FLAME CARBONIZERS FOR BIOCHAR

Kelpie Wilson

Wilson Biochar Associates

kelpiew@gmail.com

In Practice and Theory

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.

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.

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

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

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

Counterflow combustion laminar flame

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

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

Ways to Tame a Flame

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

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

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

Deep Kiln - Counter-current flow

• Passive counter-current flow as burning fuel draws air downward

• Active counter-current flow uses a blower

Ring of Fire Kiln - vortex generation

Reflected (re-radiated) heat and thermal gradients

produce vortex flows

Kon Tiki – cross-current vortex generation

Rim shield around the cone draws air to feed the flames, generating

cross-current vortex flows

Flame Carbonizers vs Pile Burning:

The Fuel Problem in Oregon

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

Top lit makes a difference

But to save any char you need water to quench

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.

Open Ricks

Rick in Pan

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

Oregon Kiln

Oregon Kiln in the Backyard

Oregon Kiln in the Woods

Grayback Forestry Crew

Working in the Rain

Dumping

Time and Water Needed to Quench

Willow Witt Ranch

Quenching Time

Using the jib crane to dump

Next Christmas…

Giant Slash Pile

It’s a HUGE problem! We need bigger kilns, but they need to be

mobile.

Air Curtain Burner – Counter-flow

Active counter-current flow using a blower

Air Burner with blower off – like Deep Kiln

Air Burner Biochar - Ashland Watershed

Air Burner Char

Air Burner Char

Left: char chunks. Right: mineral soil

Trees planted in Air Burner char

Left: light granitic soil. Right: soil with char mixed in.

More Ideas for Flame Carbonizing

Burner Design – tangential air & baffles

Burner Design – Electromagnetism

Controlling the flame with an electromagnetic field

Burner Design - Coanda Effect

Can we create curved surfaces that exploit the Coanda Effect?

Container Design -Tents and Wigwams

Left: Carbon Cultures biochar kiln.

Right: WigWam biochar kiln by Scott McKain of UBET

Container Design – Coking Ovens

Non-Recovery Coking Oven

Channels flue gas underneath for more heat transfer

Container Design - Cob Ovens

Make a little biochar with your pizza or make a little pizza

with your biochar!

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.