sheldrake wrote: ↑
Wed Nov 17, 2021 12:46 pm
Woodchopper wrote: ↑
Wed Nov 17, 2021 12:14 pm
sheldrake wrote: ↑
Wed Nov 17, 2021 12:10 pm
Main concern with hydrogen for me is how explosive and easily ignited it is. Somebody with a chemical engineering degree reassure me pls.
Is it any worse than petrol or jet fuel in that respect?
Yes, it a) can leak more easily b) is easier to ignite c) can react with ferrous pipes to make them brittle and d) can burn with a flame that's hard to see so that you accidentally walk into it.
Until somebody with the right kind of engineering experience can explain how we've gotten much better at handling it I would be very nervous about running my domestic boiler off it, for example.
I have a degree in chemical engineering and have worked for 25 years with pressurised flammable fluids (usually known as the oil and gas industry). Although I do understand that you shouldn't argue from a place of expertise and just say "trust me, I'm an expert", if I had to list all my references for the below it'd be an insanely long post!
a) Yes. Hydrogen molecules are smaller than methane (the main constituent in natural gas) or the molecules in petrol (mainly octane) and jet fuel (lots of aromatic compounds). The smaller the molecule, the better the seals between, eg, valves and pipes or pipe-to-pipe flanges, have to be. Natural gas transmission systems keep the quantity of fugitive emissions very low (much lower than, eg, water pipelines) but if you carry hydrogen in a system designed for natural gas the quantity of fugitive emissions could be an order of magnitude or more higher.
As an aside, it's not always about the size of the molecules, as jet fuel carried in a system designed for natural gas will also result in high fugitive emissions, as the butane, toluene, etc in jet fuel can destroy any elastomeric seals which typically get used for natural gas. It's not just a matter of better seals with smaller gaps, but also the interactions of the materials used. See also c) below.
b) Yes. Hydrogen is easier to ignite in two ways. Firstly, it requires much less energy to ignite (typically about ~10% of natural gas) so while natural gas requires an induced spark to ignite it, hydrogen can ignite from static electricity (and the flow of gas can sometimes create it's own spark large enough to ignite!) If there is a black surface exposed to the sun, this can ignite hydrogen without even a spark. Secondly, while natural gas needs to be in a concentration of 5-15% in air to sustain a fire (lower than 5% and there's not enough fuel, higher than 15% and there's too much fuel and it starves itself of oxygen) hydrogen will ignite in concentrations of 4%-75% in air. This means that any release of hydrogen is far more likely to ignite than a release of natural gas. By contrast, releases of petrol and jet fuel are actually quite difficult to ignite.
c) Yes. Hydrogen can cause embrittlement of steel (and other materials, but pipes are usually steel). This embrittlement, also known as hydrogen induced cracking, is worse with harder steels, so you'd be better off using a 'weaker' steel which requires a thicker wall for the same pressure rating. Any copper pipes in your home would fair even worse, as copper alloys usually include oxygen, which the hydrogen will react with to create water microbubbles within the copper pipe. Needless to say, this isn't what you want!
d) Yes. Hydrogen burning is a simple equation (hydrogen + oxygen = water) and burns with a flame which is almost invisible. Mind you, methane burns with an almost invisible flame, too, and the flame which you can see in your boiler/hob is mainly caused by impurities which are added to make the flame and smell more noticeable. If hydrogen were used for domestic supply, then I would expect these impurities (typically mercaptans) to be added to the hydrogen, too, and probably in greater quantities than for natural gas.
We had a discussion here (or possibly the old place) about plans to add up to 20% hydrogen into natural gas for domestic supply. To me that's a really bad idea, as you increase the amount of fugitive emissions and reduce the safety of domestic appliances whilst still needing 80% of the natural gas (possibly more like 85-90%, as hydrogen doesn't release as much energy when it burns).
If you are going to transport hydrogen you need to do it in a transmission system designed for hydrogen, not one designed for natural gas and with crossed fingers. Retro-fitting a natural gas transmission system to be compatible with hydrogen would probably cost at least as much as just creating a new purpose-built hydrogen transmission system.
Also, your domestic boiler couldn't run properly off hydrogen without replacing the burners, sensors and control system, which would probably be as expensive as buying a new, hydrogen-designed boiler. Even ovens, hobs, gas fires would need modifications or new appliances to operate using hydrogen as a fuel rather than natural gas.
The internal combustion engine doesn't cope well with switching the fuel from petrol to diesel or vice versa, and the difference between natural gas and hydrogen is substantially greater than the difference between petrol and diesel. Just because hydrogen and natural gas are both flammable gases doesn't mean that they are compatible. The old phrase IABMCTT comes in very handy here!
"My interest is in the future, because I'm going to spend the rest of my life there"