This document provides an overview of biochar, a solid product derived from the thermal degradation of biomass, detailing its production methods, properties, and potential uses in climate change mitigation. Key production techniques include slow pyrolysis, fast pyrolysis, gasification, and hydrothermal carbonization, each affecting yield and stability differently. The document emphasizes biochar's role in enhancing soil fertility, reducing greenhouse gas emissions, and improving nutrient retention, while also outlining sustainability criteria for its production.

1. A Short Introduction to Biochar
Jim Amonette
Pacific Northwest National Laboratory
Richland, WA 99352 USA
jim.amonette@pnl.gov
National Society of Consulting Soil Scientists
Morning Plenary
04 March 2010
PNNL-SA-71407

2. Outline
What is Biochar?
How is it Made?
Pyrolysis and Hydrothermal Carbonization Processes
Feedstocks
Yields
What are its Properties?
Chemical
Physical
How can it be Used to Mitigate Climate Change?
General Concept
Sustainability
Need for Modern Technology
Biochar, Biofuels and N2O
Where does it fit in the Environmental Technology Landscape?
JE Amonette 04Mar2010

3. What is Biochar?
Product
Solid product resulting from advanced thermal degradation of
biomass
Technology
Biofuel—process heat, bio-oil, and gases (steam, volatile HCs)
Soil Amendment—sorbent for cations and organics, liming agent,
inoculation carrier
Climate Change Mitigation—highly stable pool for C, avoidance of
N2O and CH4 emissions, carbon negative energy, increased net
primary productivity (NPP)
JE Amonette 04Mar2010

4. How is Biochar Made?
Major Techniques:
Slow Pyrolysis
traditional (dirty, low char yields) and modern (clean, high char yields)
Flash Pyrolysis
modern, high pressure, higher char yields
Fast Pyrolysis
modern, maximizes bio-oil production, low char yields
Gasification
modern, maximizes bio-gas production, minimizes bio-oil production,
low char yields but highly stable, high ash content
Hydrothermal Carbonization
under development, wet feedstock, high pressure, highest “char”
yield but quite different composition and probably not as stable as
pyrolytic carbons
JE Amonette 04Mar2010

5. Slow Pyrolysis—Continuous Auger Feed
Exhaust gas
and heat
Gas
Generator
turbine
Lignocellulosic Electricity Air
feedstock
Mill Gas
cleaner
and
Flue separator
Hopper Steam gas
Pyrolysis Pyrolysis
Dryer reactor gases
Cyclone
Feeder Combustor
Motor
Heat Char
Air
Biochar
storage
courtesy Robert Brown
JE Amonette 04Mar2010

6. Fast Pyrolysis Fluidized Bed Reactor
Lignocellulosic Pyrolysis gases
feedstock
Vapor, gas,
Flue Cyclone
Mill char
gas products
Quencher
Hopper
Bio -oil
Pyrolysis Char storage
reactor
Biochar
Motor Feeder Bio-oil
storage
Fluidizing gas
Combustor
Air
Brown (2009)
JE Amonette 04Mar2010

7. Pyrolysis
Competition between three processes as biomass is
heated:
Biochar and gas formation
Liquid and tar formation
Gasification and carbonization
Relative rates for these processes depend on:
Highest treatment temperature (HTT)
Heating rate
Volatile removal rate
Feedstock residence time
JE Amonette 04Mar2010

8. Competition Among Pyrolysis Processes
Spruce Wood, Slow Pyrolysis, Vacuum
(Demirbas, 2001)
Factors favoring 90
biochar formation 80
Char
Gas
70
Lower temperature 60
Tar+Liquid
Yield, wt%
50
Slower heating rates 40
Slower volatilization 30
20
rates 10
0
Longer feedstock 200 300 400 500 600 700 800 900
residence times High Heating Temperature, C
In general, process is Eastern Red Maple Wood, Fast Pyrolysis, High Purge Rate
(Scott et al., 1988)
more important than
feedstock in 90
80
Char
determining products 70
Gas
Liquid
of pyrolysis 60
Yield, wt%
50
40
30
20
10
0
200 300 400 500 600 700 800 900
JE Amonette 04Mar2010
High Heating Temperature, C

