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CLIMIT-Forskning, utvikling og demo av CO2-håndtering

Corrosion and cross chemical reactions in pipelines transporting CO2 with impurities

Alternative title: Korrosjon og kjemiske reaksjoner i rørledninger som transporterer CO2 med urenheter

Awarded: NOK 10.0 mill.

Captured CO2 will always contain smaller amounts of certain impurities. It is well known that some of these impurities may react and form corrosive species or solids. To achieve a safe and reliable transport of CO2, it is important to document what CO2 qualities that is needed to avoid corrosion and formation of solids. The acceptable levels (maximum concentrations) of impurities like H2O, H2S, NOx, SOx, CO, O2 must be established. Previous experiments at IFE have shown that even ppm levels of these impurities may react and form elemental sulphur and strong acids (sulphuric acid and nitric acid). Limited relevant field and laboratory data exists, and there is a need for reliable test equipment and research to establish a safe operational window for impurity content in the CO2 that is going to be transported to the storage site. In particular, it is feared that impurity reactions may take place if captured CO2 from multiple sources is comingled, for example in a CO2 transport network (pipelines). The main objective of the project is to generate experimental data that can be used to determine a safe operation window for transport of dense phase anthropogenic CO2 containing mixtures of impurities. It is experimentally challenging to study low levels of impurities (ppm-level) at high pressures, in particular since the impurities may be fully consumed due to cross chemical reactions and corrosion. IFE has built test equipment (loop, autoclaves) that are especially designed for this type of studies. This equipment allows for continuous dosing of low level of impurities in liquid and supercritical (dense phase) CO2. The project has documented that certain CO2 blends are perfectly safe without risk of corrosion or undesirable reaction products. However, it has also been experimentally documented that certain CO2 blends may result in formation of strong acids (corrosive to carbon steel), depending on the concentration and type of impurities that are present. Therefore, it is very important for an operator of a CO2 transportation system to have full control of the impurities in the system, and to remove (clean) impurities that may cause problems. Experiments with the impurities NO2, SO2, H2S and O2 have shown that H2S and NO2 reacts and form SO2, NO and water. Due to oxidation of H2S to SO2, the total concentration of SO2 will increase. The experiments have shown that strong acids forms when the SO2 concentration exceeds a critical limit around 65ppmv. It is therefore important to keep the sum of SO2 and H2S significantly less than 65 ppmv. In experiments with 10 ppmv each of NO2, SO2 and H2S, and 20 ppmv of O2 there were no acid formation, but reaction between H2S and NO2, and NO and O2, were still taking place. For CO2 blends with fewer impurities, like NO2 + H2O or SO2 + O2 +H2O, higher concentrations could be accepted, but the limits have to be specifically specified for each impurity combination. The project has measured the solubility of elemental sulphur, sulfuric acid and nitric acid in dense phase CO2. These results have been used to develop a solubility model that is available in the software from OLI systems. It is therefore possible to calculate the solubility of these components as a function of pressure and temperature. A long-term goal is to continue this work and extend the model, so it can be used to simulate which reactions that will take place in a given CO2 stream for a certain condition. The solubility of sulphur at 25, 45 and 60 °C has been measured in the pressure range 80-280 bar and a good fit was obtained with the concentrations predicted with by the model. The solubility varies with CO2 pressure and temperature, and it is typically in the range of 1 ? 250 mg per kg CO2. The solubility of sulphuric acid and nitric acid in CO2 has been measured at 25 °C and 48 °C at 80, 100 and 170 bar. The effect of temperature and pressure is complex, but it is clear that nitric acid has much higher solubility (~500 ? 2500 ppmv) than sulphuric acid (~0.2 - 2ppmv). Due to the low solubility it is difficult to remove sulphuric acid once it has been formed, and corrosion will therefore continue until the acid is consumed or eventually dissolved.

The project has experimentally verified several CO2 blends (CO2 with ppm-levels of impurities) that are safe for CO2 transportation systems. In addition, it has been demonstrated multiple times that certain CO2 blends may result in corrosion and a separate liquid phase that contains strong acids. Furthermore, it has been shown that the acceptable limit (maximum concentration) of impurities must be based on which impurities that are present together. The solubility of elemental sulphur, nitric acid and sulfuric acid in dense phase CO2 has been measured experimentally and the results have been implemented in the OLI software. Solubilities of these components can now be calculated as a function of pressure and temperature.

Although dense phase CO2 has been transported for more than 30 years, there is limited knowledge about corrosion and bulk phase reactions when the CO2 contains flue gas impurities like SOx, NOx, O2, and CO, in addition to H2O and H2S. A number of tentative CO2 specifications and recommendations for maximum acceptable impurity concentrations are published, but the justification for the proposed recommendations can be questioned. Apparently none of the reported CO2 compositions presently transported in pipelines include flue gas impurities and as concluded in a recent review hardly any lab data were found supporting the suggested CO2 specifications. The lack of relevant corrosion data from the lab and the field makes corrosion predictions impossible and the maximum impurity concentration specified for pipelines in some of the recent projects are therefore very strict, probably too conservative. The objective of the project is to determine the safe operation window for transport of dense phase anthropogenic CO2 containing mixtures of impurities. Corrosion and cross chemical reaction will be studied in IFE's dense phase CO2 lab. The lab is equipped with a state of the art loop built in the KDC I project (Project 221162, Impurity reactions in dense phase CO2-corrosion and solid formation) and advanced autoclave systems where impurities can be dosed and analyzed continuously. The project will deliver an experimental data base 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.

Funding scheme:

CLIMIT-Forskning, utvikling og demo av CO2-håndtering