入口温度对天然气超声速液化性能的影响

Effect of Inlet Temperature on Supersonic Liquefaction Characteristics of Natural Gas

为揭示入口温度对天然气混合物超声速液化特性的影响,本文建立了双组分天然气混合物超声速凝结流动数学模型,研究不同入口温度下Laval喷管内甲烷-乙烷混合气体自发凝结过程。结果表明:保持Laval喷管入口压力及气体成分不变,降低入口温度,混合气体成核位置前移,成核率、液滴半径、液滴生长率、液滴数目、液相质量分数均随之增大,凝结液化效率提高。采用本文设计的Laval喷管结构,在入口压力为6 MPa、入口温度为265 K、甲烷与乙烷摩尔体积比为9∶1时,Laval喷管内可获得的最大成核率为0.982 2×10^(21)(m^3·s)^(-1),最大液滴半径为4.719 4×10^(-7) m,单位质量最大液滴数目为5.070 4×10^(14) kg^(-1),最大液相质量分数为7.812 1%。当入口温度高于275 K时,Laval喷管液化效率急剧下降。实际生产中可通过降低入口温度、减小喷管与外界环境的热量交换等措施来促进天然气的凝结,提高Laval喷管的液化效率。

To reveal the effect of inlet temperature on the supersonic liquefaction characteristics of natural-gas mixtures,a mathematical model for the supersonic condensation flow of two-component natural gas mixtures was established in this study.The spontaneous condensation process of methane-ethane mixed gas in a Laval nozzle at different inlet temperatures was studied.The results indicate that when the inlet pressure and gas composition of the Laval nozzle remained the same,with the decrease in the inlet temperature,the nucleation position of the mixed gas moved forward;the nucleation rate,droplet radius,droplet number,and liquid mass fraction were all increased;and the liquefaction characteristics was improved.By using the Laval nozzle structure designed in this study,inlet gas pressure of 6 MPa,inlet gas temperature of 265 K,molar volume ratio of methane to ethane of 9:1 resulted in maximum nucleation rate of 0.982 2×1021(m^3·s)^-1 in the Laval nozzle,maximum droplet radius of 4.719 4×10^-7 m,maximum droplet number of the unit mass of 5.070 4×10^14 kg^-1,and maximum liquid mass fraction of 7.812 1%.The liquefaction efficiency of the Laval nozzle sharply decreased when the inlet temperature was higher than 275 K.In an actual production,the liquefaction efficiency of the Laval nozzle can be improved by lowering the inlet temperature and reducing the heat exchange between the Laval nozzle and outside environment.