Boil-off gas treatment system

Abstract

The present invention relates to a boil-off gas treatment system. The boil-off gas treatment system according to an embodiment of the present invention comprises: a storage part in which liquefied gas is stored; a supercooling part which is connected to the storage part, and which supercools boil-off gas generated from the liquefied gas stored in the storage part so as to generate supercooled boil-off gas; a compression part which is connected to the supercooling part, and which receives and compresses the supercooled boil-off gas from the supercooling part so as to generate compressed supercooled boil-off gas; and a phase change unit which is connected to the compression part so as to receive the compressed supercooled boil-off gas from the compression part, and which induces the compressed supercooled boil-off gas to be phase-changed into a liquid / solid-based slush state.

Description

Evaporative gas treatment system

[0001] The present invention relates to an evaporation gas treatment system.

[0002] Interest in and demand for liquefied natural gas (LNG), which emits relatively less carbon than conventional fossil fuels, is rapidly increasing worldwide.

[0003] This liquefied natural gas is transported in its gaseous state through onshore or offshore gas pipelines, or stored in a liquefied state aboard liquefied natural gas carriers and transported to distant consumer destinations. Liquefied natural gas is obtained by cryogenically cooling natural gas, significantly reducing its volume compared to its gaseous state, making it ideal for long-distance transport by sea.

[0004] Meanwhile, a liquefied natural gas carrier is intended to store liquefied natural gas and transport the stored liquefied natural gas to a land-based location. To this end, the liquefied natural gas carrier is equipped with a storage tank that can withstand the extremely low temperatures of liquefied natural gas.

[0005] At this time, since the liquefaction temperature of the liquefied natural gas is an extremely low temperature of approximately -163℃ at atmospheric pressure, the liquefied natural gas will vaporize even if the temperature of the liquefied natural gas is slightly higher than -163℃ at atmospheric pressure. Taking the case of a conventional liquefied natural gas carrier as an example, although the storage tank of the liquefied natural gas carrier is insulated, external heat is continuously transferred to the liquefied natural gas, so as the liquefied natural gas is continuously vaporized within the storage tank while being transported by the liquefied natural gas carrier, boil-off gas (BOG) is generated within the storage tank.

[0006] The boil-off gas generated within the storage tank increases the pressure within the storage tank and, due to the swaying of the LNG carrier, accelerates the flow of the LNG, potentially causing structural problems in the storage tank. Therefore, it is necessary to properly handle the boil-off gas generated within the storage tank. Furthermore, boil-off gas represents a loss of the LNG stored within the storage tank, and therefore, its handling is a critical issue for the transport efficiency of LNG.

[0007] Meanwhile, in order to process boil-off gas in the storage tank of a liquefied natural gas carrier, a method of discharging boil-off gas inside the storage tank to the outside of the storage tank and incinerating it, a method of discharging boil-off gas inside the storage tank to the outside of the storage tank and re-liquefying it through a re-liquefaction device and then returning it to the storage tank, a method of using boil-off gas as fuel for the ship's propulsion engine, etc. are being used alone or in combination.

[0008] In particular, in the case of a method in which the boil-off gas inside the storage tank is discharged to the outside of the storage tank, re-liquefied through a re-liquefaction device, and then returned to the storage tank, the boil-off gas is expanded using a turbo expander or a pressure reducing valve to re-liquefy the boil-off gas. However, in the case of a turbo expander, although it can reach a lower temperature with a lower compression ratio than a pressure reducing valve, it has the problem of requiring a large flow rate and being a complex system. In addition, in the case of a pressure reducing valve, although the system is not as complex as that of a turbo expander, it has the problem of requiring a higher compression ratio than that of a turbo expander. Furthermore, if the boil-off gas is expanded using a multi-stage compressor to improve the problems of the conventional turbo expander and pressure reducing valve, there is the problem of poor space utilization because more space is required for the installation of the multi-stage compressor.

[0009] Therefore, there is a need for technological development for a evaporation gas treatment system that is not only compact in structure and thus has excellent space utilization, but can also easily reach the temperature required for re-liquefaction of evaporation gas with a lower compression ratio than conventional systems.

