Large CO₂ Pilot: Energy Consumption,Emission, and Corrosion

The extreme temperatures and weather patterns that the world today is witnesses are caused by the emission of greenhouse gases, CO₂ being the main contributor. To mitigate the increasing level of CO₂ in the atmosphere the Danish Government has outlined that carbon capture, utilisation, and storage (CCUS) is the main technology to achieve the goal of becoming net-zero emission free.

Chemical absorption of CO₂ using aqueous amine solvents is the most mature technology to be implemented on already existing waste-to-energy plants, biogas plants, cement factories etc. Currently, the technology is impeded by the high regeneration energy for stripping off CO2 leading to a high cost of capture. Furthermore, solvent emission to the atmosphere, and corrosion of the materials used for the capture and downstream processes are crucial to be dealt with. A joint communication from leading Northern European industrial stakeholders to the policy makers was presented. It explores the industrial CO₂ purity limits and highlight possible technologies, infrastructure, and political tools for implementing a robust CCUS ecosystem. CCUS cannot be implemented without interoperability between the capture, transport, and storage stakeholders.

This thesis consists of three main topics within CCUS: energy consumption, emissions, and corrosion. This Ph.D. study aims to demonstrate that energy reductions for the capture process can be obtained by using 1) the CESAR1 (33 wt% 2-amino-2-methyl-1-propanol and 12 wt% piperazine) solvent, and 2) advanced pilot process configurations. Additionally, it aims to elucidate the effect of solvent emission. Furthermore, the study aims to create new fundamental insights of CO2 corrosion by studying the solubility of FeCO3 in various media (i.e. water, aqueous NaCl solutions, aqueous HCl solutions) with the goal of improving corrosion models used in CCUS.

Energy savings of the capture process were demonstrated in this study at the waste-to-energy (WtE) plant Amager Bakke, Denmark. Pilot-scale CO2 capture was conducted using a mobile plant capable of processing up to 145 kg gas/h. The pilot campaigns were performed with the CESAR1 solvent. Initial testing resulted in specific reboiler duties of 3.0-3.2 GJ/tCO₂. The testing of the solvent served as a baseline for assessing the more advanced process configurations. Five advanced process configurations campaigns were conducted, which were lean vapor compression (LVC), absorber intercooling (IC), cold rich solvent split (CRSS), a combination of IC and CRSS, and rich recycle (RR). Energy reductions of 14%, 3-4%, 4%, and 6% were achieved with LVC, IC, CRSS, and IC+CRSS. The energy consumption was increased with 8% for the RR configuration. This was due to a higher inlet gas temperature to the capture plant.

In a separate study, solvent degradation, and emissions of 30 wt% monoethanolamine (MEA) were analysed utilising flue gas from the WtE plant. Low emissions of nitrosamines, and nitramines were observed in the depleted flue gas from the capture plant. The wash tower consisting of an acid wash, intended for removing impurities from the depleted flue gas achieved a reduction of up to 83% of the MEA emissions. Less impurities were observed in the CO₂ product stream as well. Heat stable salts were observed to accumulate over time in the solvent, with primary products being formate and acetate. Iron concentration was below 10 mg/L.

Addressing CO₂ corrosion throughout the CCUS value chain, the solubility of FeCO₃ was studied in various systems (water, NaCl-H₂O, HCl-H₂O), across the temperature ranging from 5 to 120 °C. It was observed that temperature had an insignificant influence on the solubility. However, the FeCO3 solubility increased in aqueous HCl solutions compared to water, and aqueous NaCl solutions. The Extended UNIQUAC model was successfully applied for the estimation new parameters for Gibbs energy of formation and enthalpy of formation for FeCO₃ based on experimental solubility data, showcasing its applicability in predicting solubility in different systems.