Effect of sequential extraction on sodium capture capability of sodium⁃rich coal ash

The sodium⁃rich coal in Xinjiang is abundant and has good combustion performance. However， the high so⁃ dium content in coal results in fouling and slagging on the convective heating surface of boiler， which seriously re⁃ stricts its development and utilization. In this study， the Wucaiwan coal (WCW) was extracted sequentially by water/ ammonium acetate solution/HCl solution， and then was burnt into ash. The sodium capture capability of the WCW coal ash samples was determined and then the effect of the sequential extraction on the sodium capture perform⁃ ances of the ash samples was investigated. Meanwhile， according to the composition of the Hami (HM) coal ash， SiO2 and Al2 O3 were added into the WCW coal， and the effect of SiO2 and Al2 O3 additions on the sodium capture performance of the ash sample was analyzed. The results show that the sequential extraction can remove calcium from the WCW coal， which restrains the formation of calcium⁃containing materials such as wolwolite ( CaSi3 O9 ) and calcium aluminate (Ca12Al14O33)， and thus the capture reaction of the sodium by silicon and aluminum materials in the coal ash was promoted. The ash sample (WCW-A2-900) prepared from water/ammonium acetate solution ex⁃ tracted the WCW coal at the sodium capture temperature of 900 °C has the highest sodium capture amount， which is 125.23% higher than raw coal ash. With the increasing sodium capture temperature， the sodium capture performance of the WCW coal ash is enhanced due to the formation of the stable aluminosilicates from the silicon and aluminum in coal ash with sodium vapor. When the reaction temperature exceeds 900 °C， the sodium capture amount of the WCW- A2 - 900 and the WCW - A3 - 900， which is still higher than that of the WCW coal ash， decreased obviously due to their decreasing physical adsorption capability. The additions of silicon and aluminum matter can en⁃ hance the sodium capture performance of the WCW-900， but the improvement is limited because the calcium content of the resulted WCWH coal is still higher than that of the HM coal.