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Production

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Biochar is a high-carbon, fine-grained residue that today is produced through modern pyrolysis processes; it is the direct thermal decomposition of biomass in the absence of oxygen (preventing combustion), which produces a mixture of solids (the biochar proper), liquid (bio-oil), and gas (syngas) products. The specific yield from the pyrolysis is dependent on process condition, such as temperature, residence time and heating rate.[1] These parameters can be optimized to produce either energy or biochar.[2] Temperatures of 400–500 °C (673–773 K) produce more char, while temperatures above 700 °C (973 K) favor the yield of liquid and gas fuel components.[3] Pyrolysis occurs more quickly at the higher temperatures, typically requiring seconds instead of hours. The increasing heating rate will also lead to a decrease of pyrolysis biochar yield, while the temperature is in the range of 350–600 °C (623–873 K).[4] Typical yields are 60% bio-oil, 20% biochar, and 20% syngas. By comparison, slow pyrolysis can produce substantially more char (~35%);[3] it is this which contributes to the observed soil fertility of terra preta. Once initialized, both processes produce net energy. For typical inputs, the energy required to run a “fast” pyrolyzer is approximately 15% of the energy that it outputs.[5] Modern pyrolysis plants can use the syngas created by the pyrolysis process and output 3–9 times the amount of energy required to run.[6]

The Amazonian pit/trench method[6] harvests neither bio-oil nor syngas, and releases a large amount of CO2, black carbon, and other greenhouse gases (GHGs) (and potentially, toxins) into the air, though less greenhouse gasses than captured during the growth of the biomass. Commercial-scale systems process agricultural waste, paper byproducts, and even municipal waste and typically eliminate these side effects by capturing and using the liquid and gas products. The production of biochar as an output is not a priority in most cases.

Centralized, decentralized, and mobile systems

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In a centralized system, all biomass in a region is brought to a central plant for processing. Alternatively, each farmer or group of farmers can operate a lower-tech kiln. Finally, a truck equipped with a pyrolyzer can move from place to place to pyrolyze biomass. Vehicle power comes from the syngas stream, while the biochar remains on the farm. The biofuel is sent to a refinery or storage site. Factors that influence the choice of system type include the cost of transportation of the liquid and solid byproducts, the amount of material to be processed, and the ability to feed directly into the power grid.

For crops that are not exclusively for biochar production, the Residue-to-Product Ratio (RPR) and the collection factor (CF) the percent of the residue not used for other things, measure the approximate amount of feedstock that can be obtained for pyrolysis after harvesting the primary product. For instance, Brazil harvests approximately 460 million tons (MT) of sugarcane annually,[7] with an RPR of 0.30, and a CF of 0.70 for the sugarcane tops, which normally are burned in the field.[8] This translates into approximately 100 MT of residue annually, which could be pyrolyzed to create energy and soil additives. Adding in the bagasse (sugarcane waste) (RPR=0.29 CF=1.0), which is otherwise burned (inefficiently) in boilers, raises the total to 230 MT of pyrolysis feedstock. Some plant residue, however, must remain on the soil to avoid increased costs and emissions from nitrogen fertilizers.[9]

Pyrolysis technologies for processing loose and leafy biomass produce both biochar and syngas.[10]

Thermo-catalytic depolymerization

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Alternatively, "thermo-catalytic depolymerization", which utilizes microwaves, has recently been used to efficiently convert organic matter to biochar on an industrial scale, producing ~50% char.[11][12]

Properties

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The physical and chemical properties of biochars decided by feedstocks and technologies are crucial for the application of biochars in the industry and environment. Different characterization data are employed to biochars and determine their performances in a specific use. For example, the guideline published by Internation Biochar Initiative provided standardized methods in evaluating the product quality of biochar for soil application.[13]These properties of biochar can be characterized by various aspects, including the proximate and elemental composition, pH value, porosity etc., which correlate to different biochar properties. The atomic ratios of biochar, including H/C and O/C ratio, correlate the biochar properties that relevant to the soil organic removal such as polarity and aromaticity.[14] The van-Krevelen diagram can be used to show the evolution of biochar atomic ratios in the production process.[15] In the carbonization process, both the H/C and O/C ratio decreased due to the release of functional groups which contain hydrogen and oxygen.[16]

