[Stoves] Strata combustor general principles

Sat Oct 10 19:07:11 CDT 2015

Dear Kirk

      Something is wrong in  your  concept op pressure .

     One : you measure pressure- difference in and outside the stove   ,an
OPEN STOVE  vessel!

Only in a closed vessel BOM-  combuster  you get a real pressure due
solid/gas volume-expansion, versus container volume ;mind 12gram carbon
gives 22,4 Liter =44gram CO2 or 22,4 liter CO=28gram !!! 

Depends the air you give it . Gas from pyrolyse is different .CO +H2+CO2
+organic gas methanol  aceton  acetic acid ao .

      Then you have GAS expansion to law PV/T=pv/t   versus  absolute
temperature - 273°C in the calculation

In and out the stove you get the ARCHIMES law too ! Compare floating in
water-pressure up ,depends displaced water or air with its density
difference .     Air MOL equivalent =27   CO=28 CO2=44    H2=2

      A high chimney as mine is 8 meter ,it  SUCKS till 3 mm water column
PRESSURE-DIFFERENCE as the 10 Kw  stove make the noise as a wolf 
..!

Your idea to measure gas escape surface- pressure must be done about ,with a
cup shaped pressure sensor of 1cm² and 1mm long,, pressed on a flat  peace
of gas- steaming wood
of 450 °C.

But it is non-sense to try it!

You need the “FLOW” in a stove as most important related to stove dimensions
.

Mind :Flow is related to your unmeasurable pressure difference .

Flow is measured with a  PITOT tube of 1-2 mm and 20 cm long .

You can make a flow indicator by an extra vessel around the stove with an
unic total air input ,with a square tube input  with  a balancing hanging
cat-door 1x5 cm ,metallised MILAR=polyester of microns thick.(Or  thinnest
Alu foil ) To get minimum  air resistance! 

You measure the movement by an  oblique laser rayon .. Movement multiplied
by reflection longer distance  !    For a TLUD stove  without a fan..

        With fan : a   15 cm PC fan you cannot use  with a cone 12 to 3 cm !
All FLOW RETURNS due FLOW CONE RESISTANCE !!!

You need PRESSURE to OVERCOME the  fuel compaction resistance !

An inversely used vacuum cleaner  motor at 1/10 of its voltage and power  is
best !!    Regulate FLOW, is airspeed to the best BURNSPEED but 
..! (15-30
volt for 230V  AC motor )

Give the gasses “REACTION TIME “ !!!

And mind pyrolyse /combustion needs 1versus 9  air quantity !

Succes !

P.F.

Van: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] Namens kgharris
Verzonden: vrijdag 18 september 2015 4:21

Onderwerp: Re: [Stoves] Strata combustor general principles

Frans,

It is exciting to have you bring up these concerns.  There is a question I
have had for a long time, and your contribution reminds me about it.  It has
to do with the pressures within the stove.  Perhaps you and the list can
help answer this question.

First to address your concerns.  There is a sweet spot as to how much
blockage the stove can manage.  It lies between to much, which blocks the
flow and creates the attenuation you describe, and to little so that the
combustor doesn't work.  I did not know that the venturi created a back
pressure, I assumed that the back pressure was created by the obstruction of
the tubes and fan.  I found the sweet spot by emperical experimentation.  I
now know that this balance includes back pressure from the Venturi, if I
understand you correctly.  So the equation now includes the resistance of
three things: tubes, stationary fan blade, and Venturi back pressure.  I
included your concern into the design without my even knowing it.  Its all a
balance.  Thank you for your input, it is very good to help me understand
more about the stove.  The combustor has been tested at Aprovecho and does
work, so the idea is good.

The question I have had for so long is this:  When the wood gas emerges from
the wood what is its pressure and how long does it take for the wood gas to
drop to near atmospheric pressure?  When I measured the pressure in a stove
with a manometer which measured down to 1/100th of an inch of water column,
it measured at atmospheric pressure throughout the stove.  The water column
did not move at all (I understand from Crispin that I must measure down to
1/1000th of an inch to find pressure differences).  Since the water column
did not move when I measured the pressure at the pyrolytic front, that
implies that the wood gas either reaches atmospheric pressure quickly or
comes out of the wood at near atmospheric pressure.  Whatever the case, the
wood gas comes out of the wood with enough force to push the atmosphere,
which weighs twice as much as the wood gas, out of the stove.  That is a
considerable amount of force.  I wonder how much pressure pyrolysis could
build up in a confined container?  A lot I would guess, enough to cause an
explosion.  Is the pressure of the emerging wood gas dependent on the
pressure of the gas it emerges into?

