Hydrogen fueled vehicle using Mg? 1

[vcebrad]

Interesting article on a hydrogen fueled vehicle...

http://www.isracast.com/tech_news/231005_tech.htm

Thoughts?

 

[swall]

Reminds me of generating acetylene in a miner's carbide lamp. Just add water to calcium carbide pellets and you get a combustible gas for illumination. But, then you have to dispose of a volume of ash comparable to the carbide pellets you started with.

 

[EHudson]

It takes a bunch of electricity to produce a pound of aluminum so the idea of drivng to work using old beer cans or magnesium may not be exactly 'free'.

 

[vcebrad]

Yeah, the little diagram on their website might be missing a few items, like the amount of solar/nuclear/coal-fired energy it takes to refine, process, and shape those kind of metals.

 

[crysta1c1ear]

We know that hydrogen is now often described as an 'energy carrier' rather than as a 'fuel', since some source of energy is required to create the hydrogen in the first place.

One of the problems with hydrogen seems to be space needed to store it. I think we have all seen the pictures of vehicles with a fuel cell at one end, hydrogen tanks at the other, and not much in between.

I can therefore understand the logic of generating hydrogen in the vehicle rather than carrying the hydrogen around. However, if something like aluminium is going to be used as the source of power for a vehicle, why bother to generate hydrogen and then burn the hydrogen in a combustion engine or fuel cell.

When I first did some investigation to find out what fuel cells are, I didn't come across hydrogen fuel cells and automotive applications. Nowadays one has to sift through things to read anything else, but at the time, the information I found on fuel cells, was aluminium fuel cells to provide power to telephone exchanges in the event of failure of mains electric power.

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I have a little digital clock at home. Two electrodes are plugged into a potato from the garden, an apple off the tree, or whatever else happens to be in season. It appears to many that the clock is powered by the apple. However, over time, the zinc on the zinc electrode [I assume that's what it is] is eaten away, and really the clock is running as a fuel cell with the fuel being the zinc electrode which will need replacing from time to time.

I would be surprised if creating hydrogen and then using it[/] proved to be more energy efficient than a fuel cell directly powered by aluminium, or magnesium, or whatever these guys decide to use as their fuel.

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Last month the rage was the Russian scientists that have persuaded the UK government to part with some cash in the hope that spinning water inside a vehicle can generate the hydrogen required to power it - a sort of perpetual motion idea, as the hydrogen gets turned back into water!

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Fuel cells are just batteries that don't get recharged. If I keep replacing the lead and sulphuric acid in a lead acid battery (and clearing out the waste, eg lead sulphate) then I have a lead and acid powered fuel cell.

Without any calculations to back it up, I intuitively feel that lead would be more effciently used this way, than somehow trying to generate hydrogen from it and then trying to use the hydrogen, and the same would apply to magnesium, aluminium, etc.

I'd need a good explanation to be convinced that what they are proposing has any real merit, but I'm a hydrogen sceptic anyway - at least until most houses are running off electricity from non-hydrocarbon sources.

 

[GregLocock]

Electrical energy to smelt aluminium runs at 16 kWh/kg, or 58 MJ.

1 kg of Al reacted with water will produce at best 0.11 kg of hydrogen (some hydroxide is formed which will reduce the yield)

because

3H20+2 Al= Al 2 O 3+ 3H2

AW 1 16 27

MW 18 27

N 3 2 1 3

RW 54 54 6

so we burn 1 kg of Aluminium ot get 0.11 kg of hydrogen

And when we burn the hydrogen at say 60% efficiency (ie equal to the best practical fuel cell seen) we'd get 0.11*120 MJ*.6= 8 MJ of useful work

So, we're putting in 56 MJ of electrical energy and getting 8 back.

Are these guys lying scumbags or just incredibly incompetent?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ccw]

Greg,

The Mg + H2O reaction is exothermic. I've seen lab demo of burning Mg underwater. I've not seen this for Al. The heat from the exothermic reaction creates steam and this was also going to be used in conjunction with the reburn of hydrogen as shown in the isracast schematic.

As a comparison what does the conversion of crude oil at 1000 ft. down into IC engine shaft output look like:

energy in->->->->energy out ?

 

[GregLocock]

No, that is not a fair comparison either, you have ignored the energy input to make the electricity.







Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[cnova]

Since they estimate that you'll need ~ 220 lbs of metal to provide the equivalent of a tank of gas and wholesale aluminum prices are currently running at $0.83US / lb.....

$180 for a tank of "fuel"!

.....I have some prime swamp land for sale!

Stupidity is the basic building block of the universe. F.Z.

 

[vcebrad]

Out of curiousity, anybody have any idea how much work is required to pump up and refine petroleum? I'm assuming the numbers are different for say gasoline and diesel. I've seen some stats on biodiesel claim it produces about 30% more energy than it takes to "make" it (not including the solar energy required for the soybeans or crop of course). I'm wondering how some of the other fuels like hydrogen (in the exapmples above) and gasoline compare.

 

[GregLocock]

OK, I had seen figures that roughly 88% of the calorific value of the oil that gets to the bore ends up as useful product.

However, this does not square very well with claims that only 50% of the oil pumped up is actually useable as liquid fuel, the rest gets used as asphalt etc.

Farming is a very fuel intensive business, I am not surprised to hear that if you grow the biomass on a typical first world farm then it ends up energy negative. Biomass should be generated from unusable by-products, not as the primary crop (hello sugar farmers).



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tbuelna]

Why bother with processing the Mg to produce hydrogen. Burning metals directly produces lots more energy. That's why they add aluminum powder to solid rocket motors.

http://www.keralanext.com/news/index.asp?id=409921

 

[turbocohen]

Still, fossil fuels are still much cheaper, even as a source of hydrogen. People will follow the technology that leaves more money in their pocket.

 

[whoaru99]

A little reading from one perspective on hydrogen as fuel.

http://www.caranddriver.com/article.asp?section_id=27&article_id=9978&page_number=1

 

[turbocohen]

carbon tolerant stationary fuel cells make a little sense. a little

 

[unclesyd]

The first two are very detailed papers on future fuels with an emphasis on H2. The third is a synopsis on the first two.
In my humble opinion these studies give a far better picture of future fuel systems than I’ve seen.

http://www.dotynmr.com/PDF/Doty_FutureFuels.pdf

http://www.dotynmr.com/PDF/Doty_H2Price.pdf

http://www.dotynmr.com/PDF/Doty_Practical_Energy_Brief.pdf

 

[ATBradbury]

You could also use Iron to generate Iron Oxide and Hydrogen gas, which goes direct to the engine. Then you are left with a tank of Iron Oxide. This can (in theory) be regenerated via addition of hydrogen at a later stage (i.e. the refilling station) which converts the Iron Oxide back to Fe. The advantage is no hydrogen pressure, but the disadvantage is I calculated a low energy/kg of the fuel, and thats after a lot of other problems have been 'ironed out'!!! Still, it should be substantially superior to batteries, as they currently exist, in terms of power density. Efficiency, thanks to that IC engine, will not be high though. A better venue might be Carbon Fuel, in diect carbon fuel cells.

 

[ATBradbury]

I forgot to put, the Iron generates hydrogen through the addition of water, which also has to be carried.

 

[ornerynorsk]

Has anyone ever heard of something called "diminishing returns". Gee, let's just convert the fuel source 5 or 6 times, and end up with an overall efficiency of disgustingly close to nothing. Fuel must be used with as little processing, as close to its natural form, as possible. The aluminum thing makes no practical sense whatsoever. Neat idea, but not practical.