气流床气化技术是大型高效煤气化技术发展的主流方向.主要采用液态排渣工艺.在液态排渣过程中.煤中灰分在高温下在炉内壁面形成液态熔融渣层.渣层的导热系数是影响熔融渣层的厚度分布和传热特性的重要热物性参数.进而影响煤气化炉的稳定运行.采用(CaO-Al2O3-SiO2-MgO-Fe2O3)5种氧化物组分模拟煤灰渣.搭建瞬态热丝实验台测量高温熔渣导热系数.结合分子动力学模拟方法构建熔渣微观结构.探究高温下五元熔渣微观结构及其导热特性.在研究温度范围内.导热系数的测量结果和模拟结果有较好的一致性.所有渣样呈现出相同的变化趋势.即随着温度的升高.导热系数逐渐降低.在确定组分下.高温熔渣导热系数的对数与温度倒数呈线性关系.构建了硅铝质量比在2.43左右时.导热系数与温度和硅铝和之间的经验公式.并在实际煤灰上进行了验证.预测值误差基本在18%以内.且能较好的预测灰渣导热系数的变化趋势.结合熔渣微观结构研究发现.温度升高会促进熔渣无序性增强.减弱原子间结合力.增大原子间距,同时会造成桥氧降低.非桥氧增加.加强四面体结构的非简谐性.这是导致导热系数随温度升高先急剧下降后趋于平缓的主要原因.

Entrained flow gasifier is the main trend of large-scale high-efficiency coal industrial gasification technology. To ensure smooth slagging,the operation temperature of entrained flow gasifier is generally higher than the ash melting point,thereby forming a stable slag layer deposit on the wall of gasifier. The built up of the slag layer is a characteristic of the entrained-flow gasifier,and its thickness distribution and heat transfer characteristics affect the stable operation of gasification,which is closely related to the thermal conductivity of molten slag. A non-stationary hot wire experimental method and molecular dynamics simulation method were combined to investigate the thermal conductivity of the CaO-Al2O3-SiO2-MgO-Fe2O3 molten slag under its microstructure. A good agreement between the measured and calculated thermal conductivity over the entire operating temperature range is observed,and one can find that thermal conductivity of all slag samples gradually decreases as the temperature increases. A linear relationship between the logarithm of the thermal conductivity of the high-temperature slag and the reciprocal of the temperature is constructed under the determined composition. An empirical formula between the thermal conductivity and temperature and the silicon-aluminum is established when w(SiO2/Al2O3) is around 2.43. The empirical formula is verified on the actual coal ash. A good agreement within the deviation of 18% between the measured and calculated thermal conductivity over the entire operating temperature range is observed. Based on the research of the slag microstructure,it is found that the increasing temperature promotes the enhancement of slag disorder and weakens the bonding force between atoms,resulting in lengthening the interatomic distance in the tetrahedral structure. High temperature also reduces the number of bridging oxygens,and strengthens the anharmonicity of the tetrahedral structure. As a result,the thermal conductivity decreases sharply with increasing temperature and then tends to level off.

1 实验

   1.1 样品制备

   1.2 导热系数实验测量

2 分子动力学模拟方法

   2.1 分子结构计算

   2.2 导热系数计算

3 结果与讨论

   3.1 导热系数测量实验结果

   3.2 微观结构特征

   3.3 高温熔渣导热机理

4 结论