# Enhancement of CO2 Removal Efficacy of Fluidized Bed Using Particle Mixing
## 3 Results and Discussion
### Experimental Results  
First, we discuss the case of the CO2 adsorption without the particles mixing, i.e., the fluidized bed containing only the activated carbon powder. Two different sets of experiments--Experiment 1 and Experiment 2--were carried out by keeping the inlet nitrogen flow fixed at 0.5 LPM and changing the CO2 flow as shown in Figure 6. The concentration profiles are shown for both adsorption and desorption processes. During the adsorption, the CO2 concentration asymptotically reached a constant value, which was expected as the bed of activated carbon gradually got saturated with the adsorbate. Similarly, a gradual decrease in the concentration was evident once the process of desorption was started by discontinuing the flow of the inlet CO2 and leaving the nitrogen flow unchanged. The data recording in this particular experiment was stopped after 5000 s of desorption unlike other experiments where CO2 concentration was monitored for 7200 s (2 h) as mentioned before. Note that 2 h purging  
Figure 4: Flow rates of nitrogen and carbon dioxide during the experiment comprising consecutive purging, adsorption, and desorption steps. Figure 5: Response of O2/CO2 analyzer during the experiment comprising 2 h of purging, 2 h of adsorption, and 2 h of desorption steps over a total period of 6 h (**a**) CO2 concentration; (**b**) O2 concentration. was always carried out to ensure removal of any remaining traces of the CO\({}_{2}\) in the fluidized bed before starting the process of adsorption. We have presented the experimental data in Figure 7, where the ordinate is the normalized CO\({}_{2}\) concentration obtained by dividing the instantaneous concentration by the inlet CO\({}_{2}\) concentration; the abscissa is time plotted on the logarithmic scale. Clearly, the CO\({}_{2}\) profile for Experiment 1 initially showed higher concentration compared to the one for Experiment 2. This can be attributed to faster saturation of the absorbent present in the fluidized bed due the higher CO\({}_{2}\) concentration in the inlet gas. In Figure 7b, the case of particle premixing is presented when small amount of external particle was added to the bed (X\({}_{1}\) = 0.05). Its breakthrough curves show similar trend observed for the monocomponent bed of activated carbon. The adsorption behavior of the bed for X\({}_{1}\) = 0.10, 0.30 is shown in Figure 7c,d, respectively, for both experiments. Figure 6: Variation in CO\({}_{2}\) concentration with time during the adsorption and desorption processes for the monocomponent fluidized bed of activated carbon (**a**) Experiment 1; (**b**) Experiment 2. Figure 7: Response of the fluidized bed with particle mixing in different proportions of external group B particles (**a**) X\({}_{1}\) = 0.00; (**b**) X\({}_{1}\) = 0.05; (**c**) X\({}_{1}\) = 0.10; (**d**) X\({}_{1}\) = 0.30. Our main objective was to examine the effect of particle mixing on the adsorption characteristics of the fluidized bed containing activated carbon. This is shown in Figure 8 for both high and low concentrations of the CO\({}_{2}\) in the inlet gas. Clearly, particle mixing made a significant difference on the CO\({}_{2}\) removal. As seen in Figure 8a, the addition of 25 g Group B particle surprisingly led to a concentration profile that exhibited higher CO\({}_{2}\) concentration than the monocomponent-activated carbon bed. This was a clear indication of lower CO\({}_{2}\) removal efficacy of the bed in this case. However, when the amount of external particles was increased to 50 g (X\({}_{1}\) = 0.10), the breakthrough curve showed a significant shift right, towards much lower CO\({}_{2}\) concentration compared to the previous two cases. Moreover, the time of breakthrough was also much higher. Increasing the fraction of particles to 150 g did not help as the breakthrough curve again shifted left, indicating lower CO\({}_{2}\) removal efficacy. Next, we consider the case of lower CO\({}_{2}\) concentration in the inlet gas (Figure 8b).