Testing of nanostructured gas separation membranes in the flue gas of a post-combustion power plant

Nanostructured gas separation membranes are promising candidates for the separation of CO2 from the flue gas of fossil power plants. Well-defined atomic structures in the range of a few Angstrom are required to separate CO2 from N2 in existing post-combustion power plants, and H2 from CO2 in prospective integrated gasification combined cycle (IGCC) power plants. Today, CO2/N2 and H2/CO2 gas separation with membranes has been demonstrated mainly on a laboratory scale, while less is known about membrane performance and stability under real conditions. To extend the state of knowledge, a test bed was put into operation in the flue gas stream of a hard-coal-fired power plant (EnBW Rheinhafendampfkraftwerk, Karlsruhe), which enabled the long-term functional test of ceramic as well as polymer gas separation membranes for up to 1100 h. For the first time, a CO2 enrichment from 12 vol.% in the flue gas to 57 vol.% in the permeate of a polymer membrane was demonstrated. Due to operating this membrane in direct contact with flue gas, the flow rate was reduced from 0.86 to 0.07 m3/m2 h bar within the first 400 h. This reduction was mainly caused by the deposition of ash particles and gypsum suggesting the need of developing effective membrane protection strategies. In addition, ceramic supported Ti0.5Zr0.5O2 and metal supported Co–SiO2 membranes were tested under the same conditions. Even if demonstration of CO2 gas separation with ceramic membranes requires further modifications of the membrane materials, the long-term exposure in the power plant led to notable results regarding adherence of functional layers and chemical stability.