Contents lists available at ScienceDirect International Journal of Greenhouse Gas Control journal homepage: www.elsevier.com/locate/ijggc Enhancing the Supersonic Gas Separation operating envelope through process control strategies of the feed conditioning plant for offshore CO 2 removal from natural gas Nurzatil Aqmar Othman a , Lemma Dendena Tufa c , Haslinda Zabiri b, *, Abdullah Al-Mubarak Md Jalil a , Khairul Rostani a a PETRONAS Research Sdn Bhd, Lot 3288 & 3289, Off Jalan Ayer Itam, Kawasan Institusi Bangi, 43000 Kajang, Selangor b CO2 Research Center (CO2RES), Institute of Contaminant Management, Universiti Teknologi PETRONAS, Bandar Seri Iskandar 32610 Perak, Malaysia c School of Chemical and Bio-Engineering, Addis Ababa Institute of Technology, King George VI St Addis Ababa 1000, Addis Ababa, Ethiopia ARTICLEINFO Keywords: CO 2 capture Natural gas Supersonic Gas Separation Plant-wide control ABSTRACT Centrifugal Fluid Separation technology, in particular Supersonic Gas Separation (SGS), is one of the potential technologies considered for offshore CO 2 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 hydro- carbon dew pointing. For CO 2 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 CO 2 composition of its feed require a robustfeedconditioningprocessplant.ForarelativelynewtechnologysuchasSGSforCO 2 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 CO 2 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 CO 2 compo- sition. 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. 1. Literature review 1.1. CO 2 separation from natural gas Natural gas is a vital component of the world’s energy supply. It is the cleanest, safest and most useful of all energy sources. Natural gas is amixtureofhydrocarbongasesandthecompositionvariesaccordingto where it is found. Most of the composition is made up of methane, which usually makes up to 80–95 % of the gas. The remaining is made up of other hydrocarbon gases, such as ethane, propane, butane and others. Other elements, like carbon dioxide, hydrogen sulphide, mer- cury, nitrogen and water vapour, may also co-exist in the gas streams (AMTEC, 2010). Higherlevelofimpuritiesinthegasfieldsposedmorechallengesfor production. As for CO 2 , its presence has the overall effect of reducing the heating value of the natural gas, thus reducing the commercial value of the sales gas to buyers (Ahmad et al., 2010). Furthermore, in the presence of water, CO 2 forms a weak, corrosive acid which affects the gas transportation and storage systems badly through corrosion (Tantaline, 2018). As a result, higher cost is incurred for maintenance as plant life decreases. Based on these issues, CO 2 separation from natural gas is extremely important prior to gas processing stage to meet customer’s demand. There are several CO 2 removal technologies currently being applied https://doi.org/10.1016/j.ijggc.2019.102928 Received 18 June 2019; Received in revised form 10 November 2019; Accepted 27 November 2019 Abbreviations: CO 2 ,carbondioxide;SGS,SupersonicGasSeparation;CAPEX,capitalexpenditure;CO 2 -NG,carbondioxide-naturalgas;PID,proportional-derivative- integral; MPC, Model Predictive Control; EES, Engineering Equation Solver; REFPROP, Reference Properties; PTS, PETRONAS Technical Standards; FOPDT, First Order Process Dead Time; CS, Control Strategy; OP, output parameter; PV, process variable; CV, controlled variable; MV, manipulated variable; PFD, Process Flow Diagram; Am 3 /hr, actual cubic meter per hour ⁎ Corresponding author. E-mail address: haslindazabiri@utp.edu.my (H. Zabiri). International Journal of Greenhouse Gas Control 94 (2020) 102928 1750-5836/ © 2019 Elsevier Ltd. All rights reserved. T