The CO2Mix phase equilibrium facility is specifically designed for highly accurate phase equilibrium measurements. An analytical technique is used, where the composition of all fluid phases present in the cell at equilibrium is measured. The facility is primarily designed for vapor-liquid equilibrium (VLE). The pressure and temperature range of the setup are from -60 to 150°C and from 3 to 200 bar, respectively. Material selections and ventilation are adapted to the most relevant impurities in CCS, which could include toxic, moderately corrosive as well as explosive impurities. The fluid phases are sampled and injected directly into a gas chromatograph (GC) for chemical analysis. The test cell has several injection valves connected to precise syringe pumps, such that the total composition can be varied during the experimental series, e.g. to adjust the liquid level during measurements on a binary system to avoid having to refill the cell. The test cell consists of a sapphire tube between two titanium flanges, and temperature control is provided by thermostatic baths. Visual access is possible to the cell contents during experiments using a borescope. Temperature, pressure, and composition measurements are calibrated using traceable standards.
Installation 2: Setup for accurate gravimetric preparation of CO2-rich mixtures Adjacent to the phase equilibrium setup there is a setup for gravimetric preparation of gas mixtures. It is used to prepare mixtures for calibration of the phase equilibrium setup, but could also be used independently to prepare gases for other types of measurements. A heated gas cylinder roller is also available to ensure uniform composition. Mixtures are prepared in 10 l gas cylinders
The phase equilibrium setup is designed for accuracy better than 10 mK in temperature, and 0.1% in pressure. The accuracy in the composition measurements will depend on the system under study and state point, but almost all VLE measurements performed so far have a compounded estimated accuracy of 0.05% or better. Visual observation of the cell content is very helpful in these measurements, particularly around critical points and for observation of solids, hydrates, and a second liquid phase. The setup has provided data with high degree of consistency compared to existing literature data. The calibration gas preparation setup has precision in the order of 10 ppm absolute accuracy. The final accuracy of the calibration gas is typically limited by the purity of the source gases or adsorption depending on the mixture components, gas cylinder inner surface, and purity of the source gases.
Highly accurate phase equilibrium measurements and preparation of calibration gas mixtures involving CO2 and impurities typically found in CCS. For each new system to be studied, composition measurements used in the VLE setup should be calibrated with a set of calibration gas mixtures.