The document compares flame cap kiln and rotatable covered cavity kiln technologies for biochar production. It outlines key advantages of the rotatable covered cavity kiln design, including improved control over air flows, emissions, and heat availability. This new design addresses limitations of traditional open-top and covered cavity kilns by allowing biomass tumbling for more complete charring and easier fuel loading and unloading. The rotatable design also enables scaling kiln sizes up or down to suit different operations. Initial prototypes demonstrated feasibility of the innovative kiln concept for clean, efficient small-to-medium scale biochar production.

1. Comparison of Flame Cap
(FC or Open Cavity) Kiln and
Rotatable Covered Cavity
(RoCC) Kiln Technologies
A Presentation at the 3rd Biochar Workshop
Butte College, Oroville, CA 27 – 28 February 2020
Paul S. Anderson, PhD Email: psanders@ilstu.edu
Woodgas Pyrolytics, Inc. www.woodgas.com

2. RoCC kiln
• 4-foot diameter, 5-foot long.
• Shortly after ignition.
• 27 February 2020
• Berkeley Olive Grove, Oroville, CA.

3. Farm-scale Char Production:
Affordable 4C Kilns for
Quarter-Ton to One-Ton of
Biochar Per Workday
Presentation on 1 July 2019 by
Paul S. Anderson, PhD ( psanders@ilstu.edu )
US Biochar Initiative Conference, Ft. Collins, Colorado
Several slides are taken or modified from an earlier presentation.
[ See drtlud.com/resources and woodgas.com/resources ]

4. Review of Sizes for Pyrolytic Biomass Reduction
& Biochar Production• Based on input of biomass per day
• Small 1 kg to 1 ton input
• Retort: Regular and Adam Retort
• TLUD (Top-Lit UpDraft): Stoves and barrels
• Flame cap or cavity kiln: Cone; pyramid;
trough; Kon Tiki
• Medium Missing size for 1 t to 20 t input
• Large 20 ton to 200 t/day (20 t/hr x 10 hr)
• Air curtain: By Air Burner Co. and
ROI Carbonator 500 (Approx. $150 K to $600 K)
• Heated screw and Rotary kilns: (Installations
from $300 K to $1.2 million)
• Furnaces that have char in the ashes.

5. The Challenges: To have Medium-size facilities
with clean emissions, safety and biochar
• A full review would take all the available time and still be incomplete.
Small = flame cap || Large = air curtain
Exposed flames and || High volume of air
possible emissions. || has much combustion.
BOTH feature the use of air to "cover" the top to control emissions.
Note the missing middle for medium size char production technology.
• A fundamental issue: When the volume (pile) of biomass gets to be large,
the biomass and char partially insulate and isolate the biomass in the center.
• Without sufficient air (with O2), there is not sufficient heat, so pyrolysis slows
or even stops.

6. Review of "Flame Cap" kiln technology
• Kelpie Wilson, Hans-Peter Schmidt & others have provided great explanations:
• https://greenyourhead.typepad.com/wilson_biochar_associates/Flame-Kilns.html
• https://www.biochar-journal.org/en/ct/39 (Kon Tiki design.)
• Two major principles and major features of flame cap pyrolysis:
• The flame of burning gases above the biomass prevents (mostly) the entrance of air with
oxygen from reaching downward the created hot charcoal.
• The walled structure is where charcoal becomes buried under successive layers of
biomass being pyrolyzed.
• Product names have referenced the shape of the walled structure:
• Japanese cone kiln Pyramid kiln Trough kiln Trench kiln Pit kiln Barrel kiln (upright).
• Also, for specific designs: Oregon kiln Kon-Tiki pyrolyzer & Moxham kiln.
• All rely on a lower space, a cavity, for the collection of charcoal (w/o air entrance).
•A proposed additional inclusive name is "cavity kilns".
There are numerous topless or uncovered or open cavity kilns. (see next)

7. Flame Cap or Open Cavity Kilns
• Flame cap kiln is a cavity kiln with an open top:
• Cone, pyramid, trough, barrel/tube (vertical), trench/pit, etc.
• None have features to facilitate re-exposure of once-covered fuel.
• The cavities where charcoal collects remain relatively cool.
• There is less stress on the metal than from the higher
temperatures of burning charcoal.

