# Net energy gain for industrial wood chips



## Eric Johnson (Jul 24, 2007)

Does anybody know offhand what the net energy gain is when burning wood chips? I'm talking about the difference between the energy used to harvest, process, transport, etc. a ton of chips, and the amount of energy produced.


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## mtarbert (Jul 25, 2007)

I don't think there is enough information in your post to come to an educated conclusion.
  First: Why is the wood being chipped?
  Second: How far is it being transported?
 Third: In what type of stove are the "Chips" being burned.

  If you are getting the chips for free and with a minimul delivery charge It has been my exsperience that chips can be a good way to heat ones home but....if you are buying them for anywhere near the price of firewood at the same weight....stick to splits.
   Just MTC
  Mike


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## BrotherBart (Jul 25, 2007)

What you are looking for is called the "energy balance" Eric. I don't know what it is for burning straight chips but I have seen claims that for cellulose ethanol that wood chips yield a 16 to 1 ratio. That is that you get sixteen times more out of it than it eats in the total production cycle right up the the fire. Gasoline is only something like five to one and corn three to one.

Of course, as has been said, the distance between the trees and the boiler are controlling the numbers.


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## jpl1nh (Jul 25, 2007)

Great question Eric.  Bet wood looks pretty good  though.  Off the topic a bit, it doesn't get anymore efficient than my Stihl in the woods behind my house,  my maul, and my wheelbarrow, then heating my house.  Even the doctor likes that equation!


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## keyman512us (Jul 25, 2007)

mtarbert said:
			
		

> I don't think there is enough information in your post to come to an educated conclusion.
> First: Why is the wood being chipped?
> Second: How far is it being transported?
> Third: In what type of stove are the "Chips" being burned.
> ...



Not to "rain on the parade" MT...but just keep in mind he did include the term "Industrial" wood chips...i.e. small power plants, process boilers, and steam generators... (This particular 'application' is one that is 'followed' by a few folks here on the forum) To answer "some of your questions" though...take my locale for instance...there are FIVE large chip fired aplications within 15 miles of where I live. Everything from heat for buildings, to making steam for specific industry...to a 17MW commercial grid conected power generating station. And believe it or not...doesn't matter how 'good the tree is' it ALL gets chipped. How far some of it is transported "would make you want to shake your head".

In other parts of the world...chip is viewed differently. Some countries make North America look like a "third world society".

I'm sure the numbers have to take into account the $$$ factor to a great degree... last I knew the local papermill was saving somewhere around 8500 gallons of #6 oil per day by burning 2 Trailer truck loads per day. Their silo holds a little over a weeks supply of chips. I'm sure the BTU content of chip is less than oil (what isn't though??)...BUT...

I'm not even gonna try to take a shot at the overall #'s... I'll wait for TMonter to chime in...he always has good 'insider info'... 

Good idea for a discussion though Eric... Thinking of utilizing chips somewhere in the future???


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## Eric Johnson (Jul 25, 2007)

You can buy chip gasifiers that work pretty well, I'm told. The big problems is getting/storing a reliable source of chips. Sawmills have them, but they sell most of them to paper mills and they're on a quota, so their big customer always comes first. Whole-tree chips are cheaper, but don't work as well as clean sawmill chips. My firewood is free for the cutting and hauling, so that's what I'm sticking with.

Actually, one of my readers asked the question about net energy return, and I thought I'd throw it out to the forum.

I did contact an expert on the topic, however, who informs me that green whole tree chips burned in a power plant to make steam yield a 3:1 ratio. In other words, it takes one unit of fossil fuel (let's say a gallon) to make three units (let's say three gallon equivalents) of energy. That's not half bad. It gets better if you're burning sawmill chips, since you can assume that all the harvesting and production costs are bourne by the main product, which is lumber. So somebody else is paying the freight, if you want to look at it that way.

He also says that the ratio is even better with wood-based alcohol fuel, though he didn't say how much better, probably because it hasn't been tested in a big way commercially--yet.

Finally, he notes that when you look at the total btu potential of a wood chip, you're only recovering 33% when you burn the chip in an industrial boiler to create steam. You're still working with the same 3:1 energy input/output ratio, but there are more efficient ways to recover energy from wood.


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## slowzuki (Aug 2, 2007)

I haven't done the math but the fellow I talked to used about 5 gallons of diesel to drag the 14 cord of poplar to his back door.  His neighbour burned about 10 gallons chipping it for him which also blows it into the storage bunker.  Then they heated their house with it, green chips.  The house used about 6-8 cord of dry maple hardwood before.  It uses some electricity too to run the intermitant auger and continuous fan.


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## smirnov3 (Aug 2, 2007)

slowzuki said:
			
		

> I haven't done the math but the fellow I talked to used about 5 gallons of diesel to drag the 14 cord of poplar to his back door.  His neighbour burned about 10 gallons chipping it for him which also blows it into the storage bunker.  Then they heated their house with it, green chips.  The house used about 6-8 cord of dry maple hardwood before.  It uses some electricity too to run the intermitant auger and continuous fan.



What did he burn the chips in? I didn't think there were any commercial green chip stoves for residential use.


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## Eric Johnson (Aug 2, 2007)

ChipTec, up in Vermont, sells one. Theirs is based on a design by a guy named Cliff Valley, who produced them commercially in Rutland, VT (or maybe it was White River Jct.) back in the early '80s. Nice little rig that burned green chips.


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## slowzuki (Aug 2, 2007)

A company in PEI makes them too.  His is the smallest model, most are commercial sized for schools and such.  Neat rig, the hopper is designed to be filled with a bucket on a skidsteer.  He just uses a garbage pail to fill it.

The burner just basically hooks onto the side of a tarm looking euro wood boiler where the oil fired unit would go.  A fd fan blows on the burn cup in the burner and an auger drops chips onto it based on heat demand.  Like a giant pellet stove.


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## Eric Johnson (Aug 2, 2007)

That's right--probably the same design. It's actually a stand-alone gasifier; you have to connect it to a boiler of some sort. I guess it just shoots flame into whatever heat exchanger you choose, in other words.

Hey Ken, it's a hot evening, so I'm down in the basement soldering and scratching my head.


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