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Porous support resistance on the permeation of asymmetric LSCF membrane in the presence of sweep gas

pubblicazioni - Poster

Porous support resistance on the permeation of asymmetric LSCF membrane in the presence of sweep gas

Nel lavoro sono stati studiati gli effetti della CO2 sul processo di permeazione e sulla stabilità di membrane LSCF in atmosfere ricche di CO2. Sono stati condotti test di permeazione ad alta temperatura (800-950 ° C) variando il rapporto He/CO2 (fino al 70% di CO2) nella corrente di gas sweep.I risultati indicano che la riduzione del flusso di ossigeno è principalmente dovuta all’adsorbimento competitivo tra CO2 e O2 puro.

Oxygen transport membranes (OTMs) can be efficiently integrated in oxyfuel power plants for oxygen production in place of cryogenic air separation units. In such a plant, part of the flue gas is recirculated to dilute oxygen before the combustion chamber, in order to avoid the uncontrolled increase of the flame temperature during combustion [1].

Since the flue gas, mainly constituted by CO2 (68%) and steam (28%), is fed to the permeate side of the OTM module as sweep gas, membrane stability and performance in CO2-rich atmosphere is getting an important issue.

In the FP-7 Project GREEN-CC, the effects of CO2 on the permeation process and membrane stability in CO2-rich atmosphere have been studied by feeding different CO2 concentration in the sweep gas stream. High temperature (800-950°C) permeation tests have been performed on an asymmetric La0.6Sr0.4Co0.2Fe0.8O3-δ membrane, manufactured by sequential tape casting by Forschungszentrum Jülich, by feeding air on the membrane side and varying He/CO2 concentration (up to the 70% of CO2) in the sweep gas stream. Results in terms of oxygen flux as a function of time at different temperatures are shown in Figure 1. Oxygen flux rapidly decreases and reaches a stable value when carbon dioxide is fed in the sweep gas stream.

When the sweep gas is switched back to pure helium, oxygen flux is immediately restored. As shown in Figure 2, the relative oxygen flux reduction, with respect to results in absence of CO2 in the sweep gas, is increasing as a function of CO2 concentration and decreasing with temperature. Under conditions comparable to oxyfuel power plants (850°C, 70% of CO2 in the sweep gas), flux reduction is 34%, approximately. According to the literature [2], results suggest that the oxygen flux reduction is mainly due to the competitive adsorption between CO2 and pure O2. Moreover binary gas diffusion limitations can play an important role, due to the different binary diffusion coefficients of O2/He and O2/CO2 mixture, as can be shown by specific calculations.

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