[Stoves] Emissions from Residential Wood Combustion: EffectofMoisture on Emissions

Sun Dec 31 13:58:26 CST 2006

Frank,

Moisture Content

Moisture content in wood fuel is calculated as the percentage difference
between the wet weight of the wood and the dry weight of the wood. If the
percentage is calculated relative to the wet weight, it is called the wet
basis moisture content.
MCwb=(Ww-Wd)/Ww ×100%

If the percentage is calculated relative to the dry weight, it is called the
dry basis moisture content.
MCdb=(Ww-Wd)/Wd ×100%

The two methods of reporting moisture content are related by the equation:
MCdb = MCwb/(100-Mwb)x 100%

From: Residential Wood Burning Emissions in British Columbia
Environment Protection Division, Ministry of Environment, British Columbia
April 1, 2004, Revised May 17, 2005
http://www.env.gov.bc.ca/air/airquality/pdfs/wood_emissions.pdf

Tom Miles

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of frank at compostlab.com
Sent: Sunday, December 31, 2006 11:03 AM
To: Crispin Pemberton-Pigott; Discussion of biomass cooking stoves
Subject: Re: [Stoves] Emissions from Residential Wood Combustion:
EffectofMoisture on Emissions

Crispin, anyone,

How is moisture calculated on a 'dry basis'? On a wet basis it is % water in
the wood. 100 grams wood that includes 20 grams water is 20% moisture on a
wet
basis. Reported on a dry basis it would always be 0 % moisture. 

Is a 'dry basis' 100 grams of dry wood + 20 mls water reported as 20%
moisture
on a dry basis? I've never used these units.

Thanks
Frank

On Sat, 30 Dec 2006 17:13:56 -0500, Crispin Pemberton-Pigott wrote
> 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>
> 
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--
Frank Shields
Soil Control Lab
42 Hangar Way
Watsonville, CA  95076
(831) 724-5422tel
(831) 724-3188fax
www.compostlab.com
www.greenrooflab.com

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