JP6812272B2 - LNG manufacturing system with recondenser - Google Patents

Description

The present invention relates to an LNG manufacturing system including a recondenser that recondenses (reliquefies) boil-off gas (BOG, Boil off Gas).

FIG. 6 shows a general LNG manufacturing system. Natural gas (NG, Natural Gas) is sent to the CO ₂ removal process 62 in the subsequent stage by the compressor 61. In the CO ₂ removal process 62, CO ₂ is removed from natural gas using a predetermined solvent. After the CO ₂ is removed, the NG is sent to the drying process 63. After removal in the drying process 63, NG is subjected to a predetermined drying treatment. After drying, the NG is sent to the liquefaction process 64. In the liquefaction process 64, the NG is liquefied after drying using the liquid refrigerant sent from the refrigeration system 65. The liquid natural gas (LNG) obtained by liquefaction is sent to the LNG storage tank 66. Then, in the LNG loading process 68, LNG is sent from the LNG storage tank 66 at a predetermined timing (for example, the timing of transferring the LNG to the transport ship tank). Here, the LNG in the LNG storage tank 66 may be vaporized by natural heat input to generate BOG. In addition, a large amount of BOG may be generated when LNG is transferred from the LNG storage tank 66 to the transport ship tank in the LNG loading process 68. In addition, BOG may occur because the piping is cooled when the LNG is transferred to the transport ship tank.

The LNG storage tank 66, which is installed in an LNG manufacturing terminal, often has a large capacity, and the design pressure is generally set to the vicinity of atmospheric pressure from the viewpoint of technology and cost. Therefore, it is necessary to exhaust the BOG from the LNG storage tank 66 even if the pressure rises a little. This pressure increase is also caused by the piston effect (also referred to as “pushing effect”) associated with the supply of LNG from the liquefaction process 64 to the LNG storage tank 66, so that the supply of LNG to the LNG storage tank 66 is steady. It was inviting the exhaust of BOG. In addition, a flash loss of reduced pressure was also generated due to the filling of the LNG storage tank 66 from the liquefaction apparatus of the liquefaction process 54. LNG loss due to flash loss may account for about 50% of the amount of BOG generated.

However, since it is not desirable from the environmental and economic aspects to exhaust the BOG to the atmosphere, conventionally, the BOG is returned to the drying process 63 by the compressor 67, and after drying, the BOG is supplied to the liquefaction process 64 together with the NG. This makes it possible to reliquefy the BOG. Alternatively, it may be used as a heat source for regenerating the desiccant or the like in the drying process 63.
However, in the case of the above-mentioned reliquefaction of BOG, the total amount of NG sent from the drying process 63 to the liquefaction process 64 includes the recycled BOG. Also, its use as a fuel gas means that the entire amount of LNG produced cannot be transferred to the transport tank.

Further, since the BOG is required to be in a high pressure state for reliquefaction of the BOG, a compressor 67 is required for recycling the BOG to be returned to the drying process 63. Therefore, a large amount of energy consumption was required for the compression.

Further, when the BOG is returned to the drying process 63 as described above, the BOG can be reliquefied only during the production of LNG, and when the BOG must be discharged from the LNG storage tank when the LNG is not produced, air is used. There was no choice but to exhaust the BOG inside. That is, the timing of reliquefaction was limited, and there was no degree of freedom in the reliquefaction process.

The LNG manufacturing system described in Patent Document 1 does not present any solution to the above problem.

U.S. Pat. No. 2011/0094261

An object of the present invention is to provide an LNG manufacturing system including a recondenser capable of recondensing BOG (boil-off gas) without using a BOG compressor and without depending on an LNG liquefaction process.

The first LNG manufacturing system of the present invention is
A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the refrigerator,
An LNG tank for storing liquid natural gas (LNG) liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
A recondenser that recondenses (reliquefies) the boil-off gas generated by applying heat to the liquid natural gas with the refrigerant sent from the refrigerator.
It is provided with a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank.

The second LNG manufacturing system of the present invention is
A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the first refrigerator,
An LNG tank for storing liquid natural gas liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
A recondenser that recondenses the boil-off gas (BOG) generated by applying heat to the liquid natural gas with the refrigerant sent from the second refrigerator.
It is provided with a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank.
In the above invention, the refrigerant sent from the first refrigerator and the refrigerant sent from the second refrigerator may be the same refrigerant or different refrigerants. For example, the refrigerant from the first refrigerator is a mixture of hydrocarbons and the like, and the refrigerant from the second refrigerator is nitrogen and the like.

The third LNG manufacturing system of the present invention is
A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the refrigerator,
An LNG tank for storing liquid natural gas liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
The first recondensation process in which the boil-off gas generated by applying heat to the liquid natural gas is liquefied by the refrigerant sent from the refrigerator, and the boil-off gas that is larger than that in the first recondensation process is processed. A recondenser that switches between the refrigerant sent from the refrigerator and the second recondensing process that is liquefied by the refrigerant sent from the refrigerant buffer.
It is provided with a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank.
In the above invention, the refrigerant sent from the refrigerator and the refrigerant sent from the refrigerant buffer may be the same refrigerant or different refrigerants. For example, the refrigerant from the refrigerator is a mixture of hydrocarbons and the like, and the refrigerant from the refrigerant buffer is nitrogen and the like.
In the first recondensing process, the refrigerant is sent from the refrigerator to the recondenser, and in the second recondensing process, the refrigerant is sent from the refrigerator to the recondenser. The refrigerant may be sent from the refrigerant buffer to the recondenser. When switching from the first recondensation process to the second recondensation process, the operation of the refrigerator may be stopped or may be continuously operated without stopping.
The recapacitor may have a switching control unit that switches between the first recondensing process and the second recondensing process.
When transferring the BOG to the LNG carrier, the switching control unit may switch from the first recondensing process to the second recondensing process.
When the pressure value measured by the pressure gauge arranged in the LNG tank or the feed line that sends the BOG to the recondenser becomes a predetermined value or more, the switching control unit starts from the first recondensing process. You may switch to the second recondensing process.

