Information about wood as energy

Hello all,

I would like to give the woodgas science category some love and share with this very helpful community some of the knowledge I’ve learned.

While trying to understand wood gasification and its potential, I discovered that not all wood or even parts of the the same wood are equal. There are different things that effect how much energy can be extracted. We have all heard about moisture content, hard and soft wood, and fuel size but what about volume, gravity, structure, heartwood and sapwood, and the chemical properties of cellulose, lignin, and hemicellulose. All these vary greatly between wood species. A combination of these variations limit what can ultimately be extracted as productive energy. This is why no one has really solid numbers for run time per wood weight or volume.

Knowing the type of wood will give you a hint to it’s structure. A softwood has less structure and allows water to move through the wood faster than a hardwood would. Having less structure also means a lower density per same volume of space. This translates into faster extraction of oils and water from the wood and less cellulose to break down into volatiles.

I’m sure most of you will remember the gravity lesson from science class where you measure how much water is displaced by a submerged object. If you know the percentage of holocellulose verses lignin (the difference that makes it a hard or soft wood) and you know the gravity and density, you can figure out this run time if you are under identical circumstances.

Moisture content is important because it cost energy to extract it from the wood so the wood may then be consumed. This is besides the interference (cooling of the reaction), pressures, and volume loss that cause problems in gasification for internal combustion engines. The maximum moisture content of wood is related to its gravity. The maximum practical limit for living wood is 80% moisture content. You will find that heartwood and sapwood contain their own percentages with the sapwood containing the majority in softwoods. This difference is dependent on external factors such as season, soil, elevation, and region. To burn a piece of wood, you must first heat the wood until the water is able to escape the bounds of the wood structure. Think of how much energy is needed to boil water in the temperature you are in and than how much energy to give it enough steam pressure to push through the cellulose structure of the wood. Only then can you start breaking down the wood itself. Sapwood has what is called free water, hardwood has bound water. As you can gather from the terms, free water is easy to remove and bound water is not as easy.

So what is wood made of anyways!? Where does this hydrogen and CO that is being produced come from? Wood is made up of glucose (sugar), xylose (sugar), mannose (sugar), galactose (sugar), arabinose (sugar), glucoronic acid, rhamnose (deoxy sugar), phenylalanine (amino acid), sinapyl alcohol, coniferyl alcohol, and para-coumaryl alcohol. This combination means that wood acts as a polyalcohol, which is also called sugar alcohol (surprise surprise). As you can see the wood is mostly made up of carbon, hydrogen, oxygen, nitrogen, and some extras that don’t really add up to anything. Carbon and oxygen split up the majority with hydrogen containing less than 8% and nitrogen less than 1% of volume. If you look at the cellulose molecule, you will find an oxygen atom bonding the repeating group together. This is the first bond to go at 435-625 F. This separates the sugars which start to break down at 620-715 F. The alcohols break down between 475 and 933 F. The tar byproducts produced break down between 1,470 and 2,375 F.

Converting these volatile compounds that wood releases into other useful compounds and straight elements is what gasifiers are all about. They are basically breaking down the sugar and alcohol in wood into cleaner burning gases.

Have a great day j;-)


Thank you, that was some very good help full reading for me.
Keep on Gasifiing. Bob

Hi J,

How do gasifies go about breaking down the sugars and alcohols? Is it just heat?

Thanks, jeff

Thanks Bob.

Hi Jeff,

The information I have is about the pyrolysis of wood. I’m still getting up to speed reading the documentation about what happens in the char bed when the compounds I talked about pass through.

From what I understand so far, is that it is all about heat without oxygen and nothing to do with activated carbon outside of providing surface area to help react all the oxygen. I think that it would be a good experiment to increase the number of air nozzles by layering them in the cone. Not more air, mind you, but more air being distributed along the char area in the cone. It says in the documentation in the library that the char cools the gas to 800 C almost right away. Increasing the length of supplied air will keep the temperatures up where they need to be to crack tar for longer. I think that using a ceramic cone might also be something to try to help hold heat and provide surface area.


Hi Jason,

OK, so that helps to explain the advantage of heating the inlet air.

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Yes, preheating the air will increase the normal temperature of the wood, boiling off water, before it reaches the area of energy where pyrolysis can begin. If the chamber and wood is already 212 F, there is no energy being spent to boil the water in the combustion zone.

