[Stoves] Broken Brick Mixed with Charcoal

[IPC]

Dear All

Just a small contribution on Crispin's briquettes.  We tested several
versions of coal/charcoal/ binder cylinders with vertical holes in them
several years ago.  The cylinders were about 10cm in diameter, 10cm high and
had about 10 holes each 1cm diameter through them.

Crispin says "The emissions are high for about the first hour then settle
down to a low level for the remainder of a (perhaps) 4 hour burn cycle"
which sounds very like the sort of thing we achieved. While the visible
emissions were low once the briquettes were burning and all volatiles had
been driven off (as smoke), the gaseous emissions were not low - very high
CO levels and significant nasties from the sulphur in the coal.  Also we
picked up some unusual compounds (some aldehydes) during the smoke period,
which we believe came from the binders used, as well as a lot of pyrenes.  

We concluded at the time that the route was not worth pursuing because of
the totality of the emissions. Perhaps things have improved, but I felt our
experience was worth sharing nevertheless.

(Dr)Philip Lloyd
Energy Research Centre
University of Cape Town
Private Bag Rondebosch 7701
South Africa
Tel +27 (0)21 650 3896
Fax +27 (0)21 650 2830




-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: 28 December 2007 04:15
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Broken Brick Mixed with Charcoal

Dear Friends

In addition to Dr N's comments I note the following observation made by
Bernice Chan from the University of Waterloo who is accompanying a fuel
consumption baseline team.

Testing of a Korean coal briquette stove in Ulaanbaatar is in progress.  It
is a top loading stove using round briquettes with vertical holes through
them.  The emissions are high for about the first hour then settle down to a
low level for the remainder of a (perhaps) 4 hour burn cycle after which new
briquettes are added. The combustion is a figure 8 shape with two stacks.
The burned briquettes are removed and a new one or two or three are added.

The briquette has quite a high binder level (not sure but at least 20%) and
uses a coal with a 20% ash content so the amount of actual combustible coal
is not all that high.  The moisture content is low and something like 1/2
the burnable portion is volatiles, the carbon content of which is unknown.
Fixed carbon runs into the +80% range.

The burn rate of the briquette is quite low, the CO pretty low after an hour
and the thermal efficiency pretty good - certainly better than a traditional
stove.

The increase in efficiency seems to be primarily because of a relatively
constant burn rate more than any other factor.  This fits well with the
observations of the charcoal stoves: lower peak burn rate, reduced air flow,
possibly a higher combustion efficiency with the CO reacting on the hot
surface to CO2.

Charcoal tends to burn in a way that creates a covering of ash which keeps
each piece from being a useful hot surface on which to react. Perhaps this
is the reason for the observed improvement.

Regards
Crispin


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