Plasma Enhancement Gases separation via ceramic porous membranes for plasma exhaust processing system of DEMO

Abstract

Abstract Plasma Enhancement Gases (PEGs), i.e. N2 and noble gases, are used to mitigate the heat load over plasma facing components. Therefore, in DEMO, the tokamak exhaust stream will contain a certain amount of these PEGs which require a dedicated purification and separation unit. In the last years, PEG separation using microporous ceramic membranes has been studied at ENEA Frascati laboratories in the framework of the EUROfusion programme. The experiments conducted with a binary gas mixture have revealed the poor separation capability of the multi-channel membranes as a consequence of their high permeance. In this activity, the behaviour of a commercial microporous single-channel membrane made of alpha alumina has been theoretically studied to evaluate its efficacy in separating H2 from PEGs. The analysis has considered a total feed flow rate of 20 L min−1 (at STP) having an equimolar composition of H2 with one of the following species: PEG (Ar or N2), D2 or He. The separation capability has been evaluated by assuming the upstream pressure in the range 200−1000 kPa and keeping the downstream pressure at 100 kPa. Considering the values of the permeances assessed in our previous work for single gas tests, the membrane length needed to achieve a given target of separation has been evaluated as a function of the H2 mole fraction in the retentate stream.