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Id like to build a kiln that is somewhere in-between and then build a grinder that can handle the torrified wood. Id have no problem putting the wood in with the charcoal in the charcoal gasifiers. So the gasifier I think could still be simple.
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Kristijan - that’s where my instinct to use engine exhaust comes for. That heat is consistent and won’t lead to combustion. Exhaust gas is “wet” in that it has a lot of water vapor but above 100c it will still dry and heat wood. And direct application of exhaust gas won’t light the wood on fire - no oxygen.
Just have a staging area for your wood fuel that gets bathed in exhaust gas. As long as the exhaust stays hot, you’ll get dry, torrefied wood.
Channel the raw wood through a covered chute on its way to the gasifier. Then channel engine exhaust through the same chute. Wood progresses slowly through the chute getting its heat treatment before falling into the gasifier. The “fresh exhaust” is introduced close to the gasifier and flows towards the raw wood source - counter-flow style. This is so the wood is treated by the hottest exhaust last.
The trick is diverting the exhaust gas away from the raw wood before the temperatures drop below 100c and the exhaust condenses all its water on the wood. There should be plenty of embodied heat in the exhaust gas to treat raw wood. In any case - it’ll be bone dry from 500c heating, at least if the chunks aren’t too big.
Exhaust heat is free and consistent. Best to use it?
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One challenge is smoke, or heavy steam and you can catch fire.
But Ive dried using direct exhaust gas, the fuel was wet but it is from interior moisture that has bled out on top of the exhaust gas. The wood is degassing in this process so it dont matter if the exhaust is wet, the wood can not absorb it in that environment.
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What if we were to build a TLUD with a drop out bottom? So you build up charcoal on the bottom half and the top half will be torified. Once you have processed the fuel drop the bottom out into a catch container.
Chips or small chunks would probably be best for that.
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I built a charcoal maker somewhat like that It was a 55 gallon drum shaped into a cone with a sliding door on the base. It sits over a two foot section of an other drum. Burns small branches and stuff. Got the idea from Don Mannes charcoal maker. Char comes out almost fuel size. I’m going to start using it again shortly. I’ll post new pictures. This picture is when I first built it so it’s just sitting on a trash can.
When I first rejoined the site I had a discussion with Oregon Carl about reusing waste heat from charcoal making. My solution ended up being a combo radiant greenhouse heater and hot water heater. Haven’t used it yet. I think I only have one pic. It’s a 30 gallon compressor tank inside a 44 gallon well pressure tank. I’ll do better pictures or a video when I start using it. Inside the inner tank is a copper coil. Along side the heater is a 500 gallon water tank. The heater gets fed fuel from the top. Chunked wood would be best. As it burns it heats the water in the jacket between the tanks and other water thermosyphons up the coil to heat the water in the storage tank. Char can be continuously shoveled out an access door at the bottom and put into a sealed cooling container. I would still like to get more out of the flue exhaust. I’ll be thinking about that.
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A lot of good info in the above postings, let me ad some insights…
Moist or anything other than Carbon in the fuel does have its benefits and purposes.
Pure dry wood does not spread out fire , transmit heat, as a little moist does inside.
Pure carbon, you could hold a 1200ºC glowing carbon piece ( one side ) and hold your fingers just few distance away on the non glowing part…
Pure dry wood into a charcoaler ( retort) takes a different time , different tactics then when a bit moister is inside…
Lets say you make a wonderfull perfect fuel, any kind… then its easy to build a gasifier purposed for said fuel.
Hence why i choose charcoal…
If you drip water on glowing charcoal or oil, plastic, anything as burning/burnable liquid… it will each time take some and give some energy, most certainly it will change / enrich your gas
If you drip tar/condensates from the charcoaling unit instead of water, you’ll get a richer/more powerfull gas per volume as hydrogen have less energy per volume then CO or other gasses
(ethyleen, methane, pentane… ) that wil be present when adding different stuff in the glowing zone…
Bottom line:
Different fuel/mixture = different gas proportions = different system to use
If you breakdown the mass balance from a woodgasifier, how much condensate, soot, ashes, carbon residue is produced or how much input is turned into shaftpower ?
