混空轻烃燃气液相析出成核热力学分析

Thermodynamic analysis of droplet nucleation causing liquid-phase precipitation in air-hydrocarbon mixture gas

混空轻烃燃气是将液态轻烃原料汽化、与空气按一定比例混合制成的可燃气体,是一种清洁燃料。但以戊烷为主的轻烃原料常温下为液态,汽化混合后的燃气存在露点较高问题。采用成核热力学理论研究局部温度、压力变化引起的相变/成核驱动力,进而研究液滴的成核能,得到混空轻烃燃气液相析出的成核机理、成核能及其与过冷度和过饱和度的关联关系。结果表明,相变/成核所需过冷度和过饱和度随温度、压力的增加而降低;尽管发生完全相变所需过冷度及过饱和度较高,较难达到,但液相析出成核所需过冷度及过饱和度则极易达到,因此防止燃料露点形成的重点是控制从成核到完全相变的发生。

Air-hydrocarbon mixture gas is a combustible gas made by mixing the vaporized liquid light hydrocarbon and air with a specific ratio, which is a kind of clean fuel. However, the adopted light hydrocarbons are liquid state at standard condition, causing the high dew point of the mixing gas. In this work, the nucleation thermodynamic theory was used to study the phase transition or nucleation force caused by the changes of temperature and pressure on some zones, and the nucleation energy of droplets. The nucleation mechanism, nucleation energy and their relationships with the subcooled temperature and supersaturation of the airhydrocarbon mixture gas were obtained from these studies. It was shown that the subcooled temperature and supersaturation required by phase transition or nucleation decreased with the increase of temperature and pressure.Although the subcooled temperature and supersaturation required for complete phase transition would unlikely be reached due to the fluctuation of the working condition, the subcooled temperature and supersaturation required for nucleation can easily take place. Therefore, it is important to control the occurrence from nucleation to complete phase transition for preventing the formation of dew point. The research results provided the reference for the research on the safety of storage and transportation of air-hydrocarbon mixture gas.