Charcoal retort

[Nessalco]

I'm building a biochar retort over the next few days. I've never used a retort, so a question arises. For maximum efficiency, it is usually recommended that you dry the feedstock. However, some reading I've done suggests that starting with green feedstock takes longer but keeps the overall temperature of the pyrolosis lower.

 

Opinions? Is it necessary or desirable to dry the feedstock first?

 

FWIW, I'm kind of excited - I have about 40 pounds of dried sumac waiting to cook.

 

Kevin

[schroedinger]

It is not necessary to dry it, but if it is allready dry you will still get a supperior product.

[Sparx88]

Ditto. Dry or fresh paulownia produce the same.

[Nessalco]

Excellent. Thank you.

 

Kevin

[Arthur]

With willow it's 10% weight yield from wet wood or 20% yield from seasoned wood. You pay for the fuel to dry off the moisture that would dry up anyway. Plus the steam driven off smells horrid so let it dry first or risk annoying the neighbours.

[Shunt]

With willow it's 10% weight yield from wet wood or 20% yield from seasoned wood. You pay for the fuel to dry off the moisture that would dry up anyway. Plus the steam driven off smells horrid so let it dry first or risk annoying the neighbours.

+1 Arthur

 

Also, the inside of the retort gets nasty from unseasoned wood, and the added fuel to "burn it out" for the next batch just adds a extra step to the process, which is labor intensive enough already. I cut many varieties of firewood and stoked an Ashley wood heater for 20 years in my shop for heat.

 

Not quite the same as a retort, but uncured woods in a retort take more fire for longer than cured. The process of making charcoal for pyro is one of the most debated and talked about topics in pyrotechnics for good cause.

[Nessalco]

OK. Maybe I can figure out how to use the waste heat from the process as part of the drying process....

[FloridaCracker]

Have you tired a TLUD yet? Cured splits of wood work great in one and you don't have to use extra wood to cook the retort. You also don't need to watch the heat and cook times as much as the TLUD is essentially self regulating. Also, the charcoal produced in a TLUD often seems hotter but that probably has to do with how an individual cooks the retort.

[Nessalco]

I used a TLUD system to make charcoal last year. It was OK, but the batch size was pretty small. Also, shutting off the airflow was occasionally problematic.

[FloridaCracker]

If you are using split wood in either I would imagine they are pretty close though I don't take the time to weigh things. I do pack a retort a bit tighter and the TLUD a bit looser to let air flow thru. It seems like a lot of people use shavings in the TLUD which probably produces a lot less because it's much less dense. A 5 gallon TLUD with wood splits stacked horizontally makes quite a bit of charcoal.

 

I do keep a couple 1 gallon retorts around because I like a good camp fire in the coming months. It only takes a few minutes to fill the retort while sitting around the fire and then cook a couple batches while relaxing with a few beers. But that is the only time I use a retort anymore.

 

It's worth trying both ways to see which you prefer. The TLUD seems to have more advantages IMO, at least when using the same split wood feedstock. I make my feedstock about 3/4"-1" square and maybe 7"-8" long.

[Nessalco]

I'm not sure the design I'm building has 'reached' the pyro world yet - at least I haven't seen it mentioned.

 

http://www.biochar-international.org/sites/default/files/backyard_biochar_kiln_instructions.pdf

 

I'm going with a slightly smaller retort, of 30 gallons, and I'm going to add a compartment to help dry the next charge of feedstock. I need 20-30 pounds a year of finished charcoal, and this seems the quickest way to get it.

 

I'm hoping this design will help with one major problem cooking sumac - the smoke is extremely irritating, and will cause symptoms for hours after exposure, With this design, after the gas (called syngas) lights up you can walk away and forget it. When pyrolosis is complete the generation of syngas stops, the burner goes out, and you simply have to wait for it to cool. Being able to build the kiln in a remote spot and stay well away during the cook are the attractions.

 

Why cook sumac if it's so irritating? It makes some serious charcoal - at least on par with pawlonia or balsa, and some folks claim better. For comparison, when I ram spolettes with willow (from Custom Charcoal) BP, I get a very consistent timing of 2.9 seconds/inch. Using sumac BP I've run it down as low as 1.9 sec/inch. It makes excellent - really hot - powder, which I hope will improve the breaks on my shells.

 

Costs are way less than quoted in the article. I found a muffler shop that is bending up the vent pipe/burner assembly for me for $40. I have all the block on hand, and all the steel.

 

Kevin

Edited September 15, 2015 by Nessalco

[FloridaCracker]

I have seen something very similar but it uses chips or pellets that continually fall into the cooker as the pyrolysis occurs. Except the charcoal eventually falls down where it was burnt as the heat supply.

 

The purpose? The volatile rich smoke went to a gasoline engine where the smoke was now the atomized fuel. Pretty cool. I guess back in the world wars these converted engines were more popular since fuel supplies were going to the war and in short supply but there was plenty of wood.

 

I was introduced to it by a Vietnam vet that was a "prepper" long before you ever heard the term. He thought he was going to fool me asking what I thought it was. But seeing the wood/charcoal/ash and having seen the intense jet of burning smoke coming from many cooking retorts I immediately knew. It wasn't all that complicated but more so than I needed for my charcoal needs.

