[Stoves] burning particulates

Fri Feb 5 11:47:19 CST 2021

Hi Andrew and Daniel - you might find this of interest, seems these systems
are still in use in Spain
https://www.notechmagazine.com/2017/02/medieval-heating-system-lives-on-in-spain.html
and more on hypocausts here
https://www.lowtechmagazine.com/2017/03/heat-storage-hypocausts-air-heating-middle-ages.html
as well.

a
Teddy Kinyanjui
Sustainability Director

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On Thu, Feb 4, 2021 at 8:54 PM <ajheggie at gmail.com> wrote:

> 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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