[ water treatment ]
this project seeks to provide green hydrogen for both mobility and industrial end users . For the first phase , an alkaline electrolyser was chosen , requiring a flow of ultrapure water of 4.5 m 3 / h with a conductivity of < 5 µ S / cm . The water was sourced from the drinking water network with a hardness of 11 ° dH and no free chlorine . In this case the quality criteria could be met using a double-pass RO system combined with CO 2 removal and with an ion exchange softener in front of the RO membranes to ensure very low concentration of multivalent ions .
Internal polishing of water
For electrolyser systems like PEM and AEM operating directly on ultrapure water , water treatment does not stop with the make-up water . After entering the electrolyser system , the water is continuously contaminated with metal ions from the piping and process equipment as well as with ions and organics from the electrolyser stack . These contaminants must be removed to maintain the lifetime of electrolyser .
Fig . 7 . Water treatment system for the 20 MW HySynergy project
The way to solve this problem is to introduce a side stream polisher internally in the electrolyser on the anode circulation system .
Two processes are available for handling the side stream polishing : mixed bed ion exchange and EDI . In this application , EDI is limited due to operational temperatures and the fact that it produces a concentrate waste stream . Mixed beds are the preferred option because they allow for zero waste of water and a higher
Fig . 8 . Pumping requirement for circulation of ultrapure water over the electrolyser stack
28 Hydrogen Tech World | Issue 6 | October 2022