[Stoves] Shields E450c as a way to test char-making stoves (attn: GACC testers)

[Frank Shields]

Dear Jim and All, 


My take on all this is this:

For a test to work we need it to be simple, fool proof and with as few
variables as possible. It needs to be a test procedure that can be repeated
and sent to other labs and all getting close to the same results. All (most)
ASTM, AOAC, EPA, SM etc. procedures are this way. 

Test procedures we know work are: 
1) Moisture (105c), Ash (550c), Organic Matter (550c), grinding a large
sample and using appropriate means reduce it to a representative sample,
TGA, Calorimeter, look-up tables we all agree on.

Test procedures I think we can add to the above (know work) are: 
1) take an oven dry biomass sample > reduce size > obtain representative
sample > load into a pipe one end tight -other loose > heat to above 450c
and then determine percent weight loss. 

Tests that I believe do NOT work are: 
1) take 100 units of fuel and burn in a stove > turn off > and then collect
the weight of left over material. It should be the same in all reps and test
preformed at other labs.
2) Take a sample with a mix (biomass, torrefied wood, char and ash) and
split for reps and among labs > separate each fraction in different piles
with all reps and labs coming up with the same weights.
3) Assign an energy value to each of the separated piles above. Compare each
of the energy values assigned to ones determined using a calorimeter.  They
should be the same.    
We cannot use tests that do not work. 

So what I am attempting to do is put together a method made of test
procedures we know work. 

We know from the work done by Tom Reed that most all volatiles are gone from
the biomass by the time a temperature of 450c is reached. We know that the
secondary is the source of heat for the pot with very little from heat
within the stove body. The secondary goes out and the pot no longer heats.
We know (big?) that’s it’s the oxygen IN the fuel that releases the gasses
and, when that is gone, primary O2 provides heat inside the stove when org-C
goes to CO or CO2. Primary O2 does little to heat the pot but, rather heats
the stove. 

Do I have this right? Are we all in agreement so far? : )

So I suggest we use the easily calculated energy value of the gasses
released before the stove reaches 450c and we call this energy E450c. We use
the pipe procedure to get the two fractions OR we determine using an agreed
upon look-up table of both energy of a specific biomass and the energy of
char (Tom Reed table). Or for the labs evaluating stoves we use calorimeter
and TGA on the fuel used. All tests in the 'Test Procedures We Know Work'
category. 

It doesn't matter if we are testing TLUD or Rocket stoves because they both
have a secondary burner and that uses E450c energy. If the Rocket burns more
char than the TLUD (it will) I still think the results will be mostly the
same because I think the primary O2 just heats the stove body and creates
air flow. The secondary heats the pot on both Rocket and TLUD. But if the
char burning in the Rocket does, in fact, provide more heat to the pot that
will result in the Rocket as a more efficient stove -as well it should. So
the char burning and/or fuel left over is all taken into consideration just
as much as the present method does! The E450c is just a common energy value.


For Ron Larson; We are not now (proposed method) measuring the amount
(weight) of char left over. One needs to gather and weigh. I think a good
TLUD will produce a good consistent quality char. That can easily be
determined if you gather some, get a representative sample into the pipe and
heat to 450c and determine the weight loss. A good char will have little
weight loss where torrefied biomass will have a lot. If there is little
weight loss you can then take the char out of the pipe and heat to 550c in
air you will get the ash. Now you have the carbon value in the char you
produced. Or you can send it to a lab. With the present method you are not
getting what you think you are.  


Also: This statement from Andrew I find interesting and making me wonder
what the role of oxygen IN fuel really is.  
"My understanding is that the pyrolysis is only weakly exothermic between
330 and 450 but the reactions driving this are mostly cracking of pyrolysis
products within the bits of wood. There may be small amounts of free oxygen
from air in interstitial spaces of the wood that will react with nascent
char and produce a small part of this heat but any oxygen already bound to
the wood molecule will not contribute to oxidation overall as it is has
already given up its bond energy." AJH


Thanks

Frank


Frank Shields
Control Laboratories; Inc.
42 Hangar Way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at biocharlab.com
www.controllabs.com








-----Original Message-----
From: Jetter, James [mailto:Jetter.Jim at epa.gov] 
Sent: Thursday, October 17, 2013 1:00 PM
To: Paul Anderson; Discussion of biomass cooking stoves
Cc: Frank Shields; David BERITAULT - Geres Cambodia; KARSTEN BECHTEL CREEC;
Ranyee Chiang; Hugh McLaughlin; Tami bond; Thomas Reed; Thomas Reed - 2013
address
Subject: RE: Shields E450c as a way to test char-making stoves (attn: GACC
testers)

Paul and All,

I would be very interested to hear Dr. Reed's opinion of this idea.

>From the publication Dr. Reed co-authored, entitled An Atlas of Thermal Data
for Biomass and Other Fuels:
http://www.nrel.gov/docs/legosti/old/7965.pdf
"Thermal analysis data is useful both for researchers and practicing
engineers.  For researchers the thermal analysis data provide the
information for the identification of different reaction mechanism,
determination of kinetic parameters and optimization of conditions to favor
one reaction over the other.  The specific temperatures at which various
heterogeneous reactions occur, their reaction rates and the energies
involved in these reactions are invaluable information for engineers
involved in system design."