According to each of the above configurations, when processing a BOG having a preset predetermined range amount (flow rate per unit time) or a predetermined range pressure value, a first recondensing process (a process of liquefying with a refrigerant from a refrigerator). When processing a BOG that exceeds the predetermined range amount or the predetermined range pressure value, the second recondensing process (while maintaining the liquefaction by the refrigerant sent from the refrigerator, the refrigerant sent from the refrigerant buffer is used. Since the process of liquefying the BOG can be executed, the BOG can be recondensed without using a BOG compressor and without depending on the LNG liquefaction process.

In the above-mentioned first to third LNG production systems, the natural gas sent to the liquefaction apparatus may be subjected to a predetermined treatment in advance. For example, the LNG production system may include a removing device for removing predetermined impurities from the natural gas and a drying device for drying the natural gas treated by the removing device.
The transfer line may be provided with piping and a sluice valve.
The return line may be provided with a pipe, a pump for sending LNG, and an automatic on-off valve.
A feed line for sending the BOG from the LNG tank to the recondenser may be provided. The feed line may be provided with piping and one or more of an automatic on-off valve, a flow rate control valve, and a pressure regulating valve.
A pressure gauge may be provided to measure the pressure in the LNG tank. When the pressure value of this pressure gauge becomes equal to or higher than a predetermined value, the valves of the feed line and the return line may be opened and the BOG may be sent to the recondenser through the feed line.
When the pressure value of the pressure gauge installed on the feed line exceeds a predetermined value, the recondenser may be controlled so as to increase the cooling power of the recondenser. For example, the amount of the refrigerant sent from the refrigerator (first or second refrigerator) may be controlled to be increased.
The LNG carrier may be, for example, a loading station container, a loading pier, a loading station truck, or the like.
A recovery line for returning the BOG existing in the LNG carrier to the LNG tank may be provided.

In the third LNG manufacturing system,
The refrigerant stored in the refrigerant buffer may be supplied from a refrigerator or an external refrigerator.
The recondenser has a separate configuration of a pipe through which the refrigerant sent from the refrigerator passes and a pipe through which the refrigerant sent from the refrigerant buffer passes, and the return refrigerant may be returned to the refrigerator together.
The recondenser may have a first heat exchanger into which the refrigerant sent from the refrigerator is introduced and a second heat exchanger into which the refrigerant sent from the refrigerant buffer is introduced.

In the above-mentioned first to third LNG manufacturing systems, the recondenser preferably has the following configuration.
The recondenser
It is designed to recondense (liquefy) the boil-off gas with a refrigerant at a pressure lower than the operating pressure of the LNG tank.

According to this configuration, the BOG can be recondensed at a pressure lower than the operating pressure of the LNG tank without using a conventional BOG compressor.

The recondenser
A heat exchanger into which the refrigerant is introduced may be provided inside, and the BOG may be introduced into the heat exchanger and cooled by the refrigerant. This makes it possible to effectively liquefy the BOG in the form of a heat exchanger.

The volume (external volume) of the heat exchanger may be smaller than the internal volume (internal space volume) of the recondenser, and the heat exchanger may be arranged in the internal space of the recondenser.
This makes it possible to effectively liquefy the BOG in the form of a heat exchanger. The liquefied LNG collects at the bottom of the recondenser. The accumulated LNG can be sent to the LNG tank by a liquid feed pump.

The pressure in the recondenser or heat exchanger may be adjusted as follows.
(1) Before sending the BOG, the refrigerant is sent to precool the inside of the recondenser or the heat exchanger. After a lapse of a predetermined time, or when the temperature inside the recondenser or the heat exchanger reaches a predetermined temperature, the introduction of BOG is started.
(2) The introduced BOG is liquefied and accumulates at the bottom of the recondenser or heat exchanger. The liquefied LNG accumulated on the bottom can be sent to the LNG tank by a pump, a pressurizing device, or the like.

The fourth LNG manufacturing system of the present invention is
A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the refrigerator,
An LNG tank for storing liquid natural gas liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
An LNG lead-out line that draws out the liquid natural gas from the LNG tank,
A subcooler provided in the LNG lead-out line for cooling the liquid natural gas with a refrigerant (for example, liquid nitrogen).
A recondenser that recondenses the boil-off gas generated by applying heat to the liquid natural gas with the liquid natural gas cooled by the subcooler.
It is provided with a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank.
In the present invention, the recondenser may recondense (liquefy) the boil-off gas with LNG cooled by the subcooler at a pressure lower than the operating pressure of the LNG tank.

According to this configuration, the liquid natural gas is first cooled by using a refrigerant such as LN _2, and the boil-off gas is liquefied by the cooled liquid natural gas. As a result, the boil-off gas can be effectively recondensed at a pressure lower than the operating pressure of the LNG tank.

In the fourth invention, the subcooler is controlled so that the temperature of the liquid natural gas becomes higher than the freezing point of the liquid natural gas by a pressure regulating valve or a flow rate regulating valve installed in the refrigerant line through which the refrigerant flows. May be good.

