[Stoves] burning woodgas

[ajheggie at gmail.com]

Good stuff Norbert, I saw from the archive that you had responded but
had to wait till the post arrived in my inbox later today before I
could reply.

On Tue, 27 Jul 2021 at 05:59, Norbert Senf <norbert.senf at gmail.com> wrote:

> Hi Andrew:
> Some additional observations based on your last comments:
>
> PM 2.5 is a subset of PM 10. Woodsmoke is actually 99% PM 1.0 (or smaller).
> Coming onto the scene and not much studied yet are nanoparticles. These don't
> have any weight to speak of.

The late Prof Philip Lloyd told us of some studies conducted in 1974
mostly with silica dust in mines I think, it was in a thread here on
25th May 2018. If I interpreted him correctly hr said PM 10 down to
PM2.5 were effectively filtered by the nasal passageways, PM2.5 down
to PM 0.5 were the range most likely to be retained in the lungs and
thence into the blood stream and any smaller particles  had a low
chance of settling and were exhaled.
>
> Conversion factors for PM were hard to find. I have a rough calculator now in Excel that
> has checked out reasonably well.
> At 75% efficiency (HHV) and normalized to 13% O2,

This is about 200% excess air?

> 1 g/kg =  85.5 mg/m3 at standard temperature and pressure

So this is milligrams not micrograms? I spell it out because the "mu"
symbol si sometimes  missed by strict ASCI clients.
> =  0.194 lb/MMBtu
> = 83.4 mg/MJ
>
I'm trying to work back to what dilution would be needed to get to the
25 micrograms PM per m3 which is acceptable risk to health.

> Blue smoke is tar. Like with cigarette smoke (smoldering combustion), the particles are small enough to refract light, which causes the blue color.

Yes I see now, thanks for the correction.


On Tue, 27 Jul 2021 at 10:31, Norbert Senf <norbert.senf at gmail.com> wrote:
>
> Hi Andrew:
> There's a fairly clear distinction between the PM resulting from flaming and from smoldering. Ie. soot vs tar, or elemental carbon and organic carbon (EC and OC).
> I found a study from Switzerland comparing the toxicity of the two, and it appears that OC is about 10X as toxic as EC.

Yes I see that, it's the polycyclic aromatic hydrocarbons in the sooty
clump that are the carcinogens. I think diesel exhaust particulates
are reckoned to be 60% black carbon, the rest PAHs or other PICs

> In a pellet stove or masonry heater, for example you see around 1 g/kg of EC, whereas in an "outdoor boiler" like farmers around here use, you can see as high as 100 g/kg of OC.
> This implies that burning the same piece of wood could give you 1000 X the toxicity in one device compared to the other.

Yes that seems very logical and I know the type of boiler you mean,
there is no way the secondary burn can avoid impinging on a water
cooled steel surface and they are often black with tar, completely
different from the insulating fire brick secondary combustion area in
the Kob wood chip boilers I used to deal with.
Thanks for the good input Norbert

Andrew