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 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 depressurization of a vessel and for fluid dynamics in a pipeline, where phase change occurs because of changing boundary conditions.