Re: CO emissions response to Andrew

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

On Mon, 16 Sep 2002 03:17:38 -0700, "Dean Still" <dstill@epud.net>
wrote:

>Dear Andrew,
>
>Great to hear from you.

I am pleased someone reads my posts :-)
>
> Batch loading has advantages and a few disadvantages. I hear from Crispin
>that batch loading can be much preferred but our experience in Central
>America is that pushing the sticks into the fire, as into a three stone
>fire, is traditional.

One thing is certain from reading stoves, you cannot change cultural
preferences, I was not making a judgement, I am happy to play with
either system.

> I don't think that we'll find that batch loading is
>necessarily lower in CO emissions,

With the exception of the redd-larson idd stove in char making mode I
do not think batch loading stoves are ever good at start up and
reloading. 

> my very limited experience so far is that
>even smoke free fires can be spewing a lot of CO into the room. It would be
>great if the money gods were to give each of us a combustion analyzer...

I have only had brief use of CO meters, I do intend to buy something
better soon.

I did ask the list some time back and recently Tami seemed to comment
on this business of visible pollution. I think if there is visible
smoke there is bound to be high CO, so a clean burning fire is within
the set of no visible smoke i.e if you can see the smoke it is not
good eb=nough.

>This is a complicated problem...to tell when the stove is really clean
>burning is not evident to eyes or nose."

I use eyes watering to judge if the PICs are bad in the absence of
smoke. I find the nose can be misleading as a smell I had previously
attributed to air starved combustion was recognisable even with low CO
and visibly clean combustion. I guess it is an organic compound that
survives higher temperatures than I attain. I have been told that it
is necessary to reach 1300C to properly break down organic acids in
pyrolysis gas.
>
>I wanted to try various clean burning strategies in the August class, like:
>>
>>1.) Have smoke go through coals
>
>Why? The coals will still need to burn and thence will require excess
>air in the stove part.
>
>"The Rocket stove forces a lot of air through the coals so that they are
>very hot. Directing all hot flue gases to go down through the bed of coals
>might force the uncombusted particles to catch fire, i.e., downdraft through
>coals. A hot bed of coals under the fire is in the worst place to scrub hot
>flue gases, they rise up and away."

I think I have misunderstood the arrangement, I understand one of the
benefits of down draught combustion is that all gases are forced
through the high temperature zone.
>
>>2.) Force smoke to scrape against surfaces above 1200F.
>
>I guess you mean flue gas rather than smoke, or are you intending the
>surface to feed back some energy to the "smoke" to burn it out?
>
>" Directing unburnt combustibles between two glowing very hot surfaces  (or
>variations of same idea) should help to ignite them."

I think this is a bit like the "gas wick" function in the idd stove, I
actually doubt the effect is any more than controlling the gas
velocities to match the flame speed, anyway there is a cost in heating
the surfaces to above spontaneous combustion temperature and that is
heat loss through the surfaces unless you have access to kaowool type
insulation, now a catalytic surface is something else!

>This to prevent "runaway" pyrolysis upsetting the fuel:air ratio?
>
>"We want to burn all wood at very high temperatures. Having too much air
>isn't a problem, I think, if it doesn't cool the fire."

I think we are running into a misunderstanding. I was commenting on
your requirement to keep wood cool until it entered the combustion
zone, once in the combustion zone I think we all agree the three Ts.
BTW excess air always cools the fire because you have only a given
amount of energy in the fuel and increasing air beyond stoichiometric
serves to spread the heat over a larger mass flow. The art is to
maximise the amount of fuel cleanly combusted by increasing the excess
air, this tends to be a function of the quality of the fuel, my wet
fuels seem to need 50% excess air, natural gas manages on 5%.

>"I agree, except that: the easiest way to produce less smoke in a Rocket
>stove is to make the insulated chimney above the fire higher. But the excess
>draft created by the taller chimney pulls too much air past the sticks
>lowering exit temperatures. Bad for cooking efficiency...So, using up the
>excess draft by tumbling hot flue gases in the chimney seemed a possible way
>to make the taller chimney (which gives more time for combustion to occur)
>practical."

I think I disagree this last point, it is a shame that I cannot be
present whilst you run some of these tests, maybe one day...

AJH

-
Stoves List Archives and Website:
http://www.crest.org/discussion/stoves/200209/
http://crest.org/discussiongroups/resources/stoves/
>
Stoves List Moderators:
Ron Larson, ronallarson@qwest.net
Elsen L. Karstad, elk@wananchi.com www.chardust.com

Other Biomass Stoves Events and Information:
http://www.crest.org/articles/static/1/1010424940_7.html Bioenergy
http://www.crest.org/articles/static/1/1011975339_7.html Gasification
http://www.crest.org/articles/static/1/1011975672_7.html Carbon

List-Post: <mailto:stoves@crest.org>
List-Help: <mailto:stoves-help@crest.org>
List-Unsubscribe: <mailto:stoves-unsubscribe@crest.org>
List-Subscribe: <mailto:stoves-subscribe@crest.org>
>
For information about CHAMBERS STOVES
>http://www.repp.org/discussiongroups/resources/stoves/Chambers/Chambers.htm