高碱煤含钠矿物沉积层的高温熔融及多相反应过程分析

采用纯矿物试剂模拟燃用高碱煤时炉内受热面典型的灰沉积层化学组成，利用热机械分析（TMA）、TG-DSC分析、高温煅烧实验结合XRD、SEM-EDS表征方法研究了不同Na₂SO₄含量灰沉积层的高温熔融过程及矿物间的多相反应机理。结果表明，掺混Na₂SO₄后沉积层熔化特征温度显著降低，Na₂SO₄的主要反应途径与掺混比例有关，当掺混比低于20%时，Na₂SO₄与SiO₂、CaO、Al₂O₃反应主要转变为CaSO₄和钠的硅铝酸盐；掺混比大于40%时则主要与CaSO₄生成低熔点的钠钙复合硫酸盐。富Na₂SO₄沉积层颗粒在800℃时开始黏结；900-950℃时，霞石、钠长石等钠的硅铝酸盐发生低温共熔，同时Na₂SO₄和CaSO₄生成的复合硫酸盐开始熔融，逐渐形成液相；1200-1250℃时，镁黄长石与含钙矿物发生强烈共熔，温度超过1300℃后矿物完全熔融成为自由液相。

Melting behavior and heterogeneous reaction of Na-bearing deposits at high temperature during high-alkali coal combustion

The pure chemicals were used to simulate the composition of typical ash deposits on heat exchanger surfaces during high-alkali coal combustion, and the thermal mechanical analysis (TMA), TG-DSC analysis and high-temperature calcination were performed to investigate the high temperature melting characteristics of the deposits with varying content of Na₂SO₄. Subsequently, XRD and SEM-EDS techniques were applied to investigate the reaction products and detailed mechanism. The results indicate that the melting characteristic temperature of deposits decreases significantly after blending with Na₂SO₄, and the transformation of Na₂SO₄ is closely related to the blending ratio. When the blending ratio is below 20% (mass ratio), most Na₂SO₄ is converted to CaSO₄ and sodium aluminosilicate, while Na₂SO₄ would react with CaSO₄ and generate sulfate double salts when the blending ratio is over 40%. Moreover, the particles of Na₂SO₄ enriched deposits begin to adhere at 800℃. When the temperature is elevated to 900-950℃, the low-temperature eutectics are easily formed in the presence of nepheline and albite, and the eutectics and Na-Ca sulfate double salts are gradually molten. The large amount of co-melting of akermanite and Ca-bearing minerals was observed at temperatures of 1200-1250℃, and the minerals are completely melted at temperatures over 1300℃.