WO2016151636A1 - Production system and production method for natural gas - Google Patents

Abstract

[Problem] To efficiently liquefy source gas by bringing the source gas cooling curve and the refrigerant temperature rise curve close to each other in source gas cooling using a refrigerant without requiring the addition of external energy. [Solution] A production system 1 is equipped with: a compressor 20 which compresses source gas; a group of refrigerant expanders 54, 63, which includes at least one refrigerant expander for generating power by causing a refrigerant circulating in the production system to expand; and a heat exchanger 25 which cools the source gas compressed by the compressor 20 by heat exchanging the source gas with the refrigerant. The production system 1 is configured so that the compressor 20 compresses the source gas by utilizing the power generated by the refrigerant expander 63 (54).

Description

Natural gas production system and production method

The present invention relates to a natural gas production system and a production method for producing liquefied natural gas by cooling natural gas.

Natural gas collected from gas fields and the like is liquefied at a liquefaction base or the like, and is handled as LNG (liquefied natural gas) for storage and transportation. LNG cooled to about -162 ° C has advantages such as a significantly reduced volume compared to natural gas (gas), and no need to store at high pressure. In general, in natural gas liquefaction, moisture, acid gas components such as carbon dioxide and hydrogen sulfide, and other impurities such as mercury are removed in advance, and a heavy component having a relatively high freezing point (benzene). , Toluene, xylene, C5 + hydrocarbons over pentane, etc.) are removed, and the raw material gas is liquefied.

As a method for liquefying a raw material gas, various types of liquefaction processes using heat exchange with a refrigerant (heat exchanger) are widely used. As the refrigerant for heat exchange, hydrocarbons such as methane, ethane, ethylene, propane and butane, nitrogen, and the like are used as a single refrigerant (a refrigerant composed of a single component) or a mixed refrigerant. In the raw material gas liquefaction process, in order to reduce the power required for the refrigerant cycle (refrigeration cycle) for cooling the refrigerant (such as the power of the compressor used for compressing the refrigerant), It is desirable to reduce the difference in temperature (that is, to reduce the loss of effective energy by bringing the cooling curve of the source gas close to the temperature rise curve of the refrigerant).

In order to approximate the cooling curve of the raw material gas and the temperature rising curve of the refrigerant in the heat exchange, for example, depending on the cooling process of the raw material gas, a plurality of single refrigerants (for example, combinations of refrigerant cycles of methane, ethylene, and propane) It is conceivable to perform heat exchange using a mixed refrigerant, but when using a plurality of single refrigerants or mixed refrigerants, the cost for obtaining, storing and supplying the refrigerant, and the refrigerant cycle are realized. Therefore, there is a problem that the equipment costs for the increase. On the other hand, when only a single-phase (gas) refrigerant such as a nitrogen refrigerant is used, there is a possibility that the cost can be reduced compared to a case where a plurality of single refrigerants or mixed refrigerants are used. However, since it is difficult to bring the cooling curve of the raw material gas close to the temperature rise curve of the refrigerant in heat exchange, there is a problem that the liquefaction efficiency (refrigeration cycle efficiency, etc.) is poor.

Therefore, for example, in a production system using nitrogen refrigerant for cooling the raw material gas, the refrigerant flow compressed and cooled in the refrigerant cycle is branched into a plurality of flows, and these refrigerant flows are respectively introduced into the expander. The refrigerant is introduced into a series of different heat exchangers so that the temperature rise curve of the refrigerant approaches the cooling curve of the raw material gas, and the refrigerant compressor is connected to the shaft of the expander in the refrigerant cycle. There is known a natural gas liquefaction process in which energy generated by expansion of a refrigerant is recovered by being connected to each other (see Patent Document 1).

US Pat. No. 5,768,912

By the way, the conventional natural gas production system as described in Patent Document 1 is intended to suppress energy loss in the liquefaction process of the raw material gas by bringing the temperature rise curve of the refrigerant close to the cooling curve of the raw material gas. is there.

However, as a result of intensive studies, the inventors of the present application have found that the raw material gas introduced into the heat exchanger is not required (or suppressed) from the outside in the liquefaction process as in Patent Document 1 described above. It was found that a more efficient liquefaction process can be realized by increasing the pressure and bringing the cooling curve of the source gas on the upstream side (high temperature side) closer to the temperature rising curve of the refrigerant.

The present invention has been devised in view of such problems of the prior art, and cooling of a raw material gas using a refrigerant without requiring (or suppressing) the addition of external energy. It is a main object of the present invention to provide a natural gas production system and production method capable of efficiently liquefying a raw material gas by bringing the cooling curve of the raw material gas close to the temperature rising curve of the refrigerant.

A first aspect of the present invention is a natural gas production system (1) for producing liquefied natural gas from a raw material gas containing natural gas, the raw material gas compressor for compressing the raw material gas flowing in the production system. (20), a refrigerant expander group (54, 63) including at least one refrigerant expander that generates power by expanding a refrigerant circulating in the manufacturing system, and compressed by the source gas compressor A first heat exchange section (25) that cools the source gas by heat exchange with the refrigerant, and the source gas compressor uses the power generated in the refrigerant expander, thereby Is compressed.

