Abstract:

The sodium content of Zhundong coal is high and the boiler will face severe slagging problems during the combustion. Synthetic coals were obtained by adding ash model compounds to ultrapure coal which was obtained from the Zhundong coal. And the effects of Na₂O on the combustion performance and ash fusion characteristics of coal were studied by using thermogravimetric-differential scanning calorimetry (TG/DTG/DSC), X-ray diffraction (XRD) and ash fusion temperature test. The results showed that: sodium mainly affected the ignition temperature (T_i) and the stage of char combustion of the synthetic coal. The increasing of sodium would rise the T_i. When the mass fraction of Na₂O increased from 5% to 8%, the rate of char combustion decreased first and then accelerated. Sodium could improve the burnout characteristics of coal and would decrease ash fusion temperature which was more obviously when Na₂O>5%. The fluxing effect of sodium to mullite in the ternary phase diagram was the important reason of the decreasing ash fusion temperature. XRD analysis showed that quartz, which acts as a framework in ash, can react with refractory minerals (such as xonotlite and MgO) to generate low-melting feldspar minerals under the fluxing action of sodium. These feldspar minerals would promote ash melting under high temperature and decrease ash fusion temperature. At the same time, the generated nepheline could intensify ash fusion.

Key words: synthetic coal, ash fusion, coal combustion, morphology, phase equilibria

摘要：

准东煤中钠含量高，燃用时锅炉会出现严重结渣问题。通过向准东煤为原料制取的超纯煤中添加灰的模型化合物，得到合成煤。并在此基础上利用热重-差示扫描量热分析法（TG/DTG/DSC）、X射线衍射仪（XRD）和灰熔融温度测定分析手段，研究Na₂O含量对煤燃烧特性和灰熔融性的影响。结果表明：钠主要影响合成煤的着火温度（T_i）与焦炭燃烧阶段，钠含量增加使T_i升高，并且Na₂O在灰中质量分数由5%升高至8%后，钠含量增加使焦炭燃烧速率先减小后加快，并能够改善煤粉燃尽特性。钠能够降低灰熔融温度，并在Na₂O质量分数高于5%后，温度下降更加明显。在三元相图中钠对莫来石的助熔作用是造成灰熔融温度降低的重要原因。XRD分析表明Na₂O含量增加，充当骨架作用的石英在钠的助熔作用下与难熔矿物硅钙石、MgO等生成低熔点长石类矿物，这类矿物在高温下有助熔作用，能够降低灰熔融温度。同时还生成助熔性含钠矿物霞石，加剧了灰熔融。

关键词: 合成煤, 灰熔融, 煤燃烧, 形态学, 相平衡