Sodium transformation characteristic of high sodium coal in circulating fluidized bed at different air equivalence ratios

Abstract

Reacting atmosphere has great influence on sodium migration during high sodium coal thermal conversion, and influence the slagging and deposition characteristics further. The effect of different air equivalence ratios (ERs) on sodium migration and transformation during thermal conversion of high sodium Zhundong coal in circulating fluidized bed was investigated. The effect of ERs on the sodium content in circulating ash and bottom ash was similar. As the decrease of ER, the sodium content in the ashes increased due to the effect of carbon inhibition. Sodium in the bottom ash exists mainly as NaAlSiO4 and NaAlSi3O8, namely insoluble sodium. As to the fly ash, the sodium content decreased with the ER increase under reducing atmosphere, whereas the sodium content increased with the ER increase under oxidizing atmosphere. Sodium mainly exists as NaCl under reducing atmosphere and Na2SO4 was the main sodium existence under oxidizing atmosphere. The variety of sodium content in the ashes with the flue gas temperature was different under different reacting atmospheres. The ash fusion temperatures were also influenced by the atmosphere to a great extent. The fly ash fusion temperature was higher than that of bottom ash at the same ER. With lower ERs under reducing atmosphere and higher ERs under oxidizing atmosphere, the risk of slagging in the furnace and fouling in tail heating surface should be paid attention during the thermal conversion of high sodium coal.