Polynuclear aromatic hydrocarbons in fly ash from pressurized fluidized bed gasification of fuel blends. A discussion of the contribution of textile to PAHs

The identification and quantification of 20 different polynuclear aromatic hydrocarbons (PAHs) in the fly ash from a pressurized fluidized bed (PFB) air gasification system based:on hot gas filtering were determined by GC-MS analysis. A comparison was made on the basis of the results from two different sets of experiments with varied gasifier feedstock. The first set included four experiments with pure wood biomass as the gasifier fuel. In the second set a mixture of biomass and 10 wt % textile waste was used. The comparison showed that the distribution of the PAHs in the fly ash was strongly dependent on the gasifier feedstock but that the operational parameters, such as pressure and air/fuel ratio, showed minor effects. The relative content of the heavier compounds was larger for the pure biomass: experiments, while the lighter compounds became predominant in the case of the mixtures. The study showed that the decisive parameter influencing the formation was the structure of each PAH rather than its molecular weight. Thermal decomposition of the added textile resulted in the formation of phenylic radicals. The excessive occurrence of such intermediates/compounds favored the formation of the simple structured PAHs with relatively low molecular weights. The largest contribution of the textile was to PAHs consisting of two benzene rings with at least one C-C bond between, such as dibenzofurane, fluorene, and biphenyl. Formation of the PAHs consisting of two joined benzene rings, such as naphthalene and 1- and 2-methylnaphthalene, was also strongly affected by the textile addition. The smallest effect of the mixing was observed in the contents of the heavier compounds consisting of more than three benzene:rings. The differences in the relative concentrations of same compounds, such as phenanthrene and triphenylene, can be explained in the terms of their reactivity