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The Haber-Bosch process used in ammonia production is done at high temperatures (400-500 °C), so you can use "hot" hydrogen to power it (i.e. to heat input nitr
by fuoqi 5y ago
The Haber-Bosch process used in ammonia production is done at high temperatures (400-500 °C), so you can use "hot" hydrogen to power it (i.e. to heat input nitrogen) and maybe even extract some of leftover energy in produced ammonia heat to generate electricity. Same with steel production, you don't need to cool hydrogen before using it, on the contrary, high temperatures are useful in such cases.
Using "hot" hydrogen would mean that you have to build ammonia and steel plants right near nuclear reactors, which can be somewhat difficult, but potential efficiency benefits could be big enough to offset it.
- pfdietz 5y agoHB consumes energy in its compressors, but releases that energy as heat on the catalyst. Hot hydrogen doesn't compress well, so you'd cool it beforehand.
- fuoqi 5y agoFor HB you need pressure of 250-350 bars, while existing PWRs routinely work with 150 bars of coolant pressure. I assume it's possible to produce hydrogen with the necessary pressure using VHTRs, i.e. you would get hydrogen already pressurized and hot. You would still need to run compressors on input water, but it's much easier than working with hydrogen later.
- pfdietz 5y agoProducing hydrogen at pressure doesn't eliminate the energy needed, it just forces the electrolyser to act as the compressor (the voltage goes up).
- fuoqi 5y agoPlease, read the thread carefully. The point is that with VHTRs you don't need the usual electrolysis to split water into hydrogen and oxygen. Instead you can use high temperatures produced by a reactor to power conversion directly, thus improving the process efficiency. The most common option is the sulfur–iodine cycle. Granted, it's not so suitable for producing hot pressurized hydrogen (though it may be possible to separate iodine and hydrogen without condensation), but there are other options for thermochemical water splitting like high temperature electrolysis, which requires less electricity than electrolysis under STP.
- pfdietz 5y agoThermochemical cycles like that have been explored for decades and have gotten nowhere. For some wonderous reason, systems that involve vaporized high temperature sulfuric acid and the like have not proved to be practical. Falling cost of electrolysers and electrical power make that approach even more of a nonstarter.