Liquid cargo hold subdivision method for reducing oscillation of FLNG cargo hold

Abstract

According to the liquid cargo tank subdivision method for reducing the oscillation of the FLNG cargo tanks, multiple rows of I-shaped tanks, multiple rows of II-shaped tanks and multiple rows of III-shaped tanks are arranged from the bow to the stern of a liquid cargo tank ship, the number of each row of I-shaped tanks is at least three, the number of each row of II-shaped tanks is at least two, the distance between every two adjacent I-shaped tanks and the distance between every two adjacent II-shaped tanks are not smaller than 600 mm, and the distance between every two adjacent III-shaped tanks is not smaller than 600 mm. And at least one III-type cabin is arranged in each row. The relationship of the cabin capacities of the three is as follows: 98% Ca * n1 = 98% Cb, and 98% Cb * 2 = 98% Cc. LNG liquefied by the upper module firstly enters the I-type cabins, after two adjacent I-type cabins are filled with the LNG, the LNG is moved into the II-type cabins, after two adjacent II-type cabins are filled with the LNG, the LNG is moved into the III-type cabin, and circulation is conducted in sequence till the liquid cargo tanks of the whole ship are filled with the LNG. According to the invention, the liquid cargo tank sloshing problem faced by the original FLNG is converted into the I-type tank sloshing problem. In the subdivision mode, the II-type cabins and the III-type cabins only have two states of full cabins and empty cabins, so that the shaking phenomenon does not exist.

Description

Technical Field

[0001] The present invention belongs to the field of offshore FLNG ship design and construction, and in particular relates to a liquid cargo tank subdivision method for reducing FLNG cargo tank sloshing. Background Art

[0002] Since the 21st century, with the development of economy and the improvement of people's environmental awareness, clean energy has been increasingly favored by people in various countries. As a hydrocarbon, natural gas has the advantages of high combustion calorific value, clean and pollution-free, and wide application. In recent years, its development momentum has been extremely rapid.

[0003] At present, the development of offshore LNG is mainly based on the FLNG model, which is a floating equipment that integrates offshore natural gas extraction, liquefaction, storage and transmission.

[0004] Sloshing load is one of the main design loads of LNG cargo tanks. In order to minimize the sloshing of LNG in the cargo tanks, the loading rate of LNG carriers is strictly limited to ≤10% or ≥70%.

[0005] However, for FLNG, since it is a natural gas liquefaction plant, the LNG it produces is stored in the FLNG cargo tank at any time. Therefore, the cargo tank loading rate needs to meet 0%~98%. This causes the sloshing load of the FLNG cargo tank to be much greater than that of the LNG transport ship, which in turn leads to a significant increase in the cost of the FLNG cargo tank and even brings safety hazards, which seriously restricts the development of FLNG. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a liquid cargo tank subdivision method for reducing FLNG cargo tank sloshing based on the Mark III membrane tank cargo containment system (liquid cargo tank). The technical solution adopted is: A liquid cargo tank subdivision method for reducing the sloshing of an FLNG cargo tank, wherein multiple rows of type I tanks, multiple rows of type II tanks and multiple rows of type III tanks are arranged from the bow to the stern of a liquid cargo tank ship, the number of type I tanks in each row is at least three, the double-hull ballast tank width of the type I tank is 2m to 4m, the spacing between adjacent type I tanks is not less than 600mm, the spacing of structural members is between 400mm and 800mm, and the inherent sloshing period of the type I tank is far away from the hull rolling period.

[0007] There shall be at least two Type II tanks in each row. The distance between adjacent Type II tanks shall not be less than 600mm. The distance between structural members shall be between 400mm and 800mm. The inherent sloshing period of Type II tanks shall be far away from the rolling period of the hull.

[0008] There shall be at least one Type III tank in each row, and the width of the double-hull ballast tank of Type III tank shall be 2m to 4m.

[0009] The relationship between the three cabin capacities is: 98%Ca×n1=98%Cb.

[0010] 98%Cb×2=98%Cc.

[0011] Where Ca is the capacity of type I tank, Cb is the capacity of type II tank, Cc is the capacity of type III tank, and n1 is the number of type I tanks minus 1.

[0012] The above-mentioned method of liquid cargo tank subdivision for reducing FLNG cargo tank sloshing, further, the inherent sloshing period of Type I tank is:

[0013] Here, n is 1.

