KR20120005158A - Method and apparatus for liquefying natural gas - Google Patents

Abstract

PURPOSE: Natural gas liquefying method and device are provided to minimize an impact due to fluctuation on the sea and stably and efficiently perform a liquefying process. CONSTITUTION: A natural gas liquefying device heat-exchanges natural gas with a heat exchange unit for liquefying. The heat exchange unit comprises a low-temperature heat exchanger(3), an extra-low-temperature heat exchanger(4), and a refrigerant circuit. The low-gas heat exchanger is formed as a worm core to cool natural gas extracted from a gas well. The extra-low-temperature heat exchanger is formed as a cold core to liquefy natural gas cooled by the low-temperature heat exchanger. The refrigerant circuit supplies compressed and condensed refrigerant to the heat exchangers.

Description

Natural Gas Liquefaction Method and Apparatus {METHOD AND APPARATUS FOR LIQUEFYING NATURAL GAS}

The present invention relates to a method and apparatus for liquefying natural gas, and to install a large heat exchanger used for natural gas liquefaction by separating a plurality of heat exchangers to be mounted and used on a floating structure used floating at sea. It relates to a natural gas liquefaction method and apparatus adapted to the. More specifically, when the BAHX (Brazed Aluminum Heat Exchanger) is used as a large cryogenic heat exchanger for natural gas liquefaction, it is installed in a cold box by separating it into a cold core and a worm core to prevent thermal stress expected in an abnormal situation. The present invention relates to a natural gas liquefaction method and apparatus that is suitable for use at sea by mitigating a shock caused by and separating a large heat exchanger into a low temperature heat exchanger and an ultra low temperature heat exchanger when using a spiral wound heat exchanger (SWHE).

Natural gas is transported in a gaseous state through onshore or offshore gas piping, or to a distant consumer while stored in an LNG carrier in the form of liquefied liquefied natural gas (LNG). Liquefied natural gas is obtained by cooling natural gas to cryogenic temperature, and its volume is reduced to about 1/600 than that of natural gas in gas state, so it is very suitable for long distance transportation by sea.

The liquefaction method of the natural gas currently used is made by passing natural gas inside a heat exchanger and cooling it. U.S. Patent Nos. 3,735,600, 3,433,026 and the like disclose a liquefaction method of supplying natural gas to a heat exchanger to liquefy.

In the present specification, natural gas means a mixture containing methane but other hydrocarbon components or nitrogen as a main component, and includes any form (gas phase, liquid phase or mixed phase of gas phase and liquid phase). It is a concept.

In order to store and transport the natural gas in the liquid state, the natural gas must be cooled to about -151 ° C to -163 ° C, where LNG has a pressure of about atmospheric pressure. In the prior art, in a land liquefaction facility, methods such as a cascade process, a mixed refrigerant process, a refrigerant gas expander process, and the like are used for cooling natural gas.

Recently, floating structures such as LNG FPSO (Floating, Production, Storage and Offloading) have been proposed, which can produce and store natural gas directly from natural gas sources extracted from gas wells, not on land. There is a need for a liquefaction device for natural gas.

The liquefaction method of natural gas on land cannot be applied directly to floating structures at sea, and needs to be improved to suit the marine environment. In the case of LNG FPSO, small and medium sized liquefaction facilities are highly feasible, and as a suitable liquefaction process, a gas refrigerant expansion process or a mixed refrigerant process attracts attention.

However, such a liquefaction facility uses heat exchangers such as BAHX (Brazed Aluminum Heat Exchanger) or SWHE (Spiral Wound Heat Exchanger), and BAHX has the advantage that the heat transfer area per unit volume is large and relatively inexpensive. Due to the rapid change, there is a risk of damage due to thermal shock, SWHE has a high rigidity, expensive and high (for example, about 50m) may cause a problem that the cooling efficiency is lowered when the flow occurs at sea.

The present invention for solving these problems, instead of installing one huge heat exchanger in the floating structure to liquefy the natural gas, a plurality of relatively small heat exchanger is installed and transmits cold heat to the plurality of heat exchangers In order to provide a natural gas liquefaction method and apparatus for minimizing the effects of fluctuations in the sea and performing the liquefaction process stably and efficiently by configuring the refrigerant circuit circulating the refrigerant in one circuit.

According to the present invention for achieving the above object, a natural gas liquefaction apparatus for liquefying natural gas by heat exchange with a refrigerant in the heat exchange means, the heat exchange means, and a low temperature heat exchanger for cooling the natural gas extracted from the gas well to low temperature And a cryogenic heat exchanger for further cooling and liquefying the natural gas cooled by the low temperature heat exchanger, wherein the refrigerant heated by the natural gas in the cryogenic heat exchanger is supplied to the low temperature heat exchanger before being supplied to the cryogenic heat exchanger. A natural gas liquefaction apparatus is provided, wherein the refrigerant is pre-cooled, and the refrigerant supplied from the cryogenic heat exchanger to the low temperature heat exchanger protects the low temperature heat exchanger from thermal shock by a thermal shock prevention means.

When the low temperature heat exchanger and the cryogenic heat exchanger are plate heat exchangers of PFHE type, they may be installed in one cold box.

The thermal shock prevention means is preferably a gas-liquid separator for separating the refrigerant supplied from the cryogenic heat exchanger to the low temperature heat exchanger into a gaseous refrigerant and a liquid refrigerant.

Preferably, the refrigerant circulates along a refrigerant circuit consisting of a single closed circuit which passes through the low temperature heat exchanger and the cryogenic heat exchanger sequentially, at least partially liquefies natural gas, and then returns via the low temperature heat exchanger.

The natural gas liquefaction apparatus further includes a cold separator for separating natural gas cooled at a low temperature in the low temperature heat exchanger into a natural gas in a gas state and a natural gas in a liquid state to supply a gaseous natural gas to the cryogenic heat exchanger. It is desirable to.

The natural gas liquefaction apparatus preferably includes means for separating the natural gas in the liquid state separated from the cold separator by component.

The plurality of low temperature heat exchangers are installed, and the gaseous state refrigerant and the liquid state refrigerant separated through the gas-liquid separator are each supplied to the plurality of low temperature heat exchangers through separate supply lines.

The refrigerant circuit preferably has at least one compression unit including a refrigerant compressor for compressing a refrigerant for cooling the natural gas through heat exchange with natural gas and a refrigerant condenser for condensing the compressed refrigerant.

The refrigerant supplied to the low temperature heat exchanger from the compression unit is preferably supplied separately from the gaseous state and the liquid state through the discharge separator.

