[Stoves] Smokeless transition

[Marquitusus]

Paul, Crispin, Kirk and all,
First I wanted to say THANKYOU very much for sharing so much knowledge. I feel like I have done a complete degree in TLUD science in just a few emails! The day after reading your firsts answers to my question, I achieved a smokeless transition. That is the power of this discussion group!
I achieved that just increasing the chimney height (about 175% of the reactor's height) and, following Crispin's notes: opening more secondary air holes below the surface of the fuel bed. I suppose this creates a some type of "pilot flame", as say Kirk, keeping high temperatures in the charcoal's surface, and thus, maintaining the flame in the transition phase.I still don't know if this result is enough reliable and replicable, as I used the fuel itself as the main element of the control of the air flow (Crispin said) and the used fuel (almond husks) is far from being homogenic and predictable (particle size varies from 5mm to 5cm)
Note to Kirk : it didn't work for me the "basket method" proposed by Julien. Maybe it can work for others fuels and other drafts, as I only tried it once with a shorter chimney (about 100% of the reactor's height)
About the burning/not burning the charcoal discussion, my position is clear: it depends of what we want/need in each case.What I want in this case is:  to heat an light-mass earth oven, with mininum attend to the fire, fast temperature gain at the begining, keeping constant temperature at about 200ºC, and maximum time of use (and, of course, smokeless and clean!). In this very specific case, I choose to burn the charcoal, as I gain about 50% more time to cook and don't worry about refuelling the reactor.
Some bad smellsAlthough no visible smoke was produced in the process, it did some bad smell. This smell is not present when I burn other fuels (pellets, wood chips,...) only with almond husks, so I suppose it's related to chemical specific composition of this fuel. Anyway, I think the answer should be improving the combustion of the gases. In this way, I'm experimenting with Kirk's Wonderwerk combustor design, with the metal tube inserted in the combustor giving secondary air. I'll post the results.
Last smoke to removeAt the very end of the process, when the char has been already pirolised and very little lefts, I had smoke. It was a different smoke, very light and odorless, and lasts about 2 minutes. I suspect it is the last remains of CO gases, which are not enough to mantain the flame. Maybe the solution is to open a third layer of secondary air entrance very near to the bottom, as Crispin suggested?
Thanks to all!
Marc
From: crispinpigott at outlook.com
To: stoves at lists.bioenergylists.org
Date: Fri, 12 Dec 2014 17:16:57 -0500
Subject: Re: [Stoves] Smokeless transition

Dear Paul Yes, and I tried to explain it in a way that agrees with your analysis. If making char for combustion, you would want to have a low formation temperature to leave some volatiles (otherwise it is hard to ignite and you have to light more at a time). If you want biochar it should have a relatively high final temperature to create the surface area. If you want to burn it then burn as much as possible during gasification which makes the transition to burning charcoal gas much easier/less of a system adjustment. I hope you noted the comment about running the primary into the side of the fuel near the bottom, not through the bottom plate. This reduces damage to the metal by pushing the heat into the fuel instead of the metal. As the fuel burns away fuel drops from above. When the holes are small it gives the heat getting into the metal a chance to move through creating preheated air. RegardsCrispin   Crispin,

For anyone wanting to burn the char in the device, your explanation  is fine and is much appreciated.

The biggest difference in our positions is that I and some others do NOT want to burn the char.   Reasons can include wanting it for biochar, or to burn it in a different device later, or to protect the fuel container for the high heat of char-gasification, or for some reason of simplified design such as using less expensive materials of controls, and probably a few more reasons.

For centuries, one objective of scientifically designed combustion devices was to obtain the maximum of energy possible, and that meant to leave the minimum of carbon behind in with the ashes.   But as you pointed out, things have been changing.  

I got started in 2001 with what has become known as TLUDs by Tom Reed.   Clean combustion was the feature.   The TLUD stoves happened to make charcoal.   It was a "by-product" that became a "co-product" that for some is the "main-product".    

Paul

 
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