In the natural gas production system according to the first aspect, since the raw material gas compressor that uses the power generated by the refrigerant expander is arranged on the upstream side of the first heat exchange unit, the addition of energy from the outside It is possible to efficiently liquefy the raw material gas by reducing the temperature difference between the refrigerant and the raw material gas in cooling the raw material gas using the refrigerant without requiring (or suppressing) .

The second aspect of the present invention relates to the first aspect, wherein the first aspect is disposed downstream of the first heat exchange unit in the flow of the source gas, and further cools the source gas by heat exchange with the refrigerant. It further comprises a two heat exchanging section (26).

In the natural gas production system according to the second aspect, by using a plurality of heat exchangers, the temperature difference between the refrigerant and the raw material gas in cooling the raw material gas using the refrigerant is reduced, thereby efficiently supplying the raw material gas. It becomes possible to liquefy.

The third aspect of the present invention relates to the first or second aspect, wherein the refrigerant is composed of a single component and a single phase.

In the natural gas production system according to the third aspect, even when a refrigerant such as nitrogen having a single component and a single phase is used, it is difficult to bring the cooling curve of the raw material gas close to the temperature rising curve of the refrigerant. The liquefaction efficiency of gas can be improved reliably.

According to a fourth aspect of the present invention, there is provided a natural gas production system (1) for producing liquefied natural gas from a raw material gas containing natural gas, and generating power by expanding a refrigerant circulating in the production system. A refrigerant expander group (54, 63) including at least one refrigerant expander (63), and a first heat exchange unit (25) that cools the raw material gas flowing in the manufacturing system by heat exchange with the refrigerant. And reducing or removing heavy components in the raw material gas by distilling the raw material gas from the first heat exchanging portion disposed downstream of the first heat exchange portion in the flow of the raw material gas A distillation apparatus (15) that is disposed downstream of the distillation apparatus in the flow of the raw material gas, a raw material gas compressor (20) that compresses the raw material gas, and a front in the flow of the raw material gas A second heat exchange section (26) disposed downstream of the raw material gas compressor and further cooling the raw material gas by heat exchange with the refrigerant, wherein the raw material gas compressor is generated in the refrigerant expander The raw material gas is compressed by using the power.

In the natural gas production system according to the fourth aspect, since the raw material gas compressor that uses the power generated by the refrigerant expander is arranged downstream of the distillation apparatus, it is necessary to add energy from the outside. Without reducing (or suppressing), it is possible to efficiently liquefy the source gas by reducing the temperature difference between the refrigerant and the source gas in cooling the source gas using the refrigerant. Moreover, in this manufacturing system, since the distillation apparatus is arrange | positioned in the downstream of a heat exchanger, it becomes possible to abbreviate | omit facilities, such as another cooler in the upstream of a distillation apparatus. In this manufacturing system, since the raw material gas compressor is disposed between the first and second heat exchangers, the first and second heat exchangers and the raw material gas compressor are integrated and installed. Can be made compact. In this manufacturing system, since the distillation apparatus is arranged upstream of the raw material gas compressor, the raw material gas becomes critical due to compression by the raw material gas compressor, and there is no problem that processing in the distillation apparatus becomes difficult.

According to a fifth aspect of the present invention, there is provided a natural gas production method for producing liquefied natural gas from a raw material gas containing natural gas, the raw material gas compression step for compressing the raw material gas flowing in the production system, and the production A refrigerant expansion step for generating power by expanding a refrigerant circulating in the system; and a first heat exchange step for cooling the raw material gas compressed in the raw material gas compression step by heat exchange with the refrigerant. In the raw material gas compression step, the raw material gas is compressed by using the power generated in the refrigerant expansion step.

A sixth aspect of the present invention is a natural gas production method for producing liquefied natural gas from a raw material gas containing natural gas, and a refrigerant expansion step for generating power by expanding a refrigerant circulating in the production system. A first heat exchange step of cooling the raw material gas flowing in the manufacturing system by heat exchange with the refrigerant, and distilling the raw material gas cooled in the first heat exchange step, whereby the raw material gas A distillation step for reducing or removing heavy components therein, a source gas compression step for compressing the source gas distilled in the distillation step, and the source gas compressed in the source gas compression step with the refrigerant A second heat exchange step for further cooling by heat exchange, and the raw material gas compression step uses the power generated in the refrigerant expansion step. More, characterized by compressing the raw material gas.

As described above, according to the present invention, in the natural gas production system, the raw material gas is efficiently liquefied by bringing the cooling curve of the raw material gas close to the temperature rising curve of the refrigerant in the cooling of the raw material gas using the refrigerant. It becomes possible.

