Curtis McCue

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.

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.

I would like to emphasize that there is a chemical difference between biochar and *most* charcoal, because most charcoal is prepared in a way that preserves a lot of the volatile components in order to keep the energy content high (i.e., if you're making charcoal to burn, you typically want it to have a high energy content, and you do that by minimizing the loss of volatile components).  Biochar, on the other hand, is produced with the goal of burning off all of those volatile components.

Why is this important?  It's important because a lot of those volatile components are soil contaminants that you don't want around your food.  It's almost like having soil contaminated with diesel fuel.  That's why most folks in the biochar field recommend against buying sacks of lump charcoal from the store and grinding it up to put in your garden -- you'd be amending your soil with some pretty ugly (and persistent) chemicals.  Some of those compounds can be broken down by soil bacteria, but it's a.very.slow.process.  So, they can do a good job on the trace amounts commonly found in biochar, but have a more difficult time handling the amount present in charcoal intended for burning.

(Note that the one exception re: charcoal is charcoal meant for things like smithing, which (like biochar) is made with the goal of burning off all the volatile components, to yield a high purity carbon source.)

Thank you so much, that is pretty much exactly what I was looking for!  So glad to see it actually works

I was thinking about those glass propane patio heaters the other day (tower of flame shooting up a glass cylinder or pyramid), and was wondering if a similar setup could replace the (upper part of the) riser on a rocket stove.  You obviously wouldn't want it running as hot as a typical rocket stove (maybe a large excess of secondary/tertiary air, maybe even a setup where the gases from the combustion chamber are actually sheathed in the added air?), any other design considerations that come to mind?  I know this wouldn't be running at top efficiency, but that's not always why we do things . . .

Hi, all.  I'm looking to build a Hookway biochar retort, which basically consists of a rocket stove running through a 55 gallon steel drum that holds the biochar feedstock.  As the feedstock pyrolyzes, the flammable gases are fed into the combustion chamber to sustain the charring process.

The original plans call for using 6" diameter stainless steel (304) pipe, but I have the opportunity to pick up some 5" 304 stainless pipe at a much lower cost.  Given that the combustion chamber is about 1 foot long, and the heat riser is about 3 feet tall, would you expect 5" pipe to still work satisfactorily?

Thanks for your insights.

For the feed tube, I eventually hope to use 304 stainless.  But for prototyping, I may start with something else.

Your design sounds interesting.  I wonder if you can reduce the risk of burnback by having a slight incline to your feed, or a slight constriction that results in a higher air flow rate through a small section.

I really want to enable continuous or fed batch pyrolysis for smaller scale biochar production, and my feedstock of interest (shredded sweet sorghum bagasse) is better suited for retorts because of the small particles present.  I'm thinking of trying out a design where the feedstock travels in a metal chute through a combustion chamber insulated with ceramic fiber board, and then the finished product can be collected in an airlock at the end (maybe even some quenching there too).  

Heat could be provided either by a regular fire or maybe a small rocket stove.  The chute would contain vents that allow the pyrolysis gases to escape into the combustion chamber so that they could be burned before going up the chimney, and a thermocouple inside the chute could be used to indicate when the feedstock train needs to advance (you could theoretically use this signal to automate the system).

Something that intrigues me is the suggestion to incorporate a catalytic combustor from a woodstove, to facilitate ignition of the pyrolysis gases.  I hate seeing all the energy lost in afterburners.  But I also don't know how best to place 1) the combustor, 2) the vents on the chute, or 3) the secondary air supply.

I put the chute on a slight decline so that gravity helps move the material along (maybe less pushing = less compaction?); and maybe also help move the pyrolysis gases away from the finished material, towards the starting material.  (i.e., I would rather have the volatiles condense on the incoming material than on the finished product).  But I don't know if any of that really makes a difference.

Anyway, this is very much in the brainstorming stage, and I'd appreciate hearing any suggestions you might have.

Ellendra Nauriel wrote:Anyway, picture one of those self-feeding pellet stoves, but with a funnel-shaped burn chamber along the lines of a kon-tiki. At the bottom of the funnel is another auger, treating the burn chamber as if it were a hopper, and feeding the hot char through to a dousing chamber.

Tbh, I don't know much about pellet stoves, but it sounds like they have a constant feed rate (e.g., pounds per hour) that is turned on or off by a room thermostat.  Inside, there are low/high temp sensors (up to 300F?) to control things like fans and shut off the feed if things get too hot.  I'm not sure how to apply that to a pyrolytic setup, unless maybe you are able to monitor the combustion of pyrolysis gases (as opposed to combustion of the char).

Here is a quick sketch of what I have in mind for a manual continuous system (not to scale).  PNG for viewing, SVG for editing