[Stoves] burning woodgas

[ajheggie at gmail.com]

On Sat, 24 Jul 2021 at 21:06, Norbert Senf <norbert.senf at gmail.com> wrote:
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> On Sat, Jul 24, 2021 at 2:49 AM <stoves-request at lists.bioenergylists.org> wrote:
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> Ajheggie wrote:
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>> Norbert, are you able to put any figures on the range of particulate
>> emissions as the smoke goes clear? i.e. if there is no visible smoke
>> what range are the PM emissions in?
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> Hi Andrew:
> Very roughly,  I'd say under 2 grams PM / kilogram dry fuel for wood in our type of device.
> We did testing on 5 typical North American pellet stoves at the Stove Challenge a few years back, and they don't have visible emissions, although I haven't looked super carefully.
> They were all in the range of about 1 - 2 g/kg.


Thanks again Norbert for putting some figures on it, and that is from
a better controlled full on burn in a masonry stove which is likely to
be better than a cook stove can achieve.

I find it difficult to get a handle on  the different ways of quoting
particulate emissions, nowadays we seem to see more emphasis on PM2.5
than PM10 as being more concerning to health. PM 2.5 being a subset of
PM 10.

I was trying to estimate, given your figure of 2 grams particulates
per kg of dry wood burned producing no visible smoke, how that might
relate to a concentration of micrograms per cubic  metre of exhaust
gas cooled to ambient temperature.

For my first approximation I considered the flue gases having 10% O2,
so 100% excess air.
It takes about 6kg of air, that is at around 1.4 m3 per kg of air, to
burn 1kg of dry wood stoichiometrically so say about 20m3 of cold flue
gas given that the wood is converted to CO2 and H2O and there was a
small amount of moisture associated with the wood.

At ambient temperature that gives 0.1 gram per m3 of cold exhaust,
Vented from a stove into a living space this would need diluting 4000
fold to reach WHO recommended maxima. It seems incredibly bad so have
I made a fundamental mistake?

> The big dividing line is smoldering vs flaming combustion. My experience is mainly with flaming, where you get soot (elemental carbon) from flame quenching. It is light and odorless.
> With smoldering you get tars, which often are yellow on the filter, strong organic odor, heavy.

Yes we often see a blue haze associated with a quenched flame,
smouldering gives a more milky smoke tinged with yellow.

Andrew