So many idea’s are possible, so many builds to read about , with pleasure, so many different insights.
Keep thinking out of the boxes, keep sharing…
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Kristijan had really got me thinking a few months ago about Charcoal. In a down draft configuration, added charcoal can really be thought of as a moisture catalyst instead of just a fuel.
I remember reading Chris S’s intro to the WK Gasifier how he used mostly charcoal in a FEMA. The charcoal was sucking in the tar to help it get burned away!
I think premade fuel grade charcoal can be a huge bandage to downdraft reactors with moisture issues. Like how Kristijan says to try a mixture of wood and charcoal.
I too look at it that way. A condensing hopper kinda works the same, shifts the ratio between carbon and water in the fuel. But unlike you guys used to the luxory of huge pickup beds l had to come up with a smaller, cooler and lighter way and for me mix fuel in a downdraft gasifier is what works for me.
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Do you think mixing charcoal would make a Hot Hopper reactor work better?
Depends on what you mean with better?
Let me throw in my experiances with hot hoppers. I had one with my Chevy. It was a tiny 10gal or so hopper insulated with rockwool on the sides. It was a raw wood gasifier, chunks. Driveing looked like this. Because the residual heat from previous runs baked off the water it lit up like gunpowder. And within a half mile of driveing l had full woodgas power. Then, after say 6 miles the new, raw wood started to emit steam and by the time l got to work it was cooking off so much steam it was not able to idle any more. Hopper gas wuld displace air from gasifiers intake causing catastrophic cooldown. Not only is this mode a nusence because no idle, its also when tar gets made!
But it kinda worked for me, mostly driveing to work each day. But! It was the longer drives that got interesting! So, the hopper hets super hot on the inside. Time for refuel. Fresh chunks in, back on the highway. In a few miles the wood gets so hot inside it starts to pirolise in the entire hopper! It becomes a charcoal kiln on wheels.
This creates super hot steam and hopper gas wich must pass trugh the charbed. Displacing some intake air and with that nitrogen, this gas super rich gas is incredibly powerfull. Im talking like my small 1.6l car got up to 130kmh no problem. Close to gasoline power.
So where is the problem? Apart from severe heat stress on the components, specialy hopper lid seals, now imagine this self propelled charcoal making hopper when you slow down. All this superheated tary gas needs to go somewhere and there is A LOT of it. Not only will suffocate with super rich gas, gases will start to spit out gasifier intake like a smoke bomb, with the engine runing! It is in this mode that the engine floods with tar and water.
Dont get me started on refueling! Imagine opening a charcoal making kiln on the roadside!
Then we come to condensing hoppers. Thats a great solution if you got the ability, space and can afford heat. And complexity. Also, what many dont realise, the hopper doing its thing internaly, circulating heat to the outside, comes at a price! Something needs to produce the energy to boil off and recondense the steam. This, althugh small, energy is taken from the gasifier. Every bit counts…
What l currently like to do is mix wood chunks with just the right amount of ENGINE GRADE charcoal that every void between the wood chunks is filled with charcoal. Koen hinted wonderfully whats the point of this. Its the incredible heat insulation ability of charcoal!
In a way, l wrap each chunk of wood with insulation 
since the voids are filled, there can not be any convection currents in the hopper, and the litle amount that is present is sucked by charcoal and downflowing fuel. Only the actual peace of wood in contact with live charcoal and oxigen will catch fire, no more. No pirolisis zone! Charcoal blocks all radiant heat upwards so no wood preheats in a top lair, but it doesent need to because again we got charcoal to boost the heat up and restore the function we lost with eliminating the pirolisis zone!
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Fuel mixing is where our down draft charcoal units have an advantage I think. If you mix in raw or torified fuel with the charcoal in the down draft the fuel has to flow through the combustion zone before reduction process. Its just the opposite for an updraft.
I am now experimenting with leaving all the raw wood drop through in the charcoal to see what happens.
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This is what I have been doing with my WK Gasifier, mix wood and Charcoal. Kristijan and I call it Rocket Fuel mix. When he was there with JO at Argos 2019 we tried it out.
