OT: Using ammonia as a fuel

[Chris Hogg]

I occasionally see references to using ammonia as a carbon-free fuel, rather than e.g. methane (which isn't) or hydrogen (with its hazards, real and imaginary). See

. But I have a vague memory from chemistry lessons in the distant past of our chemistry master demonstrating burning a gas of some sort that had a cold flame, almost invisible but faintly blue. My memory is that the gas was ammonia. If it was, then the ideas of using it as a fuel seem dubious. If it wasn't ammonia, what was it?

At least with ammonia you'd know pretty soon if you had a leak!

[Jethro_uk]

So what do you do with the carbon you burn to make ammonia ? (is that the Haber Bosch process ?)

Digging into O level chemistry, my memory is that ammonia isn't very flammable (needs a catalyst). Although it makes great bombs.

[Andy Burns]

There was an article somewhere(!) recently about ammonia as a fuel for ships instead of bunker oil, no carbon so no CO2, much less energy dense but I suppose that matters less when you're floating.

[The Natural Philosopher]

But lots of NOx!

[NY]

Stink bombs!

[Jeff Layman]

Maybe Carbon disulfide and nitrous oxide burning together:

Carbon disulfide itself burns with a blue flame, but I doubt the temperature of reaction is low!

The only compound I know that burns with a cold flame is thiophosphoryl fluoride, but that, according to the Wiki article, burns with a yellow flame:

However, at

, on page 312, it refers to a blue flame.

More info on cold flames here:

but I still don't see anything with a cold blue flame.

[The Natural Philosopher]

Its all very strange, any synthetic chemical fuel when 'burnt' will return to what it was made of, mostly, so none are more or less 'sustainable' than any others...so why not make diesel which we know exactly how to use and have a trillion dollar infrastructure in place to distribute?

[newshound]

Heats of combustion: Ammonia, 22 kJ/g. Methane, 50 kJ/g. Ammonia is easier to keep liquid so potentially it would be easy to get higher energy density than methane, but not as good as (liquid) propane or butane, or petrol/diesel etc.

But of course you need to supply energy from somewhere to make it.

[Martin Brown]

There are couple of problems with ammonia as a fuel.

1. You have to make it first - Haber process isn't too bad for that but you will need a good source of abundant hydrogen.
2. It is rather toxic.

I can recall the dyestuffs ice maker for azo dyes had a huge industrial scale freezer with a 20' flywheel compressing ammonia to make sort of hollow ice cubes each about the size of a man that would be smashed up to cool the reaction. You could smell it from half a mile away.

From your description I would hazard a guess it was the classic CS2 and NO demo but you don't mention the insane squeal that accompanies the blue flame. Otherwise a near invisible flame could be methanol vapour.

And you would be dead because of it if you didn't get a normal air set on PDQ. There used to be deaths from ammonia leaks back when domestic fridges used ammonia as the working fluid.

[Theo]

"The simplest option, Dolan says, is to use the green ammonia as fertilizer, like today's ammonia but without the carbon penalty. Beyond that, ammonia could be converted into electricity in a power plant customized to burn ammonia, or in a traditional fuel cell, as the South Australia plant plans to do. But currently, ammonia's highest value is as a rich source of hydrogen, used to power fuel cell vehicles. Whereas ammonia fertilizer sells for about $750 a ton, hydrogen for fuel cell vehicles can go for more than

10 times that amount."

and Australians are planning a big solar/wind farm in the outback to generate it - easier to transport ammonia than hydrogen:

Theo

[Jethro_uk]

Indeed.

Want to use hydrogen as a fuel ? Bolt on some carbon and oxygen. Job done.

[Jethro_uk]

The most interesting thing I've read about ammonia is that it can be used as a lifting gas.

[Tim+]

Nah, just burn iron instead. ;-)

Tim

[The Natural Philosopher]

No need to even bolt on oxygen. What is a turbo for, anyway?

[Chris Hogg]

Thanks Jeff. It was some 50+ years ago, and memories fade... :-( Perhaps my phrase 'cold flame' wasn't entirely accurate and 'cool flame' might have been better.

But that Wiki article on cool flames says "The spectra of cool flames consist of several bands and are dominated by the blue and violet ones ? thus the flame usually appears pale blue". It also lists isopropyl alcohol as burning with a cool flame. Perhaps it was that - bear in mind this was a demonstration by a chemistry teacher in a school chemistry lab in the late 1950's, so unlikely to be anything sophisticated. Could have sworn it was ammonia though...

[Tim Lamb]

Umm. So how much energy is involved in creating the iron dust?

[Chris Hogg]

My mother had an Electrolux fridge in the 1960's, that used ammonia. At one time, for a week or so, there was a faint smell of ammonia in the kitchen. I traced it to a pinhole leak in the fridge cooling system. Fortunately the particular pipe that was leaking ran across the top at the back so was readily accessible. I sealed the leak with many layers of string impregnated with araldite, tightly wound round and round! The fridge lasted a good few years after that, and my mother lasted even longer (95, died 5 years ago).

Up until I think the 1980's, ammonia was used in the investment casting process to quickly set off the mould binder, ethyl silicate, and so allow rapid and repeated build-up of the mould on the wax former. There was always a smell of ammonia in an investment casting factory, and visiting one was a head-clearing experience! Not used now for H&S reasons.

I often wondered about the atmosphere in less-well-run old peoples' homes, some of which smelt strongly of ammonia, much worse that in investment casting factories.

[Tim+]

Oodles, but the point is it?s easily transportable, no CO2 when burnt and can be recycled electrolytically using off peak electricity. Probably won?t at home on but an interesting idea.

Tim

[Chris Hogg]

'recycled electrolytically'...hmm...how does that work then, as I always thought all electrolytic process were done either in solution or as molten salt? Iron oxide isn't either soluble or simply melted.

[Jeff Layman]

I first learnt about thiophosphoryl fluoride from a remarkable inorganic chemistry book I bought in the late 50s (I was mad on chemistry at school - still am!). I got it slightly wrong, as PSF3 burns with a grey-green flame in air, but yellow in dry oxygen. There can be quite a difference between a cold flame and a cool one, as the latter depends somewhat on what your "hot" baseline is. Yes, chemistry demos in the late 50s were quite unsophisticated - I can remember our chemistry teacher cutting off too big a lump of metallic sodium and chucking it into some warm water ("to speed up the reaction"). It sure did when it got too hot, ignited the hydrogen it produced, and exploded. He had to quickly scrape a piece of burning sodium off the blackboard! It was many years before elf'n'safety, thank goodness...