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Materials
|
KOH |
Temperature |
Pressure |
Operation |
30 % |
80 ° C |
30 bar |
Design |
40 % |
120 ° C |
40 bar |
Table 4 . Operating and design parameters of a typical alkaline electrolyzer
on the caustic side is acceptable . If no corrosion is tolerable on the caustic side , DSS 2507 or 2906 should also be considered for sweet water cooling . For direct cooling systems using seawater , DSS 2507 is recommended due to its superior corrosion resistance in seawater compared to DSS 2906 .
Conclusion Alkaline electrolysis of water to produce hydrogen is the most mature and cheapest technology available . The MOCs commonly used for alkaline electrolyzers are often standard austenitic grades such as 304L or 316L , which are relatively cheap while still providing a good service life . However , in certain cases , it is desirable to have a very long service life of the equipment , up to 30 years , with minimal or no maintenance or part replacement throughout that time . This places a very high demand on the corrosion resistance of the MOCs used , and the standard austenitic grades may not be suitable for such requirements . It has been shown in this article that duplex grades have superior corrosion resistance in caustic environments compared to 304L and 316L . Specifically , duplex grade 2906 has been shown to have suitable corrosion resistance in caustic environments to achieve more than 30 years of service life without significant material loss , even under upset conditions involving higher caustic concentrations
and temperatures . DSS 2507 is a suitable material choice for heat exchangers using brackish water or seawater for direct cooling . This is because the corrosivity of the caustic stream will be lower in a cooling service , and DSS 2507 has better corrosion resistance in chloride-bearing cooling waters compared to DSS 2906 . However , duplex grades are not suitable for service in contact with high-pressure hydrogen gas . For these parts of the electrolyzer , high-alloyed austenitic grades should be used . There remains a question regarding the potential increased susceptibility of stainless steel grades to caustic stress corrosion cracking ( SCC ) in the presence of highpressure oxygen . Further investigation is needed to explore this topic in greater detail .
References
1 . Leander , D ., & Philipp , A . ( 2019 ). Tappi PEERS : Conference Proceedings 19PEERS .
2 . Alleima Technical Center , Corrosion Tables , Sodium Hydroxide .
3 . Leander , D ., & Juhlin , A . ( 2004 ). AB Sandvik Materials Technology . R & D Report 040134TE .
4 . International Journal of Hydrogen Energy 35.18 ( 2010 ): 9736 – 9745 .
5 . San Marci , C ., & Somerday , B . P . ( 2012 ). Sandia Report SAND2012-7321 .
6 . Francis , R . “ Duplex Stainless Steels and Chloride SCC – How Resistant Are They ?” Paper presented at the Duplex World Seminar & Summit 2022 , Rotterdam , The Netherlands .