[Stoves] rice husk combustion products

[Crispin Pemberton-Pigott]

Dear Kelpie

If you have access to a Dusttrak DRX your charcoal dust questions could be
answered fairly quickly. The PM4 and smaller (the interesting ones for
health) are really small compared with visible dust like that found around a
charcoal packing operation. In other words, they are likely to be large, or
very large compared with smoke particles. The thing is they can contain all
sorts of chemicals manufactured during the charring process. So the problem
might be more the chemistry of the particle that its 'carbon-ness' (OC or
BC).

Charcoal usually has quite a bit of volatile material in it, like tars that
would have been liquids until the light fractions were boiled off. 

On the rice hull question, there are lessons from Alex English and Roger
Samson. The melting temperature of the silica in rice hull is very high,
however if there is enough Chlorine and or Potassium around, it acts as a
flux, reducing the melting temperature to that found in flames. In your
favour is the fact that rice hull gasifiers run at quite low temperatures so
are unlikely to be able to initiate melting and thus formation of the
fibres. Perhaps Alex will comment.

Roger worked out how to remove the Cl and K which is to leave them out in
the rain through a Canadian winter. He found that works for Switchgrass. In
fact it works so well we are amazed. It may make a difference how long the
rice hull has been sitting around. Does anyone have a Cl-K analysis of rice
hull? Frank? Is there any flux in there? My guess is you are not at risk
from that perspective.

If it is burned at a high temperature, and the fluxes are there, you might
be able to melt the silica. However it may immediately bind to some of the
carbon or prefer to make lumps, not fibres. This is interesting. Certainly
worth looking into.

The most practical method would be to collect the particles on a filter and
examine them. A DRX or GRIMM particle counter will give you size segregation
and then the filter will show what they look like and are made of. Prof
Lodoysamba has been using nuclear techniques to find out what the particles
are made of, quite successfully. Mathematical treatment of the results gives
apportionment to source. That in turn provides information on what happened
to the elements in the fuel that were burned. It would be pretty straight
forward for particles collected directly from the rice hull using
environment.

Regards
Crispin



-----Original Message-----

Hi all,
this discussion on small particles and health effects is very interesting.
Thank you Erin for putting together the chart and starting the discussion.
We have been interested in how small biochar particles can fractionate and
under what conditions and whether or not there could be health impacts from
breathing charcoal dust. I have not been able to find any research on the
charcoal dust question as all of the health studies of charcoal workers
focus on breathing the smoke emissions. Does anyone have any literature or
any observation of health impacts on workers in charcoal briquetting
factories, for instance? Any situation where potential impact from breathing
charcoal dust could be separated from the impacts of breathing smoke
emissions?

Of greater concern it seems, is the residuals from rice husk combustion and
gasification. At high temperatures, the carbonized rice husk ash can
crystallize and make a nasty long fiber particle leading to silicosis. But
what happens at the temperature of a rice husk cook stove? Is this ash
dangerous to people? Again, I cannot seem to find any literature on public
health in the rice growing regions that points to a health problem from rice
husk char or ash. Anyone got any info on this?

Many thanks,

--
Kelpie Wilson