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 http://hypography.com/forums/science-projects-homework/6465-solar-parabolic-trough-charcoal-oven.html

we've been talking plans that sound comparable to these.

and could always use a fresh prospective

 

or this thread might help you.

http://hypography.com/forums/earth-science/2786-biomass.html

 

and here are some plans I found on cooking with biomass fuels.

Institutional Rocket Stove | BioEnergy Lists: Biomass Cooking Stoves

 

Biomass Cooking Stoves

[Turtle]

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! :) :D

[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. :)

 

 

:D

[DougF]

Yes fine job congratulations and keep up the good work. :hihi:

[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. :hihi:(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.:hihi:

[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]

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! :singer:

[palmtreepathos]

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.

 

the hot air that would be escaping the retort would actually be very flammable wood gas... a secondary souce of further flame. This is often done in charcoal makers. The pipe and pressure would also keep the flame from traveling back up into the retort. It may need to be capped when your burn is finished to restrict air intake as the char cools though.

[Fukudairafarm]

Ok, I decided to give it another try without re-routing the woodgas last weekend. I packed the 20L retort with split bamboo. This time I sealed the lid, and drilled a 5mm hole in the top. I tried to fit on a 90 degree elbow on the front of the stove, but it was not very effective. Lots of smoke and backdrafts. I finally was forced to remove the elbow and feed the stove horizontally as before.

Firing the stove with split bamboo, it took a LONG time before I saw any sort of outgassing. After an hour and a half of constant firing, some feeble wisps of steam began to come out. I kept on feeding it for another hour, but the ammount of steam/gas didn't get much bigger.

I have come to the conclusion that in the current configuration, it is not economical timewise to make charcoal in the retort.

I am still trying to figure out how to attach a pipe to the retort to direct the woodgas to the combustion chamber. Any ideas?

 

Some more observations-

-A sleeve around the retort should help it heat more quickly.

-Or perhaps just putting the rocket stove aside for a while, I have been toying with the idea of just putting the retort on a campfire and seeing what happens.

-Raising the interior chimney of the rocket stove (putting another can on the original stove with a taller chimney) could increase the draft enough to allow vertical feeding. But it would make the already none to stable configuration more unsteady.

-I just got the book Super-efficient woodstoves you can build by Ianto Evans a few days ago, and it really has some great ideas.

[Philip Small]

... I packed the 20L retort with split bamboo. ...

 

I am thinking that 20L is too large a retort in proportion to the 10cm stove.

 

... I am still trying to figure out how to attach a pipe to the retort to direct the woodgas to the combustion chamber. Any ideas? ...

 

Bulkhead connector. Any double-nut-able union, coupler or flare fitting might be adaptable, maybe even a simple threaded nipple, if long enough. Brass fittings at automotive/plumbing supply store?

 

... I have been toying with the idea of just putting the retort on a campfire ...

 

I recommend as a good learning experience. Also, retort is the best way to make writing charcoal, char cloth for flint-and-steel fire starting, and where char uniformity and consistency is of value.

 

...Raising the interior chimney of the rocket stove ... But it would make the already none to stable configuration more unsteady. ...

 

More draft is a brilliant option, may address retort oversize concern I have as well as your feed hopper challenge. If you layer the base of your rocket with sand/gravel instead of ash, bet the stability increases.

 

... Super-efficient woodstoves you can build by Ianto Evans a few days ago, and it really has some great ideas ....

 

Lucky.

 

Phil

[Fukudairafarm]

well, I am fed up with Japanese hardware stores. I have been searching for any sort of metallic hose fittings/nozzles, couplings, fittings or nipples, or bendable metallic tubing, but have found only plastic. When I asked the clerk at the local home center, he looked at me like I was some sort of dinosaur. I may have to ask my dad to send me a package of copper tubing. He will probably think I am building a still... Hey, not a bad idea tho...

 

Oh, and Phil, I also wondered about lining the base of the stove with sand, but the Evan's book says that might not work as well because of the high thermal mass. A low mass insulated interior chimney is preferrable apparently. But I think I would trade some initial efficiency for some stability... If I ever get some metal fittings to run a pipe, do you think I should attach it to the top, bottom or middle of the retort?

[Philip Small]

I also wondered about lining the base of the stove with sand, but the Evan's book says that might not work as well because of the high thermal mass. A low mass insulated interior chimney is preferrable apparently. But I think I would trade some initial efficiency for some stability... If I ever get some metal fittings to run a pipe, do you think I should attach it to the top, bottom or middle of the retort?

 

No doubt mass around the elbow changes how responsive the draft is to changes in heat intensity. On a small stove, like yours, that could be pretty important.

 

A Justa (see here and here) named for Doña Justa Nuñez of Suyapa, Honduras who helped to design it, is a rocket-based stove adapted to indoor cooking that uses masonry. The first link mentions "with ceramic bricks used for the combustion chamber". High thermal mass in the elbow area may not be ideal but it is not unworkable.

 

Ideally in your config, the elbow would be high enough that you would have room to separate a bottom layer of sand from the elbow with ash or vermicullite. Even 20-50 mm separation would help keep the draft bright. Another thought is a ring of cement inside the bottom, well separated from the elbow. Wouldn't be hard to make a form for this.

 

I would attach the gas relief tube to the underbelly of the retort. If the tube is small enough to bend without pinching it, I would run it down along (close or touching) the inside of the flue and, at the discharge end, give it a turn to direct the woodgas up the flue.

 

Hope this all works in reality as well as it does in my imagination.

 

Flame on!

[Philip Small]

High thermal mass in the elbow area may not be ideal but it is not unworkable.

 

Update: I have since learned, from pdfs here and here, that the body of the Doña Justa stove is partly filled with earth and insulated with ash. Makes sense.

[Fukudairafarm]

Update:

Well, I finally got around to working on a new rocket stove for the project. The new stove is a brick tower vertical feeder. I just cobbled it together this morning and took it for a test run before I mortar it in place. Even just dry fit, with quite a few gaps, it worked great!

 

If you have some spare brick laying around, it is easy to put together.

(Pictures hopefully coming soon, until then)

The lowest level is 8 bricks on edge in a long rectangle. (three each side, one each end)

The second level is the same (of course staggered).

On the third level, I made two squares, one on each end of the rectangle, and filled in the middle with three bricks on edge

Then I just built a chimney on one end to six bricks high.

That ended the construction.

 

To light it was a breeze too. I just crumpled up some newspaper and put it in the bottom of the feedbox and lit it.

When it was going, I took some very fine split wood (a little thicker than disposable chopsticks) and stood it up in the feeding hopper upstream of the paper. The fire backed into it, and started roaring down the tunnel and up the chimney. (I did have to blow once or twice down the feedbox to make the fire start down the tunnel and begin to draw)

After that, I just stood up some split bamboo in the feed hopper behind the wood, and it ate into that too. The material in the front burns from the tip, and gravity feeds it down.

On trick is to lever the older material towards the front when you add the newer in the back.

 

After I get it mortared together, I plan to insulate the thing with some vermiculite, maybe with a light clay slip so it will stick together (think "hypertufa" with clay instead of cement). I think that will really improve the efficiency as well.

 

Coming soon: Making a skirt for the retort to keep the wind from robbing all my heat.

Also, I finally got some 1/2 inch outside diameter copper tubing (thanks Dad!) and will be working on the woodgas feed over the weekend (I hope). The latest idea is to drill a 1/2" hole in the lid, loose fit the tube and arrange it to the firebox, and finally seal the junction with either a stiff flour dough or some sand/clay. It would break everytime you moved it, but it wouldn't cost anything.