Offshore processing of CO2 rich natural gas with supersonic separator versus conventional routes

Abstract

The supersonic separator (SS) was investigated for treating humid natural gas with 44%mol CO2 in offshore rigs and compared to the conventional Water Dew Point Adjustment (WDPA) via TEG Absorption, Hydrocarbon Dew Point Adjustment (HCDPA) via Joule-Thomson Expansion (JTE) and CO2 removal via Membrane Permeation (MP). SS was tested as a single-step operation for WDPA + HCDPA. To simulate SS and MP, two Unit Operation Extensions (UOE) were developed for simulator HYSYS 8.8 (AspenTech). MP-UOE uses an empirical approach calibrated with operation data, whereas SS-UOE is entirely funded on thermodynamics, not demanding calibration. MP-UOE and SS-UOE use the thermodynamic infrastructure of HYSYS: property packages and several proved multiphase flash algorithms. MP-UOE and SS-UOE performed accordingly the expected characteristics of the respective operations and were critical to accomplish this analysis as SS and MP are not available in simulators. In terms of final gas quality (WDP ≤ -45oC @1.01 bar, HCDP ≤ 0oC @45 bar, %CO2 ≤ 15%mol) the best process configuration was found to be a hybrid one: SS WDPA + HDPA and MP CO2 removal, with low footprint and low power demand (-6.9%) relative to conventional 3-step way. If used for CO2 removal, SS could abate CO2 from 44% to 21.85%mol. Albeit less effective than MP, SS CO2 removal is a noticeable option that produces fuel gas for power generation with %CO2 ≈ 20% as required by new turbo-shafts. Moreover, CO2 is withdrawn from SS as a pumpable liquid allowing a cut of 44% in the power demanded for CO2 separation and injection as EOR agent.