[Stoves] Charcoal Stoves

[AJH]

On Mon, 12 Jun 2006 15:29:21 -0700, Tom Miles wrote:

>Dean's "CO Emissions From a Charcoal Rocket Stove" plot is on the
>www.bioenerglists.org site at
>http://bioenergylists.org/en/node/546

This chart looks very similar to the shape of the flue gas CO that my
mate reported for his batch loaded cross draught gasifier, the first
spike as the new batch caught alight from the remaining coals followed
by very good combustion until there was a small bed of embers on the
grate which didn't properly support the secondary burn.

>[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Dean Still

>
>We have been experimenting with charcoal burning for the last week or so
>trying to improve a charcoal burning stove from Mauritania. Saturday I cut
>off the bottom of a Rocket stove and plastered shut the fuel entrance in the
>side. This created an insulated vertical cylinder 33 cm tall. I installed a
>grate in the bottom. 600 grams of charcoal were placed on the grate and lit.
>
>Photos and test results have been sent to Tom to post.
>
>>From the start of the burn there were flames above the fire. After 
>>about 15
>minutes the cylinder above the fire was at 650C and full of flame. At this
>point almost all of the CO was being consumed.

It looks like you have converted the rocket into a simple updraught
gasifier, this is quite unlike the shallow bed of charcoal I was
looking at.

>In My Opinion:
>
>In our previous tests with a Jiko type stove improving heat transfer by
>radiation and conduction helped to decrease fuel use and emissions. 
>
>The Rocket charcoal stove creates a zone of heat and flame above the burning
>charcoal that reduces CO. Heat transfer to the pot is mostly by convection.
>The tall insulated Rocket 'chimney' above the fire creates velocity that
>increases heat transfer to the pot by thinning the boundary layer of still
>air under the pot. 

It also increases the superficial velocity through the coals and hence
gasifies the char to CO.

> 2/3rds of the energy in wood is lost when making it into charcoal.

Yes apart from the special, little used, cases like the TLUD or retort
systems that recover heat for drying.

> Burning wood remains a much more
>energy efficient method for cooking.

I agree for the most part.

> Reducing CO by creating a hot zone of
>flame above the charcoal is a simple way to make it a bit safer, when used.

Unless the flame goes out....


Andrew Heggie