Greetings All,
Ron wrote:
[RWL: I am trying to determine if BLDD and TLUD are different during
start-up. Wood and "extremely dense smoke" sure don't have to go together.
Your use of "migh" and "always" in last sentence need further comment. I
have gathered from the comments of John Davies, that coal was always
pretty bad until one had turned the coal to coke. My hope is that with a
controllable fan, one could start the wood fires more readily. Even for a
family without electricity, I would guess that a PV-powered fan/blower
system would prove cost-effective.]
*******************
Yes coal, is particularly bad with the traditional fire BLUD ( bottom lit
up draft ) as it has such a high heat absorption during the pyrolysis stage
that it cools the flammable gasses, from the ignition wood and/or heated
coal, to below the ignition temperature. This is true during light up.
During top addition, it tends to give off volatiles in an uncontrolled
manner, not having enough air to combust. So both lighting and adding fuel
causes copious smoke.
With the TLUD with a secondary burn these problems are totally eradicated,
but there is no way to add fuel to the bottom
of the fuel pile. With the coal stove, fans are not necessary, as the
chimney is doing the same work. My TLUD coal stove gives of visible smoke
for about the first minute after light up, and this is due to the kindling
wood and starter fluid ( kerosene ) not having enough air, during the
initial intense volatile eruption, until the starter fluid is exhausted. and
that is the end of the smoke.
Now the BLDD and Cross Draft End lit stoves are burning in the exact same
sequence as the TLUD, the great advantage being that new fuel can be added
to the cold side of the fire by gravity, and the gas path moving away from
the pyrolysis zone and new fuel, through or past the glowing coke, and onto
the secondary burner. In other words it becomes a TLUD working in a
horizontal or inverted fashion. This enables a constant rate of pyrolysis,
coke burn and secondary burn happening simultaneously and in sequence.
There are no hot unburned gasses passing through a pile of cold coal.
It has been found that top lighting coal in a brazier gives off 90% less
smoke than bottom lighting, but 10% is still "too much" ( This can be
likened to a TLUD without a secondary burner )
I am not trying to answer for Crispin, but sharing my understanding of the
smoke problems associated with coal.
I am sure that the same problems exist with biomass, but maybe to a lesser
degree, due to the physical differences.
Keep up the good work,
John Davies.
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