Overcoming the challenges of modeling and transporting CO2

Garry Hanmer , Senior Simulation Consultant

CO2 transportation

Transporting small quantities of CO2 in its gaseous or liquid phase is a common practice, but for larger volumes, high-pressure systems become necessary. In these cases, CO2 is typically transported in a supercritical state under conditions of elevated pressure and temperature. CO2 is in a more compact form in this state, so the risk of phase transition during transportation increases.

Maintaining the supercritical state demands precise control over pressure and temperature, which introduces complexity to both pipeline design and operation. The supercritical phase of CO2 occurs at temperatures and pressures above the critical point, with a critical temperature of 31.1 degrees Celsius (304 Kelvin) and a critical pressure of 73.8 bar. In this phase, CO2 exhibits properties of both gas and liquid.

Effectively managing phase transitions during CO2 transport is crucial. Insulation, pressure control, and temperature management are essential components in preventing unintended phase changes that could adversely impact pipeline efficiency and integrity.

The challenge and how pipeline simulation can help

Understanding CO2’s behavior across different phases is essential for the effective design of transportation and storage systems.

The logistical complexities of transporting CO2 over extended distances requires the consistent maintenance of pressure and temperature conditions along the entire pipeline route. An unexpected change in the pressure or temperature conditions can affect the pipeline's efficiency, giving rise to safety concerns or equipment malfunctions.

Ensuring the long-term integrity of the pipelines requires proactive maintenance strategies. Regular inspections, both internally and externally, along with addressing potential sources of wear and tear, are vital but can be logistically demanding, particularly in remote or inaccessible areas.

The timely detection of leaks presents challenges due to the nature of CO2, requiring advanced and reliable leak detection systems. These systems are essential for quick responses to minimize the environmental and safety impact of potential leaks.

Using pipeline simulation software like Atmos SIM, a digital twin involving virtual replicas of the pipeline and its operational conditions can be built. Modeling a pipeline also enables real-time monitoring, analysis and decision-making, which enhances the overall operational efficiency and safety of the pipeline.

The challenges of modeling CO2

CO2 undergoes significant phase transitions with variations in temperatures and pressures. Simulating the complex behavior during these transitions demands advanced models and precise thermodynamic data.

The physical pipelines operate under dynamic conditions, experiencing fluctuating pressures and temperatures. Simulating these variations accurately is crucial for understanding the pipeline and fluid behavior to ensure safe and efficient operations. Challenges to simulation accuracy also arise from factors like impurities present in the transported fluid.

Integrating with SCADA systems can help with incorporating real-time data into simulations for real-time decision-making, however the variability in CO2 properties, such as impurity levels, introduces uncertainties that must be addressed for realistic simulations. Continuously validating simulation models against real-world data and calibrating them for accuracy remains an ongoing challenge.

Which equation of state is most appropriate for modeling CO2?

Selecting the most appropriate equation of state for modeling CO2 requires careful consideration. The chosen equation of state must be applicable to compositional fluids and exhibit accuracy across the entire operational range of pressures and temperatures, among other things.

We recently tested four equations of state on a 75 km pure CO2 pipeline.

Discover which equation of state performed best in the full version of this article.

Read it here