Tom, Crispin and tangled thread followers,
It's a challenge to keep up with the chat while traveling....
I guess Tom's numbers below would be illuminated by numbers for pressure
drop across the bed or the fixed reaction zone/throat.
Quite a different beast the batch TLUD.
With restricted primary air, the throatless throat of a TLUD's
descending pyrolysis front can travel downward at as little as 3 inches
per hour through a 40 pound per cubic foot pellet fuel with a energy
yield of say 5000 Btus per pound (this number could be challenged).
The peak temperature in the pyro front would be just under 500C or ~900F.
So this example represents something close to a low or slow end
scenario of 50000 btus/ft2/hr or 158kW/m2. The pressure drop across the
bed or front would be so small as to be difficult to measure. The
primary air introduction could be through a drinking straw or two/ft2.
(Possible slight exaggeration alert!)
Not hard to drive up those numbers with more primary air. With natural
draft from modest chimneys can certainly double the rate. High pressure
blowers can turn it into something that sounds like a rocket but at this
point I am uncertain what the upper limit might be.
Beastly different again is the Pasifier.
Using the same fuel (non charcoal making mode-so 8000btus/lb), and the
grate area in the up draft portion, I get 150000btus/ft2/hr under 0.1"wc
pressure drop, and up to triple that, so far, with higher suction in
electrically powered draft mode.
Then again the pellet world is a bit ivory towerish.
Later, I should be able to offer wrougher numbers for wrougher fuels
with my wood chip "linear" Dasifier.
Alex
On 29/09/2012 4:08 PM, Tom Miles wrote:
Crispin, Alex,
If my calculations are correct the burn rate for downdraft gasifiers
is in the order of 70-100 lb/ft2/hr (340-490 kg/m2/hr; 1688-2400
kW/m2) with a high performer being about 140 lb/ft2/hr (65 kg/m2/hr;
3377 kW/m2). So in 24 in diameter you can fire from 220-315 lb/hr
(100-143 kg/hr), or up to 440 lb/hr (200 kg) dry (15% MC) fuel.
What is the burn rate for a TLUD?
Tom
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