## 3 Results and Discussion
### Studying the Effect of the Inlet Gas Flow Rate on the Performance of the Absorber  
The performance of the absorber for CO\({}_{2}\) capture was measured by estimating the absorbed rate of CO\({}_{2}\). The absorbed rate \(N_{\text{CO}_{2}}\) of CO\({}_{2}\) was calculated using the equation  
\[N_{\text{CO}_{2}}=\left[\left(y_{\text{CO}_{2},\text{in}}-y_{\text{CO}_{2},\text {out}}\right)F_{gas,in}\right] \tag{12}\]  
where \(y_{\text{CO}_{2},\text{in}}\) is the inlet volumetric fraction of CO\({}_{2}\), \(y_{\text{CO}_{2},\text{out}}\) is the outlet volumetric fraction of CO\({}_{2}\), and \(F_{gas,in}\) is the inlet gas flow rate. \(y_{\text{CO}_{2},\text{out}}\) was measured by the gas analysis unit, where \(y_{\text{CO}_{2},\text{in}}\) was calculated as  
\[y_{\text{CO}_{2},\text{in}}=\frac{F_{\text{CO}_{2},\text{ in}}}{F_{gas,in}}= \frac{F_{\text{CO}_{2},\text{ in}}}{F_{\text{CO}_{2},\text{ in}}+F_{air,in}} \tag{13}\]  
\(F_{\text{CO}_{2},\text{ in}}\) is the inlet CO\({}_{2}\) flow rate, and \(F_{air,in}\) is the inlet air flow rate.  
Figure 10 illustrates the effect of inlet gas flow rate on CO\({}_{2}\) absorption rate when the inlet gas flow rate is changed in the range of 12-24 Nm\({}^{3}\)/h. There is a significant effect on the CO\({}_{2}\) absorption rate. The trend of this effect is similar for all pressure values studied. It can be seen that the CO\({}_{2}\) absorption rate is almost constant when the flow rate is changed between 12 and 16 Nm\({}^{3}\)/h, whereas the CO\({}_{2}\) absorption rate increases clearly when the gas flow rate is increased between 16 and 20 Nm\({}^{3}\)/h, while the CO\({}_{2}\) absorption rate decreases significantly when the flow rate is increased between 20 and 24 Nm\({}^{3}\)/h.  
Such trends in absorber performance can be interpreted by the increasing superficial velocity of the gas in the absorber as the flow rate increases. Increasing the gas velocity has different effects on the absorber performance. Increasing the superficial velocity of the gas affects the hydrodynamic characteristics of the tray, as shown in Figures 5-9. Specifically, in the case of liquid holdup, increasing the liquid holdup on the tray improves the mass transfer between the liquid and gas phases, resulting in an increase in the amount of CO\({}_{2}\) absorbed, and vice versa. In addition, as the superficial velocity of the gas increases, the interfacial area between the gas and liquid phases increases, as seen in the increase in froth height when the gas flow rate at the inlet is increased (as seen in Figure 9), leading to an increase in mass transfer and the amount of CO\({}_{2}\) absorbed.  
Figure 10: Effect inlet gas flow rates on the absorbed rate of CO\({}_{2}\) at pressure 0.22, 0.24, and 0.26 MPa.  
On the other hand, increasing the superficial velocity above a certain value does not enhance the liquid holdup, as can be seen in Figure 7. In addition, increasing the superficial velocity will decrease the residence time of the gas in the absorber, thus decreasing the contact time between the gas and liquid phases, leading to a decrease in mass transfer between the gas and liquid phases, which could explain the decrease in CO\({}_{2}\) absorption rate when the flow rate is increased between 20 and 24 Nm\({}^{3}\)/h.