 

Pretty neat but there is little that is new. Many things were done and forgot about long ago and are now being resurrected, perfected, or modified for a different application. Looking through old books can be very enlightening. I had an antique book when I was a kid called something like "The big book of boy's hobbies" and it contained everything you can imagine including a section on pyrotechnics if I remember correctly, and helped fuel a young kids imagination. At least this kid and probably helped steer me into being an engineer. But I digress.

 

Let us know how it turns out. Probably over kill for most but it might spur people to go into the charcoal business and start supplying charcoal to the pyro community. Or "biochar" to the pot growers and organic farmers.

[FloridaCracker]

Are you going to use a wood fire or propane/natural gas to get it going?

 

Are you also building the concrete block structure around everything? If so you must have plenty of room and more importantly, an understanding wife!

 

Edit: missed the part about you already having the blocks.

 

I wonder if you could use a couple 50 gallon drums to replace the concrete structure as well as make your warming chamber to pre dry/cook the wood. If you have a friend with a welder it would probably be pretty easy to do along with being smaller and cheaper than all those blocks.

 

I also wonder if the wood on the bottom will be cooked much more thoroughly and the stuff on top or in the middle much less, so that the volatile content varies greatly with some charcoal being hotter and some cooked to death? I guess if it's all ground together and mixed up it will average out but it sounds like you are trying to make hot stuff.

 

If you found a barrel that fit just inside another you could drill holes around the inside can to vent gas and weld a handle to the lid that sticks through an arc cut in the outer lid. A second outer lid with just a hole for the handle should stop heat loss thru the cut arc. You could then rotate the inner can as it cooks and rotating over 270 degrees should allow a fairly even cook. Even turning it 180° a couple times would be a lot more even cook. You could have a second inner can full of wood and switch them out after one is done cooking and really crank out some charcoal since it won't have to cool down inside the cooker.

 

You might also think about a way to stop air from going into the gas vents to prevent ash. The design in the .pdf doesn't include anything so maybe it's not an issue. Or they may not care about some ash when making biochar. A section of pipe that slides over the other and covers the gas vents could work but you would have to find a close fitting pipe. Or you could make an end cap that slides off and have a rod with a rag tied to the end and stick it in past the vent holes to block the pipe. And if you had the can inside a can, pull the inner and drop into a bigger one and put the lid on like some do with current methods.

 

If you don't want to get that complicated, though it could probably be done in an afternoon or two with someone that is handy with a welder, I would suggest at least adding a wire shelf across the bottom to raise the lower wood 4"-5" from the bottom of the can. That would at least get the wood off the direct heat on the can and reduce the amount of over cooked charcoal a bit.

 

I guess the engineer in me is always trying to modify things and these are a few things that popped in my mind after looking at the drawing better. Now that you have piqued my interest I might have to play around if I can still find some metal drums.

 

Good luck with the project.

Edited September 15, 2015 by FloridaCracker

[Nessalco]

Thanks for the thoughts. Many of those ideas have crossed my mind as well. I'm going to start with the simplest form - pretty much as illustrated in the pdf, though I am adding a grate in the bottom of the retort, as you suggested. This one is going to be proof of concept, so I want to see what results I get with the simplest approach. I won't be using 'good' wood to load the retort, rather I'll use scrap dimensional lumber from a local factory. See what kind of return I get, and what the ash situation looks like. The initial fire will be wood, since I have acres of it to get rid of.

 

Part of what intrigued me about this approach is the claim that you will get a 25-50% yield. When cooking with a TLUD, I usually got in the 18-22% range. I'm also considering ways to control the airflow to the fire box, in an attempt to keep the temperature down. You can get effective pyrolosis at temperatures as low as 200C, and the lower the temp the higher the production of char. I doubt I could keep it that low, but I think 400C would be a reasonable temp. I found this article to be very interesting http://biocharfarms.org/biochar_production_energy/

 

I too wondered about blocking the vent after the cook, but for the initial run I'm not going to do so. None of the articles indicated it to be necessary, and this approach is used in some pretty high end retorts - as well as by a bunch of DIY folk. Trying to keep it simple.

 

I have plenty of room for these projects, and the nearest neighbors are half a mile away. More importantly is that understanding wife - heck, she's sourcing the barrels for me

 

Unfortunately, it will be a couple weeks before I can get to this. I'm leaving Friday for Orlando, and won't return until 10/1.

 

Kevin

Edited September 16, 2015 by Nessalco

[Mumbles]

Have you come across OldGuy's barrel retort design thread? It might not be exactly what you're looking for, but there was some interesting discussion on pyrolysis temperatures, and cooking under a slight pressure. The designs share some similarities, and might provide some ideas for getting your retort made.

 

http://www.amateurpyro.com/forums/topic/6890-oldguys-triple-barrel-charcoal-retort-design/

[schroedinger]

The design you are building is essentially a bottom lid retort design. The pricinp used by many peoples when using a retort is to just fill a 200 L (needs holes in the lowest 1/4 ) barrel with a 60 l retort and firewood. Now you light it up with the hole of the retort upside. This way you can easly see when you are done cooking. When the flame comming from the hole dies out you are done. With this method you need the most external firewood.

 

With a bottom lid design you place the barrel with the hole on the down side and use a bigger retort 100-120 l in a 200 l (again with holes) barrel is good. Now you light the firewood on the top and let it burn down. As the gasses sta4t to escape they will heat the retort just like in your design. The problem here is that it can be hard to find the right proportions to make the retort stop burning at the right time. But if you don't use much wood around the barrel it works good. Also this method only works with pre dried wood.