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Does quenching biochar matter?  RSS feed

 
Todd Parr
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Location: Wisconsin, zone 4
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I watched a video recently that said that quenching biochar imparts some advantage to it.  The video wasn't very clear on exactly how it improves it, it just alluded to quenching somehow opening the pores in the charcoal better or something.  Anyone know if there is really an advantage to quenching?  I have done it, but normally don't because I use it mixed in with my chicken bedding first and I don't want to introduce moisture into the coop.  If it is going straight into the compost pile or the chicken yard, quenching isn't a problem.  Any thoughts?
 
Craig Dobbson
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can you post a link to the video?   How are you stopping the burn when you make biochar? 

When I make it, I use the trench method and usually just cover it with soil once it's reached char level.  That smothers the fire and leaves me with dry, clean biochar.  I just leave it buried for a couple of weeks and then carefully remove the top layer of soil so I don't get too much soil in my char.  Then I empty the trench with a spade, into old feed sacks.  I use the stuff, in worm bins, garden beds, houseplants and in the chicken coop.   

Quenching is usually how people put out their biochar fires.  I guess it would help to provide moisture to the colonies of microorganisms that we're trying to harbor in the pores of the char.  I don't know if the rapid cooling addds any other benefit.  Maybe.

 
Todd Parr
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Craig, I'll see if I can find the video again.  I stop the burn on mine two different ways depending on the method I'm using.  If I'm using the barrel-in-a-barrel method, when the inner barrel stops producing wood gas, I pull it out and put it into another 55 gal barrel that has no openings and put the lid on it.  I leave it overnight and by then it's cool.  If I use the 55gal barrel full of wood with another barrel on top as a chimney, when the wood burns down to the bottom vents, I cover them with dirt, pull the top barrel off and put a lid on the barrel with the charcoal in it.  Once again, leave it overnight to cool.  I haven't dug a pit yet to try that method, but may this weekend, depending on weather.  If I do, I'll use your method of covering it with dirt unless I can find some compelling reason to quench it.
 
Genevieve Higgs
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Could it have to do with steam?  Like a popcorn type expansion
 
Todd Parr
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Genevieve Higgs wrote:Could it have to do with steam?  Like a popcorn type expansion


That's exactly what the guy in the video made it sound like.  I just hadn't heard it before, so I'm not sure if it is valid and I don't know of any way to test it short of maybe with a microscope.
 
Casie Becker
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You could probably test it by comparing weight by volume. That is of course assuming that it expands like vermiculite or perlite.
 
Todd Parr
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Casie, that's a good point that I hadn't thought of.

Here is a study that points to the importance of quenching, although not for the reasons given in the video I watched.

Quenching biochar
 
Tom Rodgers
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Thanks Todd, I enjoy reading this type of paper. One detail that was alluded to as an X factor was in fact the water itself. I noticed that distilled water was used, as a "control" to eliminate contaminants in the water. What is kinda cool about water though, especially in its purest form, is that the electromagnetic energy in the very bonds of the water itself are strong enough to lift the water up into a bubble when it is on a clean surface, such as the waxed hood of a car. We have seen this many times.and the droplets can stand up and be suprisingly tall. What we do not register is that the characteristic of spreading out and attaching to surfaces we would actually consider to be wetness or wettability, and that means the opposite action would be an act of dryness, measurable in its electrical values among materials including water. So long story short, water is one of the drier substances on the planet relative to that capacity. Adding anything to the water, such as one might with a form of fertilizer, will help break this internal attraction and promote wetness.

Having said that, I also noticed the article seemed to connotate a direction without my particular purpose. Specifically that the char was problematic if it did not absorb water immediately and that the clogged pores were problematic. I do not see this as a problem, because the char has an extraordinary love of oxygen, the other mega nutrient with water. As it simply sits exposed, it will suck oxygen out of the air, and begin oxidation. This characteristic seems to be a concern to some who point out that it offsets the carbon sequestration effect. I view it as aeration for roots. As this oxidation occurs, the surfaces change, and water suddenly finds itself sitting on a surface much like old oxidized chalky paint like an old car would have, and there is no water drops standing up or resisting wetting that kind of surface as you know. From what I have read, older incorporated char becomes so oxidized that its porosity becomes that of modern activated charcoal over a period of years.

Secondarily, I tend to be in that camp which sees the organic residuals, described in the article as tars, as food for bugs. I think its a good thing over time to not open up the porosity to the exent possible in a manual fashion, rather letting nature do this work. Activatied carbon is highly porous, but this is arrived at through exceptionally high temps, or additional chemistry, and at a loss of volume of 2/3 of the char. Its just overkill that slows the adoption of the char into the biosphere.  I would soak the char in a myco enhanced liquid fertilizer compost or compost tea type mix, after I let it sit dry and aired out a while.

This stuff is so cool!
 
Greg Martin
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Steam is a known method of eliminating tars from charcoal and is one of the methods for generation of activated carbon.  When the Biochar is still very hot and water is sprayed onto the pile it generates very hot steam that can react with the tars to chemically break them down.  I usually spray with a hose for quite some time before adding buckets of water to finish the quench.  With my pit charring the hose can't keep up with putting out the Biochar, but it does a great job of generating lots of active steam. (~5' diameter pit, ~1.5' deep)

I tried rapid quenching once with a large barrel of water....that was a mistake!  It created a large cloud of tiny charcoal powder that billowed up ominously into the air.  Fortunately it came up away from me so that I didn't breathe any of that in.  With the hose method of steam generation the pile slowly comes down in temperature so that when I start dumping pails of water in there is no violent reaction....much safer. 
 
Tj Jefferson
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I use my awesome heavy clay soil to cover the top of the pit with a little lower area in the middle, then pour at least 5 gallons into the pit slowly, infiltrating through the soil. It does seem to make smaller pieces that are super fluffy. I leave it covered in the pit for at least a day. Then I move it to the compost pile, water it for an hour with a sprinkler, mix it in the compost again and repeat the watering/mixing at least a week later. I have absolutely no source for this regimen, but nothing is dying and the compost matures much faster than without the char (I have one pile that is no-char).
 
Tom Rodgers
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I admire the design of the Kon-Tiki Cone Kiln. It is a large metal cone with 70 degree walls, it has a water pipe inlet with a valve attached to the bottom, and a drain pipe. It quenches from the bottom up, and the wonderfully filtered water can be reused by irrigating it back out to plants or other purpose. I see they are working on further development of  air control jackets for enhanced pyrolisis zone control on windy days as well as emissions control,  but the water piping is a noteable idea.
 
I do some of my very best work in water. Like this tiny ad:
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