[Stoves] The Blues

[Andrew Heggie]

On Sun, 13 Jan 2019 at 02:02, Ronal W. Larson <rongretlarson at comcast.net> wrote:

>  I see the word "Gasifiers" here a lot and want to emphasize instead the word "pyrolysis".  This list has a sister group called "gasification" - that never has any discussion of making charcoal - only of consuming it.

The gasification list has dwindled worse than stoves, there have been
no posts since November.

Anyway stoves isn't only about TLUD, so gasification of whole wood
happens in many stoves.

I hope we can get more insight into this business of how rice hull
burners have a blue flame which only seems to happen when burning wood
if the gases and air are well mixed. The paper Alex linked to suggests
potassium  has an effect in burning sooty particles, interestingly it
does point out that the amorphous parts burn out earlier than the
graphitic bits, which is what I would have expected as graphite
resists oxidation.

It doesn't help with whether the higher ash content in rice husks
causes some interaction that leads to a bluer flame.

I have a new wood burning room heater that has an insulated firebox
and a glass window. Once up to temperature and turned down it acts as
a pyrolyser and the flames are a lazy purple blue  floating above the
hot wood, unfortunately my camera does not record what my eyes see
otherwise I would post a picture of the secondary air inlets combining
with the offgas.

I have never seen any rice husks so cannot comment from personal experience.

I understand how this happens in wood burning in that, when the flame
is diffuse, the burning takes place in two stages, firstly the
offgases dissociate and oxygen diffuses into the flame and combines
with hydrogen, then the carbon rich remainder rises in the heat and
radiates the characteristic yellow until it too combines with oxygen.
When the gases are premixed the reaction is more instantaneous and the
flame colour is bluer, often with a tinge of purple, which is more
characteristic of CO, H2 and potassium.

You can often see this at the base of a candle flame, it is bluer and
if the wick shortens the flame becomes bluer.

Andrew