Liquefied gas transfer device for reducing boil-off gas

Provided is a liquefied gas transfer device for reducing boil-off gas. The liquefied gas transfer device for reducing boil-off gas comprises: at least one transfer pipe formed in a vertical direction inside a quay for storing liquefied gas so as to transfer the liquefied gas; a branch pipe which is branched from a lower part of the transfer pipe to one side of the transfer pipe, and which has an end part opened toward a bottom surface of the quay; a valve which is connected to the branch pipe and/or the transfer pipe, and which opens and closes the branch pipe or the transfer pipe so as to move the liquefied gas from the transfer pipe to the branch pipe; and a resistance member disposed inside the branch pipe so as to interrupt the flow of the liquefied gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of International Patent Application No. PCT/KR2014/006009 filed on Jul. 4, 2014, which claims priority to Korean Patent Application No. 10-2013-0078804 filed on Jul. 5, 2013, the disclosures of which are hereby incorporated in their entireties by reference.

TECHNICAL FIELD

The present invention relates to a liquefied gas transportation apparatus which transports a liquefied gas, and more particularly, to a liquefied gas transportation apparatus which reduces the occurrence of boil-off gas while transporting a liquefied gas.

BACKGROUND ART

Liquefied natural gas (LNG), which is one of liquefied gases, is a fossil fuel buried underground and is formed by changing a natural gas, a main ingredient of which is hydrocarbons, into an extremely low temperature liquid state through pressurizing and cooling processes. Since a liquefied gas has a significantly reduced volume compared with a gaseous state, transportation and storage thereof are relatively easy, and for example, it is possible to transport the liquefied gas to a consumption place at a long distance using a dedicated carrying vessel, etc. provided with a particularly manufactured quay capable of maintaining an extremely low temperature state.

A transportation apparatus, which allows such a liquefied gas to flow into the quay for shipping or loading the liquefied gas or to flow outside the quay for unloading, is provided in the quay. Such a transportation apparatus is generally formed of one or more transportation pipes and includes a pump device for moving the liquefied gas into or from the pipes. Korean Patent Publication No. 10-2012-0013255 discloses an example of the transportation apparatus.

However, during a typical transportation process, since a flow rate or speed of a liquefied gas rapidly changes, a pressure inside the transportation pipes drops and the liquefied gas boils off, thereby excessively generating boil-off gas. Such limitation may further increase when the transportation pipes are vertically installed in such a way that the liquefied gas rapidly drops from tops of the pipes in the direction of gravity.

Also, the boil-off gas may occur when a liquefied gas which flows at a high speed is rapidly discharged to a broad space inside the quay with a low pressure. Accordingly, it is necessary to develop an apparatus capable of being applied to a liquefied gas transportation process to minimize the occurrence of boil-off gas.

PRIOR ART DOCUMENT

DISCLOSURE

Technical Problem

To overcome such a limitation, it is an aspect of the present invention to provide a liquefied gas transportation apparatus for reducing boil-off gas, which reduces the occurrence of boil-off gas while transporting a liquefied gas.

Aspects of the present invention are not limited thereto and additional aspects of the invention will be obvious to one of ordinary skill in the art from the following description.

Technical Solution

One aspect of the present invention provides a liquefied natural gas (LNG) transportation apparatus for reducing boil-off gas, including at least one transportation pipe which is vertically formed in a quay which stores LNG and transports the LNG, a branch pipe which branches off from a bottom of the transportation pipe toward one side of the transportation pipe, and an end portion thereof is open toward a bottom surface of the quay, a valve which is connected to at least one of the branch pipe and the transportation pipe and opens and closes one of the branch pipe and the transportation pipe to move the LNG from the transportation pipe to the branch pipe, and a resistor member which intervenes in the branch pipe to interrupt a flow of the LNG.

The resistor member may be an orifice plate which includes at least one flow hole through which the LNG passes.

The transportation pipe may include a first transportation pipe which allows the LNG to flow into the quay and a second transportation pipe which allows the LNG to flow into the quay or to be discharged outside the quay, and the branch pipe may branch off from the second transportation pipe.

The transportation pipe may further include a connection pipe which connects the first transportation pipe with the second transportation pipe, and the LNG may selectively move to one of the first transportation pipe and the second transportation pipe along the connection pipe.

