Abstract:

In entrained flow gasifiers, crystallization inside the slag can increase the viscosity of the slag, changing the flow from Newtonian to non-Newtonian. In order to get an understanding of the crystallization characteristics of the slag, the single hot thermocouple technique(SHTT) and a high-temperature quenching furnace were set up to study the crystallization process. The crystals morphology under different temperatures and cooling rates were recorded and the temperature-time-transformation (TTT) diagram was obtained which can illustrate the influence of temperature. The decrease of temperature can increase the driving force and reduce the required time for crystallization. But further decrease of temperature would increase the viscosity which limited the movement of ions. The slag was quenched at different temperatures and it is found that the crystalline phases changed at different temperatures. Diopside is the main crystal at high temperature with some anorthite at low temperature. The high cooling rate can reduce the size of the crystals but has little effect on the crystalline types.

Key words: gasification, entrained flow bed, non-Newtonian slags, crystallization, crystalline phases

摘要：

气流床气化炉内熔渣的结晶会对渣层的黏度产生重要影响,使熔渣由牛顿流体转变为非牛顿流体。采用单热电偶在线观察系统(SHTT)、高温淬冷炉、X射线衍射(XRD)等对一种五元组分的模拟煤灰渣从结晶的角度进行研究,在线记录了晶体的生长形貌,获得了熔渣析晶的时间-温度-转变(TTT)曲线,研究熔渣在不同温度和冷却速率下的结晶特性以及晶体的类型。实验结果表明温度的降低使结晶驱动力增加,结晶孕育时间减少,但温度过低使黏度增加,晶体生长受限,因此生成的晶体尺寸较小。熔渣的结晶在不同温度区间析出的矿物不同,主要的晶体产物在高温区为透辉石,低温区有少量钙长石生成。冷却速率的增加会使晶体的生长尺寸减小,非晶态含量增加,但对晶体的种类影响不大。

关键词: 气化, 气流床, 非牛顿熔渣, 结晶, 晶相类型