The block diagram which shows the flow of the liquefaction process in the manufacturing system of the natural gas which concerns on 1st Embodiment The block diagram which shows the flow of the liquefaction process in the conventional natural gas manufacturing system as a reference example corresponding to 1st Embodiment Explanatory drawing which shows the cooling curve of the raw material gas in the manufacturing system of the natural gas shown in FIG. 1, and the temperature rising curve of a refrigerant | coolant Explanatory drawing which shows the cooling curve of the raw material gas in the manufacturing system of the natural gas shown in FIG. 2, and the temperature rising curve of a refrigerant | coolant The block diagram which shows the flow of the liquefaction process in the manufacturing system of the natural gas which concerns on 2nd Embodiment. The block diagram which shows the flow of the liquefaction process in the manufacturing system of the natural gas which concerns on 3rd Embodiment

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a configuration diagram showing the flow of a liquefaction process in the natural gas production system 1 according to the first embodiment of the present invention. The natural gas production system 1 has equipment for generating LNG (liquefied natural gas) by cooling a raw material gas containing natural gas using a low-temperature refrigerant.

As shown in FIG. 1, in the manufacturing system 1, the raw material gas is introduced into the manufacturing system 1 via the line L <b> 1 and cooled to a temperature that can be liquefied at a pressure of about atmospheric pressure while being transported in the manufacturing system 1. The In this embodiment, the raw material gas supplied to the manufacturing system 1 is a gas containing, for example, about 80 to 98 mol% of methane, the temperature is about 36 ° C., the pressure is about 5200 kPaA, and the flow rate is about 50,000 kg / hr. However, the present invention is not limited to this, and the component, temperature, pressure, and flow rate of the raw material gas can be changed as necessary. Such raw material gas is not particularly limited, but is collected as natural gas such as shale gas, tight sand gas, coal bed methane, methane hydrate, and the like.

Note that the term “source gas” in the present specification does not mean that the gas is strictly in a gaseous state, but refers to an object of liquefaction treatment flowing through the manufacturing system 1 (including a partially liquefied state during the treatment). ) Although detailed explanation is omitted, in the production system 1, as a pretreatment facility for natural gas, a separation facility for separating natural gas condensate, an acidic gas removal facility for removing acidic gas components such as carbon dioxide and hydrogen sulfide, Known equipment such as mercury removal equipment for removing mercury and water removal equipment for removing water can be provided as necessary, and natural gas from which impurities and the like have been removed by these equipment is used as a raw material gas. .

The raw material gas introduced through the line L1 is compressed by the compressor 11, cooled by the cooler 12, further expanded by the expander 13, and then introduced into the distillation device 15. The compressor 11 includes a centrifugal compressor in which an impeller that compresses a raw material gas is attached to a shaft 16 that is coaxial with the expander 13. In the cooler 12, the raw material gas can be cooled by using a part of the refrigerant that is also used in the heat exchangers 25, 26, and 27 described later. The expander 13 is composed of a turbine device for reducing the pressure of the raw material gas by isentropically expanding the flowing raw material gas and taking out the power generated by the expansion. The power generated by the expansion of the raw material gas in the expander 13 can be used as power for compressing the raw material gas in the compressor 11 via the coaxial shaft 16.

Note that the temperature and pressure of the raw material gas after being compressed by the compressor 11 are about 39 ° C. and about 5300 kPaA, respectively. The temperature and pressure of the raw material gas after cooling by the cooler 12 are about −49 ° C. and about 5200 kPa A, respectively, and the temperature and pressure of the raw material gas after expansion by the expander 13 are about −54 ° C. and about 4800kPaA. The raw material gas is introduced from the expander 13 into the distillation apparatus 15 via the line L2.

The distillation apparatus 15 includes a rectifying column having a plurality of shelves therein, and removes heavy components having a relatively high freezing point contained in the raw material gas (that is, each component constituting the heavy components is desired to be obtained). The rectification process is carried out to reduce the concentration to below. In the distillation apparatus 15, a liquid containing a relatively high concentration heavy component is discharged through a line L <b> 3 connected to the tower bottom of the distillation apparatus 15. The components that make up the heavy component and the concentration of each component vary depending on the source of the natural gas, etc., but here benzene, toluene, xylene, C5 + hydrocarbons over pentane, etc. are used as the heavy component in the source gas. included. The distillation apparatus 15 can avoid troubles caused by solidification of heavy components in each apparatus or piping on the downstream side in the manufacturing system 1 by removing such heavy components from the raw material gas. it can. A part of the liquid staying at the bottom of the distillation apparatus 15 is sent to the reboiler 18 provided in the line L4 from the bottom of the tower, and is heated by the heat medium (steam or oil) supplied from the outside in the reboiler 18. Thereafter, it is circulated again to the distillation apparatus 15.

On the other hand, in the distillation apparatus 15, a raw material gas (light component) mainly composed of methane, which is a low-boiling component, is separated as an overhead distillate, and the raw material gas is supplied via a line L5 to a compressor (raw material gas compressor). ) 20. The temperature and pressure of the raw material gas sent from the distillation apparatus 15 to the line L5 are about 27 ° C. and about 4700 kPaA, respectively.

