Engineering Solutions for CO2 Conversion. Группа авторов

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Engineering Solutions for CO2 Conversion - Группа авторов


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on the way to start running carbon capture systems in industrial facilities at pilot and large scales.

      1.2.2 Pre‐combustion

      The most notable pre‐combustion project was the Kemper County IGCC plant in the United States, which stopped its operation in 2017.This demonstration facility would place this arrangement at high TRL, while other testing campaigns would reach up to a TRL of 6.

Schematic illustration of the pre-combustion capture AQ for power generation in IGCC.

      Source: Adapted from Jansen et al. [72].

      1.2.3 Oxyfuel

      In the oxyfuel process, the air is split into nitrogen and oxygen, generally using an air separation unit (ASU), for the combustion of fuel with nearly pure oxygen. The consequence is a higher flame temperature and a highly concentrated CO2 stream (60–75%, wet and might contain impurities and incondensable components) that can be further purified to meet the final use specifications. The CO2‐rich gas is typically recirculated to manage the unstable flame and its high temperature. Nowadays, the progress on oxyfuel combustion is focused on the reduction of air separation costs and the enhancement of process configuration to reduce capture costs. Further information can be found, for example, in Ref. [10]. Based on the current progress, the most advanced arrangements can be assessed as TRL 7.

      1.2.4 Post‐combustion

Schematic illustration of the process schematic of a simplified commercial scale natural gas Allam cycle.

      Source: Adapted from Allam et al. [4].

      1.2.4.1 Adsorption

      Adsorption refers to the uptake of CO2 molecules onto the surface of another material. Based on the nature of interactions, adsorption can be classified into two types: (i) physical adsorption and (ii) chemical adsorption. In physical adsorption, the molecules are physisorbed because of physical forces (dipole–dipole, electrostatic, apolar, hydrophobic associations, or van der Waals) and the bond energy is 8–41 kcal mol−1, while in chemical adsorption, the molecules are chemisorbed (chemical bond; covalent, ionic, or metallic) and the bond energy is about 60–418 kcal mol−1 [11].

      A theoretical advantage of adsorption against other processes is that the regeneration energy should be lower compared to absorption because the heat capacity of a solid sorbent is lower than that of aqueous solvents. However, other parameters, such as working capacity and heat of adsorption, should also be considered [12]. The higher the heat of adsorption, the stronger the interaction between the CO2 molecules and adsorbent‐active sites and thus the higher the energy demand for the regeneration. The potential disadvantages for adsorbents include particle attrition, handling of large volumes of sorbents, and thermal management of large‐scale adsorber vessels.

      Solid sorbents can be classified according to the temperature range where adsorption is performed. Low‐temperature solid adsorbents (<200 °C) include carbon‐based, zeolite‐based, metal–organic framework (MOFs)‐based, several alkali metal carbonate‐based, and amine‐based solid adsorbents. Intermediate‐temperature (200–400 °C) solid adsorbents include hydrotalcite‐like compounds or anionic clays, while high‐temperature (>400 °C) sorbents refer to calcium‐based adsorbents and several alkali ceramic‐based adsorbents.

Schematic illustration of the adsorption process: (a) difference of physisorption and chemisorption, (b) a packed bed configuration, and (c) a fluidized bed configuration.
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