In the fourth invention, the number of subcoolers may be two or two or more. When there are two sub-coolers, the first sub-cooler is used to process the first recondensing process, which is liquefied by the refrigerant sent from the first sub-cooler, and the boil-off gas, which is larger than that during the first recondensing process. The second recondensing process, which is liquefied by the refrigerant sent from the second subcooler and the refrigerant sent from the second subcooler, may be switched between each other. When switching from the first recondensation process to the second recondensation process, the operation of the refrigerator may be stopped or may be continuously operated without stopping.
The recapacitor may have a switching control unit that switches between the first recondensing process and the second recondensing process.
The switching control unit may switch from the first recondensing process to the second recondensing process when transferring the boil-off gas to the LNG carrier.
When the pressure value measured by the pressure gauge arranged in the LNG tank or the feed line that sends the BOG to the recondenser becomes a predetermined value or more, the switching control unit starts from the first recondensing process. You may switch to the second recondensing process.
The refrigerant of the second subcooler may be supplied from a refrigerant buffer in which the refrigerant is stored in advance.

In the above LNG manufacturing system, the pump for sending liquid natural gas (LNG) from the LNG tank to the transfer line may be an in-tank type pump installed inside the LNG tank, and is arranged on the transfer line. It may be a pump.

It is a figure which shows the configuration example of the LNG manufacturing system of Embodiment 1. It is a figure which shows the configuration example of the LNG manufacturing system of Embodiment 2. It is a figure which shows the structural example of the LNG manufacturing system of Embodiment 3. It is a figure which shows the structural example of a recondenser. It is a figure which shows the structural example of a recondenser. It is a figure which shows the structural example of a recondenser. It is a figure which shows the structural example of the LNG manufacturing system of Embodiment 4. It is a figure which shows the structural example of a recondenser. It is a figure which shows the structural example of a recondenser. It is a figure which shows the configuration example of the conventional LNG manufacturing system.

Some embodiments of the present invention will be described below. The embodiments described below describe an example of the present invention. The present invention is not limited to the following embodiments, and includes various modifications implemented without changing the gist of the present invention. It should be noted that not all of the configurations described below are essential configurations of the present invention.

(Embodiment 1)
The LNG manufacturing system 1 of the first embodiment will be described with reference to FIG. The LNG manufacturing system 1 has a first line L1 for transferring natural gas to a subsequent process, a compressor 11, and a second line L2 (for example, a pipe). As a subsequent process, a removal unit 12 is arranged, where a predetermined substance (for example, CO2) is removed from NG. Next, the removed NG is sent to the drying device 13 through the third line L3 and dried. Then, after drying, the NG is sent to the liquefier 14 through the fourth line L4 and liquefied. Refrigerant (liquid refrigerant) is sent from the refrigerator 15 to the liquefier 14, and NG is cooled to obtain LNG. Further, the heat-exchanged refrigerant returns to the refrigerator 15 in a vaporized state. LNG is sent to and stored in the LNG tank 16 through the fifth line L5. The first line L1 to the fifth line L5 are composed of, for example, a pipe and an on-off valve. A predetermined control device (controller) controls the operation of each device of the LNG manufacturing system 1, the opening and closing of valves, the production amount of LNG, and the like.

An in-tank type first pump P1 is arranged in the LNG tank 16, and the first pump P1 sends LNG in the tank to the LNG carrier 18 through the transfer line L6. Examples of the LNG carrier 18 include a loading station container, a loading pier, and a loading station truck. The BOG existing in the LNG carrier 18 is sent to the LNG tank 16 through the collection line A2. A second feed line may be provided in place of or in addition to the recovery line A2 to feed the BOG present in the LNG carrier 18 to the recondenser 17.

In the LNG tank 16, BOG is generated by heat input. BOG is also generated when LNG is sent from the liquefier 14. BOG is also generated when LNG is sent to the LNG carrier 18. In this way, the BOG in the LNG tank 16 is sent to the recondenser 17 through the first feed line A1. Further, the BOG in the transfer line L6 is sent to the recondenser 17 through the third feed line A3.

A refrigerant (liquid refrigerant) is introduced into the recondenser 17 from the refrigerator 15 through the refrigerant line B1. The refrigerant recondenses (liquefies) the BOG sent on each feed line. The configuration of the recondenser 17 will be described later. The LNG obtained by recondensing (liquefying) is returned to the LNG tank 16 through the return line A4. A second pump P2 is arranged on the return line A4, and the second pump P2 is operated to send LNG to the LNG tank 16.
According to this embodiment, a series of processes in which the BOG is sent to the drying device and sent to the liquefaction device together with the NG to be liquefied as in the prior art is not required. Therefore, it is not necessary to operate the entire LNG manufacturing system, and only the refrigerator 15 needs to be operated. Since the BOG can be recondensed into LNG with the recondenser 17, all of the liquefaction capacity of the liquefaction device 14 can be directed to the liquefaction of the NG sent from the drying device.

(Recondenser)
4A and 4B show an embodiment of the recondenser 17. In FIG. 4A, the recondenser 17 has an outer wall 171 and a heat exchanger 172 coated on the outer wall 171. A refrigerant (liquid refrigerant) is introduced into the heat exchanger 172 from the refrigerator 15 through the refrigerant line B1, and the BOG is cooled by the cold heat of the refrigerant. The refrigerant evaporates and returns to the refrigerating equipment 15 through the refrigerant return line B2. LNG is sent from the recondenser 17 to the LNG tank 16 by the second pump P2.

The recondenser 17 is designed to recondense (liquefy) the BOG with a refrigerant at a pressure lower than the operating pressure of the LNG tank 16.

The first feed line A1 may be provided with a safety valve in case the pressure in the LNG tank 16 becomes abnormally high. Further, the first feed line A1 is provided with an automatic on-off valve 42 for feeding and controlling the BOG to the recondenser 17. Further, the first feed line A1 is provided with a pressure gauge and a pressure regulating valve 41 controlled according to the values of the pressure gauge.

