Thread: The science behind burning wood

No matter how long or much wood I burn, I am still entertained and inquisitive of the science behind burning wood. I shove 1-2 cords of wood into the stove, and I am left with 3-4 gallons of ashes. I still think that is amazing! OK Maybe I am as easily entertained as a 6th grade chemistry lab student. But really, you put a solid piece of wood in, heat is applied, then heat is released, gases are created, chemical (or is that physical?) reactions occur, smoke is produced, and ash is left behind. How cool is that?

Where does all the extra "stuff" go? Does the smoke carry away the volume of solids from the wood with it? Is there a cord of wood "dust" dropped out of the sky for every cord of wood burned? Water vapor takes up part of the space, and enters the water cycle again. Hey I am solving world drought here!

These are all thoughts that I must ponder while feeding the fire and watching the snow fall.

What if you sealed wood into a chamber, and heated that chamber to 400, 800, 1200, degrees. What would be left at each phase. How would this differ from a open stove with air/oxygen going in and waste gases coming out. Would you have charcoal, or at some point does it break down and become just ash.

ponder ponder ponder....

I tell my daughter we send the wood to tree heaven, and we can find new ones in the spring out in the woods. Works for us. I'm sure some day she will be a bio-chemical engineer and tell me the truth, and I might be heart broken.

Please post a picture of your stove that holds 1-2 cords of wood.

Originally Posted by hanniedog

Please post a picture of your stove that holds 1-2 cords of wood.

Hey I shove 6 cords through mine!

Cabin fever affects each of us differently.

Wow. Where to start? The simple answer is that it all goes up in smoke. You are converting the carbon in wood which is bound up with hydrogen and oxygen and converting that to gases like CO2 and CO, as well as H2O and other compounds. What gases are made are determined by burning temps. there is also particulates that are emitted (which is the actual smoke), but that should not be a significant mass of material, as we are talking grams per hour.

Instead of thinking about volume (cords) you need to think about mass and the conservation of mass (never created nor destroyed, just changed form). So, while you burn a cord of wood and get 4 gallons of ash, I generate 3-4 gallons of ash every four or five days (because of different ash density). The difference in mass between the cord of wood and the mass of ash removed is the mass that has been "lost" through your chimney.

Charcoal is made when wood is burned in an oxygen deficient environment.

Originally Posted by hanniedog

Please post a picture of your stove that holds 1-2 cords of wood.

I never said how long it takes to get that much wood through the stove.



Just as I suspected, I am moving a massload of wood somewhere. I'm planning on doing more research and when I get the particulates figured out, I'll report back. I still say that must be a lot of wood or changed form mass going out the chimney. If I only lost a few grams, then the ash bucket would be so dense and heavy, I would never be able to get it outside.

Burn baby burn.

I gotta get moving, the snow snakes are really getting going and I better get them under control before they over run the place.

Originally Posted by Mike PA

Wow. Where to start? The simple answer is that it all goes up in smoke...

Hmmmmmm.... That’s not quite 100% correct.

The burning of wood is a chemical reaction, requiring (enough) heat and oxygen. Wood, like all living things, is hydrogen, oxygen, nitrogen and carbon based but also contains varying amounts other elements. During combustion molecules are broken down and most of the carbon atoms bond with oxygen atoms forming carbon oxides (CO, CO2, etc.) Also, large amounts of hydrogen, hydrogen oxides, nitrogen and nitrogen oxides are released along with smaller amounts of other gasses. These gasses are colorless, un-like smoke they can’t be seen by the human eye. Heat and light is produced during the chemical reaction and is released as radiation. The left-over ash is made up of heavier trace elements that couldn’t be converted it, such as iron, lead, potassium, calcium and so-forth. The hotter the fire, the less ash left behind.

Smoke is made up of un-converted particulate matter (solids) that gets carried away before it’s converted, usually produced during low(er) temperatures (like when the fire is just getting started or under low oxygen levels). Get the fire hot enough, feed it plenty of oxygen, and more of the “smoke” gets consumed (or chemically converted) in the flame.

Now we get to Einstein’s famous equation, E=MC2, which can be shortened to E=M, or Energy=Mass.
Energy, or mass, cannot be lost; it can only be converted from one form into another. In other words, if you start with 10 pounds of wood and you could capture all the smoke, ash and gasses created by the fire they should weigh 10 pounds... Except it doesn’t quite work that way, you’d come up a bit short because you’ve forgotten to allow for the heat and light radiation. The heat and light radiation also contains some of the mass, mostly electrons, anti-electrons, photons and some other, more exotic, sub-atomic particles cast off during the break-down and re-formation of molecules. You would also have to capture all those particles (not to be confused with particulates) and add them to your bag of smoke, ash and gasses before it would weigh the full 10 pounds.

Hope this helps? :smoking:

Originally Posted by Mike PA

Wow. Where to start? The simple answer is that it all goes up in smoke. You are converting the carbon in wood which is bound up with hydrogen and oxygen and converting that to gases like CO2 and CO, as well as H2O and other compounds. What gases are made are determined by burning temps. there is also particulates that are emitted (which is the actual smoke), but that should not be a significant mass of material, as we are talking grams per hour.

Instead of thinking about volume (cords) you need to think about mass and the conservation of mass (never created nor destroyed, just changed form). So, while you burn a cord of wood and get 4 gallons of ash, I generate 3-4 gallons of ash every four or five days (because of different ash density). The difference in mass between the cord of wood and the mass of ash removed is the mass that has been "lost" through your chimney.

