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vbottle28 (Mechanical) (OP)
1 Mar 13 12:02
Hi, i'm trying to get my hands on either a graph or an equation linking the moisture content of wood to its calorific value (kJ/kg) other units are fine though...
Most sources seem to say "if your wood is 30% is approximately xx" but its for a model so i actually need to know the variation.

Would be great if anyone has a source I haven't managed to find...

Thanks for any help in advance.
Helpful Member!(3)  25362 (Chemical)
1 Mar 13 12:29
This link may be what you need:

http://www.epa.gov/burnwise/workshop2011/WoodCombu...

Go to page 22 for a graph on the effect of moisture content (MC).
ione (Mechanical)
1 Mar 13 13:38
Don't know whether you were already aware about the link below, anyway......

http://www.biomassenergycentre.org.uk/portal/page?...
rmw (Mechanical)
1 Mar 13 20:03
Good link 25362.

Vbottle 28, What kind of wood are we talking about? I have burned lots of Southern Pine bark & sawdust in boilers that was under the best conditions ~50% moisture. You could typically grab a handfull of the pure sawdust and squeeze it real hard and water would run out of it between your fingers. The softwood calorific value was considered to be 4500 B/lb. Then on some days it rained and the moisture content was even higher. And some wood was stored "under water" which meant that there were contstant spraying by sprinklers that distributed water across the entire stack of logs continually to keep the insects at bay. (Engineered a few of those systems too.) The calorific value of hardwood wasn't quite so high, but the moisture content was typically lower, but not by much. Rather burn the pine than the hardwood.

The link by 25362 on slide 21 says some wood can be up to 150% water. That's a puzzler. That would be almost like sponge wood.

What the article says about much of the calorific value of wood going to dry the wood so it would burn is real, so pay attention to your moisture content.

rmw
vbottle28 (Mechanical) (OP)
2 Mar 13 14:38
Thanks 25362, That should probably do the trick. ione, found that one before, not incredibly clear what was going on so i gave up on it, thanks though!

rmw, from what i've found out so far, the calorific value of wood is pretty consistent, at least softwoods are consistent and hardwoods are, not exactly the same but close enough for my simple model. I'm going to be doing real tests and checking the moisture content before i burn and so i just need to be able to enter the m.c. value into my model for comparison.

Thanks guys :)
Helpful Member!  ione (Mechanical)
2 Mar 13 15:03
vbottle28,
The xls spreadsheet in the link above gives the net calorific value (GJ/t) of some woods vs moisture content up to 65 %, and I thought you were looking for something like this.
DRWeig (Electrical)
2 Mar 13 16:10
Both great links.

Just a clarification for those who might not be familiar with the moisture content percentages:

The EPA paper (25362) quotes the dry-wood basis percent of moisture, so it can be greater than 100 percent.

The nice spreadsheets from ione quote the wet-wood basis moisture content, so it's always less than 100 percent.

Best to you,

Goober Dave

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racookpe1978 (Nuclear)
2 Mar 13 16:22
RMW:

Why would water spray keep off insects from pine?
Seems like it would encourage infestation.
Compositepro (Chemical)
2 Mar 13 16:59
The heat content of wood and hydrocarbons, on a mass basis, are all pretty similar because they are all chemically very similar as far as combustion is concerned. There are very big differences in density, however. Wood is sold by volume (cord or rick), and the combustion process in a wood burner is controlled by the volume and surface area of wood. Very few people wood say that soft woods and hard woods are the same.
rmw (Mechanical)
2 Mar 13 22:37
CompositPro, They sure don't burn the same.

Mr. Cook, I don't know, and I like you have always been baffled by that process, but if you have lived in the deep south, passing any kind of storage yard containing southern pine one would witness huge sprinkler systems wetting all the wood in storage.

I guess you'd have to go to the pulp & paper forum to see if anyone there knows the answer.

For me, it meant some revenue designing the pumping and piping systems needed to sprinkle the logs. Fairly easy work, and lucrative too, because they had to be dependable. If they broke down, the bug attack started, don't you know.

rmw
EnergyMix (Nuclear)
3 Mar 13 15:42
I always thought the water was to keep the wood from drying out. Something about it being a fire issue.

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Compositepro (Chemical)
3 Mar 13 16:49
Lumber yards keep their logs wet to prevent them from checking and splitting due to drying on the outside while the inside is still wet. Wet wood is also much easier to cut than dry wood, which probably explains why pulp wood wood is kept wet.
rmw (Mechanical)
3 Mar 13 20:56
I've done work in lots of lumber (as well as plywood, particle borard and OSB) mills as well as pulp/paper mills. I have yet to see pulp wood (round wood) being sprinkled. The turnaround time for (round wood) pulp wood was just too fast while saw logs and "peelers" (at plywood plants) were typically stored 'under water' as they put it. But the reason was given that it was for the prevention of attack by bugs. In some seasons, no sprinkling was done and I don't remember for the life of me what the difference was. They did log a lot harder in dry seasons in order to have inventory during wetter seasons when the vehicles couldn't get into the woods.

On the other hand, logs at chip mills - places where logs were debarked and chipped and the bark and chips were shipped to distant pulp mills separately, the logs were stored 'under water' at times.

Trying to burn bark from logs stored 'under water' was almost mission impossible.

Someone who really knows the reason why may happen up on this and tell us. Or, I could try to get a call through to some of my old clients, problem being that they are really getting old now.

rmw
rmw (Mechanical)
3 Mar 13 20:57
And, yes, I have seen log stacks with ice hanging off the logs, so they did sprinkle in winter too. What self respecting bug would have been out in that weather.

rmw
rmw (Mechanical)
3 Mar 13 21:08
Ahh, the marvel that is Google....


http://openagricola.nal.usda.gov/Record/IND2046242...

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