I just start up my gasifer pour in some wood and then charcoal on top of it , pour in some more wood and Charcoal on top of it. It mixes as you go down the road. You do not need to add any moisture to the charcoal because the wood will give off moisture as it gets cooked down.
This also helps with the hopper condensation water will be less but the tar will still be about the same, maybe a little less. When I did this I had no exhaust preheater air going into the drop box. Now with the extra preheated air it works even better.
All of my dumped charcoal ash is screened and the charcoal goes back into my gasifer for a second complete burn. Only fine
Charcoal dust, and ashes are left, and it goes to the garden.
Bob
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One more thing I forgot to share, if you put your charcoal that you made with your gasifer back in for the second burn your mileage for a pound of wood will increase with every added load. Even my fire pit charcoal helps increase my mileage. There’s nothing like sitting around a campfire making fuel for the truck with friends having a good time.
Bob
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My common sense brain tells me that it helps reduce the caloric cost to pyrolyze as much wood, and fills up more space that the chunks can’t naturally fill all the way. I’m probably wrong on the first point.
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You are right in both statements, the waste charcoal being added back in is free heat in caloric valve that would normally be lost to the garden. And is does fill in spaces and help move H2O through the system making H2. This is because there is no heat being used to make it into charcoal and the charcoal creates more heat. It is a win win anytime you do this.
All it takes is some screening out the ash and fines. You do not want to put fine charcoal engine grade charcoal into the hopper it will constipate the charcoal bed and that is not good.
I have been doing this for two or more years now, and it works for me. It give me the extra power to go up hills with out having to blend in gasoline fuel. I look at it this way. After passing the nozzles the gasifer is a charcoal gasifer just with extra moisture to deal with, and more soot to filter out of the moist gases.
I still have in operation my grate shaker.
I occasionally use it going down the road. Most of the builds do not use them any more. A push of the buttom shake the grate fill more power to the engine with out moving the gas pedel. Got charcoal use it the second time around. Use it and reuse it up and it is gone.
Bob
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The charcoal ads to the active glowing carbon % needed to do all kinda conversions.
In my experience, more carbon = less Tar passing thru
Hence: Charcoal gasifier with highest % carbon = no tar 
But, the converted tar ads an non neglectible quantity of mixed potent gasses.
Somehow i can see and measure more benefit from adding Tar/condensates instead of water.
In a stationary system its easy to manage to get and maintain a steady state level.
A homebrewed versitail system is far more challenging, a kinda art-form to operate them , not for lazy mindsettings…
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Not sure what you mean by this; it seems to go against what you are trying to say?
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When you are already burning wood you are Making fines already. Some of the smaller engine grade charcoal seems to plug my gasifer up at the grate. Pop corn size and larger is alright. It might work for someone else gasifer.
It just doesn’t work for my setup. I plugged my Char bed up at the grate trying to use the finer charcoal. It would work great in a charcoal only gasifer. I like to run my charcoal bed loose and slip charcoal. This is how I make it so fast. I dump my ash often. 200 to 250 max miles. I save the smaller charcoal for my charcoal gasifer. I have three 30 gallon barrels of it for my emergency generating use.
Nothing going to waste until it is just ready to go into the garden and that is not waste at all.
I just reuse and reuse and reuse that wood I worked preparing by the sweat off my brow.
Bob
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Fines in the garden are a good use.
I had a thought that fines could be introduced to the gasifier on sort of a fluidized basis. One option would be to meter out the fines directly into the intake air, very close to the nozzle (for better safety) or as it’s own feed into the combustion zone (though again, near the air nozzle so it fluidizes. Such a “booster” would be especially good in a wood gasifier that’s running a bit cool from say moist fuel.
Fines have very high surface area and so fluidized in fresh air they will burn very quickly and vigorously - maybe too quickly? It’d be careful with amounts and blow back if you investigate. And avoid optimal stoichiometric ratios of air and carbon in the delivery. You want either a very lean mix of fines (air intake) or a very rich mix (directly introduced - separate from air intake).
Think of it like water drip in reverse?
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