CO₂ gas absorption by CH₃OH based nanofluids in an annular contactor at low rotational speeds

In this work, carbon dioxide (CO₂) absorption experiments are performed in a custom designed vertical annular contactor (AC) at low rotational speeds. Methanol is used as solvent and Al₂O₃, SiO₂ and TiO₂ nanoparticles are combined with the methanol to produce nanofluids. The AC performance is compared to that of a modified version in which trays are added to enhance the CO₂ absorption rate (T-AC). Experiments in co-current and counter-current flows are carried out. In addition, two-phase flow patterns in the AC and in the modified version are analyzed by using a high speed visualization system. The results show no effect on the absorption rate for pure methanol at Re_ω<17,000. In the counter-current flow, however, nanofluids show a better performance in the AC with maximum enhancements of 4.6% for TiO₂, 1.2% for Al₂O₃ and 1.1% for SiO₂ compared to pure methanol. The addition of trays enhances the CO₂ absorption rate up to 9%, 10%, 6% and 5% for pure methanol, Al₂O₃, SiO₂, and TiO₂, respectively for the counter-current flow. Likewise, the highest rotation effectiveness is found in the T-AC for Al₂O₃ and TiO₂ with 24.2% and 14.4%, respectively.