Hydrogen Storage
1. Upon storing hydrogen in metal cylinders, in the form of compressed gas, how early, in general, we end up with ‘hydrogen embrittlement’ – that leads to the deterioration of metal cylinders?
Whether multi-layered coatings in such cases, would be able to mitigate hydrogen diffusion in steels?
Even, if random molecular diffusion of hydrogen is assumed to be curtailed, would it remain feasible to curtail surface diffusion as well as Knudsen diffusion, which would essentially ensure hydrogen seal/permeation in high-strength steels, which, in general, remains to be more susceptible to hydrogen embrittlement?
2. If liquefaction method of hydrogen storage is followed, then, would it remain feasible to prevent imbibition of hydrogen in metal cylinders?
3. If hydrogen is compressed @ 500 bar, can we prevent (a) free molecular diffusion, (b) embrittlement and (c) imbibition?
4. For lengthy transportation, whether, liquid organic hydrogen carrier (where, molecules can be hydrogenated and dehydrogenated to prevent any disasters during hydrogen transport) would remain to be successful?
If so, how about the temperature variations and enthalpy changes associated with the long-range hydrogen transportation?
Whether the energy losses and efficiencies associated with both the first law (the ratio of the amount of energy delivered to perform a task to the amount of energy that must be applied to achieve the task) and 2nd law (the ratio of minimum amount of available energy required to carry out a task to the actual amount of available energy used) of efficiencies will remain to be curtailed during its long term transportation (say, greater than 250 km)?
Suresh Kumar Govindarajan
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These are some possible points of discussion as I have gathered with help of AI
Hydrogen Embrittlement in Metal Cylinders
- Steel type: High-strength steels are more susceptible than low-strength ones.
- Hydrogen pressure: Higher pressure increases diffusion and embrittlement risk.
- Temperature: Warmer temperatures accelerate hydrogen diffusion.
- Presence of imperfections: Microcracks and inclusions can act as starting points for embrittlement.
Generally, embrittlement becomes a concern after months to years of exposure in compressed gas storage, depending on the factors mentioned above.
Multi-layered coatings: These can be effective in mitigating hydrogen diffusion. They work by creating a barrier path that lengthens the diffusion time. However, no coating is perfect, and complete elimination of diffusion might not be achievable.
Surface and Knudsen Diffusion: Even with limited random diffusion, surface and Knudsen diffusion can still occur. While multi-layered coatings can help with surface diffusion, Knudsen diffusion is more challenging due to its dependence on pore size within the material. Selecting steels with minimal such pores can help to some extent.
Hydrogen Storage Methods
- Free molecular diffusion: This can be significant at high pressures.
- Embrittlement: Risk of embrittlement still exists, especially for high-strength steels used in these tanks. Careful material selection and design considerations are crucial.
- Imbibition: Similar to liquefaction, some minimal hydrogen absorption can still occur.
Organic Liquid Hydrogen Carriers (LOHC)
Temperature Variations and Enthalpy Changes: LOHC processes involve exothermic hydrogenation and endothermic dehydrogenation reactions. During transport, temperature control is necessary to manage these energy changes. While some insulation can help, maintaining consistent temperature over long distances can be challenging.
Energy Efficiency: The efficiency of LOHC systems depends on the specific carrier molecule and process conditions. There are energy losses associated with both hydrogenation and dehydrogenation. Researchers are continuously working on improving these processes to minimize energy losses and improve overall efficiency.
Long-Distance Transport: LOHC remains a promising option for long-distance transport (greater than 250 km). Both first and second law efficiencies are crucial considerations, and research is ongoing to optimize these aspects.
Overall: While challenges exist, LOHC offers significant advantages for long-distance hydrogen transport.
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