[Stoves] World stove, fantasy draft, flame caps, TLOD, TFOD, DS

[Kirk H.]

Kelpie,

It is festinating the parallels you draw between these down-draft stoves and flame cap kilns.  This is a whole new way to look at how they work.

You brought up the flows from volatilization and oxidation.  The emerging gasses will flow upward as well as downward as you describe.  But there is also gas flowing down from above, so for this hypothesis there must be circulation patterns, as described by Crispin.  All of this is as Dr. Anderson describes as too many speculations.  I think this discussion has defined some questions which may lead to real science and answers.

Thank you for you contributions, the slide show, and expanding my thoughts,

Kirk H.

Sent from Mail for Windows 10

From: Kelpie Wilson
Sent: Sunday, April 1, 2018 5:01 PM
To: stoves at lists.bioenergylists.org
Subject: [Stoves] World stove, fantasy draft, flame caps, TLOD, TFOD, DS

Hi friends,
sorry but I get the email digest and cannot figure out how to reply to a subject thread, so I'll just start a new one.

This is so interesting! I just got back from a workshop tour of Nebraska and Kansas, teaching flame cap pyrolysis for making biochar from invasive eastern red cedar. This use of waste biomass for biochar has been my focus in recent years, rather than stoves or TLUDs. 

So many times, I have seen flames from these kilns flowing upward and then turning back down. The flame tips have a downward hook at the top as something sucks the the air back down. These are Down Suckers, thank you Paul for that term!

You can see a nice example of this pictured in my slides here: 
https://www.slideshare.net/kelpiew/flame-carbonizers-for-biochar-in-practice-and-theory

Of course these flame cap kilns have no bottom air, but in the beginning stages of a burn, the air does flow down the sides and up the center of the fuel stack so they do operate in an updraft mode of sorts. So some of it is the air flow down the sides that is sucking the air from above and causing the flame tips to hook downward. However, in the later stages of the burn, we have completely filled in the kiln with hot glowing coals and air still comes from the top because the combustion must create a negative pressure to pull air in from the top. Which of these down-sucking affects might be taking place in a small stove?

I also have to agree with Gordon, and with Bill Knauss, that there must be positive pressure from the wood gas as heat forces the volatiles out of the wood. That would be how the Everything Nice/World Stove works. Heat from the flame on top volatilizes gas down inside the stove. Pressurized gas flows up to the top of the fuel bed, feeding the flame, but some flows out through the side holes, gaining speed as it passes through the venturis, creating more negative pressure to draw more gas. In the annular space it pre-mixes with secondary air for better combustion. This pre-mixed gas then merges with the flame on top.

It is not all about draft and buoyancy. Gas flows also occur from volatilization and oxidation. 

So the World Stove is definitely not a down-draft gasifier, but it is more than a TLUD. In fact, I have felt for awhile that a flame cap kiln is more like a retort than anything, since it is closed on the bottom. The flame itself closes the retort and acts as heat exchanger at the same time. 

The World Stove just acts like a self-heating retort with a flame cap, as pressurized syngas leaves and recirculates to the flame. 

I agree that I would really like to see someone evaluate Nat's claims about N-enriched char from his stove. That would be proof that down-sucking gas actually moves from the top through the fuel like a sweep gas. Not too sure that could actually happen. The venturi effect would have to be very strong.

Kelpie

-- 
Ms.Kelpie Wilson
Wilson Biochar Associates
Email: kelpiew at gmail.com
Oregon home office: 541-592-3083
Mobile: 541-218-9890
Skype: kelpie.wilson

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