[Stoves] Magh Smoke Burner Stove

[Tom Miles]

Andrew and all,

Thank you for the response and ensuing discussion. I was looking for simple
direct numbers to see if the apparent char yield was anywhere close to the
fixed carbon content of the fuel. 

Assume that to apply charcoal to the soil to improve yield on my rural
smallholder garden plot I need 500g charcoal/m2 plus compost or another form
of fertilizer to feed the plants. From a batch of 500g wood fuel in my TLUD
I can get 100 g charcoal (500 g less 15% MC x 75%). So I need five meals of
charcoal to supply charcoal to 1 m2 of garden. Now if I can estimate the
benefit from the improved yield from 1 m2 of garden plot. . .

Alternatively I can take the charcoal and mix it with clay and roll it into
a ball to make a fuel for myself or to sell. I can burn it efficiently in my
six brick sprocket rocket (viz. Goyer in Uganda).

Tom

   

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of AJH
Sent: Tuesday, April 10, 2007 3:52 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Magh Smoke Burner Stove

On Mon, 9 Apr 2007 15:51:11 -0700, Tom Miles wrote:

>Part of the fixed carbon in the fuel is undoubtedly consumed during
>gasification.

In fact as I have said many times before everything points to the fact
that the bulk of the heat used for the pyrolysis process is from a low
temperature oxidation of the carbon content, you'll see reports that
the char yield falls with the moisture content of the fuel, in fact it
is difficult to sustain a tlud secondary burn when the mc exceeds 30%.

If you look at the post Tom Reed crossposted from John Bertl you will
appreciate why this may be so, also it indicates why the size of
particle a tlud may be limited, because the rate, and hence time
involved, is determined by the amount of heat that can be conducted
into the wood particle, and this is to do with both surface area
(proportionately this decreases with square of dimension) and path
length (increases linearly with dimension).


> What is the carbon conversion efficiency of the TLUD?

I've not managed better than 25% of the dry weight, whereas with a low
temperature retort I've achieved 45% albeit with a <80% fixed carbon,
at a guess.

> Has
>anyone compared the actual amount of char produced in a TLUD with the
amount
>of char that would be produced if only the volatiles were burned? 

That's a "how long is a piece of string " question because it depends
on the initial composition of the biomass and the temperature of
pyrolysis (and dwell time the wood is subjected to the temperature)
With wood slow pyrolysis at >450C will yield a char with ~82% fixed
carbon.

AJH


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