The valve may be formed as a check valve which is connected to a bottom of the second transportation pipe to prevent the LNG discharged along the second transportation pipe from flowing backward, and the branch pipe may branch off from the check valve.

An end portion of the first transportation pipe may be located at a place higher than those of end portions of the second transportation pipe and the branch pipe from the bottom surface of the quay.

The apparatus may further include a fluid mixing device inserted into the branch pipe and disposed between an end portion of the branch pipe and the resistor member.

The valve may include an opening and closing unit which selectively opens and closes the branch pipe and the transportation pipe.

Advantageous Effects

According to the embodiment of the present invention, a liquefied gas transportation apparatus can effectively reduce the occurrence of boil-off gas by preventing boil-off of a liquefied gas and can easily load the liquefied gas in a quay while maintaining a minimal boil-off gas amount.

MODE FOR INVENTION

Advantages, features, and methods of achieving the same will be specified with reference to embodiments that will be described in detail with reference to the attached drawings. However, the present invention will not be limited to the embodiments described below and may be embodied in various different forms. Merely, the embodiments are provided to completely disclose the present invention and to allow one of ordinary skill in the art to fully understand the present invention. The present invention should be defined only by the claims thereof. Hereinafter, throughout the specification, like reference numerals designate like elements.

A liquefied gas transportation apparatus for reducing boil-off gas in accordance with one embodiment of the present invention may be used for transporting various liquefied gases, for example, liquefied petroleum gas (LPG), liquefied natural gas (LNG), liquefied carbon dioxide (L-CO2), etc.

Hereinafter, for example, an LNG transportation apparatus for transporting LNG will be described.

Hereinafter, referring toFIGS. 1 to 7, an LNG transportation apparatus for reducing boil-off gas in accordance with one embodiment of the present invention will be described in detail.

FIG. 1is a perspective view of the LNG transportation apparatus for reducing boil-off gas in accordance with one embodiment of the present invention.FIG. 2is a partially enlarged perspective view illustrating a second transportation pipe and a branch pipe of the transportation apparatus ofFIG. 1.

First, referring toFIG. 1, an LNG transportation apparatus1for reducing boil-off gas in accordance with one embodiment of the present invention includes a first transportation pipe10, second transportation pipes20, and a discharge pipe50, which are vertically formed in a quay2. The LNG transportation apparatus1for reducing boil-off gas transports LNG using at least one of the transportation pipes.

A branch pipe40branches off from a bottom of the transportation pipe toward one side of the transportation pipe. The branch pipe40includes a resistor member which interrupts a flow of a LNG therein, thereby reducing a flow rate or flow speed of the LNG. Accordingly, when a LNG flows into the quay2through the branch pipe40, the LNG may be properly maintained inside the transportation pipe from the bottom at which the branch pipe40is located to a top which is inserted into the quay2.

Hereby, a pressure inside the transportation pipe increases. Accordingly, boil-off of the LNG caused by an unexpected pressure drop in a pipe conduit may be prevented and the occurrence of boil-off gas generated by vaporization of the LNG may be effectively reduced.

The branch pipe40may branch off from any one of the transportation pipes including the first transportation pipe10, the second transportation pipe20, and the discharge pipe50. Hereinafter, in accordance with one embodiment of the present invention, it will be described that the branch pipe40branches off from the second transportation pipe20which allows the LNG to flow into or be discharged from the quay2. When the branch pipe40is formed at the second transportation pipe20, the LNG may be easily loaded in the quay2using both the first transportation pipe10and the second transportation pipe20while maintaining a minimal inflow of boil-off gas. It will be described below in detail.

Hereinafter, respective components and functions of the LNG transportation apparatus1for reducing boil-off gas will be described in more detail.

Referring toFIGS. 1 and 2, the first transportation pipe10, the second transportation pipe20, and the discharge pipe50are vertically installed on one side of the quay2. Here, the first transportation pipe10may be a transportation pipe which allows the LNG to flow into the quay2, and the second transportation pipe20may be a transportation pipe which allows the LNG to flow into the quay2or to be discharged outside the quay2. That is, the second transportation pipe20may be used as a general discharge pipe which discharges the LNG outside the quay2but may be used in various ways using the branch pipe40. In accordance with one embodiment of the present invention, the branch pipe40branches off from the second transportation pipe20. The discharge pipe50is a pipe for completely discharging the LNG which remains in the quay2to the outside of the quay2and may be adjacently installed to the first transportation pipe10and the second transportation pipe20.