The compressor 20 includes a centrifugal compressor in which an impeller for compressing a raw material gas is attached to a shaft 21 coaxial with a refrigerant expander (second refrigerant expander) 63 described later. The power generated by the expansion is used as power for compressing the raw material gas. In the manufacturing system 1, three heat exchangers 25, 26, and 27 that constitute a main heat exchanger are sequentially provided from the upstream side to the downstream side of the flow of the source gas in the system. The raw material gas compressed by the compressor 20 is introduced into the heat exchanger 25 via the line L6. Here, the temperature and pressure of the raw material gas sent from the compressor 20 to the line L6 are about 98 ° C. and about 10000 kPaA, respectively.

Each of the heat exchangers 25, 26, and 27 is a plate fin type heat exchanger, and is a pipe line through which a raw material gas to be cooled flows (hereinafter referred to as “raw material gas pipe line”) and a pipe line through which a refrigerant flows (hereinafter referred to as “raw material gas pipe line”). , "Refrigerant conduit"). Further, the heat exchangers 25 and 26 are provided with pipe lines (hereinafter referred to as “pre-cooling pipe lines”) for precooling the refrigerant. In addition, the structure of the heat exchangers 25, 26, and 27 is not specifically limited, For example, you may comprise with a spool (Spool Wound) type heat exchanger.

The raw material gas cooled by flowing through the raw material gas pipe 31 of the heat exchanger (first heat exchanging unit) 25 located on the most upstream side becomes a temperature of about 9 ° C. and a pressure of about 9900 kPaA via the line L7. It is introduced into a heat exchanger (second heat exchange section) 26 located in the middle. Therefore, the raw material gas cooled by flowing through the raw material gas pipe 32 of the heat exchanger 26 has a temperature of about −86 ° C. and a pressure of about 9800 kPaA, and is located on the most downstream side via the line L8 ( It is introduced into the third heat exchanging part) 27. Thereafter, the raw material gas cooled by flowing through the raw material gas pipe 33 of the heat exchanger 27 is sent to the line L9 at a temperature of about −155 ° C. and a pressure of about 9600 kPaA, and further, an expansion valve provided in the line L9. The gas-liquid separation tank 36 is introduced through 35.

The temperature and pressure of the raw material gas introduced into the gas-liquid separation tank 36 are about −162 ° C. and about 101 kPa A, respectively, by the expansion of the expansion valve 35, and the raw material gas is in a liquefied state (ie, LNG). In the gas-liquid separation tank 36, a gas phase component containing a part of vaporized natural gas and other gas (for example, nitrogen) is discharged out of the system via the line L10, while a liquid phase component composed of LNG is lined. Obtained via L11. The LNG is sent to a storage facility such as an LNG tank (not shown) by a transport pump 38 provided in the line L11.

In addition, about the apparatus etc. (The compressors 11 and 20, the cooler 12, the expander 13, the distillation apparatus 15, the heat exchangers 25, 26, and 27 other apparatus mentioned later) used in the manufacturing system 1 are included in this invention. Any known device (or configuration) can be employed as long as it performs a necessary function within the above range.

Next, the refrigerant cycle in the manufacturing system 1 will be described. A refrigerant cycle (refrigeration cycle) using nitrogen refrigerant is applied to the manufacturing system 1, and this nitrogen refrigerant circulates in the system through the heat exchangers 25, 26, and 27 for cooling the raw material gas. . The nitrogen refrigerant may contain a small amount of gas components other than nitrogen as long as it does not affect the cooling of the source gas. Moreover, as a refrigerant | coolant used with the manufacturing system 1, the refrigerant | coolant which consists of a single component and a single phase like nitrogen is especially preferable, However, This invention is applicable also to another well-known refrigerant | coolant.

In the manufacturing system 1, the refrigerant after the source gas is cooled on the upstream side of the source gas flow (that is, the temperature of the refrigerant heated through the refrigerant line (first refrigerant line) 40 of the heat exchanger 25) is It is introduced into a compressor (refrigerant compressor) 42 via a line L12 and compressed to a predetermined pressure. The temperature and pressure of the refrigerant sent from the heat exchanger 25 to the line L12 are about 27 ° C. and about 120 kPaA, respectively. The compressor 42 is provided with an intermediate cooler 43 for cooling the refrigerant compressed to an intermediate pressure, and a line L13 on the downstream side of the compressor 42 has a rear portion for cooling the compressed refrigerant. A cooler 44 is provided. The temperature and pressure of the refrigerant sent from the compressor 42 to the line L13 are about 110 ° C. and about 4300 kPa A, respectively, and the temperature and pressure of the refrigerant after cooling by the rear cooler 44 are about 30 ° C. and about 4200 kPa A, respectively. It is.