The natural gas liquefaction apparatus further includes a refrigerant compressor for compressing the refrigerant, and a refrigerant condenser for condensing the compressed refrigerant, and the refrigerant compressor is preferably a multistage compressor.

The coolant supplied to the low temperature heat exchanger is a first refrigerant supply line for supplying the coolant in a liquid state separated by an intermediate separator among the partially condensed refrigerants cooled by an intermediate cooler between the plurality of refrigerant compressors to the low temperature heat exchanger. And second compressing the gaseous refrigerant separated by the intermediate separator by the refrigerant compressor again, partially condensing by the refrigerant condenser, and then supplying the liquid refrigerant separated in the discharge separator to the low temperature heat exchanger. Preferably, a refrigerant supply line and a third refrigerant supply line supplying a gaseous refrigerant separated from the discharge separator to the low temperature heat exchanger are supplied.

The refrigerant supplied to the low temperature heat exchanger through the third refrigerant supply line is cooled and partially condensed by the refrigerant returning from the cryogenic heat exchanger, and separated into a gaseous refrigerant and a liquid refrigerant by the first refrigerant separator. It is preferable to cool the natural gas in the cryogenic heat exchanger after each expansion.

The refrigerant supplied to the low temperature heat exchanger through the first and second refrigerant supply lines may be expanded and then supplied to the low temperature heat exchanger to cool the natural gas.

The expanded refrigerant is preferably mixed with the refrigerant supplied from the cryogenic heat exchanger to the low temperature heat exchanger and the thermal shock prevention means and returned to the low temperature heat exchanger.

The low temperature heat exchanger and the cryogenic heat exchanger may be a heat exchanger of a plate fin heat exchanger (PFHE) type or a spiral wound heat exchanger (SWHE) type.

According to another aspect of the present invention, a natural gas liquefaction apparatus for liquefying natural gas by heat exchange with a refrigerant on a floating structure to be used floating in the sea, the natural gas is disposed on the upper deck of the floating structure extracted from the gas well A low temperature heat exchanger for cooling the gas to low temperature; An ultra low temperature heat exchanger disposed on an upper deck of the floating structure to further cool and liquefy natural gas cooled by the low temperature heat exchanger; Thermal shock prevention means disposed between the cryogenic heat exchanger and the low temperature heat exchanger to protect the low temperature heat exchanger from thermal shock by preventing a cryogenic refrigerant discharged from the cryogenic heat exchanger from being directly supplied to the low temperature heat exchanger; There is provided a natural gas liquefaction apparatus comprising a.

According to still another aspect of the present invention, there is provided a floating structure which is used while floating in the sea, comprising: a low temperature heat exchanger arranged on an upper deck of the floating structure to cool a natural gas extracted from a gas well to a low temperature; An ultra low temperature heat exchanger disposed on an upper deck of the floating structure to further cool and liquefy natural gas cooled by the low temperature heat exchanger; Thermal shock prevention means disposed between the cryogenic heat exchanger and the low temperature heat exchanger to protect the low temperature heat exchanger from thermal shock by preventing a cryogenic refrigerant discharged from the cryogenic heat exchanger from being directly supplied to the low temperature heat exchanger; There is provided a floating structure comprising a natural gas liquefaction apparatus comprising a.

The floating structure is preferably LNG FPSO.

According to another aspect of the present invention, a natural gas liquefaction method for liquefying natural gas by heat exchange with a refrigerant in a heat exchange means, the natural gas extracted from the gas well to cool in a low temperature heat exchanger, the low temperature heat exchanger The natural gas is further cooled in a cryogenic heat exchanger to at least partially liquefy, and the refrigerant heated by natural gas in the cryogenic heat exchanger is further heated in a thermal shock prevention means and supplied to the low temperature heat exchanger to protect the low temperature heat exchanger from thermal shock. It is provided a natural gas liquefaction method characterized in that.

According to the present invention as described above, instead of installing one huge heat exchanger in the floating structure to liquefy natural gas, a plurality of relatively small heat exchangers are installed and refrigerant for transferring cold heat to the plurality of heat exchangers. A natural gas liquefaction method and apparatus including a refrigerant circuit circulating in a single circuit may be provided.

Accordingly, according to the present invention, when BAHX is used as a cryogenic heat exchanger in a floating structure to liquefy natural gas, the temperature difference across one core in the conventional case is about 25 ° C. by separately installing the cold core and the warm core in the cold box. It is possible to reduce roughly half of what reached 200 ° C, thereby mitigating the impact of thermal stress anticipated in an abnormal situation. When using SWHX, one large heat exchanger is separated into a low temperature heat exchanger and an ultra low temperature heat exchanger, and thus, This can minimize the risk of deterioration of the heat exchanger.

In addition, according to the present invention, by installing a separator between the plurality of heat exchangers, the cool refrigerant discharged from the lower temperature heat exchanger among the plurality of heat exchangers can be introduced into the relatively high temperature heat exchanger to mitigate thermal shock that may occur. do.

1 is a conceptual diagram of a floating structure equipped with a natural gas liquefaction apparatus according to the present invention,
2 is a conceptual diagram for explaining a natural gas liquefaction apparatus according to the first embodiment of the present invention, and
3 is a conceptual diagram for explaining a natural gas liquefaction apparatus according to a second embodiment of the present invention.

Hereinafter, a natural gas liquefaction method and apparatus according to a preferred embodiment of the present invention will be described in detail with reference to the drawings.

The natural gas liquefaction apparatus according to the present invention may be installed and used in LNG plants installed on land or offshore, ships such as LNG transport ships, and offshore structures such as LNG FPSO (Floating, Production, Storage and Offloading). The LNG FPSO is a floating offshore structure used to directly liquefy the produced natural gas at sea and store it in an LNG storage tank, and, if necessary, to transfer LNG stored in the LNG storage tank to an LNG carrier.

As shown in FIG. 1, the natural gas liquefaction apparatus 1 according to the present invention for liquefying natural gas extracted from a gas well, installed in the floating structure 2, is extracted from a gas well and then subjected to water through a pretreatment process. Low temperature heat exchanger (3) as a worm core for cooling natural gas from which impurities such as carbon dioxide and acid gas have been removed, and natural gas cooled to low temperature in the low temperature heat exchanger (3). A cryogenic heat exchanger (4) as a cold core and a refrigerant circuit for liquefying natural gas by supplying compressed and condensed refrigerant to the low temperature heat exchanger (3) and the cryogenic heat exchanger (4) and exchanging heat with natural gas (5) is included.

The low temperature heat exchanger 3 as a warm core and the cryogenic heat exchanger 4 as a cold core are preferably installed in one cold box because they can reduce heat loss. In the present specification, the expression "warm core" should be interpreted to mean relatively high temperature compared to "cold core".