A connection pipe30is connected between the first transportation pipe10and the second transportation pipe20. Accordingly, when flowing into the quay2, the LNG may selectively move through the first transportation pipe10or the second transportation pipe20along the connection pipe30. For this, control valves110and310(refer toFIGS. 4 to 6) may be formed on one side of the connection pipe30and the first transportation pipe10. The transportation pipes which consist of the first transportation pipe10, the second transportation pipe20, and the discharge pipe50are mutually connected and integrally formed, and as shown in the drawings, may extend outside the quay2through an opening formed on a top end of the quay2.

The branch pipe40, as shown inFIG. 2, branches off from a bottom of the second transportation pipe20and an end portion thereof is open toward a bottom surface of the quay2. The branch pipe40, in detail, may branch off from a check valve201connected to the second transportation pipe20, and as shown in the drawings, may be formed in a shape of being bent at least once toward the bottom surface of the quay2.

An orifice plate410is inserted into the branch pipe40. The orifice plate410includes at least one flow hole411to pass only a part of the LNG which flows into the branch pipe40through the flow hole411. That is, the orifice plate410acts as a resistor member which interrupts a flow of the LNG in the branch pipe40to prevent a pressure drop in the second transportation pipe20and maintains the second transportation pipe20with a certain pressure or more. The orifice plate410may be formed in a disc shape corresponding to a cross-sectional shape of the branch pipe40, but is not limited thereto, and may be modified in various shapes unlike the shape of the branch pipe40.

The resistor member interrupts a flow of a fluid in a pipe conduit to reduce a flow rate or a flow speed of the fluid and is not limited to a plate-shaped member such as the orifice plate410. Accordingly, the orifice plate410described above is an example of the resistor member and members having various shapes, which are not standardized, may be inserted into the branch pipe40and may function as the resistor member.

A fluid mixing device420is formed between the end portion of the branch pipe40and the orifice plate410. The fluid mixing device420, for example, may be formed as a static mixer into which helical wings formed to intersect with one another while being twisted are inserted and may mix a slight amount of boil-off gas which arrives at the branch pipe40with the LNG which is in a state of being just before discharge, thereby preventing the boil-off gas from directly flowing into the quay2. Also, the fluid mixing device420, like the orifice plate410, interrupts a movement of the LNG to prevent the pressure drop inside the second transportation pipe20.

The check valve201is formed between the branch pipe40and the second transportation pipe20. The check valve201is coupled with the bottom of the second transportation pipe20, in detail, a pump connection pipe210which connects the second transportation pipe20with a pump220and may move the LNG which flows into the second transportation pipe20to the branch pipe40. That is, the check valve201functions as a valve which controls a flow path of the LNG to allow the LNG supplied to the transportation pipe to be discharged through the branch pipe40. Meanwhile, the check valve201may include an opening and closing unit201a(refer toFIG. 3) which opens in one direction therein to prevent the LNG from flowing backward to the pump220connected to the second transportation pipe20.

A valve which controls the flow path of the LNG is not limited to the check valve201. The branch pipe40or the transportation pipe may be opened and closed using various valves in addition thereto to easily move the LNG from the transportation pipe to the branch pipe40. Also, such a valve may be connected not only to the transportation pipe but also to the branch pipe40or may be connected to both the transportation pipe and the branch pipe40as necessary.

The bottom of the second transportation pipe20is formed of two portions such as the pump connection pipe210and a buffer pipe230. The pump connection pipe210is connected to the pump220via the check valve201, and the buffer pipe230extends toward the bottom surface of the quay2while an end portion thereof is closed. Accordingly, the LNG which flows into the second transportation pipe20arrives at the check valve201along the pump connection pipe210, and then a path thereof is controlled to move to the branch pipe40. The buffer pipe230is to maintain a part of the LNG which drops in a direction of gravity when the LNG flows in or out. Here, a length thereof may be appropriately controlled as necessary.

