[ water treatment ]
cost-effective for water flows relevant to green hydrogen plants .
VC can utilize the electrolyzer waste heat to preheat the incoming seawater and hereby lower overall energy cost , while VD can use the waste heat directly to evaporate seawater under vacuum conditions .
In the desalination industry , membrane-based SWRO is the prevalent technology . So why consider thermal desalination for green hydrogen ? For two main reasons : 1 . Ability to utilize waste heat 2 . Combine water treatment and cooling
Places where thermal desalination is used today are characterized by access to cheap waste heat that can be used to drive the process . In electrolysis , avout 20 % of the electrical energy is lost as waste heat . This means that for every 1 m ³ of ultrapure water that is electrolyzed , 1,000 kWh of waste heat is generated . In addition , if the waste heat is used to produce ultrapure water , the water treatment process will also cool the electrolyzer , eliminating the need for a cooling tower .
Comparison in the context of green hydrogen
To evaluate how well each desalination technology is suited for green hydrogen , they are compared based on the following parameters :
• Product water quality
• Robustness and flexibility
• Footprint
• Energy requirement
• Capital cost
Both SWRO and thermal desalination deliver high quality product water , but thermal methods can typically achieve higher purity . SWRO systems will typically be able to produce water with 100 – 200 ppm NaCl , equal to 200 – 400 µ S / cm . In comparison thermal desalination methods will deliver product water quality in the range of 2 – 10 ppm NaCl , equal to 4 – 20 µ S / cm . This means that to be comparable in terms of water quality , a SWRO system must be followed by a second low pressure RO pass to further filter the permeate . Using a second RO step , operated at 10 – 20 bar , the water quality can be improved to 2 – 5 ppm NaCl or 2 – 10 µ S / cm .
In terms of robustness , thermal desalination systems have a more durable design with fewer moving parts
24 Hydrogen Tech World | Issue 16 | June 2024