Effect of impurities on CO2 stream properties
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CO2 obtained by capture process (such as post combustion, pre combustion and oxy-fuel combustion) is not 100% pure and may contain impurities such as H2, Ar, CO, H2S and water. The presence of such impurities in CO2 stream can lead to challenging flow assurance and processing issues. The gaseous CO2-rich stream is generally compressed to be transported as liquid in order to avoid two-phase flow and increase the density of the system. One aim of this work is to evaluate the effect of impurities on the physical properties of CO2 such as density, viscosity, speed of sound and on the phase behaviour of such systems. Speed of sound and isothermal compressibility of CO2/impurities mixtures were measured at condition above the saturation curve and temperature from 268.15 to 301.15 K. A new volume correction was implemented to the Peng-Robinson equation of state in order to minimise the error associated with the isothermal compressibility prediction. Moreover, density and viscosity are two of the most important properties in transport properties. Therefore, the effect of impurities on density and viscosity were experimentally and theoretically investigated in liquid CO2 and liquid CO2/impurities systems. The viscosity measurements were performed using in-house capillary tube apparatus in the range from 280 to 343.15 K and pressure up to 40 MPa. Two viscosity models, LBC and Pedersen, were modified in order to predict the viscosity of both pure and impure CO2. The density measurements were carried-out using an Anton Paar densitometer in both liquid and supercritical regions from 283.15 to 423.15 K. In order to improve the accuracy of EOSs in density of CO/impurities systems, a new modification was developed based on mixing the volume obtained from EOSs (SRK, PR and VPT) and the volume obtained from CO2-MBWR. The presence of water may result in ice and/or gas hydrate formation and cause blockage of pipelines. Several measurements were also conducted to evaluate the hydrate stability zone of pure and rich CO2 systems in free water. A thermodynamic model based on the VPT EOS was adopted to predict the hydrate phase of the systems. In addition, few saturation measurements of synthetic alkane mixture plus pure or impure CO2 were performed at 344.3 K in order to investigate the effect of impurities on the saturation pressure of CO2/alkane system. IFT and swelling factor properties on CO2/n-decane mixture were investigated at 310.95 K from ambient to near the minimum miscibility pressure of the mixture. The experiments were extended to cover the presence of impurities on the properties at the same range of pressure. Minimum miscibility pressure of the systems was estimated by both Vanishing Interfacial Tension method and multiple-mixing-cell calculation.