Further comprising at least partially liquefying the cooled compressed feed gas in step (f). The method according to claim 1,
Further comprising cooling the compressed feed gas in the step (e) before the step (f). The method according to claim 1,
Wherein the overhead effluent is cooled by introducing the overhead effluent into the hot zone of the spool wound heat exchanger in step (c). The method of claim 5,
Wherein the cooled compressed raw material gas in the step (f) is further cooled by introducing the cooled compressed raw material gas into an intermediate region of the spool reducing heat exchanger. The method according to claim 1,
The removal of the heavy component in the step (b) is performed in a distillation apparatus. The method of claim 7,
Further comprising the step of circulating the liquid component in step (d) to the distillation apparatus. The method according to claim 1,
Further comprising the step of heat-exchanging the overhead effluent and the depressurized feed gas in step (b) prior to step (c). The method according to claim 1,
The step (f) includes a step of heat-exchanging the gaseous component in the step (d), the compressed raw material gas in the step (e), and the decompressed raw material gas in the step (a) / RTI > A method of cooling a natural gas feed,
(a) reducing the pressure of the natural gas feed to produce a depressurized feed gas;
(b) removing the heavy fraction from the depressurized feed gas to produce a top bottom effluent and a bottom bottom effluent;
(c) exchanging heat between said depressurized feed gas and said overhead effluent to produce at least a heat exchanged overhead effluent;
(d) cooling said heat exchanged overhead effluent to produce a cooled overhead effluent;
(e) separating the cooled top effluent into a gaseous component and a liquid component;
(f) increasing the pressure of the gaseous component to produce a compressed feed gas; And
(g) cooling the compressed feed gas. The method of claim 11,
Further comprising the step of cooling the decompressed feed gas in step (a) before removing the heavy fraction in the step (b). The method of claim 11,
In the step (g), the compressed raw material gas is cooled by introducing the compressed raw material gas into at least one heat exchanger. The method of claim 11,
The removal of the heavy component in the step (b) is performed in a distillation apparatus. 15. The method of claim 14,
Further comprising the step of circulating the liquid component in step (e) to the distillation apparatus. A method of cooling a natural gas feed,
(a) reducing the pressure of the natural gas feed to produce a depressurized feed gas;
(b) removing the heavy fraction from the depressurized feed gas to produce a top bottom effluent and a bottom bottom effluent;
(c) cooling said overhead effluent to produce a cooled top effluent;
(d) separating the cooled top effluent into a gaseous component and a liquid component;
(e) increasing the pressure of the gaseous component to produce a compressed feed gas; And
(f) heat-exchanging the compressed feed gas and the decompressed feed gas in the step before step (b) to produce at least a heat exchanged compressed feed gas. 18. The method of claim 16,
Further comprising cooling the decompressed feed gas in step (a) prior to heat exchange in step (f). A method of cooling a natural gas feed,
(a) reducing the pressure of the natural gas feed to produce a depressurized feed gas;
(b) in the distillation apparatus to remove the heavy fraction from the depressurized feed gas to produce a top bottom effluent and a bottom bottom effluent;
(c) cooling and partially liquefying the overhead effluent to produce a cooled top effluent;
(d) separating said cooled overhead effluent to produce a gaseous component and a liquid component;
(e) circulating the liquid component to the distillation apparatus;
(f) heat-exchanging between the depressurized raw gas and the gaseous component so as to generate at least a heat exchanged gaseous component; And
(g) increasing the pressure of the heat exchanged gaseous component to produce a compressed feed gas. 19. The method of claim 18,
Further comprising cooling the decompressed feed gas in step (a) prior to heat exchange in step (f). A method of cooling a natural gas feed,
(a) reducing the pressure of the natural gas feed to produce a depressurized feed gas;
(b) removing the heavy fraction from the depressurized feed gas to produce a top bottom effluent and a bottom bottom effluent;
(c) increasing the pressure of the overhead effluent to produce a pressurized feed gas; And
