KR102034476B1 - Apparatus and process for liquefying natural gas containing nitrogen, and natural gas station including the apparatus for liquefying natural gas - Google Patents

Abstract

The present invention relates to a liquefaction apparatus and a liquefaction method for liquefaction of natural gas containing nitrogen. According to the present invention, the natural gas liquefaction apparatus containing nitrogen includes: a gas compressor which compresses natural gas containing nitrogen; a heat exchange unit which cools the compressed natural gas compressed by the gas compressor; a gas expansion valve which expands natural gas cooled in the heat exchange unit; and a hold-up drum which separates gas and liquid from a gas-liquid mixture generated when the natural gas passes through the gas expansion valve. The heat exchange unit includes a low temperature unit heat exchanger for cooling compressed natural gas by using recovery gas of a gas state, in which gas and liquid are separated in the hold-up drum, as a refrigerant. The present invention more includes: a recovery gas compressor which compresses recovery gas with increased temperature while cooling the compressed natural gas in the low temperature unit heat exchanger, and joins a nitrogen-containing natural gas stream supplied to the gas compressor; a gas engine which produces electric power by using the recovery gas with increased temperature as a fuel while cooling the compressed natural gas in the low temperature unit heat exchanger; and a gas purging valve which is controlled to supply at least one part of the recovery gas to the gas engine according to the nitrogen content of the recovery gas. The present invention is able to liquefy natural gas efficiently.

Description

Natural gas liquefaction apparatus and liquefaction method containing nitrogen, and natural gas filling station including natural gas liquefaction system

The present invention relates to a natural gas liquefaction apparatus and a liquefaction method for liquefying natural gas containing nitrogen, and a natural gas filling station comprising such a natural gas liquefaction apparatus.

The abundance of natural gas makes it possible for Liquefied Natural Gas (LNG) to replace diesel in many high horsepower industries, including ground transportation, sea transportation and rail transportation. This new paradigm has generated worldwide attention for small LNG plants where gas is liquefied and transported to other demand.

The core value of a small liquefaction system is that by placing production facilities at the point where demand arises, it is possible to reduce the cost of long-distance road transport for LNG truck transportation, and by more closely matching production and demand points, It can reduce costs. It also makes it possible to address small market segments that have historically been unable to provide cryogenic liquefaction facilities, for example gas utility peak shaving in small demand.

On the other hand, natural gas transported through the pipeline (hereinafter referred to as 'pipeline natural gas') typically contains 2 mole% of nitrogen, and may contain up to 5.5 mole%. Limit natural gas not connected to the pipeline network may contain up to 10 mole% nitrogen.

In addition to nitrogen, impurities such as carbon dioxide (CO ₂ ) and water (H ₂ O), which are included in natural gas, can be easily removed by conventional techniques. On the other hand, since nitrogen is not easily removed, the nitrogen content in the pipeline network is allowed to a certain level.

On the other hand, of the known and practically available natural gas liquefaction technologies, the two simplest techniques that can be applied modularly are: 1) pre-cooled Joule-Thomson cycle and 2) closed Brayton / cloud cycle. Nitrogen refrigerant cycle, also called (closed Brayton / Claude cycle). Both techniques are relatively simple and have a robust cycle, but the efficiency is not high.

The precooled Joule-Thompson cycle includes a closed cycle for pre-cooling the partially liquefied compressed natural gas using expansion through a Joule-Thompson valve, and as a closed cycle refrigerant, for example, fluorocarbon or propane Use propane

Nitrogen refrigerant cycles include closed cycles using compressors, turboexpanders, and heat exchangers, and use nitrogen (N ₂ ) as the working fluid of the closed cycle. Nitrogen gas is cooled and liquefied in a heat exchanger for use in precooling natural gas feeds.

Liquefaction techniques available in addition to these two cycles use more complex cycles, including mixed refrigerants that are primarily arranged in different modes. One of the major issues facing the widespread use of mixed refrigerants is the risk of leaking some working fluid in the compression system.

In the mixed refrigerant system, the working fluid, that is, the mixed refrigerant, leaks at different rates, respectively, so that the compositions constituting the mixed refrigerant change the composition of the mixed refrigerant. Maintaining the mixed refrigerant is an important issue, as a result of which the composition must be constantly monitored and certain compounds must be added to maintain the optimum composition. In addition, lighter components in the composition of the mixed refrigerant will typically leak at a faster rate, which must be compensated for continuously.

Accordingly, the present invention is to provide a natural gas filling station including a self-cooling liquefaction apparatus and a liquefaction method for liquefying natural gas efficiently in the presence of impurities such as nitrogen and bicarbonate, and a natural gas liquefaction apparatus.

According to an aspect of the present invention for achieving the above object, a gas compressor for compressing natural gas containing nitrogen; A heat exchanger for cooling the compressed natural gas compressed by the gas compressor; A gas expansion valve for expanding natural gas cooled in the heat exchanger; And a hold-up drum for gas-liquid separation of the gas-liquid mixture generated while the natural gas passes through the gas expansion valve, wherein the heat exchange unit uses the recovered gas in a gaseous state separated from the hold-up drum as a refrigerant. And a low temperature heat exchanger for cooling the compressed natural gas, wherein the low temperature heat exchanger compresses the recovery gas whose temperature rises while cooling the compressed natural gas and joins the nitrogen-containing natural gas stream supplied to the gas compressor. Gas compressors; A gas engine for producing electric power by using the recovered gas whose temperature rises as a fuel while cooling the compressed natural gas in the low temperature part heat exchanger; And a gas purging valve controlled to supply at least a portion of the recovery gas to the gas engine according to the nitrogen content of the recovery gas.

Preferably, the LNG storage tank for storing the liquefied natural gas (LNG) of the liquid state gas-separated from the hold-up drum and supplying the stored LNG to the LNG demand destination; may further include a.

Preferably, further comprising a refrigerant cycle for circulating a refrigerant for cooling the compressed natural gas to the heat exchange unit, wherein the heat exchange unit, the compressed natural gas by heat-exchanging the refrigerant circulating the refrigerant cycle and the compressed natural gas It may further include a refrigerant heat exchanger for precooling.

Preferably, the heat exchange unit further comprises a high temperature unit heat exchanger for pre-cooling the compressed natural gas by further recovering the cold heat of the recovered gas discharged after the heat exchange in the low temperature unit heat exchanger, wherein the heat exchange unit, The high temperature part heat exchanger, the refrigerant heat exchanger, and the low temperature part heat exchanger may be sequentially arranged in series.

Preferably, the refrigerant cycle, the refrigerant compressor for compressing the refrigerant to be supplied to the refrigerant heat exchanger; And a refrigerant expansion valve for adiabatic expansion of the compressed refrigerant compressed by the refrigerant compressor, wherein the liquid refrigerant adiabatic expanded by the refrigerant expansion valve is supplied to the refrigerant heat exchanger, and vaporized after heat exchange in the refrigerant heat exchanger. The refrigerant may form a closed cycle that is recycled to the refrigerant compressor.

Preferably, the gas compressor, the recovery gas compressor and the refrigerant compressor may be driven using the electric power produced by the gas engine.

Preferably, the CNG storage tank for storing the compressed natural gas compressed in the gas compressor; A CNG supply line branched from a nineteenth line through which the compressed natural gas compressed in the gas compressor is transferred to the heat exchange unit, and connected to the CNG storage tank; And a CNG supply valve configured to control opening and closing so that at least some of the compressed natural gas flows into the CNG supply line.

Preferably, the fifty line for providing a path so that the boil-off gas discharged from the LNG storage tank is supplied to the gas engine; And an boil-off gas recovery line branched from the fifty-th line to provide a path for supplying the boil-off gas to a recovery gas compressor.

According to another aspect of the present invention for achieving the above object, a natural gas liquefaction apparatus; A control unit which controls the CNG to produce only CNG, only LNG, or simultaneously produce CNG and LNG; An LNG charging unit for supplying the LNG produced by the natural gas liquefaction apparatus to a natural gas fuel vehicle; And a CNG filling unit for supplying the CNG produced by the natural gas liquefaction apparatus to a natural gas fuel vehicle.

In addition, according to another aspect of the present invention for achieving the above object, by compressing, cooling and expanding the nitrogen-containing natural gas to produce liquefied natural gas, the cooling step of cooling the natural gas is the natural gas Natural gas is cooled by using the recovery gas generated in the expansion process to expand as a refrigerant, and the recovery gas whose temperature rises after being used as the refrigerant is compressed to join the nitrogen-containing natural gas introduced into the compression process. In order to maintain the nitrogen content of the liquefied natural gas, a method of liquefying natural gas containing nitrogen, which purges a part of the recovery gas used as the refrigerant and generates electric power using the purge gas as a fuel, is provided.

Preferably, the cooling step may further include a step of precooling the natural gas using the refrigerant circulating the refrigerant cycle.

Preferably, the cooling step may further include a step of precooling the natural gas by recovering cold heat of the recovery gas used as the refrigerant.

Preferably, at least a portion of the compressed natural gas is branched and stored in the form of compressed natural gas, so that liquefied natural gas or compressed natural gas produced according to the demand of the natural gas demander may be supplied individually or simultaneously.

Preferably, the liquefied natural gas may be supplied to the fuel for generating electric power by evaporation gas generated by natural vaporization, or may be recycled to the compression process.

According to an aspect of the present invention for achieving the above object, a gas compressor for compressing natural gas; A heat exchanger for cooling the compressed natural gas compressed by the gas compressor; A gas expansion valve for adiabatic expansion of natural gas cooled in the heat exchange unit; A hold-up drum for gas-liquid separating the gas-liquid mixture produced while the natural gas passes through a gas expansion valve; LNG storage tank for storing the liquid liquefied natural gas (LNG) in the liquid state separated from the hold-up drum and supply the stored LNG to the LNG demand destination; A pre-treatment cooler that slips a portion of the LNG and uses it as a refrigerant to liquefy heavy hydrocarbons contained in natural gas supplied to the gas compressor; And a heavy hydrocarbon separator for gas-liquid separating the natural gas stream transferred from the pretreatment cooler to supply the gaseous natural gas from which the heavy hydrocarbons in the liquid state are separated to the gas compressor.

