Abstract

A lab-scale bubble-column scrubber is used to capture CO₂ gas and produce ammonia bicarbonate (ABC) using aqueous ammonia as an absorbent under a constant pH and temperature. The CO₂ concentration is adjusted by mixing N₂ and CO₂ in the range of 15–60 vol % at 55 °C. The process variables are the pH of the solution, temperature, gas-flow rate and the concentration of gas. The effects of the process variables on the removal efficiency (E), absorption rate (R_A) and overall mass-transfer coefficient (K_Ga) were explored. A multiple-tube mass balance model was used to determine R_A and K_Ga, in which R_A and K_Ga were in the range of 2.14 × 10⁻⁴–1.09 × 10⁻³ mol/(s·L) and 0.0136–0.5669 1/s, respectively. Results found that, R_A showed an obvious increase with the increase in pH, inlet gas concentration and gas temperature, while K_Ga decreased with an increase in inlet gas concentration. Using linear regression, an empirical expression for K_Ga/E was obtained. On the other hand, ammonia bicarbonate crystals could be produced at a pH of 9.5 when the gas concentration was higher than 30% and γ (=F_g/F_A, the gas-liquid molar flow rate ratio) ≥ 1.5. View Full-Text