Amonette: Biochar Introduction

A Short Introduction to Biochar

Jim AmonettePacific Northwest National Laboratory

Richland, WA 99352 [email protected]

National Society of Consulting Soil ScientistsMorning Plenary04 March 2010

PNNL-SA-71407

JE Amonette 04Mar2010

OutlineWhat is Biochar?How is it Made?

Pyrolysis and Hydrothermal Carbonization ProcessesFeedstocksYields

What are its Properties?ChemicalPhysical

How can it be Used to Mitigate Climate Change?General ConceptSustainabilityNeed for Modern TechnologyBiochar, Biofuels and N2O

Where does it fit in the Environmental Technology Landscape?


What is Biochar?

ProductSolid product resulting from advanced thermal degradation of biomass

TechnologyBiofuel—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)


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 yieldsFast Pyrolysis

modern, maximizes bio-oil production, low char yieldsGasification

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


Slow Pyrolysis—Continuous Auger Feed

Gas turbine

Hopper

Heat

Fluegas

Exhaust gasand heat

Generator

Cyclone

DryerPyrolysis gases

Lignocellulosicfeedstock

Pyrolysisreactor

FeederMotor

Char

Biocharstorage

Combustor

Steam

Air

Gas cleaner and separator

Electricity Air

Mill

Gas turbine

Hopper

Heat

Fluegas

Exhaust gasand heat

Generator

Cyclone

DryerPyrolysis gases



Pyrolysisreactor

Pyrolysisreactor

FeederMotor

Char

Biocharstorage

Combustor

Steam

Air

Gas cleaner and separator

Electricity Air

Mill

courtesy Robert Brown


Fast Pyrolysis Fluidized Bed Reactor

Brown (2009)

Mill

Air

Quencher

Bio-oil

Bio-oilstorage

Hopper

Fluidizing gas

Flue gas

Vapor, gas, char

products

Cyclone

Combustor

Pyrolysis gasesLignocellulosicfeedstock

Pyrolysisreactor

Char

FeederMotorBiocharstorage

Mill

Air

Quencher

Bio-oil

Bio-oilstorageBio-oilstorage

Hopper

Fluidizing gas

Flue gas

Vapor, gas, char

products

Cyclone

Combustor

Pyrolysis gasesLignocellulosicfeedstock

Pyrolysisreactor

Pyrolysisreactor

Char

FeederMotorBiocharstorage


Pyrolysis

Competition between three processes as biomass is heated:

Biochar and gas formationLiquid and tar formationGasification and carbonization

Relative rates for these processes depend on:Highest treatment temperature (HTT) Heating rateVolatile removal rateFeedstock residence time


Competition Among Pyrolysis Processes

Factors favoring biochar formation

Lower temperatureSlower heating ratesSlower volatilization ratesLonger feedstock residence times

In general, process is more important than feedstock in determining products of pyrolysis

Eastern Red Maple Wood, Fast Pyrolysis, High Purge Rate (Scott et al., 1988)

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Spruce Wood, Slow Pyrolysis, Vacuum (Demirbas, 2001)

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Transformations during pyrolysis

Keiluweit et al., 2010 EST online


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),.


Feedstocks

Essentially all forms of biomass can be converted to biocharPreferable 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 varyLignin content can affect char yields

Lignin Content, Temperature, and Char YieldSlow Pyrolysis, Vacuum (Demirbas, 2001)

y = 0.39x + 26.76R2 = 0.99

y = 0.33x + 15.29R2 = 0.96

05

101520253035404550

0 10 20 30 40 50 60

Biomass Lignin Content, wt%

Char

Yie

ld, w

t%

Char (277 C)Char (877 C)

Corn Cob WoodHusks, Shells, Kernels


What are the Properties of Biochar?Pine Wood Char

Corn Cob Char

Oak Wood Char


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Volatile Matter, %

Fixe

d C

, %

HydrothermalSlow PyrolysisFast PyrolysisGasificationAsh-Free Line50% VM/FC100% VM/FC

JE Amonette 29 August 2009

IncreasingAsh Content

Proximate AnalysisProvides quick sense of stability and chemistry in three parameters:

Volatile matter is mass lost in heating charcoal to 950°C in covered crucible for 6 minutesAsh content is mass of residue after combustionFixed C is remainder

