[Stoves] Patung Patong The Brick Stove Carbonizer Jan to June 2015.pdf

Julien Winter winter.julien at gmail.com
Thu Jun 4 22:03:56 CDT 2015


Hello Joshua;

Nice stove!  Thanks for sharing your experiences.  I am particularly
interested, because I and a colleague in Bangladesh are also trying to
build TLUDs out of concrete and clay.  All metal stoves are relatively
expensive because all the materials have to be imported.

We are taking a different approach to the burner, because the riser is
1.2-1.3 times wider than the gasifier reactor, following the premise that
it is good to leave as much space for horizontal flame expansion as
possible.  There are also no fins for mixing the flame (yet), because I
want to see if we can get a clean burn without them.

When I look at your schematic drawing, and first photograph, I find that
there aperture for secondary air is much smaller than what I am used to.
Have you tried experimenting with different amounts of secondary air.  In
my experience (and yours, too, I expect), the ratio of primary to secondary
air is the most important design feature to get low emissions.  If I recall
correctly, in Dr. S Varunkumar thesis, "Packed bed gasification-combustion
in biomass based domestic stoves and combustion systems," he found that the
ratio of secondary air to primary air ranged from 3:1 to 6:1, with the
higher ratio for slower gasification rates, and Tom Reed suggested 4:1
(both using force air TLUDs).

It would be nice to get a feel for air mixes by measuring CO and O2
emissions, but there is a complementary low technology approach.  What I
did, for a particular type of burner, was for a given primary air aperture,
adjust the secondary air holes (size and geometry) until I got the fastest
gasification rate.  Making the famous "all thing being equal assumption," I
reasoned that if I got a hotter gas flame through good mixing and optimum
air/pyrogas ratio, then I would also get stronger draft of primary air,
hence faster gasification rates. Gasification rate was easily measured as
(dry fuel - residual char) / (duration of raw fuel pyrolysis).  I measured
fuel moisture by drying it at 105 °C.  You may be able to get a good enough
estimate of fuel moisture without an oven by sun-drying.  It is extremely
important that your fuel is uniform, that you randomly assign batches of
fuel to runs of your stove, and that you replicate your treatments,
preferably three to four times.  The "all things being equal" assumption
(also called in Latin "*ceteris paribus*") will fail if you compare two
burners that structure the gas flame differently.

The way you have used bricks is full of useful ideas.  I like your pot
support and pot skirt.

Thanks again for sharing your experience.  As you can see, we are following
a slightly different design approach, so it will be interesting to compare
our results to yours in a year or so.  I hope that we can post our
experiences for Bangladesh soon.

All the best,
Julien.


--
Julien Winter
Cobourg, ON, CANADA
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