8. Covered Cavity Kiln
• In 2014, after one attempt with a half barrel,
Anderson left a top on his cavity, creating a
"covered cavity kiln".
• Provisional Patent Application but not pursued.
Released into public knowledge in 2015.
• Named: Clean Controlled Covered Cavity (4C) kiln.
• Five of the 4C kilns were built and used
occasionally by Anderson and Doug McCarty.
• Encouraging results for biochar but too labor
intensive. Insufficient reasons to launch a product.
• No known replications by anyone.

9. Anderson 4C Kiln – Barrel (55 gallon = 0.2 m3 ) :
For Farm and Forest Pyrolytic Biomass Reduction and Biochar Production
http://www.drtlud.com/wp-content/uploads/2019/01/4C-Kiln-for-CHAB-2019-01-23.pdf
YIMBY = Yes In My Back Yard
I have never had a complaint about
smoke release. I have been quite
careful to keep the flame cap burning.

10. Advantages of Covered Cavity Kilns
• Lower emissions:
• Less influence of winds.
• More time keeping combustion gases concentrated.
• Door facilitates control of direction and volume of entering air.
• Controlled exit of emissions via chimneys.
• Allows for monitoring with instruments to control operations.
• Controlled (channeled) exit of heat
• Facilitates finding uses of the heat.
• Facilitates using the heat to pre-dry incoming fuel.
• Reduces risks of sparks and starting wildfires.
• Char extraction options instead of tipping or shoveling.
• Can be scaled larger more easily. (to be discussed).
• Good quality char. (see next). (The only testing thus far.)

11. Char quality: Test results of
char from Anderson 4C kiln
Based on our testing it looks like excellent char. The ash is 10% so
reporting on an ash-free basis it brings the carbon much higher in this
natural fraction. The butane activity is a mid-ranged based on typical
findings on dry wt basis. -- Frank Shields Oct. 2014

12. Disadvantages of Cavity Kilns,
both open-top and covered
• Fuel input is gradual and frequent and requires
presence and attention of the user.
• Possible incomplete charring if the biomass fuel
becomes buried between incoming biomass and
the bed of produced char that is cooling.
• Lack of control of internal temperatures, resulting from
**** Lack of control of air flows.****
• [Note: We will deal with these problems.]

13. Larger-size attempts with 4C kiln technology
210 gallon 0.8 m3 (above)
http://www.drtlud.com/wp-
content/uploads/2019/01/4C-Kiln-
for-CHAB-2019-01-23.pdf
275-gallon 1.0 m3
http://www.drtlud.com/wp-
content/uploads/2019/01/4C-Kiln-for-CHAB-
2019-01-23.pdf

14. Anderson 4C Kiln – Large Tank
(4x6x8 ft) (1200 gallon or 4.5 m3 or 6 yd3 )
First public demonstration was held on Friday 19 July 2019 in
Goodfield, Illinois at a meeting of the Illinois Biochar Group (IBG). Above: Fabrication
underway of a 4x6x4 ft
test unit with ~2.4 m3
capacity.
Biochar was produced and therefore it was successful, but not sufficient
to justify further work with this type of design. It was too labor
intensive, awkward to use, and too hot to approach for necessary
functions for mixing and extraction.

