Transport of CO₂ in pressurized vessels is increasingly important in carbon capture and storage systems. Operational scenarios can entail vessel depressurization, which is associated with safety concerns such as dry-ice formation and cold temperatures causing steel embrittlement. Understanding the depressurization process is therefore important to ensure safe and efficient operation of CO2 transport systems. CO₂ pressure vessels are operated at conditions close to the critical or triple point of CO2, leading to complex phase change phenomena during depressurization. When depressurizing liquid phase CO₂, flash boiling causes bubbles to form, leading to a two-phase mixture throughout the vessel. Gas phase CO₂ accumulates at the top of the vessel, while a two-phase mixture remains at the bottom. During depressurization, the state of the CO₂ at the bottom of the vessel can reach triple point conditions. Then, the liquid phase CO₂ is converted into a mixture of solid and gas. It has been shown experimentally that the solid and gas phase form a porous structure that floats on top of the remaining liquid. The vessel content is commonly described using a one-dimensional drift-flux model [1]. However, this model does not handle the presence of solid-phase CO₂ and cannot capture the behavior of the vessel at triple point conditions. In the present work, the tank contents is modeled using a one-dimensional drift-flux model with a sharp interface between a region with liquid-vapor flow below a region with solid-gas flow. The sharp interface is handled numerically using an adaptation of the Ghost Fluid Method. The new drift-flux model describes depressurization of CO₂ in all the relevant temperature and pressure regimes, from high pressure supercritical conditions to solid sublimation at atmospheric pressure. The model is validated against depressurization experiments in the ECCSEL depressurization facility, showing good agreement with mass, pressure and temperature measurements.