Beyond the basics of what biochar is and what it can do, there is a wide frontier for its deployment. The way that biochar is made and used will vary from one situation to the next, depending on many factors. There is no universal template for a biochar system.
As an example, the Cook County, MN Highway Department, has an unusual mandate to help control invasive species, which were being propagated by their existing practices. So the department teamed up with the state ag inspector and an environmental technician to make biochar from them. Not only would the soil be improved on site and elsewhere in the county, but reestablishment and fuel loading would be largely eliminated.
The $10–20,000 equipment budget for their first two kilns suggests that a Big Box kiln design was chosen. Another municipality working at this scale (3,300 square miles) with greater revenue sources might have chosen a CharBoss, or even a TigerCat Carbonizer, which was used in the Oakland Hills to pyrolyze entire trees. Besides budget and scale, other factors influencing their choices would be the high accessibility of their highway right-of-ways and the fairly level terrain.
This set of factors is a far cry from the forested slopes and winding roads of western United States, where the approach tends toward using hand crews with Ring of Fire kilns and water trailers. In the vertiginous, largely undeveloped forest of southern Humboldt County where I live, a kiln that does not require water for quenching makes even more sense than a Ring of Fire, so I chose the air-quenched Vuthisa design. And wherever funds are sufficiently tight, biochar can be made in piles or pits with little more than your own time and sweat.