A Method for Optimal Operation of BOG Compressors in a LNG Gasification Plant

Abstract

A LNG (liquefied natural gas) gasification plant is mainly composed of LNG storage tanks, LNG pumps, LNG vaporizers, and the gas pipelines. The plant receives LNG from a carrier, and stores it in a cryogenic liquid state. The liquid temperature is approximately −160ºC and the pressure is slightly above atmosphere in LNG storage tanks. Because of heat transfer from surroundings, part of LNG in the tank is continuously evaporated as boil off gas (BOG), which should be removed by compressors in order to maintain the tank pressure within a safe range. An algorithm for optimal operation of BOG compressors in a LNG gasification plant is proposed, which uses an empirical BOR (boil off rate) model, a MILP (mixed integer linear programming) formulation, and a simplified dynamic tank model. Given the values for a set of process state variables, the proposed algorithm generates an optimal operation schedule for BOG compressors, which minimizes the power consumption while preparing against the potential failure of one of the operating compressors. The performance of the proposed method is compared with that of the conventional method in terms of safety and energy. Given the values for a set of process state variables, the proposed algorithm generates an optimal operation schedule for BOG compressors, which minimizes the power consumption while preparing against the potential failure of one of the operating compressors.