9. Transformations during pyrolysis
JE Amonette 04Mar2010
Keiluweit et al., 2010 EST online

10. Wood Char Yields from Pyrolysis
Figure adapted from Amonette and Joseph (2009) showing data of Figueiredo et al. (1989), Demirbas (2001),
Antal et al. (2000), Scott et al. (1988), and Schenkel (1999) as presented by Antal and Gronli (2003),.
JE Amonette 04Mar2010

11. Feedstocks
Essentially all forms of biomass can be converted to biochar
Preferable forms include: forest thinnings, crop residues (e.g., corn
stover, alfalfa stems, grain husks), yard waste, paper sludge,
manures, bone meal
Trace element (Si, K, Ca, P) and lignin contents vary
Lignin content can affect char yields
Lignin Content, Temperature, and Char Yield
Slow Pyrolysis, Vacuum (Demirbas, 2001)
50
y = 0.39x + 26.76
45
R2 = 0.99
40
Husks, Shells, Kernels
Char Yield, wt%
35
30
25 Corn Cob Wood y = 0.33x + 15.29
R2 = 0.96
20
15
Char (277 C)
10 Char (877 C)
5
0
0 10 20 30 40 50 60
Biomass Lignin Content, wt%
JE Amonette 04Mar2010

12. What are the Properties of Biochar?
Pine Wood Char
Oak Wood Char
Corn Cob Char
JE Amonette 04Mar2010

13. Proximate Analysis
Provides quick sense of
stability and chemistry in
three parameters:
100 Hydrothermal
Volatile matter is mass Slow Pyrolysis
lost in heating charcoal 90 Fast Pyrolysis
to 950°C in covered Gasification
crucible for 6 minutes 80 Ash-Free Line
50% VM/FC
Ash content is mass of 70 100% VM/FC
residue after
combustion 60
Fixed C is remainder Fixed C, % 50
High ash content (KCl, 40
SiO2), seen in corn
30
stovers, wheatstraw,
switchgrass, and 20
manure chars (CaO) 10 Increasing
Pyrolytic chars tend to Ash
0 Content
have VM/FC ratios of 0 10 20 30 40 50 60
0.5 to 1.0 Volatile Matter, %
JE Amonette 29 August 2009
Higher fixed C contents
suggest greater C
stability
JE Amonette 04Mar2010

14. Other chemical properties
pH typically alkaline
pH as high as 11 measured for fresh biochars prepared at higher
temperatures; good liming agent
pH near neutral (5-8) for weathered biochars and those reacted
with steam during or after pyrolysis
Nutrient retention
Cation exchange capacity increases as biochars weather by
oxidation; improved retention of NH4+, K+, Ca2+, and Mg2+
N from feedstock retained to same degree as C (i.e., half
volatilized during pyrolysis); unclear how much is available to
plants
P retention improved significantly; present as ash and sorbed
from soil, particularly when manure derived
Hydrophobic surfaces (basal planes of aromatic structures) tend
to retain organic compounds
JE Amonette 04Mar2010

15. Physical properties
High surface area Pine Wood Char
increases with HTT
Important for nutrient retention
Typically adds porosity to
soils, thereby decreasing
bulk density
Some reports of higher
water holding capacity,
perhaps due to optimal pore
sizes for water retention and
release (tens of microns) 40 μm
JE Amonette 04Mar2010

16. Climate Change is Accelerating
http://www.columbia.edu/~mhs119/UpdatedFigures/
Velicogna (2009)
http://www.columbia.edu/~mhs119/SeaLevel/ http://data.giss.nasa.gov/gistemp/graphs/
JE Amonette 04Mar2010

17. How can biochar help
mitigate climate change?
Create stable C pool using
biochar in soil
Use energy from pyrolysis to
offset fossil C emissions
Avoid emissions of N2O and
CH4
Increase net primary productivity
of sub-optimal land
Boundary conditions for biochar
contribution shown to right
Maximum levels are not
sustainable
Biochar cannot solve climate
change alone
JE Amonette 04Mar2010