The pump220is connected to the pump connection pipe210. The pump220is used to discharge the LNG loaded in the quay2to the outside of the quay2, and for example, may be formed as a centrifugal pump which allows the fluid to flow using torque of an impeller. The check valve201described above may not only prevent the LNG from flowing backward to the pump220to allow the LNG to be smoothly unloaded when the LNG is discharged to the outside of the quay2along the second transportation pipe20by driving of the pump220, but also may provide the LNG to the branch pipe40to allow the LNG to smoothly flow into the quay2when the LNG is loaded in the quay2.

FIG. 3is a cross-sectional view illustrating insides of the branch pipe and the check valve ofFIG. 2.

Hereinafter, referring toFIG. 3, a pressure maintenance function of the LNG transportation apparatus for reducing boil-off gas in accordance with one embodiment of the present invention will be described in more detail.

The LNG which flows into the second transportation pipe20descends in the direction of gravity to arrive at the bottom of the second transportation pipe20and flows into the check valve201along the pump connection pipe210again (refer toFIG. 3for an arrow). Here, as shown in the drawings, the opening and closing unit201ais closed in such a way that the LNG does not proceed toward the pump220and all of the same is provided to the branch pipe40. Meanwhile, the opening and closing unit201ais opened when the LNG is unloaded and may be formed to rotate toward the branch pipe40to close the branch pipe40while being opened.

The LNG provided to the branch pipe40is prevented from flowing by the orifice plate410and only a part of the same passes through the flow hole411. Accordingly, the pressure is transferred from the orifice plate410in a reverse direction in an order of the check valve201and the pump connection pipe210, thereby maintaining the pressure inside the second transportation pipe20at a certain degree or more in which it is difficult for boil-off of the LNG to occur. Here, changes are made in the number and a distribution state of the flow hole411, thereby increasing or reducing the pressure inside the second transportation pipe20. Also, when necessary, the pressure inside the second transportation pipe20may be increased by repetitively installing the orifice plate410or additionally installing another resistor member in addition to the orifice plate410.

The LNG which passes through the orifice plate410passes through the fluid mixing device420and is discharged into the quay2. When a diameter of the branch pipe40increases, a discharge speed of the LNG may decrease. Here, a slight amount of boil-off gas which occurs inside the transportation pipe, as described above, is merely mixed with the LNG while passing through the fluid mixing device420but can not directly flow into the quay2. Also, the slight amount of boil-off gas may be condensed to a liquid state during a process of being mixed with the LNG and remaining boil-off gas is pulverized into micro bubbles to flow into the quay2. However, gas ingredients having a micro bubble size can also not float on a surface of the LNG due to a fluid static pressure of the LNG and remain at the bottom surface of the quay2and are condensed. Through this process, the pressure inside the second transportation pipe20to which the branch pipe40is connected is maintained and the occurrence of the boil-off gas is effectively reduced.

FIGS. 4 to 6are schematic operation diagrams of the transportation apparatus ofFIG. 1.FIG. 7is a flowchart illustrating a process of loading the LNG using the transportation apparatus ofFIG. 1.

Hereinafter, referring toFIGS. 4 to 7, an operation process of the LNG transportation apparatus for reducing boil-off gas in accordance with one embodiment of the present invention will be described. The operation process will be described in detail based on a process of loading the LNG shown inFIG. 7.

To load the LNG (refer toFIGS. 5 and 6for A) in the quay2, an LNG A is provided to the second transportation pipe20along arrows shown inFIG. 4(S100).

Here, the first transportation pipe10is a transportation pipe for allowing the LNG A to flow into the quay2and needs not be adjacent to the bottom surface of the quay2. On the contrary, the second transportation pipe20is a transportation pipe which allows the LNG A to flow out of the quay2, and accordingly, needs to be installed adjacent to the bottom surface of the quay2. Accordingly, an end portion of the first transportation pipe10may be located in a place higher than those of the end portions of the second transportation pipe20and the branch pipe40from the bottom surface of the quay2.

The control valves110and310capable of opening and closing a pipe conduit are formed on one side of the first transportation pipe10and the connection pipe30to cut off a path of the LNG A which flows into the transportation pipe from the first transportation pipe10and to allow the path to be toward the second transportation pipe20. Accordingly, as shown inFIG. 5, the LNG A is discharged from the bottom of the second transportation pipe20to the quay2through the branch pipe40(S200). Accordingly, the inside of the second transportation pipe20is maintained with a certain pressure or more in such a way that the LNG A may be easily transported to the quay2while reducing the occurrence of boil-off gas.