[0010] Embodiments of the present invention have been devised to solve the above-described conventional problems, and to provide a evaporation gas treatment system that is not only compactly constructed and thus has excellent space utilization, but can also easily reach the temperature required for re-liquefaction of evaporation gas with a lower compression ratio than conventional systems.

[0011] According to one aspect of the present invention, a system for processing evaporative gas may be provided, comprising: a storage unit in which liquefied gas is stored; a supercooling unit connected to the storage unit and supercooling evaporative gas generated from the liquefied gas stored in the storage unit to generate a supercooled evaporative gas; a compression unit connected to the supercooling unit and receiving the supercooled evaporative gas from the supercooling unit and compressing it to generate a compressed supercooled evaporative gas; and a phase change unit connected to the compression unit and receiving the compressed supercooled evaporative gas from the compression unit and inducing a phase change of the compressed supercooled evaporative gas into a liquid / solid based slush state.

[0012] In addition, the phase change unit may include a nozzle unit that is connected to the compression unit and provides a path for inducing the compressed supercooled evaporated gas to be discharged at a speed increased from the speed at which it was introduced; and a supply unit that is connected to the nozzle unit and supplies the liquefied gas of the storage unit to the nozzle unit.

[0013] In addition, the phase change unit may further include a cooling unit that is provided in the nozzle unit, receives the liquefied gas from the storage unit, and can cool the nozzle unit using the cooling heat of the liquefied gas.

[0014] In addition, the flow path includes a reducing portion formed so that a cross-sectional area of ​​the compressed supercooled evaporative gas can gradually decrease along a flow direction of the compressed supercooled evaporative gas; a neck portion provided at a rear end of the reducing portion; and an expanding portion provided at a rear end of the neck portion and formed so that a cross-sectional area of ​​the compressed supercooled evaporative gas can gradually increase along a flow direction of the compressed supercooled evaporative gas, wherein the compressed supercooled evaporative gas is accelerated while passing through the neck portion, and the compressed supercooled evaporative gas accelerated while passing through the neck portion can expand while passing through the expanding portion.

[0015] In addition, the supply unit includes a transfer pipe that is connected between the storage unit and the expansion unit and supplies the liquefied gas from the storage unit to the interior of the expansion unit, and the liquefied gas supplied to the interior of the expansion unit through the transfer pipe can assist the internal temperature of the expansion unit to reach a temperature at which the compressed supercooled evaporation gas can be liquefied, or can be solidified by receiving the cold heat of the compressed supercooled evaporation gas expanded in the expansion unit.

[0016] In addition, the cooling unit is provided adjacent to the expanding unit rather than the reducing unit, is installed on the outer surface of the expanding unit, and is provided with a heat exchange coil that receives the liquefied gas of the storage unit, and the cooling heat of the liquefied gas supplied to the heat exchange coil can assist the phase change of the compressed supercooled evaporation gas inside the expanding unit.

[0017] In addition, the compressed supercooled evaporation gas re-liquefied inside the nozzle unit and the solidified liquefied gas form the liquid / solid-based slush state, and the compressed supercooled evaporation gas in the liquid / solid-based slush state can be recovered to the storage unit.

[0018] According to embodiments of the present invention, not only is it compactly configured and thus has excellent space utilization, but it also has the effect of easily reaching the temperature required for re-liquefaction of evaporated gas even with a lower compression ratio than in the past.

[0019] FIG. 1 is a block diagram illustrating an evaporation gas treatment system according to one embodiment of the present invention.

[0020] Figure 2 is a process diagram illustrating the evaporation gas treatment system of Figure 1.

[0021] Figure 3 is a conceptual diagram illustrating a phase change unit of the evaporation gas treatment system of Figure 1.

[0022] Hereinafter, specific embodiments for implementing the idea of ​​the present invention will be described in detail with reference to the drawings.

[0023] In addition, when explaining the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description is omitted.

[0024] Additionally, when it is said that a component is 'connected' to another component, it should be understood that while it may be directly connected to that other component, there may also be other components in between.

