Abstract:

The flow of slag on the side walls of a high-temperature liquid furnace strongly influences the smooth operation of the high-temperature furnace. The alkali metal in the melt has an important influence on the flow characteristics of the slag and the different alkaline components have different effects on the characteristics of the melt. Through FactSage thermodynamic calculations and molecular dynamics simulations, the effects of the relative proportions of Na₂O, K₂O, FeO, CaO, and MgO on the viscosity and microstructure of coal ash melt were studied under the condition of constant SiO₂ and Al₂O₃ contents. The study found that as M₂O/MO increased, the percentage of high polymerization units Q⁴ in the melt increased, while bridge oxygen (BO) increased and non-bridging oxygen (NBO) decreased, resulting in an increase in the polymerization degree of the melt. The order of charge compensation ability of basic oxides to melt is K₂O>Na₂O>MO. When alkali metal oxides (Na₂O, K₂O) replace FeO, CaO, MgO, some of the M⁺ breaks away from the NBO to act as charge compensating ions to produce BO. The M⁺ depolymerizes to tri-cluster oxygen (TO) that maintains the charge balance to produce BO. This structural change increases the viscosity of the melt.

Key words: alkali metal oxides, molecular dynamics simulation, viscosity, slag structure, charge compensation

摘要：

熔渣在高温液态炉侧壁的流动情况强烈影响高温炉的平稳运行。熔体中碱性金属对熔融灰渣的流动特性有着重要影响，且不同碱性组分对熔体的特性影响不同。通过FactSage热力学计算和分子动力学模拟，研究在SiO₂和Al₂O₃含量不变的情况下，Na₂O、K₂O和FeO、CaO、MgO的相对比例对煤灰熔体黏度和微观结构的影响。研究发现，随着M₂O/MO的增加，熔体中的高聚合度单元Q⁴占比增大，同时桥氧(BO)增加，非桥氧(NBO)减少，使熔体的聚合度增大。碱性氧化物对熔体的电荷补偿能力由大到小依次为K₂O>Na₂O>MO。当碱金属氧化物(Na₂O、K₂O)替换FeO、CaO、MgO后部分M⁺脱离NBO充当电荷补偿离子，生成BO；脱离的M⁺解聚用于维持电荷平衡的三簇氧(TO)，生成BO。这种结构上的变化增大了熔体的黏度。

关键词: 碱金属氧化物, 分子动力学模拟, 黏度, 熔渣结构, 电荷补偿