## 3 Results and Discussion
### Checking the Feasibility of a Moving-Bed RFR  
A continuous process with sorbent circulation could be advantageous for increasing process productivity and energy consumption, as the process equipment does not need to be heated up or  
Figure 4: (**a**) CO\({}_{2}\) concentration at the inflow (430–440 ppm, 40% RH) and the outflow. (**b**) Temperature profiles during the entire adsorption phase and the initial 200 s (inset). Figure 5: Variation of sorbent saturation efficiency for CO\({}_{2}\) and H\({}_{2}\)O with time. Data correspond to the experiment presented in Figure 4.  
cooled down every cycle. The objective of the work in this section is to check the feasibility of using a moving-bed RFR with a continuous sorbent flow and to compare its performance (in terms of gas-solid contacting efficiency) with that of using a fixed-bed RFR. The moving bed was operated under the conditions listed in Table 2. Figure 6 shows the variation of outlet CO\({}_{2}\) concentration with time for both operating modes. The curve for the moving-bed RFR can be separated into three parts. First, there is a'startup' period in the first 2000 s, where the concentration in the outlet gas flow gradually increases. From around 2000 s to around 4000 s, a steady-state situation with respect to CO\({}_{2}\) adsorption was achieved, with a developed sorbent loading gradient inside the RFR. After 4000 s, there was no available lean sorbent anymore in the top buffer tank, and since the bottom rotary valve kept removing sorbents from the system, the RFR was gradually emptied. At approximately 4500 s, the empty space at the top of the wire mesh in RFR is big enough to let all of the inflow air pass through; therefore, the outflow CO\({}_{2}\) concentration reaches the concentration at the inlet. Apart from the outlet CO\({}_{2}\) concentration profile, Figure 6 shows the temperature profiles of both the bed and the inflow. It is observed that the bed temperature of the moving bed is some 3 \({}^{\circ}\)C higher than that of the fixed-bed, which can be explained by the variation of the room temperature (referring to T\({}_{\text{inflow}}\) shown in Figure 6). The bed temperature profile shown here refers to the temperature at the middle of the bed. For the moving-bed run, there was a slight step down of the temperature when the top bed became empty at 3600 s. There are initial temperature rises (at t \(<\) 200 s) for both operating modes, similar to those in Section 3.1, which are attributed to water adsorption. Assuming complete adsorption of incoming water vapor on the sorbent up to the saturation point, the adiabatic temperature rise is calculated to be around 7 \({}^{\circ}\)C, matching the experimentally observed temperature excursion. The initial temperature rise in the moving bed displays a similar pattern to the one in the fixed bed, which indicates that the rate of heat generation due to water co-adsorption dominates over any possible improvement in heat transfer in the moving-bed configuration. The steady-state situation between around 2000 s to around 4000 s indicates the mechanical feasibility of the concept. However, the CO\({}_{2}\) adsorption efficiency found was less promising. From the averaged CO\({}_{2}\) concentration (285 ppm) in this period of steady state, the average loading was calculated and compared to the sorbent loading at the same (average) sorbent adsorption time of 43 min (equal to the operating stoichiometric time). The results show a 46% reduction in working  
Figure 6: Variation of CO\({}_{2}\) outlet concentration (\(\kappa_{\text{CO2}}\)), bed temperature (T\({}_{\text{bed}}\)), and inflow temperature (T\({}_{\text{inflow}}\)) with time in the fixed-bed and the moving-bed modes, both operated at the same stoichiometric time (43 min). Conditions are presented in Table 2.  
capacity (from 0.91 to 0.49 mol/kg) as well as a reduction in gas efficiency from 62% to 35% for the moving-bed RFR.