Biochar baker?

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Biochar baker?

Postby Nutcase » Fri Dec 21, 2012 11:14 pm

Greetings. I'm in the research and planning phase for my first rocket stove, in the course of which I ran into the video on the half-barrel design, and one thing led to another. After watching that particular video a few times, and thinking about the pros and cons of front loading, consequences of good insulation, etc., I had an idea. What if the front loading section was open to the fire chamber only through a few small holes, and well sealed at the back. Would it be practical to get it hot enough to cook off the wood in a reasonable length of time? Perhaps this would throttle back the burn rate in a useful way, even if later you just somehow ejected the charcoal into the burn chamber.

Of course I would like to do this experiment myself, but I am weeks away, at best. In any case, maybe someone with hands-on experience can see a reason why this wouldn't work or wouldn't be useful.

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Re: Biochar baker?

Postby matt walker » Fri Dec 21, 2012 11:34 pm

Wow, interesting idea. What do you hope to achieve by setting it up that way? Creation of Biochar? Longer, controlled burns while still consuming all the fuel?
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Re: Biochar baker?

Postby pa_friendly_guy » Sat Dec 22, 2012 3:02 pm

I am trying to visualize how you want to set this up. I am a bit slow on the up take sometimes. Would you have a top loading burn chamber about 1/2 way back on the barrel with a wall between the burn chamber and the front opening of the barrel? Then the front chamber would be filled with wood that would dry and give off bio gas that would be vented to the burn chamber through a few small holes? If the front door fit snuggly there should not be any smoke escaping out the front. That would still give a complete burn, and a very hot burn. The wood in the front chamber could then be burned as charcoal in the unit or as Matt said used as Bio char in the garden. It would create a mini charcoal kiln at the front of the RMH but have no green house gases escaping to the atmosphere. All of the excess gases would be burned completely in the RMH. If I understand your concept correctly it does seem to have merit. We seem to keep coming up with new and creative ways of using and burning a RMH here. From heater, to grill, to smoker, to charcoal kiln, to oven, to butt warmer the uses continue to grow. :)
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Re: Biochar baker?

Postby Nutcase » Sat Dec 22, 2012 4:18 pm

Well, first and foremost, it just struck me as an interesting idea. I'm not entirely sold on biochar in the garden, but maybe it's worth the trouble. Having a system that could chew on large batches/awkward pieces efficiently wouldn't be bad. But how that will fit into my specific home heating needs and my experience level is a more complicated question.

My primary goal is to heat the house. Perhaps I can fit this in, at least as an experiment, especially if I go with a half-barrel design. However it's only going to be worth it in the long run if it makes heating the house easier. That seems possible if it allows large loads to burn off slowly—but not too slowly—and if handling the resulting charcoal isn't messy, awkward or dangerous.

At the moment I envision this basically as you describe, pa_friendly_guy. However it's less than clear to me that the retort would absorb heat at a suitable rate, with the fire generally going in the other direction. There are also issues with unloading it indoors and/or having the fire side partition removable. Pushing charcoal into the firebox might lead to excessive obstruction or wear and tear on the fire box. A lot of this stuff would be better worked out in an outside system with looser constraints on mess, efficiency and ease of modification...
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Re: Biochar baker?

Postby matt walker » Sat Dec 22, 2012 5:05 pm

Well, I wholeheartedly support the exploring of ideas like this. I love the process. I will say that there have been some recent posts over on Donkey's board "Rocket Stoves, experimenter's corner" where a group was attempting a similar thing. I won't go into the success or usefulness, just that they were trying to use a chamber over the burn tunnel to gasify wood and then feed that into the burn chamber. So, there are others thinking along the same lines.

I will say that there are now quite a few successful batch loading designs starting to appear in the rocket stove world, and they are pretty exciting. One thing that folks seem to overlook is that if you want to burn a fire at less than it's full potential for a long time, a modern box stove is a pretty advanced way to do that. The rocket stove burn chamber/heat riser combo is really a device for safely incinerating wood at full combustion, so long burns don't really play into it. While batch burners increase the burn times by a bit, they also run the risk of creating a fuel rich situation which means inefficient performance. In my opinion, it's the mass that is doing the "long burn." By burning quick and completely, then storing that heat in the building's envelope in mass, you accomplish both incredible efficiency and long useful heat from the fuel. Once you've lived with a mass heater you'll wonder why you wanted the wood to burn for so long anyway.

All that was just to say, I really like the idea, and it would be fun to play with outside. I think it would be neat to see how far you could take it.
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Re: Biochar baker?

Postby pa_friendly_guy » Sat Dec 22, 2012 7:28 pm

For your winters Matt, and most likely for mine here in Pa as well, the RMH design that we all know and love should work just fine for our heating needs. You do not seem to have to re-stock the stove with wood very often during the day and your house stays warm from the mass radiating the heat nicely. I wonder though about people who live in MUCH colder areas. tt10-99 seems to be in that position. When you are dealing with sustained temps in the -40 to -50 I would think that you would need to be putting fire in the stove a lot during the day to keep up. A longer burn time, coupled with more mass is the only way that I can see to keep warm in those extreme conditions. Modifying the stove design to provide that longer complete burn time would seem to be a good thing for those people. I am certainly NOT an expert on this subject, I am just thinking about how you deal with the different temps from different areas. Is there any one from your RMH board who live in a place with those kind of extremes? What have they been able to do to cope with extreme temps?
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Re: Biochar baker?

Postby matt walker » Sat Dec 22, 2012 7:40 pm

You may be right Guy. There is a fellow on the other board from Alaska and he is one of the proponents of the batch box, for just the reason you state.
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Re: Biochar baker?

Postby tt10_99 » Sun Dec 23, 2012 3:30 am

Well I really like the batch door plus the top feeder... for the cold it does throw a lot of heat and probally would be very hot in a house rather then a greenhouse.
Bio - char is great as is ash for the garden so if you can make bio-char you will be doing well.. I think with my next rocket half barrel I would like to raise it off the ground.. I end up sitting to get it started which is why i start it with the top load but I think raising it would be better ...
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Re: Biochar baker?

Postby Nutcase » Tue Dec 25, 2012 8:57 pm

Well, finally back from being dragooned into baking cookies and such...

Having mulled things over some more, I am thinking that making a horizontal burn chamber into a retort would be challenging. Hard to get enough heat flux without doing something complicated. Could probably get some really, really dry kindling though. But I don't trust my physical intuition without some hands-on. Maybe just sticking some copper tubes into the sides of the firebox would do something interesting.

I have gone over to Donkey's board, have a ways to go before I catch up. Lots of good info. I look forward to having something substantive to contribute to the discussion at some point.

I have some questions about the handling characteristics and performance of your "cobposite", but I'll take that to the appropriate thread.
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