# Enhancement of CO2 Removal Efficacy of Fluidized Bed Using Particle Mixing
## 1 Introduction
Moreover, fluidization is particularly suitable compared to other available techniques for handling and processing large quantities of powders. While fine powders can theoretically provide a high surface area for the adsorption, the efficacy of gas-solid contact during fluidization is often severely compromised by the agglomeration of the fine particles as a result of interparticle van der Waals forces. For example, the fluidization of fine cohesive powders of Geldart group C is rather heterogeneous and is characterized by the formation of cracks and channels through which the gas phase tends to bypass solids present in the bed, resulting in poor contact and inefficient mixing [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24]. This phenomenon can significantly lower the CO\({}_{2}\) adsorption capacity of the fine adsorbent. In order to improve the fluidization hydrodynamics of solids that exhibit poor fluidization behavior, various assisted fluidization techniques have been proposed in the literature [24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34]. These techniques are generally implemented in conjunction with conventional fluidization to provide additional energy to the fluidized bed for overcoming interparticle forces that cause powder cohesiveness and other nonhomogeneities observed during fluidization. A recent interesting example of such assisted fluidization techniques is the continuous pulsation of inlet flow at regular time intervals instead of a continuous steady inlet flow of the gas to the fluidized bed. This technique greatly improves the fluidization hydrodynamics of ultrafine powders [26; 27; 35; 36; 37; 38]. Similarly, the use of acoustic vibrations has also been reported in the literature [28; 29; 30; 39; 40; 41]. These vibrations promote deagglomeration and eliminate bed nonhomogeneities, thus improving the gas-liquid phase contact. The CO\({}_{2}\) removal efficacy of sound-assisted fluidized bed significantly improves as a result of acoustic perturbations [41; 42; 43; 44; 45]. However, although effective, this technique is inherently energy intensive and moreover requires modification in the fluidization setup for the installation of sound system. Another simple yet cost-effective assisted fluidization technique is the addition of external inert particles. A carefully chosen sample of external particles with appropriate physical properties, when mixed with resident solid phase of the fluidized bed, has been found to significantly enhance fluidization hydrodynamics [23; 30; 31; 46]. For example, the addition of Group A particles to a bed of nanopowder was found to promote deagglomeration and suppress the phenomenon of hysteresis [31; 46]. In the present work, we applied this technique to improve the CO\({}_{2}\) capture efficacy of a fluidized bed containing fine adsorbent particles. This was achieved by adding inert external particles of Geldart group B classification. This choice was dictated by the encouraging results of a recent study that clearly demonstrated the effectiveness of the particle-mixing strategy utilizing Group B particles in improving the hydrodynamics of the fluidized bed of Group C particles [47]. Two different Group C particles--activated carbon and calcium hydroxide--were considered, while the fraction of external particle used for mixing was varied. The bed hydrodynamics was characterized using the fluidization index. A statistical evaluation of results clearly indicated that the best fluidization is achieved when the proportion of inert particle is 10-15 wt % on the external particle free basis. We therefore extended the same strategy of particle mixing to improve the CO\({}_{2}\) removal efficacy of fluidized bed containing fine adsorbent particles. Needless to mention, the basic fluidization setup remains unchanged for the implementation of the proposed particle-mixing strategy; moreover, there was no extra consumption of energy besides the one associated with the pressure drop.