Studies On Floating LNG Pretreatment Technology Of Liwan Gas Field In The South China Sea

LNG Floating Production Storage and Offloading Unit (called LNG-FPSO or FLNG Technology for short), can flexibly adapt the production status of offshore gas field, and is especially suitable for the development of in-shore and deep-shore gas field. Natural gas purification is the primary link of this technology, and plays a decisive role in normal operation of the whole unit. At the present time, onshore natural gas purification technology is very mature. However, due to the restriction of special marine operating environment, the process and equipment design of floating LNG purification technology is very different from that of onshore technology. So, it is of great importance to study on the design of floating LNG purification technical scheme according to the gas source and the sea conditions.In this paper, based on the experience of onshore purification technology and with the acid gas removal process and column as the main content, floating LNG acid gas removal technical scheme of Liwan gas field in the South China Sea is determined. Firstly, according to the gas source and the sea conditions of Liwan gas field, several conventional processes of removing acid gas are summarized and compared, and mixed MDEA and DEA acid gas removal process for the Liwan gas field are chosen. The model of the most important equipment of the process, absorption and desorption columns, are selected, and the key process parameters of column are initially determined. The simulation analysis of acid gas removal process is completed, and the recommended ranges of key process parameters are given. Meanwhile, all the combined plans of the parameters are listed, and adopting the method of five-factor fuzzy industry evaluation, all the combined plans are comprehensively assessed, and the optimal process parameters are selected. According to the optimal process parameters, the structure design of absorption column is made. Through researches on the stress and strain of the column under different inclination and different operating conditions, the reliability of column structure design is analyzed. Based on the above analysis, Acid gas removal optimization technology of floating LNG unit is built. Besides, other impurities (such as, water, heavy hydrocarbon, mercury, aromatic hydrocarbon, nitrogen and so on) purification technology are comprehensively analyzed, and the purification technical methods of these impurities are primarily selected. Finally, according to the the gas source and the sea conditions of Liwan gas field and using above technology, floating LNG pretreatment technical scheme of Liwan gas field is determined.