Search

• Thermal stability analysis of As clarifies dominance of chemical adsorption. • As amount adsorbed by ash in flue gas is far less than ash's adsorption capacity. • Chemical adsorption by ash is mainly through the joint action of Ca and Fe in ash. • As Adsorption by high-Ca ash increases with temperature due to the stable product. • Instability of Fe 2 O 3 product make As amount adsorbed by high-Fe ash peak at 800 °C. Arsenic (As) transformation during flue-gas cooling process determines terminal As emission. In this study, the dominant role of chemical adsorption in gaseous As transformed to ash was confirmed. Dynamic curves of As 2 O 3 adsorption by ash at 500–900 °C were obtained. The adsorbed As amount increased linearly with time, far from reaching saturation, and the maximum amount was approximately 10 times the As content in ash collected from power plant dust collectors, indicating that the actual capacity of ash was far higher. Analysis of As form and elemental distribution directly proved that chemical adsorption by ash was mainly through the joint action of Ca and Fe, and its correlation with other components was weak. At 500–900 °C, as temperature increased, the amount of As adsorbed by CaO gradually increased, whereas that of Fe 2 O 3 first increased and then decreased. The adsorption product of CaO was stable, whereas certain forms of products of Fe 2 O 3 released at 800 °C. Therefore, as temperature increased, the amount of As adsorbed by ash with high Fe content first increased and then decreased, reaching a maximum at 800 °C °C, whereas that of ash with higher Ca content kept increasing. The strong adsorption capacity of ash with high Ca and Fe contents helps reduce terminal As emission. [ABSTRACT FROM AUTHOR]

Transformation of As in the post-combustion zone has a significant effect on its emission characteristics. In this study, redistribution of As that occurs during the interaction between flue gas and ash has been elucidated using a double-layer fixed-bed reactor at 800–1000 °C. Herein, flue gas and ash samples with different As contents and inorganic components were produced by two varieties of coals. The As content in the ash with high Ca and Al contents increased after interacting with the flue gas with a high As content, indicating gaseous As adsorption. However, the As content in the ash decreased by up to 67% for other cases. The blank experiments showed that the As occurrences in ash were thermally stable, suggesting that the decrease was caused by the action of flue gas. Accordingly, the effect of flue gas components on the release of As from the ash was investigated. It was found that a significant amount of As release was primarily caused by the reaction of gaseous Na in the flue gas with the residual As in ash. A bi-directional interaction was observed between the high-temperature flue gas and ash, which led to the redistribution of As. Unlabelled Image • Interaction between high-temperature flue gas and ash caused As transformation. • Ash with high Ca and Al contents obviously adsorbed gaseous As in the flue gas. • Gaseous Na promoted the residual As release via reaction with aluminosilicate. [ABSTRACT FROM AUTHOR]