Preferably, the heat exchange unit, a low-temperature heat exchanger for cooling the compressed natural gas using the recovered gas in the gas state separated from the hold-up drum as a refrigerant; comprises a compressed natural gas in the low-temperature heat exchanger A recovery gas compressor for compressing the recovery gas whose temperature has risen while cooling, and joining the natural gas stream supplied from the bihydrocarbon separator to the gas compressor; And a gas engine for producing electric power by using the recovery gas whose temperature has risen while cooling the compressed natural gas in the low temperature part heat exchanger as a fuel.

Preferably, in order to maintain the nitrogen content of the LNG, the gas purging valve for controlling the flow path to supply the recovery gas used as the refrigerant in the low-temperature heat exchanger to the gas engine; may further include a.

Preferably, the heat exchange unit further comprises a refrigerant cycle for circulating a refrigerant for cooling the compressed natural gas to the heat exchange unit, wherein the heat exchange unit heat exchanges the refrigerant circulating the refrigerant cycle with the compressed natural gas, A refrigerant heat exchanger for precooling the compressed natural gas; And a refrigerant compressor for compressing and recirculating the refrigerant vaporized by heat exchange in the refrigerant heat exchanger.

Preferably, the low temperature heat exchanger further comprises a high temperature heat exchanger for pre-cooling the compressed natural gas by further recovering the cold heat of the recovered gas discharged after the heat exchange after the heat exchange, wherein the heat exchange unit, the high temperature heat exchanger, refrigerant The heat exchanger and the cold side heat exchanger may be arranged sequentially in series.

Preferably, in the pre-treatment cooler, LNG having an elevated temperature may be joined to a recovery gas stream supplied to the gas engine while liquefying heavy hydrocarbons contained in natural gas.

Preferably, the CNG storage tank for storing the compressed natural gas compressed in the gas compressor; A CNG supply line branched from a nineteenth line through which the compressed natural gas compressed in the gas compressor is transferred to the heat exchange unit, and connected to the CNG storage tank; And a CNG supply valve configured to control opening and closing so that at least some of the compressed natural gas flows into the CNG supply line.

Preferably, the fifty line for providing a path so that the boil-off gas discharged from the LNG storage tank is supplied to the gas engine; And an boil-off gas recovery line branched from the fifty-th line to provide a path for supplying the boil-off gas to a recovery gas compressor.

According to another aspect of the present invention for achieving the above object, a natural gas liquefaction apparatus; A control unit which controls the CNG to produce only CNG, only LNG, or simultaneously produce CNG and LNG; An LNG charging unit for supplying the LNG produced by the natural gas liquefaction apparatus to a natural gas fuel vehicle; And a CNG filling unit for supplying the CNG produced by the natural gas liquefaction apparatus to a natural gas fuel vehicle.

In addition, according to another aspect of the present invention for achieving the above object, while producing a liquefied natural gas by compressing, cooling and expanding the natural gas, before compressing the natural gas, There is provided a natural gas liquefaction method in which a part of the slip stream which has been slipped is used as a refrigerant to liquefy heavy hydrocarbon components contained in the natural gas introduced into the compression process.

Preferably, the cooling step is to cool the natural gas using the recovery gas generated in the expansion process as a refrigerant, compressing the recovery gas used as the refrigerant, the natural hydrocarbon which is introduced into the compression process after the heavy hydrocarbon is removed In order to join the gas, in order to maintain the nitrogen content of the liquefied natural gas produced, a part of the recovery gas used as the refrigerant may be purged, and the purge gas may be used as fuel to generate electric power.

Preferably, the cooling step may further include a step of precooling the natural gas using a refrigerant circulating a refrigerant cycle, and a step of precooling the natural gas by recovering cold heat of the recovery gas used as the refrigerant. have.

Preferably, at least a portion of the compressed natural gas is branched and stored in the form of compressed natural gas, so that liquefied natural gas or compressed natural gas produced according to the demand of the natural gas demander may be supplied individually or simultaneously.

Preferably, the liquefied natural gas may be supplied to the fuel for generating electric power by evaporation gas generated by natural vaporization, or may be recycled to the compression process.

According to the natural gas liquefaction apparatus and liquefaction method containing nitrogen of the present invention, since some of the recovered gas generated in the process of expanding the liquefied natural gas is discharged and used as fuel, it is possible to control the amount of nitrogen accumulated in the recovered gas Therefore, the problem of efficiency reduction of the process due to the accumulation of nitrogen can be solved without additional equipment.

In addition, by using the recovery gas as a refrigerant for liquefying natural gas, the cost can be reduced and the operation is easy.

In addition, since the recovered gas is used as a fuel to control the amount of nitrogen to produce additional power, it is possible to supply power by itself.

In addition, in the case where the feed gas contains heavy hydrocarbons, by condensing the heavy hydrocarbons using the produced liquefied natural gas, it is possible to prevent the problem of heavy hydrocarbons freezing during the production of liquefied natural gas.

In addition, the calorific value of the liquefied natural gas produced by removing heavy hydrocarbons can be matched to the requirements of the demand destination, thereby ensuring the reliability of the supply of the liquefied natural gas.

In addition, LNG and CNG can be produced separately or simultaneously, so that LNG and CNG can be supplied to natural gas fuel sources, respectively or simultaneously.

Various other objects, features and effects of the present invention will be better understood with reference to the accompanying drawings.
1 is a configuration diagram schematically showing a natural gas liquefaction apparatus according to a first embodiment of the present invention.
Figure 2 is a schematic diagram showing a natural gas liquefaction apparatus according to a second embodiment of the present invention.
3 is a configuration diagram schematically showing a natural gas liquefaction apparatus according to a third embodiment of the present invention.
Figure 4 is a schematic diagram showing a natural gas liquefaction apparatus according to a fourth embodiment of the present invention.
FIG. 5 is a schematic view illustrating a natural gas filling station including the natural gas liquefaction apparatus illustrated in FIGS. 3 and 4.

DETAILED DESCRIPTION The following detailed description of embodiments of the invention refers to the accompanying drawings that form a part hereof, and in which is shown by way of illustration an exemplary embodiment in which the invention may be practiced. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes in the invention may be made without departing from the spirit and scope of the invention. .

Accordingly, the following detailed description of embodiments of the invention does not limit the scope of the invention as claimed, but rather describes the features and characteristics of the invention, describes the best mode of operation of the invention, and is fully skilled in the art. Is just an example for enabling the present invention, but not for limitation.

Accordingly, the scope of the invention is defined only by the appended claims.

In addition, the following detailed description and exemplary embodiments of the present invention will be best understood with reference to the accompanying drawings, wherein the components and features of the present invention are represented entirely by numbers.

Singular forms include plural references unless the context clearly dictates otherwise. Thus, for example, reference to "gas" includes reference to one or more of the above materials, and reference to "conversion" refers to one or more of the above steps. In addition, unless otherwise specified, the steps may be performed sequentially and / or in parallel, and may be performed in a common vessel or separate vessels.

As used herein in connection with a identified feature or environment, “substantially” refers to a degree of deviation that is small enough so as not to degrade the identified feature or environment unmeasurably. The exact amount of deviation allowed may vary depending on the particular case.

Hereinafter, a natural gas filling station including a natural gas liquefaction apparatus and a liquefaction method, and a natural gas liquefaction apparatus according to embodiments of the present invention will be described with reference to FIGS. 1 to 3.

One embodiment of the present invention described below is an integrated autonomous mode process for producing Liquefied Natural Gas (LNG) from a natural gas feed (feed gas) comprising nitrogen and / or heavy hydrocarbons. The present invention relates to a liquefaction process consisting of a closed loop in which a natural gas feed is pressurized, cooled, and then expanded, and the low temperature recovered gas generated as a cooling medium for cooling the natural gas feed is generated.

The process according to one embodiment of the invention described below can be carried out by the liquefier unit of this embodiment comprising a Joule-Thomson expansion system with an integrated subcooling system. In addition, in one embodiment of the present invention to be described later, the purge gas discharged in order to maintain the nitrogen content of the recovered gas is a spark or compression ignition engine combined with a generator that provides the power required for the compression process Can be supplied.

In addition, the natural gas feed, introduced into the liquefaction process of the present embodiments, may be pretreated to remove any impurities that can potentially be frozen at cryogenic temperatures. For example, the impurities to be pretreated consist mainly of carbon dioxide and water.

In addition, in describing the embodiments of the present invention described below with reference to FIGS. 1 to 3, the stream number given on each piping line of FIGS. 1 to 3 may refer to the line itself, and the line It may also refer to a fluid stream flowing along.

First, referring to FIG. 1, a natural gas liquefaction apparatus containing nitrogen according to a first embodiment of the present invention includes: gas compressors 15 and 17 for compressing natural gas to be liquefied; Heat exchangers 20, 21, 23 for cooling and liquefying the compressed natural gas compressed by the gas compressors 15, 17 by heat exchange; A gas expansion valve 25 that expands and supercools the liquefied liquefied natural gas while passing through the heat exchange parts 20, 21, and 23; And a hold-up drum 27 for gas-liquid separating the generated gas-liquid mixture while inflated by the gas expansion valve 25. The liquid phase discharged from the hold-up drum 27, that is, liquefied natural gas (LNG), may be stored in the LNG storage tank 29 and transferred from the LNG storage tank 29 to the LNG demand destination.

