[Stoves] Emissions from Residential Wood Combustion: Effect ofMoisture on Emissions

[Crispin Pemberton-Pigott]

Dear Testers

I reviewed the paper by Fernando Preto and noticed interesting and important 
things throughout the document.

For example, testing done with softwood gives consistently higher CO than 
hardwood. Higher moisture content gives consistently lower CO, all the way 
to 35% moisture (dry weight basis I believe).

This means that benchmarks proposed for emissions which have been based on 
low moisture softwoods (as is the case in the draft proposal forwarded for 
discussion in Bonn for WHO, could be quite misleading. We could set a lower 
permissible level for CO.

The reasons for this is that the proposed benckmarks were based on Rocket 
Stoves mostly optimised (dimensions and operator technique) for low CO in 
ppm.  The emissions may have been significantly lower had the wood contained 
15 to 35% moisture, and the PM 2.5's would have been affected either up or 
down.

The vast majority of particulate emissions from wood fires are PM 2.5's 
(something over 85%) and they seem to follow a path inverse to the CO 
production.

It is clear that testing of stoves has to be done with wood that is 
reasonably moist and comparable with field conditions, and then the stove 
dimensions optimised to that fuel. Also, the operator of the stove has to be 
familiar with how to operate it with that particular fuel.  Reproducing the 
exact method as used with very dry fuel will not perhaps give the best 
result.

Both the USA and Canada seem to be leaning towards using a dry weight basis 
for testing and certification.  This is inconvenient for us with our simple 
scales, but it is only a matter of mathematics and can be resolved on the 
spreadsheet.

One must again remember that these tests by Preto are 'device dependent' and 
do not constitute the expected emission of cooking stoves, only standard 
(three sets or types) of box-stoves for space heating.  Surprise still might 
be lurking.  I would not be surprised to find improved cooking stoves are 
cleaner than space heating stoves.

If a stove is going to be primarily used with hardwood, it should not be 
tested with softwood because the emissions are quite different.  The biggest 
difference of all is between dry softwood, as used in APROVECHO standardised 
testing, and moist hardwood, especially in CO production.  As make cook in 
fact use moist hardwood of many species (softwood being a lousy fuel) the 
relevance of APROVECHO's standard fuel test results is suspect.

It is likely that the target emissions or benchmarks for CO and particulates 
can be reduced if Preto's work is borne out for improved cooking stoves.

A very interesting set of developments!

Regards
Crispin

----- Original Message ----- 
From: "Tom Miles" <tmiles at trmiles.com>
To: "'Discussion of biomass cooking stoves'" <stoves at listserv.repp.org>
Sent: Saturday, December 30, 2006 2:24 PM
Subject: [Stoves] Emissions from Residential Wood Combustion: Effect 
ofMoisture on Emissions


Emissions from Residential Wood Combustion: Effect of Moisture on Emissions
Fernando Preto, Canmet Energy Technology Center, Canada, Paris, October 21,
2005
 <http://www.ieabcc.nl/meetings/task32_Paris_ssc/Preto.pdf>
http://www.ieabcc.nl/meetings/task32_Paris_ssc/Preto.pdf (1.3 MB pdf)
http://stoves.bioenergylists.org/en/canmetiea32paris
<http://stoves.bioenergylists.org/en/canmetiea32>