[Stoves] Equipment required for testing stoves

Tue Dec 11 00:09:21 CST 2012

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 
----- Original Message -----
From: "Kevin" <kchisholm at ca.inter.net> 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>, "Alex English" <english at kingston.net> 
Cc: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
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 ot hers may have concluded about t hese ancient soils . I fear that 500 years (minimum) in soil may hide the initial character that we can readily se e in a University setting . I know from being i n 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) . W o uld you call th ose temperatures high or low?] 

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 t o 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 us e char bought off the side of a remo t e Amazonian road. 
I h aven't seen any data emphasizing tests with a range of temperatures. Drs . Stephen Joseph (low) and Hugh McLaughlin (high) recommend differ ent temperature regimes.] 

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 ?] 

Does this impression make sense to you? 
[RWL4: No - certainly not as a universal truth/] 

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. 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. 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 repors) when we know so little even about the char-production tempera ture - and even the wood species, etc, etc, etc. Ron ] 

Best wishes, 

Kevin 

----- Original Message ----- 
From: rongretlarson at comcast.net 
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 

----- Original Message -----
From: "Alex English" <english at kingston.net> 
To: rongretlarson at comcast.net, "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
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, rongretlarson at comcast.net wrote: 

<blockquote>

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. 

<blockquote>

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? 

</blockquote>
No I don't. 

<blockquote>

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? 

</blockquote>
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. 

<blockquote>

c. What is the present disposition of this equipment? 

</blockquote>
Its in the recoverable bone yard. I should have shown it to Crispin when he was here.....or perhaps not:) 

Alex 

<blockquote>

Nice work 

Ron 

</blockquote>

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</blockquote>

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