According to the present invention, a mixed refrigerant in which methane, ethanol, propane, butane, nitrogen and the like are mixed at a predetermined ratio may be used as the refrigerant circulated in the refrigerant circuit 5. The mixing ratio of each component may be determined according to the process conditions.

As described above, according to the natural gas liquefaction apparatus 1 of the present invention, a plurality of heat exchangers, that is, a low temperature heat exchanger 3 and an ultra low temperature heat exchanger 4 are arranged in series, so that the natural gas liquefaction apparatus of the conventional land Compared to heat exchangers such as spiral heat exchangers (SWHE), which have been widely used, the size and especially the height of heat exchangers can be reduced. Accordingly, it is possible to minimize the influence of the movement of the floating structure and to improve the liquefaction efficiency in the marine environment that inevitably fluctuates, and to minimize the use of the support member required when installing the heat exchanger.

(First embodiment)

Next, with reference to FIG. 2, the natural gas liquefaction method and apparatus which concerns on 1st Embodiment of this invention are demonstrated in detail.

As described above with reference to FIG. 1, the natural gas liquefaction apparatus of the present invention includes a low temperature heat exchanger 3 for preliminarily pre-cooling natural gas, and a natural gas cooled at a low temperature in the low temperature heat exchanger 3. A cryogenic heat exchanger (4) for further cooling and liquefying gas, and a refrigerant circuit (5) for liquefying natural gas by supplying a refrigerant to the low temperature heat exchanger (3) and the cryogenic heat exchanger (4) and exchanging heat with natural gas. It includes.

The liquefaction process of natural gas can be carried out as follows.

The natural gas extracted from the gas well and subjected to a pretreatment process such as removing impurities is supplied to the low temperature heat exchanger (3) through the natural gas supply line (L11), and through the heat exchange with the refrigerant in the low temperature heat exchanger (3) 1 It is cooled differentially. The natural gas cooled in the low temperature heat exchanger 3 may be cooled to about -50 to 60 ° C, and may be partially condensed.

The primary cooled natural gas is supplied to the cryogenic heat exchanger 4 through the natural gas supply line L11, and is secondarily cooled through heat exchange with the refrigerant in the cryogenic heat exchanger 4. Most of the natural gas cooled in the cryogenic heat exchanger (4) can be condensed, and liquid natural gas, that is, liquefied natural gas, through a pressure reducing valve (12) and an LNG receiver (also known as an end flash drum) (13). The LNG may be transferred to and stored in an LNG storage tank. Natural gas in the gas phase can be used as fuel gas for various generators, turbines, etc., which are compressed and installed in the floating structure.

According to a modified embodiment of the present invention, the natural gas transferred from the low temperature heat exchanger (3) to the cryogenic heat exchanger (4) is a natural gas in the gas phase and a liquid natural gas in the cold separator (11) as a gas-liquid separator. After being classified as gas, only natural gas may be supplied to the cryogenic heat exchanger 4 through the first gaseous natural gas supply line L12.

In natural gas, hydrocarbon components such as methane, ethane, propane and butane are mixed, and the liquefaction point of heavy hydrocarbon components such as butane and propane, which have high carbon number, is relatively high, and the liquefaction point of methane, ethane and the like which have few carbon atoms is relatively low. Therefore, gaseous natural gas classified by the cold separator 11 contains a lot of methane, and liquid natural gas contains a lot of LPG components such as ethane, propane and butane.

The liquid natural gas classified from the cold separator 11 is continuously supplied to the demethanizer 15 through the liquid natural gas supply line L13, and then back into the gas phase and the liquid phase from the demetazer 15. The gaseous component may be classified and supplied to the cryogenic heat exchanger 4 through the second gaseous natural gas supply line L14, and the liquid component may be sold in the state of Natural Gas Liquid (NGL). NGL may be again classified in a debutanizer 16, and may be sold separately by separately separating ethane, propane, butane and the like through a post process.

The circulation process of the refrigerant may be performed as follows.

The refrigerant compressed in the refrigerant compressor 21 and at least partially condensed in the refrigerant condenser 26 may be supplied to the low temperature heat exchanger 3 through a refrigerant supply line to exchange heat with natural gas. In the low temperature heat exchanger (3), the refrigerant takes heat from the natural gas and lowers the temperature of the natural gas. As shown in FIG. 2, the coolant supplied to the low temperature heat exchanger 3 may be classified into a plurality of lines and supplied.

According to the present invention, one or more compression units in which the refrigerant compressor 21, the refrigerant condenser 26, etc. are installed may be provided. 2 compression part 20b) is illustrated. When a plurality of compression units are provided, it is advantageous in terms of load adjustment when driving the liquefaction apparatus, and even if an abnormality occurs in one compression unit, the liquefaction apparatus can be normally operated by the remaining compression units.

Since the structure of the 2nd compression part 20b is the same as that of the 1st compression part 20a, only the 1st compression part 20a is demonstrated here. As the refrigerant compressor 21 installed in the first compression unit 20a, a multi-stage compressor driven by a driving means 22 such as a gas turbine or a steam turbine may be used. In the present embodiment, it is shown that a two stage compressor is used as the refrigerant compressor, but the present invention is not limited thereto.

When the refrigerant compressor 21 is driven, the refrigerant contained in the suction drum 23 provided upstream of the refrigerant compressor is supplied to the refrigerant compressor 21 and compressed. Since the refrigerant compressor is composed of multiple stages, the refrigerant compressed to medium pressure in the first compression stage is cooled in the intermediate cooler 24 and then compressed to high pressure in the second compression stage.

In the intermediate cooler 24 the refrigerant may be partially condensed, with the components condensed mainly being heavy hydrocarbon components. The refrigerant partially condensed in the intermediate cooler 24 is separated into the gaseous phase and the liquid phase in the intermediate separator 25 so that the gas component is supplied to the secondary compression step and the liquid component is supplied to the refrigerant compressor through the first refrigerant supply line L21. At 21, the refrigerant supplied to the refrigerant condenser 26 may be joined.

On the other hand, the refrigerant of the gas component compressed at a high pressure in the second compression step is joined with the refrigerant supplied through the first refrigerant supply line (L21) and then the temperature is lowered in the refrigerant condenser 26 (also referred to as After Cooler) to partially The partial hydrocarbon condensation may be partially condensed, and the partially condensed refrigerant may be separated into the gaseous phase and the liquid phase again in the discharge separator 27 so that the liquid component is a low temperature heat exchanger through the second refrigerant supply line L22. (3) and the gaseous component may be supplied to the low temperature heat exchanger (3) via the third refrigerant supply line (L23).