High ash content (KCl, SiO2), seen in corn stovers, wheatstraw, switchgrass, and manure chars (CaO) Pyrolytic chars tend to have VM/FC ratios of 0.5 to 1.0Higher fixed C contents suggest greater C stability


Other chemical propertiespH typically alkaline

pH as high as 11 measured for fresh biochars prepared at higher temperatures; good liming agentpH near neutral (5-8) for weathered biochars and those reacted with steam during or after pyrolysis

Nutrient retentionCation 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 plantsP retention improved significantly; present as ash and sorbedfrom soil, particularly when manure derivedHydrophobic surfaces (basal planes of aromatic structures) tend to retain organic compounds


Physical properties

High surface areaincreases with HTTImportant for nutrient retention

Typically adds porosity to soils, thereby decreasing bulk densitySome reports of higher water holding capacity, perhaps due to optimal pore sizes for water retention andrelease (tens of microns)

Pine Wood Char

40 μm


Climate Change is Accelerating

Velicogna (2009)

http://data.giss.nasa.gov/gistemp/graphs/

http://www.columbia.edu/~mhs119/UpdatedFigures/

http://www.columbia.edu/~mhs119/SeaLevel/


How can biochar helpmitigate climate change?

Create stable C pool using biochar in soilUse energy from pyrolysis to offset fossil C emissionsAvoid emissions of N2O and CH4

Increase net primary productivity of sub-optimal landBoundary conditions for biocharcontribution shown to right

Maximum levels are not sustainableBiochar cannot solve climate change alone


Human-Appropriated Net Primary Productivity

Haberl et al., PNAS 2007

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 useCurrent fossil-C emissions are ca. 8 GtC/yrIncreased productivity and expanded use of residues from biochar production could have a significant impact on global C budget


Sustainability Criteria

Biomass primarily from agricultural/silvicultural residuesMinimal C debt from land-use changes (10-yr maximum payback time, < 22 Mg CO2-Ceq ha-1)No previously unmanaged lands converted for biocharproduction; abandoned croplands okModern pyrolysis technology used

eliminates soot, CH4, and N2O emissionscaptures energy released as process heat, bio-oil, and flammable gases


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 NPPDefinition of sustainable may change as climate crisis deepensCapture and storage of C emitted during pyrolysis (i.e., CCS) can add significantly when available


Methane and Traditional Methods

Traditional methods without energy recovery generate methaneSome decrease in mitigation potential resultsDifference in biocharyield is far more importantThese methods still yield a positive result

Woody BiomassNo Energy Recovery

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CH4 Emissions (Percent of all C Emissions)

Glo

bal W

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Miti

gaio

n Po

tent

ial,

g CO

2-Ce

q/kg

dry

bio

mas

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36% Biochar Yield30% Biochar Yield20% Biochar Yield10% Biochar Yield

Traditional kilns w/ no energy recovery

ModernSlowPyrolysis


Impact of Energy Recovery

Recovery of energy released during pyrolysis improves mitigation potential significantlyModern pyrolysismethods should be implemented wherever possibleEconomic decision

All Sustainable Biomass70% Pyrolysis Energy Recovery Efficiency

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CH4 Emissions (Percent of all C Emissions)

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36% Biochar Yield30% Biochar Yield20% Biochar Yield10% Biochar Yield

Traditional kilns w/ no energy recovery

ModernSlowPyrolysis


The Biofuel N2O ProblemRecent work (Crutzen et al., 2007; Del Grosso, 2008) suggests that globally, N2O production averages at 4% (+/- 1%) of N that is fixedIPCC 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 N2OBiochar avoids this issue

Ties up reactive N in a stable or slowly available pool or converts most of it to harmless N2 during pyrolysisEliminates potential N2O emissions from manures and other biomass sources converted to biocharDecreases N2O emissions in field by improving N-fertilizer use efficiency and increasing air-filled porosity


Where does Biochar Fit?

Offers a flexible blend of biofuel energy, soil fertility enhancement, and climate change mitigationLimited by biomass availability and, eventually, land disposal areaHow 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 futureBiodiversity (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 achange in the way we value cropped biofuels


Further Information and AcknowledgmentsInternational Biochar Initiative (www.biochar-international.org)

Biochar for Environmental Management: Science and Technology, Earthscan, 2009North American Biochar Conference 2010Iowa 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


References CitedAmonette, 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.’ Eos89(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.