Thermodynamic properties for pre-combustion CO2 capture and pipeline transportation
Creators: name: Dos Santos De Souza, Lorena Fernanda
Publisher: name: Imperial College London
Year: 2018

description: Carbon capture and storage is a key technology to achieve the goal of ensuring that the global temperature rise is maintained below 1.5 °C, in accordance with the 2015 Paris agreement. One possibility is to produce hydrogen through the gasification of carbonaceous fuels, such as coal, combined with the pre-combustion carbon capture process. In these process, a syngas comprised of CO and H2 is generated. In order to both facilitate carbon capture and increase the hydrogen production, the syngas is shifted in a water-gas-shift reaction. Then, CO2 is separated from the resulting stream, and subsequently transported and stored in appropriated geological formations. The gas separation processes, namely air separation and syngas separation, along with the compression of CO2 for storage, are the most expensive and challenge stages. For the design, optimisation and safe operation of these processes, accurate equations of state (EOS) are required to describe thermodynamic properties of the various mixtures of CO2 with relevant substances, including H2, N2, CH4, CO, Ar, O2 and H2S. A popular and potentially very accurate approach is to use empirical multi-fluid multi-parameter EOS. In order to adjust the interaction parameters in those models, reliable and accurate experimental thermodynamic data of (CO2 + diluent) mixtures are indispensable, in which the diluents of interest are H2, N2, CH4, CO, Ar, O2 and H2S. In this PhD project, new vapour liquid equilibrium (VLE) measurements have been made on two relevant binary systems: (CO2 + CH4) and (CO2 + CO). Additionally, measurements were made of the distribution of trace levels of H2S between the liquid and vapour phases in these two systems. The measurements were carried out at temperatures ranging from just above the triple-point to just below the critical point of CO2, and at pressures from the vapor pressure of pure CO2 up to approximately 15 MPa or, if lower, the mixture critical pressure. Furthermore, homogenous density measurements of the (CO2 + CO) system were carried out using a vibrating-tube densimeter over a temperature range of 283.15 to 373.15K and pressures up to 48 MPa. The new VLE and homogenous density data have been compared with the predictions of available thermodynamic models, including the GERG-2008 model of Kunz and Wagner, the EOS-CG model of Gernert and Span and the SAFT-γ Mie approach. Additionally, the data have been correlated with the Peng-Robinson EOS, generally incorporating a single temperature-dependent binary interaction parameter. Finally, an improved Helmholtz-energy-explicit mixture model for the (CO2 + CO) system was developed within the framework of GERG-2008 in collaboration with the Ruhr-Universität Bochum. The development of the new mixture model was only possible due to the accurate density and VLE measurements carried out in this work. In summary, new VLE and homogeneous density data are reported that help to fill important knowledge gaps relating to the thermodynamic properties of mixtures of CO2 with substances relevant to pre-combustion CO2 capture and pipeline transportation.