Here, it may be maintained that all the control valves310located on the connection pipe30are opened and the control valve110located on the first transportation pipe10is closed.

An inflow process of the LNG A as described above is continued until the LNG A arrives at a reference height of the inside of the quay2(S300). The reference height of the inside of the quay2may be identical to or slightly higher than a height of the end portion of the first transportation pipe10through which the LNG A flows in. When the LNG A arrives at the reference height, the end portion of the first transportation pipe10is located below a surface of the LNG A which flows into the quay2.

In this state, as shown inFIG. 6, opening and closing states of the control valves110and310are changed and the LNG A is provided to the first transportation pipe10(S400). Since the LNG A is discharged below the surface of the LNG which already flows in the quay2, a flow rate is reduced by resistance of a fluid and a rapid pressure drop does not occur. Hereby, the LNG A may be transported through the first transportation pipe10while reducing an amount of the boil-off gas.

The LNG A is continuously provided until loading of the LNG A is completed by filling the quay2with the LNG A to be over the reference height (S500). As described above, the second transportation pipe20connected with the branch pipe40and the first transportation pipe10not connected with the branch pipe40are used in combination to easily load the LNG A in the quay2while minimizing the occurrence of the boil-off gas.

Next, a modified example of the check valve included in one embodiment of the present invention will be described.

FIGS. 8 and 9are cross-sectional views illustrating a modified example of the check valve included in the LNG transportation apparatus for reducing boil-off gas in accordance with one embodiment.

Compared with the check valve ofFIG. 3, a check valve500according to the modified example has a little bit different shape of an opening and closing unit and a portion for coupling with the opening and closing unit but other portions may be identically formed.

The check valve500according to the modified example may be bolt-coupled with the pump connection pipe210and the branch pipe40using a flange510in the middle of the pump connection pipe210. It is shown as an example that the check valve500, the pump connection pipe210, and the branch pipe40are bolt-coupled. However, another coupling method capable of maintaining coupling-durability at an extremely low temperature is employable.

An opening and closing unit520included in the check valve500according to the modified example includes a disc530, a seat ring540fixed to the disc530, and a hinge portion550which rotatably fixes the disc530.

The disc530is formed to have a size greater than an inside diameter of the pump connection pipe210to close an inside diameter of the check valve500on the side of the pump connection pipe210.

The seat ring540is provided on one surface of the disc530in a protruding ring shape to seal a gap between the check valve500and the pump connection pipe210or to minimize an amount of the LNG which flows in or is discharged through the pump connection pipe210when the opening and closing unit520closes the pump connection pipe210.

Inside the check valve500coupled with the pump connection pipe210, an accommodating portion560capable of accommodating the seat ring540is provided corresponding to the seat ring540. The accommodating portion560is formed to have a diameter greater than the inside diameter of the check valve500to allow a front surface and an outer circumferential surface of the seat ring540to be in contact with the accommodating portion560.

The hinge portion550is to rotatably fix the disc530to the inside of the check valve500and includes a hinge pin551and a body portion552which connects the hinge pin551with the disc530.

The hinge pin551may include a torsion member (not shown) which provides a force in a direction in which the opening and closing unit520closes the pump connection pipe210when an external force does not act.

The body portion552may include a supporting portion553provided in a position opposite to the disc530and is supported by the inside of the check valve500when the opening and closing unit520is opened.

Next, an operation of the check valve500will be described.

The LNG which flows into the second transportation pipe20descends in the direction of gravity to arrive at the bottom of the second transportation pipe20and flows into the check valve500along the pump connection pipe210again (refer toFIG. 8for an arrow). Here, as shown in the drawings, the opening and closing unit520is closed in such a way that the LNG does not proceed toward the pump220and all of the same is provided to the branch pipe40. Meanwhile, when the LNG is unloaded, the pump220drives and the opening and closing unit520pivots due the driving of the pump220in such a way that the pump connection pipe210is opened and the branch pipe40is closed. Accordingly, the LNG does not proceed toward the branch pipe40and is guided to the second transportation pipe20through the pump connection pipe210and the check valve500(refer toFIG. 9).

While the embodiments of the present invention have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. Therefore, it will be understood that the embodiments described above are just exemplary but not limitative in all aspects.

BRIEF DESCRIPTION OF REFERENCE NUMERALS