[ heat transfer ]
paramount to ensure both maximum productivity and efficiency of the electrolyzer , as well as maximum equipment lifespan .
During the electrolysis process , approximately 20 – 40 % of the electrolyzer ’ s capacity is converted to excess heat . Despite the relatively low operating temperature , this heat should not be wasted . The use of heat recovery technologies allows this energy to be absorbed and used elsewhere . As a rule , recovered waste heat should be integrated back into the process in a suitable way . Alternatively , if the infrastructure allows , the heat can be sold and used on neighboring sites , for industrial processes or in the district heating network . It is also possible to use it for heat conversion processes such as the production of chilled , distilled , or hot water , as well as electricity .
However , options are limited with the lowtemperature heat generated during green hydrogen production . Current projections indicate a potential electrolysis capacity of 90 GW by 2030 , 2 which would generate 18 – 36 GW of waste heat . As more countries adopt hydrogen economy strategies and technologies continue to evolve , capacity is expected to further increase . To stay on track for the net-zero emissions target by 2050 , we would need a capacity of 200-250 GW by 2030 . 2
In order for green hydrogen production to be energy efficient and cost competitive in the long term , it is important to consider waste heat as a valuable resource .
Direct waste heat utilization in hydrogen production
A simpler solution for utilizing waste heat is to integrate it directly into the green hydrogen production process . For every 10 MW of electrolysis capacity , approximately 50 – 60 m ³ of clean water is required , highlighting the importance of efficient water recovery . With a projected capacity of 90 GW by 2030 , this translates to a global demand of up to 540,000 m ³ of water per day , roughly equivalent to the daily water consumption of the city of Los Angeles .
The treatment of the supplied water depends on its quality , which varies depending on the water source . In most cases , however , purification is necessary . The most common process for purifying water for electrolysis is reverse osmosis using chemicals . An alternative solution is vacuum evaporation , which uses the waste heat from the electrolyzer to demineralize the water and achieve the required quality for electrolysis . This process allows for direct reintegration of waste heat into hydrogen production .
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Electrolysis generates 20-40 % excess heat . Optimized temperature control is crucial for maximizing process efficiency and equipment lifetime |
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Every 10 MW electrolyser capacity needs around 60 m ³/ day of clean water . Process water desalination crucial to maximize electrolyser performance
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Green hydrogen production insights . Image © Alfa Laval
Process water production
Excess heat 20-40 %
Industrial use or district heating
Hydrogen Tech World | Issue 11 | August 2023 15