FLNG Expansion Refrigeration Natural Gas Liquefaction Process Research

Natural gas is one of the three pillars of the world’s primary energy,facing the growing shortage of land oil and gas resources,various marine countries have strengthened the exploitation of ocean oil and gas resources.In China,with the pace of the development of oil and gas resources in the South China Sea is accelerating,in the future,FLNG will be an indispensable equipment in the development of the South China Sea,it is of great significance for the deep-water development of our country to carry out the research on the FLNG related technologies.Natural gas liquefaction technology is one of the core technologies in FLNG,this paper focuses on supplying the FLNG nitrogen expansion process and improving the comprehensive evaluation process of FLNG natural gas liquefaction process.By investigation and demonstration,the N2-CH4 expansion process were introduced,then by means of the methods such as structural optimization,parameter optimization,energy analysis and fuzzy evaluation,a series of studies were completed.First of all,this paper outlined the backgrounds and the significances of the study,the researches and the summaries of natural gas liquefaction technology at home and abroad,especially the FLNG nitrogen expansion liquefaction technology,were investigated and summarized.Through the elaborating of thermal physical properties calculation of natural gas and refrigerants,the P-R equation was chosen as the calculation equation of gas-liquid phase equilibrium,and the LKP equation was used as the calculation equation of enthalpy and entropy.Secondly,in order to reduce energy consumption of the N2-CH4 expansion process,the process was improved,the CO2 precooling N2-CH4 expansion process was proposed.The improved process was simulated and the parameters of the process were analyzed by HYSYS software,then the optimization directions of these parameters were determined and the corresponding production suggestions were given.Then,by combining with the results of parameter analysis,5 parameters were selected as the optimization variables,minimum total power consumption was set as the objective function,then the CO2 precooling N2-CH4 expansion process and the N2-CH4 expansion process were optimized,the optimization results proved the success of the improvement.By means of energy analysis theory,energy analysis model of each device was established,energy loss and energy efficiency of the two processes were calculated,the reason for the difference in energy consumption between the two processes were revealed in the perspective of energy,measures to reduce the energy loss were put forward.Finally,the two optimized processes were compared with the other two optimized processes,which are the dual nitrogen expansion process and the propane precooling dual nitrogen expansion process,the results showed that the total power consumption of the CO2 precooling N2-CH4 expansion process was the lowest.By using fuzzy evaluation method,4 one-level indexes and 15 two-level indexes were selected to establish the comprehensive evaluation system of FLNG natural gas liquefaction process,by this system,and by the compiled computing software,comprehensive evaluation of the 4 processes were carried out,the results showed that the comprehensive evaluation of the CO2 precooling N2-CH4 expansion process was the highest.