Proper handling of boil-off gas (BOG) during normal operations as well as ship unloading significantly affects the efficiency of the operation and the safety of the whole gasification plant. Optimal operations of BOG compressors need to consider multiple aspects of plant safety and reduced power consumption, simultaneously satisfying all process requirements and constraints. However, due to the not-well-known characteristics of the involved dynamics, it is suspected that the BOG compressors are being operated in too great a capacity, unnecessarily consuming too much energy. A method for optimization of BOG compressor operation is proposed in this paper, which minimizes power consumption based on a mixed integer linear problem (MILP) formulation and refines the operation policies based on a safety analysis on the dynamics of the tank pressure. The proposed method is expected to be able to contribute to improving the efficiency of the whole liquefied natural gas (LNG) gasification plant operation and control.

Proper handling of boil-off gas (BOG) significantly affects the operational efficiency as well as the safety of the whole LNG gasification plant. Due to the not well-known inherent dynamics, it has been suspected that the BOG compressors are being operated at too much capacity, unnecessarily consuming too much energy. An empirical model is proposed for the estimation of the boil-off rate (BOR) in an LNG storage tank, based on the specification supplied by the LNG storage tank manufacturer. By using the BOR model, an optimal operation algorithm is proposed for a safe and energy-saving BOG compressor operation, which minimizes the power consumption while preparing against the potential failure of one of the operating compressors. Case study results indicate that the energy consumption could be reduced by a half of the conventional method, by increasing the tank pressure while the safety is maintained. The proposed method is expected to be able to contribute to improving the efficiency of the whole gasification plant operation and control without tempering the safety requirements.

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