[Stoves] the 150 gasifier in operation in Vietnam

ajheggie at gmail.com ajheggie at gmail.com
Sun Mar 4 05:59:24 CST 2012


On Sun, 4 Mar 2012 17:50:46 +0700, Paul Olivier wrote:

>
>I am not sure if I understand what you are saying here.
>From what I observed, the gases have to burn below the wire mesh.
>If they go through the wire mesh and then burn, then the wire mesh turns
>from red to black.


This is understandable and points to the same effect as the gauze in
the Davey lamp, is the black sooty deposits? Or just lower
temperature? My inference is that there would be higher products of
incomplete combustion above the wire in this scenario.


>Most of the gases burn close to the burner holes.
>But there are always gases that rise in the dome and hug the underside of
>the dome.
>There they burn right on the underside of the dome.
>The wire mesh dome gives structure to the diffusion tail
> and does not allow it to be so easily influenced by the random movement of
>air or wind.

It's hard to see what's happening here, how the dome is acting as a
shield, whether the dome is passing unburnt gas, just as in the gauze
and Bunsen burner demonstration.
>
>
>
>> I wonder how
>> this sits compared with the wire gauze in a Davey Safety lamp, which
>> is there specifically to remove the source of ignition from the gases
>> outside?
>>
>
>Again, I do not understand your point.

In the beginning of the industrial age coal was the driving energy
source and with the lack of large machines it was "won" by men
tunneling into the seams with pick axes and candles on their heads.
Apart from the obvious dangers of rock fall there was the danger from
gases seeping into the mineshaft, they were given different names from
their consequences, black damp was CO2 and water vapour from the newly
exposed coal reacting with air which caused asphyxiation (damp derives
from the german for vapour). Canaries are sensitive to reduced O2 in
the atmosphere and were used to indicate black damp. Firedamp was an
explosive mixture , mostly now known to be methane, and candle flames
could set off an explosion. Humphrey Davey produced a lamp that was
safe to use because it was not an ignition source, like a naked flame.
The principle he used was to enclose the flame in a glass cylinder to
let the light out but all the combustion air and flue gases passed
through a mine gauze, this gauze conducts the heat away from a flame
such that the flame is quenched, just like lowering a cold spoon over
a candle flame. So even though the lamp was hot it was below the auto
ignition temperature of methane:air mixture and because the flame is
quenched there is no flame or spark to trigger the explosion.

You seem already to have observed that the flame needs to complete
under the gauze. I just worry that what you observe of the dome giving
the flame structure is not just that the dome is quenching and unburnt
gases are thus not seen above the dome.

If you have access to a Bunsen burner you can readily demonstrate this
effect by placing the gauze 1cm above an ordinary gas burner before it
is ignited and then light it above the gauze, not the flame dances on
the gauze and does not jump back to the burner, at least until the
gauze gets bright red hot, if ever.

First hit on Goggle

http://www.minerslamps.net/homepage/safetylamphistory.htm
>Please clarify.
>So sorry.
Paul all of your questions are sensible, my struggling to answer them
in a way you understand is the problem, this often troubles me when I
see no responses.

AJH




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