Thermal analysis of fuels is valuable for basic research and for
understanding system design, but it seems to me that it would have limited
value as an alternative method for efficiency testing. If all the biomass
fuel in a stove is completely pyrolyzed at (or near) 450C, then I think the
proposed idea may work, but what if a portion of the fuel is not completely
pyrolyzed or is pyrolyzed at a different temperature?  What if a portion of
the char is combusted? We have seen variation in the energy content and
composition of remaining char.

Jim


From: Paul Anderson [mailto:psanders at ilstu.edu]
Sent: Monday, October 07, 2013 1:13 AM
To: Discussion of biomass cooking stoves
Cc: Frank Shields; Jetter, James; David BERITAULT - Geres Cambodia; KARSTEN
BECHTEL CREEC; Ranyee Chiang; Hugh McLaughlin; Tami bond; Thomas Reed;
Thomas Reed - 2013 address
Subject: Shields E450c as a way to test char-making stoves (attn: GACC
testers)

Stovers, especially the ones concerned about HOW to test char-making (and
batch loaded) stoves.

[[ The attachment is exactly the same content as this email message, but in
.docx format for ease of making editing comments if needed, or for
forwarding.]]

Frank Shields has proposed an alternative method for efficiency testing of
stoves that make charcoal (including the batch loaded ones.)     His
comments were made in 3 or 4 messages on the Stoves Listserv starting on 3
October 2013 under the subject of:         Re: [Stoves] Efficiencies for the
rich and poor.

Below I have snipped the key parts and put them into chronological order so
that you can see the development of Frank's thoughts.   And I give a quick
summary here of what I call the Shields E450c method (proposed):

1.  Char-making stoves (including the TLUDs) do their cooking (or provide
data for efficiency testing) with the energy from combustion of the
pyrolytic gases produced inside the stove from raw biomass.   Factors of
moisture content (MC) need to be taken into account (as is already required
in the other testing of cookstoves, eg standard WBT).

2.  The temperature of 450 deg C is measured and established as solid base
temperature for the completion of the most of the making of pyrolytic
gases.  Actually, between 400 C and 550 C there is not a great deal of
variation, and that variation could be entered into the calculations IF that
variation is considered to be significant and IF the stoves reach that or
higher temperatures for sufficient and extended time in the pyrolytic
process.  

[We note that in current discussions about revisions to the WBT regarding
char-making stoves, there is NOT a discussion (that I know of) of whether
the chars taken out and weighed were created at 400 or 500 or 600 C or
whatever temperatures.  If the temperature is not crucial for that version
of testing, the temperature of char creation is probably not too critical as
long as it is in the 450 degree range or above.   This could be discussed by
the experts IF the Shields method gains interest.]

3.  Therefore, in a stove efficiency test where there is reasonable
consistency in the yield of charcoal on a weight basis from a known biomass,
it is possible to determine the "Energy of the combusted pyrolytic gases
created when temperatures were about 450 C or above".   Frank calls this   
E450c    .   And this is the energy that is available to do the "work" of
cooking.   Some goes into the pot, and some is lost, yielding an efficiency
percentage.   When you know the starting weight of a particular fuel (with
known MC), and you will know the potential E450c energy available.   It is
directly related to the already carefully determined energy content of so
many types of biomass.    And that pyrolytic fraction (the E450c energy) has
been released when the pyrolytic process ends (very clearly seen in these
char-making stoves) and noted as number of minutes.   If you note the time
that the boiling temperature is reached, divide that by the total time and
you have the percentage of E450c energy that was expended to attain the
boil.

4.  There is no attempt to assign a value (of energy or monetary or social
or climatic impact) to the produced char.  

To Frank I say "Thank you!!".   Now the measurement experts can read below
the original messages and offer their comments.

Note:  Frank and I and Ron Larson and Hugh McLaughlin and Thomas Reed and
several others with interests in char-making stoves will be together on 13
to 17 October (a week from now) at the North American Biochar Symposium at
Amherst University in Massachusetts.  The Shields E450c approach to
measuring efficiencies might be a topic for side discussions there.  But the
real debate is within the IWA technical committees.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD  
Email:  psanders at ilstu.edu   
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com


On Oct 3, 2013, at 3:54 PM, Frank Shields <frank at compostlab.com> wrote:


Greetings Stovers,
 
Tom
 Reed coauthored a book tilted An Atlas of Thermal Data (link below) that
explains the results of Thermogravimetric data on a wide variety of  biomass
under different conditions. The results show a rapid decrease in weight that
then stabilizes around the 400c and mostly completed at 450c. Using
Thermogravimetric analysis (TGA) on biomass can separate the  fuel into two
distinct and repeatable fractions. The one fraction between ambient
temperature to 450c we know will be used during cooking as once this
restively low temperature is reached it has volatilized. It  needs no oxygen
from outside and gets it all from the fuel to form a gas then secondary air
to completely combust.  The fraction of fuel left  above 450c contains
energy that may be used or left after cooking. To compare efficiencies of
stoves it seems to me we just need to use the energy of the biomass fraction
we know will be used and use that value as the energy provided. If a stove
is designed to use some char as added  energy all the better for that stove.
We do not need to determine the char left in the stove. We need to decide to
use HHV or LHV but since we  are not testing for hydrogen and just using an
agreed upon value it doesn't matter - as I see it.