18. Human-Appropriated Net Primary Productivity
29% of all C fixed by photosynthesis aboveground
(ca. 10.2 GtC/yr) is currently used by humans!
Of this 1.5 GtC/yr is unused crop residues,
manures, etc.
An additional 1.8 GtC/yr) is not fixed due to prior
human activities (e.g., land degradation) and
current land use
Current fossil-C emissions are ca. 8 GtC/yr
Increased productivity and expanded use of
residues from biochar production could have a
significant impact on global C budget
Haberl et al., PNAS 2007
JE Amonette 04Mar2010

19. Sustainability Criteria
Biomass primarily from agricultural/silvicultural residues
Minimal C debt from land-use changes (10-yr maximum
payback time, < 22 Mg CO2-Ceq ha-1)
No previously unmanaged lands converted for biochar
production; abandoned croplands ok
Modern pyrolysis technology used
eliminates soot, CH4, and N2O emissions
captures energy released as process heat, bio-oil, and flammable
gases
JE Amonette 04Mar2010

20. How much C can biochar sequester and
offset?
As much as 130 Gt C
over next 100 yr with a
sustainable approach
that does not increase
human appropriation of
NPP
Definition of
sustainable may
change as climate
crisis deepens
Capture and storage of
C emitted during
pyrolysis (i.e., CCS)
can add significantly
when available
JE Amonette 04Mar2010

21. Methane and Traditional Methods
Woody Biomass
Traditional methods No Energy Recovery
without energy 36% Biochar Yield
600
recovery generate 30% Biochar Yield
methane 500
20% Biochar Yield
10% Biochar Yield
Global Warming Mitigaion Potential,
Some decrease in
g CO2-Ceq/kg dry biomass
mitigation potential 400 Modern
Slow
results Pyrolysis
300
Difference in biochar
yield is far more 200
important Traditional kilns
w/ no energy recovery
These methods still 100
yield a positive result
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
CH4 Emissions (Percent of all C Emissions)
JE Amonette 04Mar2010

22. Impact of Energy Recovery
All Sustainable Biomass
Recovery of energy 70% Pyrolysis Energy Recovery Efficiency
released during 600
pyrolysis improves
mitigation potential 500
Modern
Global Warming Mitigaion Potential,
significantly Slow
g CO2-Ceq/kg dry biomass
Pyrolysis
400
Modern pyrolysis
methods should be 300
implemented wherever
possible 200
36% Biochar Yield
Economic decision 30% Biochar Yield
Traditional kilns
w/ no energy recovery
100
20% Biochar Yield
10% Biochar Yield
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
CH4 Emissions (Percent of all C Emissions)
JE Amonette 04Mar2010

23. The Biofuel N2O Problem
Recent work (Crutzen et al., 2007; Del Grosso, 2008) suggests that
globally, N2O production averages at 4% (+/- 1%) of N that is fixed
IPCC reports have accounted only for field measurements of N2O
emitted, which show values close to 1%, but ignore other indicators
discussed by Crutzen et al.
If 4% is correct, then combustion of biofuels except for high cellulose
(low-N) fuels will actually increase global warming relative to
petroleum due to large global warming potential of N2O
Biochar avoids this issue
Ties up reactive N in a stable or slowly available pool or converts most of
it to harmless N2 during pyrolysis
Eliminates potential N2O emissions from manures and other biomass
sources converted to biochar
Decreases N2O emissions in field by improving N-fertilizer use efficiency
and increasing air-filled porosity
JE Amonette 04Mar2010

24. Where does Biochar Fit?
Offers a flexible blend of biofuel energy, soil fertility enhancement,
and climate change mitigation
Limited by biomass availability and, eventually, land disposal area
How much biomass can be made available for biochar production vs.
other uses?
Crop-derived biofuels cannot supply all the world’s energy needs
Maximum estimates suggest 50% of current, 33% of future
Biodiversity (HANPP)?
N2O?
Perhaps best use of harvested biomass is to make biochar to draw
down atmospheric C levels and enhance soil productivity, with energy
production as a bonus (but not the driving force).
This will require government incentives (C credits/taxes?) and a
change in the way we value cropped biofuels
JE Amonette 04Mar2010

