Re: Use for hydrogen

In message <43bb157d$0$76011$d368eab@xxxxxxxxxxxxxxx>, Mike Van Pelt <mvp@xxxxxxxxxxxxxxx> writes 
In article <sehix-CFF866.17492402012006@xxxxxxxxxxxxxxxxxxxxx>,
Steve Hix  <sehix@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

In article <f19jr1tu8utsgh27pjtn4qm7ourootfbga@xxxxxxx>,
jtingle <jtingle@xxxxxxxxx> wrote:

Using hydrogen directly would be both uneconomical and unsafe. 

Uneconomical (currently), yes. Unsafe? No worse than natural gas, and in
some ways safer. It's less toxic, and it won't pool in low areas to
build up explosive concentrations; it rises and dissipates.


Check out http://www.humboldt.edu/~serc/h2safety.html

Hydrogen is easier to light than methane (Autoignition
temperature 520C vs 630C, and minimum ignition energy in air of
0.017 mJ vs. 0.274 mJ) has very much broader flammability range
(4% to 75% vs 5.3% to 17%).


That's not necessarily a bad thing. If it ignites

 It also burns much hotter,
120kJ/kg at 2045C for hydrogen, vs. 50 kJ/kg at 1325C for methane.

I'm not sure this is relevant. The gas supply is presumably configured to deliver a fixed quantity of energy therefore it would deliver a lower weight of hydrogen.


I don't think this is necessarily a show-stopper for hydrogen,
but it does have its ... challenges, safety-wise.

It's lower density would make it leak faster and I believe that it can form interstitial hydrides that could weaken metallic structures.

I can imagine situations where it would be an ideal fuel, for instance in the middle of the Sahara and SW USA. Burn the hydrogen in air to generate electrical energy and water (contaminated with some nitrogen oxides). Pour the water on to the sand. React some more of the hydrogen with the now oxygen-depleted air to generate some ammonia, use that to neutralise the excess nitric acid in the soil.

Grow trees on the now moist sand. Heat the wood in an atmosphere of hydrogen to distil off wood-tar and reduce the complex organic compounds to hydrocarbons and water. Use catalytic cracking to turn the hydrocarbons into gasoline and fly that out of the desert in unmanned hydrogen-filled balloon tankers. Dump the waste ash back into the sand as fertiliser.

Rinse, repeat.

This is part of the scenario for a story idea I've been kicking around based on getting hydrogen from space.



--
Bernard Peek
London, UK. DBA, Manager, Trainer & Author.

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