Also, at the front end of the gas compressors 15 and 17, in order to protect the head of the gas compressors 15 and 17 from liquid droplets entrained in the feed gas supplied to the gas compressors 15 and 17, an arbitrary Gas compressor suction drum 13 to capture the condensation; may be installed.

The gas compressors 15 and 17 of the present embodiment may be a two stage compressor including a first gas compression stage 15 and a second gas compression stage 17.

On the piping line connecting the outlet of the first gas compression stage 15 and the introduction of the second gas compression stage 17, the gas stream whose temperature has risen while being compressed by the first gas compression stage 15 is converted into a second gas. Gas compressor intercooler 16 for cooling to the introduction temperature of the compression stage 17; may be installed.

In addition, on the 19th line 19 which connects the discharge part of the 2nd gas compression stage 17 and the heat exchange parts 20, 21, and 23, the gas which temperature rose while being compressed by the 2nd gas compression stage 17 was carried out. Gas compressor aftercooler 18 for cooling the stream; may be installed.

The heat exchangers 20, 21, and 23 of the present embodiment heat-exchange the compressed natural gas introduced into the heat exchangers 20, 21, and 23 through the recovery gas, which will be described later, and the nineteenth line 19. A high temperature heat exchanger 20 for cooling; And a refrigerant heat exchanger 21 for cooling the compressed natural gas by heat-exchanging the refrigerant circulating through the refrigerant cycle described below and the compressed natural gas. And a low temperature part heat exchanger 23 for cooling the compressed natural gas by heat-exchanging the recovery gas and the compressed natural gas, which will be described later.

As used herein, the term 'cooling' may mean that the temperature of the fluid is lowered by heat exchange, as well as may be accompanied by a phase change as the temperature of the fluid decreases, that is, the gas is changed into a liquid. have.

In the heat exchange part of the present embodiment, the high temperature part heat exchanger 20, the refrigerant heat exchanger 21, and the low temperature part heat exchanger 23 may be sequentially arranged in series. That is, the compressed natural gas compressed by the gas compressors 15 and 17 and introduced into the heat exchange part is liquefied by heat exchange while sequentially passing through the high temperature heat exchanger 20, the refrigerant heat exchanger 21, and the low temperature heat exchanger 23. Can be.

In addition, the term 'liquefied' herein means not only the phase change of gaseous natural gas into liquid liquefied natural gas, but also the supercritical pressure compressed above the critical pressure by the gas compressors 15 and 17. It may be a concept including natural gas in a state to obtain cold heat to become a liquid liquefied natural gas.

The natural gas liquefied by heat exchange in the hot part heat exchanger 20, the refrigerant heat exchanger 21, and the cold part heat exchanger 23 is decompressed by the gas expansion valve 25.

The gas expansion valve 25 may be a Joule-Thomson valve, and the liquefied natural gas may be supercooled by adiabatic expansion by the Joule-Thomson valve. In this process, some of the liquefied natural gas may be flashed to generate a flash gas such as a gas-liquid mixture.

In the hold-up drum 27, the gas-liquid mixture discharged from the gas expansion valve 25 is gas-liquid separated, and the separated liquid LNG is introduced into and stored in the LNG storage tank 29 through the 28th line 28. The recovered gas in the separated gaseous state is introduced into the heat exchange parts 23 and 20 and used as a refrigerant for cooling the compressed natural gas.

The recovered gas, which is used as the refrigerant and is discharged along the 42nd line 42 from the heat exchangers 23 and 20, is a natural gas feed flowing into the gas compressor suction drum 13 along the 43rd line 43; That is, may be joined to the feed gas stream 10, and some may be supplied as fuel of the gas engine 52 along the forty-fourth line 44.

According to this embodiment, in order to adjust the nitrogen content of the LNG produced according to this embodiment, gas purging to change the flow path such that the recovery gas is merged into the feed gas stream 10 or supplied as fuel of the gas engine 52. Valve 49; And a gas engine 52 connected to the generator and using natural gas as a fuel.

The gas engine 52 of the present embodiment may be a spark or compression ignition engine. In addition, boil-off gas generated by natural vaporization of recovered gas and LNG can be used as fuel.

In addition, although the LNG storage tank 29 may be insulated, cryogenic LNG is easily evaporated even by a small external factor, so that LNG is naturally vaporized to generate boil-off gas. The boil-off gas naturalized in the LNG storage tank 29 of the present embodiment may be supplied as a fuel of the gas engine 52, and the gas engine 52 may generate power by using the boil-off gas and the recovered gas as fuel. .

In addition, although not shown in the figure, the boil-off gas generated in the LNG storage tank 29 may be recovered by joining the recovery gas stream flowing into the recovery gas compressors 45 and 47 described later.

In addition, according to the present embodiment, the recovery gas compressor (45, 47) for compressing the natural gas recovered after being used as the refrigerant of the heat exchange unit (23, 20); may further include.

The recovery gas compressors 45 and 47 of the present embodiment may be a two-stage compressor including a first recovery gas compression stage 45 and a second recovery gas compression stage 47.

On the piping line connecting the discharge part of the first recovery gas compression stage 45 and the introduction part of the second recovery gas compression stage 47, the recovery gas stream which has risen in temperature while being compressed by the first recovery gas compression stage 45. The recovery gas compressor intercooler 46 for cooling to the introduction temperature of the second recovery gas compression stage 47; may be installed.

In addition, on the eleventh line 11, the feed gas is joined to the tenth line 10, which is a flow path into the gas compressor suction drum 13, from the discharge portion of the second recovered gas compression stage 47. 2, a recovery gas compressor aftercooler 48 for cooling the recovery gas stream whose temperature has risen while being compressed by the recovery gas compression stage 47 may be installed.

The refrigerant cycle of the present embodiment includes a piping line through which a refrigerant for supplying cold heat to the compressed natural gas is circulated in the refrigerant heat exchanger 21 described above, and the refrigerant compressors 62 and 64 compress the refrigerant on the pipeline line. ; And a refrigerant compressor suction drum 60 for removing liquid components such as droplets included in the refrigerant flowing into the refrigerant compressors 62 and 64. A surge drum 67 for storing the refrigerant compressed by the refrigerant compressor; And a refrigerant expansion valve 71 for supercooling the low temperature refrigerant supplied from the surge drum 67 to the refrigerant heat exchanger 21 by adiabatic expansion.

The refrigerant compressors 62 and 64 may be two-stage compressors including a first refrigerant compression stage 62 and a second refrigerant compression stage 64.

On the piping line connecting the discharge portion of the first refrigerant compression stage 62 and the introduction portion of the second refrigerant compression stage 64, the refrigerant stream, which has risen in temperature while being compressed by the first refrigerant compression stage 62, is connected to the second refrigerant. Refrigerant compressor intercooler 63 for cooling to the introduction temperature of the compression stage 64; may be installed.

In addition, on the 66th line 66 connecting the outlet of the second refrigerant compression stage 64 and the surge drum 67, the refrigerant stream compressed by the second refrigerant compression stage 64 to increase in temperature is cooled. Refrigerant compressor aftercooler 65; may be installed.

The surge drum 67 may be connected with a refrigerant injection line 68 that makes up the refrigerant lost during the cycle.

In addition, on the piping line constituting the refrigerant cycle of the present embodiment, the refrigerant purging line 72 for discharging the refrigerant circulating the refrigerant cycle; And a refrigerant purging valve 73 installed in the refrigerant purging line 72.

The refrigerant purging line 72 pretreats the feed gas stream 10 flowing into the refrigerant demand destination, for example, the natural gas liquefaction apparatus according to the present embodiment, in addition to the natural gas liquefaction unit according to the present embodiment. The refrigerant may be connected to the refrigerant demand source to circulate the refrigerant to the pretreatment unit.

The refrigerant purging valve 73 can be controlled by opening and closing and opening degree according to the flow rate or the flow rate of the coolant demand at the coolant demand destination by a control unit (not shown) or manually.

In the present embodiment, the refrigerant circulating through the refrigerant cycle may be propane. However, it is not limited thereto.

Next, a method of operating the natural gas liquefaction apparatus containing nitrogen according to the present embodiment will be described.

First, the nitrogen-containing natural gas pretreated through an impurity removal process except for nitrogen such as carbon dioxide (CO ₂ ) is introduced into the liquefaction unit along the tenth line 10.

The natural gas (feed gas stream) introduced into the liquefaction unit is introduced into the gas compressor suction drum 13, and after being used as a refrigerant in the heat exchange parts 20 and 23 before entering the gas compressor suction drum 13. It may be mixed with the recovery gas recovered along the eleventh line (11). The mixed stream of feed gas and recovery gas enters the gas compressor suction drum 13 along a twelfth line 12. In the gas compressor suction drum 13 any condensate is trapped to protect the compressor head from entrained droplets.

Liquid components such as condensate are removed from the gas compressor suction drum 13, and the dry natural gas discharged from the gas compressor suction drum 13 along the fourteenth line 14 is a natural gas compression system, that is, a gas compressor 15, 17) flows into. Dry gas in the gas compressors 15 and 17 may be compressed to 240 to 260 barg, or 245 to 255 barg, or about 249 barg.

First, the dry natural gas may enter the first gas compression stage 15 of the gas compressor and may be compressed to about 96 barg in the first gas compression stage 15.

The compressed natural gas is then cooled to about 55 ° C. in a gas compressor intercooler 16 that includes an air-cooled heat exchanger that can operate the module even at remote locations.

The cooled compressed natural gas then enters a second gas compression stage 17 of the gas compressor and is compressed to about 250 barg in the second gas compression stage 17. At this point, the natural gas may be in a supercritical or dense phase.

The compressed natural gas is then cooled to about 55 ° C. in a gas compressor aftercooler 18 that also includes an air cooled heat exchanger.

