The Study Of Small And Medium-sized Natural Gas Liquefaction Process Optimization

In recent years,the global LNG industry is developing rapidly.Natural gas liquefaction technology and equipment become perfect and mature.However,the related research in the field of LNG in China started late.Many techniques lag behind the world level and require in-depth research and development.In design of natural gas liquefaction process and liquefaction plant production,etc.,we are short of technology independent property rights.To carry out the research of natural gas liquefaction process flow and equipment has the very vital significance for localization,and high-effectiveness of liquefaction plant.In this paper,based on the characteristics of small and medium-sized natural gas liquefaction plant puts forward five kinds of liquefaction process plan:Single cycle mixed refrigerant liquefaction process,Double mixed refrigerant cycle liquefaction process,N₂-CH₄expansion refrigeration process,natural gas expansion refrigeration process and natural gas expansion refrigeration process with mixed refrigerant cycle.Using thermodynamic analysis method to establish the thermodynamic model of gas liquefaction process,and analyses the thermal process such as compression,cooling,heat exchange,throttling and expansion.Analyze the rule of natural gas liquefaction process and LNG storage characteristics,to provide theoretical basis for the select of initial parameters in liquefaction process simulation,getting the following conclusion:high pressure is easier to liquefy natural gas at;improve LNG storage pressure can increase liquefied rate in the same storage temperature;temperature before throttling should be lower than the bubble point temperature in LNG storage pressure.Establish the liquefaction process state model in HYSYS and calculate the process performance index.Under the same import and export condition,compare the various processes:natural gas expansion refrigeration process has the lowest power consumption,N₂-CH₄ expansion refrigeration process has the maximum power consumption;LNG heat exchangers have the biggest energy loss and in the refrigeration cycle the coolers have the biggest energy loss.Based on the above,choose the proper process for different liquefaction plant.For the base-type liquefaction plant,optimize the structure of the single stage mixed refrigerant liquefaction process.Increase the throttling stage of mixed refrigerant and the compression stage of refrigeration cycle series.With the system total power consumption as the objective function,establish the optimization model,and optimize the ratio of refrigerants and design parameters of liquefaction process.Use the optimizer in HYSYS to optimize the ratio of refrigerants.Use Genetic Algorithm?GA?to optimize design parameters of liquefaction process.The conclusion and observed principle about the detailed process parameters,GA optimization procedure will help to the design medium and small scale LNG facilities.