Are there advantages to wood pellets over wood chips?

  • Thread starter Stormer
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  • #1
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Both wood chips and wood pellets can be automatically feed into the burn chamber by Screw Conveyors, transport belts, and vibratory feeders. And both make char that is small enough to be automatically removed from the burn chamber. And both also has a shape and size that allows enough air to move trug the burn pile to feed the fire (unlike sawdust that will compact and stop to much air for it to burn).

But to make pellets you have to go trough two more steps (making chips into sawdust, and then pelletize it) to make them from whole wood compared to wood chips. And it takes more energy, and more machinery and time. So why are pellets used and not just wood chips? Is there any advantage i have missed? Or is it just to have a way to use sawdust waste from production of wood products for something useful? And in that case wasteful if whole wood pieces is used to make it?
 

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  • #2
jrmichler
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Wood pellets are also dried to a specified, low, moisture content. Green wood can be as much as 50% water by weight. Much of the energy from burning green wood goes to evaporating that water. It also reduces the boiler efficiency.

I saw one estimate that about 20% of the wood needs to be burned to dry the remaining wood. I saw another plot of boiler efficiency vs wood moisture. The increase in combustion efficiency was much more than the loss of wood burned to dry the wood.

Dry pellets do not rot. I don't know how fast green wood chips rot, but I remember sticking my hand into a sawmill sawdust pile. It was hot only a few inches in. Rotten wood gives off less energy when burned.
 
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  • #3
Grinkle
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Wood pellets are also dried to a specified, low, moisture content.
I guess its more efficient to dry the pellets en-masse than to let the wood self-dry as it burns, or to dry wood chips en-masse?
 
  • #4
anorlunda
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I guess its more efficient to dry the pellets en-masse than to let the wood self-dry as it burns, or to dry wood chips en-masse?
If you dry it in the fire, the energy needed to convert water to steam and to send the steam up the chimney is subtracted from the heat you put into your room. So yes, it is better to get dried wood from your supplier.
 
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