Re: Lomborg, part 4: water vapour and hydrogen economy

Interesting current statistics.

Recent worldwide production numbers for hydrogen are (U.S. DOE, 2001):

Origin         Amount in billions Nm3/year    Percent
Natural gas    240                               48
Oil            150                               30
Coal            90                               18
Electrolysis    20                                4
Total          500                              100

United States Department of Energy Hydrogen Program
http://www.eren.doe.gov/hydrogen/faqs.html


If the future hydrogen energy economy relies on the least expensive sources
of hydrogen (as economic behavior tends to suggest), we will still see a
reliance on fossil fuels for hydrogen, and the overall materials balance
will be conversion of fossil fuels to water.

Rough chemical balance of typical alkane conversion to Hydrogen (the process
is really significantly more complicated, but this paints the general mass
balance picture):

H2-CHCH2CH2CH2CH2CH-H2  =>  5H2 + H2C=C=C=C=C=CH2.
2H2 + O2 => 2H2O

The cost (in energy) of producing hydrogen through electrolysis of water is
significantly higher than the costs of extracting fossil fuels and, through
chemical reduction, producing hydrogen.  With advancements in
photoelectrolysis, perhaps using solar energy to produce hydrogen, we may
see a shift.  Yet, my current review of the scientific literature suggests
some technological limitations we have yet to overcome for electrolysis to
be a compeititive method for hydrogen manufacture, even if financial
incentives are created by governments.

________________________________
Richard Haimann, P.E.
The Lee Andrews Group
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> -----Original Message-----
> From: ecol-econ-owner@csf.colorado.edu
> [mailto:ecol-econ-owner@csf.colorado.edu]On Behalf Of Doug Woodard
> Sent: Friday, March 08, 2002 5:30 AM
> To: ecol-econ@csf.colorado.edu
> Subject: Re: Lomborg, part 4: water vapour and hydrogen economy
>
>
> I gather that emissions of CO2 are more important than emssions of H2O and
> function as a multiplier of water vapour.
>
> Probably emissions of water vapour in a hydrogen economy would be not very
> different from those produced now by the combustion of fossil fuels, since
> much of the content of fossil fuels is hydrogen and the hydrogen economy
> would involved "burning" hydrogen in fuel cells which are more efficient
> than most combustion engines, and some of the emitted water might be
> condensed.
>
> In any case, if we suppose that the total fossil fuels burnt annually are
> an oil equivalent of 2.5 times the amount of oil burnt annually and that
> the latter is 29 billion barrels (probably a slight overestimate), that
> the oil equivalent can be regarded as gasoline at C8H18, then I get
> roughly 15 cubic kilometres of water per year from the combustion of
> fossil fuels.
>
> Assuming that the average rainfall over the earth is 10 inches or 25
> centimetres, and taking the area of the earth from my National Geographic
> Atlas of the World as 510 million square kilometres,  I get 127,500
> cubic kilometres of rain through the water vapour of the atmosphere per
> year. I conclude that the water vapour emissions from a global hydrogen
> economy would probably be climatically trivial.
>
> Doug Woodard
> St. Catharines, Ontario, Canada
>
>
> On Thu, 7 Mar 2002 Fred.Blood@ci.austin.tx.us wrote:
>
> > As a side issue, as we go to the hydrogen economy, considered the energy
> > savior of the future, and most of the emissions are water vapor, the
> > strongest greenhouse gas, instead of CO2, from transportation
> and buildings
> > getting of the grid ... How will that impact the discussion?
>