Although not shown in the figure, the high pressure natural gas cooled in the gas compressor aftercooler 18 is then discharged from the gas compressor 15, 17 cylinder by a lubricating oil removal system (not shown) comprising a series of filters. Lubricant of can be removed.

By removing the lubricating oil before cooling the compressed natural gas as described above, it is possible to prevent the lubricating oil from freezing during the liquefaction process of the natural gas and potentially prevent problems such as accumulation in the cryogenic heat exchanger and other components. The lubricating oil removal system can be configured such that the concentration of lubricating oil incorporated into the high pressure natural gas is at least 1 ppm or less.

When most of the lubricating oil is removed, the high pressure natural gas is introduced into the heat exchange parts 20, 21, 23 along the nineteenth line 19 to be cooled and liquefied. The high pressure natural gas is about -50 to -75 ° C, or about -55 to-by a series of heat exchangers in the heat exchanger, that is, the high temperature heat exchanger 20, the refrigerant heat exchanger 21, and the low temperature heat exchanger 23. Cooling to 70 ° C, or about -65 ° C.

The high pressure natural gas compressed by the gas compressors 15 and 17 is first introduced into the hot part heat exchanger 20 and cooled to about 22 ° C by heat exchange with the recovered gas.

As illustrated in FIG. 1, the low temperature recovery gas supplied to the high temperature part heat exchanger 20 may be a recovery gas discharged along the 41st line 41 due to an increase in temperature after heat exchange in the low temperature part heat exchanger 23. have.

That is, in this embodiment, the recovery gas discharged from the hold-up drum 27 may be supplied to the high temperature part heat exchanger 21 after heat exchange in the low temperature part heat exchanger 23.

The high pressure natural gas cooled by the heat exchange in the high temperature part heat exchanger 20 flows into the refrigerant heat exchanger 21.

The capacity of the gas compressors 15 and 17 of the present embodiment can be controlled through the following two embodiments.

For example, the compressor head is equipped with a cylinder unloading system for individual volume control (0/50/100% of normal flow rate) and can be performed manually by an operator in a control unit (not shown). .

The cylinder unloading system means that an unloader, such as a valve, is installed in the cylinder to add mechanical functions to the gas compressors 15 and 17 itself to operate at 0%, 50%, or 100% of the normal flow rate. Can be.

As another example, by controlling the bypass gas (not shown) installed in the bypass line and the bypass line to continuously control the entire gas flow, the compressed natural gas is directly supplied to the high temperature heat exchanger 20, and compressed The natural gas flow can be controlled to match the setpoint for a given flow parameter.

That is, a bypass line (not shown) branched from the nineteenth line 19 which is the discharge side of the gas compressors 15 and 17 and joined to the fourteenth line 14 which is the inlet side of the gas compressors 15 and 17 is installed. By controlling the opening and closing amount of the bypass valve by providing a bypass valve in the bypass line, the compressor capacity can be controlled by recycling compressed natural gas to the desired flow rate by bypassing, ie, from the rear of the compressor to the front of the compressor. have. The capacity of the compressor can be controlled in the range of 25 to 100%.

The gas compressor head may also be equipped with a single distance piece that traps the vent to prevent gas from leaking into the atmosphere.

In this embodiment, the high pressure natural gas cooled in the high temperature part heat exchanger 20 flows into the refrigerant heat exchanger 21. In the refrigerant heat exchanger 21, compressed natural gas may be cooled to about −25 ° C. by heat exchange with a refrigerant circulating a refrigerant cycle, that is, a propane refrigerant in this embodiment.

The temperature of the compressed natural gas discharged after cooling from the refrigerant heat exchanger 21 may be maintained at a set value by controlling the flow rate of propane liquid flowing into the refrigerant heat exchanger 21. The flow rate of the propane liquid flowing into the refrigerant heat exchanger 21 may be continuously reset by a temperature control loop to meet the requirements of the natural gas temperature cooled and discharged in the refrigerant heat exchanger 21. This can be done by cascade control.

The compressed natural gas stream which is discharged after cooling in the refrigerant heat exchanger 21 enters the low temperature heat exchanger 23 along the twenty-second line 22. The compressed natural gas stream entering the cold heat exchanger (23) may be cooled to about −65 ° C. by heat exchange with the recovered gas entering the cold heat exchanger (23) from the hold-up drum (27).

The liquefied natural gas stream exiting the cold heat exchanger (23) enters the gas expansion valve (25) via a twenty-fourth line (24). The liquefied natural gas stream 24 may be isenthalpy expanded to 4-8 barg or 5-7 barg or about 6 barg while passing through the gas expansion valve 25.

The liquefied natural gas passing through the gas expansion valve 25 is supplied to the LNG storage tank 29 along the 28th line 28, and the remaining cold gas, that is, the recovered gas, is liquefied in the hold-up drum 27. Separated from natural gas, it can be utilized as a heat sink to cool high pressure natural gas.

The pressure of the expansion gas stream exiting the gas expansion valve 25 can be kept constant by controlling the upstream pressure. As a result of the Joule-Thomson expansion, the temperature of the expansion gas stream (line 26) may be lowered to about −133 ° C. to −135 ° C. and partially liquefied. That is, the inflation gas stream 26 may be a two-phase gas-liquid mixture.

This two-phase expansion gas stream 26, which has passed through the gas expansion valve 25, enters the hold-up drum 27, where the LNG and the remaining cryogenic gas are gas-liquid separated in the hold-up drum 27.

The LNG separated from the hold-up drum 27 is discharged from the bottom of the hold-up drum 27, and transferred to the LNG storage tank 29 along the 28th line 28, and the LNG storage tank 29. Can be stored in. The LNG storage tank 29 may be designed to operate at about 5 barg.

The cryogenic gas stream separated from the hold-up drum 27 is discharged from the upper end of the hold-up drum 27 as a recovery gas and is supplied to the low temperature fluid inlet of the low temperature heat exchanger 23. That is, the recovery gas separated from the hold-up drum 27 is utilized as a refrigerant for liquefying high pressure natural gas in the low temperature part heat exchanger 23. The recovery gas provides cold heat to the hot gas stream, ie the high pressure natural gas, flowing along the twenty-second line 22 from the refrigerant heat exchanger 21, introduced through the hot fluid inlet in the cold heat exchanger 23. The outlet temperature of the recovered gas at elevated temperature while cooling the hot gas stream may be about -28 ° C.

The high temperature part heat exchanger 20, the refrigerant heat exchanger 21, and the low temperature part heat exchanger 23 may be cryogenic heat exchangers, and may be a printed circuit heat exchanger (PCHE) or a conventional aluminum plate heat exchanger. plate exchanger).

The high temperature part heat exchanger 20, the refrigerant heat exchanger 21, and the low temperature part heat exchanger 23 may be properly insulated to minimize heat inflow from the surroundings.

In the self-refrigerated liquefaction cycle as in the present embodiment, nitrogen contained in the feed gas stream 10 is transferred from the recycle gas loop, i.e., the hold-up drum 27, to the heat exchanger 20, It can easily accumulate on the recovery gas flow line leading to the front end of the gas compressor suction drum 13 via 21, 23.

Since nitrogen has a lower liquefaction point than methane, the main component of natural gas, nitrogen remains mainly gaseous at the liquefaction temperature of methane. Therefore, the recovery gas recovered from the hold-up drum 27 contains nitrogen, and the nitrogen content is gradually increased in the recovery gas as the circulation is repeated.

In this way, in order to meet the nitrogen-containing specification in producing LNG, and to reduce the power consumption to increase the liquefaction efficiency, it is necessary to purge the recovery gas.

Therefore, according to the present embodiment, the recovered gas can be removed by gas purge means. In this embodiment, the purge of the recovery gas may be performed by the gas engine 52 upstream of the recovery gas compressors 45 and 47.

According to the present embodiment, the gas purging means may include a gas purging valve 49 and a gas engine 52. That is, according to the present embodiment, in order to maintain the nitrogen content of the recovered gas below a predetermined level, the gas compressor suction drum is controlled by controlling the gas purging valve 49 to partially or all of the recovered gas in real time. It can purge without collect | recovering to (13) side.

The purged recovery gas is supplied to the fuel of the gas engine 52 to produce electric power.

The temperature rises while cooling the compressed natural gas in the cold heat exchanger (23) and the hot heat exchanger (20), and the recovered gas stream discharged along the 42nd line (42) is branched into two streams. Most of the recovered gas stream 42 joins the feed gas stream 10 which enters the gas compressors 15 and 17 along the 43rd line 43 and the remainder of the recovered gas cycle along the 44th line 44. It is removed (purged) from the.

The purging stream 44 removed from the recovery gas cycle can be joined to the boil-off gas stream exiting the 50th line 50 from the LNG storage tank 29. The purging stream 44 and the boil-off gas stream 50 are combined and supplied to the gas engine 52 along the 51 st line 51. The gas engine 52 is a power generation system that can supply the necessary power (power) required for the system, such as the gas compressors 15 and 17, the recovery gas compressors 45 and 47, and the refrigerant gas compressors 62 and 64. have.

The recovery gas stream 43 joining the feed gas 10 along the 43rd line 43 may be about 5.6 barg.

The recovery gas stream 43 is compressed in the recovery gas compressors 45, 47 and then joined with the feed gas stream 10, thereby closing the cycle.

In the recovery gas compressors 45 and 47, the recovery gas may be compressed to about 25 to 36 barg, or about 30 to 35 barg, or about 31 barg.

The recovery gas may be introduced into the first recovery gas compression stage 45 of the recovery gas compressors 45 and 47 and compressed to about 13.5 barg.

The recovery gas whose temperature has risen while being compressed by the first recovery gas compression stage 45 flows into the recovery gas compressor intercooler 46 and is cooled to about 55 ° C. The recovery gas compressor intercooler 46 may be configured as an air-cooled heat exchanger.