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Interesting. If that’s true, it would be a boon to gasifying other non wood materials thus far the understanding has been that you needed primarily wood to provide the char for reduction. Perhaps some other permanent surface area?

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Hello Jason and welcome to the DOW.

Thanks very much for your post. With your knowledge of wood I think you will fit right in this group.

Once I was told a joke of a guy that could wear blindfolds and smell a piece of wood and tell it species , were it was grown, the side of the tree it grew on , age ,moisture content and the type of building the board was on ( which was an out house )

Perhaps it was not a joke and your were that guy :grin:



The hot carbon is critical. This wouldn’t work with hot lava rocks, for example.

Remember that those raw components you mentioned are burned up with the incoming oxygen. This consumes nearly all the pyrolysis gas, and leaves exhaust gases - CO2 and water vapor. These gases are what go into the char bed, and get converted into CO and H2. The reactions are fairly simple, but do require hot active carbon.

CO2 + C = 2 CO

H2O + C = CO + H2

So you see, in each of these the C is critical. These reactions both require massive energy input, which is why once the char cools down there is no reaction. Extra oxygen can be added to boost the heat:

O2 + C + C = 2 CO

This will penetrate some of the ways into the char bed, in what we call an “oxygen lobe”. If it reaches the grate you’ll purge out any fine particles. If it goes below the grate you have overpulled it, and you’ll see a spike in heat - the oxygen burns up the finished gas.


Thanks Wayne,

That is pretty funny. I’m not going to pretend that I’m an arborist that knows all about arboriculture :wink: Just another interested party that likes to read. I believe that biogas/syngas is part of the puzzle for energy independence. Matt is building me a micro s-1 gasifier to play with. So I’ll soon have soot on my hands and some real world experience.



Thanks Chris,

I’m still getting up to speed. I’m wondering if the ratio of carbon to oxygen in the plant matter plus heat is all you need. If you look at white oak, it has 50.4% carbon, 6.6% hydrogen, and 42.7% oxygen. Would the C and O combine to make CO with just heat and no outside air?

If you would like some of my reading…

A great paper on the thermal degradation of lignin from this library.

Structure and properties of cellulose

Maybe the next thing to try is strapping on a microwave

Thermal decomposition of cellulose insulation

Kinetics and Mechanism of Cellulose Pyrolysis

I doubt that I will ever learn all that is going on in a gasifier but one can learn quickly enough to make it go down the road.


Hi Jay,

I don’t think so. Maybe it’s tied up like in water.

Good to read that Matt is building a gasifier for you…! The teckie stuff is interesting but the hands on rocks my world.

Carry on…!


Good Morning JayMc
You were doing fine with your first post. Only other fellow to talk this way in that depth of woods components has been Greg Manning.

However now later you are making it entirely too complicated.
A feelow does not have to understand the maths and physics to throw a mean curve ball; Sink a half court; put 200 grains of stop’em into the heart/liver of an elk from a l-o-n-g ways away; make any complex manufacturing/refining system exceed the performance that the math boys and girls would say impossible.
Ha! Just ask any really good sugars candy cookers; sratch bakers; really good scratch soup makers about “feeling” into the best results.
Honestly the maths approch is really just to get very stable perdictable results, repeatedly, time after time.
Why major beers are so predictable . . . . and boring.
This is all good to impress for Investors. Good to impress the Board. Good to impress for Grant writing.
Totaly unessasry for DIY make your own powers from wood fuel. Personal space heat. Personal shaft power. Personal “others” refined down wood carbons “powers”.

Yeah. Yeah. Externally applided energies “gasification” been done, documented and beat to death in the 1990’s.
Not a single system still in use, now, today using this approce.
Back to that externally needed energy input. That energy imput will always have a cost to make/obtain whatever the base source. And those energies external have better money making/saving uses that will always out-compete wood gasification needs.

The beauty of free air woodgasification for power is that it is nearly all resources inclusive in the wood. The molecules needed. The thermal heat energy needed.
Some smaller percentage of the thermal heat needed in that first oxidization stage. The MAJORITY of the thermal energy needed is in sacrifice oxidizing some of the freed up wood charcoal THESE WERE THE CELL WALLS STRUCTURES. This highly gases exchange porous and un-measurable reactive carbons surface areas is the part that maths out poorly versus the easy O’s, H’s and C’s balances.
Why the touch, feel, smell folks can do so well at blacksmithing, woodstoveing, and gasifing for power. Nothing past simple maths to make enough availble gross wood fuel is needed. Much more important is the willingness to accept the need for the repetitive woodswaet that will be needed for in real in this world today meaningful use.

