[Stoves] Lowering emissions

Tue Jan 2 10:33:45 CST 2007

Thanks Dean

It should make for lively discussion. Most important I think is that we find
ways to deal with test conditions that have major impacts on the results
(e.g fuel type, fuel moisture, fuel size, pot size, charcoal, lids, methods
of calculation, "factors", etc.) and test them.    

It would be useful to hear specifically how Shell Foundation has used the
benchmarks and what their expectations are for the future. 

It would also be useful to hear how Aprovecho interprets the results for
stoves lying above the benchmarks, what changes you would make to bring the
stove into "compliance", and if you did make those changes what were the
results from your testing. While you make broad recommendations in your
attachments to the draft specific cases would help. I'm sure you have plenty
of examples of rockets that have gone off course. 

Regards,       

Tom

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Dean Still
Sent: Monday, January 01, 2007 11:40 PM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Lowering emissions

Dear Tom,

Shell Foundation has been using proposed benchmarks of performance that
Aprovecho devised. The discussion of benchmarks has happened at last year's
ETHOS, at a previous meeting at UCB, and at the meeting in Bonn. I look
forward to discussing benchmarks again at ETHOS. 

There are many ideas being considered concerning how to define an improved
cook stove. No one idea has been proposed as the way to go. I think that
defining an improved stove is an interesting topic that requires lots of
input from everyone. I wasn't at the meeting in Bonn but I don't think that
there was an intention for WHO to adapt a proposal. I think that the
intention was to discuss what a benchmark would look like.

I'll bring up your idea to the ETHOS Board that we form a committee on the
subject and get back to you and I'll talk to Nordica tomorrow and see what
we can put together on the stove testing data.

All Best,

Dean

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Tom Miles
Sent: Monday, January 01, 2007 10:48 PM
To: 'Discussion of biomass cooking stoves'
Cc: grant at ecoharmony.com; ethos at vrac.iastate.edu;
Mitchell.John at epamail.epa.gov; Doroski.Brenda at epamail.epa.gov
Subject: Re: [Stoves] Lowering emissions

Dean,

Thank you for taking the time to summarize and describe the Aprovecho
experiences with stove testing and design. The stoves camp is an excellent
training ground and Aprovecho has clearly been a very productive lab for
stove development. We thank you for all your efforts.

I'm interested in your progress regarding benchmark testing for stove
efficiency and emissions. This is a topic that an ETHOS/PCIA Committee
should take up at upcoming meetings and online. We look forward to seeing
the data that you reported in January 2006 which, as far as I know, has not
been published. Your data and test methods should be reviewed by peers.
(Besides the stoves community there are many individuals and accredited labs
that have been testing similar heating devices for efficiency and emissions
for more than 20 years.) And we should find other labs around the world to
validate your findings. It would be useful to receive your data well before
the ETHOS meeting. 

I understand that some preliminary meetings have taken place but I am not
clear as to what has been proposed and to whom and for what use. GTZ ProBEC
sent me a draft document titled "Performance Benchmarks for Improved
Cookstoves: A Proposal for Adoption" that was authored by Aprovecho, CEIHD,
and sponsored by Shell Foundation, dated October 2006. Apparently this was
presented to select PCIA members in Bonn, October 25, 2006 and intended for
adoption by the WHO. I understand that the "proposal" was rejected with
several comments. 

I have not received any notice through ETHOS or PCIA of a proposal, meeting,
or report of a meeting, to "adopt" the Aprovecho version of the WBT as an
international standard method for establishing efficiency or emissions
benchmarks. I have many comments and concerns of my own regarding the draft
document and would not approve the methods as proposed for establishing
international benchmarks to be used by the WHO. I think it is a great
assembly of concepts and preliminary data and a good first step but there is
clearly much work to do.

So what happens next? 

As ETHOS and PCIA members, and interested members of the stove community, we
look forward to seeing your data and results and to a revised draft proposal
that answers the questions and comments from the Bonn meeting. (Can you
distribute it prior to the ETHOS meeting?) I propose that we form an ETHOS
Committee on Standards and Methods to review the proposed test methods and
benchmarks and to recommend actions to PCIA for our meeting March 20-27 in
New Delhi.