(d) exchanging heat between said overhead effluent and said compressed feedstock gas to produce at least a cooled compressed feedstock gas. The method of claim 20,
Further comprising cooling the decompressed feed gas in step (a) before the step (b). The method of claim 20,
Further comprising cooling the compressed feed gas in step (c) before heat exchange in step (d). A system for liquefying a natural gas feed,
A first inflator for reducing the pressure of the natural gas feed to produce a decompressed feed gas;
A distillation apparatus for removing heavy materials from the depressurized feed gas to produce a top bottom effluent and a bottom bottom effluent;
A first heat exchanger for cooling the overhead effluent to produce a cooled top overflow;
A first gas-liquid separation vassel for separating the cooled top effluent into a gaseous component and a liquid component;
A first compressor for compressing the vapor phase component to generate a compressed raw material gas; And
And a second heat exchanger for exchanging heat between the gaseous component and the compressed feed gas. 24. The method of claim 23,
And a first cooler for cooling the decompressed feed gas prior to introduction into the distillation apparatus. 24. The method of claim 23,
And a second cooler for cooling the compressed feed gas before introduction into the second heat exchanger. 24. The method of claim 23,
Wherein the first heat exchanger is a warming region of a spool-reducing heat exchanger. 27. The method of claim 26,
Further comprising a third heat exchanger for cooling the compressed feed gas after the compressed feed gas passes through the second heat exchanger, wherein the third heat exchanger is a natural gas feed which is an intermediate region of the spool- Liquefaction system. 24. The method of claim 23,
And a piping for circulating the liquid component as reflux from the first gas-liquid separation tank to the distillation apparatus. 24. The method of claim 23,
And a fourth heat exchanger for heat exchange between the overhead effluent from the distillation apparatus and the depressurized feed gas. 24. The method of claim 23,
And the second heat exchanger performs heat exchange between the gaseous component, the compressed feed gas, and the decompressed feed gas. 24. The method of claim 23,
Wherein the first inflator generates power and the first compressor utilizes the power generated by the first inflator. A system for liquefying a natural gas feed,
A first inflator for reducing the pressure of the natural gas feed to produce a decompressed feed gas;
A distillation apparatus for removing heavy materials from the depressurized feed gas to produce a top bottom effluent and a bottom bottom effluent;
A first heat exchanger for heat exchange between said overhead effluent and said depressurized feed gas to produce at least a heat exchanged overhead effluent;
A second heat exchanger for cooling the heat exchanged overhead effluent to produce a cooled top overflow;
A first gas-liquid separation tank for separating the cooled tower overflow into a gaseous component and a liquid component; And
And a first compressor for compressing the gaseous component to produce a compressed raw material gas. 33. The method of claim 32,
Further comprising a first cooler for cooling the decompressed feed gas prior to introduction into the distillation apparatus. A system for liquefying a natural gas feed,
A first inflator for reducing the pressure of the natural gas feed to produce a decompressed feed gas;
A first cooler for cooling the decompressed source gas to produce a cooled depressurized source gas;
A distillation apparatus for removing heavy components from said cooled decompressed feed gas to produce a top bottom effluent and a bottom bottom effluent;
A warming region of a spool-wound heat exchanger for cooling said overhead effluent to produce a cooled overhead effluent;
A first gas-liquid separation tank for separating the cooled tower overflow into a gaseous component and a liquid component;
A piping system for circulating the liquid component to the distillation apparatus;
A first compressor for compressing the vapor phase component to generate a compressed raw material gas;
A second cooler for cooling the compressed feed gas to produce a cooled compressed feed gas;
A third heat exchanger for exchanging heat between the cooled compressed raw material gas and the gaseous component so as to produce a further cooled compressed raw material gas; And
And an intermediate region of said spool-wound heat exchanger for at least partially liquefying said further cooled compressed feed gas.

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