Uses

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Carbon sink

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Notes

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  1. ^ Tripathi, Manoj; Sabu, J.N.; Ganesan, P. (21 November 2015). "Effect of process parameters on production of biochar from biomass waste through pyrolysis: A review". Renewable and Sustainable Energy Reviews. 55: 467–481. doi:10.1016/j.rser.2015.10.122. ISSN 1364-0321.
  2. ^ Gaunt & Lehmann 2008, pp. 4152, 4155 ("Assuming that the energy in syngas is converted to electricity with an efficiency of 35%, the recovery in the life cycle energy balance ranges from 92 to 274 kg CO2 MWn−1 of electricity generated where the pyrolysis process is optimized for energy and 120 to 360 kg CO2 MWn−1 where biochar is applied to land. This compares to emissions of 600–900 kg CO
    2     MWh−1 for fossil-fuel-based technologies.)
  3. ^ a b Winsley, Peter (2007). "Biochar and bioenergy production for climate change mitigation". New Zealand Science Review. 64. (See Table 1 for differences in output for Fast, Intermediate, Slow, and Gasification).
  4. ^ Aysu, Tevfik; Küçük, M. Maşuk (16 December 2013). "Biomass pyrolysis in a fixed-bed reactor: Effects of pyrolysis parameters on product yields and characterization of products". Energy. 64 (1): 1002–1025. doi:10.1016/j.energy.2013.11.053. ISSN 0360-5442.
  5. ^ Laird 2008, pp. 100, 178–181 "The energy required to operate a fast pyrolyzer is ∼15% of the total energy that can be derived from the dry biomass. Modern systems are designed to use the syngas generated by the pyrolyzer to provide all the energy needs of the pyrolyzer."
  6. ^ a b Cite error: The named reference ReferenceA was invoked but never defined (see the help page).
  7. ^ "Production Quantity Of Sugar Cane In Brazil In 2006". FAOSTAT. 2006. Archived from the original on 6 September 2015. Retrieved 1 July 2008.
  8. ^ Perera, K.K.C.K., P.G. Rathnasiri, S.A.S. Senarath, A.G.T. Sugathapala, S.C. Bhattacharya, and P. Abdul Salam, Assessment of sustainable energy potential of non-plantation biomass resources in Sri Lanka, 29 Biomass & Bioenergy 199, 204 (2005) (showing RPRs for numerous plants, describing method for determining available agricultural waste for energy and char production).
  9. ^ Laird 2008, pp. 179 "Much of the current scientific debate on the harvesting of biomass for bioenergy is focused on how much can be harvested without doing too much damage."
  10. ^ Jorapur, Rajeev; Rajvanshi, Anil K. (1997). "Sugarcane leaf-bagasse gasifier for industrial heating applications". Biomass and Bioenergy. 13 (3): 141–146. doi:10.1016/S0961-9534(97)00014-7.
  11. ^ Karagöz, Selhan; Bhaskar, Thallada; Muto, Akinori; Sakata, Yusaku; Oshiki, Toshiyuki; Kishimoto, Tamiya (1 April 2005). "Low-temperature catalytic hydrothermal treatment of wood biomass: analysis of liquid products". Chemical Engineering Journal. 108 (1–2): 127–137. doi:10.1016/j.cej.2005.01.007. ISSN 1385-8947.
  12. ^ Jha, Alok (13 March 2009). "'Biochar' goes industrial with giant microwaves to lock carbon in charcoal". The Guardian. Retrieved 23 September 2011.
  13. ^ "Standardized production definition and product testing guidelines for biochar that is used in soil" (PDF). 2015. Retrieved 23 November 2015.
  14. ^ Crombie, Kyle; Mašek, Ondřej; Sohi, Saran P.; Brownsort, Peter; Cross, Andrew (21 December 2012). "The effect of pyrolysis conditions on biochar stability as determined by three methods". Global Change Biology Bioenergy. 5 (2): 122–131. doi:10.1111/gcbb.12030. ISSN 1757-1707.
  15. ^ Krevelen D., van (1950). "Graphical-statistical method for the study of structure and reaction processes of coal". Fuel. 29: 269–284.
  16. ^ Weber, Kathrin; Quicker, Peter (1 April 2018). "Properties of biochar". Fuel. 217: 240–261. doi:10.1016/j.fuel.2017.12.054. ISSN 0016-2361.

References

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  • Aysu, Tevfik; Küçük, M. Maşuk (16 December 2013). "Biomass pyrolysis in a fixed-bed reactor: Effects of pyrolysis parameters on product yields and characterization of products". Energy. 64 (1): 1002–1025. doi:10.1016/j.energy.2013.11.053. ISSN 0360-5442.
  • Badger, Phillip C.; Fransham, Peter (2006). "Use of mobile fast pyrolysis plants to densify biomass and reduce biomass handling costs—A preliminary assessment". Biomass & Bioenergy. 30 (4): 321–325. doi:10.1016/j.biombioe.2005.07.011.
  • Glaser, Bruno; Lehmann, Johannes; Zech, Wolfgang (2002). "Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review". Biology and Fertility of Soils. 35 (4): 219–230. doi:10.1007/s00374-002-0466-4.
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Category:Charcoal Category:Environmental soil science Category:Soil improvers Category:Wildfire ecology

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