Burn to learn man.
We are all just on our way to better
Steve Unruh


Hi Steve,

Thanks for your input…

This is why I’m interested in the math. Predictability, reliability, and dependability are goals worth reaching for. This topic is in the science category :wink:

All engines and power systems use energy to create energy. To dismiss a preheat system just because it uses some of the energy is folly. Understanding the math is necessary to building automated adjusters for choke plates, nozzles, and intake air. The fuel to air mix we are using in our engines is all math that was sorted at some point. Yeah I could pull the choke and find the right mix but I’d rather the engine do it for me.


They are not using energy to create energy, cause energy cannot be created. They are just turning it into a different kind of energy :smile:

I like your post however!


Thanks, I know that energy is transferred not created. I was thinking of using electric energy to release stored energy used to create kinetic energy to then create more electricity.

Create as in to cause to happen; bring about; arrange, as by intention or design

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Hi Jay,

When is Matt going to have your gasifier completed? What are your plans for it?

Take care…

Good Morning JayMcB
My sincere apology I did not see that your topic was in the Woodgas Science area.
This is a new dedicated sub-area on this new off of Drupal DOW format.
You topic is very approriate for this section.
Sigh. I have chosen to not participate in this section of endeavor. Sixty plus years of this approce to woodgasification for power has been a no-show. Mostly this has been due to down-pricing by the oil-for-power producers. But valid evedence in the 1950’s to early 1970’s show that the Seven Sisters Majors were perfectly willing to go to indirect and direct actions agains anyone wanting to break, or break into thier game. Then OPEC since the 70’s to now. Ha! Now only four of the sisters.
So no matter how the science and tech applications would be advanced there will be no general use of bio-mass gasification untill the middle east cheap to put on the market oil is used up. Then the next cost tiers of producers like the US, Russia, Nigeria and off shore stocks will become the big money players. Playing the same suvert any comptitions games.
For woodgas for power Real, Use, Today it be the willing to make it come Hell, High Water, and the Coming of the Regulators in working bootleg willing blacksmiths and woodstovers.
This is where my focus has been the last two years
No longer willing to woodgas science, tech "improvements talk.

Again my aplogies on the older DOW format this kind of exchanges in General Topics section was actually off-putting to many who would have been weld-up users. I am more guilty than most of doing this in the past.

Since I have squish stepped into your topic as an I Owe You Now here are a couple of real world wood ofr fuel factors that you can include in your maths developments:
Every different species of woods will have a different basic range of minerals in their cells structures.
This can vary from sightly under 1% to as high as ~10%.
This mineral ash once freed up will have a huge effect on your gasifier flows performances and down stream separation/cooling/filtering train. The actual melting/fusing temperatures of ash mineral is very close to the needed tempeature you must have in the oxidation/reduction transition zones.
The good news is woods without bark these mineral ashes are a few hundred degrees F above the best temperatures you will need.
NOT so with most high silica AG residue fuels.
My outside engry complaint was your reference to microwave and other outside heating of any of the gasifier process.
Any and all IC engine heats are fair game as those energies were wood-for-fuel derived.
Although possible to use gasifier woodgas to fuel for electricty to make "other forms of input energy ypou will never get back the transitions steps Engine → Generator-> to microwave/electrical arc/element to come ahead.
(to give you your best go-forward use the low intensity heats off any, and all transition step to out of system moistures reduce the wood fuel BEFORE going into the hopper.)

But hey. Don’t take my word for any of this. Try. Do. Prove it with results.

Carry on Guys. I’m otta the science business.
Steve Unruh


Hi Jeff,

I’m not sure when Matt will be done. I’ve tried not to put a bunch of pressure on him as I know he is busying making his business work. It should be before Christmas I think. I plan on using it with my trash pump, wood chipper, impact hammer mill, and getset. I like to go camping and gold mining. Plenty of wood here in Texas and Colorado. Once I figure out the power draw on the blower, I’m getting a solar panel and charger so I can cook with it also without running a genset. Check out that burner!