[Stoves] burning particulates

[ajheggie at gmail.com]

Hi Daniel

Just a further little anecdote, the Romans appreciated underfloor heating
too, they built fires with flues under the floors and inside the walls,
look up hypocaust.

When Ronal was here about 11 years ago for a conference I took him to the
remains of a roman fort on Hadrian's wall and we saw a bath house with this.

On Sun, 31 Jan 2021 at 22:46, Daniel Pidgeon <daniel.pidgeon at hotmail.com>
wrote:

> Andrew,
>
> Thank you for your comments regarding underfloor heating. I have read of
> the physically perceived benefits of direct contact with warmth.
> Before learning of and getting my mind set on underfloor hydronics, I
> learned of Paul Wheaton's rocket mass heaters, which I could not put inside
> my house, and quickly discarded the thought of an underfloor mass as too
> difficult an engineering process.
>
> My wife will appreciate the warmth more than I will. Although the further
> I get into middle age, the more my body and joints appreciate just being
> warm and cozy at the beginning and end of the day...
>
>
>
> Overviewing my take home, from all that I can understand, in order to keep
> the burn as smoke free and clean as possible, maintaining the flame as long
> and hot as possible is the simplest, best that can be done. The simplest
> way to do this is to keep it as oxygen rich and well mixed as possible. And
> even though this might increase the output of PM 2.5, it ought to be a
> clean burn as far as all the other nasty outputs.
>
> You talk about cooling the gas, I'm picturing something like the gasifiers
> that produce smoke for engine use. While this might make a better mix for
> the burn, it is a pretty complex bit of machinery for a backyard tinkerer.
>
> While Kirk Harris's stoves do not appear to burn the blue like you
> mention, his newer cone and condenser version appears to have the best
> oxygen input and mixing that I have seen. It appears to do enough to
> sustain the flame long enough to combust as much as possible.
>
> https://stoves.bioenergylists.org/files/harris-figf.jpg
>
>
> Thanks again for your comments, I'm looking forward to work quieting down,
> and having the time to pick up the heating project again, and eventually
> looking into maybe even testing out the emissions further than just
> eyeballing it.
>
> 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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