煤灰的酸碱比和硅铝比是影响煤灰特性的关键因素。在煤中加入添加剂或采用混煤等方法，改变煤灰硅铝比来调节煤灰的熔融特性，是改善煤高温转化过程中带来灰渣问题的重要手段。为了分析硅铝比变化对煤灰体系微观结构产生的影响，得出宏观性质改变的理论机理，基于第一性原理在1 600 ℃下模拟计算了CaO-SiO2-Al2O3体系中SiO2/Al2O3从0.5升至3.1时，径向分布函数（RDF）、平均配位数（CN）、聚合度、氧的分布等微观结构的变化规律。结果表明：SiO2/Al2O3从0.5增至3.1时，Si—O有稳定的四配位结构且平均键长为1.61×10-10 m；Al—O的平均键长为1.75×10-10 m，Al—O配位较为稳定，且配位数随着硅铝比的增加而降低，合成煤灰硅酸盐体系中Si、Al为网络形成体。随着SiO2/Al2O3从0.5增至3.1时，Q4、Q5逐渐减少，生成聚合度低的Q、Q3，其中Q4、Q5分别降低23%、10%左右，Q3、Q分别升高14%、11%左右。大量［SiO4］4-和［AlO4］5-被破坏，煤灰体系的聚合度降低，无序性升高，网络结构被破坏，导致煤灰熔融性降低。随着体系硅铝比的增加，Ot和Ob含量逐渐降低，Onb含量增加显著，其中，Ob、Ot含量分别降低7%、13%左右，Onb含量升高18%左右。体系网络结构遭到破坏变得松散，疏松的网络结构导致体系硅酸盐网络在高温下更易塌陷和瓦解，宏观表现为煤灰的熔融温度降低，更易产生低温共熔体。

The acid-base ratio and Si-Al ratio of coal ash are the key factors affecting coal ash properties. Adding additives to coal or using mixed coal to adjust coal ash fusing characteristics by changing the ratio of SiO2 to Al2O3 is an important means to improve the ash and slag problems in the high temperature coal conversion process. In order to analyze the influence of the change of Si-Al ratio on the microstructure of coal ash system and obtain the theoretical mechanism of the change of macroscopic properties，the radial distribution function (RDF)，mean coordination number (CN)，degree of polymerization，distribution of oxygen and other microstructures in CaO-SiO2-Al2O3 system were simulated and calculated when SiO2/Al2O3 increased from 0.5 to 3.1 based on first principles at 1 600 ℃. The results show that：when SiO2/Al2O3 increases from 0.5 to 3.1，Si—O has a stable four coordination structure and the average bond length is 1.61×10-10 m; the average bond length of Al—O is 1.75×10-10 m，the coordination number of Al—O is relatively stable，and the coordination number decreases with the increase of Si-Al ratio. Si and Al are network formers in the silicate system of synthetic coal ash. As SiO2/Al2O3 increases from 0.5 to 3.1，Q4 and Q5decrease gradually，forming Q and Q3 with low degree of polymerization. Among them，Q4 and Q5decrease by about 23% and 10% respectively and Q3 and Q increase by about 14% and 11% respectively. A large number of ［SiO4］4- and ［AlO4］5-are destroyed，the degree of polymerization is reduced，the disorder is increased，and the network structure is destroyed，resulting in the decrease of ash fusibility. With the increase of Si-Al ratio，Ot and Ob decrease gradually，and Onb increases significantly. Among them，Ob and Ot decrease by about 7% and 13% respectively，and Onb increases by about 18%. The network structure of the system is destroyed，and the loose network structure makes the system more prone to collapse at high temperature. The macro performance is that the melting temperature of coal ash is reduced，and it is easier to produce low-temperature eutectic.

0 引言

1 计算方法

   1.1 势函数确定

   1.2 径向分布函数和平均配位数

2 结果与分析

   2.1 径向分布函数和平均配位数

   2.2 聚合度

   2.3 氧的分布

3 结论