[Gasification] CO2 recycling

[jim mason]

gf, your musings on plasma and microwave gasfication are very
interesting.  i look forward to seeing how these schemes might work
out re the realities of energy input and output.  thermodynamics is a
relentless master.  there is no duping the king of the castle, now
matter how clever our dancing.  nontheless, please continue.  can we
in any way define and divide some of the experiments here towards
faster answers?


co2 recycling is clearly interesting to the degree that we have
adequate heat in the char zone.  such is harder in biomass gasfiiers
for the reasons doug elaborated.  note also that the endothermic
energy required to reduce co2 is greater than that for h2o.  this is
an oft forgotten fact.  i do not have the chart in front of me, but i
remember it taking about 20% less energy to reduce water thermally
than carbon dioxide.  the resulting fuel hydrogen fuel is more
attractive for engine situations, as it will support higher rpm, given
the faster flame front of hydrogen.

so all other things being equal (which they are not), it is better to
inject steam to partake of "excess" heat in the char zone, than
recycle co2 into the char zone.  note that most ICs also have a waste
heat stream in the form of  hot water and/or steam.

either way, it is deceptive to think of either h2o or co2 as fuel.
both are the end products of combustion.  they both have elements that
if separated or reformed, can again be fuel, but doing so requires an
addition of energy, which is exactly what you are trying to get out.
you can't get more energy out of these molecules than what you pack
in.

the potential "free energy" here is the waste from the internal
combustion engine.  as we are working with a gasification system that
requires process heat, the waste heat from the engine is useful for
us.  we can essentianlly increase the thermal efficiency of the engine
by recycling its waste heat for drying, pyrolysis and blast preheating
in the gasifier.  thus reducing fuel consumption.  note that IC
exhaust heat is not high enough to directly heat a char zone.  but it
is high enough for all the other zones.

integrating all these systems is one of the very low hanging fruits in
the world of small scale gasification.  contemporary sensors and
embedded control makes it much more easy than back in kalle's days.
nonetheless, kalle was on to most all the right ideas and
opportunities in small scale gasification.  i'm trying to continue
from where he left off.

jim












On 10/3/07, Daniel Chisholm <dmc at danielchisholm.com> wrote:
> On Tue, 2007-02-10 at 22:27 -0400, gfwhell at aol.com wrote:
> > ... CO2 as "recyclable" ... seems to have been missed by most.
> > The addition of steam in the proximity of hot carbon is about all that
> > is needed to produce CO.+H2
> > Maintaining the  temperature is crucial for this reaction which is,in
> > itself,  endothermic. I have been researching the possibility of
> > providing the additional heat necessary to maintain this reaction
> > which will allow the hot exhaust gas from an engine to be returned for
> > recycling. I believe it will be possible to eliminate much of the
> > nitrogen entirely from the reaction zone.. For some years now,  gases
> > have been refined and processed with the use of microwave plasma. the
> > temperature of which can reach 10000K,.
>
> Just be sure that your process makes sense when operating under the
> following rules:
>
> 2 - heat flows from high temperature to lower temperature (so the heat
> in a 400-600C engine exhaust gas stream won't flow into an 800-900C
> reaction zone - but it can be used to preheat incoming reactants)
>
> 3 - non-thermal energy is more valuable than thermal energy, typically
> by a factor of 3X-7X.  (So any electricity, shaft power, etc that your
> process uses must produce more than 3X-7X as much heat in the end, in
> order for your process to be profitable).
>
>
>
>
>
> --
> - Daniel
> Fredericton, NB  Canada
>
>
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>


-- 
--------------------------------------------------------------------------------
jim mason
website: www.whatiamupto.com
current project: mechabolic (http://www.mechabolic.org)
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