Gas evolution rates – A critical uncertainty in challenged gas-liquid separations

Abstract

While much of gas-liquid separation is considered a mature technology, key challenges remain in designing compact systems – particularly for subsea applications – and heavy oil service. Separator performance is critically important for the safe and reliable operation of downstream equipment. Incomplete removal of gas from liquid, or gas carry-under, may result in unexpected pump cavitation, hydrate formation, erosion, and slugging. Liquids entering the separator often carry entrained gas bubbles. Moreover, some of the gas remains dissolved, governed by thermodynamics, as solution gas in the liquid. Thermodynamics dictates that after a pressure drop, seen often upstream of separation, some of the solution gas must evolve out of the liquid. This process is generally assumed, without basis, to be instantaneous. Thus, conventional separator design only accounts for the entrained gas bubbles in the liquid, in addition to bulk separation. Therefore, the kinetics of solution gas evolution is a critical uncertainty in gas-liquid separator design. In compact separators or heavy oil service, the rates of gas evolution are particularly important design parameters. This review discusses the limited reports on this phenomenon, identifies pertinent insights from other areas, highlights gaps in the current understanding, and proposes a path forward.