[0014] The above-mentioned liquid cargo tank subdivision method for reducing the swaying of the FLNG cargo tank, further, is provided along the length direction of the liquid cargo tank ship, from the bow to the stern, with one row of type I tanks, two rows of type II tanks, and the rest are all type III tanks, each row of type I tanks is provided with three type I tanks, each row of type II tanks is provided with two type II tanks, and each row of type III tanks is provided with one type III tank.

[0015] The above-mentioned method of subdividing liquid cargo tanks to reduce the swaying of FLNG cargo tanks further comprises that the LNG liquefied by the upper module first enters the Type I tank, and in the process of the Type I tank changing from an empty tank to a full tank, the hull is leveled by the ballast water tank on the other side.

[0016] When the first Type I tank is full, LNG enters the second Type I tank. When the second Type I tank is full, LNG enters the third Type I tank. At this time, the LNG in the first Type I tank and the second Type I tank enters the first Type II tank.

[0017] When the third Type I tank is full, LNG enters the second Type I tank. When the second Type I tank is full, LNG enters the first Type I tank. At the same time, LNG in the third Type I tank and the second Type I tank enters the second Type II tank.

[0018] When the second type II tank is full, the LNG in the first type II tank and the second type II tank enters the first type III tank.

[0019] The cycle continues until the entire cargo tank of the ship is filled with LNG.

[0020] In the above-mentioned method for subdividing liquid cargo tanks to reduce sloshing of FLNG cargo tanks, further, the number of type I tanks is 3, and n1=2.

[0021] The beneficial effects of the present invention are: The present invention transforms the sloshing problem of liquid cargo tanks originally faced by FLNG into the sloshing problem of Type I tanks. Because in the compartment division method of the present invention, Type II tanks and Type III tanks have only two states: full tank and empty tank, and there is no sloshing phenomenon.

[0022] The sloshing problem of Type I tanks is solved by a new long strip Type I tank. The width of the tank in the ship width direction and the length of the tank in the ship length direction are selected according to the hull itself and the structural form. Compared with the traditional liquid cargo tank, it is smaller, shortening the LNG sloshing distance and thus reducing the sloshing load. At the same time, the sloshing natural period of the Type I tank and the transverse / longitudinal period of the hull are checked, and the periodic resonance is avoided, thereby greatly reducing the sloshing load of the Type I tank.

[0023] The present invention solves the sloshing problem of FLNG cargo tanks through innovative Type I tanks and a new compartment scheme. Type II and Type III tanks, the two main LNG cargo tanks, completely avoid sloshing. Type I tanks, as transition tanks, also have significantly lower sloshing loads than traditional FLNG. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a top view of the liquid cargo tank of the present invention; Figure 2 This is a cross-sectional view of cabin A; Figure 3 This is a cross-sectional view of cabin B; Figure 4 This is a cross-sectional view of cabin C; Figure 5~Figure 10 This is a schematic diagram of the process of LNG entering the cargo tank; Among them: 1-Type I cabin, 11-1 Type I cabin, 12-2 Type I cabin, 13-3 Type I cabin, 2-Type II cabin, 21-1 Type II cabin, 22-2 Type II cabin, 3-Type III cabin, 31-1 Type III cabin, 32-2 Type III cabin, 33-3 Type III cabin, 34-4 Type III cabin. DETAILED DESCRIPTION

[0025] The present invention is further described by taking a certain FLNG as an example in conjunction with the accompanying drawings.

[0026] A method for subdividing a liquid cargo tank to reduce the sloshing of a FLNG cargo tank. The Type I tank is a new narrow and long LNG tank, and its width is much smaller than the ship width and the traditional LNG tank. Therefore, the LNG sloshing distance in the tank is much smaller, and the sloshing load is greatly reduced. However, the smaller the width is, the better. Under the condition of meeting the requirements, a larger Type I tank width can enable it to carry more LNG, thereby reducing the number of Type I tanks, and then reducing the equipment such as transshipment and ventilation of each Type I tank, reducing the total cost. However, in any case, in order to meet the requirements of the subdivision scheme described in the present invention, the number of Type I tanks cannot be less than 3.

[0027] The width of Type I tank is initially determined by the ship width and hull structure. The details are as follows: Ba=(Bs-By×2) / Na-Cons, unit: mm.

[0028] Among them, Ba is the width of type I tank, Bs is the ship width, that is, the hull width, By is the width of one side of the ballast tank, Na is the number of type I tanks, which is 3 in this example, and Cons is a constant with a value between 300mm and 600mm.

