[Stoves] Kearns' comment on control of primary air flow

[Paul Anderson]

Josh and Biochar folks (and to Stovers because it relates to the TLUD 
cookstove),

Josh had a truly excellent and important presentation today as an IBI 
Webinar about water treatment with charcoal / biochar.   And TLUD 
technology for char making was well recognizied in the presentation.

He was asked about control of primary air in barrel-size TLUD ovens.   
He uses barrels with lots of holes in the grate (even using expanded 
steel.   His control method was mainly via the careful attention to the 
sized of the biomass feedstock.

There are other methods that should help simplify the char making. 
Simplest one is to have the barrel over a shallow pit, with one (or a 
few) entries as fist-size "notches" in the dirt for entry of the primary 
air.   Then, when the reaction is getting to be too much, put some dirt 
over most of the notches (be sure to leave some air entry, learn by 
experimenting.)

How to know when the reaction (pyrolysis plus the flaring of the gases) 
is too much?   Create a visual "gauge" in the side of the chimney (or 
upper barrel, in Josh's configuration).   I like to use 1/8th inch (3mm) 
holes drilled into the side in a straight vertical line, with spacing of 
4 inches (10 cm) between the holes.  Do this all the way to the top of 
the chimney.   So 10 holes would be 40 inches or 100 cm.  You can see 
the flames flickering inside the chimney.   It could be a 4 hole (16 
inch or 40 cm) tall flame. This is nice for being able to see the height 
of the flame even if you are away from the unit but can see the holes.
*********
Josh was also asked about use of the heat, but his interest is in the 
char.    EITHER the value of the heat or the value of the char might 
justify the use of the TLUD.   But when you have use for BOTH, each one 
supports the other.   Char of water filtration and heat for 
institutional cooking or a bakery, etc can match with the barrel-size 
TLUDs.   Or use many household cookstoves to gather the quantity of char 
for a village-size water purification installation that Josh has.   
Either way can get the benefits of using the heat and getting the char.
**********
About the last question to him:  Scaling up the TLUD technology larger 
than 55 gallon (200 liter) barrels has not been very successful.   If 
you try it, please report your results (favorable or not).

Paul

-- 
Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com