Thereafter, the recovery gas is introduced into the second recovery gas compression stage 47 and may be compressed up to about 31 barg. The recovery gas whose temperature has risen by compression in the second recovery gas compression stage 47 may be introduced into the recovery gas compressor aftercooler 48 and cooled to about 55 ° C. in the recovery gas compressor aftercooler 48.

The capacity of the recovery gas compressors 45 and 47 of the present embodiment can be controlled through the following two embodiments.

For example, the compressor head is equipped with a cylinder unloading system for individual volume control (0/50/100% of normal flow rate) and can be performed manually by an operator in a control unit (not shown). .

As another example, in order to maintain a desired suction pressure, it may be indirectly controlled by using a bypass valve (not shown) which allows the compressed recovery gas to return to the suction port side.

 This may be applied in the same manner as the capacity control method of the gas compressors 15 and 17 described above.

Here, the recovered gas stream 11 compressed by the recovered gas compressors 45, 47 is then joined to a new feed gas stream 10 containing nitrogen and back to the process system via a twelfth line 12. Inflow.

In addition, the natural gas liquefaction apparatus containing nitrogen of this embodiment includes the above-mentioned refrigerant cycle, and propane may be used as a working fluid of the refrigerant cycle.

According to this embodiment, by using the propane refrigerant cycle, the efficiency of the natural gas liquefaction apparatus can be increased. Propane circulating the refrigerant cycle flows into the refrigerant heat exchanger 21 in a low temperature state, cools down in the high temperature portion heat exchanger 20, and then heat exchanges with compressed natural gas introduced into the refrigerant heat exchanger 21, and compresses natural gas. The gas can be cooled to about -25 ° C.

The low pressure propane discharged along the 74th line 74 after cooling the natural gas in the refrigerant heat exchanger 21 is supplied to the refrigerant compressor suction drum 60. The refrigerant compressor suction drum 60 captures any condensate in the low pressure propane introduced into the refrigerant compressor suction drum 60 to protect the compressor heads of the refrigerant compressors 62 and 64 from droplets entrained therein. do.

The dry propane refrigerant discharged from the refrigerant compressor suction drum 60 is transferred to the refrigerant compressors 62 and 64 along the sixty-first line 61 and the first refrigerant compression stage 62 of the refrigerant compressors 62 and 64. Flows into. In the first refrigerant compression stage 62, the dry propane refrigerant is compressed to about 4.7 barg.

Propane refrigerant compressed in the first refrigerant compression stage 62 flows into the refrigerant compressor intercooler 63 and is cooled to about 55 ° C. The refrigerant compressor intercooler 63 may use an air cooled heat exchanger because of its own requirements.

Propane refrigerant cooled in the refrigerant compressor intercooler 63 flows into the second refrigerant compression stage 64. In the second refrigerant compression stage 64 propane refrigerant is compressed to about 18.5 barg.

Propane refrigerant compressed in the second refrigerant compression stage 64 flows into the refrigerant compressor aftercooler 65 and is cooled to about 55 ° C. At this time, the propane refrigerant may be completely condensed into the liquid phase.

The condensed liquid propane refrigerant is discharged through the 66th line 66 and flows into the surge drum 67 in which most propane refrigerant is stored.

The sixty-eighth line 68 may be connected to the surge drum 67 to make-up the propane refrigerant to the surge drum 67 as needed. The propane to be replenished must be properly dehydrated to have a moisture content of less than 1 ppm.

The liquid propane refrigerant is discharged from the surge drum 67 via the sixty-ninth line 69. The sixty-ninth line 69 is branched into a seventy-seventh line 70, which is a main line connected to the refrigerant heat exchanger 21, and a seventy-second line 72, connected to a refrigerant demand destination other than the refrigerant heat exchanger 21. For example, the 72nd line 72 may be connected to a pretreatment process of removing impurities such as carbon dioxide or water included in the feed gas stream 10.

A refrigerant expansion valve 71 is installed in the seventieth line 70, through which the liquid propane refrigerant is enthalpy expanded, the temperature is lowered to about −28 ° C., and the liquid propane refrigerant is partially Can be evaporated. That is, the propane refrigerant discharged from the refrigerant expansion valve 71 may be a two-phase gas-liquid mixture.

For example, Joule-Thompson expansion can be controlled by using a cascade loop such that refrigerant expansion valve 71 functions as a flow control valve. The refrigerant expansion valve 71 can be controlled according to a set value continuously reset by monitoring and maintaining the temperature downstream of the refrigerant heat exchanger 21.

The two-phase propane refrigerant stream exiting the refrigerant expansion valve 71 is completely evaporated downstream of the refrigerant heat exchanger 21 and recycled to the refrigerant compressor suction drum 60 via the 74th line 74. This causes the propane refrigerant cycle to form a closed loop.

The liquid propane refrigerant may also be supplied to the pretreatment device through the refrigerant purging line 72 to be used to precool natural gas (feed gas) containing nitrogen that is introduced after impurities such as carbon dioxide and water are removed. The propane refrigerant whose temperature has risen after being used in the pretreatment device may likewise be recycled to the refrigerant compressor suction drum 60. This configuration can maximize the overall system efficiency without requiring additional equipment for pretreatment.

The stream flowing along the seventy-second line 72 diverges from the stream flowing along the sixty-ninth line 69, and a refrigerant purging valve 73 is installed in the seventy-second line 72. The refrigerant purging valve 73 may be a Joule-Thompson valve and may inflate the propane refrigerant stream flowing along the seventy-second line 72 to about 1 barg. The refrigerant purge valve 73 can lower the propane refrigerant stream to about -25 ° C. In other words, this two-phase flow formed by the refrigerant purging valve 73 is sufficient to cool the feed gas to remove impurities such as carbon dioxide and water. The propane refrigerant completely vaporized while cooling the feed gas is recovered to the refrigerant compressor suction drum 60 again.

The capacity of the refrigerant compressors 62 and 64 of the present embodiment can be controlled through the following two embodiments.

For example, the compressor head is equipped with a cylinder unloading system for individual volume control (0/50/100% of normal flow rate) and can be performed manually by an operator in a control unit (not shown). .

As another example, using a refrigerant expansion valve 71 and / or a refrigerant purging valve 73, the propane refrigerant flow branching to the seventy-ninth line 70 and the seventy-eighth line 72 in conjunction with each other or each, Can be controlled continuously.

This may be applied in the same manner as the capacity control method of the gas compressors 15 and 17 described above.

In addition, the refrigerant compressor head may be equipped with a single distance piece that traps the vent to prevent gas from leaking into the atmosphere.

With respect to the general feed gas composition, the discharge of three sets of compressors included in this embodiment, namely, gas compressors 15 and 17, recovery gas compressors 45 and 47 and refrigerant compressors 62 and 64, according to various system parameters. The effect of varying the pressure is shown in Table 1 below. The pressure was varied from 175 bara to 300 bara at 25 bar intervals and the rate of purge gas was based on 200 kg / hr.

Discharge pressure (bara) 175 200 225 250 275 300 gas
compressor
(15,17) Flow rate (kg / hr) 2037 1912 1836 1790 1760 1742 Power (kW) 192 196 201 208 216 224 Recovery gas compressor
(45, 47) Flow rate (kg / hr) 1196 1071 995 948 919 901 Power (kW) 132 118 110 105 101 99 Refrigerant
compressor
(62, 64) Flow rate (kg / hr) 1226 1182 1139 1099 1063 1032 Power (kW) 68 66 63 61 59 58 Total power (kW)
392 379 374 374 376 380 After the Joule-Thompson Valve
Steam fraction
0.70 0.68 0.66 0.65 0.65 0.64

As also shown in the above sensitivity analysis results, power consumption is minimized when the compressed natural gas discharge pressure from the gas compressors 15 and 17 is 225 to 250 bara. In addition, in order to determine the amount of recovered gas to be purged in order to maintain the nitrogen content of the produced LNG at, for example, 1.5 mole%, the influence according to the feed gas composition is shown in Tables 2 to 4. Tables 2 through 4 show the results for different purge gas ratios. First, when Table 2 contains about 5.12 mole% of nitrogen, the Table 3 shows about 4.10 mole% of feed gas. When nitrogen is contained, Table 4 shows the amount of power consumed so that the nitrogen content of the produced LNG satisfies 1.5 mol% when the feed gas contains about 3.3 mole% of nitrogen, and the required recovery gas purge amount. Indicates.

Purge flow rate
(kg / hr) 200 180 160 150 140

power
Consumption
(kW) Gas compressor
(15, 17) 208 210 213 215 216 Recovery gas
compressor
(45, 47) 104 108 113 115 117 Refrigerant compressor
(62, 64) 61 61 61 62 62 Total compressed power consumption
(kW) 374 380 387 392 395 Nitrogen mole fraction of production LNG 0.0124 0.0133 0.0144 0.0151 0.0157 Purge Gas LHV
(kJ / kg) 37,659 37,025 36,280 35,862 35,473 Gas Engine (52)
Power output
(kWe) (@ 41% efficiency)
918
818
719
668
622 Feed gas flow rate
(kg / hr) 842 822 801 792 782

Referring to Table 2, when the feed gas contains about 5.12 mole% of nitrogen, the amount of purge required to meet the nitrogen content specification of the LNG produced, i.e. the nitrogen content of 1.5 mole%, is about 151 kg / hr.