[0025] The terminology used herein is intended solely to describe specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0026] Furthermore, the expressions "one side," "the other side," "upper side," and "lower side" in this specification are based on the drawings and may be expressed differently if the orientation of the object changes. For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted, and the size of each component does not fully reflect the actual size.

[0027] Additionally, terms that include ordinal numbers, such as "first," "second," etc., may be used to describe various components, but these components are not limited by such terms. These terms are used solely to distinguish one component from another.

[0028] The term "comprising" as used in the specification means specifying a particular characteristic, region, integer, step, operation, element and / or component, but does not exclude the presence or addition of other particular characteristics, regions, integers, steps, operations, elements, components and / or groups.

[0029] Hereinafter, an evaporation gas treatment system according to one embodiment of the present invention will be described with reference to the drawings.

[0030] FIG. 1 is a block diagram illustrating an evaporation gas treatment system according to one embodiment of the present invention, FIG. 2 is a process diagram illustrating the evaporation gas treatment system of FIG. 1, and FIG. 3 is a conceptual diagram illustrating a phase change unit of the evaporation gas treatment system of FIG. 1.

[0031] Referring to FIGS. 1 to 3, an evaporation gas treatment system (1) according to one embodiment of the present invention may include a storage unit (10), a supercooling unit (20), a compression unit (30), and a phase change unit (40).

[0032] The storage unit (10) stores liquefied gas in a liquid / solid-based slush state and can transport the liquefied gas in a liquid / solid-based slush state to a demand location. Here, the liquid / solid-based slush state means a state in which liquid and solid phases are mixed.

[0033] For this purpose, the storage unit (10) may be provided as a storage tank equipped on a liquefied gas carrier (not shown). The liquefied gas stored in the storage unit (10) has a liquid / solid-based slush state, and this liquid / solid-based slush state of the liquefied gas can be densified by solid particles. Accordingly, the storage unit (10) can store and transport a large amount of liquefied gas with a higher storage density than in the past. In addition, since the heat intruding from the outside is absorbed by the heat of fusion of the solid particles, the temperature rise of the liquefied gas is reduced, and thus the generation of evaporation gas is reduced, so that the liquefied gas can be stably stored and transported for a long period of time compared to in the past.

[0034] The supercooling unit (20) can generate supercooled vaporization gas by supercooling vaporization gas generated from liquefied gas stored in the storage unit (10). For this purpose, the supercooling unit (20) can be connected to the storage unit (10).

[0035] At this time, the supercooling unit (20) can supercool the vaporized gas by heat-exchanging the vaporized gas supplied from the storage unit (10) with a separate refrigerant. Here, the refrigerant that exchanges heat with the vaporized gas may be supplied from a separate refrigerant supply unit (2). However, this is merely an example, and the spirit of the present invention is not limited thereby. For example, the refrigerant that exchanges heat with the vaporized gas may be a liquefied gas stored in the storage unit (10). In addition, the refrigerant that exchanges heat with the vaporized gas may be replaced with various refrigerants that can supercool the liquefied gas.

[0036] The compression unit (30) can receive supercooled evaporation gas from the supercooling unit (20) and compress it to generate compressed supercooled evaporation gas. To this end, the compression unit (30) can be connected to the supercooling unit (20).

[0037] At this time, the compression unit (30) can pressurize the supercooled evaporation gas to drop the temperature of the supercooled evaporation gas to a predetermined temperature so that the supercooled evaporation gas can undergo a phase change, for example, be re-liquefied, in the nozzle unit (41) of the phase change unit (40) to be described later. As a result, a compressed supercooled evaporation gas having a lower temperature than the supercooled evaporation gas can be generated, and this compressed supercooled evaporation gas can reach a supersonic speed in the process of passing through the nozzle unit (41) of the phase change unit (40) to be described later. In addition, the compressed supercooled evaporation gas that has reached a supersonic speed can be expanded in the process of passing through the nozzle unit (41) of the phase change unit (40). The compressed supercooled evaporation gas expanded in this way can be re-liquefied or can be used to solidify the liquefied gas supplied to the nozzle unit (41) of the phase change unit (40). This will be described later.

