Abstract
We investigated the insertion of eddy promoters into a parallel-plate gas–liquid polytetrafluoroethylene (PTFE) membrane contactor to effectively enhance carbon dioxide absorption through aqueous amine solutions (monoethanolamide—MEA). In this study, a theoretical model was established and experimental work was performed to predict and to compare carbon dioxide absorption efficiency under concurrent- and countercurrent-flow operations for various MEA feed flow rates, inlet CO2 concentrations, and channel design conditions. A Sherwood number’s correlated expression was formulated, incorporating experimental data to estimate the mass transfer coefficient of the CO2 absorption in MEA flowing through a PTFE membrane. Theoretical predictions were calculated and validated through experimental data for the augmented CO2 absorption efficiency by inserting carbon-fiber spacers as an eddy promoter to reduce the concentration polarization effect. The study determined that a higher MEA feed rate, a lower feed CO2 concentration, and wider carbon-fiber spacers resulted in a higher CO2 absorption rate for concurrent- and countercurrent-flow operations. A maximum of 80% CO2 absorption efficiency enhancement was found in the device by inserting carbon-fiber spacers, as compared to that in the empty channel device. The overall CO2 absorption rate was higher for countercurrent operation than that for concurrent operation. We evaluated the effectiveness of power utilization in augmenting the CO2 absorption rate by inserting carbon-fiber spacers in the MEA feed channel and concluded that the higher the flow rate, the lower the power utilization’s effectiveness. Therefore, to increase the CO2 absorption flux, widening carbon-fiber spacers was determined to be more effective than increasing the MEA feed flow rate.
Highlights
Biogas contains more than just hydrocarbons.Through processing and conditioning, the purity of biogas is upgraded, which adds to its value.Upgrading is the process of the separation of methane from carbon dioxide and other gases from biogas.In the biogas upgrading process, impurities such as CO2 (30–45%) and H2 S (0.5–1%) are removedMembranes 2020, 10, 302; doi:10.3390/membranes10110302 www.mdpi.com/journal/membranesMembranes 2020, 10, 302 down to a level that satisfies specifications for biogas production or pipeline transport
The current design’s advantage by inserting eddy promoters is evident and provides a remarkable opportunity for the absorption efficiency of parallel-plate gas–liquid PTFE membrane contactor to be improved by a maximum of 80%, and the turbulence enhancement effectively raised to a higher convective mass-transfer coefficient [27]
The power consumption increment is relatively higher at a higher MEA feed flow rate with an essentially large turbulence resulting in a higher mass transfer coefficient for the device where carbon-fiber spacers are inserted
Summary
Biogas contains more than just hydrocarbons (typically ranging between 35% and 75% vol). Flue gases from fossil fuel combustion contain CO2 that needs to be removed in order to reduce greenhouse gas emissions Of all these applications, absorption (physical or chemical) is the most common purification technology for gas separation. The application of membrane contactors to the CO2 absorption process allows soluble gas mixture components to be selectively absorbed during a chemical reaction on the membrane’s surface in its liquid phase [9,10,11]. The current design’s advantage by inserting eddy promoters is evident and provides a remarkable opportunity for the absorption efficiency of parallel-plate gas–liquid PTFE membrane contactor to be improved by a maximum of 80%, and the turbulence enhancement effectively raised to a higher convective mass-transfer coefficient [27]. The trade-off between increasing CO2 permeates and the power utilization’s effectiveness was evaluated to find the trend of economic feasibility in channel designs and system operations
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