Here, the respective refrigerant fractions separated in the same step in each compression zone are joined together before being supplied to the low temperature heat exchanger 3.

The refrigerant fraction supplied to the low temperature heat exchanger 3 through the second refrigerant supply line L22 is expanded through the expansion valve 29 after passing through the low temperature heat exchanger 3. The refrigerant, which is expanded while passing through the expansion valve 29 and becomes low temperature, is mixed with the refrigerant returning from the cryogenic heat exchanger 4 toward the refrigerant compressor 21 and supplied to the low temperature heat exchanger 3 to cool the natural gas and The return line returns to the refrigerant compressor 21, more specifically to the suction drum 23 provided upstream of the refrigerant compressor.

Meanwhile, the refrigerant flow rate supplied to the low temperature heat exchanger 3 through the third refrigerant supply line L23 is separated into the gaseous phase and the liquid phase in the first refrigerant separator 31 so that the liquid component may separate the fourth refrigerant supply line L24. It is supplied to the cryogenic heat exchanger (4) through the gas component is supplied to the cryogenic heat exchanger (4) through the fifth refrigerant supply line (L25).

The liquid refrigerant supplied to the cryogenic heat exchanger (4) through the fourth refrigerant supply line (L24) exits from the middle of the cryogenic heat exchanger (4) to the outside and expands through the expansion valve (32) to lower the temperature. Afterwards it is supplied to the inside of the cryogenic heat exchanger 4 and sprayed again.

In addition, the refrigerant in the gas phase supplied to the cryogenic heat exchanger (4) through the fifth refrigerant supply line (L25) exits from the top of the cryogenic heat exchanger (4) to the outside and expands through the expansion valve (33) to lower the temperature. After it is supplied to the inside of the top of the cryogenic heat exchanger (4) is sprayed.

In this cryogenic heat exchanger (4), the refrigerant heated by taking heat from the natural gas is partially vaporized, and the gas and liquid phase coexist. The refrigerant in the liquid state is discharged from the lower end of the cryogenic heat exchanger (4) and supplied to the low temperature heat exchanger (3) through the first refrigerant return line (L31), and the gaseous refrigerant from the lower portion of the cryogenic heat exchanger (4). It is discharged and supplied to the low temperature heat exchanger 3 through the second refrigerant return line L32.

As described above, the refrigerant returning from the cryogenic heat exchanger 4 toward the refrigerant compressor 21 is passed through the low temperature heat exchanger 3, mixed with the expanded refrigerant, and then supplied to the low temperature heat exchanger 3.

Here, in particular, when using a plurality of low temperature heat exchanger (3) can be configured such that the refrigerant is returned to the low temperature heat exchanger (3) through the second refrigerant separator (35). The return refrigerant (i.e., the refrigerant moving from the cryogenic heat exchanger toward the refrigerant compressor) is separated into the gas phase and the liquid phase in the second refrigerant separator 35 so that the liquid component is transferred to the low temperature heat exchanger 3 through the third refrigerant return line L33. Is supplied to the low temperature heat exchanger (3) via a fourth refrigerant return line (L34).

In addition, since the refrigerant supplied from the cryogenic heat exchanger 4 to the low temperature heat exchanger 3 is transferred through the second refrigerant separator 35 as a thermal shock prevention means, the cryogenic heat exchanger may be formed by inertia even when the liquefier is emergency stopped. The cold refrigerant of 4) can be prevented from flowing into the low temperature heat exchanger 3 as it is. Accordingly, the second refrigerant separator 35 may function as a safety device against thermal shock.

When the refrigerant in the gas-liquid mixed state is separately supplied to a plurality of low temperature heat exchangers, a relatively large amount of gaseous refrigerant is supplied to a specific low temperature heat exchanger, and a relatively large amount of liquid refrigerant is supplied to another low temperature heat exchanger. There is a possibility that the operating conditions differ for each heat exchanger.

In the case where there are a plurality of low temperature heat exchangers 3, a gas component and a liquid component are configured to be supplied separately, so that the same amount of gas components and liquid components can be supplied to each of the low temperature heat exchangers 3, which is preferable.

The returning refrigerant may be mixed with the gas component and the liquid component just before being supplied to the low temperature heat exchanger 3 to pass through the low temperature heat exchanger 3. The return refrigerant heated while cooling the natural gas supplied to the cryogenic heat exchanger 4 and the supply refrigerant (i.e., the refrigerant moving from the refrigerant compressor to the cryogenic heat exchanger) while passing through the low temperature heat exchanger 3 is the fifth refrigerant return line. It returns to the suction drum 23 through L35.

On the other hand, according to a modification of the first embodiment of the present invention, the refrigerant partially condensed in the intermediate cooler 24 is separated into the gas phase and the liquid phase in the intermediate separator 25 so that the gas component is supplied to the secondary compression step and the liquid The component may be modified to be supplied to the low temperature heat exchanger 3 via a separate refrigerant supply line (not shown).

At this time, the refrigerant supplied to the low temperature heat exchanger 3 from the intermediate separator 25 through a separate refrigerant supply line may be expanded through the expansion valve after passing through the low temperature heat exchanger 3. The refrigerant, which is expanded while passing through the expansion valve and becomes low temperature, is mixed with the refrigerant returning from the cryogenic heat exchanger (4) toward the refrigerant compressor (21), and supplied to the low temperature heat exchanger (3) to cool the natural gas and return the refrigerant return line. Through the refrigerant compressor 21, more specifically, the suction drum 23 provided upstream of the refrigerant compressor can be returned.

Therefore, in the modification of 1st Embodiment, compared with the liquefaction apparatus which concerns on 1st Embodiment, the separate refrigerant | coolant supply line for supplying the liquid component isolate | separated from the intermediate separator 25 to the low temperature heat exchanger 3 (illustration O) and an expansion valve (not shown) provided in this separate refrigerant supply line.

According to the first embodiment of the present invention and a modification thereof, a plate fin heat exchanger (PFHE) type heat exchanger may be used as a low temperature heat exchanger for precooling natural gas, and an ultra low temperature heat exchanger for liquefying natural gas at least partially. A SWHE (Spiral Wound Heat Exchanger) type heat exchanger can be used. However, it can be modified to use a PFHE type heat exchanger as the cryogenic heat exchanger.

In addition, according to the first embodiment of the present invention and a modification thereof, a process of extracting NGL having a heavy hydrocarbon content from the natural gas cooled by the low temperature heat exchanger 3 and partially condensed is performed together. May be separated in a separate process, or the NGL extraction process may be omitted if it is not necessary to separate the LNG component and LPG component.

