The formation of solid CO2, commonly known as dry ice, is a critical safety concern in carbon capture and storage (CCS), as well as in LNG, cryogenic gas processing and other low-temperature applications.
When temperatures drop sufficiently, CO₂ can transition into a solid phase. This can occur directly from the gas phase at low pressures, or from the liquid phase at higher pressures. The exact conditions depend strongly on pressure, temperature and mixture composition.
Why dry ice formation is a safety risk
The formation of solid CO2 can lead to several serious operational and safety challenges:
- Blockage of critical equipment, such as vent lines and pressure relief systems
- Mechanical damage, if solid CO2 detaches and accelerates in the flow
- Pressure surges or pipeline rupture, caused by local plugging or sudden phase changes
Because these events can develop rapidly, dry ice formation must be carefully assessed already in the design and safety analysis phase.
Typical scenarios where dry ice can form
Dry ice formation is most often triggered by rapid cooling events, for example:
- Depressurization during pipeline shutdowns, ruptures or safety valve activation, where the Joule–Thomson effect causes rapid temperature drops
- Loss of temperature control in storage tanks
- Well operations, such as startup, shut-in or blow-out scenarios, where uncontrolled cooling may occur
In CCS injection wells, dry ice formation can lead to overpressure, loss of injectivity and potential wellhead damage.
The importance of accurate thermodynamic modeling
Predicting when solid CO2 forms is not straightforward. The formation limits depend on the full mixture composition, and accurate predictions require:
- A suitable Equation of State for both fluid and solid phases
- A robust phase equilibrium algorithm
- Careful selection of model combinations
In a recently published study, ThermoPhys in collaboration with PhD-candidate Tage Maltby have evaluated a wide range of thermodynamic model combinations against experimental data. The results show that while some models predict dry ice formation with high accuracy, others deviate significantly and should not be used for safety-critical calculations.
From research to practical engineering tools
The most accurate model combinations identified in the study has now been incorporated as default options for dry ice predictions in TP-Cloud, ThermoPhys’ cloud-based thermodynamic software.
TP-Cloud enables engineers to:
- Predict dry ice formation limits for CCS and natural gas mixtures
- Quantify model uncertainty
- Perform safety-relevant phase behavior calculations with confidence
The software has recently been tested by its first users, and further updates will be announced soon.
New publication
The full study has been published in Industrial & Engineering Chemistry Research and is the result of a close collaboration between ThermoPhys, PhD candidate Tage Malby, and our main research partner, NTNU.
