From: jamesh@aisb.ed.ac.uk (James Hammerton)
Newsgroups: alt.save.the.earth
Subject: Re: Food for thought... was Re: Ethanol fue
Date: 18 Nov 92 14:02:17 GMT
Reply-To: jamesh@aisb.ed.ac.uk (James Hammerton)
Organization: Dept AI, Edinburgh University, Scotland

In article <BxvL84.HDJ@news.udel.edu> todd@chester.cms.udel.edu writes:
>In article 7662@aisb.ed.ac.uk, jamesh@aisb.ed.ac.uk (James Hammerton) writes:
>
>>>># How does ethanol fuel help to solve the CO2 problem? 
>
>>Look, it is simple. You grow some plants( they absorb CO2 in the
>>process), turn them into ethanol, it burns in some engine, you grow some
>>more plants which absorb the CO2 released earlier, net effect is nil 
>>CO2 emissions, then the process repeats itself. The point is that it is
>>a cycle were the CO2 released by burning the ethanol is matched by that
>>absorbed in growing the plants to produce it, thus the overall effect over
>>the cycle is for a nil CO2 emission.
>>
>>The idea is not to continually deplete the stocks of whatever plant is
>>being used(this would lead to net increases in CO2) but to grow more
>>plants to replenish the stocks and then turn them into ethanol and use it
>>as fuel.As long as you keep replacing the plants with new ones the
>>overall effect is nil emissions.
>>
>>
>>James
>
>So then how many plants does it take to *absorb* an equal amount of CO2
>from the atmosphere that is produced from say 1 gallon of ethanol?  How
>many plants does it take to produce 1 gallon of ethanol.( sounds like a
>bad ethnic joke :-) )  What plants do you use to make ethanol?  This
>whole mass balance seems a little "unbalanced". But I am extremely curious
>at this point.Has there been work done of the benefits of growing *plants*
>for ethanol production, such that these plants act as CO2 sinks, then are
>turned around and used as a CO2 source?  I guess I'm a little dense on the
>subject.Perhaps, James you will continue this discussion,  you have my
>attention and probably some lurkers as well.  Maybe they will add to the
>discussion?? 
>
>Todd


Well, here you've got me. I don't actually know all the details about
such schemes. However a few points could be born in mind. First of all,
it has to be said that having some of the CO2 released being then reabsorbed
by growing the fuel is better than having none of it reabsorbed, even
without a balance, which would make using ethanol less of a problem than
petrol. Secondly, it strikes me that you won't convert all the plant
matter to alcohol, thus not all of the CO2 absorbed would then be
released again by burning the ethanol, though what does happen to it
is another matter. I do know that in Brazil they use sugar cane to
produce ethanol which is then used as a fuel(I believe that it is mixed
with normal petrol though, but I could be wrong, ask an expert!), so
that someone at least has done it and found it viable( it also makes
Brazil less dependent on oil imports). Note that fuel provided in this
way can be considered renewable since you can replenish what's been used.

However I can only really provide conjecture here. I don't have the
info. that would be needed to give an in depth picture of how it works,
and it does have some undesirable consequences(for example giving land 
to fuel production rather than food production) to take into account,
what I described before was the theory. For the practice I'll need to do
a bit of research. Still if there's someone out there who knows a bit
more maybe this discussion could go further, meanwhile I'll see what can
be dug up.


James