[Stoves] Particles and particle types (was Charcoal Making Stove)

[AJH]

Forwarding a bit of discussion that went off list because Tami got my
reply but the list didn't, Tami's reply to follow. AJH
On Mon, 30 Oct 2006 19:47:45 +0000, AJH wrote:

>
>On Mon, 30 Oct 2006 08:39:43 -0600, Tami Bond wrote:
>
>>
>>> Are you confident these are always large? It's the possibilities of
>>> forming small silicacious particles that concerns me.
>>>   
>>I am not confident. You're right; I think there could be silicaceous 
>>particles especially from rice straw and other material with high silica 
>>content. Aerosol from wood burning appears to be mostly carbon and 
>>associated material, with very little silica.
>
>OK and I'm sure this is the case with small naturally aspirated
>stoves, but once air velocities increase I wonder....
>
>The thing is wood ash is still 50% silica even if this is only 1% of
>the raw wood. As you may have gathered I play with forced air burners
>and I do see fly ash blown out, even to the extent that I have
>considered making use of it with an automatic ash collection system.
>My worries are about lung disorders this may cause if they are in the
>living space as pm10 or 2.5. It took a while to find a causal link to
>asbestos and lung disease.
>>>
>>> I find that flue exit temperatures of 700C are generally high enough
>>> to get visibly clean effluent if there is enough excess air when
>>>   
>>...Information like yours-- starting to get quantitative-- is very 
>>useful. Now it would be good to advance with some more quantitative 
>>information. 'Visibly clean' could be a lot of things.
>
>Yes just because I cannot see them doesn't mean there are few
>particulates.
>
>
>> If the particles 
>>are black, you can't see them as well. If we can get little PM/CO 
>>monitors, then we can do better. 
>
>Even at the $1000 mark I'll not be able to afford one but follow your
>trials with interest.
>
>
>>You seem very systematic, so when you 
>>say 'temps of 700 are... enough',  have you investigated below and above 
>>that temperature, and can share some quantitative differences, or at 
>>least your observations? 
>
>Recently I have been trying to burn very wet material with green
>foliage just to see what the possibilities are. I have air control
>with a centrifugal fan (12V for pumping up air beds) and I sample
>exhaust temperature just below the entry to the flue pipe. This
>material will not burn at all cleanly until some char is formed, then
>the char will provide all the heat to dry and pyrolyse the rest of the
>sample but the offgas and steam will not ignite, so essentially it
>smoulders away producing loads of whitish blue smoke, a mixture of
>sooty pics, water and tarry condensates. I can add some propane
>support fuel under the firebed. I add just the minimum amount to
>sustain a flame and a visibly clean exhaust. In the early stages the
>propane contributes a lot of the heat energy but over time I can
>reduce it and still maintain 700C (note this may well be an under read
>temperature) as measured by my digital multimeter and a K type thermo
>couple. I am investigating the poor heat feedback of the top lit
>approach with an aim to recuperate heat to make the thing self
>sustaining at high (70% mc wwb) moisture levels without support fuel.
>It's a follow up to the ideas we used in our high speed wood dryer.
>
>
>>And how did you maintain exhaust temp-- simply 
>>from dilution?
>
>See above I vary both input air (by obstructing the fan inlet or
>reducing voltage) and support fuel.
>
>AJH