Manufacturing Pellet-Stove Fuel

      Thoughts and information on how to process sawdust into fuel pellets. March 14, 2006

Question
How do you make wood pellets from sawdust? I understand corn starch is used in charcoal briquettes as a binding agent. Is there a binding agent in wood pellets? I would be interested in the how-to of wood pellet manufacturing.

Forum Responses
(Sawing and Drying Forum)
From contributor A:
Maybe waste oil from cars could be a binding agent. The pellets would burn better.



From contributor B:
You don't need a binding agent, it already has one. It's called lignin. You need dried sawdust and a way to compress it. I made a few sawdust logs with iron pipe and a 80 ton bearing press just messing around to see if it would work and it did.


From contributor C:
Don't the commercial processes use steam for something? Does anyone have any ideas on how to make pellets continuously? Is there some kind of auger to force sawdust through a very small orifice? It seems like it would need a lot of torque to turn it. Hydraulics would be easier to build and prototype though.


From contributor D:
Pellet mills are available as a standard product. The sawdust needs to be dry and no binders or such are required. It is a pretty capital intensive business because the dryer and pellet mill are expensive.


From Gene Wengert, forum technical advisor:
In addition to the capital and shipping costs of the finished product, business is seasonal. Itís hard to make much money and have good cash flow on something that does not sell well for 5 months a year. Of course, another issue is that the fuel value per pound is about 1/2 of what coal has. It will take a lot of volume to keep a house heated. I am old enough to remember a coal bin in the basement and a stoker and always some sort of problem with feeding. I am not sure I would try that again, even using pellets instead of coal.

In addition to the pellet machine, a machine to make small particles is needed, with a storage facility (do not want rain on dry sawdust). Then the pellets need a storage area too, and then a truck and a loader. Of course, there are all the normal business expenses. On the other hand, with the drop in paper prices, we are seeing that pulp companies are paying only $5 per ton for sawdust in some areas (usually the South where heating demands are small). The gross heating value of dry wood is $25-$30 per ton for a small business or residence.



From the original questioner:
Thank you for all your input. I am not interested in pellet manufacture for heating homes a few months out of the year. My interest with wood pellets involves external combustion of steam engine technology. Your website is rich with wood properties, values, and common sense. I've been admiring this website for 4-5 years.


From Gene Wengert, forum technical advisor:
I think you would be better off with a fluidized bed burning sawdust instead of making pellets first and then burning them to make steam. A fluidized bed can take varying MCs and varying particle size easily.


From contributor F:
I went to the pallet convention in St. Louis, MO and there was a company there who had the whole layout there on their machines that did that. They made block pallets from saw dust, but unless you are planning on investing I suggest you sell your saw dust. I know there is a market as we sell our saw dust from our notching machine.


From Gene Wengert, forum technical advisor:
Did you mean pellets or pallets?


From contributor G:
I think one way of making pellets is using an extrusion screw and a die. Look up extrusion screw and you'll find a ton of information. I'd think for a smaller operation you could get by with recycled equipment from the plastic industry and a small press (extrusion screw).


From Gene Wengert, forum technical advisor:
As part of an experiment, I made pellets at a feed mill. It worked perfectly.


From contributor A:
I installed a pellet mill for a company that made flour. The husk of the wheat was the bi-product. Steam moistened the husk bulk as it entered the screw auger. The pitch changed on the auger (which slowed the movement) and compressed the bulk which forced it through a thick steel plate (interchangeable for different sized pellets). Then a knife came around the plate, like a clock, and cut the extruded bulk to pellets. The pellets then fell down a sloped screen which had a vacuum pulling air over the pellets to dry them.


From contributor H:
You may be able to make a simple wood pellet machine by using a metal pipe and having a solid metal rod of slightly smaller diameter thrust forward to compress the sawdust into pellets. This can be operated on a continuous basis by having an electric motor power a cam wheel that is connected to the compression rod. This method is used to make extruded particleboard from sawdust.



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