According to a modification of the first embodiment of the present invention, the refrigerant compressed in the compressor is separated into three (that is, the discharge separator after passing through the liquid refrigerant fractionation, the compressor and the condenser separated in the intermediate separator 25 during compression) The refrigerant separated in the liquid phase separated in step 27) and the refrigerant separated in the gas phase separated from the discharge separator 27) are supplied to the low temperature heat exchanger 3, respectively. However, according to the first embodiment, the liquid refrigerant fraction separated in the intermediate separator 25 during compression is not directly supplied to the low temperature heat exchanger 3 but mixed with the refrigerant passing through the compressor, and then the discharge separator 27. At this time, the refrigerant is separated into a gaseous phase and a liquid phase refrigerant, and is supplied to the low temperature heat exchanger 3 through two supply lines.

According to the natural gas liquefaction method and apparatus of the first embodiment and the modifications thereof, a single mixed refrigerant cycle (SMR) constituting a single closed loop using a mixed refrigerant consisting of nitrogen and a hydrocarbon is resolved. It can be configured according to the characteristics of the environment, and by combining the natural gas liquid (NGL) treatment process, it is possible to implement a suitable liquefaction process for floating structures such as LNG FPSO having a limited space.

(2nd embodiment)

Subsequently, a natural gas liquefaction method and apparatus according to a second embodiment of the present invention will be described in more detail with reference to FIG. 3. In the description of the natural gas liquefaction apparatus according to the second embodiment, the same or similar components as those of the natural gas liquefaction apparatus according to the first embodiment are assigned the same member numbers.

Similarly to the first embodiment described above, the natural gas liquefaction apparatus according to the second embodiment also includes a worm core, that is, a low temperature heat exchanger 3 and a low temperature heat exchanger for preliminarily pre-cooling the natural gas. Cold core (ie, cryogenic heat exchanger 4) for cooling and liquefying natural gas cooled to low temperature in (3), and supplying refrigerant to the low temperature heat exchanger (3) and the cryogenic heat exchanger (4) And a refrigerant circuit 5 for liquefying natural gas by heat exchange with natural gas.

In FIG. 2 showing the first embodiment described above, a plate fin heat exchanger (PFHE) type heat exchanger is used as a low temperature heat exchanger for precooling natural gas, and a spiral heat exchanger (SWHE) is used as an ultra low temperature heat exchanger for at least partially liquefying natural gas. The heat exchanger of type) is illustrated as being used. However, in FIG. 3 showing the second embodiment, both the low temperature heat exchanger and the cryogenic heat exchanger are illustrated as using a plate fin heat exchanger (PFHE) type heat exchanger.

In addition, the low temperature heat exchanger 3 and the cryogenic heat exchanger 4 and peripheral devices and pipes may be installed in a single cold box 9, and thus it is preferable to reduce heat loss.

The liquefaction process of natural gas can be carried out as follows.

The natural gas extracted from the gas well and subjected to a pretreatment process such as removing impurities is supplied to the low temperature heat exchanger (3) through the natural gas supply line (L11), and through the heat exchange with the refrigerant in the low temperature heat exchanger (3) 1 It is cooled differentially. The natural gas cooled in the low temperature heat exchanger 3 may be cooled to about -50 to 60 ° C, and may be partially condensed.

The primary cooled natural gas is supplied to the cryogenic heat exchanger 4 through the natural gas supply line L11, and is secondarily cooled through heat exchange with the refrigerant in the cryogenic heat exchanger 4. Most of the natural gas cooled in the cryogenic heat exchanger (4) can be condensed, and liquid natural gas, that is, liquefied natural gas, through a pressure reducing valve (12) and an LNG receiver (also known as an end flash drum) (13). The LNG may be transferred to and stored in an LNG storage tank. Natural gas in the gas phase can be used as fuel gas for various generators, turbines, etc., which are compressed and installed in the floating structure.

According to a modified embodiment of the present invention, the natural gas transferred from the low temperature heat exchanger (3) to the cryogenic heat exchanger (4) is a natural gas in the gas phase and a liquid natural gas in the cold separator (11) as a gas-liquid separator. After being classified as gas, only natural gas may be supplied to the cryogenic heat exchanger 4 through the first gaseous natural gas supply line L12.

In natural gas, hydrocarbon components such as methane, ethane, propane and butane are mixed, and the liquefaction point of heavy hydrocarbon components such as butane and propane, which have high carbon number, is relatively high, and the liquefaction point of methane, ethane and the like which have few carbon atoms is relatively low. Therefore, gaseous natural gas classified by the cold separator 11 contains a lot of methane, and liquid natural gas contains a lot of LPG components such as ethane, propane and butane.

The liquid natural gas classified from the cold separator 11 is continuously supplied to the demethanizer 15 through the liquid natural gas supply line L13, and then back into the gas phase and the liquid phase from the demetazer 15. The gaseous component may be classified and supplied to the cryogenic heat exchanger 4 through the second gaseous natural gas supply line L14, and the liquid component may be sold in the state of Natural Gas Liquid (NGL). NGL may be again classified as a debutanizer (not shown), and may be sold separately by separately separating ethane, propane, butane and the like through a post process.

The circulation process of the refrigerant may be performed as follows.

The refrigerant compressed in the refrigerant compressors 21a and 21b and at least partially condensed in the refrigerant condenser 26 may be supplied to the low temperature heat exchanger 3 through the refrigerant supply line to exchange heat with natural gas. In the low temperature heat exchanger (3), the refrigerant takes heat from the natural gas and lowers the temperature of the natural gas. As shown in FIG. 2, the coolant supplied to the low temperature heat exchanger 3 may be classified into a plurality of lines and supplied.

According to the present invention, one or more compression units in which the refrigerant compressors 21a and 21b and the refrigerant condenser 26 and the like are installed may be provided, and in this embodiment, one compression unit 20 is provided. When a plurality of compression units are provided, it is advantageous in terms of load adjustment when driving the liquefaction apparatus, and even if an abnormality occurs in one compression unit, the liquefaction apparatus can be normally operated by the remaining compression units.

As the refrigerant compressor installed in the compression section 20, a multi-stage compressor driven by driving means (not shown) such as a gas turbine or a steam turbine may be used. In the present embodiment, a two-stage compressor consisting of the first refrigerant compressor 21a and the second refrigerant compressor 21b is shown to be used, but the present invention is not limited thereto.

