Enhancing the Supersonic Gas Separation operating envelope through process control strategies of the feed conditioning plant for offshore CO2 removal from natural gas

Abstract

Centrifugal Fluid Separation technology, in particular Supersonic Gas Separation (SGS), is one of the potential technologies considered for offshore CO2 capture. SGS has advantages in terms of CAPEX, hydrocarbon losses, footprint, tonnage and power requirement compared to conventional solutions such as membrane. Even though the technology has been developed since 1989, the applications are limited to mainly dehydration and hydrocarbon dew pointing. For CO2 separation from natural gas, substantial development works are needed prior to the field application as there are a lot of uncertainties in the feed conditions to be tackled. In particular, the stringent requirements of cryogenic temperature, high pressure and inlet CO2 composition of its feed require a robust feed conditioning process plant. For a relatively new technology such as SGS for CO2 removal application, it is crucial to investigate and assess the variations of feed and process conditions i.e. temperature, pressure and gas compositions prior to being applied at actual field, as these will impact the CO2 separation performance inside the separator. Hence, this paper investigates the control strategies for the SGS feed conditioning plant subjected to ±15 % disturbances in temperature and pressure, and ±5 mol% variations in feed CO2 composition. Results show that effective disturbances elimination in the first flash separator of the feed conditioning plant is crucial in minimizing the impact to the SGS operation. A comparative study reveals that standard PID controller performs significantly better in disturbance rejection than Model Predictive Control.