Charcoal production- rough rules of thumb

Has anyone got any working figures for the transformation from wood to charcoal, specifically the weight and volume ratios, and how the energy is split between the charcoal and tar gases? So far, on one successful test, I’ve got approximately one volume of charcoal chips to three volumes of woodchips- I’m hoping for a better figure with wood pellets. Does anyone have a figure for the weight ratios?

I’m getting around 18% charcoal to wood by weight. Use the direct method of charing. Also subtract the weight of water in my wood which is 20% moisture look at the fao info on this site
Also read fao publication on charcoal excellent find with google

Gary in pa

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Soooooooo… From Gary’s experience, and from here:
It looks like the weight to weight figures are between 5:1 for dry wood, and 7:1 for wet.

From here:
5 tonnes of dry wood yield between 70 and 90 MJ, or 1 tonne of charcoal, in turn yielding about 30 MJ.

The rule of thumb that I was looking for is: Two thirds of the energy in biomass is in the tar gases- does this sound about right?

The moral that I’m looking for is that I really should do something useful with the tar gases, whether cracking them to CO and hydrogen, or burn and recover the heat.

From here:

about three ninths of the fuel going into a vehicle actually drives the wheels, two ninths heat up the radiator, four ninths heat the exhaust.

You can probably see by now why I’ve got a bee in my bonnet about CHP and heat capture.


Ah. Good last post BrianH.
Now I know you are interested in actual personal usable IC engine shaft power and not just char making for the sake of it . . .
Your numbers stand up well to real in the world experiences.

IC piston engine are rule of thumb rated as 1/3 of the fuel heat converted into mechanical shaft energy; 1/3 of the fuel heat rejected out the engine cooling system; and the final 1/3rd rejected out the engine exhaust stream. Proportions will vary some with the engine design, the actual fuel used and Especially the engine load. Higher engine loads always means higher efficiencies. Important to realize that piston IC engine power is determined by the pressure/temperature differential rise in the cylinder. If you do not let out the un-to-mechanical-shaft converted heat energy the engine materials will overheat to materials failure points. If you do not let out most of the residual remaining unconverted heat and pressure energy you cannot next genrate that harvestable P/T differential on the next power cycle.

Once you step into raw tree wood fuels these “waste” gasifier and engine heats are no longer wasted as they are very much needed to dry, condition and pre-warm incoming wood fuel loads and input air. The dryer and hotter the actual gasifier incoming fuel whether raw wood or charcoal and the hotter the gasifer input air the more efficintly it will operate. It is by taking these non-ideal as individual 16% to 30% efficient processes and combining these into an intergrated system that you can then reach usable 70%+ full cycle efficiencies.
My very modern engineered made in Washington State and Washington State government certified raw wood heating stove is an actual 80% efficient at putting woodfuel heat energy to the space being heated. The other “wasted” 20% of woodfuel energy is quietly, cleanly, non-electrically and non-electronic needed draft drawing the woodstove; needed humidty and occupancy air change ventilating for a healthy house.
90%+ efficinciy systems ALL require expensive bought out refined spec grade fuels, lots of electrical pump, actuator and other motors, and electronic contols to achieve these 90%+ efficiency claimes. That last 10-15% efficincy is very expensive to obtain. Dimishing returns is very real and a finacial put into real world use system killer.

Just as you ran into local restictions contemplating using cardboard as a fuel stock, more and more places even here in the US of A if you are using wood based fuels in a CHP process it is now very resticted and directed to the point of being impractical and illegal in many places here already.
E.G. Here in Washington State ANY woodfueled HEATING device/system must pass a very specific set of lab tests using ONLY a specified predried amount of crib stacked stick form wood to be able to be “emissions” certified with a rivited on metal certification plate and be put into service. This has nothing to do with an actual closed cycle gasifier. But “der law ist der law”. I now know of actual two parties here had to cease all woodfuel based CHP work in my state ran afoul of these "local’ regulatory agencies.
So why you will not be hearing the word CHP cross my lips much anymore.

My Belgium brother-in-law living much as you do now has changed over his central oil burner and now happily space heats with commercial woodfuel pellets. He’s off that Dino fuel now. He will be expending into domestic hot water with his available woodfuel pellets next. He hopes to cut his propane denpandency then too.
Please do continue with your woodfuel engine pellet work.
He is now very interested in wood pellet fueled IC engine power for electricity as a cloudy weather supplement to his rooftop PV solar.
Ha! Ha! Operating IC piston engines on postage stamp lots with nieghbors is a whole developement project in and of itself!

Steve Unruh


Hi all, i have some info gathered about the influences at the temperatures in the charcoal process, yield rate and carbon content included.
Input material is bamboo in this case, but it is mostly same depending the wood you use, the hotter smaller yield, but more carbon and less volatiles.
i try to upload the pic of it.


interesting, yield and ash both increase from 900 to 1000 degrees.

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Does anyone have an idea of how much a gallon of charcoal weigh? Soft wood vs hard wood? I know I’ve seen it at one time. I just don’t remember where.

I have a large supply of white knit plastic horse feed bags that hold 20 gallons of charcoal. The bags weigh between 22 and 25 pounds. I weighed the bags and put a note in each one showing the date and the material the charcoal was made from. The charcoal in the bags is sorted and screened (to remove ash and fines), but not yet ground in the charcoal grinder.


So it’s a safe bet to say 1 gallon of charcoal is roughly 1 pound?

Just a bit more, like 1.2 pounds. I bought a ton of B&B Charcoal Fines, for agriculture use, and after sifting out the fines, I had many bags of larger pieces about the size of what we normally use for our gasifiers, except it was NOT usable. It is very heavy, very hard (a mixture of century old ironwood and mesquite from the Northern Mexican Desert), and smokes when burned. I have been mixing it in with the hardwood slices I use in my charcoal making cookstoves, and then it is fully processed and goes into the bags called “Engine Grade Charcoal”. The B&B is sold in grocery stores for BBQ and Smokers where they want a bit of smoke for flavor. We don’t want that.


Do you think that maybe they weren’t completely cooked down?

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Absolutely not cooked down. Impossible to break with the fingers. Sometimes when my 55 gallon barrel charcoal is down to purple-glowing embers, I can throw in a coffee can of the BBQ charcoal, and it immediately throws off blue smoke. They also pop like popcorn, so there could be water trapped inside?


Ray mentioned coffee and then popcorn , so here a little appetizer to go with it yummy charcoal


Is this a marketing ploy to get rid of the Cook’s mistakes?? :bread:


Hi Koen:
Happy Easter!!
Very interesting and useful Table. Do you recall where you got it?? What is the source of it?
Truly Yours.
Eddy Ramos.


And on the same table 2 (Post #5) on this topic, the percentages are based on volume or weight??


Hi Eddy,

i had to dig deep, but here it is


Hi Koen:
Nice to hear from you.
Sorry to hear that you have to dig it so deep, in that case it worth TWO thank:
Thank you and thank you very much! :grin:
Truly yours.
Eddy Ramos (Argentina). Also in quarantine :mask:


Excellent manual. Thanks. KOEN. I guess we’ll have to postpone that visit a bit longer with all this quarantine stuff going on. We’ll see what happens.