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Il lavoro presentato descrive i risultati di test di permeazione condotti nell’ambito del progetto europeo GREEN-CC e volti alla valutazione della resistenza del supporto poroso sulla permeazione delle membrane per separazione di ossigeno. I risultati sperimentali sono inoltre confrontati con i flussi di ossigeno valutati con la teoria del Dusty Gas Model.
La0.6Sr0.4Co0.2Fe0.8O3-δ is one of the most promising materials as oxygen transport membrane (OTM), due to its high oxygen permeability and high temperature stability .
In the last years, many efforts have been made in the manufacturing of asymmetric membranes , by deposition of a thin dense layer on a porous support, with the aim to increase membrane permeation, reduce its cost and improve mechanical resistance. Furthermore, the permeation rate can be improved by feeding a sweep gas on the permeate side, to reduce oxygen concentration and increase process driving force.
On the other hand, when the permeation rate is relatively high, limitations to the oxygen permeation through the porous support may be significant, in particular in the presence of a binary gas mixture.
In the FP-7 Project GREEN-CC, the porous support resistance in the presence of sweep gas has been studied experimentally. Asymmetric LSCF membranes have been manufactured by sequential tape casting and supplied by Forschungszentrum Jülich.
High temperature (700 – 950 °C) permeation tests have been performed by feeding air or pure oxygen on the membrane side and a sweep gas on the support side, at different sweep gas flow rates. As shown in Figure 1, for T > 850 °C, oxygen flux is slightly influenced by the increase of sweep gas flow rate, due to the higher oxygen dilution in the permeate and, consequently, by the increase of the process driving force, while, at lower temperatures, permeation is almost constant in the investigated sweep gas flow rate range.
The support resistance due to the presence of sweep gas has been estimated by an iteration method as the percentage difference between the expected oxygen flux (according to the experimentally derived Arrhenius law) and the measured flux, at a fixed sweep gas flow rate. Results show an increase of the support resistance while increasing the sweep gas flow rate and the temperature (Figure 2), due to the increase of the permeation rate.
Results are also evaluated according to the Dusty Gas Model theory, in order to estimate the influence of the binary gas diffusion in the porous support.
31 Dicembre 2016
Processi e macchinari industriali (INDUSTRIA 2016)