Frank and all,
I have snipped away the earlier messages.
See my comments imbedded below:
On 10/20/2013 2:29 PM, Frank Shields wrote:
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? : )
I am in agreement thus far except for one issue of wording. Please
separate the "combustor" and the "reactor" in the discussions of the
gasifiers such as the TLUDs. Frank wrote:
Primary O2 does little to heat the pot but, rather heats
the stove.
Actually, the last word should be "reactor" or the place where the
pyrolytic gases are being formed.
With that distinction in mind, I then point out the Rocket stoves do NOT
have a separately distinct reactor location. Instead, both pyrolysis and
SOME reasonably considerable combustion occur in the same place amidst
the fuel pieces. And that includes some combustion (oxidation, which is
also char-gasification) of the char, resulting in the loss of char (and
leaving ash behind). This can greatly complicate the use of the concept
of Shields E450c for making calculations. In other words, I think that
the E450c concept should be first developed and understood in the
context of the gasifiers, WITHOUT complications of discussing Rocket
stoves and other standard combustion devices. (see my comments in the
second paragraph below.)
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.
This part about "I think" should not be entered into the discussion. In
Rocket stoves, the primary and secondary air are so intermixed (in such
widely different proportions from one Rocket stove to another and even
dependent upon using thick pieces of fuel verses many small pieces) that
quantification is not likely to be trustworthy.
Therefore, I also disagree with the rest of Frank's paragraph below
because although E450c is a common energy value, it is obscured by the
entry of secondary air down low with the primary air. The same criticism
would be applied IF a TLUD or other gasifier were to be used with so
much air that a meaningful part of the pyrolytic gases would be consumed
even low down in the bed of char (meaning that it was actually
functioning as secondary air).
As I see it, the INITIAL value and purpose of the Shields E450c proposal
should be developed and (hopefully) accepted FOR GASIFIER SITUATION
BASED ON MINIMAL AMOUNTS OF PRIMARY AIR. Maybe later there can be
applications concerning Rockets and other stoves. But first we need to
understand (and accept if correct) how E450c can help us test batch-fed
gasifier stoves.
Paul
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
[email protected]
www.controllabs.com
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: [email protected]
Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
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