2.1. General Characteristics of Ash and Slag (ad.2 and ad.3 above) from the Polish Power Plant

The chemical composition of the ash from the biomass boiler (BFA) and the slag from the brown-coal boiler (LFS) from exemplary Polish power plant varies considerably in time. The random results of the fly ash tests from the biomass block are presented in Table 1 (metal analysis was performed with the ICP OES or Thermo iCAP 6500 Duo ICP plasma spectrometer at the request of the power plant). The biomass-fired boiler is equipped with a circulating fluidized bed furnace. The fuel used in the power plant is biomass consisting of a mixture of wood biomass in the form of shavings and sawdust from coniferous and deciduous trees, wooden pallets and bark in the form of shavings and of agricultural origin. The percentage of agricultural biomass in the total amount of biomass burned in the plant accounted for approximately 20%. The mentioned biofuels are produced from certified biomass produced by third parties and supplied by external suppliers. The main environmental benefits of using a biomass-fired boiler, compared to lignite-fired boilers, are the fact that sulfur dioxide emissions have decreased by approximately 1200 tons/year, nitrogen oxide emissions by approximately 1000 tonnes/year and particles of matter by about 100 tons/year [60]. In addition, CO2 emissions are considered to be environmentally neutral as they are produced by the combustion of biomass (the amount of CO2 emitted is equal to the amount of CO2 used during the lifespan of the plants). Last (2020), almost 14.5 thousand tonnes of ash were produced, all of which are still in the plant landfill.

Exemplary composition of fly ash from a biomass block, in %mass.

The analyses (Table 1) show that the iron content in ash has increased in recent years, and the content of manganese, aluminum, phosphorus, potassium and carbonates fluctuates strongly. It depends mainly on the quality of the biomass burned. In addition, in the sample of BAF collected from the silo in 2019 was recorded ZnO (0.063 %), Cr2O3 (0.02 %) and CuO2 (0.027 %) and in 2020: ZnO (231 mg/kg), Cr2O3 (1833 mg/kg), CuO (89 mg/kg) and CuO2 (2.47 mg/kg).

Table 2, on the other hand, shows the composition of furnace slag from exemplary sampling in the specified years from the Polish power plant, from which the material for the tests described in the research part of the work was obtained. The 474 MW unit, from which the slag was derived, was equipped with installation for the protection of the atmosphere-wet flue gas desulphurization and reduction of nitrogen compound emissions. The boiler is equipped with a dust furnace supplied with lignite dust. Last (2020) year, it produced over 57 thousand tons of slag, of which over 51 thousand tones remained in the company’s landfill. In this slag, the iron content exceeds the calcium content, it also happens that aluminum is more than calcium (Table 2).

The composition of furnace slag from lignite dust combustion, in the example years, in %mass.

Note: The content above has been extracted from a research article, so it may not display correctly.

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