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Research Papers: Materials Technology

Liquid Sloshing Suppression for Three-Phase Separators Installed on Floating Production Unit

[+] Author and Article Information
Kang Cen

School of Civil Engineering and Architecture,
Southwest Petroleum University,
Chengdu 610500, Sichuan, China
e-mail: cenkangxt@126.com

Bin Song

School of Civil Engineering and Architecture,
Southwest Petroleum University,
Chengdu 610500, Sichuan, China
e-mail: 201621000803@stu.swpu.edu.cn

Changjun Li

School of Petroleum Engineering,
Southwest Petroleum University,
Chengdu 610500, Sichuan, China
e-mail: lichangjunemail@sina.com

Min Jia

School of Civil Engineering and Architecture,
Southwest Petroleum University,
Chengdu 610500, Sichuan, China
e-mail: 201522000331@stu.swpu.edu.cn

1Corresponding authors.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received January 16, 2017; final manuscript received March 14, 2018; published online April 19, 2018. Assoc. Editor: Ould el Moctar.

J. Offshore Mech. Arct. Eng 140(4), 041403 (Apr 19, 2018) (15 pages) Paper No: OMAE-17-1010; doi: 10.1115/1.4039719 History: Received January 16, 2017; Revised March 14, 2018

In this study, a computational fluid dynamics model based on the volume of fluid (VOF) method is developed to simulate the dynamic sloshing response to external excitations. The modal analysis model based on the linear potential theory is established to predict natural sloshing frequencies and the corresponding mode shapes in three-phase separators. In addition, the effects of separator location, length-to-diameter ratio, oil/water level, porosity, and spacing of perforated baffles on the sloshing response are evaluated quantitatively. Furthermore, comprehensive approaches are proposed to mitigate the sloshing, like enhancing viscous damping effect, reducing the intensity of external excitation sources, and keeping away from the resonant frequencies. Finally, a practical application is carried out to display the optimal design of a three-phase separator. The results show that three-phase separators should be located as close as possible to the center of rotation (COR) of the floating production units (FPU). The length-to-diameter ratio is recommended to be no greater than three. Once the fluids can be separated to reach their respective interfaces, the liquid level should be increased as high as possible, whereas the water level should be lowered as far as possible. There is an almost inversely linear relationship between the antisloshing performance of a perforated baffle and its porosity. The antisloshing performance is attenuated rapidly when the spacing distance of a pair of baffles exceeds a specific range. This research extends the existing scope of sloshing suppression approaches and provides useful guidance in the design of FPU-based three-phase separators.

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Figures

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Fig. 1

Moving reference frame for the FPU-based separator

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Fig. 2

Relative elevation of free surface at the left wall of the container

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Fig. 3

Pressure versus time histories at the monitoring point A

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Fig. 4

First three modes in the container: (a) first mode shape, (b) second mode shape, and (c) third mode shape

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Fig. 5

Phase distribution of the fluids inside the separator vessel

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Fig. 6

Assumed positions for vessel placement on the FPU

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Fig. 7

Computational grids

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Fig. 8

Relative displacement versus time histories at the same monitoring point for various grid cases

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Fig. 9

Effect of separator location on the sloshing response: (a) relative displacement at the oil/gas interface along the longitudinal placement, (b) relative displacement at the oil/gas interface along the transversal placement, and (c) increment rate of the maximum displacement peak and the maximum vertical acceleration

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Fig. 10

Effect of vessel's L/D on the sloshing response: (a) relative displacement at the oil/gas interface, (b) dependence of the increment rate of the maximum displacement peak and the first natural sloshing frequency on the L/D, and (c) first sloshing mode shape for a separator vessel

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Fig. 11

Effect of liquid level on the sloshing response: (a) relative displacement at the oil/gas interface and (b) dependence of the increment rate of the maximum displacement peak and the lowest natural sloshing frequency on the hL/D

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Fig. 12

Effect of depth ratio of water layer to oil layer on the sloshing response: (a) relative displacement at the oil/gas interface, (b) relative displacement at the oil/water interface, and (c) maximum relative displacement peak

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Fig. 13

Effect of baffle porosity on the sloshing response: (a) relative displacement at the oil/gas interface and (b) antisloshing performance of baffles with various porosities

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Fig. 14

Locations of two perforated baffles

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Fig. 15

Effect of baffle spacing on the sloshing response: (a) relative displacement at the oil/gas interface for baffles with a fixed 80% opening area and (b) antisloshing performance of baffles with various spacing distances and porosities

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Fig. 16

Separator position on the FPSO

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Fig. 18

Water spilling over the weir into the oil sump: (a) t = 24.75 s and (b) t = 35.75 s

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Fig. 20

Liquid sloshing at different time: (a) t = 24.75 s, (b) t = 30.25 s, (c) t = 35.75 s, and (d) t = 41.25 s

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Fig. 21

Flow pathlines at t=35.75 s: (a) oil phase and (b) water phase

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