Perpetual pyrolyis-powered pelletizer

From a carbon dioxide reduction (CDR) standpoint, it makes the most sense to make biochar from feedstocks that would normally have a short lifetime in the environment, rather than materials that would normally keep the carbon tied up for years anyway.  This got me thinking about the big piles of leaves that we see each fall, since they seem to persist for barely a year.  But they're so poofy, it seems like they would be much easier to handle if they were in the form of fuel pellets.  But making pellets takes energy, which got me wondering:  what if you had a pelletizer powered by an engine that ran on pyrolysis gases?  So, pelletized leaves get pyrolyzed to generate the gas that fuels the machine that pelletizes the leaves that get pyrolyzed to generate the gas that fuels the machine . . .   I don't really(?) expect this to be a practical solution, but it's fun to think about.

That's one of my fave things about pyrolysis...figuring out what to do with that excess energy. You've got three main pathways:

1. Pipe off the syngas and run an engine with it. This isn't too hard, although you'd need to have some safety features to avoid building a bomb. Lots of info on how to do this...put "drive on wood" into a search engine and see what you find.

2. Pipe off liquid condensates and run an engine with that. Ther's quite a bit more engineering involved but it opens up collecting the fuel and using it later, plus more engine possibilities, e.g. diesel or turbine.

3. Finally, there's the option of combusting all the volatiles and using the process heat to run a turbine, and either use that for shaft power or to generate electricity. Steam is one obvious way to get this done, and also has the potential of blowing stuff up if you don't design it properly.

Your first point is clearly true.  Wood on growing trees does store carbon. However, it appears to me that it's only considerably more efficient if you fail to account for the time that we spend in creating the biochar.  Wood can be cut quite quickly, making lots of mass available in a short time.  If it's green, you only have to leave it there, involving no work.  Gathering leaves and making them into biochar would take an enormous amount of time that can't be used for other more useful activities.

I live in an area where trees grow very quickly.  There is an excess of trees, from a human civilization standpoint. Trees get in the way, the limbs fall off, and the wrong trees are growing in the wrong places.  People are always cutting trees and asking for them to be cut and hauled away. The Native Americans who lived before the colonists burned the Willamette Valley floor every year.  Some speculation has been offered over whether they knew that they were improving the soil through a biochar/terra preta like process.  

Where I live, the trees are going to be cut anyway. I think of them as part of the natural growth process.  Trees grow, they die, they give off carbon dioxide.  We are breaking that cycle. When we make biochar out of the wood, it doesn't turn into carbon dioxide.  It mixes with the soil and creates hotels for microbes, improving the soil and sequestering carbon for hundreds of thousands of years.  

I do think that there are places where biochar is optimally made out of corn husks, sugar canes, bamboo and other organic materials that grow naturally there, but here wood is a great option.

John S
PDX OR

Agreed, it's fun to think about. Leaves would be incredibly low density fuel though, meaning you would need to handle truckloads of them.

If you had a source of free sawdust, you could probably rig up a manually turned system that would make wood pellets using the waste heat from biochar making. The pellets could be an income source -- either as fuel or small animal bedding.

Douglas Alpenstock wrote:Agreed, it's fun to think about. Leaves would be incredibly low density fuel though, meaning you would need to handle truckloads of them.

Part of what got me thinking about this is that in my town, there's municipal leaf pickup -- folks collect their leaves and put them out in piles by the street, and then a big vacuum truck comes by and collects them, and drops off the mulched material at a city yard.  I know, I know . . . but it's probably not a practice that's going to end anytime soon, so I was wondering how to turn it into a positive.

I know some people ask which do you use- biochar, wood chips, composting, hugulkultur, leaf mold, or worm castings? My answer, of course, is yes.

I use all of them.  I don't think of them as opposed to each other as much as complimentary toward each other.   I gather leaves in the fall and make a big pile of them. Then I add a handful of them to my compost piles when I add old food, etc to the compost.  I also add old food to worm piles.  I made a trench of hugulkultur, but I also add old wood to the soil whenever I plant a tree.  I keep leaves molding and add them to the soil regularly.  I add worm castings and compost to inoculate my biochar.  I add wood chips over the whole yard now twice a year, since we have such long droughts in the summer.  It blends with the inoculated biochar to provide more moisture retention and more habitat for worm and microbe diversity.  It all works together.

John S
PDX OR

Fun thread. I agree that using underutilized, or "waste" is an attractive undertaking. I also agree with John that we need to take an "and" approach, as opposed to "or".  Are leaves best used as pelletized biochar fodder?  As fuel to make biochar from another materials? Or as a carbon source in compost? I don't know the answer, but it's an interesting discussion to have.

I've had similar questions about another waste product - paper and cardboard. Sure, you can put it in the recycle bin, but I question the % that gets recycled, especially in my local "single stream" system where cardboard is mixed with other recyclables by consumers.

Could those materials avoid the landfill by being composted? Or as a fuel source to create biochar from wood or another input? I don' think cardboard/paper is a good candidate for making biochar directly.

I often use cardboard and paper to get the fire started.  Many people use cardboard and newspaper to put over weedy areas and then put mulch.  The next season, it's ready for planting.  Maybe.  

I agree.  Technically, even though it's starting the fire, it does go into the biochar.   I try to be careful that it's brown cardboard and it doesn't have a lot of fancy colors and glues in it. Remove the stickers, etc.

John S
PDX OR

To me autumn leaves are far too valuable as mulch/compost etc to carbonize them.
Rather than making pellets, perhaps we can grow   pellet like seeds ?
Locust or perhaps Kentucky Coffee tree might be ideal.

I have used sweetgum balls for both fuel and feedstock for biochar.
They are very low energy but their structure insures excellent airflow for combustion.

As for the wasted energy, drying feed stock is job one.
Water/space heating come next.
Baking/ dehydrating would be my third choice.
I would only want to run machinery off of a charcoal gasifier.
That seems to be much simpler than wood gasification