When the refrigerant compressors 21a and 21b are driven, the refrigerant contained in the suction drum 23 provided upstream of the refrigerant compressor is first supplied to and compressed by the first refrigerant compressor 21a. Since the refrigerant compressor is configured in multiple stages, the refrigerant compressed to medium pressure in the first compression stage is cooled in the intermediate cooler 24 and then compressed to high pressure in the second compression stage, that is, the second refrigerant compressor 21b.

In the intermediate cooler 24 the refrigerant may be partially condensed, with the components condensed mainly being heavy hydrocarbon components. The refrigerant partially condensed in the intermediate cooler 24 is separated into the gaseous phase and the liquid phase in the intermediate separator 25 so that the gas component is supplied to the secondary compression step and the liquid component is supplied to the second through the first refrigerant supply line L21. The refrigerant supplied from the compressor 21b to the discharge separator 27 may be joined.

On the other hand, the refrigerant of the gas component compressed to high pressure in the second refrigerant compressor 21b is lowered in the temperature of the refrigerant condenser 26 (also referred to as After Cooler) to partially condensate some of the hydrocarbon components, partially condensed After the refrigerant is joined with the refrigerant supplied through the first refrigerant supply line L21, the refrigerant is separated into a gaseous phase and a liquid phase again in the discharge separator 27 so that the liquid component is passed through the second refrigerant supply line L22. The low temperature heat exchanger 3 may be supplied, and the gas component may be supplied to the low temperature heat exchanger 3 through the third refrigerant supply line L23.

The refrigerant fraction supplied to the low temperature heat exchanger 3 through the second refrigerant supply line L22 is expanded through the expansion valve 29 after passing through the low temperature heat exchanger 3. The refrigerant, which is expanded while passing through the expansion valve 29 and becomes low temperature, is mixed with the refrigerant returning from the cryogenic heat exchanger 4 toward the refrigerant compressor 21 and the second refrigerant separator 35, and then the low temperature heat exchanger 3 again. It may be supplied to cool the natural gas and may return to the refrigerant compressor 21, more specifically, the suction drum 23 installed upstream of the refrigerant compressor through the refrigerant return line.

Meanwhile, the refrigerant flow rate supplied to the low temperature heat exchanger 3 through the third refrigerant supply line L23 is separated into the gaseous phase and the liquid phase in the first refrigerant separator 31 so that the liquid component may separate the fourth refrigerant supply line L24. It is supplied to the cryogenic heat exchanger (4) through the gas component is supplied to the cryogenic heat exchanger (4) through the fifth refrigerant supply line (L25).

The liquid refrigerant supplied to the cryogenic heat exchanger (4) through the fourth refrigerant supply line (L24) exits from the middle of the cryogenic heat exchanger (4) to the outside and expands through the expansion valve (32) to lower the temperature. Later, the third refrigerant separator 42 may be supplied into the middle of the cryogenic heat exchanger 4 again. In the third refrigerant separator 42, the refrigerant is separated into a gaseous phase and a liquid phase, and then the liquid component and the gas component are supplied into the cryogenic heat exchanger 4 through separate lines, wherein the refrigerant of the liquid component and the refrigerant of the gas component are It may be joined just before entering the cryogenic heat exchanger 4.

In addition, the refrigerant in the gas phase supplied to the cryogenic heat exchanger 4 through the fifth refrigerant supply line L25 is expanded through the expansion valve 33 after passing through the cryogenic heat exchanger 4 to lower the temperature. Four refrigerant separators 43 are again supplied into the cryogenic heat exchanger 4. In the fourth refrigerant separator 43, the refrigerant is separated into a gaseous phase and a liquid phase, and then the liquid component and the gas component are supplied into the cryogenic heat exchanger 4 through separate lines, wherein the refrigerant of the liquid component and the refrigerant of the gas component are It may be joined just before entering the cryogenic heat exchanger 4.

In this way, when the refrigerant passing through the expansion valves 32 and 33 is divided and supplied into the gas component and the liquid component by the separator, the ratio of the refrigerant of the gas component and the refrigerant of the liquid component to be supplied is advantageous. In addition, in the case where a plurality of cryogenic heat exchangers 4 are provided, the specific cryogenic heat exchanger when the refrigerant supplied from each of the plurality of expansion valves 32 and the plurality of expansion valves 33 is supplied to each cryogenic heat exchanger 4 as it is. A relatively large amount of the refrigerant of the liquid component is supplied to the air, and a relatively large amount of the refrigerant of the gas component is supplied to the other cryogenic heat exchanger, thereby preventing the operating conditions of the cryogenic heat exchanger from being different.

The refrigerant supplied to the middle of the cryogenic heat exchanger 4 again through the expansion valve 32 and the third refrigerant separator 42 may be supplied to the refrigerant and natural gas supplied to the expansion valve 33 in the cryogenic heat exchanger 4. After cooling, it is heated and discharged, and after discharged, it returns to the refrigerant compressors 21a and 21b via the first refrigerant return line L31. Meanwhile, the refrigerant supplied into the cryogenic heat exchanger 4 again through the expansion valve 33 and the fourth refrigerant separator 43 is cooled after the natural gas is cooled in the cryogenic heat exchanger 4, and is then heated and discharged. After the discharge, the gas is returned to the refrigerant compressors 21a and 21b via the second refrigerant return line L32.

As described above, the refrigerant returning from the cryogenic heat exchanger 4 toward the refrigerant compressors 21a and 21b is mixed with the expanded refrigerant and the second refrigerant separator 35 after passing through the low temperature heat exchanger 3 to exchange the low temperature heat exchanger. It is supplied to the machine (3).

Here, in particular, in the case of using the plurality of low temperature heat exchangers 3, it is advantageous to configure the refrigerant to be returned to the low temperature heat exchanger 3 through the second refrigerant separator 35. The return refrigerant (i.e., the refrigerant moving from the cryogenic heat exchanger toward the refrigerant compressor) is separated into the gas phase and the liquid phase in the second refrigerant separator 35 so that the liquid component is transferred to the low temperature heat exchanger 3 through the third refrigerant return line L33. Is supplied to the low temperature heat exchanger (3) via a fourth refrigerant return line (L34).

In addition, since the coolant supplied from the cryogenic heat exchanger 4 to the low temperature heat exchanger 3 is transferred through the second refrigerant separator 35, the coolant of the cryogenic heat exchanger 4 is inerted by inertia even when the liquefaction apparatus is emergency stopped. The refrigerant may be prevented from flowing into the low temperature heat exchanger 3 as it is. Accordingly, the second refrigerant separator 35 may function as a safety device against thermal shock.

