[Stoves] Limiting factor for secondary burn?

[frank]

Paul, Stovers,

I want to separate and optimize the two stages of combustion. So now I 
am working on the primary.
I need to know what it is I am trying to do.

>
>
> It is true that traditional updraft gasifiers do work.  And the 
> gas-producing
> fire is at the bottom.  But they are burning char at the bottom.  And 
> unless
> the heat is very great (in order to pyrolyze some of the raw fuel 
> above the hot
> char), it does not give you usable gases at the top.  And in your very
> small-size experiment, the pile of raw fuel is (relatively speaking) 
> enormous
> above the very small bottom fire.

Do they want to burn char at the bottom? or is this necessary to keep 
the fire going?

It seems the goal is to make pure CO from heating carbon materials in 
lack of O2. From my observations in the glass the tars (what ever they 
are) does not turn to CO before being hot enough to volatilize(right ?). 
So tars should not be in the out gas because if they are it becomes 
'dirty' fuel(right ?). In fact tars do not seem to burn very well in the 
secondary burn because they coat stove pipes  and cause health problems 
(?).



>
> Please note that so many many fires and stove configurations are lit 
> at the
> bottom.  Bottom lighting is NOT the single criteria for making a 
> gasifier, even
> if you confine the fuel into a glass tube.
>
I (via my company Chip Energy) do have an bottom-fired updraft gasifier 
(see

> http://www.chipenergy.com/furnace.htm ).  But it, even with its larger 
> size and
> high-heat of operation, cannot be ignited in the way that you are 
> trying to do
> your small-scale experiment.
>
> If your white gases are actually a cloud of water vapor (which I 
> expect they
> are), they will never ignite.
>
I don't know what the white vapors are but they do not seem like water. 
The wood is very dry so it would be the water produced during the burn 
if it is water.
With labs going from Atomic Absorption (AA) to ICP to measure metals 
there are a lot of AA's in the graveyards of equipment. We just dumped a 
few and I am sure Universities must have some.  The AA has an atomizer 
below the burner that, via a gas flow and venturi effect, takes a stream 
of water and smashes against a small ball (~6mm) and turns it into a 
cloud of water mist. I have saved one of these and think they would be 
very useful when doing water effects on burns. If I can get this system 
to work that is one of many experiments I would like to do.


> You mention that "understanding woodgas" is your motivation.  So I do 
> not know
> how you got onto the track that you are following.  Tom Reed has done 
> the TLUD
> woodgas experiment in glass tubes, but he lights it at the top.  That 
> is a way
> to understand woodgas creation and combustion.
>
Everything I have done I am sure has been done a million times and I do 
not want to spend time to re-invent the wheel. That is why I am asking 
all these questions and I appreciate your help. Next experiment I will 
try a TLDD perhaps using the cardboard or some type of starter. I can 
send the larger tube down to the bottom to capture the out gas. Thinking 
about this I like it because it seems there will be more control when 
making the burn go down (you can slow or speed it up) and there will be 
less chance of unburned air going past the burn because the burn will 
take the air out of an air space above it.


Thanks
Frank


 

> Paul
>
> Quoting frank <frank at compostlab.com>:
>
>> Dear Paul,
>>
>> I got a chance to try a few more runs using cardboard as a starter 
>> and very dry wood chips (< 2 cm) for the fuel
>> .
>> I find the O2 is hard to get to 0 as Crispin suggested without the 
>> burn (glow) going out. I think the problem is that I have a flat  
>> cross section of burn and if it is not completely burning across the 
>> horizontal some un-used air goes past. I am thinking I need to funnel 
>> down the location of the burn so all the air passes through the glow. 
>> I am thinking I will need a weak spring pushing on a perforated plate 
>> to make sure the fuel is pushed to the bottom as it is being used up 
>> where the burn is.
>>
>> As I said before the top of the glass '1/2 stove' is just warm and 
>> the gases are room temperature and white. Will these gases at room 
>> temperature ignite? Or do they need to be close to the primary burn 
>> and hot?
>>
>> I am thinking I have a BLUD wood gas producing unite. I have left out 
>> the secondary burn  and hope to get to that when I get the primary 
>> burn adjusted to do what (I think) it should. Is this what i am doing??
>>
>> Thanks
>> Frank
>>
>
>
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-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com