[Stoves] air for gazification

Fri Jun 22 17:24:51 EDT 2007

Martin, and all,

>>Martin, Jeff and all,
>>
>>We may have a chance of measuring the superficial velocity in the TLUD 
>>but its much more complex to measure in the other configurations where 
>>the primary pyrolysis occurs before the gases go through the fuel. If we 
>>could come up with a Surrogate Standard that could be introduced in the 
>>inflow air and is unaffected by heat and combustion these (and many 
>>other) measurements would be much easier.
>>    
>>
>Would that not be grams of air?
>  
>
Air has O2 that changes. We need something like argon, helium, mercury 
vapor (ouch) etc.
If we could think of something we could base all the other numbers on , 
for example, a gram of the surrogate. If I am thinking of this right! 
that would make unnecessary any calculations for expansion due to heat. 
We could take a 50 cc sample at the beginning inflow, again at the 
beginning secondary and out the stack, then test for the fab three, CO, 
CO2, O2, and base the CO, CO2 and O2 per gram surrogate.
We could then get some real numbers or mass balance. Again - if I am 
thinking of this right.

>>I am not so sure we need to know the actual air speed around the 
>>particles. We need to know that the speed around them changes with 
>>changing small fuel characteristics and, from actual testing, know what 
>>characteristic are best.   If we start with one inch blocks of wood we 
>>find we cannot start the combustion in a TLUD. Cut each block in half 
>>(increase the surface area, smaller void space, denser carbon as the 
>>fuel packs into a smaller space etc- all things we can measure) then see 
>>if it works.  If not cut each of them into half again and again etc 
>>....  Finally we find the conditions that work with this fuel and stove 
>>design (computer air fan, natural draft, size of fuel container etc).  
>>As we cut each block in half the superficial velocity increases in the 
>>fuel if the inflow remains the same. So I am thinking we are really
>>    
>>
> 
>No! It is the same superficial velocity! You want to express another thing;
>see below in my posting. 
>  
>
If the SV is determined in the section from the start of the fuel to the 
end of the fuel.  The air flow remains constant in to the stove body. As 
you pack more fuel into the same space the air must rush past the fuel 
at a higher SV. Is that wrong??

> 
>  
>
>>adjusting the fuel characteristics to achieve the optimum SV -without 
>>really caring what that exact value is.
>>    
>>
> 
>We could do another way: First choose the SV (not the pressure!!), and keep
>it constant, while using different-big wood-pieces. So we have by all
>different fuel the same SV.
>  
>
This is good but SV is a flow rate in m/sec. With the same fuel packing, 
if you increase fan size you get increased SV. Or if you add a longer 
stove pipe  you get more suction(?).
So to do this we first need to standardize the pressure or draw that 
moves the air past the fuel. Then test and classify the fuel that packs 
to gives this SV.

>It is not preferable first to give a certain pressure, and look how it works
>with different-big wood-pieces. By that, the SV is different and difficult
>to compare.
>  
>
If using a computer fan that should make this easy. But if we are basing 
it on 'draw(?)' that varies during pyrolysis and combustion, (change in 
heat) we will have a greater challenge.

>It could make sense first find out, what type of fuel in the same stack-type
>would create what resistance. 
>  
>
I want to get away from 'type' of fuel and change that to 
'classification' of fuel.
 From a scale from one to five:
This small fuel has:
1) a surface area rating of 2
2) particle carbon density rating of 4
3) packed void space rating of 3
4) Ash value of 1
5) moisture rating of 1
6) packed carbon density of 3
7)

Of the tests above its the surface area determination that I have yet to 
figure out how to do. I would still like to experiment with the foger 
the theater uses. Thinking I could add something to the solution that i 
could measure (methylene blue etc?) using particles mixed in with the 
others with known area that could be pulled out and compared to the 
unknown.

Then we need to develop accurate test procedures of the gases after the 
primary burn in a stove. This will determine the best class of fuel for 
this stove.

Something like that.

Thanks
Frank

> 
>  
>
>>We just need to know the 
>>'classification' of the fuel that will give us the optimum SV value so 
>>we can find other fuels, test them and determine if the stove design 
>>will work with them also.  Or if slight changes need to be made to the 
>>design.
>>    
>>
> 
>Couldn't we better sort the fuel-type to (definite) different SVs, or
>SV-ranges?
>  
>
>>Am I getting way to detailed!??
>>    
>>
>No, so your ideas are clearly to understand!
>  
>
>>Frank
>>    
>>
>
> 
>
> 
>
>The superficial velocity (SV) is so very close to filtering-actions, and
>naturally to your soil-topics, as transport of substances or water from
>surface  into deep.
>
>Naturally, that depends extremely on the soil-structure, so does in
>fuel-stacks of stoves.
>
> 
>
>But what -_YOU_ are interesting in is different! You _DO NOT_ want to know
>the superficial velocity, because the definition of the SV does not count
>with the wood-stick-cross-section within the cross section of the stack.
>
>You want (possibly) to know, what speed the air/gasses have in the spaces
>between the wood/fuel, -and so to know the speed nearby the surface of the
>wood-pieces-.
>
> 
>
>The word "superficial velocity" leads us in a false way! Let us think better
>of: filter-speed, as I wrote, and of the migration-speed e.g. of water in
>the soil.
>
> 
>
>I would call the average-speed between the wood-peaces:
>"interstitial-filter-speed" (IFS)  (derived from the medical expression:
>Interstitium).
>
>The simplest way to get a __LITTLE__ bit closer to that IFS, we can measure
>the volume between the wood, by filling this space with water, and weight
>the out-leaking water. So we can calculate the remaining cross-section of
>the stack, through which the air flows.
>
> 
>
>I don't know this would help a lot. The only advantage I see is, that we can
>compare the real measured pressure-loss of a definite flow through the
>stack;
>
>Compare with a model: The pressure-loss, which occurs in a tube with the
>measure of the calculated cross section of the interstitial volume, (with
>the same length of the fuel-stack). That could lead to interesting
>experimental-curves: x-axis = particle size, y-axis= resistance  (= 1/ flow
>per second).
>
>This can be made first without fire, to get some basic impression, at least
>what minimum pressure is needed to work.
>
> 
>
>Possibly by that curves, made with the same type of fuel-matter (wood) , we
>can compare with same sized fuel of another type (other wood, grass-balls,
>etc.)
>
> 
>
>But these are academic questions, which are not related, in what I want to
>know. I don't want to dive so deeply into burning-theories of the
>specialists.
>
> 
>
>Regards
>
> 
>
>Martin
>
> 
>
> 
>
> 
>
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>  
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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