Abstract: In natural gas liquids (NGL) plants, the recovery of propane and butane usually declines with the variation in composition and flow
rate of the raw gas. The method of partially refluxing natural gasoline, which uses a pipe to connect the evaporator with the exit at
the bottom of the debutanizer in order to let a part of steady gasoline return to the evaporator, is one of the ways to improve the recov-
ery. Taking into consideration of influences of composition, temperature and pressure on phase equilibrium of hydrocarbon mixtures,
the SRK real gas state equation is used to study the relationship between sophistication ratio and recovery of propane and butane. The
result shows that under steady temperature and pressure conditions, improved recovery can be obtained with gasoline cycling and with
the increase in sophistication ratio. The most appropriate sophistication ratio can be determined through economic analysis.

Key words: State equation, light hydrocarbon recovery, Low-temperature separation, Natural gas