It's great to see someone else who has discovered the benefits, (and fun), of bio-char. I've been making it and using it for many years. Ever since I saw a documentary about Terra Preta. (https://en.wikipedia.org/wiki/Terra_preta)
One of my favorite ways of producing it is with a gasifier stove. I've made dozens of them over the years. It's a great way to cook with wood without much smoke.
A retort is also a simple way to make bio-char any time one has a campfire.
Here is a post I made last year about bio-char.

https://steemit.com/biochar/@stevesmith/free-retort-makes-the-cleanest-biochar