[0038] The phase change unit (40) can induce the compressed supercooled evaporated gas to change phase into a liquid / solid-based slush state. To this end, the phase change unit (40) can include a nozzle unit (41), a supply unit (42), and a cooling unit (43).

[0039] The nozzle unit (41) may be connected to the storage unit (10) and may provide a path (411) that induces the compressed supercooled evaporation gas to be discharged at a rate increased from the rate at which it was introduced. At this time, as shown by the solid arrow in FIG. 3, the compressed supercooled evaporation gas may be supplied to the front end of the nozzle unit (41), and as shown by the dotted arrow in FIG. 3, the compressed supercooled evaporation gas that has been phase-changed into a liquid / solid-based slush state inside the nozzle unit (41), for example, in the path (411), may be discharged from the rear end of the nozzle unit (41).

[0040] Meanwhile, as illustrated by the dashed-dotted arrow in FIG. 3, the liquefied gas of the storage unit (10) can be supplied through the supply unit (42) to a point between the front and rear ends of the nozzle unit (41), for example, at a point corresponding to about 20% to about 80% of the total length of the nozzle unit (41). Since the liquefied gas supplied to a point corresponding to about 20% to about 80% of the total length of the nozzle unit (41) has an incompressible liquefied state, it can serve as a refrigerant that helps the internal temperature of the nozzle unit (41) reach a temperature at which the compressed supercooled evaporation gas can be liquefied. In addition, the liquefied gas supplied to a point corresponding to about 20% to about 80% of the total length of the nozzle unit (41) can be solidified through heat exchange with the compressed supercooled evaporation gas, the temperature of which is lowered inside the nozzle unit (41). This will be described later.

[0041] At this time, the euro (411) may be composed of a reduced portion (411a), a neck portion (411b), and an enlarged portion (411c).

[0042] The reduction section (411a) can accelerate the compressed supercooled evaporation gas to the speed of sound. To this end, the reduction section (411a) can be formed so that the cross-sectional area of ​​the compressed supercooled evaporation gas can gradually decrease along the flow direction of the compressed supercooled evaporation gas.

[0043] The compressed supercooled evaporated gas accelerated to the speed of sound in the reduction section (411a) can flow to the expansion section (411c) through the neck section (411b) provided at the rear end of the reduction section (411a), and can be accelerated to a supersonic speed in the expansion section (411c).

[0044] To this end, the expanding portion (411c) may be provided at the rear end of the neck portion (411b) and may be formed so that the cross-sectional area of ​​the compressed supercooled evaporation gas can gradually increase along the flow direction of the compressed supercooled evaporation gas. In other words, the expanding portion (411c) can further increase the speed of the compressed supercooled evaporation gas that has reached a supersonic speed by utilizing the characteristic that the speed increases when the cross-sectional area of ​​the flow increases in the supersonic speed section, and can drastically reduce the pressure and temperature when the compressed supercooled evaporation gas at a supersonic speed expands.

[0045] Conventionally, the temperature of the evaporated gas was lowered by expanding it through a turbo expander or pressure reducing valve to reliquefy it. However, the compression ratio required to lower the evaporated gas temperature to an appropriate level increased, which led to problems such as increased compressor power consumption and the need for a larger installation space. Furthermore, even when multi-stage compressors were used to address these issues, the additional space required for installation presented another problem.

[0046] However, in the case of the present embodiment, since the evaporation gas is expanded supersonically through the nozzle unit (41) and the temperature of the compressed supercooled evaporation gas is drastically lowered, the desired temperature can be reached even with a lower compression ratio compared to a conventional turbo expander or pressure reducing valve, and thus the power consumed in the compression unit (30) can be reduced compared to the conventional case, thereby ensuring economic feasibility for re-liquefaction. In addition, since the nozzle unit (41) can be installed in a relatively smaller space compared to a conventional turbo expander or multi-stage compressor, space utilization can be increased in places where space is limited, for example, in a liquefied gas carrier.

