Impact of Fly Ash on the Membrane Performance in Postcombustion Carbon Capture Applications

Abstract

The presence of particulate impurities in the form of fly ash within a postcombustion carbon capture application will be difficult to avoid. In this work, the effect of fly ash on the membrane performance for both black- and brown-coal applications is examined. Deposits of either black- or brown-coal fly ash on the membrane surface had no impact on CO2 permeance when totally dry. In contrast, deposits of a mixture of fly ash and liquid water caused the membrane permeance to fall below the level expected from the presence of liquid water alone. For both black-coal fly ash (Sauter mean diameter 9.2 μm) and brown-coal fly ash (Sauter mean diameter 9.8 μm), the permeance recovers to over 98% of its original value once the moisture content of the fly ash cake falls below 50 vol %. This moisture level corresponds to that needed for bed desaturation. However, the permeance never recovers for deposits of brown-coal fly ash of smaller particle size (Sauter mean diameter 7.1 μm) once exposed to water but plateaus at between 40 and 70% of the value for the clean membrane. This reflects the formation of gypsum and other cementitious products from pozzolanic reactions, which give a nonporous fly-ash cake. The use of acid solutions of up to 6 M HCl is shown to be effective in removing the brown-coal fly ash from the membrane surface but is ineffective in removing black-coal fly ash.