Elemental Composition and Flue Gas Emissions of Different Components from Five Semi-Arid Woody Species in Pyrolysed and Non-Pyrolysed Material

Abstract

Biofuels are sustainable alternatives to fossil fuels. However, they must comply with energy efficiency requirements and contribute to environmental protection. This study was focused on elemental composition (carbon, hydrogen, nitrogen, sulphur and chlorine) of different plants’ components (stems, branches, twigs and leaves) from pyrolysed (charcoal) and non-pyrolysed samples of five semi-arid trees: Acacia berlandieri, A. wrightii, Ebenopsis ebano, Havardia pallens and Helietta parvifolia. Carbon fluctuated from 80.77% to 89.30% in charcoal and 44.99% to 49.70% in non-pyrolysed biomass, and hydrogen ranged from 2.38% to 2.69% in charcoal and 5.89% to 6.62% in non-pyrolysed biomass. Nitrogen accounted for 0.39%–0.65% (branches) and 0.32%–0.64% (stems) in charcoal, and the ranges for non-pyrolyzed material were 2.33–4.00% (leaves), 1.06%–1.76% (twigs), 0.21%–0.52% (branches) and 0.15%–0.28% (stems). Considerably higher concentrations of sulphur compared to chlorine were found, with increasing values for both elements from the base of trees to the leaves. Non-pyrolysed samples were characterized by 68.05 mg/kg–769.16 mg/kg (stems), 118.02 mg/kg–791.68 mg/kg (branches), 225.11 mg/kg–1742.25 mg/kg (twigs) and 374.73 mg/kg–6811.52 mg/kg (leaves) for sulphur, and 117.86 mg/kg–528.08 mg/kg (stems), 109.18 mg/kg–464.15 mg/kg (branches), 905.47 mg/kg–4205.19 mg/kg (twigs) and 2799.68 mg/kg–5072.76 mg/kg (leaves) for chlorine. In charcoal, the concentration ranges for sulphur were 47.54 mg/kg–376.95 mg/kg (branches) and 42.73–292.20 mg/kg (stems) and 139.34 mg/kg–419.68 mg/kg (branches) and 177.39 mg/kg–479.16 (stems) for chlorine. The study has shown that pyrolysis increased the amount of carbon and decreased the amount of hydrogen. Coincidentally, the amount of nitrogen, chlorine and sulphur could be decreased significantly by pyrolysis which means an improvement of the fuel considering the flue gas emissions. Besides the influence of the type of combustion plant and the influence of the source of biofuel, the treatment has a significant influence on the amount and composition of flue gases emitted in the combustion.