Fed batch retort

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.

Looks like a workable design in theory. What material do you envision making the feed tube with? I'm eager to see a prototype of this and what sort of tweaks it needs.

I'm heading down a similar track except that I'm going to experiment with an auger-fed rocket chamber, which will have a dropout before the transition to the heat riser. I'm also looking at using sensors to modulate the speed of the auger. No drawing yet but will try and have something soon. My biggest engineering problems are going to be around burnback and how to prevent or mitigate it.

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.

If anyone knows the difference between stopping at biochar and going all the way to syngas and diesel, I'd be happy to post our progress here. We are working on the latter and my husband is the tech guy. My understanding is rather basic.

Karen - The process of pyrolysis is just thermal decomposition of biomass. The outputs from the process are heat, syngas, condensible liquids (bio oil and wood vinegar) and biochar. We can tweak and tune the various parameters of the process to get more or less of the yields. So a gasifier set up to maximise production of syngas will have lower amounts of heat, liquids and biochar coming out. Tuning the system to get more liquids will mean less gas, etc.

When we do simple, low-tech production of biochar with a flame cap kiln or pit, we are using the evolved gas to provide the heat to drive the process and keep things hot enough to form durable forms of carbon. In a liquid-optimised system, we might run at a lower temperature in a positive-pressure retort to avoid breaking the longer hydrocarbon molecules all the way down to hydrogen and carbon monoxide (the main components of syngas). This will still yield biochar at the end of the run, but it won't be as porous or long-lived as material that is made for purpose.

Thank you Phil!!

Though my husband is very good at explaining, I find it helps me to study on my own as well. I am more of a "big picture" person and he focuses in on the details.

I had kind of a Hmmm thought as to whether I could use the ash remaining in my gardening efforts but I suspect that will depend heavily on what is going into the reactor. I know on some of our initial efforts, there are metal pieces mixed in with the ash. And probably other contaminants that wouldn't be good in the garden. He plans to eventually learn how to pull various components from the ash. But our first goal is diesel for the one ton and syn gas for the generator.

What you described as an optimal way to create bio char is very like his first reiteration of the machine.
And I just noticed I need to add my location which is west Texas.