Optimal module layout for a generic offshore LNG liquefaction process of LNG-FPSO

Abstract

Constraints related to offshore projects such as liquefied natural gas floating, production, storage, and offloading (LNG-FPSO) have been considered more important than those in onshore areas because topside process systems are located on the limited hull space. Therefore, the layout of the LNG-FPSO topside equipment shall be designed as multi-deck instead of single-deck, and this layout shall be optimised in order to reduce the area occupied by the topside equipment at the front-end engineering design stage. In this study, an optimal module layout for a generic offshore LNG liquefaction process system is derived, considering the deck penetration of long-length equipment across several decks. By considering the above, we formulate a mathematical model, which consists of 1652 unknowns, 1624 equality constraints, and 1048 inequality constraints. This mathematical model can be regarded as the optimisation problem, in which the number of unknowns is larger than the total number of equality constraints and given variables. To obtain the optimal layout, the minimisation of the total layout cost was defined as an objective function. The optimal module layout was then obtained using a mixed integer nonlinear programming.