Supersonic separator for cleaner offshore processing of natural gas with high carbon dioxide content: Environmental and economic assessments

Abstract

Supersonic separators offer a cleaner offshore processing of natural gas with carbon dioxide content from deep-water oil-gas fields. Conventional offshore gas processing comprises water dew-point adjustment via glycol-absorption, hydrocarbon dew-point adjustment via Joule-Thomson expansion, and carbon dioxide removal via membrane-permeation. Alternative processing contemplates the use of supersonic separators for adjusting gas dew-points followed by carbon dioxide capture via membrane-permeation (so-called SS-MP scheme); or for adjusting gas dew-points and also accomplishing carbon dioxide abatement (so-called SS-SS scheme). The conventional process is environmentally and economically compared with SS-MP and SS-SS for application in offshore rigs treating raw gas (44%mol carbon dioxide) to produce exportable fuel-gas (≈20%mol carbon dioxide), while dispatching carbon dioxide rich fluid (≈75%mol carbon dioxide) for enhanced oil recovery in the oil-gas field. Results show that SS-MP requires 7.8% less power than the conventional process. Moreover, implementing SS-SS deepens the advantage against the conventional operation because SS-SS produces carbon dioxide rich fluid at high-pressure, requiring much less compression power for enhanced oil recovery than the low-pressure permeate from membrane-permeation. SS-SS has lowest carbon emission (−28.3%), lowest power consumption (−21.3%) and best economic performance: lowest manufacturing cost and lowest compressor investment. Thus, SS-SS is the overall best and cleanest solution, with highest 20 years net value (+860 MMUSD) and lowest environmental impact.