[Stoves] burning particulates

Sun Jan 31 18:56:38 CST 2021

Messages that are forwarded seemed to get the ***SPAM*** tag. We found the
***SPAM*** filter. Now we're just trying to find the right switches.
Thanks. Tom

On Sun, Jan 31, 2021 at 3:31 PM Daniel Pidgeon <daniel.pidgeon at hotmail.com>
wrote:

> For the Admin,
>
> I don't know why some messages get marked as "SPAM", but they show up in
> my Inbox anyway, and I simply look for the full message subject line before
> I believe that word.
>
> But then I need to check the Junk mail box regularly, as for some reason,
> every message from Crispin every time gets sent to Junk, no matter how many
> times I tell it that it's a trusted sender!
>
> I don't get all these automatic things, just try to work around them...
>
> Daniel
> ------------------------------
> *From:* Stoves <stoves-bounces at lists.bioenergylists.org> on behalf of
> ajheggie at gmail.com <ajheggie at gmail.com>
> *Sent:* Monday, 25 January 2021 9:15 AM
> *To:* Discussion of biomass cooking stoves <
> stoves at lists.bioenergylists.org>
> *Subject:* [Stoves] burning particulates
>
> This is a repost to see if it gets propagated without the spam flag
> the list server appears to insert on certain posts
>
> We seem to have a discussion going on between stoves and the biochar
> horde but it has got a bit disjointed. I picked up on this snippet
> below  from Daniel in Australia who hopes to use a TLUD to heat his
> house by heating water. I am an advocate of underfloor heating in the
> UK and it fits well with batch burning, as like a masonry heater, you
> can burn hot and fast and the time constant of the floor slab  evens
> out the peaks from the stove. The other good thing about underfloor is
> to do with our perception of comfort, if your feet are colder than
> than your head you only feel comfortable at a higher overall
> temperature than when your feet are warmer than your head, so a warm
> floor and rising heat tends to feel more comfortable at a lower
> average temperature, i.e. you maintain a lower temperature and use
> less energy with underfloor heating.
>
> Read below for my take on Daniel's point about smoke particles.
>
> On Mon, 28 Dec 2020 at 12:22, Daniel Pidgeon <daniel.pidgeon at hotmail.com>
> wrote:
>
> >
> > I assume or figure with smoke it gets to a point when the volatile
> particles are burned off, that there are particles that no longer burn up,
> and so with further combustion, instead of burning up, they are
> disintegrated into smaller pieces, which as James mentioned, can only be
> removed by filtering rather than further combustion.
> > Kinda like if you pulverise an egg shell. There is still the same volume
> of shell, just a larger amount of smaller pieces.
> > That's my logic anyway. I will read further.
>
> Smoke is a sol of either a liquid or solid particles in air, it can be
> unburned volatiles that have condensed out in the flue but we are
> mostly concerned with those black sooty particles that are the result
> of incomplete secondary combustion. The mechanism for this, asI
> understand it, is the heat of the flame splits an oxygen molecule into
> two radicals, these then strip hydrogen atoms away from the fuel gas.
> As oxygen necessary to completely burn the carbon rich fuel remaining
> in the flame has to diffuse into the flame  it takes a while for this
> to happen and the carbon glows yellow in the flame. If the flame were
> premixed, as in a gasifier where the CO and H2 have been pre cooled
> before the air is added to make a homogenous mixture of fuel and gas,
> the carbon and hydrogen would react simultaneously and the flame would
> be blue. In our burners we cannot premix the fuel gas and air as the
> fuel gas is hot and already above its auto ignition point.
>
> If conditions in this diffuse flame are such that the flame can be
> sustained long enough for sufficient air to react with the glowing
> carbon then the flame is clean. If the flame is quenched before this
> happens, and it is dependent on chemicals in the flame as well as
> temperature[1], then the carbon does not completely burn and sooty
> particles are emitted. These consist of both black carbon and other
> partially burned species including polycyclic aromatic hydrocarbons
> (these are the one implicated in causing cancers).
>
> Now a bit of surmising on my part; once formed these sooty particles
> seem difficult to burn, some of them will have formed from chain like
> carbohydrates, like cellulose, and some from phenol like carbon rings
> in resins and lignin, we also know that as you heat carbon above about
> 450C it likes to form rings and these can grow into graphene like
> structures, graphene being a single layer of graphite. Graphite is
> highly resistant to oxidation so my thought is that if the carbon
> fails to burn out in the flame  it can form graphene like structures
> on which other Products of Incomplete Combustion can aggregate and
> once formed these are then difficult to burn out even at quite high
> temperatures, i.e. to burn cleanly you only have one shot at it.
>
> [1] Tom Reed explained that liquid fuels could be characterised by
> burning then in a wick lamp, increasing the wick length  volatises
> more fuel and creates a longer flame, the length of the flame before
> it gives off soot is related to the fuel make up, high octane fuels
> give a longer sootless fuel than low octane ones and natural resins,
> like turpenes, from pine have a very short flame before they create
> soot. I see something similar with my woodburning stove, most woods
> burn very cleanly as long as they are dry but holly and birch barch
> will produce black smoke if burned at a high rate.
>
> Any comments from the more erudite combustion scientists here?
>
>
> Andrew
>
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-- 
T R Miles Technical Consultants, Inc
1470 SW Woodward Way
Portland, OR 97225
tmiles at trmiles.com
www.trmiles.com
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