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| Stoves Archive for June 2002 |
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| 52 messages, last added Tue Nov 26 17:31:40 2002 |
[Date Index][Thread Index]
Re: charcoal stove
Dear Stovers and Gasifiers:
Typical producer gas produced in conventional downdraft gasifiers has a
heating value of 5 to 6 MJ/Nm3. Superficial velocity typically 0.1-0.3 m/s
(m3/s//m2).
In the inverted downdraft mode the gas velocity is much lower (0.01 - 0.05
m/s) because at higher velocities the charcoal upper layer blows out (unless
you put a grate over it). This lower intensity gives lower flaming
temperatures in the flaming pyrolysis zone and accounts for the MUCH higher
charcoal yields (0.2 to 0.25 rather than 0.05 - 0.1 for conventional
downdraft).
It requires typically < 1 kg of air to pyrolyse 1 kg of biomass to make
combustible volatiles from biomass, leaving behind 20% charcoal. It
requires 6 kg of air to gasify 1 kg of charcoal to CO. Therefore, when the
gasification process does not gasify the charcoal, there is much less
nitrogen in the offgas.
Andrew guesses inverted downdraft gas might be as much as 12 MJ/Nm3, and I
tend to agree with him. However, it is a difficult measurement to make
because the gas may have as much as 50% condensibles in addition to CO, H2
and rich hydrocarbons.
In any case, it is a great gas for all heat applications as long as you stay
above the dewpoint (300C???).
Onward, TOM REED BEF GASWORKS
----- Original Message -----
From: "AJH" <andrew.heggie@dtn.ntl.com>
To: <stoves@crest.org>
Sent: Sunday, June 09, 2002 7:17 AM
Subject: Re: charcoal stove
On Thu, 06 Jun 2002 18:56:34 -0500, "Paul S. Anderson"
<psanders@ilstu.edu> wrote:
>Andrew,
>
>Please tell us where there is info on your "woodchip burners"
I can assure you all, and I mean all, relevant information has been
posted to stoves by myself. The precise composition of the whole is
proprietary and I welcome enquiries ;-).
>
>AND also comment on the possibility of making use of the flared off-gas.
The flared offgas is a high quality heat source, probably in the order
of 12 MJ/kg average, my colleagues are currently coupling a different
burner up to a simple gas turbine using this gas! I do not know the
exact relationship between the gas cv and flame temperature but in
general the temperature is related to the cv divided by the mass flow.
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