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Fundamentals of biochar production

TitleFundamentals of biochar production
Publication TypeBook Chapter
Year of Publication2015
AuthorsBrown, Robert, del Campo Bernardo, Boateng Akwasi A., Garcia-Perez Manuel, and Masek Ondrej
Book TitleBiochar for Environmental Management: Science and Technology and Implementation

Biochar production cannot be properly discussed without first distinguishing it from char and charcoal. The literature contains many examples where these three terms for carbonaceous materials are freely interchanged, which causes unnecessary confusion. All three forms of carbonaceous material are produced from pyrolysis, the process of heating carbon (C)-bearing solid material under oxygen-starved conditions. Pyrogenic carbonaceous residue from pyrolysis (Chapter 1). Thus, PCM is the most general term to employ in scientific descriptions of the products of pyrolysis and fires whether from biomass or other materials. Char is the PCM residue from natural fires. Charcoal is PCM produced from pyrolysis of animal or vegetable matter in kilns for use in cooking or heating, including industrial applications such as smelting. Biochar is carbonaceous material produced specifically for application to soil for agronomic or environmental management. In 2012 the International Biochar Initiative (IBI) released the first Guidelines for 'Biochar that is used in Soil' to formally define this carbonaceous product and describe its desired characteristics. However, continuing research is required to understand what constituted 'good' biochar in agronomic and environmental management applications. Since most information on preparation of carbonaceous material stems from charcoal production, this chapter will review traditioal charcoal making processes as a first step in understanding how to design modern biochar systems. Although C is the major constituent of charcoal, its exact composition and physical properties depends upon the starting material and the conditions under which it is produced. Charcoal contains 65 per cent to 90 per cent solid C with the balannce being volatile matter and mineral matter (ash) (Antal and Gronli, 2003). Nevertheless, other thermochemical pathways are being developed that produce an array of different gaseous, liquid and solid (PCM) products while offering improved efficiency, increased quality control and fewer environemntal impacts than traditional charcoal making. Superficially charcoal resembles coal, which is also derived from vegetable matter; indeed the word charcoal may have originally meant 'the making of coal' (Encyclopedia Britanica, 1911). However, the geological processes from which coal is derived are quite different from charcoal resulting in important differences in chemical composition, porosity and reactivity. Char is readily generated in open fires, whether forest fires or campfires, under oxygen poor conditions. Thus, PCM was available to early humankind, who used it to create spectacular cave paintings during the last ice age (Bard, 2002). PCM eventually found application in other fields including agronomy, medicine matallurgy, pyrotechnics and chemical manufacture. However, its largrdt application has always been in the preparation of smokeless fuel for cooking, residential heating, smelting and steel making. The process of charcoal making removes most of the volatile matter responsible for smoke during burning. Charcoal is a relatively clean-burning fuel that represented an important innovation in the controlled use of fire. Biochar engineered as soil amendment and C sequestration agent are relatively new applications requiring significant research and development.