Rocket Stove Charcoal Retort

[Fukudairafarm]

The other day I saw a Google video about making a Winiarsky rocket stove. The plans can be found on the Aprovecho Research Center website. The Capturing Heat Booklet PDF.
It was pretty easy to build.

I also saw a Instructables presentation on making charcoal in a retort. I put the two of them together and had the brilliant (?) idea of using a rocket stove to heat a retort (a 20L steel bucket with a close fitting lid). The design in my head includes routing the outgassing from the retort to the rocket stove, but I am not sure if my skills are up to that yet. So for now I will just have a hole in the lid. (I am thinking on a 2cm hole- a total stab in the dark. If you think it is too small or large, please advise me.)

Do you think it will work? My first attempt will be a bunch of apricot tree prunings taken during the winter, broken into 8-12 cm pieces. Is there anything you would like me to try as well? Yard waste or bamboo splits? Garden weeds or old leaves? Once I get to the magic ten posts, I will put up some pictures.

Also, do you think I could light the plume from the retort on fire? That would be pretty striking at night, as well as a good indicator when the charcoal is done.

Well, gotta get to work on it again in the morning.

[DougF]

You might want to look at this thread Solar Parabolic Trough Charcoal Oven
we've been talking plans that sound comparable to these.
and could always use a fresh prospective

or this thread might help you.
biomass

and here are some plans I found on cooking with biomass fuels.
Institutional Rocket Stove | BioEnergy Lists: Biomass Cooking Stoves

Biomass Cooking Stoves

[Turtle]

Originally Posted by Fukudairafarm

Also, do you think I could light the plume from the retort on fire? That would be pretty striking at night, as well as a good indicator when the charcoal is done.

Well, gotta get to work on it again in the morning.

Yes definately you can light it. I grabbed the top link from a search on 'woodgas', and there are quite a few more. The key term in this is 'woodgas' rather than stove, etcetera.

Biomass Energy Foundation: Woodgas Home Page

Back in the 30's people started using it to power automobiles. >> FUEL MAKING

Nice work so far Farmee! Giddyup!

[Fukudairafarm]

The experiment has begun!
So far I can already tell that the rocket stove is a nice idea, but I need a self feeding design. I have to push the kindling further in every 5 minutes or so, so it is exceedingly hard to do anything else while this is burning. Especially with two small kids running around
Also, I didn't pop a hole in the lid, it sits on the can fairly tight, but the smoke and steam escapes quite nicely from the lid. When it is done, I will seal it tighter with a cinder block on the lid. I will keep you updated.

[Fukudairafarm]

Ok, it is working like a charm- except for the feeding it every 3-5 minutes. I can see how these are good for cooking, but not so good for a long, sustained burn. I am toying with the idea of putting another elbow on the front of the stove to act as a gravity feeder. Then I could get maybe 20 or more minutes between feeds...

[InfiniteNow]

This is beautiful Fukudairafarm. Thank you so much for sharing your activities with the rest of us here. Your enthusiasm is contagious.

[DougF]

Yes fine job congratulations and keep up the good work.

[Fukudairafarm]

Ok, let's see...
I fired the stove for about 2 hours and 15 minutes. It burned through one good sized chunk of firewood that I split with my hatchet, about 4 feet of one inch diameter persimmon wood, and about 6 feet of one inch arrow bamboo. I am kicking myself for not weighing all this beforehand. (I am like a kid in a candy store- I can never wait to get started!)

At the end of the two hours I had to stop feeding the stove and get ready to come to work. I wish I could have fed it longer. Inside I had about half-half charcoal to brown ends. The bottom of the can had very nice charcoal, very beautiful charcoal even. A few cracks, but otherwise it looks almost the same size and shape as what I put in. I imagine that another hour or so may have completed the process.

A few more observations and musings.
I was unable to keep the stove fired evenly due to my two "assistants" who demanded that I fill their kiddie pool and give them airplane rides. So the heat obviously had great fluctuations. My rocket stove is a very hungry beast. I had to push the fuel forward every 5 minutes for a strong fire, although it would continue burning towards the front for about 10 minutes or so, but with less heat. Directing the woodgas from the retort to the stove would greatly simplify this. Also, a vertical gravity fed firebox is a must. I will be working on that for the next test.

A question to ponder- would the woodgas burning in the firebox be enough heat to sustain the reaction until the finish without adding additional solid fuel? I am thinking maybe not, with the heat lost to radiation and all. I wonder how I could measure the amount of woodgas per kg...

Thanks for all the encouragement and help everyone- the woodgas links and all were quite helpful!
Stay tuned for the next test sometime next week hopefully.
If anyone has ideas for improvements to the basic design, or experience building something similar, I would love to hear them.

[Philip Small]

One feature of the rocket stove is excellent draw, accomplished by the heat storing mass encasing the flue. Thus the rocketstove should be able to draw in both woodgas smoke and air quite nicely under a variety of conditions. Keeping the woodgas lit could be a challenge, and I offer some solutions below. I encourage you, Fukudairafarm, to keep at it: we can all greatly benefit from your experience.

There is an upper limit to how much smoke-fuel the rocket will handle before it snuffs out the flames. Woodgas production increases as retort temperature increases. Perhaps the woodgas production rate could be controlled by raising and lowering the retort onto the hot flue gases.

Reigniting could be a major operational challenge - maybe keep a long-necked propane torch handy? Missouri charcoal makers (industrial scale) have installed propane igniters to operate their EPA required afterburners, so this solution has precedent.

Woodgas temperature will affect the snuff-out level and smoke handling capacity. I wonder if Fukudairafarm could go straight down from the bottom of the retort to the middle of the combustion zone with a tube (copper?) running down the center of the flue? That would keep the gases very hot.

Providing secondary air (preferably heated air) to the combustion zone could be highly desirable. It looks to me that one reason the flames stand so high above rocket flues when fueled to full hopper capacity is that the smoke is re-igniting at the flue exit point, an indication of insufficient air internally. Enclosing the upper portion of the flue in a sleeve would accommodate pulling air down the outside of the flue to introduce it at mid flue height. I wouldn't go too far down the flue as this would compete with the benefit of the mass encasing the bottom of the flue.

Hope this helps, and regret having little direct experience. I am still at the stage of looking for a 20L can to make the body of the rocket I want. Fukudairafarm, did you use wood ash for the inert mass in the stove body, or something else?

[Fukudairafarm]

Originally Posted by Philip Small

Woodgas temperature will affect the snuff-out level and smoke handling capacity. I wonder if Fukudairafarm could go straight down from the bottom of the retort to the middle of the combustion zone with a tube (copper?) running down the center of the flue? That would keep the gases very hot.

Hope this helps, and regret having little direct experience. I am still at the stage of looking for a 20L can to make the body of the rocket I want. Fukudairafarm, did you use wood ash for the inert mass in the stove body, or something else?

Thanks Philip for the idea of the center pipe. My only worry is that it might interfere with or cancel the draw of air. Like two fans blowing at each other. The air intake is 10cm stovepipe, so it would be like a low pressure fan, but the retort pipe would be much smaller, but probably at a much higher pressure. Anyone have any thoughts about that? Or if I put a "U" in the pipe, it would be adding to the flow and sucking more air in...

Yes, I used wood ash in the body. I had just finished cleaning out my woodstove when I found the plans for the rocket, so it was a happy coincidence. Also, I couldn't bring myself to buy vermiculite or perlite with the outrageous prices for them here at our local home centers.

Good luck in the search for the 20L can. Try resturaunts that have a deep fryer. Maybe you could get some with used oil, and make biodesiel too!