Design of a boil-off natural gas reliquefaction control system for LNG carriers

Title
Design of a boil-off natural gas reliquefaction control system for LNG carriers
Authors
신영기이윤표
Keywords
Process control; LNG; BOG; Reliquefaction; Object orientation; Dynamic modeling; Heat exchanger; Cold box; Brayton cycle
Issue Date
2009-01
Publisher
Applied energy
Citation
VOL 86, NO 1, 37-44
Abstract
Onboard boil-off gas (BOG) reliquefaction is a new technology that liquefies BOG and returns it to the cargo tanks instead of burning it off during a voyage. For the commercial development of this technology, an object-oriented dynamic simulation is presented which facilitates the design of the plant and control system for the thermal process. A reliquefaction process based on the reverse Brayton cycle has been designed, and its static thermodynamic states at the design BOG load are presented. To make the cycle work for any BOG load, an idea was sought that would achieve a heat balance with the work extracted by the expander. Dynamic simulations were conducted for all operating modes, including start-up and idle. It was found that the expander exit temperature is the key process variable for control and that the process control works successfully when three actuators are activated in three different BOG load regimes. The study also shows that control of the separator pressure to keep the vapor fraction at the throttle valve exit as low as possible is an efficient method for purging nitrogen from BOG.
URI
http://pubs.kist.re.kr/handle/201004/33275
ISSN
0306-2619
Appears in Collections:
KIST Publication > Article
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