[0029] In this example, Bs is 60000mm, By is 3500mm, Na is 3, and Cons is 467mm. The calculated value of Ba is 17200mm.

[0030] The smaller the width of the Type I tank, the shorter the distance that LNG sways horizontally in the Type I tank, and the smaller the load caused by the sloshing. However, if the width of the Type I tank is too small, the number of liquid cargo tanks will increase, and the number of corresponding supporting service equipment will also need to increase, which will increase the cost. A solution with three Type I tanks is as follows: Figure 1 The number of Type I cabins may be greater than 3, which are all within the protection scope of the present invention.

[0031] After the width of the Type I tank is initially determined, it is necessary to check the width. The purpose of this check is to ensure that the transverse natural sloshing period of the Type I tank and the transverse sloshing period of the hull do not overlap, so as to avoid the occurrence of resonance.

[0032] Furthermore, the lateral natural sloshing period of the Type I tank is calculated by the following formula [1]:

[0033] Where n is 1[2]. In this example, the calculated result of Tn is 12.7s, which is quite different from the inherent sloshing period of FLNG and will not cause resonance.

[0034] [1]: Faltinsen OM, Timokha A N. Sloshing[M]. Cambridge University Press,32Avenue of the Americas, New York, NY 20013-2473, USA, 2009. [2]: ZHAO Wen-hua, YANG Jian-min, HU Zhi-qiang, etal. Coupling between roll motions of an FLNG vessel and internals loshing[J]. Offshore Mechanics and Arctic Engineering, 2014, 136(2): 65-76. The length of the tank is determined according to the tank capacity, that is, 98%Ca×n1=98%Cb.

[0035] In this example, the width of the Type I tank has been determined as Ba=17200mm, and n1 is 2, which is 98% of the Type II tank capacity, which is twice the 98% of the Type I tank capacity. The depth of the Type I tank is the same as that of the Type II tank, so the length of the Type I tank is La=Bca / Db / 2 / Ba.

[0036] Where La is the length of cabin A, Bca is 98% of the capacity of cabin B, and Db is the depth of the Type II cabin, which is the same as the depth of the Type I cabin. In this example, Bca is 20,000 cubic meters, Db is 26,000 mm, and La is calculated to be 22,360 mm.

[0037] Type II tank is a typical LNG ship or FLNG double-row liquid cargo tank layout, symmetrical along the longitudinal section of the ship, and the tank width is as follows: Bb = (Bs-By×2) / Nb-Cons, unit: mm.

[0038] In this example, Bs is 60000mm, By is 3500mm, Nb is 2, and Cons is 500mm. The calculated result of Ba is 26000mm.

[0039] The tank length is determined based on the capacity of the Type III tank and the conditions of the Type II tank, satisfying 98%Cb×2=98%Cc. The details are as follows: Lb=Cca / Dc / 2 / Bb.

[0040] Where Lb is the length of cabin B, Cca is 98% of cabin C capacity, and Dc is the depth of Type III cabin, which is the same as the depth of Type II cabin. In this example, Cca is 40,000 cubic meters, Dc is 26,000 mm, and Lb is calculated to be 29,590 mm.

[0041] Type III tanks are typical LNG carriers or FLNG single-row cargo tanks, which are symmetrical along the longitudinal section of the midship. The tank width is determined by the following formula: Bc =Bs-By×2, unit: mm.

[0042] In this example, Bs is 60000mm, By is 3500mm, and the calculated Bc is 53000mm.

[0043] like Figure 1 and Figure 4 As shown, the capacity of Type III cabin must ensure 98%Cb×2=98%Cc, where Cb is the capacity of Type II cabin and Cc is the capacity of Type III cabin.

[0044] like Figures 5 to 10 As shown, natural gas becomes LNG after being liquefied by the upper module. LNG first enters Type I tank No. 1. In the process of Type I tank No. 1 changing from empty to full, the hull is leveled through the ballast water tank on the other side.

