# Enhancement of CO2 Removal Efficacy of Fluidized Bed Using Particle Mixing
## 1 Introduction  
Although carbon dioxide (CO2) constitutes only 0.035% of the atmosphere, it is one of the most abundant greenhouse gases (GHG). The widespread use of fossil fuel combustion in energy-intensive industrial activities accounts for 90% of total CO2 emissions [1; 2]. The transition from carbon-based energy sources to cleaner ones would be an ideal solution; however, the proposed technologies are still not mature enough to allow for their large-scale implementation. Therefore, technologies for carbon capture and sequestration (CCS) will continue to play an important role until significant changes in the energy infrastructure can be achieved. The CO2 capture process constitutes the major component of the total CCS cost [3; 4]. Research efforts have therefore focused on developing new techniques to reduce the economic cost while achieving significant levels of CO2 capture. Several technologies are available for this purpose. These include absorption, membrane separation, biofixation, and adsorption [5; 6; 7]. Commonly used in the chemical process industries, the use of absorption using solvents has alsobeen applied to postcombustion flue gases, e.g., Boundary Dam power station in Saskatchewan, Canada [8]. This technology, however, requires expensive pretreatment of the flue gases and is moreover energy-intensive. In addition, the solvent evaporation and equipment corrosion are two other important issues that also require careful consideration for the long-term viability of this technology. The use of the membrane separation technology has recently attracted considerable interest. However, some recent studies have suggested that this technology does not offer any notable advantage over chemical absorption, in terms of both energy consumption and cost [9], unless fresh approach towards the development of novel types of membranes are adopted. For example, mixed-matrix membranes (MMMs) composed of a polymer and activated carbon showed good performance in the separation of gases [10; 11]. Another environment-friendly approach proposed in the recent literature is microbial CO\({}_{2}\) biosequestration using microorganisms [12]. However, its application still requires considerable further basic research and applied development work. Among these technologies, adsorption is attractive in the long term owing to its operational flexibility, low energy requirements, and generally low maintenance costs [4; 13; 14; 15; 16]. Adsorption consists of an uptake of CO\({}_{2}\) molecules onto the solid surface, which can occur via either weak van der Waals forces (physisorption) or stronger covalent bonding (chemisorption) [15]. However, adsorption also has potential disadvantages, including handling large volumes of adsorbent, particles attrition, and thermal control of large-scale adsorber vessels. The efficiency of adsorption depends naturally on the adsorbents used. In this regard, there are a number of efficient solid adsorbents for CO\({}_{2}\) that include activated carbons, activated alumina, zeolites, ion-exchange resins, silica gel, metal oxides, mesoporous silicates, carbon fibers and their composites, and metal-organic frameworks (MOF) [17]. For the adsorption to become economically viable, the selection of a suitable adsorbent material is important. An ideal CO\({}_{2}\) adsorbent should have high adsorption capacity, high hydrophobicity and tolerance to feed impurities, stability, low cost, and ease of regeneration [17]. Activated carbon powders, when used as adsorbents, possess a number of such characteristics. For example, they are insensitive to moisture, have low cost, and require low energy for regeneration [18] despite having relatively lower adsorption capacity [19]. For gas-solid contacting during the adsorption, either fixed bed or fluidized bed mode can be implemented. The application of fluidized bed instead of fixed bed yields lower pressure drop, better phase contact, and intimate mixing that ultimately translates into greater efficiency and lower costs [20; 21].