Decarbonisation Technology - May 2023 Issue

highly permeable for CO2. In this case, the specific properties of the membrane determine the efficiency of the separation process. In adsorption methods, CO 2 binds to the surface of a solid sorbent, such as hydrotalcites, lithium zirconate, active carbon, molecular sieves, calcium oxides, or zeolites. Following this step, CO 2 is desorbed via pressure or temperature swings. Absorption techniques, on the other hand, use liquid solvents, such as aqueous monoethanolamine, diethanolamine, piperazine, or potassium carbonate, rather than solids. These absorb the CO2 gas through the formation of a chemical bond with the dissolved reactant. The CO2 -rich liquid solvent is then processed to release the CO 2 (stripping) and regenerated, returning as a CO 2 -lean chemical for reuse in more cycles, in line with circular practices. To date, absorption is the most mature solution for post-combustion installations, as it has been extensively researched and commercialised. Absorption for large-scale CO 2 capture This method offers optimum separation efficiencies, which can reach 90% and above. To achieve peak performance, it is important to leverage the most effective column components for absorption and stripping, such as bed packings and other internals. Specifically, while the number of beds and their height play a key role in the separation process, their design also heavily influences the possible outcomes, with the geometrical structure of the packings defining the hydraulic and mass transfer properties. For example, CO2 absorption towers typically perform better when equipped with structured rather than random packing. In addition, the structured packing’s microstructure, surface, and corrugation angle, as well as the number and size of holes within it, influence wetting capabilities, pressure drop, reaction regime, and, ultimately, separation efficiency. To support energy and manufacturing companies in setting up CCUS facilities that can separate CO 2 from flue gases efficiently, Sulzer Chemtech has developed a range of application- specific column components. These include the MellapakCC and AYPlusDC structured packings

whether CO 2 is captured during intermediate reactions, from waste streams, or in processes involving the burning of fuels with diluted or concentrated oxygen. While all these carbon capture methods have been applied to different setups, post- combustion strategies offer the most mature and easy-to-implement technologies. They are the most common solution utilised in commercial-scale energy plants, and similar approaches are being applied to waste-to- energy and biomass-to-energy facilities as well as to reduce carbon emissions from waste gas effluents in chemicals, metals, and cement production plants. By contrast, pre-combustion involves high capital expenditure (Capex) and operational expenses (Opex) due to the complexity of its processes and the number of operating units required. Oxy-fuel frameworks are generally economical; however, current applications have failed to offer feasible options for large- scale facilities, mainly because of various operational challenges (Kheirinik, Ahmed, & Rahmanian, 2021). Post-combustion technologies Currently, post-combustion technologies feature different technology readiness levels. The most commonly discussed methods leverage absorption or adsorption technologies to remove CO 2 from flue gases, whereas fewer approaches rely on permeation principles (membrane separation). The mechanisms behind these three alternatives can differ greatly. Membranes for carbon capture are designed so that they are Figure 2 Close-up views of MellaTech liquid distributor, and Mellapak CC and AYPlusDC structured packings (from left to right)