Respectfully,

Kirk

----- Original Message ----- 

From: Frans Peeters <mailto:peetersfrans at telenet.be>  

To: 'Discussion of biomass cooking stoves'
<mailto:stoves at lists.bioenergylists.org>  

Sent: Thursday, September 17, 2015 3:06 PM

Subject: Re: [Stoves] Strata combustor general principles

Dear,Kirk

       You don’t see :it is not a closed compressed system !

But any  reaction vessel (V1 ) with a  venturi  attenuation at the output
gives  a  back reaction in all directions ,so flow  attenuation  under the
grate air input .

By over total power the air input BECOMES SMOKE OUTPUT TOO .! So invers to
your idea ;

A V1  rocket has an input COMPRESSOR powered by the traveling speed plus a
constant fuel input so a nice VENTURY output .

1and 2 you don’t have it in a stove of half info .

       Yours

Rocket scientist

Van: Stoves [ <mailto:stoves-bounces at lists.bioenergylists.org>
mailto:stoves-bounces at lists.bioenergylists.org] Namens kgharris
Verzonden: donderdag 17 september 2015 4:58
Aan: Discussion of biomass cooking stoves
Onderwerp: Re: [Stoves] Strata combustor general principles

Dr. Boll and Crispin,

Thank you for your well considered responses.  I especially like the idea of
balancing the reactor fuel chamber volumn with the combustor size.  I will
keep this in mind as I progress, and seek that balance.  

I don't quite understand Crispins flame tube.  The stove appears to be
loaded with charcoal, so there should not be any smoke.  If the clay is
insulating clay than the tube would provide a hot environment for the CO to
burn, if there is a source of secondary air.  If the stove burns wood, by
what principles does the tube work?  Is air injected inside the tube?  This
would make use of the Venturi effect like Roberto's stove.  The flame gasses
accellerating into the tube would drop in pressure and the pressure
difference would help the atmosphere push secondary air into the flame to
equalize the pressure, providing good mixing.  This seems to me like it
might work well if that is how it works.  Is there something else that I
don't see?

Kirk  

----- Original Message ----- 

From: Boll, Martin Dr. <mailto:boll.bn at t-online.de>  

To: stoves at lists.bioenergylists.org 

Sent: Wednesday, September 16, 2015 6:35 AM

Subject: Re: [Stoves] Strata combustor general principles

Kirk, 

first of all, your stoves and thoughts about TLUD's are very interesting.
And in my opinion

 the venturi-concept, you are talking about, -how ever managed- will be
generally the next important step for better burning; - and for less blacked
pots!!! 

A presumption I made a year or two ago: 

The (nominal-) power rate of a good working stove has a more or less narrow
relation to the grate-surface, and/or the burning-chamber-volume.

 I calculated the given numbers of some different commercial stoves.  My
calculations confirmed my guess.

I dont remember the numbers, but it is easy to calculate the numbers out of
available commercial data.

Additional I remind to Crispin's postings, some time ago:

He reported, that he made the burning-chamber of some coal stoves in
Ulanbaator smaller, by just filling some space of the burning-chamber-space
with bricks. And some surface of the grate. In combination with special
incending-procedure, that gave better burning; even by transforming the may
of stoves there, there was an enormous reduction (more than 90%) of
air-pollution. 

So I suspect, if you would use the right-balanced amount of
burning-chamber-volume, you could get a step forward.  The volume within the
venturi-riser-burner-tube should be included in the calculation; but in the
tube there will be, -hopefully- a burning some similar to a LPG or NG flame,
which will afford less volume. 

You could take the power-rate which you achieve with low emission, for
extrapolating the stove dimensions for your desired 5 kW output.

Regards

Martin

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