[ water treatment ]
Water treatment for green hydrogen : what you need to know
Water is essential for the production of green hydrogen . As the market matures , crucial questions about the use of water are starting to arise . How much water is needed ? What quality is sufficient ? Where should the water come from ? Let ’ s shed some light on these fundamental questions .
By Henrik Tækker Madsen , Application Development Manager , Silhorko-Eurowater – A Grundfos Company
To have a qualified discussion about the use of water for green hydrogen production , we first need to define what we mean by ‘ water ’.
In the production of green hydrogen , it is necessary to distinguish between three types of water : 1 . Ultrapure water ( used as a feedstock for the electrolyser ) 2 . Cooling water 3 . Raw water
The quantity of ultrapure water used for electrolysis will be different from that of raw water extracted from the environment , and the quality of ultrapure water and cooling water is also different . Therefore , we need to deal with each one separately . Let ’ s first look at ultrapure water .
What is ultrapure water ?
Water suitable for electrolysis is commonly called ultrapure , but what is to be understood by this label ?
Several parameters influence what quality water must have to be suitable for electrolysis . These include the type of electrolyser , electrode material , system design and even brand of electrolyser . the electrolyser efficiency and / or irreversibly damage and degrade the electrolyser .
With so many variables and effects , it is no surprise that water treatment is often tailored to the specific project , making it very difficult to come up with a unified standard for water quality for all electrolysers .
One strategy that electrolyser manufacturers can follow to simplify the issue is to set the requirements for conductivity sufficiently low to ensure that the concentration levels of problematic ions and molecules will in all certainty be below the electrolyser requirements . A good starting point can be < 1 µ S / cm for standard alkaline electrolysers , and < 0.1 µ S / cm for PEM electrolysers and alkaline electrolysers relying on advanced electrodes . However , it is worthwhile to remember two things : firstly , water treatment constitutes a relatively minor part of the total CAPEX of a hydrogen plant , and secondly , no electrolyser was ever damaged by using water that was too clean . Ensuring high quality and reliability in the water treatment may thus be the best investment to be made for an electrolyser system .
Add to this that each of the ions and molecules in water will affect the electrolyser differently . Some can increase OPEX because of corrosion or increased need for cleaning , while others can lower
Consumption of ultrapure water
We can accurately calculate the amount of ultrapure water required for production of green hydrogen , using the atomic composition of water ,
22 Hydrogen Tech World | Issue 6 | October 2022