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Ronal W. Larson
Sent: Thursday, October 03, 2013 8:57 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Efficiencies for the rich and poor.
 
Frank:
 
   The folks working with char-making stoves are not going to understand
this sentence at all:     'We do not need to determine the char left in the
stove. '
 
    That
 is as simple a measurement as you can find.   Granted that most of the
weight loss is before 450 C,  the weight is NOT constant as you keep going
higher in temperature   You will have a fair shot at the temperature
achieved by measuring the weights in and out.  But temp is not the only
variable, there is also the time at temperature, the size of the fuel etc.
 See material in the Gaur-Reed Chapter 8.
 
[Anderson interjects:  I recognize Ron's concerns, but I believe that the
impacts will be minor compared to the overall accuracy of the measurements.
 
  Ron continues:   I know people are trying hard to determine the peak
pyrolysis 
temperature from the characteristics of the char - besides weight
differences, there is density, water-adsorbing properties, pH, and
electrical conductivity in the "simple" (poor man) category.  Some big
changes in conductivity can occur above a certain temp.   Many people would
like to know the CEC characteristics, but I know nothing on that
measurement.
 
 
  I guess I am saying that the stove itself might serve as the "pipe" 
you are describing [FOR USE IN LABORATORY MEASUREMENTS OF ENERGY IN
BIOMASS].  If you have a good guess at the temperature of the produced char,
you have a reasonable estimate of its remaining energy content, which is
what I guess you are after.   I don't have much hope that any test with a
"pipe" is going to tell you much about a particular  stove.  [ANDERSON:  But
it will tell you about the particular fuel and be totally independent of the
stove type or trying to boil water in the test.]

On 10/4/2013 12:45 PM, Frank Shields wrote:

*This I think important*
I'm thinking when we test stoves we should start with knowing the weight of
a pile of biomass. Then test and determine the total energy450c (E450c) dry
weight of the pile. Weigh the remaining pile after each test to determine
the amount of E450c used for the task(s). Using this volatile fraction as
the measured energy input (not total energy of the fuel) we can then
determine the amount of E450c it took to cook a pot of rice without the need
to subtract the energy in the char left over. Once the biomass pile has been
used up, the sum of the E450c used should add up to the total [E450c] in the
starting biomass. The char left over for the garden has no E450c so there is
nothing to subtract from the total E450c value of the starting biomass. But
if you want to know how much E450c was required to produce it, just add up
all the E450c used for the completed tasks that left the char behind. All we
need to do is make sure the stove it [is] at or above 450c when the task is
completed so to make sure all E450c in the fuel has been used. So simple...
 (I think!).
 
Thanks
 
Frank
 

Frank wrote in his next message:

There are two purposes to do a lot of testing to measure many things
including efficiency:
1. Is to learn about stoves, how they work, what chemistry is taking place,
where, why and for how long so improvements can be made. 
2. The sole purpose of comparing one stove to another. Money and sales are
at stake. Must be done right, cheap, with few variables.
 
It seems EPA and past procedures are doing all the testing for purpose one
as much as purpose two. I am just concentrating on purpose two. A stove has
many factors that increase (or decrease) efficiency. Using the E450c
fraction as a measure we have things like; insulation, size of pot, pot gap,
secondary air AND ability of the stove to use some char to help aid in the
task. If that happens it shows up in better efficiency. We center around the
E450c energy value and do things that improve on it. 
 
I think purpose one is many different separate studies so to control the
variables. And certainly should not be muddying the testing of efficiency
when $$ and reputations are involved.  
 
Regards
 
Frank
 
 
Frank Shields
Control Laboratories; Inc.
42 Hangar Way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at biocharlab.com
www.controllabs.com
  
[Frank >] The only thing that matters is us all being able to come up with
the same number. If we all have a TGA and its calibrated we should be able
to send a sample to a bunch of labs and they all report back the same number
for E450c. It's this value we give to the fuel.  If during the testing we
use larger fuels pieces that take longer for them to reach 450c in the field
it doesn't matter. We go as long as the secondary flame is still there
because when that goes out nothing happens no matter how much un-burned fuel
is left. That just means the stove is designed for smaller pieces or
different biomass or a re-design needed to handle the larger pieces. The
efficiency goes down because of that. It's the same as if the stove needs
better insulation or a change in the gap.  
   
In most situations char is of secondary concern with the first being what
the task of the secondary flame is being used for. If your main concern is
char and its quality, that is a different task. You want to know the
efficiency of making the best quality char. Meaning the E450c used from the
pile (weight) to produce good quality char. So you determine the E450c used
for different configurations and compare the different chars produced for
quality. Then determine the E450c needed to produce that best char (task). 
 
Regards
 
Frank