Homogeneous and heterogeneous formation of SO3 in flue gases burning high sulfur coal under oxy-fuel combustion conditions

摘要

The formation of SO3 when burning high-sulfur coal under oxy-fuel combustion conditions was investigated by performing experiments in which homogeneous and heterogeneous formation processes occurred using ash from five types of coal with high sulfur contents. Increasing the temperature favored homogeneous SO3 formation processes (600 degrees C-1000 degrees C). The heterogeneous formation processes to SO3 formation was related to the ash composition. Heterogeneous formation processes contributed 20.0%-57.9% of the SO3 produced. Fe2O3 catalyzes SO3 formation, but a simple positive correlation was not found between the amount of SO3 formed and the Fe2O3 content. More SO3 was formed when the ash had high sodium and potassium contents than when the ash had low sodium and potassium contents. This may have been because ash produced by high-sulfur coal has high alkali metal sulfate contents because of the abilities of sodium and potassium to capture sulfur. SO3 is released during the processes through which sulfates are transformed into aluminosilicates. Increasing the SO2 concentration promoted homogeneous and heterogeneous formation of SO3, while increasing the SO2 concentration increased the SO3 concentration but decreased the SO3 formation ratio. Heterogeneous formation of SO3 catalyzed by ash during coal combustion cannot be ignored.