Abstract
The CO2 absorption rate by using a Monoethanolamide (MEA) solution through the spiral wired channel in concentric circular membrane contactors under both concurrent-flow and countercurrent-flow operations was investigated experimentally and theoretically. The one-dimensional mathematical modeling equation developed for predicting the absorption rate and concentration distributions was solved numerically using the fourth Runge–Kutta method under various absorbent flow rate, CO2 feed flow rate and inlet CO2 concentration in the gas feed. An economical viewpoint of the spiral wired module was examined by assessing both absorption flux improvement and power consumption increment. Meanwhile, the correlated average Sherwood number to predict the mass-transfer coefficient of the CO2 absorption mechanisms in a concentric circular membrane contactor with the spiral wired annulus channel is also obtained in a generalized and simplified expression. The theoretical predictions of absorption flux improvement were validated by experimental results in good agreements. The amine solution flowing through the annulus of a concentric circular tube, which was inserted in a tight-fitting spiral wire in a small annular spacing, could enhance the CO2 absorption flux improvement due to reduction of the concentration polarization effect. A larger concentration polarization coefficient (CPC) was achieved in the countercurrent-flow operations than that in concurrent-flow operations for various operations conditions and spiral-wire pitches. The absorption flux improvement for inserting spiral wire in the concentric circular module could provide the maximum relative increment up to 46.45%.
Highlights
The accelerated industrial movement development during the last few decades results in increasing flue gases from fossil fuel combustion containing CO2 in greenhouse gas emission, which speeded the environmental concerns [1] in global warming issues
The present study develops the mathematical modeling of CO2 absorption by using an MEA solution flowing in the lumen of spiral wired concentric-tube module to generate vortices, while the gas mixture CO2 /N2 flows in the tube side
Comparisons were made for the CO2 absorption flux of modules using the spiral wired annulus channel and empty channel under both concurrentand countercurrent-flow operations
Summary
The accelerated industrial movement development during the last few decades results in increasing flue gases from fossil fuel combustion containing CO2 in greenhouse gas emission, which speeded the environmental concerns [1] in global warming issues. CO2 capture using several technologies, namely absorption [2], adsorption [3], and membrane processes [4] of which the membrane contactor is a promising alternative technology with high absorption efficiency due to offering the advantages of low energy consumption, the independent control of gas and absorbent flow rates, a large mass-transfer area, continuous operations, and the flexibility to scale up [5]. Successful intensifications of gas/liquid membrane contactors have been developed and employed providing the guideline to the judicious choice of membrane materials [9]. Previous studies proved some durable and reusable materials used for the membrane contactor of CO2 absorption, where the as-prepared hydrophobic polymethylsilsesquioxane (PMSQ) aerogels [12], and hybrid bis(trimethoxysilyl)hexane (BTMSH)/tetraethyl orthosilicate (TEOS) silica aerogels [13]
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