[0047] The supply unit (42) can supply liquefied gas from the storage unit (10) to the nozzle unit (41). The liquefied gas supplied to the nozzle unit (41) through the supply unit (42) can serve as a refrigerant that assists the phase change of the nozzle unit (41). In addition, the liquefied gas supplied to the nozzle unit (41) through the supply unit (42) can be solidified by receiving the cooling heat of the compressed supercooled evaporation gas whose temperature has been lowered in the nozzle unit (41).

[0048] To this end, a transfer pipe (421) connected between the storage unit (10) and the expansion unit (411c) of the nozzle unit (41) to transfer the liquefied gas of the storage unit (10) to the expansion unit (411c) and a pump (422) installed in the transfer pipe (421) may be included. The liquefied gas supplied to the expansion unit (411c) through the supply unit (42) in this way can be solidified by receiving the cold heat of the compressed supercooled evaporation gas expanded in the expansion unit (411c).

[0049] Specifically, since the compressed supercooled evaporation gas expanded in the expansion section (411c) reaches a supersonic speed and has a low temperature, when the liquefied gas supplied to the expansion section (411c) through the supply section (42) meets the compressed supercooled evaporation gas expanded in the expansion section (411c), the compressed supercooled evaporation gas expanded in the expansion section (411c) acts as a refrigerant to solidify the liquefied gas supplied to the expansion section (411c) through the supply section (42). The solidified liquefied gas can be recovered to the storage section (10) together with the re-liquefied compressed supercooled evaporation gas through the cooling section (43) described later. The solidified liquefied gas can not only block radiant heat in the storage section (10), but also absorb external heat penetrating into the storage section (10) as heat of fusion.

[0050] The cooling unit (43) can lower the temperature of the rear end of the nozzle unit (41) by using the cold heat of the liquefied gas supplied from the storage unit (10) to assist in the smooth phase change of the compressed supercooled evaporated gas in the nozzle unit (41).

[0051] To this end, the cooling unit (43) may be provided closer to the expansion unit (411c) than the reduction unit (411a) of the nozzle unit (41). This cooling unit (43) may be supplied with liquefied gas through a branch pipe (431) branched from a transport pipe (421) that transports liquefied gas from the storage unit (10) to the expansion unit (411c). For example, the cooling unit (43) may be provided with a heat exchange coil installed at the rear end of the nozzle unit (41).

[0052] Specifically, since the compressed supercooled evaporation gas expanded in the expansion section (411c) reaches a supersonic speed and has a low temperature, when the liquefied gas of the storage section (10) is supplied to the cooling section (43), the liquefied gas supplied to the cooling section (43) acts as a refrigerant to further lower the temperature of the compressed supercooled evaporation gas expanded in the expansion section (411c). When the temperature of the compressed supercooled evaporation gas expanded in the expansion section (411c) is further lowered, the re-liquefaction of the compressed supercooled evaporation gas expanded in the expansion section (411c) can be smoothly performed. The compressed supercooled evaporation gas re-liquefied in this way can be recovered to the storage section (10) together with the solidified liquefied gas.

[0053] Meanwhile, in this embodiment, the liquefied gas supplied to the cooling unit (43) acts as a refrigerant, and the rear end of the nozzle unit (41) is cooled by the cold heat of the liquefied gas supplied to the cooling unit (43), thereby assisting the phase change of the compressed supercooled evaporation gas inside the nozzle unit (41). However, this does not limit the spirit of the present invention. Depending on the location where the cooling unit (43) is installed, the liquefied gas supplied to the cooling unit (43) may not act as a refrigerant, but the compressed supercooled evaporation gas inside the nozzle unit (41) may act as a refrigerant, thereby solidifying the liquefied gas supplied to the cooling unit (43).

[0054] The evaporation gas treatment system (1) having the configuration described above is not only compactly configured and thus has excellent space utilization, but also has the effect of easily reaching the temperature required for re-liquefaction of evaporation gas even with a lower compression ratio than in the past.

