(258c) Dynamic Simulation Studies for Optimal Design and Operation of an LNG Liquefaction Process

Mixed refrigeration cycle (MRC) natural gas liquefaction technology is wildly used for liquefied natural gas (LNG) production due to its unique advantages. Most of the research on LNG liquefaction process were based on steady-state simulation. Only a few addressed the dynamic performance of mixed refrigerant LNG processes. Thus, the main purpose of this study is to study the dynamic behaviors of mixed-refrigerant LNG liquefaction processes. The developed methodology in this paper contains three major tasks: steady state simulation model development, dynamic simulation with control structures to handle the disturbances and then disturbances were added to investigate behaviors of the process. In the first stage for a real LNG liquefaction process, a steady state simulation is conducted. In the second stage, the dynamic simulation which was based on the results of steady-state simulation was conducted. The results of steady-state simulation and dynamic simulation compared to keep the consistency. In the third stage, based on the dynamic model, various variations from natural gas temperature, pressure, flow rate, composition are introduced as disturbances to study the dynamic responses of the studied process. The dynamic responses of LNG temperature and compressor duty are the major performance evaluation criteria under these disturbances, from which the best control strategies are investigated to maintain the stable operation of the mixed-refrigerant liquefaction process. The simulation result showed that, compressor duty takes more time to stable than the LNG temperature. The variation of feed gas temperature has little influence on the process. The feed gas flow rate and methane composition have more effect than feed gas pressure and temperature effect. The feed gas composition has heat transfer performance and the flow rate affect. The feed gas pressure affects the process in two aspects: one is heat transfer performance and another one is the flow rate of natural gas.