Many thanks,

Tom Miles

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Dean Still
Sent: Monday, January 01, 2007 6:48 PM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Lowering emissions

Dear Tom,

This has been a busy year and I have not done a great job describing in
STOVES what we have experienced here at the Aprovecho lab and in our stove
projects. I've got the day off and it's a quiet night at home so here's my
attempt at an emissions update.

If I remember correctly, Nordica told me a couple of weeks ago that we have
done over 100 Water Boiling Tests this year under the emissions hood. UCB
has refined the WBT a bit this year to include a smaller pot that is used if
the low powered stove cannot bring the 5 liters of water (in the 7 liter
pot) to boil. Nordica does most of the testing these days because she can
get about 10% coefficient of variation between tests so that 3 tests (each
test is: boil from cold start, boil from hot start, simmer for 45 minutes)
are statistically significant. 

Stove Camp was amazing! So many folks built good fan stoves! The mixing of
gases, air and flame created by low volume, high velocity jets of air
reduced CO and PM dramatically. The good fan stoves were something like 9
times cleaner compared to a Rocket stove. Even blowing air (not preheated)
up into the fire from underneath got close to accomplishing the same results
as fancier techniques like preheating air and having air blow both into and
above the fire. A five to ten dollar fan stove powered by the grid is
definitely possible. Burning wood almost as cleanly as a liquid fuel is a
reality. Unfortunately, it is easier to do this in a batch stove but I'm
sure that with a bit more experimentation someone will learn how to do about
the same thing when burning long sticks.

It seems that it is possible to 'scrub' PM by having the flue gases go over
surfaces, by extending dwell time inside the stove. PM is lower from griddle
and other chimney stoves even when the combustion chamber is not optimized. 

IN MY OPINION, lowering emissions is a compromise between making the
channels near the pot small (which decreases wood use and speeds up time to
boil) and increasing air into the fire (which decreases CO and PM). Excess
air is needed to lower emissions.

On the other hand, the 'charcoal making' stove as designed by Ron Larson,
Tom Reed, Dr. Karve reduces air to the fire so that little flame is made.
For some really weird reason that I don't understand, this technique burns
very cleanly producing low levels of CO and PM while creating the end
product of charcoal. This simple approach fascinates me and seems very
promising.

CO rises when charcoal is being made in the fire with lots of air and when
flame above charcoal in this kind of (more active) fire diminishes. But when
flame goes down, PM goes down. It is a balancing act to reduce fuel used, CO
and PM. In a Rocket type stove, the lighter the insulation around the fire,
the better. It takes something like 800C to burn up CO and the better
insulation creates a hotter fire. Also lighter insulation absorbs less heat
which results in faster time to boil and lower fuel used which equals lower
emissions.

It took 10 minutes or so for temperatures to rise to around 800C when we
burned charcoal in a highly insulative Rocket combustion chamber 16" high,
4" in diameter open at the bottom. When temperatures went above 800C or so
the CO2 stayed the same but CO went down close to zero.

The lowest emission stove is a system which includes a pot that is the best
possible heat exchanger. An optimized pot dramatically improves heat
transfer. This pot is big on the bottom and small on the top. The big bottom
has more surface area to absorb heat. The small top exposes the least
necessary surface area of water. Reducing the water surface area reduces
evaporation which is how pots loose the most energy. When the lid is used
very little energy is needed to maintain simmering 3 to 6 degrees below full
boiling temps. Dr. Alan Berick has shown that cooking oil can also be
floated on the water which forms a barrier reducing evaporation to near zero
during simmering if bubbles do not break the oil barrier.

Emissions are lowered by about 1/3 if a pot skirt is used that forces hot
flue gases to scrape against the sides as well as the bottom of the pot in a
very narrow channel. Channel size increases with firepower. The relationship
is shown in our Design Principles booklet.

As mentioned, very little power is needed to simmer if a pot lid is used.
Most wood stoves cannot keep the tiny fire going at this very low level. So
energy is wasted during simmering because the fire is larger than necessary.
I won't steal his thunder but Dr. Alan Berick will display one solution at
ETHOS.

