Dear Ron
----- Original Message -----
From: [email protected]
To: Discussion of biomass cooking stoves ; biochar-policy
Cc: Alex English ; Kevin Chisholm ; Tom Miles
Sent: Tuesday, December 11, 2012 2:09 AM
Subject: Re: [Stoves] Equipment required for testing stoves
Lists (adding biochar-policy also), Kevin, Alex, Tom (who I add, because he
speaks Portuguese and might have caught an answer when we were in Manaus a few
years ago)
See below
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From: "Kevin" <[email protected]>
To: "Discussion of biomass cooking stoves" <[email protected]>,
"Alex English" <[email protected]>
Cc: "Discussion of biomass cooking stoves" <[email protected]>
Sent: Monday, December 10, 2012 8:24:34 PM
Subject: Re: [Stoves] Equipment required for testing stoves
Dear Ron
Would you agree that the Amazonians made Terra Preta with low temperature
char?
[RWL1: I think others may have an answer - maybe based on spectroscopy.
I will start looking but don't know that field well enough to know what others
may have concluded about these ancient soils. I fear that 500 years (minimum)
in soil may hide the initial character that we can readily see in a University
setting. I know from being in several Amazonian biochar "pits" that it is
pretty hard to find a piece big enough to test. I think it entirely possible
that char left over from simple three-stone fires could have been made at
500-600 C (or higher). Would you call those temperatures high or low?]
# KC1: Obviously, I am speculating, but I would speculate that Terra Preta
was made with charcoal from a number of sources:
1: Char residue remaining after charring or burning of "wood waste from
initial jungle clearing.
2: Char residue remaining from charring or burning of agricultural waste and
weeds
3: Char and ash residue from cooking fires and possibly smudge pots
4: Organic fertilizer supplements, from humanure, composted food scraps, and
probably dredgings from oxbow lakes.
I would consider 500-600 C to be a "low temperature char." I haven't seen any
references to the existence of bellows technology in ancient Amazonia, that
would be necessary to produce significantly higher temperatures.
It is likely that the Amazonian Terrapretians would have quickly noticed if
such low temperature char additions to their agricultural practises were
causing poor results. If that was the case, they likely would have taken steps
to avoid application of char to fields. They would be looking for short term
benefits or harm. Given that they used char on a widespread basis, and that it
was basically low temperature char, it would thus seem that Terra Preta worked
with low temperature char, and it worked relatively quickly, not requiring an
aging period of several years.
If so, are there any test results to show that an "intermediate temperature
char" would give better results than the "low temperature char?"
[RWL2: I think that people like Dr. Johannes Lehmann and Evelyn Krull
may be getting to an answer for some specific soil and species. I keep looking
for it.
My note below to Alex was to make it easier for users to know what is
being used Some of my favorite biochar scientists like Drs. Julie Major and
Christoph Steiner were forced to use char bought off the side of a remote
Amazonian road.
I haven't seen any data emphasizing tests with a range of
temperatures. Drs. Stephen Joseph (low) and Hugh McLaughlin (high) recommend
different temperature regimes.]
#KC2: Is it perhaps likely that "basic low temperature biochar" is good for
general agricultural applications, but that intermediate and high temperature
chars may be better for addressing special agricultural problems.
I seem to recall that "high temperature char" and/or "activated char" gives
inferior results in a biochar application.
[RWL3: How about giving a cite for that?]
#KC3: Unfortunately, I cannot point to a specific cite.
Does this impression make sense to you?
[RWL4: No - certainly not as a universal truth/]
#KC4: Universal truths are scarce and hard to find. :-) If you put yourself
in the circumstances of an Amazonian Terrapretian of 3,000 years ago, what
would you do differently?
If so, is there a "preferred char making temperature range"?
[RWL5: I am sure that it depends a lot on the intended recipient soil -
and probably on the plant species. #KC5:1 Certainly! Jungle woods can vary in
density from balsa at about 10 lb/cubic foot, to Lignum Vitae, at about 68
pounds per cubic foot.
My focus in this exchange below with Alex is to give soil researchers and
stove users a better idea of even getting close to knowing what char-T they are
using.
#KC5:2 Char making temperature is easy to determine. It should thus be very
easy to determine the importance, or lack thereof, of char making temperature.
It would be very good to know this, to reduce variables in a test analysis.
There is a good bit of information out there relating pH to production
temperature - but pH also depends on fuel size and ash content and pH changes
over time. Who knows what else leads to a "preference"?