[0055] In addition, since liquefied gas having a liquid / solid-based slush state can be densified by solid particles, there is an effect that liquefied gas can be stored in large quantities with a higher storage density than before.

[0056] In addition, when liquefied gas having a liquid / solid-based slush state is transported through a separate pipe, the temperature rise of the liquefied gas is reduced as the heat intruding from the outside is absorbed as the heat of fusion of the solid particles, thereby reducing the generation of evaporation gas, and thus, there is an effect that the liquefied gas can be stored stably for a long period of time compared to the past.

[0057] Although the embodiments of the present invention have been described as specific embodiments, these are merely examples, and the present invention is not limited thereto, but should be construed as having the broadest scope in accordance with the basic idea disclosed in this specification. Those skilled in the art may implement patterns of shapes not specified by combining / substituting the disclosed embodiments, but this also does not depart from the scope of the present invention. In addition, those skilled in the art may easily modify or alter the disclosed embodiments based on this specification, and it is clear that such modifications or alterations also fall within the scope of the present invention.

Claims

1. A storage unit where liquefied gas is stored; A supercooling unit connected to the storage unit and supercooling the evaporation gas generated from the liquefied gas stored in the storage unit to generate a supercooled evaporation gas; A compression unit connected to the supercooling unit and receiving the supercooled evaporation gas from the supercooling unit and compressing it to generate compressed supercooled evaporation gas; and A phase change unit connected to the compression unit, receiving the compressed supercooled evaporation gas from the compression unit, and inducing the compressed supercooled evaporation gas to change into a liquid / solid based slush state. Evaporative gas treatment system.

2. In paragraph 1, The above phase change unit is, A nozzle section connected to the compression section and providing a path for causing the compressed supercooled evaporated gas to be discharged at a speed greater than the speed at which it was introduced; and A supply unit connected to the nozzle unit and supplying the liquefied gas from the storage unit to the nozzle unit, Evaporative gas treatment system.

3. In paragraph 2, The above phase change unit is, Further comprising a cooling unit provided in the nozzle unit, which receives the liquefied gas from the storage unit, and can cool the nozzle unit using the cooling heat of the liquefied gas. Evaporative gas treatment system.

4. In paragraph 3, The above euro is, A reduction section formed so that the cross-sectional area of ​​the compressed supercooled evaporated gas can be gradually reduced along the flow direction of the compressed supercooled evaporated gas; A neck provided at the rear end of the above-mentioned reduced portion; and It includes an enlarged portion provided at the rear end of the above neck and formed so that the flow cross-sectional area of ​​the compressed supercooled evaporated gas can gradually increase along the flow direction of the compressed supercooled evaporated gas. The compressed supercooled evaporative gas is accelerated while passing through the neck, and the compressed supercooled evaporative gas accelerated while passing through the neck expands while passing through the expansion section. Evaporative gas treatment system.

5. In paragraph 4, The above supply unit, It includes a transfer pipe connected between the storage unit and the expansion unit and supplying the liquefied gas of the storage unit to the interior of the expansion unit, The liquefied gas supplied into the interior of the expansion section through the above-mentioned transfer pipe assists the internal temperature of the expansion section to reach a temperature at which the compressed supercooled evaporated gas can be liquefied, or solidifies by receiving the cold heat of the compressed supercooled evaporated gas expanded in the expansion section. Evaporative gas treatment system.

6. In paragraph 4, The above cooling unit, It is provided adjacent to the enlarged portion rather than the reduced portion, is installed on the outer surface of the enlarged portion, and is provided as a heat exchange coil that receives the liquefied gas from the storage portion. The cooling heat of the liquefied gas supplied to the heat exchange coil assists the phase change of the compressed supercooled evaporated gas inside the expansion section. Evaporative gas treatment system.

7. In paragraph 2, The compressed supercooled evaporated gas and the solidified liquefied gas re-liquefied inside the nozzle section form the liquid / solid based slush state, The compressed supercooled evaporated gas in the liquid / solid based slush state is recovered into the storage unit. Evaporative gas treatment system.

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