Blowdown of CO2 vessels at low and medium pressure conditions: Experiments and simulations

Carbon Capture and Storage (CCS) involves transportation of liquefied CO2 from capture sites to permanent storage locations, which is usually achieved by pipeline transportation or maritime shipping. Over long distances, maritime shipping at pressures around 16 bara has proved to be a more effective solution than transportation through pipelines. These conditions, although safe, offer a significant pressure margin with respect to the triple point of CO2 for more cost-effective ship design with larger transportation capacity. However, the reliability of this technology has not been fully demonstrated regarding depressurization operations commonly performed to minimize hazards associated to emergencies. For CO2, this operation entails risks such as dry ice formation. This paper focuses on two purposes. First, it reports detailed and extensive experimental tests of CO2 depressurization of a tanks at low pressure (< 20 bara). An extensive review of public domain literature showed that this data is scarce [20] This work focuses on contributing to close that gap. Finally, this work will present detailed simulations of the experiments using commercial flowsheeters to assess the reliability of standards models that are commonly used for engineering studies and design. All the experimental work was carried out using a bench scale tank of 2 m3 with ample instrumentation according to an experimental design. The results of the runs were modelled using the EO-Blowdown utility implemented in UniSim Design®. The results showed that modelling of CO2 systems with the EO-Blowdown utility is reliable and can reproduce accurately most key process variables, although it has some limitations such inability to model solid phases and metastable liquids [Display omitted]