MILP-based optimization of compressor operation for boil-off gas handling in LNG storage tanks

Abstract

One important challenge in liquefied natural gas (LNG) supply chain is that of improving its power efficiency by reducing/minimizing the cost/spending of its power consumption. Such consumption is generally dominated by (i) LNG trains processing stage and (ii) boil-off gas (BOG) handling in storage tanks. In particular, the large power utilization in these two operational stages is mainly consumed by several compressors that are working at all times during LNG production and storage stages. To improve its power efficiency, this paper proposes a method to evaluate/determine the optimal number of compressors that are required by the BOG handling stage in the LNG storage tanks. The proposed method is essentially based on the use of mixed-integer linear programming (MILP) framework to determine the optimal number and duty cycle of compressors operation that will minimize the LNG power consumption while at the same time maintains the safety of the storage tanks and the overall LNG plant operation. In the proposed MILP, the objective function consists of the total power usage level of all compressors whereas the constraints include the operational and load constraints of the LNG plant. Simulation results are presented to illustrate the effectiveness of the proposed method.