CCS – Transport – Modelling of acid formation from reactive impurities

Background
Reactive impurities in CO₂ streams represent a critical and insufficiently understood challenge for the large-scale deployment of carbon capture and storage (CCS). Trace components such as NO2, SO2, and H2S can react under certain conditions to form highly corrosive acids (e.g., nitric and sulfuric acid), threatening the integrity of CCS infrastructure. Current CO₂ purity specifications are highly conservative but are not based on a mechanistic understanding of acid formation. Experimental work, particularly by Institute of Energy Technology (IFE) in Norway, has demonstrated that acid formation can occur rapidly even at low impurity levels, highlighting the need for predictive tools.

Goal
The goal of the project is to develop a physics-based, mechanistic modelling framework capable of predicting when, where, and under what conditions reactive impurities in CO₂ streams lead to acid formation and precipitation in CCS systems. This will support more reliable, cost-efficient, and safe design and operation of CCS infrastructure.

Activities
We have had the following activities in the project:
• Development of a dynamic, mechanistic modelling engine for reactive impurity systems in CO₂-rich mixtures.
• Implementation of a comprehensive reaction network covering gas-phase, liquid-phase, and surface reactions.
• Integration of thermodynamic models for electrolyte systems and solid-phase precipitation
• Application of adsorption models for reactions on carbon steel surfaces
• Estimation of unknown reaction kinetics using first-principles molecular methods
• Systematic validation of the model against 9,394 hours of experimental data from IFE (29 independent experiments).
• Translation of the validated model into pipeline and infrastructure-scale simulations within a software platform called “TPCloud”.

Results
The modelling framework successfully reproduces experimental observations at higher temperatures. We have achieved good agreement between model predictions and measured outlet concentrations and dynamic behavior. A major achievement is prediction of acid formation and precipitation onset in experiments conducted above 15 °C. We have demonstrated that the model captures the dominant physical and chemical mechanisms governing reactive impurities. We have also implemented of a beta-version engineering tool capable of simulating reactive CO₂ transport in pipelines and infrastructure systems, called “the acid analyzer”. We are now able to identify critical locations where acid formation may occur due to cooling, mixing, or flow changes.

Further Work
The following main areas should be subject to future work:
• Reduce uncertainties in reaction kinetics, particularly under low-temperature conditions relevant for ship transport and storage.
• Conduct targeted experimental campaigns and quantum kinetic calculations to fill critical data gaps.
• Further develop and refine the modelling framework for high-confidence engineering applications.
• Transition from research-grade modelling to robust decision-support tools for CCS design and operation

Publications
A blog article about reactive impurities in CCS: https://thermophys.com/reactive-impurities-in-ccs/

Technology Readiness Level (TRL)
The project has advanced from an early-stage conceptual modelling approach (TRL 2–3) to a validated modelling framework demonstrated against extensive experimental data and implemented in a prototype software tool (TRL 4).

This represents a significant increase in technological maturity, moving from theoretical development to experimentally validated and application-oriented modelling suitable for engineering analysis.

Intellectual property rights (IP)
The IP of the software developed in this project is owned by ThermoPhys AS.