15. TWO innovations for the Anderson kilns:
• Why two? Because the first one is deficient by itself.
• Covered Cavity Kiln (1st innovation, 2014) has three deficiencies
found in all flame cap cavity kilns.
• Fuel input is still gradual and requires attention of the user.
• Possible incomplete charring if the biomass fuel becomes buried.
• Lack of control of air flows.
• Rotatable Covered Cavity (RoCC) Kiln (2nd innovation, 2019) shows
how to solve these problems:
• Facilitate fuel delivery and with possible automation.
• Assure complete charring of the biomass.
• Attain better control over the air flows, emissions and availability of heat.
• Have (nearly) continuous operations as well as batch operations.
• Be sufficiently low cost with low maintenance and low labor requirements.
• Be able to scale to much larger sizes and volumes.

16. Solutions
• Tumbling of the biomass is possible if the kiln is rotated when needed.
• Let gravity do the work of mixing and exposing the torrefied biomass.
• Rotation of 240o is possible because it is a covered cavity.
• Remove the door; have an open portal that goes to different positions
for different purposes.
• Fuel loading by horizontal shelf or vertical drop (incl. bins and hoppers).
• Unloading downward. Let gravity do the work.
• Moveable grate (prongs/fingers) to help select what is discharged. Door
to cover portal is possible for special cases, including 360o rotation.
• Separate the chimneys from the kiln; place them on a detached hood.
• Utilize standardized materials, such as corrugated steel pipe (CSP) that
has many diameters and plenty of length.

17. This allows for additional benefits
• Scale from < 2-ft to > 16-ft diameters, and lengths appropriate for the
biomass and desired throughput.
• Be either portable or stationary.
• Is compatible for addition of sensors and air control.
• Have directional control of the emitted gases and heat which can
provide additional value.
• The operators are less exposed to direct fire and radiant heat.

18. Introductory images
of two RoCC Kilns
• There are MANY improvements that cannot be
seen in these initial images. Do not replicate
what is shown here.
• See RoCC Kiln Manual at woodgas.com/RoCC
and contact Paul Anderson for assistance.
• 3-foot diameter, 4-foot long. India >>>>
• 4-foot diameter, 5-foot long.
• 28 February 2020; Shortly after ignition.
• Berkeley Olive Grove, Oroville, CA. >>>>>>>
The front side is
under the hood
and has the
horizontal shelf
for feeding fuel.

19. SUMMARY:
•The Rotatable Covered Cavity (RoCC) kiln
technology and devices help fill the massive
gap in size and cost options for small and
medium biochar operations such as for
farms, woodlots, and places generating
“refuse” biomass.
•Possible scale-up to very large sizes. This will
depend on need, financing and engineering.

20. Original: Paul S. Anderson 2019-03. Text changes
and color added 2020-03.
1. Include numerous non-
monetary benefits.
2. Any one benefit could be
sufficient justification. Attaining
two benefits (or 3 or 4) is
possible w/ awesome results.
3. If possible, find uses for the
heat from pyrolysis.
4. The charcoal (biochar) can
have more value than the 30%
increase in created heat from
burned charcoal.
5. Biomass disposal by pyrolysis
can be less expensive than if
sent to landfill or burned to ash.
6. Biochar into soil is stable
Carbon Dioxide Removal (CDR)
plus available energy (BC&E).
Multiple Profit
Centers from
Pyrolysis
Pyrolytic
Devices and
Technologies
Charcoal
Products
Biochar into soil
Char gasification
Fuel, filter, etc.
Thermal
Energy
Applications of heat
Replace fossil fuels
Biomass
Disposal
Avoid landfill
Fire protection
Air quality
Other
Benefits
Chemicals
Carbon Offsets
Climate benefits

21. Economics of RoCC Pyrolysis
• The smaller units can be manually operated by one person.
• Larger units could have automated loading/unloading.
• Financial feasibility is impacted by costs of biomass feedstock, labor,
equipment, value of the char produced, and value of heat and by-products.
• There are many business models.
• Dr. Anderson has patent pending status on the RoCC process and basic components.
• It is time for others to become involved!!
• Sponsors, investors, licensees, researchers, corporations, agencies are welcome.
• Geographic territories can be allocated to those who facilitate progress.
Contact: Paul S. Anderson, PhD Email: psanders@ilstu.edu
Phone: 309-452-7072 Woodgas Pyrolytics, Inc. www.woodgas.com

