is there an ash vacuum that separates out the unburned charcoal?

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twd000

Feeling the Heat
Aug 28, 2015
428
Southern New Hampshire
I have in front of me:

  • a dead-cold 5 gallon pail of ashes (actually several pails)
  • soil test report for my lawn, indicating it needs calcium, potassium, and higher pH
  • soil test report for my garden, indicating it needs higher CEC, lower pH, and no additional calcium or potassium. CEC can be increased by adding "biochar" (soil science term for smashed up bits of charcoal)

Is there an ash vacuum that separates chunks of charcoal from the ash? Most designs I've seen look like they comingle ash and coals. I'm interested in scavenging all the charcoal bits, from the big chunks down to a couple millimeters. When I sift through the bucket, there are a lot of those tiny charcoal bits that got extinguished when I put the lid on the bucket. These would be great to add to the garden if I could separate out the fly ash.

I wouldn't be using this for emptying the stove, I use a shovel and pail for that. I would do this operation outdoors so I don't need a HEPA filter and I don't mind some fine dust blowing through the second-stage filter.

I have an extra Shop-Vac I could modify of repurpose for this endeavor. Is there some sort of cyclone separator, or two-stage filter that I could use, to end up with two pails - one full of charcoal bits, and the other full of ashes?
 

brenndatomu

Minister of Fire
Aug 21, 2013
6,407
NE Ohio
I made a charcoal screen a while back out of (2) 5 gallon buckets
I cut the bottom out of the one, put a couple pieces of 1/8" round rod through the now bottomless bucket about 3-4" up from the bottom edge, clear through the bucket, with 2-3" hanging out on each side, and the 2 rods at a right angle to each other. Then I formed a piece of 1/4" hole hardware cloth to fit snuggly down into the bucket sitting right on the 2 rods.
The screen bucket sits on the second bucket, well, sits down into it up to the point where the 1/8" rods are sticking through...pour ashes in...knock it around a bit to work the ashes through...works pretty well.
 

begreen

Mooderator
Staff member
Nov 18, 2005
89,681
South Puget Sound, WA
Just add the charcoal and the ash. It's not going to hurt the garden to have a bit of extra potassium.
 
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twd000

Feeling the Heat
Aug 28, 2015
428
Southern New Hampshire
Just add the charcoal and the ash. It's not going to hurt the garden to have a bit of extra potassium.

it's not the extra potassium that's the problem; it's the extra calcium that I don't need, that comes along for the ride.

I already have 15% more calcium than I need, which saturates the CEC sites

This study indicates wood ash contains ~3x more calcium than potassium by weight, so adding wood ash would put the soil even further out of whack

 

begreen

Mooderator
Staff member
Nov 18, 2005
89,681
South Puget Sound, WA
If you are going for bulk, then make a sifter for the cold ash. Or get a sifting shovel. You could also make a small retort for your woodstove to make biochar by taking two cans, poking a few vent holes in them, and filling them with twigs. Crimp the lip of one of the cans so that it fits into the other after they are filled with twigs. Toss on a hot coal bed. You will see flames coming out of the vent holes. When the flames stop, remove the retort and cool (you can quench with water if desired). Open the cans for some fresh char.
 

twd000

Feeling the Heat
Aug 28, 2015
428
Southern New Hampshire
If you are going for bulk, then make a sifter for the cold ash. Or get a sifting shovel. You could also make a small retort for your woodstove to make biochar by taking two cans, poking a few vent holes in them, and filling them with twigs. Crimp the lip of one of the cans so that it fits into the other after they are filled with twigs. Toss on a hot coal bed. You will see flames coming out of the vent holes. When the flames stop, remove the retort and cool (you can quench with water if desired). Open the cans for some fresh char.

the retort is an idea I've used on larger scale, but when I'm burning wood for heat 24/7, I don't want an extra step. I have a friend who has a little retort box he loads into his wood furnace to make biochar. It seems like a lot of extra cutting to make tiny sticks to fit in the box. I'd rather just process all the mixed ashes once at the end of the season.

I'm thinking of something like these two-stage separators that some people have made for woodshop dust. I could add a screen to the exhaust of the first stage to trap all the charcoal particles in the bucket while letting the finer ashes through


 

begreen

Mooderator
Staff member
Nov 18, 2005
89,681
South Puget Sound, WA
I've seen setups like this that have water in an intermediate 5 gallon bucket in case there are still some hot embers or coals.
 

twd000

Feeling the Heat
Aug 28, 2015
428
Southern New Hampshire
I've seen setups like this that have water in an intermediate 5 gallon bucket in case there are still some hot embers or coals.
water filter is an interesting idea. Do you end up with ashes and coal mixed together in the water? I did that once, expecting the charcoal to float, but it didn't work
 

begreen

Mooderator
Staff member
Nov 18, 2005
89,681
South Puget Sound, WA
I don't recall the details. It was a very old thread, back to around 2007 or so. I tried to retrieve it but the link is lost. I can ask the boss if he can retrieve it.
 
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