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Biochar
Biochar (also known as "agri-char") resembles charcoal in that it is produced through pyrolysis, the direct thermal decomposition of biomass in the absence of oxygen. While charcoal is primarily used as a fuel, biochar is generally used as a soil additive. The benefits of this are numberous: it can help reduce climate change by mitigating greenhouse gas emissions and sequestering atmospheric carbon in soil, and can improve water quality by preventing chemical run-off. Biochar can also be used in tandem with the other products of pyrolisis, bio-oil and syngas, to produce energy or for transportation fuel.
Biochar has numerous agricultural benefits when added to soil.
Author: Betchkal. Permission: Creative Commons NonCommercial ShareAlike.Production
Humans have produced biochar as a source of energy throughout modern history. Pre-Columbian Amazonian Indians made biochar from agricultural waste and used it to enhance soil productivity.1 They called it “Terra Preta de Indio.”2 The modern equivalent of terra preta is being developed using pyrolysis to heat biomass in the absence of oxygen in kilns. 3
Pyrolysis is the direct thermal decomposition of biomass in the absence of oxygen to obtain an array of solid (biochar), liquid (bio-oil) and gas (syngas) products. The specific yield from the pyrolysis can be optimized to produce any of the three products depending on process conditions.4 The yield of products from pyrolysis varies heavily with temperature. The lower the temperature, the more char is created per unit biomass.5 Modern biochar production can be combined with biofuel production in a process that is energy-positive—producing 3-9 times more energy than invested, and carbon-negative—withdrawing CO2 from the atmosphere and rebuilding geological carbon sinks.6 Even when optimized to produce char rather than energy, the energy produced per unit energy input is higher than for corn ethanol.7
High temperature pyrolysis is also known as gasification, and produces primarily syngas from the biomass.8 The two main methods of pyrolysis are “fast” pyrolysis and “slow” pyrolysis. Fast pyrolysis yields 60% bio-oil, 20% biochar, and 20% syngas, and can be done in seconds, whereas slow pyrolysis can be optimized to produce substantially more char (~50%), but takes on the order of hours to complete. For typical inputs, the energy required to run a “fast” pyrolyzer is approximately 15% of the energy that it outputs.9 Modern pyrolysis plants can be run entirely off of the syngas created by the pyrolysis process and thus output 3-9 times the amount of energy required to run.10
The ancient method for producing biochar as a soil additive was the “pit” or “trench” method, which created terra preta, or dark soil.11 While this method is still a potential to produce biochar in rural areas, it does not allow the harvest of either the bio-oil or syngas, and releases a large amount of CO2, black carbon, and other greenhouse gases (and potentially, toxins) into the air. Modern companies are producing commercial-scale systems to process agricultural waste, paper byproducts, and even municipal waste.
Technology
There are three primary methods for deploying a pyrolysis system. The first is a centralized system where all biomass in the region would be brought to a pyrolysis plant for processing. A second system would effectively mean a lower-tech pyrolysis kiln for each farmer or small group of farmers. A third system is a mobile system where a truck equipped with a pyrolyzer would be driven around to pyrolyze biomass. It would be powered using the syngas stream, return the biochar to the earth, and transport the bio-oil to a refinery or storage site. Whether a centralized system, a distributed system, or a mobile system is preferred is heavily dependent on the specific region. The cost of transportation of the liquid and solid byproducts, the amount of material to be processed in a region, and the ability to feed directly into the power grid are all factors to be considered when deciding on a specific implementation.
