Been making artisan charcoal for a few years now and am getting ready to build a new retort heated by a Rocket stove, either traditional RS or Batchbox. Am leaning towards the BB as I won't have to tend it constantly.
Just trying to figure out what size burner I will need to design and whether I'd be better off with a standard rocket style or Batch Box. I need to provide several hours of burn without having to constantly feed the fire so the BB may be the way to go. I like the traditional rocket design of being open feed but like the volume of wood I can load at one time in the BB style.
Also wondering how best to mate the burner to the oven to be as compact a unit as possible. Right now, as the sketch suggests, a horizontal core would be ideal but may not be effective. This would also help as I may need to build something that can eventually be moved with a tractor and forks.
Here are my basic burning parameters:
fuel: 12-24 inch long firewood, typically 2 to 4 inches in cross section Sometimes as branch sections other times as split wood.
Retort vessel is a stainless steel drum and will be inside a horizontal 55 gallon drum sized oven which will be insulated on all 4 sides. The retort vessel will lay in the oven such that it divides the upper and lower half of the oven to allow the flue gasses to travel along the bottom of the vessel, rise over the head of the vessel, then travel over the top of the vessel before traveling down the bottom of the vessel and exiting below the vessel. See attached sketch.
To avoid distorting the retort vessel I'd rather not have any direct flame impingement or otherwise bring the metal up to temps that will allow such a thing. However, I do need to achieve and maintain an oven temperature between 700° F and 900° F for 1 to 2 hours.
Good idea ... or at least one that I have and haven't fulfilled!
I haven't gotten as far as thinking about BTUs and temperatures and such. But a few thoughts ...
1 - Bell temperatures can approach 1000F. I think throttling the burn down to reduce those temperatures is anti-rockety because it prevents all the products from being burned.
2 - How are you going to force the flow around the retort container? I was thinking of just placing the riser tube into the middle if the barrel, just under the retort container (might need a diffuser plate there). Uncertain how to channel the hot exhaust myself, or if its even necessary (would the steel walls of the retort diffuse the heat well enough?)
3 - How will you handle the pyrolysis gases? My plan has been to pipe those gases into the rocket and burn them, setting up a beneficial cycle.
4 - BB or J-Tube ... I was going to go j-tube just because it is significantly easier to do initially, and with the injected gases its easier to maintain some wood as a pilot light during the pyrolysis stage (or, so I imagine).
5 - I was considering welding 2 or more barrels together to create a longer bell that could surround a longer retort chamber (most of my feed stock will be longer branches...so a 6' or 8' retort would minimize the amount of cutting to fit). I thought I might need to add additional rockets to bring such a mass to temperature, and then use just one to maintain and burn the pyrolytics
Welcome to permies Rick!
I am still on a long journey to rocket stove blastoff, so I am only speaking from what I've read.
I believe a batch box rocket stove can be refilled during a burn while also being able to burn an hour on a full load.
Further more experiments have shown them to operate just as well with a shorter riser than originally thought.
An 8" system should work fine with a 24" riser, a 6" with an 18" riser, etc.
An 8" batch box can be made 28" long without messing up functionality, that's roughly 125% of normal length and big enough to accept 24" fuel.
Because of these things, I recommend an 8" batch box, built offset onto one end of a 55gallon barrel.
I would exhaust this into end of the barrel, near the top and use baffles to direct it over the top and back to a point below where it entered before allowing it to escape into a verticle chimney.
I am concerned by the number of 90 degree turns you're demanding the exhaust stream make. I also don't think you need such an elaborate approach to heat your retort, although I do think one thing might have been omitted that you might want to consider.
I am unsure why you don't just stack the barrel retort atop the barrel drum, as heat rises. I think you'd need to insulate the retort heavily, and I would wonder about the long-term viability of any sheet metal in the exhaust stream, but if your insulated drum oven with biomass pyrolising inside sat atop the bell, perhaps with the bottom quarter or third exposed to the exhaust stream at the top of the bell (sitting inside a depression at the top of the bell made for it), it would cook nicely.
All that would be required is a couple of one-way pressure relief valves, with repurposed bbq venturi tubes taking the retort's wood gas exhaust to the burn tunnel. You could even have a mechanism by which you raise or lower the frame holding the retort up or down in the exhaust stream, to raise or lower the temperature, and to allow for easier lighting at the start.
You could even have a bbq or oven thermometer installed into the top of the retort, so you know how hot the coldest part of the retort is getting.
No masonry shrapnel bombs, no undercooked charcoal. And to move, or to empty, you could at least arrange something, a yoke or framework, to catch and lower the vertical retort ninety degrees for loading or emptying. If it was already suspended from a frame for raising or lowering, it could easily swivel from it's centre point at the highest extent of its travel ninety degrees and then be lowered to rest across its socket, which could be designed to have two rests cut for the drum in its loading/unloading horizontal state, corresponding with semicircular plugs of whatever mineral insulation on the top drum, probably that oven insulation stuff, shaped to fit together in the vertical orientation.
Having dealt with complex exhaust streams in the past, I am just concerned about how you'll get it started. That's a lot of twists and turns for the exhaust stream, a distinctly non-rockety thing at the beginning of a system.
Do let us know, though. The advice offered regarding capacity is sound. I would worry about safety with regards to the metal involved using any larger than an 8" system. If everything metal melts, that's a bad day for your project. Unless you get it on video and monetize it somehow. But imagine a retort of cooked charcoal melting into the top of the riser and falling into the burn tunnel, all that ambient oxygen rushing into that previously oxygen-starved pyrolysis environment. I have never seen it happen, but I know charcoal is explosive as all hell, and a 55 gallon barrel collapsing would generate a lot of charcoal dust.
Charcoal is dangerous on its own, in a traditional artisanal setting. Please be very careful in your experimentations, whatever you do. Keep us posted, and good luck.
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein
I have never made charcoal so I don't have any practical experience with that process.
I have made plenty of rockets though.
To start a batch box is the unit to build.
Yes a batch can be opened and have more wood inserted.
In fact a batch can be run with no door at all , other than a plug door to let it go out.
A batch will burn a load of wood in an hour or so BUT...
There will be glowing red coals for another hour or more after that. (using a proper door)
I don't like your sketch design. To many twists and turns .
You need that batch to vent straight up into a bell (brick or metal)
Your retort vessel just need to be suspended below the riser.
You will need to experiment on how high to keep it to maintain your desired temperature.
Only directly above that riser will it get too hot , anywhere to the side and below will be where you want your vessel to hang.
As far as being portable??? Bricks don't like being bounced, they will crack the mortar apart.
If you have a smooth hand on your forklift and nice smooth ground to move on you could move this around But be careful or you will be rebuilding.