Dear Bill, Kevin and all,
Thanks for the valuable information. As you put it very clearly,
successful gasification starts with a " Good prepared fuel" and
continues with well built gasifier.
For pellets we don't have so much experience, but we know they are made
with pressure and the heat caused by friction. On the other hand,
briquettes made with hydraulic press or screw press. Material has to be
dried to 10-15 % moisture hydraulic systems have pressure 1300-1700
kg/cm2, screw systems double that pressure up to 3000 kg/cm2 depending
on screw design... On screw systems, forming cylinder is also heated
around 300 degrees Celsius. I can break the concrete walls with the
briquettes we make, ( Sometimes the hole in the briquette gets clogged,
with pressure and heat the gas accumulated inside the forming cylinder
blows up sending the front piece of the briquette to concrete wall. In
front of every machine, we have holes in the concrete wall... ). Density
of 1 m3 of briquettes are more than 1300 kg.
Briquettes are much more uniform but harder to make compare to the
pellets. We have done gasification with briquettes and also briquette
charcoal. Both resulted in very clean gas, specially the briquette
charcoal. With the charcoal, must be careful about the heat in the
reactor. It goes over 1200 C very fast and makes clingers. They are
perfect for steam gasification since the briquette charcoal has over
7000 Kcal energy.
For the price factor, briquettes are exported at $ 175.00 per ton,
briquette charcoal is $ 500.00 per ton. It is better to use briquettes
for gasification. We have made briquettes using saw dust ( from very
light wood to hardest wood dust available) and rice husk. Rise husk is
very abrasive and eats the screws very fast.
I guess for all the people who lives in the woods, or near the woods, it
would be better to use the wood chips or chunks. As my experience,
uniformity of size is not as important as the dryness of the fuel
prepared. We have gasified rice husk and up to 4 x 4 x 5 inches, size
wood chunks (in a smaller size gasifier with only 15 cm throat I still
can't figure out how they go through the reactor, but they do...) for
thermal purposes, results were always good. If your fuel is dried, you
will get better quality gas to running engines. Gasifier can be pushed
to get more gas for thermal purposes, but to use the gas in the engine,
you must really adjust and stay in certain parameters.
As Bill said, every gasifier is different. You must play and experience
with your own gasifier. First get the gas and quantity you need. Than
you can play with the reactor design to get a cleaner gas.
Thanks to everybody sharing their experience and knowledge as much as
possible. Every time I built a gasifier and get good quality gas, I
thank to many people on and off the list, from my hearth to give me the
knowledge and courage to pursue gasification.
Best wishes to you all...
Robert Kana, Biomass Indonesia
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