KR20160126576A - Method for calculating lng boil off rate in cargo system - Google Patents

Method for calculating lng boil off rate in cargo system Download PDF

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KR20160126576A
KR20160126576A KR1020150057808A KR20150057808A KR20160126576A KR 20160126576 A KR20160126576 A KR 20160126576A KR 1020150057808 A KR1020150057808 A KR 1020150057808A KR 20150057808 A KR20150057808 A KR 20150057808A KR 20160126576 A KR20160126576 A KR 20160126576A
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cargo hold
space
computer system
lng
bor
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KR1020150057808A
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Korean (ko)
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장창환
전석희
오영태
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대우조선해양 주식회사
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    • B63B9/00—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B25/00—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby
    • B63B25/02—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods
    • B63B25/08—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid
    • B63B25/12—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed
    • B63B25/16—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed heat-insulated
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00—Details of vessels or of the filling or discharging of vessels
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/5009—

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  • Mechanical Engineering (AREA)
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  • Chemical & Material Sciences (AREA)
  • Ocean & Marine Engineering (AREA)
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  • Mathematical Physics (AREA)
  • Software Systems (AREA)
  • General Physics & Mathematics (AREA)
  • Combustion & Propulsion (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)

Abstract

The present invention relates to a method for calculating the LNG natural boiling off rate (BOR) in a cargo hold storing LNG in an LNG carrier. According to an embodiment of the present invention, there is provided a method of calculating an LNG natural rate of vaporization (BOR) in a cargo hold to be performed in a computer system, wherein the cargo hold and the periphery of the cargo hold are three- Modeling; Dividing the modeled cargo hold and the perimeter of the cargo hold into unit elements; Calculating an amount of heat input into the cargo hold using the unit element; And calculating the LNG BOR using the calorific value of the incoming LNG BOR.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for calculating LNG BOR in a cargo hold,

The present invention relates to an LNG carrier, and more particularly, to a method for calculating the LNG natural rate of vaporization (BOR) in a cargo hold storing LNG in an LNG carrier.

Generally, natural gas (NG) is made in the state of liquefied natural gas (LNG) that is liquefied at the cryogenic temperature in the place of production, is transported to the destination by a LNG carrier over a long distance, (FSRU, Floating Storage and Regasification Unit) or overland terminal, and supplied to the consumer.

Alternatively, where LNG is transported by LNG Regasification Vessel, LNG is regenerated from the LNG regasification line itself without going through LNG floating storage and regasification units or offshore terminals, .

Since the liquefaction temperature of natural gas is a cryogenic temperature of about -163 ° C at normal pressure, LNG is evaporated even if its temperature is slightly higher than -163 ° C at normal pressure. For example, in the case of a conventional LNG carrier, the hold of the LNG carrier is heat-treated, but external heat is continuously transferred to the LNG. Therefore, during transport of the LNG by the LNG carrier, (Boil-off gas) is generated in the cargo hold.

At this time, the ratio of LNG that LNG is vaporized in the cargo hold during the transportation of LNG by the LNG carrier and spontaneously evaporates is referred to as the natural vaporization rate (BOR). However, in recent years, BOR reduction has become more important as LNG carriers are required to store LNG for a long time due to low-speed operation and spot market growth for economical efficiency of LNG carriers. In order to reduce the BOR, it is necessary to accurately calculate the BOR of the LNG in order to design an efficient cargo hold insulation system. In order to calculate the BOR, it is important to accurately calculate the amount of heat input into the cargo hold.

According to the prior art, the amount of heat input was calculated by inputting dimensions and physical property values to a fixed shape like a general LNG carrier beforehand in order to calculate the heat transfer of the cargo hold. Therefore, a fixed shape must be prepared for various shapes in advance, and in a fixed shape, there is a problem that it is very limited to consider a change in the draft of the ship and partial loading of the cargo hold.

Prior Art: Korea Publication No. 10-2011-0024501 (Published on March 30, 2011)

It is an object of the present invention to provide a method of controlling the amount of LNG BOR in a cargo hold capable of easily obtaining the amount of incoming calories and LNG BOR for a cargo hold having any shape, And to provide a method for calculating LNG BOR.

According to an aspect of the present invention, there is provided a method for calculating an LNG natural rate of vaporization (BOR) in a cargo hold, the method comprising the steps of: Dimensional modeling using a finite element method; Dividing the modeled cargo hold and the perimeter of the cargo hold into unit elements; Calculating the amount of heat input into the cargo hold by the computer system using the unit element; And computing the LNG BOR using the calorific value of the inflow, wherein the computer system is calculating the LNG BOR in the cargo hold.

