Supersonic Separators for Offshore Processing of CO₂-Rich Natural Gas: Comparison with Conventional Routes

Abstract

This chapter implements the supersonic separator (SS) theory and modeling of Chap. 6 to real CO₂-rich natural gas (NG) processing systems. To do this, four process alternatives for offshore conditioning of CO₂-rich (44 mol%) NG are investigated. SS performances for water dew-point adjustment (WDPA), hydrocarbon dew-point adjustment (HCDPA), and CO₂ capture are compared to conventional technologies, namely: WDPA by TEG absorption, HCDPA by Joule–Thomson expansion (JTE), and CO₂ removal via membrane permeation (MP). Process alternatives are assessed in terms of power consumption and the following goal-attainments: lean NG with %CO₂ ≤ 15%, sufficient for turboshaft power generation; low %CO₂ LPG; and EOR fluid with %CO₂ ≥ 75%. In terms of final gas quality, the best configuration was found to be the hybrid SS for WDPA/HCDPA and MP for CO₂ removal, with lower footprint and lower power demand (−6.9%) relative to conventional process. SS for CO₂ removal successfully reduced %CO₂ from 44% to 21.85 mol%. Although less effective than MP, SS is a valid CO₂ removal option producing fuel gas with ≈20 mol% CO₂ suitable for turboshaft utilization. Moreover, CO₂ is extracted from SS as a high-pressure liquid, allowing 44.5% reduction of power for CO₂ separation/injection as EOR agent (corresponding to 30% of total power consumption).