When the refrigerant in the gas-liquid mixed state is separately supplied to a plurality of low temperature heat exchangers, a relatively large amount of gaseous refrigerant is supplied to a specific low temperature heat exchanger, and a relatively large amount of liquid refrigerant is supplied to another low temperature heat exchanger. There is a possibility that the operating conditions differ for each heat exchanger.

In the case where there are a plurality of low temperature heat exchangers 3, a gas component and a liquid component are configured to be supplied separately, so that the same amount of gas components and liquid components can be supplied to each of the low temperature heat exchangers 3, which is preferable.

The returning refrigerant may be mixed with the gas component and the liquid component just before being supplied to the low temperature heat exchanger 3 to pass through the low temperature heat exchanger 3. The return refrigerant heated while cooling the natural gas supplied to the cryogenic heat exchanger 4 and the supply refrigerant (i.e., the refrigerant moving from the refrigerant compressor to the cryogenic heat exchanger) while passing through the low temperature heat exchanger 3 is the fifth refrigerant return line. It returns to the suction drum 23 through L35.

On the other hand, according to a modification of the second embodiment of the present invention, the refrigerant partially condensed in the intermediate cooler 24 is separated into the gas phase and the liquid phase in the intermediate separator 25 so that the gas component is supplied to the secondary compression step and the liquid The component may be modified to be supplied to the low temperature heat exchanger 3 via a separate refrigerant supply line (not shown).

At this time, the refrigerant supplied to the low temperature heat exchanger 3 from the intermediate separator 25 through a separate refrigerant supply line may be expanded through the expansion valve after passing through the low temperature heat exchanger 3. The refrigerant, which is expanded while passing through the expansion valve and becomes low temperature, is mixed with the refrigerant returning from the cryogenic heat exchanger (4) toward the refrigerant compressor (21), and supplied to the low temperature heat exchanger (3) to cool the natural gas and return the refrigerant return line. Through the refrigerant compressor 21, more specifically, the suction drum 23 provided upstream of the refrigerant compressor can be returned.

Therefore, in the modification of 2nd Embodiment, compared with the liquefaction apparatus which concerns on 2nd Embodiment, the separate refrigerant | coolant supply line (shown) for supplying the liquid component isolate | separated from the intermediate separator 25 to the low temperature heat exchanger 3 is shown. O) and an expansion valve (not shown) provided in this separate refrigerant supply line.

On the other hand, according to another modified example of the second embodiment of the present invention, compared to the natural gas liquefaction apparatus according to the second embodiment may be modified to be provided with a plurality of compression unit, do not use the third and fourth refrigerant separator It can be modified to not.

According to another modification of the second embodiment, as in the above-described first embodiment, the refrigerant compressors 21a and 21b, the refrigerant condenser 26, the intermediate separator 25, the discharge separator 27, and the suction drum ( A plurality of compression units (eg, a first compression unit 20a and a second compression unit 20b; see FIG. 2) may be provided, including 23 and the like. In this case, since the configuration of the second compression unit 20b is the same as that of the first compression unit 20a, a detailed description thereof will be omitted. Although two compression units are shown in FIG. 2, the number of compression units may be three or more.

In addition, in another modification of the second embodiment, the third refrigerant separator 42 and the fourth refrigerant separator 43 can be deleted. Therefore, the liquid refrigerant supplied to the cryogenic heat exchanger 4 through the fourth refrigerant supply line L24 is discharged to the outside in the middle of the cryogenic heat exchanger 4 and expanded through the expansion valve 32 to lower the temperature. Immediately afterwards it is fed into the middle of the cryogenic heat exchanger 4 immediately. In addition, the refrigerant in the gas phase supplied to the cryogenic heat exchanger 4 through the fifth refrigerant supply line L25 is expanded through the expansion valve 33 after passing through the cryogenic heat exchanger 4 so as to lower the temperature. Immediately supplied to the cryogenic heat exchanger (4).

When there are a plurality of cryogenic heat exchangers, the refrigerant lines from the plurality of cryogenic heat exchangers are supplied by forming a refrigerant line and an expansion valve for each cryogenic heat exchanger to form a line returning to the same plurality of cryogenic heat exchangers, thereby providing liquid and gaseous refrigerants. It is possible to prevent the uneven supply of different operating conditions of each cryogenic heat exchanger.

As described above, according to the second embodiment of the present invention and its modifications, a plate fin heat exchanger (PFHE) type heat exchanger is provided as a low temperature heat exchanger for precooling natural gas and an ultra low temperature heat exchanger for at least partially liquefying natural gas. Groups can be used. However, of course, it can be modified to use a heat exchanger other than the PFHE type.

Further, according to the second embodiment of the present invention and its modifications, a process of extracting NGL-rich heavy hydrocarbons from natural gas cooled by the low temperature heat exchanger 3 and partially condensed is performed together. Therefore, it may be separated into a separate process, and if it is not necessary to separate the LNG component and LPG component, the NGL extraction process may be omitted.

According to the natural gas liquefaction method and apparatus of the second embodiment and variations thereof, a single mixed refrigerant cycle (SMR) constituting a single closed loop using a mixed refrigerant consisting of nitrogen and hydrocarbons is carried out. It is possible to implement a suitable liquefaction process for floating structures such as LNG FPSO having a limited space by configuring according to the characteristics of the marine environment and incorporating a natural gas liquid (NGL) treatment process.

As described above, the natural gas liquefaction method and apparatus according to the present invention have been described with reference to the illustrated drawings, but the present invention is not limited to the above-described embodiments and drawings, and the present invention belongs to the claims. Of course, various modifications and variations can be made by those skilled in the art.

1: natural gas liquefier, 2: floating structure, 3: low temperature heat exchanger, 4: cryogenic heat exchanger, 5: refrigerant circuit, 9: cold box, 11: cold separator, 12: pressure reducing valve, 13: LNG receiver, DESCRIPTION OF SYMBOLS 15: Demeterizer, 20: Compression part, 21a: 1st refrigerant compressor, 21b: 2nd refrigerant compressor, 23: Suction drum, 24: intermediate cooler, 25: intermediate separator, 26: refrigerant condenser, 28, 29: expansion Valve, 31: first refrigerant separator, 32, 33: expansion valve, 35: second refrigerant separator, 42: third refrigerant separator, 43: third refrigerant separator, L11: natural gas supply line, L12: first gas phase natural Gas supply line, L13: liquid natural gas supply line, L14: second gaseous natural gas supply line, L21: first refrigerant supply line, L22: second refrigerant supply line, L23: third refrigerant supply line, L24: fourth Refrigerant supply line, L25: fifth refrigerant supply line, L31: first refrigerant return line, L32: second refrigerant return line, L33: third refrigerant return line, L34: fourth Every return line, L35: the fifth coolant return line

