The Composition and Origin of PM1-2 Microspheres in High-Calcium Fly Ash from Pulverized Lignite Combustion

This article presents the results of a systematic study on the composition and origin of PM1-2 microspheres in high-calcium fly ash. The composition of individual microspheres was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. It is shown that the compositions of the analyzed microspheres satisfy the general dependency with a high correlation coefficient: [SiO2 + Al2O3] = 88.80 - 1.02 [CaO + Fe2O3 + MgO], r = -0.97. The formation pathway is parallel to the general trend: anorthite, gehlenite, esseneite, tricalcium aluminate, ferrigehlenite, and brownmillerite. The microspheres were classified into four groups depending on the content of major components: Group 1 (CaO > 40, SiO2 + Al2O3 <= 35, Fe2O3 < 23, MgO < 16 wt %); Group 2 (30 < CaO < 40, SiO2 + Al2O3 <= 40, Fe2O3 < 27, MgO < 21 wt %); Group 3 (CaO <= 30, 40 <= SiO2 + Al2O3 <= 75, Fe2O3 < 10, MgO < 10 wt %); and Group 4 (14 < CaO < 40, SiO2 + Al2O3 < 14, Fe2O3 > 30, MgO <= 14 wt %). A comparative analysis of the relationship between major component concentrations suggests the routes of PM1-2 formation from feldspars and Ca-, Mg-, and Fe-humate complexes during lignite combustion.

Automated summary

This article presents a systematic study on the composition and origin of PM1-2 microspheres in high-calcium fly ash. The compositions of the microspheres were analyzed and categorized into different groups based on their major components. The study also provides insights into the formation pathways of PM1-2 microspheres.