气流床气化炉渣层内的结晶现象对渣层的粘度和导热有重要影响。论文主要从熔渣结晶的角度，利用差热扫描量热仪（DSC）、单热偶高温在线观察系统（SHTT）、FactSage热力学软件、高温淬冷炉、X－射线衍射（XRD）等对模拟煤灰渣和实际煤灰在不同温度、冷却速率条件下的结晶过程及动力学进行研究。采用五种氧化物组分（Si-Al-Ca-Fe-Mg）模拟煤灰渣，选取硅铝比、硅铝和、CaO、Fe2O3四个变量改变模拟渣的组分比例，根据模拟渣的实验结果建立结晶预测模型，并采用实际煤灰对预测结果进行验证。论文主要取得以下结论：（1）获得熔渣结晶的时间－温度－转变(TTT)和连续－冷却－转变(CCT)曲线，探讨了温度和冷却速率对结晶的影响。温度降低会使晶体析出速率加快，结晶孕育时间缩短，但温度过低会造成粘度过大使晶体来不及充分生长，生成的晶体尺寸变小。冷却速率的增加会使结晶温度降低，结晶比例减少，晶体生长尺寸变小，高冷却速率下这种影响更为明显。（2）组分及其比例是熔渣结晶的内在影响因素。研究结果表明，硅铝比过低，结晶倾向会明显削弱；当硅铝比在一定范围内（1.5～4.5），结晶变化不大，但是结晶的温度范围会变窄。硅铝总量的降低会使结晶倾向增强，结晶温度升高，结晶速率加快，碱金属含量增多会促进透辉石、黄长石等晶体生成。CaO对结晶的影响在不同的比例范围内由于析出晶相不同而具有不同的特性： CaO比例较低的熔渣结晶倾向很弱，仅在熔渣表面生成薄层的晶体；随着CaO比例的增加，结晶倾向增强，在20～40%比例范围内初始结晶温度下降，低温区结晶倾向增强，主要生成辉石、钙长石和黄长石；CaO比例增大至超过40%时，生成硅酸钙晶体，结晶温度急剧升高，高温区结晶增强。Fe2O3比例增加，会使晶体生长速率加快，且结晶温度向高温方向移动，促使较高比例尖晶石的析出，在60/40 CO/CO2气氛下还原的渣样高温区的结晶倾向减弱，析晶需要更长的孕育时间和更高的过冷度。（3）建立五元系统对结晶倾向的判据和结晶温度的预测关系式，并采用实际煤灰进行验证。碱度大于0.7且硅铝比在1～4之间时，熔渣一般会呈现比较明显的结晶现象，碱度越大，结晶倾向越强。初始结晶温度和熔渣的全液相温度具有一定的线性相关性，建立二者预测关系式，并采用7个煤灰样品对关系式进行了验证，实验结果和预测结果吻合较好。
In entrained flow gasifiers, crystallization inside the liquid slag can increase the viscosity of the slag, affecting flow down the wall and resulting in operational problems. Although increasing attention has been paid to the influence of crystallization on viscosity, few studies have investigated crystallization kinetics in slag melts due to challenges associated with high temperature and experimental complexity. In order to gain a deep understanding of crystallization characteristics, different experimental methods have been used. Differential scanning calorimetry (DSC), single hot thermocouple technique (SHTT) and a high-temperature quenching furnace were set up to investigate the influence of temperature and cooling rates on crystallization kinetics. Five oxides have been made into synthetic slags with various Si/Al，Si+Al，CaO and Fe2O3 ratios. A prediction model for the crystallization temperature has been established based on the synthetic slag system, and the model has been verified through real ash slags. The main conclusions are as follows:(1) The temperature-time transformation (TTT) and continuous-cooling transformation (CCT) curves of the slags have been obtained which can illustrate the influence of temperature and cooling rates respectively. As the temperature decreases, higher free energy accelerates the crystallization rates and shortens the residence time. However higher degree of undercooling will increase the viscosity and restrict the growth of crystals, leading to small size of crystals. The increase of cooling rates can decrease the initial crystallization temperature and crystal size. But the influence isn’t significant until the cooling surpasses certain rate. Kissinger method is used to calculate the non-isothermal kinetics and JMA is for isothermal kinetics.(2) Components and their ratios are the intrinsic factor of crystallization characteristics. The influence of Si/Al, Si+Al, CaO, Fe2O3 and the atmosphere have been investigated. Apart from the weakest crystallization tendency of small Si/Al, the influence of Si/Al in the range of 1.5 to 4.5 is not significant, but the temperature range of crystallization becomes narrow. Decrease of total amount of Si and Al can lead to a great crystallization tendency and accelerate the precipitation. The main crystals of high amount of Si and Al are anorthite and spinel while low amount of Si+Al favors diopside and mellite. The influence of CaO between 5 to 45 wt.% is non-linear or non-proportional to the CaO content because it crossed different crystalline phases. Slags with 15-35% CaO had a higher crystallization tendency but lower crystallization temperature than slags with lower CaO contents. Diopside and anorthite were the two main crystalline phases for slags with less than 35% CaO. However, when the content of CaO exceeded 40%, the formation of Ca2SiO4 can result in higher crystallization temperature. As for the iron oxide, the high ratio of Fe2O3 enhances the crystallization tendency and favors the formation of spinel. Crystallization tendency will become weak under the reduced atmosphere 60/40 CO/CO2, which requires longer incubation time and higher undercoolings.(3) A prediction model has been established based on the experimental results of synthetic slags, and the predicted results were verified by real ash slag. The slags with higher base/acid value than 0.7 and Si/Al in the range of 1 to 4 can display stronger crystallization peak, and the higher base/acid, the stronger crystallization tendency. The influence of Fe2O3 is more significant than CaO. In addition, the initial crystallization temperature has a linear relationship with the liquidus temperature. And the predicted results of the linear correlations agree well with the experimental results.
