[Stoves] Efficiencies for the rich and poor.

Frank Shields frank at compostlab.com
Fri Oct 4 18:23:34 MDT 2013


Ron, and stovers,

 

<snip>

 

[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

 

 

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

 

 

 

 

 

    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.

 

   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.  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.

 

   But mainly, I urge you to keep measuring the weight of the char.  You
will not understand much about a char-making stove if you don't know the
weight of the produced char.

 

Ron

 

 

   

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.

 

The Rich Man:

Needs a (1) calorimeter to determine the total energy HHV of the fuel and
then used to determine the energy of the char left (remaining in the TGA).
The energy in the fraction volatilized below 450c. is then calculated. Rich
people need a (2) TGA to get an accurate value of the weight fraction
containing the energy used from the dry biomass. Very accurately heat to
450c in nitrogen then cool and char removed for calorimeter.

 

The Poor Man:

Needs a (1) look-up table of the total energy of the fuel and a (2) pipe of
fuel to heat up to determine the weight of fraction in the char left. The
energy of the char is looked up in the look up table to be able to determine
the energy fraction of the fuel that is used in the stove comparison. Notice
in Tom Reeds book that after 400c the weight stabilizes so as long as the
pipe is heated to 450c or higher there will be little error. Error relative
to other methods suggested and everyone can do the tests. Except for those
where a look-up table will not work like Richard's briquettes or where mixed
biomass is used will need the more expensive equipment. .

 

 <http://www.nrel.gov/docs/legosti/old/7965.pdf>
www.nrel.gov/docs/legosti/old/7965.pdf

 

 

 <http://www.tainstruments.com/product.aspx?siteid=11&id=11&n=1>
www.tainstruments.com/product.aspx?siteid=11&id=11&n=1

 

Understanding the complete process of a stove and all the reactions taken
place is well worth studying and should continue. But for the sake of
comparing stoves we need a foolproof procedure - it seems to me.

 

Thanks

 

Frank

 

 

 

 

Frank Shields

Control Laboratories; Inc.

42 Hangar Way

Watsonville, CA  95076

(831) 724-5422 tel

(831) 724-3188 fax

 <mailto:frank at biocharlab.com> frank at biocharlab.com

 <http://www.controllabs.com> www.controllabs.com

 

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