You can make biochar with a simple cone or ring kiln, but how does it work? This presentation explains the principles behind flame carbonizing - using an open flame to produce charcoal from biomass.

1. FLAME CARBONIZERS FOR BIOCHAR
Kelpie Wilson
Wilson Biochar Associates
kelpiew@gmail.com
In Practice and Theory

2. Japanese Cone Kiln – Moki Co.
Our inspiration comes from Japan where these simple cone-shaped
kilns were developed and sold by the Moki Company. They are
bottomless, and you simply roll them away when you are done.

3. Flame as Heat Exchanger
With the pan excluding air from the bottom and the flame
excluding air from the top, the Flame Cap Kiln acts like a retort
with the flame as a heat exchanger – transferring heat efficiently
by radiation.

4. Limits of Heat Transfer through Metal
In theory, Stirling Cycle engines approach Carnot efficiency. In practice,
exergy loss from heat transfer across metal reduces efficiency. That’s
why we use the internal combustion engine, despite its lower theoretical
efficiency. For similar reasons we may prefer a flame carbonizer to an
externally heated retort

5. Basic Flame Types
• Flames can be divided into categories:
• Pre-mixed vs Diffusion
• Laminar vs Turbulent
• Concurrent flow (axial) vs Counter-current flow or Cross-current flow
The cone kiln works with cross-
current flow that generates counter-
current vortex flows

6. Concurrent Axial Flow
• No external limits on air
entrainment
• Lean mixture cools the
flame, producing soot
• Flame length limits
radiative heat transfer
to fuel bed

7. Counterflow combustion laminar flame

8. For Best Heat Transfer:
Shorten the Flame Length
• Flame length is a function of mass flow rate and fuel bed
diameter
• Open sided piles entrain more air than enclosed piles –
giving higher air mass flow rate and higher flame length
• High flow rate flames cool faster and radiate less heat to
the fuel bed
• Piles enclosed by a surrounding cylinder have shorter,
more turbulent flames due to less entrained air
Buoyant diffusion flames: Some measurements of air entrainment, heat transfer and flame
merging. Thomas, et al. Fire Research Note. 1964

9. Flame Carbonizer Flame Types
• TLUDs* and Ricks
• Con-current Axial Flow
• Flame Kilns
• Shallow Kilns
• Cross-current vortex generation
• Deep Kilns
• Passive Counter-current flow
• Air Burners
• Active Counter-current flow
• *TLUD: Top-Lit Up-Draft gasifier

10. Ways to Tame a Flame

11. Jack Daniels Rick – with Hood
The Jack Daniels Company has made charcoal for
filtering whisky this way for decades. When the rick
collapses into glowing coals, they quench it with water

12. Optimizing TLUDs as Flame Carbonizers
• TLUDs are Flame
Carbonizers
• Not very different from
a rick in a cylinder
Design Parameters:
• Primary Air
• Secondary Air
• Flame stabilization
with swirl or tertiary air
• Burner plenum space
• Stack effects

13. Rick inside a ring - Ring of Fire
If bottom is not sealed, can burn like a TLUD. Can operate in dual mode:
• TLUD for startup
• Deep Kiln for later stages

14. Deep Kiln - Counter-current flow
• Passive counter-current flow as burning fuel draws air downward
• Active counter-current flow uses a blower

15. Ring of Fire Kiln - vortex generation
Reflected (re-radiated) heat and thermal gradients
produce vortex flows

16. Kon Tiki – cross-current vortex generation
Rim shield around the cone draws air to feed the flames, generating
cross-current vortex flows

17. Flame Carbonizers vs Pile Burning:
The Fuel Problem in Oregon

18. Tight pile construction is standard
• Tight piles don’t fall apart
• Burn hot in the center
• Burn completely to ash
• Generate smoke
• Burn forest soil

19. Top lit makes a difference
But to save any char you need water to quench

20. Very Loose Open Pile – Top Lit
Concurrent axial flow – burns fast, hot and clean, but pile falls
apart and needs tending. Can make a lot of biochar if quenched.

21. Open Ricks

22. Rick in Pan

23. Design Parameters for Oregon Kiln
• Sized for feedstock
• Logs 4 to 5 feet long
• Up to 6” diameter
• Log rick fits better in pyramid shape than cone
• Portable but Durable
• Less than 200 lbs
• 14 gauge steel
• Ergonomic for loading
• Only 2 feet high
• Economical
• Pyramid shape cheaper to fabricate than cone
• $600 for Kiln – 5’ top base, 4’ bottom base, 2’ high

24. Oregon Kiln

25. Oregon Kiln in the Backyard

26. Oregon Kiln in the Woods

27. Grayback Forestry Crew

28. Working in the Rain

29. Dumping

30. Time and Water Needed to Quench

31. Willow Witt Ranch

32. Quenching Time

33. Using the jib crane to dump

34. Next Christmas…

35. Giant Slash Pile
It’s a HUGE problem! We need bigger kilns, but they need to be
mobile.

36. Air Curtain Burner – Counter-flow
Active counter-current flow using a blower

37. Air Burner with blower off – like Deep Kiln

38. Air Burner Biochar - Ashland Watershed

39. Air Burner Char

40. Air Burner Char
Left: char chunks. Right: mineral soil

41. Trees planted in Air Burner char
Left: light granitic soil. Right: soil with char mixed in.

42. More Ideas for Flame Carbonizing

43. Burner Design – tangential air & baffles

44. Burner Design – Electromagnetism
Controlling the flame with an electromagnetic field

45. Burner Design - Coanda Effect
Can we create curved surfaces that exploit the Coanda Effect?

46. Container Design -Tents and Wigwams
Left: Carbon Cultures biochar kiln.
Right: WigWam biochar kiln by Scott McKain of UBET

47. Container Design – Coking Ovens

48. Non-Recovery Coking Oven
Channels flue gas underneath for more heat transfer

49. Container Design - Cob Ovens
Make a little biochar with your pizza or make a little pizza
with your biochar!

50. Wilson Biochar
Associates
Wilson Biochar Associates specializes
in biochar technology and market
development. We provide strategic
advice and services to businesses and
organizations.
• Technology Assessment
• Research and Analysis
• Project Development
Kelpie Wilson
Wilson Biochar Associates
Home office: 541-592-3083
Mobile: 541-218-9890
kelpiew@gmail.com
www.wilsonbiochar.com
Wilson, K. & Perkins, C. (1987). Approximating
the Ideal Stirling Cycle Through Discontinuous
Motion of the Displacer Piston. Senior Project
Report and Second Prize Winner, ASME Power
Division, Student Paper Competition.
Kelpie Wilson and Carol Ann Perkins with
Stirling Engine at CSU, Chico.