(Peter Stickney) wrote in
:

In article ,
Seraphim writes:
Stephen Harding wrote in news:3F994B53.FACA123
@cs.umass.edu:

Ralph Savelsberg wrote:

Great! However, the big question that very few people seem to be
able to answer (myself included) is where the energy to make the H2
should come from?

Natural gas. Mix methane (CH4) and very hot steam (H20) to produce
Carbon Dioxide (CO2) and Hydrogen (H2). This is a very well known
process, and is (was?) commonly used in the industrial production of
chemicals.

Erm... The Methane comes from where, exactly?

I would assume that it comes from the same place it has always come from.

Right now there are 2
sources - underground pockets, and Bovine Ddigestive tracts. The
underground sources have teh advantage of being commercially viable,
but incurs the same environmental damage as drilling for petroleum,
adn it's much riskier to store and transport. I'd rather be next to a
nuclear power plant than an LNG storage facility. Since the idea of
cracking Methane to get Hydrogen is to reduce the amount og Co2 being
generated, this method also has no advantages. The C02 is still being
created, It's just occuring at your Hydrogen Generating Plant rather
than in the car engine, or space heater, or whatever.

Well, first half the hydrogen is comming from water, so you've converted
1 mol CH4 into 4 moles H2 and 1 mol CO2. Now, its been a while sence I
had chemistry, but IIRC Delta_H of formation of water is around -240
kJ/mol (240 * 4 = -960), and Delta_H of combustion of methane is -890
kJ/mol. So if you have a good source of superheated steam (eg a nuclear
power plant) its a pretty good deal.

As for the CO2 still being produced. Its a lot easier to do something
with one large source than it is to do with millions of tiny ones.
Traping the carbon (most likely in the form of calcium carbonate) would
be a heck of a lot easier in a big stationary plant than a tiny moveing
car.

Hydrogen,
whether in gaseous or liquid form, has lousy engery density, as well.

*This* is probably the single biggest hurdle faceing a hydrogen car.
Lousy is somewhat of an understatement.

You can gat about 10 times the BTUs (Kilocalories)/gubic ft/meter
[liter/gallon] using kerosene or gasoline.

IIRC its more like 5 or 6 times for liquid H2 vs gasoline, but the point
still stands.

I'm sure you're aware that H2 is not something you can dig up
from the ground. Perhaps our hope should lie with nuclear fusion,
though that's not without its own problems either.
In my opinion H2 not the answer to a possible energy/environmental
crisis. Focussing on H2 is just replacing one problem with another.

There's so dogone much H2 around that its use for energy is almost
as attractive as splitting atoms in the long term.

But yes, those H and O atoms really like to stick together, and the
energy it takes to coax them apart is problematic at the moment.

The energy will always be probematic if water is the only thing used.
The energy it takes to free the hydrogen will be equal to the energy
you get by running it through your fuel cell, assuming that there is
no energy is lost in the process (very unlikely). Now, there are ways
around this. You can introduce something else (like Methane above)
which tends to help. Or you can use 'cheap' energy, like solar or
nuclear.

100% efficiency isn't just Very Unlikey, it's Bloody Impossible.
Don't they teach these kids Thermogoddamics any more?

If I have a glass of water, and let it sit in perfectly isolated system
(no energy loss), are you suggesting that the few molocules of water that
turn into oxygen and hydrogen, and then back into water, will, if given
enough time, cause the energy of the system to decrease?