Corrosion and cross chemical reactions in pipelines transporting CO2 with impurities
2015 – 2018
The primary objective is to determine the safe operation window for transport of dense phase anthropogenic CO2 containing mixtures of impurities. The goal is to deliver an experimental database and a model that give the CCUS industry a tool for design and operation of pipelines and other facilities that handle impure CO2 for EOR and sequestration of CO2. The main issues addressed in the project are:
• Determination of reactions points, i.e. the concentrations and temperatures/pressures where impurities react with the steel wall and/or each other (cross chemical reactions) • Determination of corrosion rates under upset conditions when the CO2 contains impurities outside the defined safe specification • Determination of type and amounts of solids formed when the CO2 composition is outside the defined safe specification • Implementation of the generated database in a thermodynamic model handling chemical reactions
Corrosion and cross chemical reactions are studied in autoclave and flow loop systems where impurities (H2O, NO2, SO2, H2S, O2) are injected from separate sources with accurate high-pressure dosing pumps and then analyzed with GC, IR-spectrometers and laser spectrometers to measure the consumption rate of impurities in the test system. Consumption of impurities confirms the formation of corrosive phases and elemental sulfur as well as consumption of reactants due to corrosion.
The testing is challenging because corrosive phases can form at very low impurity concentrations. The corrosive phases themselves can constitute less than one droplet per liter of CO2 and are thus difficult to detect. As the impurities are consumed by corrosion and cross chemical reactions (formation of elemental sulphur and acids like H2SO4 and HNO3) they need to be carefully and continuously renewed.
The work so far has focused on developing test approaches and generating solubility data for elemental sulfur, H2SO4 and HNO3 in both liquid and supercritical CO2. Generating such data was given first priority by the project as they are required for developing the first version of the thermodynamic model. The experiments have shown a large pressure and temperature dependency.
Ongoing experiments indicate that the solubility of H2SO4 is low i.e. less than 1 ppm. Once formed, it will therefore be difficult to remove and corrosion is likely until the acid had been consumed.