So, the combustion chamber, the pot and the heat delivery techniques to the
pot all contribute to lowered emissions. Efficient heat transfer to the pot
is just as important as combustion efficiency for clean cooking with wood.
(Institutional sized stoves have much lower CO and PM per liter of food
cooked compared to family sized stoves/pots.)

This just about covers what I think that I have seen this year. Of course,
what I've written are just my impressions offered as hypotheses. Happy New
Year to everyone! See some of you at ETHOS!

Best,

Dean

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Tom Miles
Sent: Sunday, December 31, 2006 9:48 AM
To: 'Discussion of biomass cooking stoves'; 'Crispin Pemberton-Pigott'
Cc: 'Marlis Kees'; 'David Hancock'
Subject: Re: [Stoves] Emissions
fromResidentialWoodCombustion:EffectofMoisture on Emissions

Thanks Dean. 

As a general comment we would all benefit if everyone included more detail
about the fuels they burn, species, moisture content, size, etc. As to fuel
species, there are differences in the way that hardwoods, softwoods and
woods of different densities decompose during gasification and combustion
that affect the design and efficiency of the stove. More information will
help us understand a particular local application or test.

Thanks

Tom 

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Dean Still
Sent: Saturday, December 30, 2006 11:40 PM
To: 'Discussion of biomass cooking stoves'; 'Crispin Pemberton-Pigott'
Cc: 'Marlis Kees'; 'David Hancock'
Subject: Re: [Stoves] Emissions from
ResidentialWoodCombustion:EffectofMoisture on Emissions

Dear Tom,

I hope to get the ok from the publisher to have an 'early release' of
results for ETHOS but we'll see. 

All Best,

Dean

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Tom Miles
Sent: Saturday, December 30, 2006 6:26 PM
To: 'Discussion of biomass cooking stoves'; 'Crispin Pemberton-Pigott'
Cc: 'Marlis Kees'; 'David Hancock'
Subject: Re: [Stoves] Emissions from Residential
WoodCombustion:EffectofMoisture on Emissions

Dean,

You presented some charts of the results of those tests in your ETHOS
presentation last year but we haven't seen complete reports with data tables
that show the different stoves, tests, fuels, conditions, etc. Will you be
putting more complete information from your benchmark tests on the Aprovecho
website?

Thanks

Tom   

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Dean Still
Sent: Saturday, December 30, 2006 5:51 PM
To: 'Crispin Pemberton-Pigott'; 'Discussion of biomass cooking stoves'
Cc: 'Marlis Kees'; 'David Hancock'
Subject: Re: [Stoves] Emissions from Residential Wood
Combustion:EffectofMoisture on Emissions

Dear Crispin,

The wood used in the Aprovecho tests is Douglas fir which is a hard
softwood. The UCB WBT accounts for wood type. 

The proposed benchmarks were not based on Rocket stoves. They were based
instead on testing many different types of stoves (more than 30 now) ranging
from the three stone fire to very clean burning stoves. Rocket types are in
the middle range.

Emissions do change depending on the moisture of the wood. So does fuel
used. The University of California at Berkeley revised Water Boiling Test
Excel spreadsheet accounts for moisture content in wood used. The wood we
have used averages around 10% moisture content in the winter. 

As I pointed out yesterday the WBT is designed to minimize confounding
variables to highlight the performance of the stove. The UCB revised
Controlled Cooking Test which follows the WBT uses all local cooks, pots,
fuels, food, techniques. The Kitchen Performance Test is the third test in
this series, a larger survey of stoves in use in kitchens. 

The proposed benchmarks are based on the WBT because Aprovecho has a
'library' of WBT tests (done under an emissions hood). One fine day we hope
to have a similar 'library' of CCT and KPT results (with emissions) from
which to evolve definitions of improved performance. 

All best,

Dean

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: Saturday, December 30, 2006 2:14 PM
To: Stoves
Cc: Marlis Kees; David Hancock
Subject: Re: [Stoves] Emissions from Residential Wood Combustion:
EffectofMoisture on Emissions

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>

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://www.bioenergylists.org