[Stoves] Burning coal in cookstoves

[IPC]

Dear Tom

Thanks for your input.  Yes, I know about the phenomenon.  Adding moisture
does keep down the smoke.  Those gas flares you see at petroleum refineries
have a constant stream of steam going into the flame for that very purpose.
At the temperature of the flame, the steam reacts with unburned carbon and
hydrocarbons and produces carbon monoxide and hydrogen, which then burn
rapidly once there is enough air.  Blowing a bit of steam into a candle
flame reduces its luminosity considerably, by the same effect.  

And "wood ash captures the sulfur in the ash." I hadn't thought of that, but
of course it must be the alkalis and alkaline earths in the wood, making
sodium/potassium/calcium/magnesium sulfates - the same process used
industrially to remove SOx from coal-fired stack emissions.  We tend to
forget how alkaline wood ash is - but the alkalinity is an essential part of
regeneration after wildfires.

Regards

(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 Tom Miles
Sent: 29 December 2007 12:12
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Burning coal in cookstoves

Philip,

We found that by burning 25% wood with 75% bituminous coal in an
institutional boiler we created a volatile flame above the coal bed that
burned out the combustible gases and particulate. Since it was a continuous
feed stoker it might not work the same way in a batch stove or furnace. 

The coal was 40% volatile, 10% MC and 20% ash 32 mm stoker coal (25 MJ/kg
LHV). The wood was wet sawdust, 50% MC, 1% ash 6-20 mm (8 KMJ/kg LHV).
Moisture from the wood cooled the coal flame and reduced agglomeration. Wood
ash captured the sulfur in the ash. High volatiles from the wood (80%) of
the fire and cleaned up the hydrocarbons which reduced emissions, cleaning
up the stack and burning out the CO. (We burned up to 2/3 wet wood with coal
at which point we were "burning" 1/3 wood, 1/3 coal and 1/3 water.) We
engineered the combustion air for good burnout at and above the grate. Now
if we could use a little wood to clean up a coal stove . . .

Tom Miles         





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