The refrigerant cooled by the rear cooler 44 is introduced into the compressor 45. The compressor 45 includes a centrifugal compressor in which an impeller that compresses refrigerant is attached to a shaft 46 that is coaxial with an expander (first refrigerant expander) 54 described later. The refrigerant introduced into the compressor 45 is compressed to a higher pressure. The line L14 on the downstream side of the compressor 45 is provided with two coolers 47 and 48 for cooling the compressed refrigerant, and the cooled refrigerant is introduced into the heat exchanger 25. The temperature and pressure of the refrigerant sent from the compressor 45 to the line L14 are about 87 ° C. and about 7000 kPa A, respectively, and the temperature and pressure of the refrigerant after cooling by the coolers 47 and 48 are about 30 ° C. and about 6900kPaA.

The refrigerant introduced into the heat exchanger 25 from the line L14 is pre-cooled by a lower temperature refrigerant flowing in the reverse direction through the refrigerant line 40 by flowing through the pre-cooling line (first pre-cooling line) 51. The precooled refrigerant is sent from the heat exchanger 25 to the line L15. The temperature and pressure of the refrigerant sent to the line L15 are about 9 ° C. and about 6900 kPaA, respectively. The downstream end of the line L15 is branched into a line L16 and a line L17, so that one flow of the refrigerant is introduced into the expander 54 via the line L16, and the other flow of the refrigerant passes through the line L17. And introduced into the heat exchanger 26. The flow rate ratio of the refrigerant branched into the line L16 and the line L17 is about 7: 3.

The expander 54 is composed of a turbine device for reducing the pressure of the refrigerant by isentropically expanding the flowing refrigerant and taking out the power generated by the expansion. The power generated by the expander 54 can be used as power for compressing the refrigerant in the compressor 45 via the coaxial shaft 46. The temperature and pressure of the refrigerant after expansion by the expander 54 are about −93 ° C. and about 1200 kPaA, respectively. The expanded refrigerant is introduced from the expander 54 to the heat exchanger 26 via the line L18. More specifically, the downstream end of the line L18 is connected to the middle of the line L19 for sending the refrigerant from the heat exchanger 27 to the heat exchanger 26, and the refrigerant flowing through the line L18 becomes the refrigerant flowing through the line L19. After joining, the heat exchanger 26 is introduced.

On the other hand, the refrigerant introduced into the heat exchanger 26 from the line L17 flows through the precooling pipeline (second precooling pipeline) 61, and thus has a lower temperature than flowing through the refrigerant pipeline (second refrigerant pipeline) 62 in the reverse direction. Precooled by the refrigerant. The precooled refrigerant is introduced from the heat exchanger 26 to the expander (second refrigerant expander) 63 via the line L20. The temperature and pressure of the refrigerant sent from the heat exchanger 26 to the line L20 are about −86 ° C. and about 6900 kPaA, respectively.

Like the expander 54, the expander 63 includes a turbine device for reducing the pressure of the refrigerant and taking out power. The power generated by the expander 63 is used as power for compressing the source gas in the source gas compressor 20 via the coaxial shaft 21 as described above. The temperature and pressure of the refrigerant after expansion by the expander 63 are about −158 ° C. and about 1200 kPaA, respectively. The expanded refrigerant is introduced into the heat exchanger 27 via the line L21.

The refrigerant introduced into the heat exchanger 27 from the line L21 is heated by heat exchange with the raw material gas flowing in the reverse direction through the raw material gas pipe 33 by flowing through the refrigerant pipe 65. Thereafter, the refrigerant is introduced from the heat exchanger 27 into the heat exchanger 26 via the line L19. The temperature and pressure of the refrigerant sent from the heat exchanger 27 to the line L19 are about −88 ° C. and about 1200 kPaA, respectively.

The refrigerant introduced into the heat exchanger 26 from the line L19 is heated by heat exchange with the raw material gas flowing in the reverse direction through the raw material gas pipe 32 by flowing through the refrigerant pipe 62. Thereafter, the refrigerant is introduced from the heat exchanger 26 into the heat exchanger 25 via the line L22. The temperature and pressure of the refrigerant sent from the heat exchanger 26 to the line L22 are about −3 ° C. and about 1200 kPaA, respectively. The refrigerant introduced into the heat exchanger 25 is sent to the line L12 after flowing through the refrigerant pipe 40, thereby completing the circulation of the refrigerant.

(Reference example)
FIG. 2 is a configuration diagram showing a flow of liquefaction processing in a conventional natural gas production system 100 as a reference example corresponding to the first embodiment. Regarding the reference example, the same components as those in the first embodiment described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the manufacturing system 100 of the reference example, the compressor 20 disposed on the upstream side of the heat exchanger 25 as shown in the first embodiment is not provided, and a relatively low-pressure raw material gas is heated via the line L6. It is introduced into the exchanger 25. The temperature and pressure of the raw material gas introduced from the line L6 are about 36 ° C. and about 5200 kPaA, respectively. Therefore, the raw material gas cooled by flowing through the raw material gas pipe 31 of the heat exchanger 25 has a temperature of about −45 ° C. and a pressure of about 5000 kPaA, and is introduced into the distillation apparatus 15 via the line L7a.

