Analysis on a Hydrophobic Hollow-Fiber Membrane Absorber and Experimental Observations of CO₂ Removal by Enhanced Absorption

Abstract

In this paper an extended analysis on a hollow-fiber membrane absorber is conducted for CO₂ removal from flue gases. A rigorous model of gas–liquid mass transfer is developed on both narrow channels in and around the hollow fibers, including the gas absorption occurring from the reaction between CO₂ and aqueous K₂CO₃ absorbent. CO₂ concentration profiles can be obtained regardless of the placement of the flowing absorbent. Experimental observations of the CO₂ concentration in both the reject and permeate outlets compared with theoretical prediction allow us to understand the influence of flow rates of feed gas as well as absorbent on CO₂ absorption. For the flowing K₂CO₃ absorbent a kinetic constant can be chosen which will provide the best possible agreement between experiment and reactive model prediction. This fact emphasizes that the pseudofirst-order kinetic can be employed to describe the facilitation effect. The overall mass transfer coefficients were determined from the experimentally observed concentration changes. The CO₂ permeation flux was found to be enhanced as the K₂CO₃ concentration was increased, suggesting that CO₂ removal is entirely controlled by the reaction. The enhanced selectivity factor for CO₂/N₂, which decreases with increasing absorbent flow rate, reached as high as 1200 with 15 wt% K₂CO₃ absorbent.

Key Words:

• Hollow-fiber membrane absorber
• Carbonates absorbent
• Carbon dioxide removal
• Mass transfer coefficient
• Enhanced selectivity