The working pressure in the LNG tank 16 has an average absolute pressure of 1.2 barA (120 KPaA), and is controlled within ± 15% as the upper and lower limit values. When a large amount of BOG is generated, the tank internal pressure becomes high. The tank internal pressure is measured with a pressure gauge, and the valve control unit (not shown) controls the opening and closing of the automatic on-off valve 42 based on the measurement result (conversion result). For example, when the tank internal pressure becomes 1.3 times 1.2 barA (120 KPaA), the BOG is sent to the recondenser 17. The pressure adjusting valve 41 measures the pressure inside the pipe of the first feed line A1 and controls the valve opening degree based on the measurement result.

The refrigerant supplied from the refrigerator 15 may be a medium having a temperature lower than the boiling point of LNG, and for example, LN2 may be used.

The internal pressure of the heat exchanger 172 is controlled to be lower than the operating pressure of the LNG tank 16 (absolute pressure average 1.2 barA (120 KPaA)) in the BOG recondensing process. The internal pressure of the heat exchanger 172 is measured by a pressure gauge and adjusted to be lower than the operating pressure of the LNG tank 16. In the present embodiment, when the refrigerant comes into contact with the BOG in the heat exchanger 172, the volume of the BOG is reduced by liquefaction and the pressure in the heat exchanger 172 is lowered. During operation, the low pressure state is maintained by continuously supplying the refrigerant. The internal pressure of the heat exchanger 172 is adjusted by controlling the flow rate of the refrigerant. A flow rate adjusting valve (not shown) may be provided in the refrigerant feed line B1, and the flow rate adjusting valve may control the flow rate of the refrigerant according to the measurement result of the pressure gauge for measuring the internal pressure of the heat exchanger 172.
The recondenser 17 is not limited to the form of the heat exchanger 172, and may be in the form of directly contacting the BOG and the refrigerant. As a method of bringing the two into contact with each other, for example, there are a means of spraying the refrigerant with a shower, a means of contacting them with a filler, and the like. The lower part of the heat exchanger 172 and the return line A4 are connected. By controlling the opening and closing of the automatic on-off valve (not shown) provided on the return line A4 and controlling the second pump P2, LNG can be sent back from the recondenser 17 to the LNG tank 16.

The procedure for recondensing the boil-off gas (BOG) will be described below.
(1) When the pressure inside the tank of the LNG tank 16 exceeds the first threshold value, the refrigerant is sent from the refrigerator 15 to the heat exchanger 172 to precool the heat exchanger 172. The temperature of the refrigerant is preferably, for example, higher than the LNG freezing point and lower than the temperature of LNG in the LNG tank 16. The temperature of the LNG to be cooled may be set based on the amount of BOG and the amount of LNG to be cooled.
(2) When the heat exchanger 172 falls below a predetermined temperature, the supply amount of the refrigerant is adjusted by a flow rate adjusting valve (not shown) provided in the refrigerant line B1 so as to maintain the temperature.
(3) When the pressure inside the tank of the LNG tank 16 exceeds the second threshold value (second threshold value> first threshold value), the automatic on-off valve 42 and the pressure adjusting valve 41 are opened, and the BOG is recondensed from the LNG tank 16. It is introduced directly into the heat exchanger 172 of 17. When introducing this BOG, the amount of refrigerant supplied to the heat exchanger 172 is adjusted to maintain the inside of the heat exchanger 172 under a negative pressure (or a pressure lower than the operating pressure of the LNG tank 16).
(4) The heat exchanger 172 is precooled, the BOG is immediately cooled and the state changes to LNG, and the LNG falls to the bottom of the heat exchanger 172.
(5) The LNG is sent back to the LNG tank 16 through the return line A4.
(6) When the recondensing process is completed, each valve is closed.
Since it is assumed that the condition (3) (tank internal pressure> second threshold value) is satisfied during the processing of (1) and / or (2), the BOG is discharged from the LNG tank 16 with a safety valve (not shown). It may be configured so that the outside air is exhausted by a vent (not shown).
The "first threshold" is, for example, 1.26 times the pressure of 1.2 barA (120 KPaA).
The "second threshold" is, for example, 1.3 times the pressure of 1.2 barA (120 KPaA).
A pressure regulating valve (not shown) or a flow rate regulating valve (not shown) may be installed in the refrigerant line B1, and the refrigerant feed amount (VN) and the BOG feed amount (VB) are set to VN> VB. You may control it.

(Another embodiment)
The recondenser of FIG. 4B will be described. In FIG. 4B, in the recondenser 17, the volume (external volume) of the heat exchanger 172 is smaller than the internal volume (internal space volume) of the recondenser 17, and the heat exchanger 172 is arranged in the internal space 173 of the recondenser. ing. BOG can be effectively liquefied in the form of a heat exchanger. The liquefied LNG collects at the bottom of the internal space 173 of the recondenser 17. The accumulated LNG can be sent to the LNG tank 16 by the second pump P2.

The upper part of the internal space 173 of the recondenser 17 (preferably above the heat exchanger 172) is directly connected to the first feed line A1. Further, the lower part of the internal space 173 of the recondenser 17 and the return line A4 are directly connected.

The internal pressure of the recondenser 17 is controlled to be lower than the operating pressure of the LNG tank 16 (absolute pressure average 1.2 barA (120 KPaA)) in the BOG recondensing process. The internal pressure of the recondenser 17 is measured by a pressure gauge and adjusted to be lower than the operating pressure of the LNG tank 16.
In this embodiment, the refrigerant is sent to the heat exchanger 172, which cools the inside of the recondenser 17. When the BOG is introduced into the cooled recondenser 17, the volume of the BOG is reduced by liquefaction and the pressure inside the recondenser 17 is lowered. During the operation, the refrigerant is continuously supplied to the heat exchanger 172 to continuously cool the inside of the recondenser 17, liquefy the BOG, and maintain the inside of the recondenser 17 in a low voltage state. The internal pressure of the recondenser 17 is adjusted by controlling the flow rate of the refrigerant. A flow rate adjusting valve may be provided in the refrigerant line B1, and the flow rate adjusting valve may control the flow rate of the refrigerant according to the measurement result of the pressure gauge for measuring the internal pressure of the recondenser 17, and the automatic flow rate adjusting valve provided in the refrigerant line B1 may be used. By controlling the opening degree of the on-off valve, the flow rate of the refrigerant may be controlled, or both of them may be controlled.