Claims (20)

A natural gas liquefaction apparatus for liquefying natural gas by heat exchange with a refrigerant in a heat exchange means,
The heat exchange means includes a low temperature heat exchanger for cooling the natural gas extracted from the gas well to a low temperature, and an ultra low temperature heat exchanger for further cooling and liquefying the natural gas cooled in the low temperature heat exchanger,
The refrigerant heated by the natural gas in the cryogenic heat exchanger is precooled to the natural gas before being supplied to the cryogenic heat exchanger and supplied to the cryogenic heat exchanger, and the refrigerant supplied from the cryogenic heat exchanger to the cryogenic heat exchanger via the thermal shock prevention means. Thereby protecting the low temperature heat exchanger from thermal shock. The method according to claim 1,
The low temperature heat exchanger and the cryogenic heat exchanger is a natural gas liquefaction apparatus, characterized in that installed in one cold box. The method according to claim 1,
The thermal shock preventing means is a gas-liquid separator for separating a refrigerant supplied from the cryogenic heat exchanger to the low temperature heat exchanger into a gaseous refrigerant and a liquid refrigerant. The method according to claim 1,
The refrigerant is circulated along a refrigerant circuit consisting of a single closed circuit which passes through the low temperature heat exchanger and the cryogenic heat exchanger sequentially to liquefy the natural gas at least partially and then return via the low temperature heat exchanger. Natural gas liquefaction device. The method according to claim 1,
The natural gas further comprises a cold separator for separating the natural gas cooled to a low temperature in the low temperature heat exchanger into a natural gas of the gas state and a natural gas of the liquid state to supply the natural gas of the gas state to the cryogenic heat exchanger. Liquefaction apparatus. The method according to claim 5,
And a means for separating the natural gas in the liquid state separated from the cold separator by component. The method according to claim 3,
The plurality of low temperature heat exchangers are installed, the natural gas liquefied device characterized in that the refrigerant in the gas state and the liquid state refrigerant separated through the gas-liquid separator is supplied to the plurality of low temperature heat exchangers through separate supply lines, respectively. The method of claim 4,
The refrigerant circuit has one or more compression units including a refrigerant compressor for compressing a refrigerant for cooling the natural gas through heat exchange with natural gas and a refrigerant condenser for condensing the compressed refrigerant. Device. The method according to claim 8,
The refrigerant supplied to the low temperature heat exchanger from the compression unit is supplied to the natural gas liquefaction apparatus is separated into the refrigerant in the gas state and the liquid state through the discharge separator. The method according to claim 1,
And a refrigerant compressor for compressing the refrigerant, and a refrigerant condenser for condensing the compressed refrigerant, wherein the refrigerant compressor is a multi-stage compressor. The method according to claim 10,
The coolant supplied to the low temperature heat exchanger is a first refrigerant supply line for supplying the coolant in a liquid state separated by an intermediate separator among the partially condensed refrigerants cooled by an intermediate cooler between the plurality of refrigerant compressors to the low temperature heat exchanger. And second compressing the gaseous refrigerant separated by the intermediate separator by the refrigerant compressor again, partially condensing by the refrigerant condenser, and then supplying the liquid refrigerant separated in the discharge separator to the low temperature heat exchanger. And a third refrigerant supply line supplying a refrigerant supply line and a gaseous refrigerant separated from the discharge separator to the low temperature heat exchanger. The method of claim 11,
The refrigerant supplied to the low temperature heat exchanger through the third refrigerant supply line is cooled and partially condensed by the refrigerant returning from the cryogenic heat exchanger, and separated into a gaseous refrigerant and a liquid refrigerant by the first refrigerant separator. And natural gas liquefaction apparatus for cooling the natural gas in the cryogenic heat exchanger after each expansion. The method of claim 11,
The refrigerant supplied to the low temperature heat exchanger through the first and second refrigerant supply lines is expanded and then supplied to the low temperature heat exchanger to cool the natural gas. The method according to claim 13,
The expanded refrigerant is a natural gas liquefaction device, characterized in that the refrigerant supplied to the low temperature heat exchanger from the cryogenic heat exchanger and the heat shock preventing means is mixed and returned to the low temperature heat exchanger. The method according to claim 1,
The low temperature heat exchanger and the cryogenic heat exchanger is a natural gas liquefaction apparatus, characterized in that the heat exchanger of the plate fin heat exchanger (PFHE) type. The method according to claim 1,
The low temperature heat exchanger is a plate fin heat exchanger (PFHE) type heat exchanger, the cryogenic heat exchanger is a natural heat exchanger (SWHE) type heat exchanger. A natural gas liquefaction apparatus for liquefying natural gas by heat exchange with a refrigerant on a floating structure used floating in the sea,
A low temperature heat exchanger disposed on an upper deck of the floating structure to cool the natural gas extracted from the gas well to a low temperature;
An ultra low temperature heat exchanger disposed on an upper deck of the floating structure to further cool and liquefy natural gas cooled by the low temperature heat exchanger;
Thermal shock prevention means disposed between the cryogenic heat exchanger and the low temperature heat exchanger to protect the low temperature heat exchanger from thermal shock by preventing a cryogenic refrigerant discharged from the cryogenic heat exchanger from being directly supplied to the low temperature heat exchanger;
Natural gas liquefaction apparatus comprising a. Floating structures used floating at sea,
A low temperature heat exchanger disposed on an upper deck of the floating structure to cool the natural gas extracted from the gas well to a low temperature;
An ultra low temperature heat exchanger disposed on an upper deck of the floating structure to further cool and liquefy natural gas cooled by the low temperature heat exchanger;
Thermal shock prevention means disposed between the cryogenic heat exchanger and the low temperature heat exchanger to protect the low temperature heat exchanger from thermal shock by preventing a cryogenic refrigerant discharged from the cryogenic heat exchanger from being directly supplied to the low temperature heat exchanger;
Floating structure comprising a natural gas liquefaction device comprising a. The method according to claim 18,
The floating structure is a floating structure, characterized in that the LNG FPSO. A natural gas liquefaction method for liquefying natural gas by heat exchange with a refrigerant in a heat exchange means,
The natural gas extracted from the gas well is cooled to low temperature in a low temperature heat exchanger, and the natural gas cooled in the low temperature heat exchanger is further cooled in an ultra low temperature heat exchanger to at least partially liquefy, and heated by natural gas in the ultra low temperature heat exchanger. A natural gas liquefaction method, characterized in that for protecting the low temperature heat exchanger from thermal shock by further heating a refrigerant in the thermal shock prevention means and supplying it to the low temperature heat exchanger.

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