Purge flow rate
(kg / hr) 200 180 160 140 120 110 100


power
Consumption
(kW) gas
compressor
(15, 17)
212
214
216
218
221
223
224 Recovery gas
compressor
(45, 47)
104
108
111
115
120
122
125 Refrigerant
compressor
(62, 64)
62
62
62
62
62
63

63 Total compression power
Consumption
(kW)
378
384
390
396
403
407
411 Production of LNG
Nitrogen mole fraction 0.0107 0.0115 0.0123 0.0133 0.0146 0.0153 0.0161 Purge Gas LHV
(kJ / kg) 37,941 39,426 38,843 38,159 37,345 36,899 36,390 Gas Engine (52)
Power output
(kWe) (@ 41% efficiency)
977
875
773
673
573
525
476 Feed gas flow rate
(kg / hr) 842 823 803 783 763 753 743

Referring to Table 3, when the feed gas contains about 4.10 mole% of nitrogen, the amount of purge required to meet the nitrogen content specification of the LNG produced, i.e. the nitrogen content of 1.5 mole%, is about 113 kg / hr.

Purge flow rate
(kg / hr) 200 180 160 140 120 100 80 70

power
Consumption
(kW) gas
compressor
(15, 17)
214
215

217
219
221
223
226
227 Recovery gas
compressor
(45, 47)
103
106
110
113
117
121
126
128 Refrigerant
compressor
(62, 64)
63
63
63
63
63
63
63
63 Total compression power
Consumption
(kW)
379
384
389
395
401
407
415
419 Production of LNG
Nitrogen mole fraction 0.0090 0.0095 0.0102 0.0110 0.0120 0.0131 0.0146 0.0155 Purge Gas LHV
(kJ / kg) 41,846 41,439 40,962 40,398 39,732 38,973 38,023 37,477 Gas Engine (52)
Power output
(kWe) (@ 41% efficiency)
1025
921
817
714
612
512
413
364 Feed gas flow rate
(kg / hr) 842 823 803 783 763 743 723 713

Referring to Table 4, when the feed gas contains about 3.30 mole% of nitrogen, the amount of purge required to meet the nitrogen content specification of the LNG produced, that is, to bring the nitrogen content to 1.5 mol%, is about 75 kg / hr. The natural gas liquefaction apparatus according to the present embodiment is a two-stages compression of the feed gas stream 10 containing nitrogen, that is, two stages of gas compressors 15 and 17 and a recovery gas compression. Six-stage reciprocating compressors with common electric drive such as two-stage compression, two-stage recovery gas compressors 45, 47 and propane refrigerants, two-stage compression, ie refrigerant compressors 62, 64. ) May be included.

The gas compressors 15 and 17, the recovery gas compressors 45 and 47, and the refrigerant compressors 62 and 64 may be driven in respective axes, or may be connected and operated in one axis.

In addition, in the liquefaction method according to the present embodiment, it is a key consideration to maintain a functional autonomy capable of treating nitrogen-containing natural gas feed. The purge is maintained at a level that provides a constant nitrogen concentration in the recovery gas recycle stream. This purge targets a gas engine 52 coupled to a generator that provides the power needed to drive a compression system. In addition, the process heat transfer devices are all air-cooled to maintain process autonomy. This completely separates all site requirements and processes, allowing the system to be utilized to liquefy natural gas at all sites and locations.

Next, a natural gas liquefaction apparatus and a liquefaction method containing nitrogen according to the second embodiment of the present invention will be described with reference to FIG. 2.

The second embodiment of the present invention is a modification of the first embodiment and, unlike the first embodiment, before the feed gas stream 100 enters the gas compressor suction drum 13, the pretreatment cooler 101 and the heavy hydrocarbons. After passing through the separator 103, the gas is mixed with the recycled gas 11 to be recycled and introduced into the gas compressor suction drum 13.

Hereinafter, a natural gas liquefaction apparatus and a liquefaction method containing nitrogen according to the second embodiment of the present invention to be described later will be described with emphasis on the differences from the first embodiment, the same technology applied to the first embodiment The description of the features will be omitted. Components that refer to the same reference numerals may be applied in the same manner as in the first embodiment even if there is no mention or detailed description.

The feed gas stream 100, ie, natural gas, which is transferred from the natural gas producer to the natural gas liquefaction apparatus of this embodiment via a pipeline network, has different specifications depending on the natural gas producer.

In particular, it is such as is produced in a certain area some feed gas stream is conveyed through a pipeline has a high content of C ₄ or C ₅ or more hydrocarbon. LNG produced by liquefying natural gas containing heavy hydrocarbons without proper treatment of heavy hydrocarbons cannot meet the specifications required by the LNG demand, especially LHV (low calorific value), and the liquefaction point in the process of producing LNG The problem arises in which the high hydrocarbon content freezes.

Accordingly, the present embodiment relates to a natural gas liquefaction apparatus and a liquefaction method for liquefying a feed gas stream 100 containing nitrogen and heavy hydrocarbons to meet the specifications required by LNG demand.

The feed gas stream 100 entering the liquefaction apparatus of this embodiment, ie natural gas, contains nitrogen and heavy hydrocarbons. In addition, the feed gas stream 100 flowing into the liquefaction apparatus may be natural gas in which impurities are removed by a pretreatment apparatus (not shown) that removes impurities such as carbon dioxide and water, as in the first embodiment.

The natural gas liquefaction apparatus according to the present embodiment includes: a pretreatment cooler 101 installed upstream of the gas compressor suction drum 13 to cool the feed gas stream, that is, natural gas by heat exchange; And a heavy hydrocarbon separator (103) for gas-liquid separation of the generated gas-liquid mixture while passing through the pretreatment cooler (101).

The pretreatment cooler 101 liquefies the heavy hydrocarbon component contained in the feed gas stream comprising nitrogen and heavy hydrocarbons.

The feed gas stream 100 is discharged from the pretreatment cooler 101 and sent to the heavy hydrocarbon separator 103. In the heavy hydrocarbon separator 103, the heavy hydrocarbon component contained in the feed gas stream 100 is condensed and gas-liquid separated. A gaseous feed gas stream comprising nitrogen from which the heavy hydrocarbon component is separated in the heavy hydrocarbon separator 103 is supplied to the gas compressor suction drum 13 via line 104 and the heavy hydrocarbon separator 103 The heavy hydrocarbon component separated in the liquid state at may be discharged from the heavy hydrocarbon separator (103) and supplied to the heavy hydrocarbon demand (106).

In addition, according to the present embodiment, the heavy hydrocarbon discharge valve 105 for controlling the discharge and the discharge flow rate of the heavy hydrocarbons in the liquid state discharged from the heavy hydrocarbon separator 103 may further include.

The heavy hydrocarbon condensed in the heavy hydrocarbon separator 103 and separated and discharged from natural gas is, for example, C ₂ or more, or C ₃ or more, such as ethane, propane, i-butane, n-butane, i-pentane, n-pentane, etc. Or a C ₄ or higher hydrocarbon component.

Butane and pentane may cause problems such as freezing of the piping lines and the respective devices constituting the liquefaction apparatus of this embodiment, so that heavy hydrocarbons are removed from the natural gas feed, i.e., the feed gas stream, to be applied to the liquefaction process. There is a need.

The natural gas containing nitrogen discharged after the heavy hydrocarbon is separated from the heavy hydrocarbon separator 103 is mixed with the recovery gas 11 and then passed through the gas compressor suction drum 13 as in the first embodiment. Flows into (15, 17) and is compressed by gas compressors (15, 17). The compressed natural gas compressed in the gas compressor (15.17) is recovered by the recovered gas stream 41 in the hot part heat exchanger 20, by propane refrigerant in the refrigerant heat exchanger 21, and by the propane refrigerant in the cold part heat exchanger 23. Cooled and liquefied by the gas stream.

The natural gas liquefied while passing through the hot part heat exchanger 20, the refrigerant heat exchanger 21, and the cold part heat exchanger 23 is adiabaticly expanded by the gas expansion valve 25, and is supercooled while passing through the gas expansion valve 25. The liquefied natural gas is introduced into the hold-up drum 27. A gas-liquid mixture is formed by flash or the like while passing through the gas expansion valve 25, and the gas-liquid mixture is gas-liquid separated in the hold-up drum 27, and the LNG in the liquid state is stored in the LNG storage tank 29. The separated gaseous state is a recovery gas, and is utilized as a cold heat source for cooling natural gas in the low temperature part heat exchanger 23 and the high temperature part heat exchanger 20.

The recovery gas whose temperature is increased while liquefying natural gas in the low temperature part heat exchanger 23 and the high temperature part heat exchanger 20 is compressed by the recovery gas compressors 45 and 47 and then supplied to the gas compressor suction drum 13. Form a cycle that joins stream 104.

Since the recovery gas separated from the hold-up drum 27 is mainly composed of methane and nitrogen having the lowest liquefaction point, when the process is repeated, the recovery gas containing high concentration of nitrogen is continuously added to the feed gas stream 104. Therefore, not only the nitrogen content of the LNG produced is increased, but also the nitrogen has a liquefaction temperature much lower than the liquefaction temperature of the natural gas mainly composed of methane, thereby degrading the liquefaction efficiency of natural gas.

Therefore, according to this embodiment, whenever the nitrogen content of the recovery gas is higher than a predetermined specific value, or periodically at any time, the gas purging valve 49 is controlled to recover the recovery gas compressors 45 and 47 from the high temperature portion heat exchanger 20. Some or all of the recovery gas directed to) may be discharged (purged) from the recovery gas cycle.

The purged recovery gas (purged gas) is supplied to the fuel of the gas engine 52 for producing electric power, and the electric power produced by the gas engine 52 is used as a power source of the natural gas liquefaction apparatus according to the present embodiment. For example, gas compressors 15 and 17 may be used.

In addition, according to the present exemplary embodiment, some or all of the LNG produced, for example, LNG transferred from the LNG storage tank 29 to the LNG demand destination along the 110th line 110 may be branched to the 112th line 112. The pretreatment cooler 101 can be used as a cold heat source to liquefy the heavy hydrocarbons contained in the feed gas stream.

