Effect of NaCl vapor concentration on sodium⁃capturing performance and sintering temperature of coal ash

Zhundong coal in Xinjiang is a kind of high⁃quality fuel with low mining cost， low ash yield and sulfur con⁃ tent， but high sodium content leads to the fouling and slagging during its combustion process， which seriously hin⁃ ders the further utilization of the sodium⁃rich coal. In this study， two kinds of sodium⁃rich coals， the Wucaiwan coal (WCW) and the Hami coal (HM)， and one low sodium⁃content coal， the Pingshuo coal (PS)， were burned into ash at 900 °C ， and the sodium capture experiments of the coal ashes were conducted in the atmosphere of the NaCl vapor with 38%， 51% and 76% concentration. The sodium content in the coal ash before and after the so⁃ dium capture experiment was measured by the ICP-OES analyzer， and the mineral changes in the coal ash samples were analyzed by XRD. Finally， the pressure drop method was used to determine the sintering temperature of the coal ash sample， and then the effect of the sodium vapor concentration on the sintering characteristics of the coal ash was explored. The results show that in the range of the employed NaCl vapor concentrations， in terms of the sodi⁃ um⁃capturing amount， the PS coal ash is the highest， the HM coal ash is the second， and the WCW coal ash is the lowest. Silicon and aluminum in the coal ash samples can enhance its sodium⁃capturing performance， while calcium in the coal ash will react with the silicon and aluminum contained in the minerals， and thus result in the decrease in the chemical fixation capability of the silicon and aluminum for the sodium contained vapor， which is not conducive to the sodium capture process of the coal ash samples. With the increase of NaCl vapor concentration， the sodium⁃capture amount increases， and the decrease in the sintering temperature of the coal ash is positively correlated with the sodium⁃capturing amount. The decrease in the sintering temperature of the HM and the WCW coal ashes is greater than that of the PS coal ash because the melting point of the sodium⁃containing compounds produced by the chemical fixed sodium of the HM and the WCW coal ashes is lower than that of the PS coal ash and the forming reaction of low melting point sodium⁃containing compounds is promoted by the increasing the NaCl vapor concentration. In addition， the sintering behavior of the PS coal ash with loose structure and rich internal pores was not observed at 900 °C ， thus the reaction degree of the ash with the NaCl vapor was relatively high， and its sinte⁃ ring temperature of the resulted ash was less affected by the NaCl vapor concentration.