Impact of Supersaturation Ratio on the Kinetics of Gas Evolution at Elevated Pressures

The kinetics of gas evolution in supersaturated solutions is a critical uncertainty in the design and operation of gas/liquid separators. Incorrectly predicting the amount of gas that evolves in a gas/liquid separator can lead to gas carry under with the liquid, resulting in equipment damage downstream of the separator. Central to addressing this problem is the measurement of the gas evolution rate at specific levels of supersaturation. The supersaturation ratio (S) is defined as S=Pg,oPg,ss−1, where Pg,o is the pressure before depressurization and Pg,ss is the pressure after depressurization. Exxsol D-110, a model oil, was used as the liquid phase, and methane was used as the gaseous phase. The rate of gas evolution was investigated at six supersaturation ratios (0.15, 0.30, 0.70, 1.30, 2.00, and 2.83) and at three different rates of energy dissipation (mixing speeds: 100, 250, and 500 rpm). The rate of gas absorption into the oil was within 20% of the rate of gas evolution up to a supersaturation ratio of 1.30. At a supersaturation ratio of 2.83, the rate of gas evolution was higher than the rate of absorption. At a supersaturation ratio of 2.00, the rate of gas evolution was higher than the rate of absorption only at 500 rpm. Thus, the supersaturation ratio and the rate of energy dissipation (mixing speed/shear environment) are key parameters that affect the rate of gas evolution.