The LNG discharged after heat exchange with the feed gas stream in the pretreatment cooler 101 may be supplied as a fuel of the gas engine 52. LNG supplied from the pretreatment cooler 101 to the gas engine 52 may be supplied after being mixed with the purging gas.

Table 5 shows an energy resin and a material resin (heat & material balace) according to the removal of bicarbonate through one embodiment of the present invention. The stream number is referred to FIG. 2.

The composition of the feed gas stream 100 shown in Table 5 is a representative example of a typical gas composition applied to a liquefaction process. This feed gas stream 100 flows in an alternating direction with the production LNG slip stream 112 in the pretreatment cooler 101. In the pretreatment cooler 101, the feed gas stream 100 may be cooled to about −39 ° C. The vapor fraction of the feed gas stream 102 cooled in the pretreatment cooler 101 may be 0.97 and the liquid fraction may be 0.03.

The feed gas stream 102 after cooling in the pretreatment cooler 101 enters the heavy hydrocarbon separator 103, and the liquid separated in the heavy hydrocarbon separator 103, ie, the heavy hydrocarbon component, of the heavy hydrocarbon discharge valve 105 is removed. Discharged by control.

In addition, the vapor fraction 104 separated in the heavy hydrocarbon separator 103 is mixed with the recycle gas stream 11 to be recycled to form a mixed stream 12. Mixed stream 12 enters gas compressor suction drum 13 and is fed to first gas compression stage 15 of gas compressors 15 and 17.

The liquid fraction discharged by the heavy hydrocarbon discharge valve 105 from the heavy hydrocarbon separator 103 is converted to steam at atmospheric pressure and may be supplied to the gas engine 52 as an auxiliary fuel source although not shown in the drawing. have.

The cold heat medium for cooling the feed gas stream 100 may be provided by extracting the slipstream 112 from the produced LNG stream 110.

In the present embodiment, when the flow rate of the LNG 110 transferred from the LNG storage tank 29 to the LNG demand destination is about 843.3 kg / hr, the slip extracted to liquefy the heavy hydrocarbons contained in the feed gas stream 100 Stream 112 may be about 203.9 kg / hr.

This is a necessary process, although not an energy efficient process, because it is essential to remove significant amounts of heavy hydrocarbons that can be frozen in large quantities in the liquefaction process.

As described above, according to the exemplary embodiments of the present invention, the natural gas for liquefaction may contain impurities such as carbon dioxide (CO ₂ ), water (H ₂ O), light hydrocarbons, and nitrogen (N ₂ ). CO ₂ and H ₂ O can be easily removed using molecular sieves, while light hydrocarbons can be treated by condensing them. Nitrogen removal presents an important technical proposition. The invention proposed for liquefying natural gas containing nitrogen carries out a Joule-Thompson cycle through recycle expansion in the feed and purges the appropriate amount to maintain a constant N ₂ composition of the gas.

In addition, the working fluid of the refrigerant cycle circulating through the refrigerant heat exchanger 21 of the present embodiments, ie, closed loop-cooling using a refrigerant such as propane, can also be used to precool the compressed natural gas, which is an overall system. Improve the efficiency.

The purging gas stream 44 is supplied to the fuel of the gas engine 52, which is a spark or compression ignition engine that produces power directly driving the electric motor drive compressor.

In addition, the natural gas liquefaction apparatus according to the embodiments of the present invention described above provides a self-contained refrigeration unit in a remote location.

Next, a natural gas liquefaction apparatus 3 and a liquefaction method according to a third embodiment of the present invention will be described with reference to FIG. 3.

The third embodiment of the present invention is a modified example of the first embodiment, and further includes a CNG storage tank CT and a CNG supply line CL1 as compared to the natural gas liquefaction apparatus according to the first embodiment. The difference is that natural gas (CNG) can be produced separately or simultaneously.

 Hereinafter, the natural gas liquefaction apparatus 3 and the liquefaction method according to the third embodiment of the present invention to be described later will be described with emphasis on the differences from the first embodiment, the same technical features as the first embodiment The description thereof will be omitted. Components that refer to the same reference numerals may be applied in the same manner as in the first embodiment even if there is no mention or detailed description.

Natural gas liquefaction apparatus 3 according to the present embodiment, the CNG storage tank (CT) for storing the compressed natural gas compressed by the gas compressor (15, 17); A CNG supply line (CL1) branched from a nineteenth line (19) where compressed natural gas is transferred from a gas compressor (15, 17) to a heat exchange unit (20, 21, 23) and connected to a CNG storage tank (CT); And a recovery gas stream (BOG; boil-off gas) generated in the LNG storage tank 29 or a recovery gas stream flowing into the recovery gas compressors 45 and 47 from the boil-off gas or the flash gas generated during the process. And a boil-off gas recovery line 52 for joining 43).

According to the present embodiment, the BOG discharged from the LNG storage tank 29 or the gas engine 52 or the recovery gas compressors 45 and 47 are not discharged or burned into the atmosphere. It can be recovered and treated environmentally and economically.

The CNG transferred along the CNG supply line CL1 is stored in the CNG storage tank CT. The operating pressure of the CNG storage tank CT may be about 250 bar and may be a pressure tank.

According to the present embodiment, CNG is stored in the state of compressed natural gas without supplying some or all of the compressed natural gas compressed to about 250 bar in the gas compressors 15 and 17 to the heat exchange unit 20, 21, 23. Can be stored in the tank CT.

That is, the natural gas liquefaction apparatus 3 according to the present embodiment may produce LNG and CNG, respectively, and may simultaneously produce, and LCNG (Liquefied and / or Compressed) capable of supplying LNG and CNG separately or simultaneously to a gas demand destination. Natural Gas) production equipment.

The output of LNG and the production of CNG can be adjusted by controlling the flow rate of the compressed natural gas branching to the CNG supply line CL1 according to the demand of the gas demand source.

In addition, the LCNG production method using the natural gas liquefaction apparatus 3, that is, the LCNG production apparatus 3 of the present embodiment is divided into three modes: 1) CNG production mode, 2) LNG production mode, and 3) simultaneous LCNG production mode. Can work.

The three modes according to the present embodiment control the operations of the gas compressors 15 and 17, the recovery gas compressors 45 and 47 and the refrigerant compressors 62 and 64 remotely or manually by a controller (not shown). It can control by adjusting the CNG supply flow volume to CNG supply line CL1.

The flow rate of the CNG branched from the nineteenth line 19 to the CNG supply line CL1 may be adjusted by opening / closing and opening amount control of a CNG supply valve (not shown).

The CNG supply valve (not shown) may be a three-way valve installed at a branch point of the nineteenth line 19 and the CNG supply line CL1, but is not limited thereto. The CNG supply valve may include a nineteenth line 19 and CNG supply line (CL1) may be configured by installing a shutoff valve for controlling the opening and closing of the line and a flow control valve for regulating the flow rate of the fluid. In this embodiment, the CNG supply valve will be described with an example provided as a three-way valve.

First, in the CNG production mode in which only CNG is produced without producing LNG, the CNG supply valve is controlled to open and close, and the gas is compressed by the gas compressors 15 and 17 and cooled by the gas compressor aftercooler 18. Natural gas, that is, CNG may not be transferred to the heat exchange units 20, 21, 23, but the entire amount may be transferred to the CNG supply line CL1.

In addition, in the CNG production mode, only the gas compressors 15 and 17 are controlled to operate at the total flow rate, that is, the capacity of 100%, and the recovery gas compressors 45 and 47 and the refrigerant compressors 62 and 64 are not operated.

Next, in the LNG production mode in which only the LNG is produced without producing CNG, the opening and closing amounts of the CNG supply valves are controlled, compressed by the gas compressors 15 and 17, and cooled by the gas compressor aftercooler 18. Compressed natural gas may not be introduced into the CNG supply line CL1, and the entire compressed natural gas may be transferred to the heat exchange units 20, 21, and 23.

In the LNG production mode, all of the gas compressors 15 and 17, the recovery gas compressors 45 and 47, and the refrigerant compressors 62 and 64 are operated according to the respective loads.

Lastly, in the LCNG simultaneous production mode for producing LNG and CNG simultaneously, the opening and closing amount of the CNG supply valve is controlled to be compressed by the gas compressors 15 and 17 and cooled by the gas compressor aftercooler 18. Some of the natural gas may be supplied to the heat exchange units 20, 21, 23, and the others may be branched to the CNG supply line CL1, respectively.

In addition, in the LCNG simultaneous production mode, all of the gas compressors 15 and 17, the recovery gas compressors 45 and 47, and the refrigerant compressors 62 and 64 are operated in accordance with each load.

For example, when 50% of the compressed natural gas compressed by the gas compressors 15 and 17 is to be produced by LNG and the remaining 50% by CNG, the gas compressors 15 and 17 are loaded at 100% duty. And the recovery gas compressors 45 and 47 and the refrigerant compressors 62 and 64 are operated at 50% duty, respectively.

The gas compressors 15 and 17, the recovery gas compressors 45 and 47, and the refrigerant compressors 62 and 64 may be driven in respective axes, or may be connected and operated in one axis. In the case of being operated together by connecting to one axis, as described in the first and second embodiments described above, the flow rate of each compressor may be adjusted by using an unloader or a bypass system for each compressor.

Next, a natural gas liquefaction apparatus 4 and a liquefaction method according to a fourth embodiment of the present invention will be described with reference to FIG. 4.

The fourth embodiment of the present invention is a modified example of the second and third embodiments, and compared with the natural gas liquefaction apparatus according to the second embodiment, the CNG storage tank CT, the CNG supply line CL1 and the boil-off gas recovery line. In addition to the 52, there is a difference in that it can produce each of the LNG and Compressed Natural Gas (CNG) or simultaneously, the feed gas stream 100 compared to the natural gas liquefaction apparatus according to the third embodiment ) Is introduced into the gas compressor suction drum 13 after being passed through the pretreatment cooler 101 and the heavy hydrocarbon separator 103 and then recycled to the gas gas that is recycled. There is a difference in that.

