[Stoves] Hydrogen from charcoal

[Saastamoinen Jaakko]

Dear Crispin, Karve and all,

H2 can be both from combustion air and fuel as charcoal contains also some hydrogen. As discussed in the list, H2 can be formed both from gasification and from water-gas shift reaction if temperature is high enough.  Temperature can rise high locally inside char bed in the location where O2 is completely consumed allowing reactions to take place there and H2 not to be burned (because oxygen has been consumed). H2 is probably not from wet charcoal, since moisture is driven out (by drying) as H2O at lower temperature, except if combustion air comes from a dyer.

Hydrogen is very reactive. H2 burns faster than CO (if oxygen is present). CO emissions correlate well with hydrocarbon emissions in fireplaces for heating purposes. I believe that H2 is so reactive that emissions of it are minor, if there is oxygen in the gas and temperature is high enough. Was oxygen concentration in gas zero?  Both H2 and O2 could be averagely present in the gas in high temperature (and found when gas is cooled), if H2 produced is channelled somehow so that it does not mix well with O2.

Moisture in combustion air reduces CO emission from charcoal bed by two ways (if there is enough oxygen):

1)      The mixture of CO and H2 is ignited and burned better than just CO due to high reactivity of H2 producing heat to sustain combustion (also of CO) .

2)      The combustion chemistry of CO involves radicals formed from H2O even the simple reaction CO+½O2=CO2 does not show it. So increase in H2O accelerates burning rate of CO.

Regards

Jaakko


From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Anand Karve
Sent: 8. syyskuuta 2013 14:19
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Hydrogen from charcoal

Either the charcoal is wet or the air is laden with moisture. If you introduced water into a charcoal brazier, you get a nice blue flame of burning water gas.
A.D.Karve
On Sat, Sep 7, 2013 at 2:47 AM, Steve Taylor <steveastrouk at gmail.com<mailto:steveastrouk at gmail.com>> wrote:

Wet charcoal?
On 6 Sep 2013 20:31, "Crispin Pemberton-Pigott" <crispinpigott at gmail.com<mailto:crispinpigott at gmail.com>> wrote:
Dear Friends

This is a plot of CO(EF) and H2(EF) for a charcoal stove.

[cid:image001.jpg at 01CEAD8A.0BC97FD0]
What do you suppose is the source this hydrogen?

Note for interest that the ratio between H2 and CO is surprisingly constant throughout the test. It is not the ratio of the H and C in the fuel (at all).

Regards
Crispin






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--
***
Dr. A.D. Karve
Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)
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