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Rocket Stove Wood Kiln

 
Fred Morgan
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Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest
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Hi all, Ernie, Erica and myself have been experimenting with a Wood Kiln made with a rocket stove. My company paid them to do a design (which I promptly argued about lol ) which has been a great help. The kiln is now working, this morning the kiln was significantly warmer than outside, which is impressive, it is also meaning the cob we poured in is finally getting dry. I figure first wood load will go in early next week.

We started off with a six inch system, Ernie and Erica recommend 10 inch. The truth was somewhere in between. The biggest danger on a kiln is too much heat, not too little, so I went with the smallest possible.

The final product looks similar to what Ernie and Erica recommended, but with two barrels, instead of one. One of the issues here is that you can't get 8 inch chimney, so I had to work with 6 inch. It has been fine, though. It takes no longer to feed two systems next to each other, as one. And starting the second system is merely using gloves to move some burning wood over... Two six inch systems end up generating roughly the heat of one eight inch, if my math is right. We have lots of drums so there was no extra cost in the drums.

Burn time tends to be 1 hour, so we feed it every 45 minutes or so. My office is about 200 meters away, so it gives me a break from sitting. Also, I have a worker who works in the gardens we have, cuts grass, clears brush, etc for this part of the plantation, he checks it when I can't.

Our business is wood, so scraps I have, more than I can use most likely. So far, for the two kilns, they use about 1 sack (think feed sack) of waste wood every two days. The mill can produce all the wood needed for a week, in one day. We burn for 10 hours, and let it rest over night. This produces a much better result in drying, because the danger in drying is to dry the outside of the wood too fast, resulting in case hardening. Sort of like when you sear meat so that inside stays moist. Same idea, but that is a problem with wood, you want the inside to be as dry as the outside.

The plan is to build three more once we finish a complete cycle with this one. My current cost per board feet in drying wood is 20 cents. (we have a kiln that runs on electric). Each kiln should hold roughly 2500 BF, which means a load which should dry in about 3 weeks, will save us 500 USD, in other words, more than it cost to make. With 4 kilns running, we will save about 2,000 dollars a month - and I get rid of scrap wood, which can be an issue at times.

Kiln dried wood is very much in demand here and our own factory consumes a lot.
 
Dale Hodgins
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Your description lacks photos. They were worth a thousand words when I last checked. I will follow your progress on this since I will soon need to KD some maple and alder. I've decided to solicit milling business for hardwoods as a profitable way to bring materials for hugelkultur wood to my door. Bark and other scrap will go into the beds.
 
Fred Morgan
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Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest
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Hi Dale, hopefully I will find some time to post some photos, but nothing special really. I have the barrels outside of the kiln, behind a concrete wall, to reduce the danger of fire. Since you keep the fire going for so many hours, and you aren't sitting around while it is burning, it is very important to protect from fire.

Remember too, I am in the tropics, during your winter, we don't have to get up to freezing point first, if you know what I mean.
 
Gabriel Leirbag
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Is there any way you could post some pictures or some sort of diagram describing your design? I have been really interested in a rocket heated kiln design. Any help would be greatly appreciated.
 
Fred Morgan
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Gabriel Leirbag wrote:Is there any way you could post some pictures or some sort of diagram describing your design? I have been really interested in a rocket heated kiln design. Any help would be greatly appreciated.


Ernie and Erica helped in the design and I have been evolving it since then. It started with a RMS system, using six inch chimney with a straight run under the floor. (the floor is around 5 meters long). One of the things I have been working with is how to have a longer burn, since we keep it lit for 10 hours a day, and more. Wood has a lot of mass, and of course, the temperatures are higher. Yesterday we made a firebox as the input using metal. Now we can go 2.5 hours (we estimate) without adding wood, which is a great improvement over 30 to 40 minutes. It uses less wood as well and the temperatures are higher overall.

When we finish our testing, I will be more than happy to post pictures and designs.
 
Satamax Antone
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Fred, are you aware of this thread over at Donkey's forum?

http://donkey32.proboards.com/index.cgi?board=experiment&action=display&thread=511 May be another way to load the thing.
 
Gabriel Leirbag
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What exactly is the process for drying wood with this type of kiln? Vs the process of a solar kiln it seems like it could be more efficient.
 
Fred Morgan
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The process of drying is the same for solar, one thing we do is let it rest overnight. If you dry wood too fast, you get case-hardening, i.e. the outside dries, but inside isn't and the outside becomes sealed. Much like when you sear a piece of meat to hold in the moisture.

Kiln drying wood is easy, but complex. (okay, a contradiction). If you have never done it before, you should do a lot of reading. Slower is better, what is complex is drying fast with good quality, the faster you dry, the more you have to know.

 
R Scott
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Gabriel Leirbag wrote:What exactly is the process for drying wood with this type of kiln? Vs the process of a solar kiln it seems like it could be more efficient.


Solar kilns don't work in the rainy season.

The side-by-side 6" systems sound like a great way to control the system--a high/low switch.

Do you run your vent air around the barrels or is that just waste heat?
 
Fred Morgan
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I built adobe ovens on top of the barrel, and put a chimney at the top of them, this takes most of the heat from the top of the barrel and sends it into the kiln. It is also a great place to cook!
 
Dale Hodgins
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Fred Morgan wrote:I built adobe ovens on top of the barrel, and put a chimney at the top of them, this takes most of the heat from the top of the barrel and sends it into the kiln. It is also a great place to cook!


Hey Fred, Just thought I'd bring this to the top since it's closely related to a plan I'm formulating for a solar assisted RMH to even out diurnal issues with solar kilns. Did you get any photos yet ?

Here's the link- http://www.permies.com/t/19518/stoves/Solar-Powered-Rocket-Mass-Heater
 
Fred Morgan
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Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest
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Now that I have a near final design, I will get you some photos, and perhaps better, a sketch up design. Learned a lot in the process, and the kilns work incredibly well. Not sure how adaptable to a greenhouse since my goal is lots of heat, like 125 F, and cool down over night.

 
Erica Wisner
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Hi Fred,
I was scouting the forums for photos of your wood kiln, too, and came across several threads.
I would love to see how you've modified the design to work better. I think I get the large fuel box / lid / air feed idea, but of course I could be envisioning it wrong. I'm also curious if you've done a large fueling box with a smokeless burn, because that's always interesting.

(If you are not posting pictures or design drawings out of respect for our initial work with the design, please don't let that stop you. I wouldn't want people re-selling my original designs, but this project was such a collaboration from the start that you should feel free to share any results you're getting.)

Can you post some photos here or on your Finca Leola site, when time allows?
Or if you prefer, you could send them privately.

If you think the design is running well enough for general replication, we could talk about me doing a summary for you, and/or perhaps including it in the special-case appendices to our Builder's Guide.

Yours,
Erica W
 
Wink, wink, nudge, nudge, say no more ...   2016 PDC and Appropriate Technology Course at Wheaton Labs http://permies.com/pdc
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