In the distillation apparatus 15, a liquid containing a heavy component having a relatively high concentration is discharged through a line L <b> 3 connected to the tower bottom of the distillation apparatus 15. The temperature and pressure of the heavy liquid discharged from the line L3 are about −48 ° C. and about 4500 kPaA, respectively. On the other hand, in the distillation apparatus 15, a raw material gas (light component) mainly composed of methane, which is a low-boiling component, is separated as a column top distillate, and the raw material gas is introduced into the heat exchanger 26 via a line L7b. Is done. The temperature and pressure of the raw material gas sent from the distillation apparatus 15 to the line L7b are about −48 ° C. and about 4500 kPaA, respectively.

Therefore, the raw material gas cooled by flowing through the raw material gas pipe 32 of the heat exchanger 26 has a temperature of about −87 ° C. and a pressure of about 4400 kPaA, and is introduced into the heat exchanger 27 via the line L8. Thereafter, the raw material gas cooled by flowing through the raw material gas pipe 33 of the heat exchanger 27 is sent to the line L9 at a temperature of about −155 ° C. and a pressure of about 4200 kPaA, and further, an expansion valve provided in the line L9. The gas-liquid separation tank 36 is introduced through 35. The temperature and pressure of the raw material gas introduced from the expansion valve 35 into the gas-liquid separation tank 36 are about −162 ° C. and about 101 kPaA, respectively, and the raw material gas is in a liquefied state.

Next, the refrigerant cycle in the manufacturing system 100 will be described. Nitrogen refrigerant is used in the manufacturing system 100 as in the first embodiment. The refrigerant after the source gas is cooled in the manufacturing system 100 (that is, the temperature is raised through the refrigerant pipe 40 of the heat exchanger 25) is introduced into the compressor 42 via the line L12 and compressed to a predetermined pressure. Is done. The temperature and pressure of the refrigerant sent from the heat exchanger 25 to the line L12 are about 28 ° C. and about 1200 kPaA, respectively. The temperature and pressure of the refrigerant sent from the compressor 42 to the line L13 are about 105 ° C. and about 4000 kPaA, respectively. Further, the temperature and pressure of the refrigerant after cooling by the rear cooler 44 are about 30 ° C. and about 30 ° C., respectively. About 3900kPaA.

The downstream end of the line L13 branches into a line L14a and a line L14b, whereby one flow of the refrigerant is introduced into the compressor 45 via the line L14a, and the other flow of the refrigerant passes through the line L14b. It is introduced into the compressor 145. The compressor 45 includes a centrifugal compressor in which an impeller for compressing a refrigerant is attached to a shaft 46 coaxial with the expander 54. The refrigerant compressed by the compressor 45 is sent out toward the heat exchanger 25 via the line L14c.

On the other hand, the compressor 145 includes a centrifugal compressor in which an impeller for compressing a refrigerant is attached to a shaft 121 coaxial with the expander 63. In this reference example, unlike the case of the first embodiment described above, the power generated by the expansion of the raw material gas in the expander 63 is used to compress the refrigerant in the refrigerant compressor 145 via the coaxial shaft 121. Used as power. The refrigerant introduced into the compressor 145 from the line L14b is compressed by the compressor 145 and then sent to the heat exchanger 25 via the line L14d.

Here, the downstream end of the line L14c is connected to the intermediate portion of the line L14d, and the refrigerant flowing through the line L14c merges with the refrigerant flowing through the line L14d, and is further cooled by the coolers 47 and 48 before heat exchange. Introduced into the vessel 25. The temperature and pressure of the refrigerant after joining the lines L14c and L14d (before cooling by the coolers 47 and 48) are about 96 ° C. and about 7000 PaA, respectively, and the temperature and pressure of the refrigerant after cooling by the coolers 47 and 48 are respectively Are about 30 ° C. and about 6900 PaA, respectively.

The refrigerant introduced into the heat exchanger 25 from the line L14d is precooled by a lower temperature refrigerant flowing in the reverse direction through the refrigerant line 40 by flowing through the precooling line 51, and is sent to the line L15. The temperature and pressure of the refrigerant sent to the line L15 are about −19 ° C. and about 6900 kPaA, respectively. The downstream end of the line L15 branches to a line L16 and a line L17, and is introduced into the expander 54 via the line L16. The temperature and pressure of the refrigerant after expansion by the expander 54 are about −112 ° C. and about 1200 kPaA, respectively. The expanded refrigerant is introduced from the expander 54 to the heat exchanger 26 via the line L18 and the line L19.

On the other hand, the refrigerant flowing through the line L17 is pre-cooled in the heat exchanger 26 and then introduced from the heat exchanger 26 into the expander 63 via the line L20. The temperature and pressure of the refrigerant after pre-cooling in the heat exchanger 26 are about −87 ° C. and about 6900 kPaA, respectively. The temperature and pressure of the refrigerant after expansion by the expander 63 are about −158 ° C. and about 1200 kPaA, respectively. The refrigerant after expansion by the expander 63 is introduced into the heat exchanger 27 via the line L21.