The procedure for recondensing the boil-off gas (BOG) will be described below.
(1) When the pressure inside the LNG tank 16 exceeds the first threshold value, the refrigerant is sent to the heat exchanger 172 to precool the recondenser 17. The temperature of the refrigerant is preferably, for example, higher than the LNG freezing point and lower than the temperature of LNG in the LNG tank 16. The temperature of the LNG to be cooled may be set based on the amount of BOG and the amount of LNG to be cooled.
(2) When the recondenser 17 falls below a predetermined temperature, the supply amount of the refrigerant is adjusted by a flow rate adjusting valve (not shown) provided in the refrigerant line B1 so as to maintain the temperature.
(3) When the pressure inside the tank of the LNG tank 17 exceeds the second threshold value (second threshold value> first threshold value), the automatic on-off valve 42 and the pressure adjusting valve 41 are opened, and the BOG is recondensed from the LNG tank 16. Introduce to 17. When introducing this BOG, the amount of refrigerant supplied to the heat exchanger 172 is adjusted to maintain the inside of the condenser 172 under negative pressure (or lower than the operating pressure of the LNG tank 16).
(4) The recondenser 17 is precooled, the BOG is immediately cooled and the state changes to LNG, and the LNG accumulates at the bottom of the recondenser 17.
(5) The LNG accumulated at the bottom of the recondenser 17 is sent back to the LNG tank 16 through the return line A4.
(6) When the recondensing process is completed, each valve is closed.
Since it is assumed that the condition (3) (tank internal pressure> second threshold value) is satisfied during the processing of (1) and / or (2), the BOG is discharged from the LNG tank 16 with a safety valve (not shown). It may be configured so that the outside air is exhausted by a vent (not shown).
The "first threshold" is, for example, 1.26 times the pressure of 1.2 barA (120 KPaA).
The "second threshold" is, for example, 1.3 times the pressure of 1.2 barA (120 KPaA).
A pressure regulating valve (not shown) or a flow rate regulating valve (not shown) may be installed in the refrigerant line B1, and the refrigerant feed amount (VN) and the BOG feed amount (VB) are set to VN> VB. You may control it.

(Embodiment 2)
The LNG manufacturing system 2 of the second embodiment will be described with reference to FIG. Since the elements having the same reference numerals as those of the LNG manufacturing system 1 of the first embodiment have the same functions, the description thereof will be omitted or briefly described.

The LNG manufacturing system 2 of the second embodiment has a first refrigerator 15 and a second refrigerator 20. The first refrigerator sends the refrigerant to the cooling device 14. The second refrigerator 20 sends the refrigerant (liquid refrigerant) to the recondenser 17 through the refrigerant line C1 (corresponding to B1 in FIG. 1), and returns the refrigerant used as the cooling heat source in the recondenser 17 to the return line C2 (FIG. 1). Return through (corresponding to B2 of).
As a result, since the second refrigerator 20 is provided separately from the first refrigerator 15, the refrigerant is supplied from the large refrigerator to the operating cooling device 14, and also to the recondenser 17. There is no need to install a refrigerator that is larger than necessary, and it is sufficient to install a refrigerator of medium size or smaller, the installation space can be reduced, and the initial cost and running cost can be reduced.

(Embodiment 3)
The LNG manufacturing system 3 of the third embodiment will be described with reference to FIG. Since the elements having the same reference numerals as those of the LNG manufacturing system 1 of the first embodiment have the same functions, the description thereof will be omitted or briefly described.

The recondenser 17 of the LNG manufacturing system 3 of the third embodiment is a refrigerator for processing the first recondensation process of liquefying by the refrigerant sent from the refrigerator 15 and the BOG that is larger than that of the first recondensation process. The second recondensation process, which is liquefied by the refrigerant sent from 15 and the refrigerant sent from the refrigerant buffer 30, can be switched between each other.
In the refrigerant buffer 30, the refrigerant is supplied from the refrigerator 15 through the first supply line E1 and / or the refrigerant is supplied from the external refrigerant source through the second supply line E2 and stored in advance. When the recondenser 17 operates, the refrigerant is introduced from the refrigerant buffer 30 into the recondenser 17 through the buffer line D1.

The recondenser 17 has a switching control unit (not shown) for switching between the first recondensing process and the second recondensing process.
When the BOG is transferred to the LNG carrier 18, the switching control unit transfers the BOG to the LNG carrier 18, for example, according to the timing of the scheduled transfer start, or according to the timing when the detection unit detects that the LNG has been transferred from the LNG tank 16. , The first recondensation process can be switched to the second recondensation process. As the detection unit, for example, a detection unit that detects that the transport ship has entered the port, a detection unit that detects that the automatic on-off valve of the transfer line L6 has opened, and a control signal that controls the automatic on-off valve are used as a detection signal. Examples thereof include a detection unit for detecting that the measurement result of the flow meter arranged on the transfer line L6 exceeds the threshold value.
Further, the switching control unit is a pressure value measured by a pressure gauge in the LNG tank 16 or a pressure value measured by a pressure gauge arranged at at least one of the feed line A1, the recovery line A2 and the feed line A3. When is greater than or equal to a predetermined value, the first recondensation process can be switched to the second recondensation process.

