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" <[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. <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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