wood combustion factor - temp v. h2o content

[woodbooga]

Got a serious Q for the more experienced and/or geeky-new nerd cool set.

Scenario:
Reached a cache of marginally-seasoned wood in the pile. Pretty small qty.

Knowing that this wood is suboptimally seasoned, I "bake" the wood for a bit in the oven of the cookstove. By the time this wood goes in the box, it is end-checked and 300*+. Think "quick kiln."

I suspect the moisture is more than the preferred 20%, but the decreased h20 + high temp make this wood go up quick.

Is the combustion less than, more than, or equal to a seasoned stick?

 

[bobt]

I would say that you probably stumped everyone as nobody has responded before this, but Iwill take a shot at it.

I have been known to try to burn some pretty unseasoned wood similar to what you did.

However, I had no oven, but simply piled the wood close to the wood stove. It helped quite a bit.

I do not believe you "baked' the wood to optimal water content, but seeing that you already raised the temp much higher than room temp, you realized a pretty good burn rate.

I still think that your btu output was somewhat less than optimimal, but certainly acceptable.

If I were you, I certainly would do it again if needed. Good idea!

Bob

 

[CTYank]

Got a serious Q for the more experienced and/or geeky-new nerd cool set.

Scenario:
Reached a cache of marginally-seasoned wood in the pile. Pretty small qty.

Knowing that this wood is suboptimally seasoned, I "bake" the wood for a bit in the oven of the cookstove. By the time this wood goes in the box, it is end-checked and 300*+. Think "quick kiln."

I suspect the moisture is more than the preferred 20%, but the decreased h20 + high temp make this wood go up quick.

Is the combustion less than, more than, or equal to a seasoned stick?

"Seasoned" stick is vague and nebulous. Undefined, given that various states have wildly different statutory definitions. (Ohio's is <=50% MC- huge help.) If you mean "air-dried to X% MC throughout" then please specify the MC. (See the issue involved?)

I find that stacking the splits near the stove for days or weeks gets the MC way down, without risk of mucking up the frau's stove. You might be concerned about that. Here, I'm talking slow kiln.

 

[Whitespider]

OK, here’s the “geeky-new nerd” answer.

The same stick of wood holds the same potential BTU’s whether it’s seasoned, green, dry or wet (actually, when wet, the potential BTU’s are higher because even water can be a source of energy). A wood fire isn’t hot enough to “burn” water, so anytime water is present in the wood (even 1%) some of the potential wood fiber BTU’s will be used to convert water into steam. The steam than carries those BTU’s out the flue, they are lost.

Now for the “geeky-new nerd” question… Assuming it’s gas or electric, have you considered what it’s costing you to run the cookstove to dry an armload of wood?

 

[Marc]

OK, here’s the “geeky-new nerd” answer.

The same stick of wood holds the same potential BTU’s whether it’s seasoned, green, dry or wet (actually, when wet, the potential BTU’s are higher because even water can be a source of energy). A wood fire isn’t hot enough to “burn” water, so anytime water is present in the wood (even 1%) some of the potential wood fiber BTU’s will be used to convert water into steam. The steam than carries those BTU’s out the flue, they are lost.

Now for the “geeky-new nerd” question… Assuming it’s gas or electric, have you considered what it’s costing you to run the cookstove to dry an armload of wood?

:bulgy-eyes:

Eh? Can you expound on that a little?

 

[logbutcher]

Dear Booga--- Old Downeast saying for people "from away" trying to become a local :

You can put a cat in the oven. It won't come out as a cupcake.

Now, how did you try to season ?:bang:

 

[branchbuzzer]

Got a serious Q for the more experienced and/or geeky-new nerd cool set.

Scenario:
Reached a cache of marginally-seasoned wood in the pile. Pretty small qty.

Knowing that this wood is suboptimally seasoned, I "bake" the wood for a bit in the oven of the cookstove. By the time this wood goes in the box, it is end-checked and 300*+. Think "quick kiln."

I suspect the moisture is more than the preferred 20%, but the decreased h20 + high temp make this wood go up quick.

Is the combustion less than, more than, or equal to a seasoned stick?

I'd say it's still less. It lights easy because you've preheated it and taken some of the moisture out of the outside wood, but the outside is just releasing the BTUs at a faster rate than normal. Plus you still had to use BTUs to get the wood up to temperature, whether it was inside the oven chamber of the cookstove or not, the wood/water is absorbing heat from the firebox. Same way a pot of water on top of a stove absorbs BTUs.

 

[Whitespider]

:bulgy-eyes:

Eh? Can you expound on that a little?

Nuclear Fission

 

[woodbooga]

Dear Booga--- Old Downeast saying for people "from away" trying to become a local :

You can put a cat in the oven. It won't come out as a cupcake.

Now, how did you try to season ?:bang:

I think I know him - that's the tall hairy short bald guy from over to Tatnick. He keeps a bucket if water next to his woodbox and dunks in both ends of a stick before burning to extend the burntime.

Nice guy but can't cook a cupcake worth a damn.

 

[Marc]

Got a serious Q for the more experienced and/or geeky-new nerd cool set.

Scenario:
Reached a cache of marginally-seasoned wood in the pile. Pretty small qty.

Knowing that this wood is suboptimally seasoned, I "bake" the wood for a bit in the oven of the cookstove. By the time this wood goes in the box, it is end-checked and 300*+. Think "quick kiln."

I suspect the moisture is more than the preferred 20%, but the decreased h20 + high temp make this wood go up quick.

Is the combustion less than, more than, or equal to a seasoned stick?

Like the answer to most "roughly" defined problems, the true answer is: depends.

You still don't know the moisture content of the wood after it comes out of the oven and that is really going to be the determining factor. The specific heat of water, how much energy it can absorb per given temperature increase, 4.2 kJ/(kgK) is three orders of magnitude smaller than the latent heat of vaporization (2,270 kJ/kg). So taking a kg of water from ambient to boiling temperature requires about 294 kJ. To convert that same kg of water at 100C to vapor at 100C requires an energy input of 2,270 kJ. Similarly, the specific heat of your average hardwood (oak) is only 2 kJ/(kgK).

The takeaway from that babble is that you still need to know moisture content because conversion of liquid water to steam is the biggest energy draw. Not only does it take usuable energy from the heater it lowers the temperature of your combustion reaction resulting in less efficient combustion and more potential heat energy up the chimney. So calculating the heat loss using geen wood isn't as straightforward as crunching the numbers on heating water and wood and the water-steam conversion.

In any case, if it's burning well and you don't see a lot of smoke coming out of your chimney, I'd say the MC is probably lower than you think. And while you're still using heat to bake and dry the wood that would other wise be heat for your house, if you're not gettign that lower combustion efficiency effect that you would throwing the green wood straight into the firebox you're still coming out ahead.

'N stuff.

 

[Felman]

Water boils @212*f, some air circulation would remove the moisture better I think?