Method using a density-energy state function with a reference equation of state for fluid-dynamics simulation of vapor-liquid-solid carbon dioxide

With the advent of CO₂ capture and storage (CCS) as an important remedy for reducing atmospheric CO₂ emissions, it has become necessary to develop accurate and efficient simulation tools. Among other things, such tools should handle the depressurization from supercritical pressures down to atmospheric conditions. This might involve the formation of solid CO₂ (dry ice) as the state passes the triple point. In this work, we propose a dynamic simulation method that handles the dry-ice formation. The method uses the Span--Wagner reference equation of state, with additional relations for thermodynamic properties along the sublimation line. A density-energy state function formulation is employed, which naturally follows from mass and energy conservation. To illustrate the method's capabilities, demanding test cases are considered, both for the depressurization of a vessel and for fluid dynamics in a pipeline, where phase change occurs due to changing boundary conditions.