In particular, the modeling step may include the steps of: the computer system modeling each of the plates constituting the cargo hold and the hull as surface elements; And modeling the space separated by the plates into a volume element.

In addition, the modeling may further include modeling the stiffener attached to the plates constituting the cargo hold and the hull by a fin element.

The unit element may include a first space, a second space, and a plate that separates the first space and the second space between the first space and the second space.

According to an embodiment of the present invention, the step of calculating the inflow heat quantity may further include a step of the computer system applying a heat transfer theory to the unit element to obtain a temperature distribution of the cargo hold and a peripheral portion of the cargo hold .

According to an embodiment of the present invention, the computer system further includes a step of receiving, after the modeling step, the physical property values for the face elements and the physical property values for the volume elements, The physical property for the volume element can be used in the step of calculating the input heat quantity.

In addition, the physical property for the surface element may include the thickness and the thermal conductivity coefficient of the plate modeled by the surface element.

In addition, the physical property for the volume element may include a convection coefficient of the substance present in the space modeled by the volume element.

In addition, the convection coefficient may be determined in consideration of the stiffener attached to the plate that is in contact with the modeled space.

In addition, the step of calculating the BOR may include the step of the computer system calculating the BOR using the calorific value of the inflow and the volume of the cargo hold.

According to the embodiment of the present invention, the cargo window and the peripheral portion of the cargo hold can be modeled in three dimensions using the finite element method, so that the calorific value of the cargo and the LNG BOR can be easily obtained for a cargo hold having any shape, It is possible to easily obtain the influent calorific value and the LNG BOR.

In addition, it is possible to calculate the inflow heat quantity at one time without calculating the inflow heat quantity by dividing the cross section and the longitudinal section by comparing with the case of two-dimensionally modeling the cargo hold and the peripheral portion of the cargo hold by three-dimensionally modeling, BOR can be accurately calculated for a cargo hold.

1 is a flowchart illustrating a method of calculating an LNG BOR in a cargo hold according to an embodiment of the present invention.
2 is a perspective view showing a cargo hold.
3 is a view showing a model of a cargo hold and a peripheral portion of the cargo hold.
Figure 4 is a diagram illustrating modeling of a portion of a cargo hold by a finite element method.
5 is a view showing the elements used when the cargo hold is modeled by the finite element method.
FIG. 6 is a diagram showing the heat transfer in a unit element of a model of a cargo hold and a periphery of a cargo hold by the finite element method. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

A method for calculating the LNG natural rate of vaporization (BOR) in a cargo hold according to an embodiment of the present invention will be described in detail with reference to the drawings. 1 is a flow diagram illustrating a method for calculating an LNG BOR in a cargo hold in accordance with an embodiment of the present invention implemented in a computer system.

The computer system is a concept including a PC, a mobile phone, and various digital electronic devices, and can be interpreted as including all the devices having a processor and a memory and executing programs to perform operations. The computer system may be provided with a program for performing the steps described later with reference to FIG. The computer system includes an input unit for inputting information so that a service related to the present invention can be performed, a display unit for displaying information related to the present invention, a database storing information related to the present invention, And a control unit for dividing the modeled cargo hold and the perimeter of the cargo hold into unit elements and calculating the LNG BOR based on the inflow amount into the cargo hold calculated using the divided unit elements.

A method of calculating the LNG BOR in a cargo hold executed in such a computer system will now be described with reference to FIG.

As shown in FIG. 1, in the embodiment of the present invention, the computer system models the cargo hold and the periphery of the cargo hold as finite elements, calculates the total calorific value flowing into the cargo hold, and calculates the BOR using the calorific value.

First, a method of modeling the cargo hold and the perimeter of the cargo hold in three dimensions using the finite element method will be described. In operation S110, the computer system models the periphery of the cargo hold and the cargo hold three-dimensionally using a finite element (S110).

Fig. 2 is a perspective view showing a cargo hold, and Fig. 3 is a view showing a model of a cargo hold and a peripheral portion of the cargo hold.

2 and 3, the cargo hold 240 is surrounded by the inner hull plate 210 and the inner hull plate 210 is surrounded by the hull outer plate 220. The cargo hold 240 is supported by the inner hull plate 210. The inner surface of the ship's inner panel 210 and the outer surface of the ship's outer panel 220 are spaced apart from each other by a predetermined space. Stiffeners 230 are installed toward the space. The upper portion of the outer shell 220 is in contact with the air, and the lower portion of the outer shell 220 is in contact with the water.