The refrigerant flowing through the line L21 is heated by heat exchange with the raw material gas in the heat exchanger 27 and then introduced from the heat exchanger 27 into the heat exchanger 26 via the line L19. The temperature and pressure of the refrigerant joined to the line L18 after the temperature rise in the heat exchanger 27 are about −104 ° C. and about 1200 kPaA, respectively.

The refrigerant introduced from the line L19 to the heat exchanger 26 is heated by heat exchange with the raw material gas or the like in the heat exchanger 26, and then introduced from the heat exchanger 26 to the heat exchanger 25 via the line L22. The The refrigerant introduced into the heat exchanger 25 is sent to the line L12 after flowing through the refrigerant pipe 40, thereby completing the circulation of the refrigerant.

(Effect of 1st Embodiment)
FIG. 3 is an explanatory diagram showing an example of simulation results of a raw material gas cooling curve and a refrigerant temperature rising curve in the natural gas production system according to the first embodiment shown in FIG. 1, and FIG. It is explanatory drawing which shows an example of the simulation result of the cooling curve of source gas and the temperature rising curve of a refrigerant | coolant in the manufacturing system (reference example) of the natural gas shown in FIG. 3 and 4, the vertical axis and the horizontal axis are the temperature (° C.) and the heat duty (GJ / h) of the raw material gas and the nitrogen refrigerant, respectively.

As described above, in the natural gas production system 1 according to the first embodiment, the compressor 20 that compresses the raw material gas, the expander 63 that generates power by expanding the nitrogen refrigerant, and the compressor 20 are compressed. A heat exchanger 25 that cools the source gas by heat exchange with the nitrogen refrigerant is provided, and the compressor 20 uses the power generated in the expander 63 to compress the source gas. Thereby, in the cooling curve of the source gas and the temperature rising curve of the nitrogen refrigerant according to the first embodiment shown in FIG. 3, the source gas compressed to the critical pressure or higher as compared with the reference example shown in FIG. 4. The cooling curve is linear, and the temperature rise curve of the refrigerant gas is made closer to the cooling curve of the source gas in the medium temperature range (about -30 to -90 ° C) and the low temperature range (about -90 ° C to -158 ° C). Is possible.

(Second Embodiment)
FIG. 5 is a configuration diagram showing the flow of the liquefaction process in the natural gas production system according to the second embodiment of the present invention. In the second embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions thereof are omitted. Further, regarding the second embodiment, matters not particularly mentioned below are the same as those of the first embodiment described above.

In the second embodiment, the compressor 20 that compresses the raw material gas is connected coaxially to the shaft 46 of the refrigerant expander 54. Thereby, the power generated by the expansion of the refrigerant in the expander 54 can be used as power for compressing the raw material gas in the raw material gas compressor 20 via the coaxial shaft 46.

Here, the refrigerant cooled by the rear cooler 44 is introduced into the compressor 245 through the line L13. The compressor 245 includes a centrifugal compressor in which an impeller that compresses refrigerant is attached to a shaft 221 that is coaxial with an expander 63 described later. The line L14 on the downstream side of the compressor 42 is provided with two coolers 47 and 48 for cooling the compressed refrigerant, and the cooled refrigerant is introduced into the heat exchanger 25.

As described above, the refrigerant expander connected to the source gas compressor 20 can be changed as appropriate (the same applies to the third embodiment described later). In some cases, a configuration in which power generated by a plurality of refrigerant expanders is used in one or more compressors of source gas is also possible.

(Third embodiment)
FIG. 6 is a configuration diagram showing the flow of liquefaction processing in the natural gas production system according to the third embodiment of the present invention. In the third embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted. Regarding the third embodiment, items not particularly mentioned below are the same as those in the first embodiment.

In the third embodiment, as in the case of the above-described reference example, the distillation apparatus 15 is disposed on the downstream side of the heat exchanger 25 and flows through the raw material gas pipe 31 of the heat exchanger 25 and is cooled. Is introduced into the distillation apparatus 15 via the line L7a. The raw material gas (light component) mainly composed of methane separated as a column top distillate in the distillation apparatus 15 is introduced into the compressor 20 via a line L7b. As in the case of the first embodiment, the compressor 20 is attached to the shaft 21 coaxial with the expander 63, and the power generated by the expander 63 can be used as power for compressing the raw material gas. It is.

The raw material gas compressed by the compressor 20 is introduced into the heat exchanger 26 via the line L7c. The source gas cooled by flowing through the source gas line 32 of the heat exchanger 26 is introduced into the heat exchanger 27 via the line L8, and the subsequent source gas flow is the same as in the case of the first embodiment. It is.

