[ water treatment ]
flexibility in meeting the process requirements of the electrolyser system .
The side stream loop should be dimensioned to remove contaminants at a rate equal to or higher than the release rate to avoid accumulation in the electrolyser . The release rate is complicated to estimate as it depends both on material choices in the process equipment and the electrolyser as well as on operating conditions . Typically , the flow of the polisher loop will be in the range of 2 – 10 % of the anode circulation flow rate . The higher the percentage , the higher the quality of the water sent to the electrolyser will be .
Pumps
Finally , we must also address the need for pumping and the effect it has on water quality . Pumps are used in several places in electrolyser systems , but the most central role is for circulation over the electrolyser stack . Large amounts of heat and gasses are released during electrolysis , and to remove gasses and maintain an acceptable temperature differential across the stack , very high flow rates are required . To keep the temperature increase between 2 – 4 ° C , a flow rate of 50 – 100 m 3 / h per MW is required . That means that the flow rate is 250 – 500 times larger than the flow of make-up water into the electrolyser system . Because of this , pumps take up a significant part of the CAPEX for a green hydrogen system , 10 – 20 % of the combined CAPEX for stack components and balance of plant , and this presents operators with a difficult challenge . The cost of pumps pushes for cost-effective solutions , but the strict quality requirements as well as the harsh operating conditions push for high-quality and specialised products . Part of the solution to this challenge is to adopt a holistic approach and think about water treatment in combination with pumping . By improving the polishing system , the polisher can help overcome the release of metals and thus lower the requirements for the pumps used for recirculation .
Looking ahead , it is clear that water treatment will play an essential role for the green hydrogen industry , and like the other components in a green hydrogen plant , water treatment systems will also face important questions about scalability , modularity , redundancy , etc . as the industry matures . Figure 9 shows an example of what such large-scale installations could look like .
Fig . 9 . Modular water treatment solution for a 300 MW electrolyser
About the author
Henrik Tækker Madsen , PhD , is a water treatment specialist working within the interplay between water and energy . He works as Application Development Manager at the water treatment company Silhorko-Eurowater A / S – part of Grundfos , where he leads the work on establishing industry-leading knowledge within various water applications , including electrolysis . Dr . Madsen is a chemical engineer with more than 10 years of experience in business development , sales , R & D and innovation .
Hydrogen Tech World | Issue 6 | October 2022 29