An example of the recondenser 17 of the third embodiment will be described with reference to FIG. 4C. The recondenser 17 has a first heat exchanger 172 and a second heat exchanger 174 in its internal space 173. Refrigerant is introduced into the first heat exchanger 172 from the refrigerator 15 during the first recondensing process to cool the BOG. When the amount of BOG generated is large, the switching control unit switches from the first recondensing process to the second recondensing process. While operating the first heat exchanger 172, the second heat exchanger 174 is further operated. The refrigerant is introduced from the refrigerant buffer 30 through the buffer line D1 into the second heat exchanger 174. As a result, cooling is performed by the two heat exchangers, so that when the amount of BOG delivered is higher than usual during peak hours (for example, when processing a large amount of BOG generated when LNG is delivered to an LNG transport ship). Etc.), the BOG can be effectively cooled to LNG, and this LNG can be returned to the LNG tank 16. The refrigerant used in the second heat exchanger 174 is configured to join the refrigerant return line B2 of the first heat exchanger 172 through the refrigerant return line D2, but the refrigerant return line D2 is not limited to this. It may be connected to the refrigerator 15.

In addition, the switching control unit detects that when the transfer of BOG to the LNG carrier 18 is completed, for example, according to the scheduled end timing of the transfer, or that the LNG transfer from the LNG tank 16 is completed. The second recondensing process can be switched to the first recondensing process according to the detected timing. The detection unit includes, for example, a detection unit that detects that the automatic on-off valve of the transfer line L6 is closed, a detection unit that uses a control signal for controlling the automatic on-off valve as a detection signal, and a flow meter arranged on the transfer line L6. Examples thereof include a detection unit that detects that the measurement result is less than the threshold value.
Further, the switching control unit is a pressure value measured by a pressure gauge in the LNG tank 16 or a pressure value measured by a pressure gauge arranged at at least one of the feed line A1, the recovery line A2 and the feed line A3. When is less than a predetermined value, the second recondensation process can be switched to the first recondensation process.

(Another embodiment)
In the above embodiment, two heat exchangers are arranged in the recondenser 17, but the cooling capacity of the heat exchangers may be the same or different.
In the present embodiment, the combination of the refrigerant buffer and the heat exchanger is provided so as to be one set, but the present invention is not limited to this, and two or more sets may be provided.

(Embodiment 4)
The LNG manufacturing system 5 of the fourth embodiment will be described with reference to FIGS. 5A to 5B. Since the elements having the same reference numerals as those of the LNG manufacturing system 1 of the first embodiment have the same functions, the description thereof will be omitted or briefly described.
In the fourth embodiment, the refrigerator in the LNG manufacturing system is not used, but the LNG in the LNG tank is used. That is, in the fourth embodiment, LNG is subcooled to a predetermined temperature with a refrigerant, and this is sent to a recondenser to be brought into contact with BOG to liquefy the BOG.

In the fourth embodiment, the first feed A1 for sending BOG from the LNG tank 16, the LNG lead-out line E1 for leading out LNG from the LNG tank 16, the subcooler 52 for cooling the LNG with a refrigerant, and the operating pressure of the LNG tank 16 Under low pressure, the recondenser 57 that liquefies the BOG sent through the first feed line A1 of the BOG with LNG cooled by the subcooler 15 and the LNG liquefied by the BOG by the recondenser 57 are returned to the LNG tank 16. It has a line A4. Each configuration will be described in detail below.

The first feed line A1 may be provided with a safety valve (not shown) in case the pressure in the LNG tank 16 becomes abnormally high. Further, the first feed line A1 is provided with an automatic on-off valve 42 and a pressure adjusting valve 41 for feeding and controlling the BOG to the condenser 10.

The working pressure in the LNG tank 16 has an average absolute pressure of 1.2 barA (120 KPaA), and is controlled within ± 15% as the upper and lower limit values. When a large amount of BOG is generated, the tank internal pressure becomes high. The tank internal pressure is measured with a pressure gauge, and the valve control unit (not shown) controls the opening and closing of the automatic on-off valve 42 based on the measurement result (conversion result). For example, when the tank internal pressure becomes 1.3 times 1.2 barA (120 KPaA), the BOG is sent to the recondenser 57. The pressure adjusting valve 41 measures the pressure inside the pipe of the first feed line A1 and controls the valve opening degree based on the measurement result.

LNG is introduced into the subcooler 52 from the LNG tank 16 through the LNG lead-out line E1. A valve control unit (not shown) controls the opening and closing of the automatic on-off valve 51 provided in the LNG lead-out line E1 and controls the liquid feed pump P5 to send LNG from the LNG tank 16 to the subcooler 52. It is sent to the recondenser 57 in the subsequent stage. Instead of the liquid feed pump P5, the in-tank liquid feed pump P1 may be configured to send LNG.

The refrigerant of the subcooler 52 may be a medium having a temperature lower than the boiling point of LNG, and LN2 is used in this embodiment. LN2 is introduced from an LN2 source (for example, an LN2 tank) into a subcooler 52 through a refrigerant line F1 and is used as a cold heat source for cooling LNG passing through the subcooler 52. LN2 may be gasified when discharged from the subcooler 52 through the discharge line F2, or may be discharged as a fluid in which a liquid and a gas are mixed. The discharged fluid (LN2 and / or GN2) may be discharged to the atmosphere or recycled.

In the subcooler 52, the LNG is controlled to have a temperature higher than the LNG freezing point by a pressure adjusting valve (not shown) or a flow rate adjusting valve (not shown) installed in the refrigerant line F1 through which the refrigerant (LN2) flows. You may.