As described above, the distillation apparatus 15 can be disposed between the heat exchanger 25 and the heat exchanger 26. In this case, the overhead distillate of the distillation apparatus 15 is compressed by the compressor 20. A configuration to be introduced into the heat exchanger 26 later is preferable.

In the natural gas production system 1 according to the third embodiment, as in the case of the first embodiment, it is possible to bring the temperature rising curve closer to the cooling curve. Moreover, in this manufacturing system 1, since the distillation apparatus 15 is arrange | positioned in the downstream of the heat exchanger 25, it is possible to abbreviate | omit facilities, such as the cooler 12 in the upstream of the distillation apparatus 15 as shown in FIG. is there. Further, in this manufacturing system 1, since the compressor 20 is arranged between the heat exchangers 25 and 26, the heat exchangers 25 to 27 and the compressor 20 can be integrated to make the equipment compact. It becomes. In this manufacturing system 1, since the distillation apparatus 15 is arranged on the upstream side of the compressor 20, there is no problem that the raw material gas becomes critical due to compression by the compressor 20 and the processing in the distillation apparatus 15 becomes difficult.

As mentioned above, although this invention was demonstrated based on specific embodiment, these embodiment is an illustration to the last and this invention is not limited by these embodiment. The constituent elements of the natural gas production system and production method according to the present invention shown in the above-described embodiments are not necessarily all essential, and can be appropriately selected at least without departing from the scope of the present invention. It is. Moreover, the combination of the component shown in each embodiment is not necessarily essential, and the component of several embodiment can be selected suitably and used, at least, unless it deviates from the scope of the present invention.

1 Production System 15 Distillation Device 20 Compressor (Raw Gas Compressor)
25 Heat exchanger (first heat exchange part)
26 Heat exchanger (second heat exchanger)
27 Heat exchanger (third heat exchanger)
31, 32, 33 Raw material gas line 40 Refrigerant line (first refrigerant line)
42, 45 Compressor 43 Intermediate cooler 44 Rear coolers 47, 48 Cooler 51 Precooling line (first precooling line)
54 Expander (refrigerating expander)
61 Precooling pipeline (second precooling pipeline)
62 Refrigerant pipeline (second refrigerant pipeline)
63 Expander (refrigerant expander)
65 Refrigerant pipeline

Claims (6)

A natural gas production system for producing liquefied natural gas from a raw material gas containing natural gas,
A raw material gas compressor for compressing the raw material gas flowing in the manufacturing system;
A refrigerant expander group including at least one refrigerant expander that generates power by expanding a refrigerant circulating in the manufacturing system;
A first heat exchange unit that cools the source gas compressed by the source gas compressor by heat exchange with the refrigerant;
The raw material gas compressor compresses the raw material gas by using the power generated in the refrigerant expander. 2. The apparatus according to claim 1, further comprising a second heat exchange unit that is disposed downstream of the first heat exchange unit in the flow of the source gas and further cools the source gas by heat exchange with the refrigerant. The natural gas production system described in 1. 3. The natural gas production system according to claim 1, wherein the refrigerant comprises a single component and a single phase. A natural gas production system for producing liquefied natural gas from a raw material gas containing natural gas,
A refrigerant expander group including at least one refrigerant expander that generates power by expanding a refrigerant circulating in the manufacturing system;
A first heat exchange section that cools the source gas flowing in the manufacturing system by heat exchange with the refrigerant;
Distillation is arranged downstream of the first heat exchange unit in the flow of the source gas, and distills the source gas from the first heat exchange unit to reduce or remove heavy components in the source gas. Equipment,
A raw material gas compressor arranged on the downstream side of the distillation apparatus in the flow of the raw material gas and compressing the raw material gas;
A second heat exchange part that is disposed downstream of the source gas compressor in the source gas flow and further cools the source gas by heat exchange with the refrigerant;
The raw material gas compressor compresses the raw material gas by using the power generated in the refrigerant expander. A method for producing natural gas, which produces liquefied natural gas from a raw material gas containing natural gas,
A raw material gas compression step for compressing the raw material gas flowing in the manufacturing system;
A refrigerant expansion step of generating power by expanding a refrigerant circulating in the manufacturing system;
A first heat exchange step of cooling the raw material gas compressed in the raw material gas compression step by heat exchange with the refrigerant,
In the raw material gas compression step, the raw material gas is compressed by using the power generated in the refrigerant expansion step. A method for producing natural gas, which produces liquefied natural gas from a raw material gas containing natural gas,
A refrigerant expansion step for generating power by expanding the refrigerant circulating in the manufacturing system;
A first heat exchange step for cooling the source gas flowing in the manufacturing system by heat exchange with the refrigerant;
A distillation step of reducing or removing heavy components in the raw material gas by distilling the raw material gas cooled in the first heat exchange step;
A raw material gas compression step for compressing the raw material gas distilled in the distillation step;
A second heat exchange step of further cooling the raw material gas compressed in the raw material gas compression step by heat exchange with the refrigerant,
In the raw material gas compression step, the raw material gas is compressed by using the power generated in the refrigerant expansion step.

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