https://doi.org/10.1016/j.ijggc.2013.12.005
”
4.3.1. Justification for case study
The study is performed to investigate the effect of lean MEA temperature on the performance of RPB absorber. The key driving forces for absorption, mass transfer and chemical reaction, are known to respectively decrease and increase with temperature (Kvamsdal et al., 2010). Conventional absorber performance is already known to be hindered by increase in lean MEA temperature due to the possibility of temperature bulge within the absorber column (Freguia and Rochelle, 2003). Based on this, capture performance with lean MEA temperature should be studied for RPB absorbers.
4.3.2. Setup of the case study
To implement the case study, 1000 rpm rotor speed, 0.66 kg/s lean MEA flow rate. Process conditions are shown in Table 6. The lean MEA temperature is varied from 25 °C, 30 °C, 35 °C, 40 °C, …, to 80 °C at 55 wt% and 75 wt% lean MEA concentrations.
Table 6. Process conditions for lean MEA temperature studies.
| Variable | 55 wt% MEA Con. | 75 wt% MEA Con. |
|---|---|---|
| Rotor speed (RPM) | 1000 | 1000 |
| Lean pressure (atm.) | 1 | 1 |
| Flue gas flow rate (kmol/h) | 2.87 | 2.87 |
| Flue gas composition (vol%) | ||
| H2O | 17.1 | 17.1 |
| CO2 | 4.4 | 4.4 |
| N2 | 78.5 | 78.5 |
| Lean-MEA flow rate (kg/s) | 0.66 | 0.66 |
| Lean-MEA composition (wt%) | ||
| H2O | 41.03 | 22.32 |
| CO2 | 3.97 | 2.68 |
| MEA | 55.00 | 75.00 |
4.3.3. Results and discussions
Fig. 7 shows the effect of varying lean MEA temperature on CO2 capture level at different lean MEA concentrations (55 wt% MEA and 75 wt% MEA). The results show that CO2 capture level increases significantly from 25 °C to 50 °C lean MEA temperatures. Lean MEA temperature increase above 50 °C has no significant impact on the CO2 capture level. Improvement of RPB performance as temperature increases can be associated to decrease in viscosity of the lean MEA solvent as explain by Lewis and Whitman (1924) that the ratio of viscosity to density (kinematic viscosity) of the film fluid is probably the controlling factor in determining film thickness. Haslam et al. (1924) said that if film resistance is directly proportional to film thickness, then film conductivity is the inverse of kinematic viscosity. The effect of temperature on density of gas is great, but temperature affects the density of lean MEA only slightly (Maceiras et al., 2008). Again an increase in temperature causes an increase in viscosity of a gas but the same increase in temperature might greatly lower the viscosity of lean MEA. This improves mass transfer due to thinner liquid film since absorption of CO2 into alkanolamines solutions is a liquid film controlled process (Jassim et al., 2007). Also Increasing lean solvent temperature leads to increase in chemical reaction rate.
Fig. 7. Effect of lean-MEA temperature on CO2 capture level.
“