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 1100h. For the first time, a CO₂ enrichment from 12vol.% in the flue gas to 57vol.% 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 0.07m³/m²hbar within the first 400h. 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 Ti_0.5Zr_0.5O₂ 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.