Composition, biomass organic components

Whereas this type of calorimetry has been extremely valuable in obtaining heats of combustion of pure substances of known composition, the general literature shows that there is considerable variability associated with measuring the heat of combustion of biomass. The difficulties may be associated with an inability to account for exactly what is going on in the calorimeter by means of reaction equation giving all the reactants and products. Also, uncertainties may exist as to what comprises "ash", and what comprises the organic component, so that it becomes equally uncertain what the mass is that loses heat." [146]. 

Complex pyrolysis chemistry takes place in the conversion system of any conventional solid-fuel combustion system. The pyrolytic properties of biomass are controlled by the chemical composition of its major components, namely cellulose, hemicellulose, and lignin. Pyrolysis of these biopolymers proceeds through a series of complex, concurrent and consecutive reactions and provides a variety of products which can be divided into char, volatile (non-condensible) organic compounds (VOC), condensible organic compounds (tar), and permanent gases (water vapour, nitrogen oxides, carbon dioxide). The pyrolysis products should finally be completely oxidised in the combustion system (Figure 14). Emission problems arise as a consequence of bad control over the combustion system. 

After release from fires, organic and some inorganic components undergo rapid or more delayed chemical transformation in the atmosphere. The physical properties as well as chemical composition of smoke particles may alter on the way from the source areas (biomass burning areas) to the measurement sites in Northern Europe. There are several reasons why particle properties change. Chemical components can, e.g., become oxidized or substituted in particles, but also the condensation of secondary material onto the LRT particles during the transport changes the particle properties. 

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