The Torrefaction Process... Anybody know how to cook wood?

[Dolmetscher007]

For anyone out there who is not yet familiar with Torrefaction, it is a process of "baking" wood at temps between 200 and 320 degree Celsius (392 - 608 F), in an oven that has had all oxygen removed. Don't quote me on those temperatures btw... I got them from Wikipedia, and they sound a little too hot based on some other articles I've read.

The guitar industry has adopted using torrefied wood because you have basically aged the wood ~100 years in the course of a few hours. You have also increased the price of the damn guitar to the, "your firstborn child" level. I build guitars, and I can't imagine that it must be too hard to bake some wood myself. Here are the variables that I see...

***Disclaimer... If you are one of those, "You kids get off my lawn," finger-waggers that immediately thinks something like this must be impossible to do yourself, or that even if you could, it would be more trouble than it's worth... please just move on. I know it's nuts, and I am pretty sure that it IS more trouble than it's worth, but I am a dreamer, and I like asking questions and talking about out-there things like this with fun, cool, and imaginative folks on the internet. There's no need to wander through and take a dump on this thread just because it caught your eye and sounded a little nutty. Thanks guys!

Vessel: For my purposes, I'd only need to "bake" boards that are ~2 in. thick, and around 8" x 20". Since the temperatures are only around 350-400 degrees F, a standard kitchen oven should be up to those dimensions and temp. However, since all the oxygen must be removed, I'd have to have an inner box that is air-tight, and has a valve on it that I could hook up to a pump to remove the oxygen. I know a lot of guys that weld, so I imagine this part isn't as ridiculously hard to make as it might sound.  One problem that I would think would still be a problem is... the small amount of water still inside the wood would boil, and I imagine would be re-introducing O2. I guess you'd have to re-pump the air out every so-often until all the water vapor was gone.

Temperature: Torrefication is also the exact same process that is used to turn ordinary hardwood into charcoal. I only have a loose idea that the temperatures are between 300 and 400 degrees F. 

Time: I have read that Torrefied wood is baked for "several/many" hours. I can do several test runs, but other than the color of the wood, and maybe a moisture meter, how would I ever know when it's "done?" The moisture meter would probably measure zero or close-to-zero within the first couple hour or so. If the color also changes immediately, I might just be drying the wood out, and cooking it a little, but not thoroughly "torrefying" it. 

Flames/Bomb: I know from watching YouTube videos, that when charcoal is made, wood is superheated in an oxygen-poor env. until the volatile oils, resins, etc. ignite into a blue flame and burn off, leaving Charcoal. I do not want to turn a heavy steel box into a high temp pressure cooker, that blows my kitchen apart when the oils in some chunky maple boards ignite.

Anybody have any suggestions, experience, or research resources that I might take a look at? For the record, I'd do this in a crappy Craigslist oven out in my yard, but still. ;-) 

[Spanky]

You can kiln dry wood to 0 on moisture.  But, thats all I know about it.

[Chestnut]

So the pressure vessel concern in my mind is high. I assume the professional way to do this would be to have the heating element inside the oxygen deprived chamber that has a pressure release so when the gasses and water vapor expands it has an exit so you don't create a bomb. This creates issues with igniting the gasses ect inside the vessel. I think the difference between charcoal and torrification is that charcoal burns off the gasses and torrification just leases them without iginition.

Your over my head. Can't you just umm buy the wood torrified for you?

also GET OFF MY LAWN YOU FLEA BRAINED WOOL HEAD!

[Tom King]

I did a google search for:   how to torrefy wood          and found lots of information.   Looks like it's easy if you have the right oven.

 

[Tom King]

and a google search for:   torrefy wood at home       found a different set of answers:

https://www.acousticguitarforum.com/forums/showthread.php?t=373393

Looks like Martin gets someone else to torrefy theirs.

[wdwerker]

Maybe  vacuum pump to pull the oxygen & any moisture vapors out ? Or should it be charged with something like nitrogen ? 

[Jim DaddyO]

It does not have to be a pressure vessel.  If you use an inert gas, like argon, it is heavier than air and will "pour" into a tub.  This will displace the air, and thus give you an oxygen free environment to bake your wood at.

At least that is my theory.  Nice thing is that argon can be had at any welding supply place.  CO2 is also heavier than air, but not as heavy as argon, so more prone to be displaced by vibration and such, thus perhaps allowing oxygen (air) to come into contact with the wood.

[difalkner]

There are some guys over at www.luthiercom.org doing their own torrefaction on tonewoods.  You'll need to sign up with a login to ask questions or even read the posts.  Good group of guys, though.

David

[Mark J]

When the moisture is released from the wood it will be H2O.  The water molecules won't disassociate into H2 and O2 at that temperature.  So I don't think you need to worry after you do the first purge.

[Pondhockey]

You already have better answers but I'll chime in that pressure cooker valves are low tech and there are at least several possible easy ways to reduce or eliminate O2.  

On the other hand, at high temp you could drive endothermic reactions that conceivable could involve CO2, H2O or other gases.

 

[drzaius]

I'm following this out of curiosity. I really have nothing to offer, other than good luck.

[MattSC]

Ive never torrefied wood however I have made charcoal before.  To start I would try to cook the wood without charring it.   This may take some experimenting as far as temperature control vs charring.  This can be accomplished by simply taking a metal canister with a hole in the lid for venting on a hotplate.  Start with the cheapest wood source you have.  If this environment still has too much oxygen the next stage would be to go with a pressure cooker type design with an input and output line.  The input could be charged with CO2 to purge the oxygen then the input is shutoff.  The output should have a check valve to allow air to only escape please take great care to not close off the escape line.  Just another thought... Ive seen knifemakers wrap their stainless steel blades in a special metallic blanket to protect the steel from oxygen during the heat treat process.  Also this comment doesnt address safety concerns which should be researched before attempting.

[RealEddBenson]

55 Gallon Drum with a pressure release valve, a Thermometer, and and a line carrying Argon to evacuate the oxygen....
Black Iron pipe with holes drilled and hooked up to a propane tank, to heat...
I'm about to build one, and I saw all of the concern about pressure building up....

[Mark J]

I can't give you any advice, but it would certainly be interesting to follow along with what you're doing.

[Lewis McKinnie]

On 10/17/2018 at 3:28 PM, wdwerker said:

Maybe  vacuum pump to pull the oxygen & any moisture vapors out ? Or should it be charged with something like nitrogen ? 

First, you are wrong to declare that if you boil off water, you get oxygen (O2). Water molecules are H2O, and they are NOT disassembled into their constituent atoms by boiling. Disassociation of water molecules doesn’t begin to happen until 2,200°C. (About 4,000°F).  Second, you would not need or want a vacuum, and you don’t need argon to do this. Much easier to get a tank full of nitrogen and pump it into your container. Nitrogen gas is used, among other things, to inflate tires in auto racing circles. You should be able to obtain a small tank of nitrogen somewhere. Air is already 80% nitrogen. Pump pure nitrogen into the container and it will displace the “air”, including its 17% or so content of O2.