Biochar fast pyrolysis

Slow pyrolysis of biomass operates at relatively low heating rates (0. l-2°C/s) and longer solid and vapor residence time (2-30 min) to favor biochar yield (Nanda et al., 2014b). Slow pyrolysis operates at temperature lower than that of fast pyrolysis, t q)ically 400 10°C and has a gas residence time usually > 5 s. Slow pyrolysis is similar to carbonization (for low temperatures and long residence times). During conventional pyrolysis, biomass is slowly devolatilized facilitating the formation of chars and some tars as the main products. This process yields different range of products with their properties dependent on temperature, inert gas flow rate and residence time. 

Brewer, C. E., Schmidt-Rohr, K., Satrio, J. A., Brown, R. C. Characterization of biochar from fast pyrolysis and gasdrcation systems. Environ Prog Sustain Energy 2009, 28, 386-3%. 

Brown, T.R., Wright, M.M. and Brown, R.C. (2011) Estimating profitability of two biochar production scenarios slow pyrolysis vs fast pyrolysis. Biofuels, Bioproducts and Biorefining, vol 5, pp. 54—68. 

Fast pyrolysis char is a byproduct of pyrolysis which is high in carbon, contains low amounts of hydrogen and almost all of the ash which was present in the feed material (Brewer et al., 2009 Chun et al., 2004 Westerhof, 2011 Jeffery et al., 2011). The pyrolysis char can be separated from the other products where it can be used for other applications such as Biochar or more usually in all current fast pyrolysis demonstration and commercial processes, it is burned to provide process heat in a secondary... 

Brewer, C.E., et al., 2009. Characterization of biochar from fast pyrolysis and gasification systems. Environmental Progress Sustainable Energy 28 (3), 386—396. 

Most thermochemical conversion technologies used for production of biofuels and biochemicals yield solid residues as a byproduct. Depending on the technology, this residue contains more or less carbon, and can therefore be considered biochar in its own right, or a biochar precursor. The key relevant technologies, fast pyrolysis, gasification, and hydrothermal carbonization are discussed individually in the following sections. 

Given the specifics of the fast pyrolysis process in terms of feedstock requirements and process conditions, ie, fast heating and short residence time in reactor, it can be expected to yield biochar with a different set of properties compared to other conversion processes, such as slow pyrolysis or gasification. The short residence time can lead to incomplete charring of the biomass particle, as observed by Bruun et al. (2011,2012). This in turn leads to lower environmental stability of biochar, and therefore lower carbon sequestration potential. This is the case even when the biomass conversion during pyrolysis is apparently complete, as reported in Brewer et al. (2009). These authors observed lower stability of fast pyrolysis biochar, assessed based on fixed carbon content and aromaticity, compared to slow pyrolysis and gasification biochar produced from the same feedstock. 

Besides stability, reflecting chemical composition, the physical properties of fast pyrolysis biochar also differ from those of slow pyrolysis biochar. Research by Bruun et al. (2012) showed somewhat higher surface area of fast pyrolysis biochar, and its... 

In terms of integration with biofuel production, utilization of fast pyrolysis biochar instead of its combustion for process heat has been shown to positively affect the life-cycle GHG emissions of biofuel production (Zaimes et al., 2015), and offer a potentially attractive option for carbon sequestration and transportation fuel production (Brown et al., 2011). 

Bmun, E.W., Hauggaard-Nielsen, H., Ibrahim, N., Egsgaard, H., Ambus, P., Jensen, P.A., Dam-Johansen, K., 2011. Influence of fast pyrolysis temperature on biochar labile fraction and short-term carbon loss in a loamy soil. Biomass Bioenergy 35 (3), 1182—1189. http //dx.doi.0rg/lO.lOl6/j.biombioe.2OlO.i2.OO8. 

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