25. Further Information and Acknowledgments
International Biochar Initiative
(www.biochar-international.org)
Biochar for Environmental Management: Science and
Technology, Earthscan, 2009
North American Biochar Conference 2010
Iowa State University, June 27-30, 2010
Research supported by
USDOE Office of Fossil Energy through the National Energy Technology
Laboratory
USDOE Office of Biological and Environmental Research (OBER) through
the Carbon Sequestration in Terrestrial Ecosystems (CSiTE) project.
Research was performed at the W.R. Wiley Environmental Molecular Sciences
Laboratory, a national scientific user facility at the Pacific Northwest National
Laboratory (PNNL) sponsored by the USDOE-OBER.
PNNL is operated for the USDOE by Battelle Memorial Institute under contract
DE AC06 76RL01830.
PNNL-SA-64398
JE Amonette 04Mar2010

26. References Cited
Amonette, J. E., and Joseph, S. 2009. Characteristics of biochar: Micro-chemical properties. Chapter 3 in (J. Lehmann
and S. Joseph, eds.) Biochar for Environmental Management: Science and Technology. Earthscan, London, UK
and Sterling, VA.
Antal, M. J. Jr. and Grønli, M. 2003. ‘The art, science, and technology of charcoal production’, Industrial and Engineering
Chemistry Research, vol 42, pp1619-1640
Antal, M. J. Jr., Allen, S. G., Dai, X.-F., Shimizu, B., Tam, M. S. and Grønli, M. 2000. ‘Attainment of the theoretical yield of
carbon from biomass’, Industrial and Engineering Chemistry Research, vol 39, pp4024-4031
Brown, R. 2009. Biochar production technology. Chapter 7 in (J. Lehmann and S. Joseph, eds.) Biochar for
Environmental Management: Science and Technology. Earthscan, London, UK and Sterling, VA.
Crutzen, P. J., Mosier, A. R., Smith, K. A., and Winiwarter, W. 2007. ‘N2O release from agro-biofuel production negates
global warming reduction by replacing fossil fuels.’ Atmos. Chem. Discuss. 7:11191-11205.
Del Grosso, S. J., Wirth, T., Ogle, S. M., and Parton, W. J. 2008. ‘Estimating agricultural nitrous oxide emissions.’ Eos
89(51):529-530.
Demirbas, A. (2001) ‘Carbonization ranking of selected biomass for charcoal, liquid and gaseous products’, Energy
Conversion and Management, vol 42, pp1229-1238
Figueiredo, J. L., Valenzuela, C., Bernalte, A. and Encinar, J. M. 1989. ‘Pyrolysis of holm-oak wood: influence of
temperature and particle size’, Fuel, vol 68, pp1012-1017
Haberl, H. Heinz Erb, K., Krausmann, F., Gaube, V., Bondeau, A., Plutzar, C., Gingrich, S., Lucht, W., and Fischer-
Kowalski, M. 2007. ‘Quantifying and mapping the human appropriation of net primary production in earth’s
terrestrial ecosystems.’ Proc. Natl. Acad. Sci. 104:12942-12947.
Schenkel, Y. 1999. ‘Modelisation des flux massiques et energetiques dans la carbonisation du bois en four cornue’, PhD
thesis, Université des Sciences Agronomiques de Gembloux, Gembloux, Belgium
Scott, D. S., Piskorz, J., Bergougnou, M. A., Graham, R. and Overend, R. P. 1988. ‘The role of temperature in the fast
pyrolysis of cellulose and wood’, Industrial and Engineering Chemistry Research, 27, 8-15.
Velicogna, I. 2009. ‘Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE’,
Geophysical Research Letters, 36, L19503.
JE Amonette 04Mar2010