Amonette: Biochar Introduction


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What is Biochar?
How is it Made?
How can it be Used to Mitigate Climate Change?
Where does it fit in the Environmental Technology Landscape.

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Amonette: Biochar Introduction

  1. 1. A Short Introduction to Biochar Jim Amonette Pacific Northwest National Laboratory Richland, WA 99352 USA National Society of Consulting Soil Scientists Morning Plenary 04 March 2010 PNNL-SA-71407
  2. 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. 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. 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. 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. 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. 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. 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. 9. Transformations during pyrolysis JE Amonette 04Mar2010 Keiluweit et al., 2010 EST online
  10. 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. 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. 12. What are the Properties of Biochar? Pine Wood Char Oak Wood Char Corn Cob Char JE Amonette 04Mar2010
  13. 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. 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. 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. 16. Climate Change is Accelerating Velicogna (2009) JE Amonette 04Mar2010
  17. 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. 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. 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. 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. 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. 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. 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. 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. 25. Further Information and Acknowledgments International Biochar Initiative ( 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. 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