Zhien Zhang

Numerical Simulation and Analysis of CO2 Removal in a Polypropylene Hollow Fiber Membrane Contactor

This present study shows a comprehensive 2D numerical model for removal of CO2 in a polypropylene (PP) hollow fiber membrane contactor (HFMC) using the computational fluid dynamics (CFD) method. Monoethanolamine (MEA) solution was used as the liquid absorbent in a nonwetting mode. The simulation results represented that higher liquid velocity and concentration and lower gas velocity and concentration led to higher percent of CO2 removal. The most proper parameters for CO2 removal were less than 1 mol m−3 gas concentration and 0.2 m s−1 gas flow rate, and for MEA the values were above 8 mol m−3 concentration and approximately 1 m s−1 liquid velocity. Furthermore, the model was validated with the experiment results. Therefore, the modeling results provided references to the selection of absorbents and operation parameters in the experimental study and pilot-scale applications.

Numerical investigation of the effects of polypropylene hollow fibre membrane structure on the performance of CO2 removal from flue gas

Carbon dioxide (CO2) absorption from flue gas by hollow fibre membrane contactors is considered as a clean, highly efficient and promising decarburisation technique. Herein, a two-dimensional mathematical model is developed for CO2 absorption from parallel countercurrent mixed gas by a hollow fibre membrane contactor. Using the finite element method, the fibre membrane structure effect on CO2 removal efficiency and mass transfer performance were simulated, including the inner diameter, wall thickness, length, packing density, porosity and tortuosity factor. Three absorbents were chosen: EEA (ethyl-ethanolamine), EDA (ethylenediamine) and PZ (piperazine). The axial and radial diffusion in the membrane contactor, diffusion in the fibre and membrane pores and non-wetting conditions were considered. The simulation results showed that the CO2 removal efficiency and mass transfer rate were reduced with increasing wall thickness, inner diameter and tortuosity factor, and the performance was enhanced with increasing length, packing density and porosity. However, the effects of porosity and tortuosity factor were weak; thus, it was very favourable for making the module. The CO2 removal performance was excellent for a wall thickness in the range of 30–50 μm, an inner diameter of 90–110 μm, a length greater than 150 mm, and a packing density of 21–25% of the membrane structure.

Analysis of CO2 Capture From Power-Plant Flue Gas Using the Membrane Gas Absorption (MGA) Method

Currently membrane gas absorption (MGA) is a novel approach for gas separation. In the present work, a wide-ranging 2D mathematical model for CO2 absorption from the N2/CO2 mixture is proposed. Single solvents [H2O, ethylenediamine (EDA), diethanolamine (DEA), monoethanolamine (MEA), piperazine (PZ)] and blended solvents [DEA/PZ] were used as the absorbents. The non-wetting mode for the membrane contactor was considered in the calculations. The effects of gas concentration and velocity, and liquid concentration and velocity on CO2 removal were observed. The simulation results were verified with the experimental data showing a good agreement. The modeling results indicate that gas concentration and velocity have a negative effect on the capture process, while liquid concentration and velocity enhance CO2 capture. Also, it is noted that PZ has the best absorption performance than other single absorbents. The chemical solvents are much better than the physical solvent for the absorption of CO2. For mixed absorbents based on amine solutions, the CO2 removal efficiency could be about 20% higher than that of the single solutions. Thus, this model could provide the optimum operating conditions for acid gas absorption in the hollow fiber membrane module. It is also proved that the MGA approach exhibits a good potential in power-plant waste gas purification.Copyright