Unless crops are going to be dedicated to biochar production, the residue-to-product ratio (RPR) for the feedstock material is a useful gauge of the approximate amount of feedstock that can be obtained for pyrolysis after the primary product is harvested and the waste remains. The amount of crop residue available to be used for pyrolysis can be determined by using the RPR, and the collection factor (the percent of the residue not used for other things). For instance, Brazil harvests approximately 460Mt of sugar cane annually.12 with an RPR of 0.30, and a collection factor (CF) of 0.70 for the sugar cane tops, which are normally burned on the field.13 This translates into approximately 100Mt of residue which can be pyrolyzed to create energy and soil additives annually. Adding in the bagasse (sugar cane waste) (RPR=0.29 CF=1.0) which is currently burned inefficiently in boilers, raises the total to 230 Mt of pyrolysis feedstock just from sugar cane residues. Some plant residue, however, must remain on the soil to avoid heavily increased costs and emissions from nitrogen fertilizers.14
Johannes Lehmann, of Cornell University, estimates that pyrolysis will be cost feasible when the cost of a CO2 ton reaches $3715 (as of the end of June 2008, CO2 is trading at ~$45/ton on the ECX) – so using pyrolysis for bio-energy production is feasible, even though it may be more expensive than fossil fuels at the moment. 15
Applications
Biochar has been identified as a carbon sink with enormous potential because of the very low technical requirements and many applications. Biochar's beneficial properties for soil also lend them to important agricultural applications.
Biochar as a carbon sink
Biochar can be used to sequester carbon on centurial or even millennial time scales. Plant matter absorbs CO2 from the atmosphere while growing. In the natural carbon cycle, plant matter decomposes rapidly after the plant dies, which emits CO2. Instead of allowing the plant matter to decompose, pyrolysis can be used to sequester the carbon in a much more stable form. Biochar thus removes circulating CO2 from the atmosphere and stores it in virtually permanent soil carbon pools, making it a truly carbon-negative process. In places like the Rocky Mountains, where beetles have been killing of vast swathes of pine trees, the utilization of pyrolysis to char the trees instead of letting them decompose into the atmosphere would offset substantial amounts of CO2 emissions. Although some organic matter is necessary for agricultural soil to maintain its productivity, much of the agricultural waste can be turned directly into biochar, bio-oil, and syngas.16 The use of pyrolysis also provides an opportunity for the processing of municipal waste into useful clean energy rather than increased problems with land space for storage.17
Biochar is believed to have long mean residence times in the soil. While the methods by which biochar mineralizes (turns into CO2 ) are not completely known,18 evidence from soil samples in the Amazon shows large concentrations of black carbon (biochar) remaining after they were abandoned thousands of years ago.19 The amount of time the biochar will remain in the soil depends on the feedstock material, how charred the material is, the surface:volume ratio of the particles, and the conditions of the soil the biochar is placed in.20 Estimates for the residence time range from 100 to 10,000 yrs, with 5,000 being a common estimate.21 Lab experiments confirm a decrease in carbon mineralization with increasing temperature, so carefully controlled charring of plant matter can increase the soil residence time of the biochar.22
Under some circumstances, the addition of biochar to the soil has been found to accelerate the mineralization of the existing soil organic matter,23 but this would only reduce the net benefit gained by sequestering carbon in the soil by this method. Furthermore, the suggested soil conditions for the integration of biochar are in heavily degraded tropical soils used for agriculture, not organic matter rich boreal forest soils.
Agricultural Applications
In addition to its potential for carbon sequestration, biochar has numerous co-benefits when added to soil. It can prevent the leaching of nutrients out of the soil,24 increase the available nutrients for plant growth,25 increase water retention,26 and reduce the amount of fertilizer required. Additionally, it has been shown to decrease N20 and CH4 emissions from soil, thus further reducing greenhouse gas emissions27 Biochar can be utilized in many applications as a replacement for or coterminous strategy with other bio-energy production strategies. One is switching from “slash-and-burn” to “slash-and-char” to prevent the rapid deforestation and subsequent degradation of soils.Biochar can be used as a soil amendment to increase plant growth yield,28 improve water quality, reduce soil emissions of greenhouse gases, reduce leaching of nutrients, reduce soil acidity, and reduce irrigation and fertilizer requirements.29 These properties are very dependent on the properties of the biochar, 30 and may depend on regional conditions including soil type, condition (depleted or healthy), temperature, and humidity.31 Modest additions of biochar to soil were found to reduce N2O emissions by up to 80% and completely suppress methane emissions.32
Switching from slash-and-burn to slash-and-char techniques in Brazil can both decrease deforestation of the Amazon and increase the crop yield. Under the current method of slash-and-burn, only 3% of the carbon from the organic material is left in the soil.33 Switching to slash-and-char can sequester up to 50% of the carbon in a highly stable form.34 Adding the biochar back into the soil rather than removing it all for energy production is necessary to avoid heavy increases in the cost and emissions from more required nitrogen fertilizers.35 Additionally, by improving the soil tilth, fertility, and productivity, the biochar enhanced soils can sustain agricultural production, whereas non-amended soils quickly become depleted of nutrients, and the fields are abandoned, leading to a continuous slash-and-burn cycle and the continued loss of tropical rainforest.
