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

Kevin kchisholm at ca.inter.net
Mon Mar 19 09:59:15 CDT 2012 

Dear Stephen, Luke, and Greg

I think, like Luke, that pressure or suction should not matter. However, you and Greg, who have first hand operating experience find that it does. Reality trumps theory every time!! :-)

I further think that there is not necessarily a conflict here. If we go deeper into the problem, it is not so much the pressure or vacuum that causes the gases to flow through the bed, but rather the differential pressure. Basically, I would suggest that if a difference between operation under pressure and operation under suction is observed, there is a different "differential pressure situation" existing.

Consider a test installation as follows: A 6" diameter pipe, with a 1/8" screen in the middle, on which a bed of 1" glass marbles, 1' deep, is placed.

Consider 3 test cases as follows:
1: System closed at the top, open on the bottom. Air is supplied above the bed at +10" WG pressure
2: System open on the top, and closed at the bottom. Air is "sucked out" through the bed, from the bottom, with a vacuum of -10" WG suction.
3: System closed at the top, and air is supplied at +5" pressure, and system is closed at the bottom, and air is withdrawn at a vacuum of -5" WG suction.

In all three cases, the "differential pressure", or "pressure drop" across the marble bed is 10" WG.

Can anyone provide a rational explanation of why air flow in all three cases would not be identical for all practical purposes?

Stephen's observation of "top tar when under pressure, but none when under vacuum" could be easily explained by a hopper seal that was less than perfect.

Best wishes,

Kevin
  ----- Original Message ----- 
  From: sabbadess at aol.com 
  To: gasification at lists.bioenergylists.org 
  Sent: Monday, March 19, 2012 7:41 AM
  Subject: Re: [Gasification] On the subject of H2 and O (was N2 removal)


  Luke,

  I am going to challenge the statement that pressure vs. suction is the same thing.  I thought the same thing three years ago, but after running my machine in both modes I've come to the conclusion that it's just not true.  I now think of the flows going into the nozzles like a rope.  If you push a rope into the machine until it come out the exit flange it's going to go in, bunch up, pack up, and go in many different directions before finally exiting.  From a flow standpoint it will be a mess.

  If you run the machine under suction, it's like pulling the rope through the machine from the exit flange.  Everything is straight, smooth, and directed toward the exit.  The result is that the pyrolysis zone is thinner and there are fewer up drafts carrying heat up into the fuel hopper.  The thinner pyrolysis zone means that there is less tar for the available oxygen to incinerate(or "crack" if you like that theory) so everything runs cleaner.

  When I used to run my machine under pressure I would see a "sea" of flammable thick tar gas in the hopper when I would refuel it.  Now under suction I don't see any smoke in the hopper.

  Just my experiences.

  Stephen Abbadessa
  -----Original Message-----
  From: Luke Gardner <lgardner at wwest.net>
  To: Discussion of biomass pyrolysis and gasification <gasification at lists.bioenergylists.org>
  Sent: Sun, Mar 18, 2012 10:22 pm
  Subject: Re: [Gasification] On the subject of H2 and O (was N2 removal)


Greg,
I don't have a lot of time today,  but I have been loosely following along, 
and I Can't help but wonder if things might not be a little easier to 
understand if a Guy stops thinking in temperature and pressure, and started 
thinking about the material of discussion in terms of its kinetic energy.
14.7, or 101.325 aren't magical universal pivot points that natural laws 
swing upon, "normal" Air pressure, isn't hardly ever " normal" at all.  It 
is as much  a figment of our human imagination as monday, or leap day, or 
the millenium.  The only difference between a "suction" and "pressure" 
gasifier is a few PSI and your point of view.
resectfully,
Luke

-----Original Message----- 
From: Greg Manning
Sent: Sunday, March 18, 2012 12:30 PM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] On the subject of H2 and O (was N2 removal)

meant NOT at a great amount (as in very small) sorry all.

G.

On Sun, Mar 18, 2012 at 2:26 PM, Greg Manning <a31ford at gmail.com> wrote:
> KELBURN,
>
> THANK YOU !
>
>  This is the EXACT thing I needed to see.... proves my point, EXACTLY.
>
>  I am now of the firm beleif that we CAN (And DO) water gas shift in
> suction type gasifiers, where as, blown (pressureized) gasifiers can
> NOT do W/G shift.
>
> I think the W/G shift is at a great amount, BUT, it sure proves my
> caclulations, almost dead on.
>
> Thank you Thank you Thank you Thank you
>
> Greg
>
>
>
> On Sun, Mar 18, 2012 at 12:14 PM, Kelburn Koontz <kelburn_k at yahoo.com> 
> wrote:
>> Making Ice with Vacuum
>> http://www.youtube.com/watch?v=pOYgdQp4euc
>>
>> Check out the ideal gas law.
>>
>> Thanks,
>> Kel
>>
>>
>> On Sun, 2012-03-18 at 08:10 -0700, Mark Ludlow wrote:
>>> “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.”
>>>
>>>
>>>
>>> Not so! Not enough latent heat is lost. Sensible heat must be removed
>>> also. In outer space, where there are huge radiative heat losses this
>>> applies. If folks could make ice with simple vacuum pumps, who would
>>> mess with refrigeration? It takes energy to evaporate water, not just
>>> vacuum.
>>>
>>>
>>>
>>> Plus, when a gas is adsorbed onto a sieve, energy is released. It
>>> takes the same energy (and then some) to regenerate the sieves. No
>>> free lunch; no where.
>>>
>>>
>>>
>>>
>>>
>>> From: gasification-bounces at lists.bioenergylists.org
>>> [mailto:gasification-bounces at lists.bioenergylists.org] On Behalf Of
>>> sabbadess at aol.com
>>> Sent: Sunday, March 18, 2012 7:55 AM
>>> To: gasification at lists.bioenergylists.org
>>> Subject: Re: [Gasification] On the subject of H2 and O (was N2
>>> removal)
>>>
>>>
>>>
>>> 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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>>
>>
>>
>> _______________________________________________
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>
>
>
> --
>  Regards,
>
> Greg Manning,
> Brandon, Manitoba, Canada



-- 
Regards,

Greg Manning,
Brandon, Manitoba, Canada

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