[Gasification] On the subject of H2 and O (was N2 removal)

[sabbadess at aol.com]

Hi Greg,

Sure.  Let's to a simple example so my feeble mind can follow it.  When I drop cold chips in my gasifier there is some moisture content in the chips...this is liquid water in the wood cells.  As the chips burn down into the hearth they get hot and the water changes to steam.  This phase change absorbs some amount of energy.  Then as the steam goes through the char, some of it does the water gas shift if there is enough heat.  This absorbs even more energy.  The remaining steam ends up as condensate in the cooler.  

The steam produced in cavitation is like putting water in a bell jar and pulling a vacuum.  If there is enough vacuum the water will boil, converting it's temperature into energy for the phase change.  Eventually you end up with a chunk of ice in the bell jar.

The water gas shift will not happen in the phase change because there isn't sufficient activation energy availble to make the reaction go.  If it did work that way, there would be hydrogen bubbles coming off boat propellers.  That would make a COOL rooster tail!

Gasifiers do not run a low enough pressure to vaporize the water, like the bell jar.  I can get the numbers if you want, but you need to be in -13psi range.  That's way more than we pull.

Any clearer or still muddy??

Stephen
-----Original Message-----
From: Greg Manning <a31ford at gmail.com>
To: Discussion of biomass pyrolysis and gasification <gasification at lists.bioenergylists.org>
Sent: Sun, Mar 18, 2012 10:09 am
Subject: Re: [Gasification] On the subject of H2 and O (was N2 removal)


Hi Stephen, thanks for the reply.
OK, I somewhat understand you, BUT, wouldn't water be doing a phase
hange in the core of a gasifier as well ?
What I was getting at, is if steam is produced in cavitation in cold
ater, then wouldn't the shift effect also happen within the core
uring phase transition (from water as a liquid, to water as a vapor,
hen heated by the core) within the same boundaries of effect as water
o steam in the trailing edge of a propeller ? (all of these
ituations involve lower that normal pressure zones).
Aren't contrails produced in water vapor on the wing tips of an
irplane because of this same pressure drop phase shift, causing a
ew-point change?
The core of most gasifiers runs in a dynamic lower than atmospheric
ressure ( a very low internal barometric pressure) (suction based
nits), so the same shifts should apply  during phase transition,
houldn't they ?
I understand that a pressure fed gasifier would behave differently
and I've personally observed this) than a suction based one, I'm
peaking about suction based gasifiers.
Somewhat lost,
reg

n Sun, Mar 18, 2012 at 8:26 AM,  <sabbadess at aol.com> wrote:
 Greg,

 The energy doesn't change.  The bond energy in the water is constant
 regardless of pressure.

 The cavitation issue is different.  It is a phase change phenomenon, not a
 chemical change one.

 Stephen
 -----Original Message-----
 From: Greg Manning <a31ford at gmail.com>
 To: Discussion of biomass pyrolysis and gasification
 <gasification at lists.bioenergylists.org>
 Sent: Sun, Mar 18, 2012 9:02 am
 Subject: [Gasification] On the subject of H2 and O (was N2 removal)

 Greetings List.
 Since we are speaking input air, I thought I might ask a somewhat
 related question.
 Water gas shift. I know there are many that have talked about this,
 and I understand the basics.
 However, here is the question.
 At what negative pressure ( negative in/wc) does the shift move down
 the temperature scale, to the point of being within the 1000 - 1200 c
 area ?
 We all know that propeller cavitation produces steam in water that is
 10 c (or there abouts), I have to assume (not being a chemist) that
 the same negative pressure effect would also apply to other principals
 when dealing with water.
 --
  Regards,
 Greg Manning,
 Brandon, Manitoba, Canada
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-- 
Regards,
Greg Manning,
randon, Manitoba, Canada
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