Experimental investigation of selected thermophysical properties of CO2 mixtures relevant for CCS

In order to realize the 2-degree scenario of IEA, more than 6 gigatonnes of anthropogenic CO2 have to be captured, transported, and stored. Such a large-scale deployment of CCS will for instance include a transport infrastructure with a capacity at least comparable to what we have for natural gas today. The ability to describe and predict the behavior of the fluids involved in the CCS chain is absolutely necessary for further development, design, and improvement of CCS processes. Knowledge of the actual mixture behavior under the conditions of the particular process will allow identification of possibly encountered problems, specification of safe concentration limits for involved impurities, and design optimal processes in terms of efficiency, economy, and safety. The objective of this project has been to fill some of the existing gaps in knowledge of thermo-physical properties of CO2-rich mixtures relevant for CCS conditioning and transport. Measurements on phase equilibria have been performed by SINTEF Energy Research, whereas density and speed and sound measurements are performed at Ruhr- Universität Bochum (RUB). RUB and NTNU have had one PhD candidate each financed by the project. SINTEF Energy has in the project designed and commissioned a setup for equilibrium measurements and associated experimental infrastructure, following a discussion with the industrial partners to ensure relevance with regards to mixtures to be studied, conditions, and accuracy. Accurate phase equilibrium measurements of CO2-N2 isotherms have been completed in 2014, and a need to revise current models have been identified. The findings will soon be summarized in a paper in a scientific reference journal. In 2015, 5 isotherms have been measured for each of the binary CO2-O2 and CO2-Ar systems, both to high accuracy. Large deviations with existing models have been revealed. For instance, the pressure needed to ensure single phase operation at 0 °C for a CO2-O2 mixture is almost 20 bar lower than predicted by the best current models. Such results were expected since existing data for CO2-O2 are 45-50 years old and do not cover the critical regions. Also with regards to density and speed of sound the data situation is poor, and measurements that have taken place at RUB on CO2-Ar mixtures provide much needed knowledge. Dissemination of the project results has highly prioritized. The project has been presented in popularized form through the BIGCCS website, blog articles, annual reports, and national and international meetings, including meetings with industry partners of BIGCCS at least twice a year and a seminar in connection with the ISO/TC 265 meeting for CCS standardization. The project has been presented at international conferences such as TCCS-6, GHGT-11, TCCS-7, GHGT-12, TCCS-8 and 19th symposium of thermophysical properties in Boulder. The two PhD students have submitted their theses and will have their defense early in 2016. 7 articles have been published, and 4 additional manuscripts are for review or under final preparation for reference journal publication. Through the publishing in these highly ranked reference journals, the data are automatically included in widely available databases of property measurements. The work has been well received in the international scientific community and has enabled new contacts with highly esteemed groups around the world.

Among the efforts to reduce the global warming effects CCS technology is anticipated to play an important role. The realization of large scale CCS will require further development and substantial scale-up of the technology compared to the scales that are tested at present. For further developing, designing, and improving CCS processes, it is absolutely necessary to be able to describe and predict the behaviour of the working fluids involved in the CCS chain. This is usually done by use of equations of sta te (EOS). For EOS development very accurate experimental values of the density over the whole fluid region (gases and liquids) are needed. This project will focus on measurements of phase equilibria (TPx), density and speed of sound for CO2 rich mixtures (75mol%