Effect of SO₂, O₂, NO₂, and H₂O Concentrations on Chemical Reactions and Corrosion of Carbon Steel in Dense Phase CO₂

Abstract

Carbon capture, utilization, and storage is expected to be an important method for reducing CO2emissions to prevent global warming. Several species (impurities) could follow the CO2through the capture plant as carry over. It is expected that nitrogen dioxide (NO2), sulfur dioxide (SO2), oxygen (O2), and water (H2O) can be present as impurities (concentrations at the ppmv level) in the captured CO2. The exact composition will depend on the flue gas type, the CO2capturing process, and multiple other parameters. Some of these impurities are reactive and may cause corrosion in carbon steel pipelines and could therefore be a threat for safe CO2transport. The present study used a novel experimental setup to realistically simulate a CO2transport pipeline system with a controlled and variable concentration of impurities at a total pressure of 10 MPa and a temperature of 25°C. The water concentration was increased and decreased with constant concentration of SO2and O2, to observe and identify possible reactions or threshold levels which could cause corrosion. A similar experiment was conducted with NO2. First, experiments were performed without steel coupons, to observe uncatalyzed reactions, and then with coupons to measure corrosion rates. The first sign of corrosion appeared at 350 ppmv of water with NO2present. At 670 ppmv water with 75 ppmv NO2the overall corrosion rate was about 0.57 mm/y and the main product was iron oxide. The corrosion process for SO2, O2, and water was much slower, and the first sign of corrosion appeared around 1,900 ppmv of water, with about 75 ppmv of SO2and 230 ppmv of O2. The corrosion rate increased some when the water concentration was increased to 2,400 ppmv, but the overall corrosion rate was only 3.6 μm/y and the main product on the surface was iron sulfate.

Nitric and Sulfuric Acid Solubility in Dense Phase CO2

“…Hoa et al showed that, at low pressure, the condensation of SO 2 and NO 2 with water resulted in the formation of H 2 SO 4 and HNO 3 , which led to strong pitting and localized corrosion in the presence of H 2 SO 4 , while HNO 3 induced only high general corrosion. This might be related to different corrosion mechanisms as both Hoa et al and Morland et al suggested, but it could also be an indication of a difference in solubility.…”

Early Stage of Corrosion Formation on Pipeline Steel X70 Under Oxyfuel Atmosphere at Low Temperature

“…Since the experiments were carried out below the dew point of H 2 SO 4 , presumably small acid droplets were formed in the atmosphere [33,34]. Further evidence of the acid formation and the catalytic role of NO 2 have been further proved, even under higher pressure by recent works from Morland et al [35][36][37]. These acids condensed at the specimen's surface, being the coldest point in the system due to the Peltier element underneath.…”

The Challenge of Monitoring Impurity Content of CO2 Streams

“…Corrosion and impurity reactions can form solid and liquid phases [3][4][5]. These products (solids, liquids) may separate from the CO 2 bulk phase due to density differences and either stick to the wall or follow the CO 2 stream.…”

“…Due to the large number of possible impurities, the number of possible chemical reactions is high. The most important reactions that were identified in the Kjeller dense phase CO 2 project (KDC) [3,4,9,15,21] were…”

“…It has been shown experimentally that certain combinations of impurities react if they are present above a critical concentration [3][4][5]. It was demonstrated that H 2 O, H 2 S, SO 2 , NO 2 , and O 2 at concentrations much less than 100 ppmv reacted and created separate aqueous phases containing high concentrations (several mol/kg) of sulfuric and nitric acid.…”