Hydrogen as a replacement for Natural Gas

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cvb
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Hydrogen as a replacement for Natural Gas

Post by cvb » Sat Nov 14, 2020 12:48 pm

Somebody, government type, is thinking of replacing natural gas to homes with hydrogen. This would be for over a million people.

I think it sounds stupid and dangerous but it well out of my wheelhouse.

Does anybody have any ideas/knowledge?

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Martin Y
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Re: Hydrogen as a replacement for Natural Gas

Post by Martin Y » Sat Nov 14, 2020 1:13 pm

I was sceptical because I assumed the stuff would just leak, but it seems not. I gather you can substitute a percentage of natural gas with hydrogen (somewhere around 18-20%) without having to change burners or deal with new problems like some metals becoming brittle or flames becoming invisible. One of the universities is running a pilot scheme. There was a thread about it on the old forum.

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Martin Y
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Re: Hydrogen as a replacement for Natural Gas

Post by Martin Y » Sat Nov 14, 2020 1:19 pm

... so if you can build a low carbon process that generates hydrogen you could probably just add it to the natural gas supply so long as it's less than 20% and save a lot of carbon. But about 95% of current hydrogen production is from fossil fuels.

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Martin Y
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Re: Hydrogen as a replacement for Natural Gas

Post by Martin Y » Sat Nov 14, 2020 1:23 pm

Mrs Y tells me it's Keele. Project called HyDeploy.

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bjn
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Re: Hydrogen as a replacement for Natural Gas

Post by bjn » Sat Nov 14, 2020 4:01 pm

That's my understanding as well. The old school coal gas used to have a significant proportion of hydrogen in it.

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Martin_B
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Re: Hydrogen as a replacement for Natural Gas

Post by Martin_B » Sat Nov 14, 2020 11:47 pm

If you increase the hydrogen content above ~20% then you run into problems with temperature controlled burners (hydrogen burns at a slightly different temperature to methane), optical controlled burners (hydrogen burns at a different colour - mostly clear - compared to methane) and also metering stations; hydrogen and methane have different calorific values, so unless you are constantly measuring the hydrogen content you don't know how much energy value the gas has.

Also, hydrogen is just a smaller molecule than methane and metal pipes which don't leak any natural gas might not be so leak-tight for hydrogen. Water pipes are considered to leak somewhere from 10-25% of the water pumped into them prior to reaching the end user; the national gas grid pipework leaks a tiny fraction of a percentage of it's contents. Plus, any leaks have the potential to create flammable clouds (hydrogen also has a much wider flammable range (4-75%) than methane's 5-15% in air, and has a much lower required ignition energy, which makes ignition more likely).

Added to that is an issue known as Hydrogen Induced Cracking (HIC) in which hydrogen in a gas can combine with the carbon in carbon-based steels, which weaken the metal and can cause cracks. Stainless steels are better at resisting this, but much of the national grid pipework is built of metal which would be susceptible to HIC. If you get HIC in pipework it becomes more brittle, less able to handle temperature changes with expansion & contraction, less able to handle pressure changes, and more likely to fail catastrophically.

HIC occurs more rapidly at high temperatures but at ambient temperature the amount of hydrogen/carbon interaction in low quality carbon steel is non-zero and can occur even with small amounts of hydrogen present (certainly less than 20%) and is cumulative, so any hydrogen absorption will weaken the pipe permanently.

So this sounds like a great idea to the non-engineer, but a technical challenge to someone with some knowledge of the British national grid pipework (old, cheaply built and already in need of replacement for some sections). It's not that this can't be done, but it won't be cheap.
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Grumble
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Re: Hydrogen as a replacement for Natural Gas

Post by Grumble » Sun Nov 15, 2020 7:32 am

I’m no expert on HIC, but doesn’t it mainly occur with hydrogen produced as a result of corrosion, which is initially H. rather than H2? H. will form H2 quite quickly and it’s the formation of H2 that’s the main cause of interstitial cracking, is my understanding. You can create the same effect by forcing H2 in under a higher pressure, but the gas network isn’t a high pressure system. Not saying it won’t be a problem at all, but how much of a problem is not an easy question to answer.
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science_fox
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Re: Hydrogen as a replacement for Natural Gas

Post by science_fox » Sun Nov 15, 2020 10:44 am

Martin_B wrote:
Sat Nov 14, 2020 11:47 pm
any leaks have the potential to create flammable clouds (hydrogen also has a much wider flammable range (4-75%) than methane's 5-15% in air, and has a much lower required ignition energy, which makes ignition more likely).
But Hydrogen is so much lighter than methane that clouds are unlikely, like He, H2 doesn't form clouds it just escapes upwards unless there'e a really impermeable ceiling above you. It's the difference between 4% and 5% that's potentially the concern, not that H2 is flammable at 75%.

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