<div dir="ltr"><div><div><div><div>Crispin,<br><br></div>We have measured the temperature of the syngas as it exits the reactor, and as the reaction proceeds from top to bottom in a TLUD, the temperature of the gas right before combustion drops significantly. Of course one could insulate the reactor, but this would put a lot of stress on the metal used to construct the reactor. I think therefore that it is safe to conclude that a lot of the heat generated as char is combusted would also be lost through the wall of the reactor. Also when char is consumed, the temperature within the reactor rises to dangerously high levels. The bottom of the reactor turns red hot, and at this high heat, metal quickly degrades. <br>
<br>Suppose that the reactor is not insulated and that char begins to burn 50 cm below the pot. It is hard to imagine anything more inefficient than this.<br><br></div><div>One of the reasons that I moved in the direction of reducing the height of the reactor was to minimize heat loss. As the reaction proceeds from top to bottom, the temperature of the syngas drops by as much as 250 C. At this lower temperature, the syngas does not combust in the same manner as at the higher temperatures. The flame is not as rich, it becomes more ethereal, and the speed at which water boils is impacted.<br>
<br></div><div>So I tried to reduce the height of the reactor as much as I could, while still maintaining a burn time on loose biomass of at least 40 minutes. This led me to choose a reactor height of 50 cm for loose biomass such as rice hulls and coffee husks. But when I switched to pellets, I discovered that I could have a net reactor height of only eight inches with a burn time as long as 1.5 hours. <br>
<a href="https://dl.dropboxusercontent.com/u/22013094/150%20Gasifier/Short/Photos/IMG_1568.JPG">https://dl.dropboxusercontent.com/u/22013094/150%20Gasifier/Short/Photos/IMG_1568.JPG</a><br>This gives a very hot gas throughout the burn, and the reaction zone itself is much closer to the pot. But for normal cooking over a period of about 40 minutes, the net reactor height could be reduced even further to about four inches.<br>
<br></div><div>With pellets we can design TLUDs that are lightweight and compact. But one thing that I have learned in this regard. Do not try to burn the biochar pellets when the burn comes to an end. The heat generated here is absolutely horrendous. These are temperatures at which a blacksmith works.<br>
</div><br></div>Thanks.<br></div>Paul<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Jul 19, 2013 at 8:23 PM, Crispin Pemberton-Pigott <span dir="ltr"><<a href="mailto:crispinpigott@gmail.com" target="_blank">crispinpigott@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Julien<br>
<br>
I think it is a mistake (or a poor assumption) to assume that a 'small char<br>
fire' is a) at the bottom, b) is not an effective heat source and c)<br>
represents a loss of some kind.<br>
<br>
The distance between a heat source and a pot is not as indicative of<br>
anything significant.<br>
<br>
My rule is: Never Assume Anything.<br>
<br>
Calculate first, then observe, as appropriate.<br>
<br>
The simmering that is sometimes done in a cooking event is often well<br>
supplied with heat with a low power char fire at the end.<br>
<br>
Convective heat transfer can be very efficient. Basically the argument that<br>
distance matters is an assumption that most heat transfer from burning char<br>
is from radiant. This is nearly never true in a real fire. If the convective<br>
heat transfer is done with a low excess air level, it can be very good.<br>
<br>
Regards<br>
<span class="HOEnZb"><font color="#888888">Crispin<br>
</font></span><div class="HOEnZb"><div class="h5"><br>
<br>
-----Original Message-----<br>
From: Stoves [mailto:<a href="mailto:stoves-bounces@lists.bioenergylists.org">stoves-bounces@lists.bioenergylists.org</a>] On Behalf Of<br>
Julien Winter<br>
Sent: Friday, July 19, 2013 9:08 PM<br>
To: Discussion of biomass cooking stoves<br>
Subject: [Stoves] Comparing the fate of fuel energy between stoves -- a<br>
simple table?<br>
<br>
Hello Stovers;<br>
<br>
I am in Dhaka, Bangladesh, and I am going into a meeting in a couple of days<br>
to talk about biochar production through cookstoves. I have already been<br>
asked a question about whether biochar-making is a cost (in fuel) that<br>
stove-user may not want to make. For example, "why not burn the fuel to ash<br>
and not save the biochar?" ... to which I reply that for a ND-TLUD, 70% of<br>
the fuel energy was in the gas fire, and the carbon fire is a long way from<br>
the pot, and a TLUD is a great deal more efficient that a traditional stove,<br>
and who would want a high temperature carbon fire at the bottom of one's<br>
cherished stove anyway.<br>
<br>
I realize that there are some huge ceteris paribus assumptions to be made<br>
about standard conditions for comparing different stove types and fuels, but<br>
can anybody have a crack at filling in this "simple" table?<br>
I just want some ballpark figures to help justify biocharmakery.<br>
<br>
FATE OF THE ENERGY CONTAINED IN A WOOD FUEL<br>
<br>
STOVE_TYPE COOKING BIOCHAR LOST<br>
============================================<br>
----------------------- (%)<br>
-----------------------------<br>
1) ND-TLUD<br>
2) 3-stone<br>
3) Anila<br>
4) Chula<br>
5) etc.<br>
<br>
I have just put in some stove names as examples. The value for %energy in<br>
biochar is zero for many stoves, so many comparisons amounts to a comparison<br>
of stove efficiencies.<br>
<br>
As must be the case for many less well off countries, the most ecologically<br>
sound method of making biochar in Bangladesh will be through their<br>
cookstoves, and the biggest, most immediate impact of biochar on people's<br>
lives will be to improve the fertility of homestead gardens. That is easy<br>
to say; it will be a lot harder to do.<br>
<br>
Thanks,<br>
Julien.<br>
<br>
--<br>
Julien Winter<br>
Cobourg, ON, CANADA<br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Paul A. Olivier PhD<br>26/5 Phu Dong Thien Vuong<br>Dalat<br>Vietnam<br>
<br>Louisiana telephone: 1-337-447-4124 (rings Vietnam)<br>Mobile: 090-694-1573 (in Vietnam)<br>Skype address: Xpolivier<br><a href="http://www.esrla.com/" target="_blank">http://www.esrla.com/</a>
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