Using pyrolysis to produce bio-energy also has the added benefit of not requiring infrastructure changes the way processing biomass for cellulosic ethanol does. Additionally, the biochar produced can be applied by the currently used tillage machinery or equipment used to apply fertilizer.36
Bio-oil and Syngas
Bio-oil, a co-product of biochar in pyrolisis, can be used as a replacement for numerous applications where fuel oil is used, including fueling space heaters, furnaces, and boilers.37 Additionally, it can be used to fuel some combustion turbines and reciprocating engines, and as a source to create several chemicals.38 If bio-oil is used without modification, care must be taken to prevent emissions of black carbon and other particulates. Syngas and bio-oil can also be “upgraded” to transportation fuels like biodiesel and gasoline substitutes.39 If biochar is used for the production of energy rather than as a soil amendment, it can be directly substituted for any application that uses coal. Pyrolysis also may be the most cost-effective way of producing electrical energy from biomaterial.40 Syngas can be burned directly, used as a fuel for gas engines and gas turbines, or potentially used in the production of methanol and hydrogen.41
Bio-oil has a much higher energy density than the raw biomass material.42 Mobile pyrolysis units can be used to lower the costs of transportation of the biomass itself if the biochar is returned to the soil and the syngas stream is used to power the process.43 Bio-oil contains organic acids which are corrosive to steel containers, has a high water vapor content which is detrimental to ignition, and contains some biochar in the liquid which can block injectors.44
Legislation and Standards
In the United States, Senator Baucus (Dem-Montana) co-sponsored a bill along with his fellow Senator Tester (Dem-Montana) called Water Efficiency via Carbon Harvesting and Restoration Act, or WE CHAR. It focuses on promoting biochar technology to address invasive species and forest biomass. It includes grants and loans for biochar market research and development, biochar characterization and environmental analyses. It directs USDI and USDA to provide loan guarantees for biochar technologies and on-the-ground production with an emphasis on biomass from public lands. And the USGS would do biomas availability assessments.45
The Clean Energy Partnerships Act of 2009 is a bill designed to ensure that any US domestic cap-and-trade bill provides maximum incentives and opportunities for the US agricultural and forestry sectors to provide high-quality offsets and GHG emissions reductions for credit or financial incentives. Carbon offsets play a critical role in keeping the costs of a cap-and-trade program low for society as well as for capped sectors and entities, while providing valuable emissions reductions and income generation opportunities for the agricultural sector. The bill specifically identifies biochar production and use as eligible for offset credits, and identifies biochar as a high priority for USDA R&D, with funding authorized by the bill.46
Concerns and Criticism
Some environmentalist groups have expressed concerns that biochar could be commodified by private companies and lead to monocropping and commercial tree plantations in order to supply the plant mass needed to make biochar. This in turn could lead to displacement of natural forest ecosystems in favor of single-species tree plantations. Others have likewise expressed concern that patents on the process of pyrolysis will make small, decentralized systems of biochar production and distribution difficult to implement legally.
