This is an interesting short clip on pellet making:
http://science.discovery.com/tv-shows/how-its-made/videos/how-its-made-wood-pellets.htm
http://science.discovery.com/tv-shows/how-its-made/videos/how-its-made-wood-pellets.htm
How it's made: Pellets
- Thread starter begreen
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Dang! Stupid "webwasher" here at work, won't let me see any videos, youtube or otherwise.
Hafta wait til I get home...
I wonder how dangerous it is to be aound there with all that sawdust, or do these companies have methods to contain/make it safe, and if so how often disasters happen.
I wonder about spontaneous combustion from the wood chips composting if they get wet. It seems like we were hearing about a pellet mill fire once a year a while back.
They show all those dryers and they have so much equipment that can cause a spark it just looks like its a disaster waiting to happen.
Bioburner
Moderator
The dies the wood go through gets screaming hot and I know of a couple fires as the super hot pellets get a breath of air.
It's when dried dust is airborne that it becomes dangerous.
The pellets get up to 210F going through the pellet machines. Much less than that and the lignin doesn't get hot enough. The only time a pellet machine has fire problems is if the bearings in a roll come apart and start grinding metal to metal inside. Then the sparks coming from that will get sucked up by dust recovery so it's important to have spark detection equipment and either a wet system or rapid abort gates. But the fire itself in the pellet machine isn't a big deal and can be put out with a garden hose. I suppose if you're using additives like oil or polystyrene, that could be a big problem.
Dryers commonly have smoldering material in them after a shutdown because they then have fuel, heat, and an oxygen supply. The dryer design I'm familiar with is a single pass, recycled air dryer. It is at its safest when running at capacity. The air is recycled back through the dryer inlet which reduces the oxygen content of the air in the dryer. Also, while it's running, the air is laden with the moisture being evaporated from the wood. The dryer I'm familiar with also has several points where you can spray water at the push of a button to soak it down and put out any fires. Or, it will shut down and spray automatically if left unattended and any of the temperatures go higher than a specific limit for that section.
We're burning pellet dust in the dryer so it's like an extremely large pellet furnace (50MM BTU/hr). Except at that scale it is ground into a flour and blown in and burnt in suspension rather than on a grate. Just like a pellet stove, it has to be cleaned quite often. The air flow tubes, after the cyclone where condensation can collect, every 1 to 1½ weeks. The ash from the burner about 3 times per year.
There's a picture tour on my website on how pellets are made and I give out walking tours to anyone that wants to come by.
The pellets get up to 210F going through the pellet machines. Much less than that and the lignin doesn't get hot enough. The only time a pellet machine has fire problems is if the bearings in a roll come apart and start grinding metal to metal inside. Then the sparks coming from that will get sucked up by dust recovery so it's important to have spark detection equipment and either a wet system or rapid abort gates. But the fire itself in the pellet machine isn't a big deal and can be put out with a garden hose. I suppose if you're using additives like oil or polystyrene, that could be a big problem.
Dryers commonly have smoldering material in them after a shutdown because they then have fuel, heat, and an oxygen supply. The dryer design I'm familiar with is a single pass, recycled air dryer. It is at its safest when running at capacity. The air is recycled back through the dryer inlet which reduces the oxygen content of the air in the dryer. Also, while it's running, the air is laden with the moisture being evaporated from the wood. The dryer I'm familiar with also has several points where you can spray water at the push of a button to soak it down and put out any fires. Or, it will shut down and spray automatically if left unattended and any of the temperatures go higher than a specific limit for that section.
We're burning pellet dust in the dryer so it's like an extremely large pellet furnace (50MM BTU/hr). Except at that scale it is ground into a flour and blown in and burnt in suspension rather than on a grate. Just like a pellet stove, it has to be cleaned quite often. The air flow tubes, after the cyclone where condensation can collect, every 1 to 1½ weeks. The ash from the burner about 3 times per year.
There's a picture tour on my website on how pellets are made and I give out walking tours to anyone that wants to come by.
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