22. Table of sizes of RoCC Char makers
(Version 2020-03-08; Draft still in need of refinement; Some rounding.)
(Based on cylinders; Extrapolations from Column B; Estimated variability of +/- 50%)
A B C D E F
Size >>>>
Issue (below)
55 gallon (Barrel) ~140 < 180 gallon 464 gallon (4x5 ft)
(8 barrels) (1.7 m3)
750 gallon (4x8 ft)
( 14 barrels)
1500 gallon
(~ 20 barrels)
a Dimensions
(Diameter x Length)
(D) 2 x 3 ft = 9 ft3 3 x 4 ft (28 ft3)
(210 gal)
4 x 5 ft (62 ft3)
(464 gal)
4 x 8 ft = 100 ft3
(2.8 m3)
4 x 16 ft= 200 ft3
(~5.6 m3)
b Fuel input (kg/hr)
(extrapolation from Col B)
~25 kg ~50 lbs
(~3 - ~2.5 kg/ft3/hr)
~84 kg/hr 180 - 200 kg/hr 250 – 300 kg
( Quarter ton )
500 kg 1000 lbs
( Half ton )
c Char output (kg/hr @ 20% yield)
[ CO2e reduction per hour]
5 kg 1 wheelbarrow (WB)
[ 18 kg ]
~16 kg/hr
[ 58 kg ]
40 kg
[ 146 kg ]
50 kg
[ ~ 183 kg ]
100 kg
[ 366 kg ]
d Thermal energy output as 70%
of total (30% remains in char)
12 MJ/kg/hr 8 BTU/lb/hr
300 MJ
83 kW-h
284 K BTU
Almost 1 M BTU
(Under EPA interest
threshold)
2400 MJ
666 kW-h
2.3 M BTU
3000 MJ
830 kW-h
2.8 M BTU
6000 MJ
1660 kW-h
5.6 M BTU
e
f
A (repeated) F ( with new units) G I J K
Size >>>>
Issue (below)
1500-gallon 200 ft3
4x16 ft; 5x10 ftf; 6x7 ft
3000-gallon 400 ft3
11.3 m3
7500-gallon 1000 ft3
28 m3 = 20 ft container
15,000 gal 2000 ft3
56 m3 = 40 ft container
30 K gallon 4000 ft3
113 m3 (RR tank car)
a Diameter / Length 4 x 6 x 8ft = 200 ft3
(~5.6 m3)
6 x 14 ft or 7 x 10 ft
8 x 8 ft
8 x 20 ft
10 x 13 ft 12 x 9 ft
12 x 18 ft 14x 13 ft
16 x 10 ft
10 x 52 ft (RR tank car)
16 x 20 ft
b Fuel input (estimate per hr)
(extrapolation from Col B)
500 kg
( Half ton )
1000 kg
~ One ton per hour
2.5 tons per hour 5 tons per hour
(~3 - ~2.5 kg/ft3/hr)
~10 tons/hr
c Char output ( w/ 20% yield)
[ CO2e reduction per hour ]
100 kg
[ 0.36 t ]
200 kg/hr
[ 0.73 t ]
500 kg/hr
[ 1.8 t ]
1 t/hr
[ 3.6 t ]
Estimate 2 tons/hour
[ 7.2 t/hr ]
d Thermal energy output as 70%
of total (30% remains in char)
12 MJ/kg 8 K BTU/lb
6 GJ Gigajoules
1.66 MW-h
5.6 M BTU
12 GJ Gigajoules
3 MW-h
10 M BTU
30 GJ
8 MW-h
28 M BTU
60 GJ
16 MW-h
57M BTU
~120 GJ
33 MW-h
114 M BTU
e
f