Re: GAS-L: feeding biomass into pressurised systems

[AJH <andrew.heggie@dtn.ntl.com>]

On Sat, 3 Aug 2002 09:11:04 -0600, "Tom Reed" <tombreed@attbi.com>
wrote:

>
>WOOD AS NORMALLY BURNED IS REALLY TWO FUELS - THE ~ 80% VOLATILE FUEL GASES
>COMING OFF AT 300-400 C AND THE REMAINING 20% CHARACOAL.  THE VOLATILE GASES
>HAVE AN AIR/FUEL RATIO OF ABOUT 4.5; THE CHARCOAL HAS AN A/F OF 12, SO THE
>MIXTURE IS 6 - IF YOU CAN FIGURE OUT HOW TO BURN ALL AT ONCE (AS IN PELLET
>HEATING STOVES).

This is the path I have taken, however the pellet stove and pellet
fuel is a special case which will not pertain with lesser fuels. This
is one reason why I wish to move to a stoker, the dramatic change in
combustion volume leads to a need to vary air supply with batch loads.
This may not be too significant with an energy dense fuel but it is
with a fuel with poor mass and energy densities. Wood pellets are
about 600KG/m3 and dry, my fuels are <250kg/m3 and 50% water.
>
> So there is a need for a cheap
>simple method of metering fuel into the combustion chamber.
>
>IN THE WGCS WE RECOMMEND ADDING ADDITIONAL FUEL 1 LAYER AT A TIME WHEN YOU
>REACH THE CHARCOAL STAGE.  THE PRODUCES PYROLYSIS GASES AT THE SAME RATE AS
>THE INITIAL INVERTED DOWNDRAFT GASIFICATION.

I have no scope for this as the pot is in the way, also fuel need to
be added in the primary combustion zone which sits at a small pressure
above atmospheric.
>
>At the moment I have to rely on a low powered fan for combustion air, so I
>can accept a similar electrical method of fuel metering.
>
>ONE SELDOM NEEDS TO COOK MORE THAN THE 45 MINUTES SUPPLIED BY WOOD PELLETS,
>AND OFTEN THE 12 MINUTES FROM CHIPS IS ENOUGH FOR A CUPPA.

I had gathered the impression that many foods needed much longer
processing than this? As I said pellets are not an option, I am
looking at utilising agriwastes.

>  HOWEVER,
>CONTINUAL FEEDING WOULD BE DESIRABLE FOR SPACE HEATING STOVES, INDUSTRIAL
>COOKING ETC.  IN THIS CASE A SIMPLE AUGER INTO THE SIDE OF THE UNIT WILL DO
>THE JOB.  CAN BE MOTOR CONTROLLED OR HAND CRANK DEPENDING ON APPLICATION.
>SINCE ONLY AIR IS RISING THROUGH THE MASS THIS WON'T INTERFERE WITH THE
>GASIFICATION.

This is not so in my device, on the larger scale I can afford the
luxury of an ID fan, on the cookstove I cannot. An auger will not
contain the offgas and combustion products unless it deforms the
biomass sufficiently to remove air paths, this is what I took the
screw plug feeder to do. I also feel that augers will be too power
hungry in this application.

>
>I DIFFER TO TOM MILES IN ALL THESE INDUSTRIAL SIZE QUESTIONS...

I have not yet seen Tom M offer any comment on any options so How can
we differ?

AJH

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