Biomass properties fixed carbon

Biomass and coal have fundamentally different fuel properties that can lead to benefits or deterrents to co-firing. For instance, biomass is a more volatile fuel than coal and has higher oxygen content. Coal, on the other hand, has more fixed carbon than biomass. Wood fuels tend to contain very little ash (on the order of 1% ash or less) and consequently increasing the ratio of wood in biomass/coal blends can reduce the amount of ash that needs to be disposed. A negative aspect of biomass is that it can contain more chlorine than coal. This is particularly true for some grasses, straws, and other agricultural residues. 

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. 

---