Vessel Blowdown of CO ₂-Rich Fluids: Experiments and Simulations

Abstract

In carbon capture and storage projects using CO₂ ship transport from capture to injection sites, CO₂ leakage can occur at onshore storage vessels or in the ship vessels. In order to quantify the consequences of CO₂ leaks, that may lead to dry ice formation, process tools suitable for CO₂-rich fluids are needed. Sophisticated thermodynamic models that take into account solid CO₂ formation are required to simulate depressurization of vessels containing pure CO₂ or CO₂-rich fluids. The tuning and validation of these complex models require reliable experimental measurements. However, for the time being, very few and poorly documented experimental data exist in the literature.

The main objectives of the CARDICE (CARbon Dioxide ICE) Joint Industry Project were to perform CO₂ blowdown experiments and to use the experimental data to benchmark and improve the VessFire process software.

Blowdown experiments were carried out by Ineris. The set-up consisted of a 2 m3 spherical vessel that can handle high pressure (200 bara) and low temperature (-60°C). The first set of tests considered gas releases of pure methane and methane/carbon dioxide mixtures, from high pressure and ambient temperature. A second set of tests consisted of pure CO2 releases at vapour/liquid equilibrium, with initial temperatures varying from -20°C down to -40°C, and corresponding saturation pressures of 20 down to 10 bara. All the tests were conducted successfully with acceptable measurements and without any safety issue. These pilot scale tests are unique and provide very valuable data for assessing process software tools & models.

VessFire, developed by Petrell, is a hybrid 0D-3D tool based on fluid dynamics modelling and a finite-element method for the heat transfer within the walls. Vessfire can handle non-equilibrium thermodynamics of vapour, liquid and solid phases, including the phase changes. With the help of the test results, it was possible to evaluate the performance of Vessfire and identify its strengths and weaknesses for modelling of blowdown operations. Vessfire is considered as a potential tool that can be used for design and simulation of blowdown of single CO₂ vessels.

Keywords: Vessel Depressurization; CO2 Blowdown; Dry Ice Formation; Heat Transfer; Process Software