Abstract
The production of thermal energy is one of the sources of environmental pollution, especially when it uses traditional fossil fuels (in particular hard and brown coal). Burning conventional fuels contributes to air pollution because of emitting gases and producing waste after the process of burning in the form of ash. The work below was aimed at determining the indirect emission of PAHs in the form of fly ash, depending on the type of fuel burned. The conducted research showed which solid fuel combustion content leaves the lowest content of PAH in the fly ash. This work contains the analysis and assessment of the content of 16 PAHs (polycyclic aromatic hydrocarbons) in fly ash from the combustion of five selected solid fuels in low-power boilers. The following fuels were chosen for the research: hard coal with granulation above 60 mm, coal with the grain size of 25–80 mm, coal with the grain size of 8–25 mm, pellets with the grain size of 6 mm, and mixed dry wood. The results of the research showed that the most frequent and most concentrated compounds were naphthalene and acenaphthylene from the PAH group. These hydrocarbons have the smallest number of rings in a molecule. It was also found that the content of the LMW (Low Molecular Weight Polycyclic Aromatic Hydrocarbons) fractions in the fly ash from the analyzed fuels in ∑PAHs exceeds 57% in the case of 6 mm pellets and in the case of the ash from wood and hard coal when the grain size >60 mm. The opposite dependence can be observed in the case of the HMW (High Molecular Weight Polycyclic Aromatic Hydrocarbons) fraction.
Highlights
Polycyclic aromatic hydrocarbons are classified as persistent organic pollutants (POP), which are widely spread in the environment as a result of industrialization [1,2]
The greatest concentration of them was noticed in the sample of fly ash from the combustion of wooden biomass in the form of mixed firewood
The analysis showed that naphthalene had the biggest share of all PAHs in the fly ash samples (Figure 8)
Summary
Polycyclic aromatic hydrocarbons are classified as persistent organic pollutants (POP), which are widely spread in the environment as a result of industrialization [1,2]. PAHs are lipophile compounds consisting of two to seven aromatic benzene rings in linear, angular, or cluster arrangements. They result from the stability of the compounds in the environment, and stable PAHs tend to accumulate mainly in soil and sediments. The physicochemical properties, distribution, and behavior of the PAH in the environment differ significantly due to their molecular masses. Together with the increase in the molecular mass, the melting point, the boiling point, and the lipophilicity of the PAH increases in relation to the log KOW (the octanol/water partition coefficient), and the solubility in water decreases, which suggests increased solubility in lipid compounds [3,4].
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