[Stoves] Emissions from briquettes vs pine wood

Crispin Pemberton-Pigott crispinpigott at gmail.com
Sat Dec 4 10:28:52 CST 2010


Dear Timothy

Further to Paul's questions and answers, I thought I should mention
something that you and Xavier may find helpful.

When measuring the CO2, CO and other emissions from a stove (or any
combustion) is it important to know whether the 'increase' was due perhaps
to reduced dilution by excess air passing through the stove.

If you make a stove you can quantify the emissions or measure the
concentration. These are quite different things. Quantification means
calculating the whole volume then the mass on the ingredients. Measuring
concentration as they pass out of the stove does not really tell us much
about the total emitted.

The PEMS hood and the software that goes with it, or the SeTAR Centre
methods (and others) measure the whole quantity emitted.   I feel this was
not explicitly covered by Paul's response.

>2.  Having higher CO2 does not match up with higher CO and PM.
>     Either:
>      a.   The amount of fuel (energy value, not the weight) in the  
>briquette is greater than the fuel of the pine wood.    or
>
>      b.  The fire is more intense for the briquette, resulting in  
>higher CO2 during a shorter period of time.    or
>
>      c.  Something else that needs to be mentioned.

Well the something else is excess air. If you do not know how diluted the
gas stream was (because of variable amounts of air passing through the
stove) it is pretty difficult to assess if one or other of the gases has
increased or decreased.

John Davies in South Africa is trying to develop a low cost measuring
instrument that will be able to collect enough information to asses in real
time what is being emitted and how diluted it is.

My message is on mostly caution: if the CO has reduced in ppm, you want to
see that the CO2 level has simultaneously increased, indicating better
combustion with less excess air.

If CO drops by 25% and CO2 by 50%, it is definitely working worse than
before, in a more diluted environment. Dividing the CO by CO2 will give a
common measure of 'combustion inefficiency'. This metric is widely used to
regulate the emissions from fuel burning products. The dilution is
immaterial when one makes such a measurement, hence its usefulness.

Regards
Crispin





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