And we also hear from Dr. Spokas that what happens after char
production is maybe as much or more important. I think it is absolutely
amazing that we hear so many good reports (and few bad reports) when we know so
little even about the char-production temperature - and even the wood species,
etc, etc, etc. Ron]
#KC: With that many "good reports" and so few "bad reports", and with so many
char variables, this would tend to downplay the importance of char variables.
The "bad reports", presuming that they were competently done, could provide
very important insights into what works, and what doesn't.
Best wishes,
Kevin
Best wishes,
Kevin
----- Original Message -----
From: [email protected]
To: Alex English
Cc: Discussion of biomass cooking stoves
Sent: Monday, December 10, 2012 9:46 PM
Subject: Re: [Stoves] Equipment required for testing stoves
Alex:
Thanks:
I see only a few remaining questions related to the thermocouples. My
interest is only in being able to report to the soil scientists the temperature
at which the char was produced.
Q1. I think we should be able to say that a time average of a central
thermocouple measurement showing a slight drop over time of the highest numbers
is a pretty good estimate - that could be reproduced for "any" similar "flaming
pyrolysis" approacd. The properties (pH, surface areas, labile component, etc)
of such char should be compared (a Master's thesis?) with char produced via
other means. I think Nat Mulcahy's non-flaming pyrolysis approach can produce
varying temperature char. An all-electric heating approach in any oxygen-free
environment , operated at different temperature should also be used to compare
the char properties with those from stoves. Maybe that data is already out
there??
Q2. I think there could be some influence of the initial fuel moisture
content. Do you (anyone) have an opinion on that? I am trying to avoid
having to always measure temperatures, but still be able to give an indication
of the "likely" char temperature, by knowing how long a specific volume or
weight of fuel lasted.
Q3. I wonder if the char temperature as measured by a thermocouple
system like yours would also be a function of the fuel itself (species,
characteristic size, shape, etc.)
Q4. I am pretty sure that the top and bottom char will be significantly
different in a typical cooking cycle, where a very high flame temperature is
desired at first (affecting only the top part of the fuel load), and then a
much lower temperature desired later (affecting only the lowest portion of the
fuel load). My question, for anyone, is whether an average temperature is at
all valuable, if the average (obtained from the total duration of the
pyrolysis) covered a wide range of production temperatures. Actually I have
heard so many different opinions on the best production temperature - maybe a
mixture of char temperatures might be an advantage. Thoughts?
Ron
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From: "Alex English" <[email protected]>
To: [email protected], "Discussion of biomass cooking stoves"
<[email protected]>
Sent: Monday, December 10, 2012 4:38:56 AM
Subject: Re: [Stoves] Equipment required for testing stoves
Ron,
On 09/12/2012 8:33 PM, [email protected] wrote:
Alex etal
Thanks for the cite. I think I understand most of the plot - which was
of amazing duration!. I am especially amazed at how uniform (and high) the
flame temperature was in the late time plot, even as the other plots were
dropping.
It is a very steady gas producer. Conditions are constant except for the
distance and path composition between the pyrolysis front and the burner. If it
can be done over 100cm then why not 200 or 300.
a. Since you have this one from 2000, you probably have quite a
few more - from which I/we might extract a good bit more information/ Any
other similar plots around that you can post?
No I don't.
b. I am surprised that the "pyrolysis gas temperature" was so much
lower than the temperature of the char. Where was the probe for this
measurement - and had there been some mixing of secondary air at this point?
No mixing of secondary air at that point. That occurs in and above in a 5cm
burner mixing pipe. The tmperature difference is largely due to the nature of
unshielded thermocouples in gas.For the most part thermocouples radiate away
heat according to the temperatures of the surfaces that make up the sphere
around them. A thermocouple buried in the pellets that are all carbonizing at
700C will give a fairly accurate measurement. A thermocouple in the gas above
the top of the pellet bed will radiate to the pellet bed and, in this case the
uninsulated container walls. The more that pellet bed shrinks the larger the
portion of the radiant sphere that is the cool container walls. The larger the
thermocouple, the greater the radiant cooling , the lower the measurement. The
higher the temperature the greater the radiant loss, to the forth power. All
the gas is also radiating and convecting heat to the container walls. So there
are two reasons for a slow drop in gas temperature, and one reason for not
trusting either. The same holds true for the absolute value of post combustion
measurement.
There are gas-aspirated pyrometers which shield a thermocouple with ceramic
layers that approach gas temperatures and give better numbers. We will soon be
using an 10 footer to probe the chain grate stoker gasses in carbonizer-
pyrolysis-gasifier mode.
Grate fun.
c. What is the present disposition of this equipment?
Its in the recoverable bone yard. I should have shown it to Crispin when he
was here.....or perhaps not:)
Alex
Nice work
Ron
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