Resources
Biochar Soil Management (Cornell University)
International Biochar Initiative
Major endorsements
Biochar has begun to gain some high-level endorses - both politicians and scientists. Former Colorado Sentor and now Secretary of Interior Ken Salazar has done the most to nurse this biofuels system in his Biochar provisions in the 2007 and 2008 farm bill.47 NASA's Dr. James Hansen identifies biochar and land management as the central technology for carbon negative energy systems, and thus critical to global warming solutions.48 Dr. James Lovelock, famous for the Gaia hypothesis, has gone as far as to say that b says Biochar is "The only hope for mankind"
Charles Mann ("1491") in the Sept. National Geographic has a wonderful soils article which places Terra Preta / Biochar soils center stage.
http://ngm.nationalgeographic.com/20...soil/mann-text
Al Gore got the CO2 absorption thing wrong, ( at NABC Vilsack did same), but his focus on Soil Carbon is right on;
http://www.newsweek.com/id/220552/page/3
Tony Blair & Richard Branson in the UK and conservative party opposition leader John Turnbull in Oz.
Footnotes
1. : Dawit Solomon, Molecular signature and sources of biochemical recalcitrance of organic C in Amazonian Dark Earths, 71 Geochemica et Cosmochemica Acta 2285, 2286 (2007).
2. : Bruno Glaser, et al., Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review, 35 Biology and Fertility Soils 219, 220 (2002).
3. : Johannes Lehmann, A handful of carbon, 447 Nature 143, 143 (2007).
4. : John L. Gaunt and Johannes Lehmann, Energy Balance and Emissions Associated with Biochar Sequestration and Pyrolysis Bioenergy Production, 42 Envtl. Sci. & Tech. 4152, 4155 (2008).
5. : Peter Winsley, Biochar and bioenergy production for climate change mitigation, 64 New Zealand Sci. Rev. 5 (2007). (See Table 1 for differences in output for Fast, Intermediate, Slow, and Gasification).
6. : Johannes Lehmann, Bio-energy in the black, 5 Front Ecol Environ 381, 385 (2007).
7. : John L. Gaunt and Johannes Lehmann, Energy Balance and Emissions Associated with Biochar Sequestration and Pyrolysis Bioenergy Production, 42 Envtl. Sci. & Tech. 4152 (2008).
8. : Peter Winsley, Biochar and bioenergy production for climate change mitigation, 64 New Zealand Sci. Rev. 5 (2007).
9. : David A. Laird, The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, While Improving Soil and Air Quality, 100 Agronomy J. 178, 179 (2008).
10. Johannes Lehmann, Bio-energy in the black, 381, 385.
11. : Johannes Lehmann, Bio-energy in the black, 386.
12. : FAOSTAT 2006. Retrieved on 1 July 2008 (production quantity of sugar cane in Brazil in 2006).
13. K.K.C.K. Perera et al., Assessment of sustainable energy potential of non-plantation biomass resources in Sri Lanka, 29 Biomass & Bioenergy 199, 204 (2005).
14. : David A. Laird, The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, While Improving Soil and Air Quality, 179.
15. : Johannes Lehmann, Bio-energy in the black, 144.
16. : The question scientists are debating is precisely how much can be removed. Adding the char back into the soil makes up for a large amount of the SOM needed, but it may not be sufficient in all cases.
17. : Y. Shinogi, et el., Basic characteristics of low-temperature carbon products from waste sludge, 7 Advances Envtl. Res. 661, (2003) (“The results showed there are not harmful levels (based on the Japanese standard) of heavy metals and harmful substances.”)
18. : C.A. Masiello, New directions in black carbon organic geochemistry, 92 Marine Chemistry 201, 202 (2004).
19. : Johannes Lehmann et al., Biochar Sequestration In Terrestrial Ecosystems – A Review, 11 Mitigation and Adaptation Strategies for Global Change 403, 404 (2006).
20. : Chih-Hsin Cheng, et el., Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along a climosequence, 72 Geochimica et Cosmochemica Acta 1598, 1599 (2008).
21. : Chih-Hsin Cheng, et al., Stability of black carbon in soils across a climatic gradient, 113 J. Geophysical Res. G02027, 8 (2008).
22. : Baldock and Smernik (2002) used red pine (Pinus resinosa) wood charred at different temperatures. After 120 days incubation in sand, 20% of C was mineralized from wood heated at 70 C (essentially unaltered). Carbon mineralization decreased to 13% for wood heated to 150 C, and to less than 2% for chars produced at 200–350 C, with increasing proportions of aromatic C.
