[Stoves] Efficiencies for the rich and poor.

Fri Oct 4 12:45:43 CDT 2013

Greetings Ron, Stovers,

When a stove is used to do a variety of things like: cook, heat a home and
make char for the garden we need just to make a larger circle around the
stove to include the bundle of biomass stock piled in the corner of the home
as the reference. When a forest is being removed at too fast a rate we need
to extend the circle to the outside of the village. Back to the home; we use
the pile of biomass to do lots of things so we keep track of how fast we are
using up the pile. It's not calculating the energy to cook the food AND how
we are going to account for the char left over we put on the garden or how
to account for heating the home when we are through with dinner. We can only
account for all these uses by enlarging the circle and monitoring the bundle
of biomass in the corner. 

*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 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 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 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

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.

   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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