Optimization of FLNG liquefaction process used for the development of deepwater gas field in the South China Sea

Liquefaction process of natural gas is one of the key technologies of offshore Floating Liquid Natural Gas (FLNG), and at present, there isn't any standard dedicated to the design of FLNG liquefaction process at home and abroad, so it is necessary to study the liquefaction process and optimization method for FLNG. In the paper, a certain deepwater gas field in the South China Sea was taken as the research object. According to the characteristics of offshore FLNG and the investigation on liquefaction processes in foreign FLNG projects, the selection principles and optimization methods of FLNG liquefaction processes were proposed, and accordingly six liquefaction processes that may be suitable for the target gas field were screened out. Then, these six liquefaction processes were compared comprehensively from the aspects of compression power, cooling load and main equipment. And the liquefaction process of propane pre-cooling and dual nitrogen expansion sub-cooling was preliminarily selected as the liquefaction process of the deepwater gas field in the South China Sea, and its offshore adaptability was verified using software dynamic simulation and tests. The software dynamic simulation results are consistent with the experimental results, indicating the accuracy of the dynamic model and the feasibility of applying the dynamic simulation to predict the experimental results. It is revealed that the liquefaction process of propane pre-cooling and dual nitrogen expansion sub-cooling is better in dynamic performance and offshore adaptability. And it was ultimately selected as the FLNG liquefaction process of target gas field. This optimization method provides the technical support and reference for the selection of liquefaction processes in other FLNG projects.