23. : Wardle, David, et al., Fire-Derived Charcoal Causes Loss of Forest Humus, 320 Science 1 (2 May 2008).
24. : Christoph Steiner, et el., Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil, 291 Plant & Soil 275, 287 (2007).
25. : Christoph Steiner, et el., Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil, 291 Plant & Soil 275, 287 (2007).
26. : Bruno Glaser, et al., Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review, 223.
27. : John L. Gaunt and Johannes Lehmann, Energy Balance and Emissions Associated with Biochar Sequestration and Pyrolysis Bioenergy Production, 4152.
28. Lehmann, Johannes, and Jose Pereira da Silva Jr., et al., Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments, 249 Plant & Soil 343, 355 (2003).
29. : Danny Day et al., Economical CO2, SOx, and NOx capture from fossil-fuel utilization with combined renewable hydrogen production and large-scale carbon sequestration, 30 Energy 2558, 2560.
30. : Bruno Glaser, et al., Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review, 224.
31. : Dr. Wardle points out that plant growth has been observed in tropical (depleted) soils by referencing Lehmann, but that in the boreal (high native SOM content) forest this experiment was run in, it accelerated the native soil organic matter loss. Wardle, 23.
32. : Johannes Lehmann, Bioenergy in the Black, 5 at 384.
33. : Bruno Glaser, et al., Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review, 225 (“The published data average at about 3% charcoal formation of the original biomass C.”)
34. : Johannes Lehmann, Biochar sequestration in terrestrial ecosystems, 19 at 407.
35. : John L. Gaunt and Johannes Lehmann, Energy Balance and Emissions Associated with Biochar Sequestration and Pyrolysis Bioenergy Production, 4152.
36. : Johannes Lehmann, A handful of carbon, 143.
37. Phillip C. Badger and Peter Fransham, Use of mobile fast pyrolysis plants to densify biomass and reduce biomass handling costs—A preliminary assessment, 30 Biomass & Bioenergy 321, 322 (2006)
38. : Philip C. Badger and Peter Fransham, Use of mobile fast pyrolysis plants to densify biomass and reduce biomass handling costs—A preliminary assessment, 30 Biomass & Bioenergy 321, 322 (2006).
39. : David A. Laird, The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, While Improving Soil and Air Quality, 178.
40. : Bridgwater, A. V., A.J. Toft, and J.G. Brammer, A techno-economic comparison of power production by biomass fast pyrolysis with gasification and combustion, 6 Renewable & Sustainable Energy Rev. 181, 231 (“the fast pyrolysis and diesel engine system is clearly the most economic of the novel systems at scales up to 15 MWe”);
41. : McKendry, Peter, Energy production from biomass (part 2): conversion technologies, 83 Bioresource Tech. 47, 48-49 (2002).
42. : Philip C. Badger and Peter Fransham, Use of mobile fast pyrolysis plants to densify biomass and reduce biomass handling costs—A preliminary assessment, 30 Biomass & Bioenergy, 323.
43. : Philip C. Badger and Peter Fransham, Use of mobile fast pyrolysis plants to densify biomass and reduce biomass handling costs—A preliminary assessment, 30 Biomass & Bioenergy, 322.
44. : Serdar Yaman, Pyrolysis of biomass to produce fuels and chemical feedstocks, 45 Energy Conversion & Mgmt 651, 659 (2003).
45. WashingtonWatch.com - S. 1713, The Water Efficiency via Carbon Harvesting and Restoration (WECHAR) Act of 2009
46. Clean Energy Partnership Act of 2009, Biochar International, http://www.biochar-international.org...s/END09F94.pdf.
47. http://www.biochar-international.org...gislation.html
48. http://arxiv.org/ftp/arxiv/papers/0804/0804.1126.pdf
This article was originally sourced and adapted, with permission, from:"Significant Climate Mitigation Is Available from Biochar," Institute for Governance & Sustainable Development (IGSD) (2008).
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