Making charcoal in a Keith gasifier

As some of you know, my truck has been down for a few months. I’ve been keeping it lit every week, to prevent rusting. But this process uses more char than it does wood, and eventually you will run out of good charcoal.

I’ve been looking into charcoal making for awhile now, and it occurred to me that I have a good fire-proof sturdy vessel already - the gasifier itself. So I want to make charcoal in the gasifier. My efforts may prove useful to other woodgassers who need some charcoal.

My first attempts were not worth discussing, I used too wet wood and force fed the air with a blower. Needless to say I got nothing. I tried a few variations on this, but no luck. I was always losing char, not making it.

After consulting with Gary Gilmore, I tried it again, with a top down approach and no blowers. This batch has just now finished and is cooling down. I peeked in at it and it looks pretty good, although there is some wood that went unconverted. By far my best attempt ever. I will get some pics in the morning.

In the meantime here’s a video.

OK, so I pulled out the charcoal this morning. I found some of the wood was still left unconverted, but quite a bit was charcoal. Overall I’m happy with the process, and would do it again. Out of 5 bags of wood I got about 1.5 bags of charcoal and half a bag of “brands” or charred wood. All the brands were in the hopper out of the direct path of the air. Everything past the nozzles was good charcoal.

If I were starting a brand new gasifier, it might work to just fill it with wood, make charcoal this way, leave it closed up overnight, and start the gasifier normally. It’s at least as quick as the bagged charcoal method. With some refinement I think we’ve got a winner. I’ll try it again as time permits.

Another video:

I’m sure it’s posted some where on here, but what happened to your truck that it has been down so long?

Hi Chad,

It had a major air leak in the grate area. We’ve actually rebuilt it and it’s back on the road now. Thread here:

Does charcoal work as fuel in the Keith gasifier ?

The Keith design operates like a charcoal gasifier when it first starts. That’s why there’s very little smoke. Then as it warms up it begins gasifying the wood.

As for straight charcoal; I think it would work OK, but the temperatures might increase. Without moist wood to control the reaction, you might get a lot of extra heat. It’s just a guess since I’ve never tried it. Possibly moistening the charcoal would help with this. It’s an unknown until someone tries it.

As much work as it is to make charcoal, you’d be better off just burning the wood directly.

Chris S: Aren’t I correct in remembering that a WK gasifier produces a fair amount of Hydrogen gas, a powerful fuel? From my readings and viewings on the Charcoal Gasification side of the forums, I gather that straight charcoal doesn’t produce any H2. Raw wood with it’s volitile compounds and H2O is needed for the H2 and also some of the more complex hydrocarbon fuel chains.

From what I’ve read, the charcoal making process removes a vast majority of the energy potential over raw wood, something like 4/5ths if I remember right.

Brian, you are correct that hydrogen is a powerful fuel and that the charcoal making process removes nearly all this element. You loose a little more than 1/2 of the energy potential in wood when you char it. Your 4/5 rule is closer to the weight loss ratio. Figure around 80% loss in the weight of wood when you convert it to charcoal. (Do not forget to add in the weight of water in the wood when calculating loss)
Charcoal has some distinct advantages. No tars to deal with, light weigh fuel, light weight gas generator, light weight filter, easy to make and grade charcoal, easy to build a gas generator. It is ideal for small engine usage with quick start up time.
Many people are bothered by the “wasted” heat given off when making charcoal. Did you know that if you let a piece of wood rot away, it will give off the same amount of heat as if you burned ? The heat capture will come about some day as I build a stove to make char and heat the shop. But in the mean time, there are tons of wood rotting away and I am on a mission to char it. (most of it will go for biochar)
Gary in PA


I’m wanting to try something similar in heat capture.We heat only with wood and was thinking about a 8x18" pipe with a lid and vent hole to fill with 2x2’s or round wood and place in the woodstove in a good bed of coals with another chunk of wood or two and let it cook off in the stove and capture the heat from the gas to help heat our house,then pull out the pipe and place in a ash bucket and let it cool outside before placing in a steel 5 gal bucket.
I think a lot of charcoal could be produced over the heating season just from larger prunings from the yard.
It’s more than a pipe dream and hope to try it next fall.

Paul, this is kind of funny. About 2 hours ago I found this website and they tell how to make “biochar” in a stove.
I know others have been doing this, but after reading this article, I looked into my Harman top loading stove and thought “Maybe I’ll give this a try.” We will have at least another week of lows in the 20s, so maybe I’ll slap something together tomorrow and give it a try. I know it will work, just not sure if it is worth the bother. Time will tell.
Gary in PA

Gary,that is what I had in mind but wasn’t sure what type of lid to make but his threaded rod style seems like it might be the ticket.

Hi Paul, Gary,
This winter I got overloaded with stuff to do so I let my 2 barrel retort go cold (and snow covered).To compensate I’ve been playing around with the vessels in the fire method. It works great and what is remarkable is how primitive a container you can use. I started with some paint cans which work but are small and lately I made up some square boxes that fit through the front door and go along the side. They work great and what’s even beter they force more heat onto my water heat exchanger. These ones were make with scrap; just some steel stud track and some flashing held together with sheet metal screws. No need for airtightness, punch a few holes where you want most of the gas to escape and that’s it. These are just disposable prototypes but I have 10 runs on each of them so far. I prefer the squares to the circular containers now. I run one in the evening only at this time of year but on colder days I could tag team them. Once it is burnt down and coolish I remove it from the stove and place it in a metal garbage can with a lid and take it outside. The biggest drawbacks are the loading unloading of the bins and the loss of coals that results. I throw one in onto a good hot fire and stoke the fire with some small pieces of softwood for fast heat. Once it goes off the heat drives the process. No pictures of them sorry… Got to go collect sap…
David Baillie

Thanks David,when you mention it,a square container would fit better in the stove.

I use 5 gallon paint cans, and the whole Gilmore-compliant process usually only takes about an hour from the time I light it until the time I shut down the retort. True - it doesn’t make much at one time, but doesn’t take as long either.

Since we have 9 months of summer in Texas, we only have a small heat stove, and don’t need it often enough to justify building a charcoal-making system into it.