Optimization and performance evaluation of equations of state for supercritical CO2-rich mixtures for application in the NET Power cycle

Abstract

In this paper the interaction parameters of six equations of state (EoS) were calibrated from density and phase equilibrium experimental data of supercritical CO₂-rich mixtures. The Peng-Robinson (PR), Soave-Redlich-Kwong (SRK), Lee-Kesler-Plöcker (LKP), Benedict-Webb-Rubin-Starling (BWRS), perturbed chain SAFT (PC-SAFT) and Cubic-Plus-Association (CPA) EoSs were considered. As a novelty, the pressure, temperature and composition ranges for calibration were (1 – 49) MPa, (293.18 – 423.15) K, and (72.6 – 99.8) % mol CO₂, which are close to those found in the innovative oxy-combustion NET Power cycle, particularizing the optimization of the EoSs for application in this power cycle. The performance of the EoSs, including the GERG-2008 EoS, was assessed in an isentropic compression process from 7.4 MPa to 30 MPa. The LKP EoS reported the lowest average deviation, 2.03 %, in modeling the bubble and dew lines of the supercritical CO₂ – H₂O mixture. The GERG-2008 EoS was the most reliable model capturing the density of the supercritical CO₂-rich mixtures, reporting an average deviation of 1.34 %. Therefore, the combination GERG-2008 + LKP is recommended for NET Power cycle modeling purposes. Only the CPA and GERG-2008 models captured the liquid-like properties of the CO₂-rich mixture during the compression. This resulted in a specific compression work of 33.02 kJ kg⁻¹ for GERG-2008, while the PR, SRK, LKP, and PC-SAFT EoSs reported a value up to 1.54, 1.65, 1.53, and 1.70 times higher.