[Stoves] Gasifiers and combustors: was: Limiting factor for secondary burn?

[Paul S. Anderson]

Dear all,

I have come to the realization that combustion of the created gases from a
gasifer is not a defining characteristic of "gasifiers."  Instead, we should
(and often do) say things like "gasifier with close-coupled combustion" or
"gasifier with clean gases sent to internal combustion engines."

In a TLUD (top-lit updraft) gasifier such as Reed's Woodgas Campstove or my
Champion stove and many others, the gasifier part is the "making of the 
gases".
And when those gases are "dirty or tarry," we could call it a "smoke maker" or
a "pyrolysizer".    Likewise, we could call the combustor of tarry gases a
"smoke burner."

Here is a test about what is a gasifier or not.  [There should be 
adequate draft
from a fan or sufficient chimney/suction.]  Bring the unit to normal 
operation,
then extinguish the combustor of the gases.  A gasifier is the initial part of
the full device/system and it should continue to make gases (smoke) on and on
and on and on as long as fuel is present.  AND those gases should be 
able to be
RE-ignited and extinguished and re-ignited again and again with relative ease
and consistency, showing that the gases are created separately from the
combustion of those gases.

In the TLUDs, the close-coupled combustor is usually built into the whole unit
and it is called a TLUD gasifier for short, but is actually a "TLUD gasifier
with close-coupled combustion."  Extinguish the upper flame of the Woodgas
Campstove and you have a smoke-machine, a real gas maker.  But throw in a lit
match and it will combust (have flame) again.

I think Tom was typing too fast when he wrote:
Quoting Thomas Reed <tombreed at comcast.net>:

> A *toplit* *updraft gasifier*,  burns most of the volatiles to make
> combustible gas and charcoal.

Instead:  A *toplit* *updraft gasifier*,  burns [a small amount] of the
volatiles [created by pyrolysis] to make combustible gas [which is the vast
majority of the pyrolysis gases] and charcoal [that is left behind].

     or

Instead:  A *toplit* *updraft gasifier* makes combustible gas and charcoal.
Then most of the volatiles (combustible gases) are burned in a combustor of
some sort, such as the arrangement for secondary air to enter at the 
top of the
Woodgas Campstove.

My point is, making combustible gases (whether clean or dirty) is the work of
the gasifier.  The combusting (burning) of those gases is the work of the
combustor arrangement.

And by having that separation, the stoves or devices that incorporate a 
gasifier
can have cleaner combustion than the non-gasifier stoves or devices.

Said another way, stoves with gasifiers in them are "gas burners" when 
it comes
to the key issue of combustion for cooking, etc.  The gasifier stoves are NOT
"wood burners", but only use the wood and other solid biomass to create the
gases that are combusted soon after but separately from the creation of the
gases.

Paul


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