[Gasification] Getting both heat and char .....

Doug doug.williams.nz at gmail.com
Thu Jan 5 20:19:52 CST 2017


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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