Hereinafter, the nitrogen-containing natural gas liquefaction apparatus 4 and the liquefaction method according to the fourth embodiment of the present invention described below may refer to the second and third embodiments described above, and the second and third embodiments. For the technical features that are applied in the same manner as described above will be omitted. Components that refer to the same reference numerals may be applied in the same manner as in the second and third embodiments even if there is no mention or detailed description.

That is, according to the present embodiment, using the pretreatment cooler 101 and the heavy hydrocarbon separator 103 to control the heavy hydrocarbon components contained in the natural gas stream 100, the CNG feed valve and the gas compressor (15, 17) The operation and load of the recovery gas compressors 45 and 47 and the refrigerant compressors 62 and 64 can be controlled to produce LNG and CNG, respectively, or simultaneously.

Next, a natural gas filling station and a natural gas filling method including the natural gas liquefaction apparatus according to the third embodiment or the natural gas liquefaction apparatus according to the fourth embodiment will be described with reference to FIG. 5.

The natural gas filling station according to the present embodiment includes a natural gas liquefaction apparatus 3 according to the third embodiment shown in FIG. 3 or a natural gas liquefaction apparatus 4 according to the fourth embodiment shown in FIG. 4. . In other words, the natural gas filling station according to the present embodiment is a natural gas liquefaction apparatus 3 according to the third embodiment or the natural gas liquefaction apparatus 4 according to the fourth embodiment and the natural gas liquefied Natural gas fueled vehicles that use gas as fuel can be fueled.

In this embodiment, a natural gas filling station and a charging method including the natural gas liquefaction apparatus 3 according to the third embodiment will be described as an example.

Natural gas filling station according to the present embodiment, the natural gas liquefaction apparatus (3); LNG filling unit (LF) for filling the LNG produced by the natural gas liquefaction device 3 with a natural gas fuel vehicle; And a CNG charging unit (CF) for charging CNG (Compressed Natural Gas) produced by the natural gas liquefaction apparatus 3 with a natural gas fuel vehicle.

The LNG filling unit LF of the present embodiment includes: an LNG heater LH for adjusting a temperature of LNG stored in the LNG storage tank 29 to a filling condition required by a natural gas fuel vehicle; And an LNG dispenser (LD) for filling the LNG fuel vehicle with temperature controlled LNG from the LNG heater (LH).

The CNG filling unit CF of the present embodiment includes: a CNG heater CH for adjusting a temperature of CNG stored in the CNG storage tank CT to a charging condition required by a natural gas fuel vehicle; Deodorant adding device (CO) for adding a deodorant to the CNG; A buffer tank (CB) for stabilizing the flow rate and pressure of the CNG charged to the natural gas fuel vehicle and removing liquid components such as droplets contained in the CNG; And a CNG dispenser (CD) for injecting CNG into the natural gas fuel vehicle.

The natural gas filling station according to the present embodiment may charge CNG in a natural gas fuel vehicle requiring CNG, and LNG in a natural gas fuel vehicle requiring LNG. The natural gas filling and the natural gas filling to the natural gas fueled vehicle requiring LNG can be performed individually or simultaneously.

The production of LNG and CNG in the natural gas liquefaction apparatus 3 may be carried out individually or simultaneously depending on the water level of the LNG storage tank 29 and the pressure of the CNG storage tank CT.

As described above, while specific embodiments have been shown and described, it should be understood that various modifications may be made and contemplated herein. In addition, the present invention is not limited by the specific embodiments provided herein. Although the present invention has been described with reference to the foregoing specification, descriptions and examples of preferred embodiments of the present specification are not to be interpreted in a limiting sense. In addition, it is to be understood that not all aspects of the invention are limited to the specific descriptions, configurations, or relative proportions described herein for the various conditions and variables. Various modifications and details of embodiments of the invention will be apparent to those skilled in the art. Accordingly, it is contemplated that the present invention may include any such modifications, variations and equivalents.

13: gas compressor suction drum
15, 17: gas compressor
20: high temperature part heat exchanger
21: refrigerant heat exchanger
23: low temperature heat exchanger
25: gas expansion valve
27: Hold-up Drum
20: LNG storage tank
49: gas purging valve
52: gas engine
45, 47: recovery gas compressor
60: refrigerant compressor suction drum
62, 64: refrigerant compressor
67: Surge Drum
71: refrigerant expansion valve
73: refrigerant purging valve
CL: CNG Supply Line
CT: CNG Storage Tank
LF: LNG Filling Unit
CF: CNG Filling Unit

Claims (14)

A gas compressor for compressing natural gas containing nitrogen;
A heat exchanger for cooling the compressed natural gas compressed by the gas compressor;
A gas expansion valve for expanding natural gas cooled in the heat exchanger; And
And a hold-up drum for gas-liquid separating the gas-liquid mixture produced while the natural gas passes through the gas expansion valve.
The heat exchange unit,
A refrigerant heat exchanger for heat-exchanging the refrigerant circulating a refrigerant cycle with the compressed natural gas to precool the compressed natural gas;
A low temperature heat exchanger for cooling the compressed natural gas by using a recovered gas in a gaseous state separated from the hold-up drum as a refrigerant; And
And a high temperature part heat exchanger for pre-cooling the compressed natural gas by further recovering cold heat of the recovered gas discharged after the heat exchange in the low temperature part heat exchanger.
The heat exchange unit, the high temperature portion heat exchanger, the refrigerant heat exchanger and the low temperature portion heat exchanger are sequentially arranged in series,
A recovery gas compressor for compressing the recovery gas whose temperature has risen while cooling the compressed natural gas in the low temperature part heat exchanger, and joining the nitrogen-containing natural gas stream supplied to the gas compressor;
A gas engine for producing electric power by using the recovered gas whose temperature rises as a fuel while cooling the compressed natural gas in the low temperature part heat exchanger; And
The purge gas as much as the purge amount necessary to ensure that the nitrogen content of the recovery gas meets the nitrogen-containing specification of the liquefied natural gas further comprises a gas purging valve controlled to be supplied to the gas engine. Gas liquefaction system. The method according to claim 1,
The natural gas liquefaction apparatus further comprises a; LNG storage tank for storing the liquid liquefied natural gas (LNG) in the liquid state separated from the hold-up drum and supply the stored LNG to the LNG demand destination. delete delete The method according to claim 1,
Refrigerant cycle for circulating a refrigerant for cooling the compressed natural gas to the refrigerant heat exchanger;
The refrigerant cycle,
A refrigerant compressor for compressing a refrigerant to be supplied to the refrigerant heat exchanger; And
And a refrigerant expansion valve for adiabatic expansion of the compressed refrigerant compressed by the refrigerant compressor.
The natural gas containing nitrogen which forms a closed cycle in which the liquid refrigerant thermally insulated by the refrigerant expansion valve is supplied to the refrigerant heat exchanger, and the refrigerant vaporized after heat exchange in the refrigerant heat exchanger is recycled to the refrigerant compressor. Liquefaction apparatus. The method according to claim 5,
The gas compressor, recovery gas compressor and refrigerant compressor,
A nitrogen-containing natural gas liquefaction apparatus, which is driven by using the electric power produced by the gas engine. The method according to claim 2,
A CNG storage tank storing compressed natural gas compressed by the gas compressor;
A CNG supply line branched from a nineteenth line through which the compressed natural gas compressed in the gas compressor is transferred to the heat exchange unit, and connected to the CNG storage tank; And
And a CNG supply valve configured to control opening and closing so that at least a portion of the compressed natural gas flows into the CNG supply line.
Natural gas liquefaction apparatus, capable of producing LNG and CNG either individually or simultaneously. The method according to claim 2,
A fifty-th line providing a path for supplying the boil-off gas discharged from the LNG storage tank to the gas engine; And
And a boil-off gas recovery line branched from the fifty-th line to provide a path for supplying the boil-off gas to a recovery gas compressor. Natural gas liquefaction apparatus according to any one of claims 1 to 2 and 5 to 8;
A control unit which controls the CNG to produce only CNG, only LNG, or simultaneously produce CNG and LNG;
An LNG charging unit for supplying the LNG produced by the natural gas liquefaction apparatus to a natural gas fuel vehicle; And
And a CNG filling unit for supplying the CNG produced by the natural gas liquefaction apparatus to a natural gas fuel vehicle. Compresses, cools and expands nitrogen-containing natural gas to produce liquefied natural gas,
The recovery gas generated in the expansion process of expanding the natural gas is recovered and compressed, and the compressed recovery gas joins the natural gas flow introduced into the compression process of compressing the natural gas.
Cooling process for cooling the natural gas,
The compressed natural gas compressed by the compression process is first cooled by heat exchange with a refrigerant circulating in a refrigerant cycle,
The first cooled compressed natural gas is heat-exchanged with the recovered gas before compression for second cooling,
The recovered gas whose temperature is raised by secondary cooling the compressed natural gas is further recovered by cooling by heat-exchanging with the compressed natural gas before the primary cooling to precool the compressed natural gas.
Liquefaction of nitrogen-containing natural gas, which purges as much as necessary to maintain the nitrogen content of the produced liquefied natural gas among the recovered gas used as the refrigerant, and generates electric power using the purged recovery gas as a fuel. Way. delete delete The method according to claim 10,
At least a portion of the compressed natural gas is branched and stored in the form of compressed natural gas, the natural gas liquefaction method, respectively or simultaneously supplying liquefied natural gas or compressed natural gas produced according to the requirements of the natural gas demand. The method according to claim 10,
The natural gas liquefaction method of supplying the boil-off gas generated by the natural liquefied natural gas to the fuel for producing electric power, or recycle to the compression process.

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