[Gasification] On the subject of H2 and O (was N2 removal)
sabbadess at aol.com
sabbadess at aol.com
Sun Mar 18 10:30:17 CDT 2012
Greg,
I can't answer why you are seeing higher temps than calculated. It certainly does prove the impact of moisture on gasification, though.
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 11:12 am
Subject: Re: [Gasification] On the subject of H2 and O (was N2 removal)
lol, Stephen
I understand you, it's just that in the core, in the restriction, I
as reading Tom Reeds Superficial Velocity paper, and IMO the flow
ate at 4 in/wc suction would cause quite a drop with a velocity of
300 ft/sec. (NOT VOLUME)
What I'm saying is that when there is too much moisture I understand
he energy transfer to the water is quite great, and the W/G Shift is
ow (or none), however, with inlet air that has been run through an
air dryer" (like the ones used in automotive paint booths) AND, very
ry feedstock, the core temperature (just under the hearth) is WAY
igher than if I run just normal air, and reasonably dry feedstock,
The difference is greater than the energy balance that I calculate,
o one of two is the answer,
A) my balance is skewed, OR,
B) there is "extra" heat energy in the later portion of the process,
hat I cannot account for. (assuming a greater W/G shift, would bring
t back in line)
Greg
On Sun, Mar 18, 2012 at 9:54 AM, <sabbadess at aol.com> wrote:
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
change in the core of a gasifier as well ?
What I was getting at, is if steam is produced in cavitation in cold
water, then wouldn't the shift effect also happen within the core
during phase transition (from water as a liquid, to water as a vapor,
when heated by the core) within the same boundaries of effect as water
to steam in the trailing edge of a propeller ? (all of these
situations involve lower that normal pressure zones).
Aren't contrails produced in water vapor on the wing tips of an
airplane because of this same pressure drop phase shift, causing a
dew-point change?
The core of most gasifiers runs in a dynamic lower than atmospheric
pressure ( a very low internal barometric pressure) (suction based
units), so the same shifts should apply during phase transition,
shouldn'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
speaking about suction based gasifiers.
Somewhat lost,
Greg
On 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,
Brandon, Manitoba, Canada
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Regards,
Greg Manning,
randon, Manitoba, Canada
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