Process Design and Optimization of Natural Gas Liquefaction Processes

Abstract

The design of liquefaction cycles requires detailed investigation for heat exchange between natural gas stream and refrigerant fluid streams to minimize shaft power consumed in the compressors of refrigeration cycles. Heat Integration study is essential for evaluating the effectiveness of heat exchange in the liquefaction cycles, as this conceptual technique provides graphical indication for the constrained part of heat exchange, with which systematic design guidelines for improving the efficiency of liquefaction cycles can be obtained. Recently, great attention has been paid to the design and optimization of natural gas liquefaction cycles for FPSO (Floating Production Storage and Offloading) applications. In this study, N₂ expander cycles and SMR (Single mixed refrigerant) cycles have been studied as the compactness of the cycle is very high, which is one of key criteria for the selection of liquefaction technology in LNG (Natural Liquefied Gas) FPSO applications. Investigation has been made to minimize shaftpower required for the cycles. Optimization framework has been developed such that GA (genetic algorithm) optimizer is interacted with process simulators, which avoids considerable efforts for building process model and simulating it within the optimizer. Case study will be presented to discuss how the new optimization strategy is effectively applied in the design of liquefaction cycles.