Charcoal is made when wood is burned in an oxygen deficient environment.

This^

The easiest way to look at it is as a box, something is going in and something is going out.

Going in: Air (includes oxygen and other gasses), and wood

Going out: Ash, CO2 and other gasses, plus a small amount of particulates in the form of smoke.

The Other gasses going out includes the other inert gasses that went in, and other gasses that are a by-product of combustion. Those can literally be a number of different gasses depending on the particular wood type and fire, one of the more notable possibilities is CO (carbon monoxide).

No, there is not a cloud of ash equivalent to a cord of wood floating around out there somewhere. The great majority of what is expelled from your stove is just gasses.

Talk about mass...I had beans last night with the ribs...got gassy this morning...must have lost 10 lbs.LOL

It is a chemical reaction...it is the rapid oxidation of the wood, which produces light and heat. It is the same process that makes iron rust...but a lot faster.

All it takes is heat, O2 and a fuel source.

As I understand it, almost all things are made of carbon or a form of it. My wood is converting from whatever it might be now, to carbon oxides, and drifting away. Man I am one chemical converting dude, Nifty! (edited because you can't say an excitement word left over from the 70's)

So my sealed box, no matter how hot it would get, assuming I could trap all water vapor and stuff, would not weigh any less, because 1. there is no oxygen to allow the carbon to convert to an oxide and 2. there is no getting out of the box for the little carbon particles. Your stuck sucker, go sit with the other random bits. So if you got wood hotter than most wood fires, but with no oxygen, do you get charcoal or does it turn into something else?

"No, there is not a cloud of ash equivalent to a cord of wood floating around out there somewhere." Ahh, but there is a equivalent of amount of carbon, just held in different form. How much does a ton of carbon weigh.... What about a face cord of carbon....

I tried explaining this to the girlfriend as I was cleaning out the non-carbon based heavy minerals and trace elements left behind in the mass-combustion chamber this afternoon. Being a girl, she just didn't get it. Finally I said think of it as a giant hole in the atmosphere that all the carbon oxides go into, taking the mass with it. She said oh, you mean like a mass hole. I said yes, exactly. She said she thought the mass hole was the guy putting all the wood into the stove. But then she made me a grilled cheese sandwich for lunch, so it was all good.

Originally Posted by johncinco

So my sealed box... ...So if you got wood hotter than most wood fires, but with no oxygen, do you get charcoal or does it turn into something else?

No, you would not get charcoal. With no oxygen present the wood cannot burn, you just get hot wood. In theory, if you got it really, really hot enough the wood could vaporize (become a gas) and hotter still it would become plasma, but when it cooled it would still be wood. But... There are oxygen atoms in wood so a small amount of charring or burning would occur. To get charcoal you burn wood at very low added oxygen levels, and then extinguish the fire when the wood has been charred. This removes most of the hydrogen, nitrogen and oxygen and leaving more of the carbon behind.

Originally Posted by johncinco

...How much does a ton of carbon weigh.... What about a face cord of carbon....

Well, a ton of carbon weighs 2000 pounds... And the purest form of carbon is diamond which weighs approximately 219.24 pounds per cubic foot, and if a face cord is considered one-third cord it would be equal to 42.66666 cubic feet (219.24 x 42.66666 = 9354.2)... So, a face cord of carbon weighs approximately 4.7 tons.

Ummmm.....

Heating wood without the presence of oxygen results in a pile of charcoal.

That's what charcoal kilns are for.

Now we get to Einstein’s famous equation, E=MC2, which can be shortened to E=M, or Energy=Mass.
Energy, or mass, cannot be lost; it can only be converted from one form into another. In other words, if you start with 10 pounds of wood and you could capture all the smoke, ash and gasses created by the fire they should weigh 10 pounds... Except it doesn’t quite work that way, you’d come up a bit short because you’ve forgotten to allow for the heat and light radiation. The heat and light radiation also contains some of the mass, mostly electrons, anti-electrons, photons and some other, more exotic, sub-atomic particles cast off during the break-down and re-formation of molecules. You would also have to capture all those particles (not to be confused with particulates) and add them to your bag of smoke, ash and gasses before it would weigh the full 10 pounds.

Hope this helps? :smoking:[/QUOTE]

If we look at the older physical law of conservation of matter we could say that if you measured the mass of a cord of wood, then burned it in a closed sytem so that we could trap and measure the mass of all off the products of the combustion reaction (ash, smoke particulates, water vapor, and other gasses etc.) the total mass of these products would be exactly equal to the original mass of the cord of wood.

Taking into account E=mc2, lets say we burn a cord of wood that origionally weighs 4845 lbs (2200kg rounded), and the energy produced is 30 Million BTU (30 billion joules rounded) (taken from 1st btu chart on the btu sticky). Do the calculation for mass lost based on energy produced or 30 million BTU's and it comes out to .0000004 kg (.0000008 lbs) of mass converted to energy. In other words I think we can neglect Einstein's equation when it comes to burning wood. But you are right. It would be an interesting experiment to try. I wouldn't want to do it though.

Originally Posted by CrappieKeith

Hey I shove 6 cords through mine!

I would fix some of the cracks. More of the chunka would stay in it.

Harry K