That is, the cargo hold and its periphery are composed of a plate forming the structure of the cargo hold or hull, a space defined by the plates, and a stiffener attached to the plate. Therefore, to model the cargo hold and the perimeter of the cargo hold using the finite element method, the plate is modeled as a surface element, the space is modeled as a volume element, and the stiffener is modeled as a fin element.

Figure 4 is a diagram illustrating modeling of a portion of a cargo hold by a finite element method. That is, as shown in FIG. 4, a plate as a structure of a cargo hold or hull is modeled as a surface element, a space defined by the plates is modeled as a volume element, and a stiffener attached to the plate is modeled as a fin element.

5 is a view showing the elements used when the cargo hold is modeled by the finite element method. As shown in FIG. 5, a surface element is defined as a polygon element having three or more finite number of nodes, and the physical properties include an area made of a polygon, a thickness of the plate, and a thermal conductivity coefficient of the plate. Then, the temperature at both surfaces of the plate is taken as an input / output value.

A volume element is defined as an element having a volume having four or more finite number of nodes. The physical properties are convection coefficients of gas or liquid in space. Then, one temperature in the space is taken as an input / output value. A fin element can be defined as one of the properties of a surface element. When modeling the perimeter of the cargo hold and the cargo hold, the fin element can be implemented to influence the convection coefficient of the space in contact with the plate to which the stiffener is attached, receiving the shape of the stiffeners.

Air and seawater, which are the peripheral part of the cargo hold, are treated as a space and modeled as a volumetric element to give a boundary condition as temperature.

Next, the computer system receives the property values of the elements that model the periphery of the cargo hold and the cargo hold (S120). That is, for a plate modeled as a surface element, an area made of a polygon, a thickness of the plate, and a thermal conductivity coefficient of the plate are input. For the space modeled by the volume element, a convection coefficient of the gas or liquid existing in the space is input. At this time, as described above, the portion for the stiffeners modeled with the fin elements can be determined in consideration of the stiffener in the convection coefficient of the space in contact with the plate to which the stiffener is attached.

Then, the computer system constructs a determinant for temperature (S130). For calculation of the heat transfer, the cargo hold and the periphery of the cargo hold can be divided into unit elements as shown in Fig. FIG. 6 is a diagram showing the heat transfer in a unit element of a model of a cargo hold and a periphery of a cargo hold by the finite element method. FIG. As shown in FIG. 6, the unit element may comprise a first space, a second space, and a plate existing between the first space and the second space.

Since the space has one temperature and the plate has two temperatures, one on each side of the plate, the unit element has a total of four temperatures. That is, as shown in FIG. 6, the unit element has the temperature T 0 of the first space, the temperatures T 1 and T 2 of the both sides of the plate, and the temperature T 3 of the second space.

Using the heat transfer theory, we can express the relation of four temperatures by four equations.

First, the amount of heat transferred in each step between the elements in the unit element is obtained as follows.

When the amount of heat transferred by the convection between the temperatures T 0 and T 1 is q 1 , q 1 is obtained as in Equation (1).

Figure pat00001

Here, A is the area of the plate, h 1 is the convection coefficient of the first space, T 0 is the temperature of the first space, and T 1 is the temperature of one side of the plate in contact with the first space.

Then, when the amount of heat transferred by conduction between the temperatures T 1 and T 2 is q 2 , q 2 is obtained as shown in Equation (2).

Figure pat00002

Where A is the cross-sectional length of the plate, k is the coefficient of conduction of the plate, t is the thickness of the plate, and T 1 and T 2 are the temperatures of both sides of the plate.

When the amount of heat transferred by the convection between the temperatures T 2 and T 3 is q 3 , q 3 is obtained as shown in Equation (3).

Figure pat00003

Here, A is the cross-sectional length of the plate, h 2 is the convection coefficient of the second space, T 2 is the temperature of one surface of the plate in contact with the second space, and T 3 is the temperature of the second space.

At this time, since the heat quantity q 1 transferred by the convection in the first space and the heat quantity q 2 transmitted by the conduction between the plates are the same, they can be expressed as shown in Equation (4) Since the transmitted heat quantity q 2 and the heat quantity q 3 transferred by convection in the second space are equal to each other,

Figure pat00004

Figure pat00005

Since the sum of the amounts of heat flowing in and out of the first space is 0, it can be expressed as Equation (6), and the total sum of the heat flowing in and out of the second space is 0,

Figure pat00006

Here, Σf (T i ) is the amount of heat transferred between the first space and the first space, excluding the plate between the first space and the second space.