The internal pressure of the recondenser 57 is controlled to be lower than the operating pressure of the LNG tank 16 (average 1.2 barA (120 KPaA) in absolute pressure) in the BOG recondensing process. The internal pressure of the recondenser 57 is measured by a pressure gauge and adjusted to be lower than the operating pressure of the LNG tank 16.
In the present embodiment, when the LNG cooled by the subcooler 52 comes into contact with the BOG in the recondenser 57, the volume of the BOG is reduced by liquefaction and the pressure in the recondenser 57 is lowered. During operation, a cooled LNG is continuously supplied to maintain a low pressure state. The internal pressure of the recondenser 57 is adjusted by controlling the flow rate of the cooled LNG. A flow rate adjusting valve is provided on the LNG feed line E2 between the subcooler 52 and the recondenser 57, and the flow rate adjusting valve controls the LNG flow rate according to the measurement result of the pressure gauge that measures the internal pressure of the recondenser 57. Alternatively, the flow rate of LNG may be controlled by controlling the opening degree of the automatic on-off valve 51, or both of them may be controlled.
When the BOG introduced into the recondenser 57 is brought into contact with the cooled LNG, the BOG is liquefied to become LNG, and the LNG accumulates at the bottom of the recondenser 57. As a method of bringing the two into contact with each other, for example, there are means of spraying LNG cooled by the subcooler 52 with a shower, means of contacting the two with a filler, and the like.

The lower part of the recondenser 57 and the return line A4 are connected. A valve control unit (not shown) controls the opening and closing of the automatic on-off valve 54 provided on the return line A4, and also controls the liquid feed pump P2, so that LNG can be sent back from the recondenser 57 to the LNG tank 16.

The processing procedure of the recondensing process of BOG will be described below. Each valve 41-41, 51, 54 is in a closed state except for the recondensing process.
(1) When the pressure inside the LNG tank 16 exceeds the first threshold value, a refrigerant (for example, LN2) is sent to the subcooler 52.
(2) When the sub-cooler 52 reaches a predetermined temperature or lower, LNG is sent from the LNG tank 16 to the sub-cooler 52 to be cooled. For example, the temperature of the LNG to be cooled is preferably higher than the LNG freezing point and lower than the temperature of the LNG in the LNG tank 16. The temperature of the LNG to be cooled may be set based on the amount of BOG and the amount of LNG to be cooled.
(3) The cooled LNG is sent to the recondenser 57 to precool the recondenser 57. The automatic on-off valve 54 of the return line A4 is closed.
(4) When the pressure inside the tank of the LNG tank 16 exceeds the second threshold value (second threshold value> first threshold value), the automatic on-off valve 42 and the pressure adjusting valve 41 are opened, and the BOG is recondensed from the LNG tank 16. Introduce to 57.
(5) The recondenser 57 is precooled, and when the cooled LNG is introduced into the recondenser 57 together with the BOG, the BOG is cooled and the state changes to LNG, and the LNG is at the bottom of the recondenser 57. Accumulate.
(6) When a predetermined amount of LNG has accumulated at the bottom of the recondenser 57 (or at a predetermined timing), the automatic on-off valve 54 is opened, the liquid feed pump P2 is controlled, and the LNG is transferred from the recondenser 57 to the LNG. Send back to tank 16.
(7) When the recondensing process is completed, each valve is closed.
Since it is assumed that the condition (4) (tank internal pressure> second threshold value) is satisfied during the processing of (1) to (3), the BOG is discharged from the LNG tank 16 by a safety valve (not shown). Alternatively, the outside air may be exhausted by a vent (not shown).
The "first threshold" is, for example, 1.26 times the pressure of 1.2 barA (120 KPaA).
The "second threshold" is, for example, 1.3 times the pressure of 1.2 barA (120 KPaA).

(Embodiment 5)
The LNG manufacturing system of the fifth embodiment will be described with reference to FIG. 5C. Since the elements having the same reference numerals as the LNG manufacturing systems 1 and 5 of the first and fourth embodiments have the same function, the description thereof will be omitted or briefly described.

In the fifth embodiment, the first and second subcoolers are arranged, and the first recondensation process of liquefying by the refrigerant sent from the first subcooler 52 and the BOG more than that of the first recondensation process are processed. In order to do so, the process is switched to the second recondensing process in which the refrigerant sent from the first subcooler 52 and the refrigerant sent from the second subcooler 521 liquefy. According to this, when processing a BOG having a preset predetermined range amount (flow rate per unit time) or a predetermined range pressure value, it is liquefied by the first recondensing process (LNG cooled by the first subcooler). When the BOG exceeding the predetermined range amount or the predetermined range pressure value is processed, the second recondensing process (the process of liquefying with LNG cooled by the first subcooler) is maintained, and the second process is performed. The process of liquefying with LNG cooled by the subcooler can be performed at the same time).

The switching control unit (not shown) may switch from the first recondensing process to the second recondensing process when transferring the BOG to the LNG carrier, and the feed line A1 that sends the BOG to the recondenser 57 in the LNG tank. When the pressure value measured by the pressure gauge arranged in is equal to or higher than a predetermined value, the first recondensing process may be switched to the second recondensing process.

In the present embodiment, the refrigerant sent to the first subcooler 52 and the refrigerant sent to the second subcooler 521 may be the same refrigerant or different refrigerants. For example, the refrigerant to the first subcooler 52 is a mixture of hydrocarbons and the like, and the refrigerant to the second subcooler 521 is nitrogen and the like.

The switching control unit can switch from the first recondensing process to the second recondensing process at the timing of the third embodiment. When switching to the second recondensing process, the valve control unit (not shown) controls the opening and closing of the sluice valve 53, sends LNG to the second subcooler 521, and sends it to the recondenser 57 in the subsequent stage. That is, in the first recondensing process, the LNG cooled from the first subcooler 52 was sent to the recondenser 57 through the LNG feed line E2, but it is switched to the second recondensing process and the first subcooler 52 In addition to the LNG cooled from the terminal being sent to the recondenser 57, the LNG cooled from the second subcooler 521 is sent to the recondenser 57 through the LNG feed line E21.

