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Il lavoro riporta i risultati di test di permeazione a lungo termine di membrane per separazione di ossigeno in presenza di CO2, condotti ad elevata elevata temperatura.
Oxy-fuel process, in which pure oxygen is used instead of air for the combustion, is considered a promising technology for CO2 capture, thanks to the high thermal efficiency and low capital cost .Oxygen transport membrane (OTM) module can be efficiently integrated in oxyfuel power plants for oxygen production in place of cryogenic air separation units. In such a plant the flue gas can be recirculated and used to dilute oxygen in the permeate side of the module, before the combustion chamber, in order to avoid the uncontrolled increase of the flame temperature during combustion .
Since in the oxyfuel process the flue gas is mainly constituted by CO2, the OTM must show good stability and performance in CO2-rich atmosphere. In the FP-7 Project GREEN-CC the effect of CO2 on the membrane performances has been studied by performing permeation tests in the presence of CO2 in the sweep gas.High temperature (800-950°C) permeation tests have been performed on asymmetric La0.6Sr0.4Co0.2Fe0.8O3-δ membranes by feeding air or pure oxygen on the membrane side and varying He/CO2 concentration, up to the 80% of CO2, in the sweep gas stream. Results, in terms of oxygen flux as a function of time at different temperatures, show that the 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. 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. The membrane stability in CO2-rich atmosphere has been verified by performing long term permeation tests at 850°C.After 850 h of test the measured oxygen flux reduction is 10%, and no significant change to membrane microstructure was observed.
31 Dicembre 2017
Processi e macchinari industriali (INDUSTRIA 2017)