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.
Highlights
Energy produced from biomass is a sustainable alternative in the long-term perspective to petroleum to lower emissions of carbon dioxide (CO2) and sulphur oxide (SOx), as well as nitrogen oxides (NOx) [1,2]
As a by-product of fuel combustion [6], flue gas is composed of Greenhouse Gases (GHG) that consist of CO2, N2, oxygen (O2) and water (H2O), sulphur dioxide (SO2), nitrogen oxides (NOx) and hydrogen chloride (HCl), entailing negative effects on the environment [7])
The range of nitrogen concentrations for charcoal from 0.32 to 0.65% compared to the range for non-pyrolyzed material (0.15%–0.52%) showed that treatment by pyrolysis of the biomass leads to an increase of nitrogen content on a mass basis of the resulting material
Summary
Energy produced from biomass is a sustainable alternative in the long-term perspective to petroleum to lower emissions of carbon dioxide (CO2) and sulphur oxide (SOx), as well as nitrogen oxides (NOx) [1,2]. It reduces energy dependence and contributes to increased employment in rural areas and technological development. As a by-product of fuel combustion [6], flue gas is composed of Greenhouse Gases (GHG) that consist of CO2, N2, oxygen (O2) and water (H2O), sulphur dioxide (SO2), nitrogen oxides (NOx) and hydrogen chloride (HCl), entailing negative effects on the environment [7]). Burning biomass is a precursor of significant amounts of short-living global warming substances, such as black carbon, and significantly contributes to ozone formation by photochemical reactions among its precursor VOCs and NOx [8]
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