Figure pat00007

Here, Σf (T j) is the amount of heat flow between the first space and a second space in contact with the plates and a second space other than the space between the plates.

Equations (4) to (7) are applied to a unit element, and then applied to the entire finite element model to express a plurality of equations. When a given temperature is input in a boundary condition,

Figure pat00008

Here, [K] is a matrix defined by geometric information and heat transfer coefficients of elements, {T} is a matrix representing temperature, and {C} represents a constant vector defined by boundary conditions and the like.

The computer system calculates the temperature using the determinant for temperature (S140).

At this time, the computer system can arbitrarily set the initial temperature to calculate the heat transfer coefficient, which is a function of the temperature. After the initial temperature is set, the temperature converged through the iteration until the temperature converges (S150) The temperature distribution and the heat input to the cargo hold are calculated for the periphery of the cargo hold (S160). The computer system calculates the BOR using the calorific value of the cargo hold and the volume of the cargo hold (S170).

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

210: Cargo hold
220: Hull
230: Stiffener

Claims (10)

CLAIMS What is claimed is: 1. A method for calculating an LNG natural rate of reclamation (BOR) in a cargo hold operating in a computer system,
Modeling the cargo hold and the periphery of the cargo hold in three dimensions using a finite element method;
Dividing the modeled cargo hold and the perimeter of the cargo hold into unit elements;
Calculating the amount of heat input into the cargo hold by the computer system using the unit element; And
Wherein the computer system calculates the LNG BOR using the calorific value of the incoming LNG. The method according to claim 1,
The modeling step
The computer system modeling each of the plates constituting the cargo hold and the hull by a surface element; And
Wherein the computer system includes modeling the space separated by the plates into a volume element. The method of claim 2,
Wherein the modeling step further comprises modeling a stiffener attached to the plates constituting the cargo hold and the hull, as a fin element, by the computer system. The method of claim 3,
Wherein the unit element comprises a first space, a second space, and a plate separating the first space and the second space between the first space and the second space. The method of claim 4,
The step of calculating the incoming calorie amount
Further comprising the computer system applying heat transfer theory to the unit element to obtain a temperature distribution of the cargo hold and a periphery of the cargo hold. The method of claim 3,
After the modeling step,
Further comprising the step of the computer system receiving physical property values for the surface elements and physical properties for the volume elements,
Wherein the physical property for the surface element and the physical property for the volume element are used in calculating the calorific value of the LNG BOR in the cargo hold. The method of claim 6,
Wherein the material properties for the face element include the thickness and thermal conductivity of the plate modeled by the face element. The method of claim 6,
Wherein the physical property for the volume element comprises a convection coefficient of a material present in the space modeled by the volume element. The method of claim 8,
Wherein said convection coefficient is determined in consideration of a stiffener attached to a plate in contact with said modeled space. The method according to claim 1,
The step of calculating the BOR
Wherein said computer system calculates said BOR using said calorific value and said volume of said cargo hold.
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101954599B1 (en) * 2018-12-03 2019-03-06 주식회사 바론시스템 Boiled-off gas collection monimoring system based on 3d modeling
KR101975275B1 (en) * 2018-12-19 2019-08-29 (주)건일엔지니어링 System for monitoring the recovery system of boiled-off gas
US20200158289A1 (en) * 2017-04-10 2020-05-21 Nippon Yusen Kabushiki Kaisha Tank state estimation method and tank state estimation program

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20110024501A (en) 2009-09-02 2011-03-09 삼성중공업 주식회사 Evaluation method for input of heat into cargo system

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20110024501A (en) 2009-09-02 2011-03-09 삼성중공업 주식회사 Evaluation method for input of heat into cargo system

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20200158289A1 (en) * 2017-04-10 2020-05-21 Nippon Yusen Kabushiki Kaisha Tank state estimation method and tank state estimation program
US11499679B2 (en) * 2017-04-10 2022-11-15 Nippon Yusen Kabushiki Kaisha Tank state estimation method and tank state estimation program
KR101954599B1 (en) * 2018-12-03 2019-03-06 주식회사 바론시스템 Boiled-off gas collection monimoring system based on 3d modeling
KR101975275B1 (en) * 2018-12-19 2019-08-29 (주)건일엔지니어링 System for monitoring the recovery system of boiled-off gas
WO2020130246A1 (en) * 2018-12-19 2020-06-25 (주)건일엔지니어링 Monitoring system for bog recovery system

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