[0045] When the No. 1 Type I tank is fully loaded, LNG enters the No. 2 Type I tank, which is located in the middle of the ship and does not need to be adjusted. When the No. 2 Type I tank is fully loaded, LNG enters the No. 3 Type I tank, and at the same time, the LNG in the No. 1 Type I tank and the No. 2 Type I tank begins to be transferred to the No. 1 Type II tank. Because 98%Ca×n1=98%Cb, for the design of 3 Type I tanks, n1=2, so the LNG in the No. 1 Type I tank and the No. 2 Type I tank can fill the No. 1 Type II tank. Therefore, when all the LNG in the No. 1 Type I tank and the No. 2 Type I tank enters the No. 1 Type II tank, the No. 1 Type II tank is in a fully loaded state without sloshing.

[0046] After Type I tank No. 3 is fully loaded, the LNG in Type I tank No. 1 and Type I tank No. 2 has entered Type II tank No. 1, and now LNG begins to enter Type I tank No. 2.

[0047] When the No. 2 Type I tank is fully loaded again, LNG enters the No. 1 Type I tank, and the LNG in the No. 2 Type I tank and the No. 3 Type I tank is transferred to the No. 2 Type II tank. Similarly, because 98%Ca×n1=98%Cb, the No. 2 Type II tank will also be fully loaded, and no sloshing will occur. At this time, the No. 1 Type II tank and the No. 2 Type II tank are both fully loaded, and the LNG in the No. 1 Type II tank and the No. 2 Type II tank is transferred to the No. 1 Type III tank. Because 98%Cb×2=98%Cc, the No. 1 Type III tank will also be full, and no sloshing will occur.

[0048] Continue to cycle the above process to fill other Type III tanks.

[0049] At this point, the operation of the liquid cargo tank form and subdivision scheme for reducing the sloshing of the FLNG cargo tank of the present invention is completed.

Claims

1. A method for subdividing a liquid cargo tank to reduce sloshing of a FLNG cargo tank, characterized in that: From the bow to the stern of the tank ship, there are multiple rows of Type I tanks, multiple rows of Type II tanks and multiple rows of Type III tanks. The number of Type I tanks in each row is at least three. The width of the double-hull ballast tank of Type I tank is 2m to 4m. The spacing between adjacent Type I tanks is not less than 600mm. The distance between structural members is between 400mm and 800mm. The natural sloshing period of Type I tanks should be far away from the rolling period of the hull. There should be at least two Type II tanks in each row. The distance between adjacent Type II tanks should be no less than 600mm. The distance between structural members should be between 400mm and 800mm. The natural sloshing period of Type II tanks should be far away from the rolling period of the ship. There shall be at least one Type III tank in each row, and the width of the double-hull ballast tank of Type III tank shall be 2m to 4m; The relationship between the three cabin capacities is: 98%Ca×n1=98%Cb, 98%Cb×2=98%Cc, Where Ca is the capacity of type I tank, Cb is the capacity of type II tank, Cc is the capacity of type III tank, and n1 is the number of type I tanks minus 1.

2. A method for subdividing a liquid cargo tank to reduce sloshing of a FLNG cargo tank according to claim 1, characterized in that: The inherent sloshing period of type I tank is:

3. Among them, n is 1.

4. A method for subdividing a liquid cargo tank to reduce sloshing of a FLNG cargo tank according to claim 1, characterized in that: Along the length direction of the liquid cargo tank ship, from the bow to the stern, there are one row of Type I tanks, two rows of Type II tanks, and the rest are all Type III tanks. Each row of Type I tanks is equipped with three Type I tanks, each row of Type II tanks is equipped with two Type II tanks, and each row of Type III tanks is equipped with one Type III tank.

5. A method for subdividing a liquid cargo tank to reduce sloshing of a FLNG cargo tank according to claim 3, characterized in that: The LNG liquefied by the upper module first enters the Type I tank. During the process of the Type I tank changing from empty to full, the hull is leveled through the ballast water tank on the other side. When the first Type I tank is full, LNG enters the second Type I tank. When the second Type I tank is full, LNG enters the third Type I tank. At this time, the LNG in the first Type I tank and the second Type I tank enters the first Type II tank. When the third Type I tank is full, LNG enters the second Type I tank. When the second Type I tank is full, LNG enters the first Type I tank. At the same time, LNG in the third Type I tank and the second Type I tank enters the second Type II tank. When the second type II tank is full, the LNG in the first type II tank and the second type II tank enters the first type III tank; The cycle continues until the entire cargo tank of the ship is filled with LNG.

6. A method for subdividing a liquid cargo tank to reduce sloshing of a FLNG cargo tank according to claim 1, characterized in that: The number of Type I cabins is 3, n1=2.

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