Study On Liquefaction Process Of Sea - Based Natural Gas

Currently, with the development of offshore oil and gas exploration technology, a growing number of offshore natural gas resources is found. In order to use the offshore natural gas resources economically, floating LNG technology, usually abbreviated to FLNG, was increasingly studied by domestic and international oil and gas development companies. Offshore natural gas liquefaction process, as the key of LNG technology, shows the significant influence on the utilization of offshore natural gas.In this paper, on the basis of reference to the onshore liquefaction process, two offshore natural gas liquefaction process scheme were studied for the specific gas originated from gas field of South China Sea. One is the dual nitrogen expander process with CO2pre-cooling, the other one is CO2pre-cooling and utilizing cold energy of liquid nitrogen gasification and dual nitrogen expander process. HYSYS software was used to simulate and calculate of the two liquefaction processes. The results show that, the CO2pre-cooling and utilizing cold energy of liquid nitrogen gasification and dual nitrogen expander process is suit for the offshore natural gas liquefaction.Analyzed the influence of boost pressure of liquid nitrogen, pre-cooling temperature of CO2, the first expand pressure of nitrogen and parameters of CO2pre-cooling cycle on liquid nitrogen flow, CO2flow, LNG flow and unit energy consumption. Defined the boost pressure of liquid nitrogen at5000kPa, pre-cooling temperature of CO2at237.15K. With the help of HYSYS optimization module, optimized the first expand pressure of nitrogen and the process parameters of CO2pre-cooling cycle. When the first expand pressure of nitrogen is790.28kPa, the pressure of CO2is5741.07kPa, throttling pressure of CO2is1193.00kPa and the first compression pressure of CO2is2412.11kPa, the process minimum unit energy consumption is6.97kW/kmol.In order to study the liquefaction process adaptability, this thesis analyzed the influence of feed gas pressure, temperature, composition and flow on liquid nitrogen flow, CO2flow, LNG flow and unit energy consumption. The results show that within the scope of study, the process has better adaptability. At the same time, the analysis and model selection of compressor, distillation column and other equipment were given.