The refrigerant of the second subcooler 521 may be a medium having a temperature lower than the boiling point of LNG, and LN2 is used in this embodiment. LN2 is introduced into the second subcooler 521 from the LN2 source (for example, the LN2 tank) through the refrigerant line F11, and is used as a cooling heat source for cooling the LNG passing through the second subcooler 521. LN2 may be gasified when discharged from the second subcooler 521 through the discharge line F21, or may be discharged as a fluid in which a liquid and a gas are mixed. The discharged fluid (LN2 and / or GN2) may be discharged to the atmosphere or recycled. Further, in the second subcooler 521, the LNG is set to a temperature higher than the LNG freezing point by a pressure adjusting valve (not shown) or a flow rate adjusting valve (not shown) installed in the refrigerant line F11 through which the refrigerant (LN2) flows. It may be controlled by.

(Another embodiment)
In the above embodiments 4 and 5, each automatic on-off valve, pressure adjusting valve, and liquid feeding pump are provided in each line, but the arrangement is not limited to the above, and some or all of them may be omitted depending on the purpose. There may be.

Further, in the above-described embodiments 4 and 5, in the BOG recondensing process, cooled LNG was sent to precool the recondenser 57 before the BOG was sent to the recondenser 57, but the cooling is not limited to this. The LNG and the BOG may be sent together. In this case, the amount of cooled LNG (VL) and the amount of BOG (VB) may be controlled to VL> VB. A flow rate adjusting valve may be provided in each of the LNG introduction line E1, the line E2, and the first feed line A1 of the BOG to control the flow rate of each feed amount.

Further, in the above-described embodiments 4 and 5, the return line A4 is provided with the liquid feed pump P2, but the return line A4 may not be provided with the liquid feed pump. The LNG whose state has been changed from the BOG in the recondenser 57 may be sent to the LNG tank 16 by gravity.

Further, the refrigerant of the second subcooler 521 may be supplied from a refrigerant buffer in which the refrigerant is stored in advance.

In all the above embodiments, the pump P1 is an in-tank type, but the pump P1 is not limited to this, and may be a pump arranged on the transfer line L6.

1 LNG manufacturing system 14 Cooling device 15 Refrigerator 16 LNG tank 17 Recondenser 18 LNG carrier L6 Transfer line

Claims (12)

A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the refrigerator,
An LNG tank for storing liquid natural gas liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
A recondenser that recondenses the boil-off gas generated by applying heat to the liquid natural gas , which is sent from the LNG tank without going through a compressor, with the refrigerant sent from the refrigerator.
An LNG manufacturing system including a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank. A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the first refrigerator,
An LNG tank for storing liquid natural gas liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
A recondenser that recondenses the boil-off gas generated by applying heat to the liquid natural gas , which is sent from the LNG tank without going through a compressor, with the refrigerant sent from the second refrigerator.
An LNG manufacturing system including a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank. A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the refrigerator,
An LNG tank for storing liquid natural gas liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
The first recondensing process in which the boil-off gas generated by applying heat to the liquid natural gas sent from the LNG tank without passing through a compressor is liquefied by the refrigerant sent from the refrigerator, and the above-mentioned A recondenser that switches between the refrigerant sent from the refrigerator and the second recondensing process that is liquefied by the refrigerant sent from the refrigerant buffer in order to process more boil-off gas than during the first recondensation process. When,
An LNG manufacturing system including a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank. The recondenser
The LNG manufacturing system according to any one of claims 1 to 3, which is designed to recondense the boil-off gas with a refrigerant at a pressure lower than the operating pressure of the LNG tank. The recondenser
The LNG according to any one of claims 1 to 4, wherein a heat exchanger into which the refrigerant is introduced is provided inside, and the boil-off gas is introduced into the heat exchanger and cooled by the refrigerant. Manufacturing system. The fifth aspect of claim 5, wherein the volume (external volume) of the heat exchanger is smaller than the internal volume (internal space volume) of the recondenser, and the heat exchanger is arranged in the internal space of the recondenser. LNG manufacturing system. The boil-off gas in the LNG tank, which is provided in the LNG production system that liquefies natural gas to produce liquid natural gas and stores the liquefied liquid natural gas, is sent from the LNG tank without going through a compressor. It is a recondenser that is recondensed with refrigerant.
A recondenser with a return line that sends the recondensed liquid natural gas directly to the LNG tank. The recondenser
The recondenser according to claim 7, which is designed to recondense the boil-off gas with a refrigerant at a pressure lower than the operating pressure of the LNG tank. The recondenser
The recondenser according to claim 7 or 8, wherein a heat exchanger into which the refrigerant is introduced is provided inside, and the boil-off gas is introduced into the heat exchanger and cooled by the refrigerant. The ninth aspect of claim 9, wherein the volume (external volume) of the heat exchanger is smaller than the internal volume (internal space volume) of the recondenser, and the heat exchanger is arranged in the internal space of the recondenser. Recondenser. A liquefaction device that cools and liquefies natural gas with the refrigerant sent from the refrigerator,
An LNG tank for storing liquid natural gas liquefied by the liquefier, and
A transfer line for transferring the liquid natural gas from the LNG tank, and
An LNG carrier, which is arranged after the transfer line and for transferring the liquid natural gas,
An LNG lead-out line that draws out the liquid natural gas from the LNG tank,
A sub-cooler provided in the LNG lead-out line for cooling the liquid natural gas with a refrigerant, and
A recondenser that recondenses the boil-off gas generated by applying heat to the liquid natural gas sent from the LNG tank without passing through a compressor with the liquid natural gas cooled by the subcooler.
An LNG manufacturing system including a return line for sending liquid natural gas liquefied from the recondenser to the LNG tank. The recondenser
The LNG manufacturing system according to claim 11, wherein the boil-off gas is designed to be recondensed with a refrigerant at a pressure lower than the operating pressure of the LNG tank.

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