Doug,
The AVUD method is ignited at the level of the "grate" (actually a pipe
with holes on side and bottom, so the char can pass around the pipe,
drop below the hot zone, and be extracted at regular intervals). The
heat rises and pyrolyzes the biomass above, and additional fuel is added
regularly on top of the fuel pile. That makes it a continuous
process. No need to stop.
The tarry gases exit and are combusted with turbulent air, coming from
an air compressor. The combustion is quite complete and clean. This
has similarities to the Dasifier made by Agua Das almost 20 years
ago. You should read these materials at my website:
http://www.drtlud.com/?s=dasifier that link leads to
http://www.drtlud.com/wp-content/uploads/2015/01/Dasifier-Foundry-Gasifier.pdf
and see a 2012 video with Das himself melting metal with woodgas at:
https://www.youtube.com/watch?v=t08tj4NWUQY
Many years ago Das was one of my teachers and mentors, and a good friend
of Tom Reed.
Paul
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: [email protected]
Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 1/5/2017 8:19 PM, Doug wrote:
Hi Paul,
There is a difference in how pyrolysis (smoke gas ) can evolve, and
from what I see of the AVUD design, it appears that it still follows
the top lit philosophy. Maybe I scan read too fast, but neither write
ups stated how the bed is ignited. My understanding from the drawing,
is that the bed is ignited at the top, and they burn down towards the
grate which has air aspirated or blows at low pressure in from the
bottom. This changes both how the gas evolves and it's hydrocarbon
content, depending on they type of fuel available. While it can be
considered pyrolysis gas, it certainly has to be a higher quality than
the chocking yellow smoke gas that most charcoal makers see full of
hydrocarbons. The give away is that pyrolysis gas burns red/yellow
with air, and better quality gas burns blue. What is considered a good
color for your stoves?
When the fire is located at the grate of an updraft and interfacing
the incoming air, high temperature oxidation forms at the bottom of
the bed, and depending on the air pressure, can build an oxidation bed
up to 4" deep, driving incandescent CO2 up through the incoming raw
fuel. It is one might say, almost instant charring. Fine chars and
carbon blacks are carried out of these types of air flows. Our
charmaker has a controllable blower type fan capable of 15" W.G. max.
and this is able to push the gas through a 48" vertical bed loaded
from the top.
Hope that clarifies how the carbon escapes.
Doug W.
On 06/01/17 11:26, Paul Anderson wrote:
I agree that what Rolf is seeking is not a TLUD.
You wrote:
May be the ash from the carbon dust will settle in the tunnel
depending on combustion gas velocity. Usually, a correctly sized
flue stack is required to assist with removing the exhaust gas, and
this is where ash dust can become an emission.
I have not experienced carbon dust or ash from carbon dust or ash
dust with the AVUD design.
Again, thank you for your strong support for gasification of biomass.
Paul
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