还原性气氛下熔渣析铁的影响因素

Influencing factors of iron precipitation of slag under reducing conditions

气化炉在运行过程中出现的堵渣问题严重影响装置的稳定运行,熔渣析铁是导致气化炉结渣、堵渣的主要原因之一。选取含铁量较高的镇雄煤,运用X射线衍射(XRD)、扫描电子显微镜和X射线能谱仪(SEM-EDX)等测试手段,分析了不同还原性气氛、不同温度下渣样的矿物组成、表观形貌和微区化学组成,探究了还原性气氛下熔渣析铁的影响因素。结果表明:还原性气氛下影响熔渣析铁的因素主要有还原性气氛浓度、反应温度、灰渣中钙长石的含量和硫的含量。还原性气氛浓度的增大促进了铁质矿物间的转化,较高CO体积分数的渣样中含有更多形态的含铁矿物,CO体积分数达到25%可在渣样中检测到单质铁;在相同还原性气氛下,随温度的升高,高价态含铁矿物逐渐被还原,在CO体积分数大于25%的气氛中,温度不低于1 200℃时有单质铁析出;钙长石的形成与铁质矿物的富集和单质铁析出有内在联系。

It is worthwhile indicating that slag blockage seriously affect the long period operation of entrained bed coal gasification system. Slag formation is related to the gasifier type, the gasification conditions and mineral transformation of coal, of which iron precipitation is one of the main reasons to form slag lump. For exploring the influence factors of iron precipitation of slag in gasification conditions, a typical south China high iron content coal, Zhenxiong coal（ Yun- nan Province）, was selected to investigate the crystalline mineral constituents, surface morphologies and micro-chemi- cal composition of slag sample under different reducing atmosphere conditions and temperature by using X-ray diffrac- tion spectroscopy（XRD） and scanning electron microscopy/energy dispersive X-ray spectroscopy（SEM-EDX）. The results show that the main factors impacting iron precipitation in slag formation process include the CO concentration of the reducing atmosphere, temperature, the content of anorthite formation as well as sulfur content in slag. With the in- crease of CO concentration of the reducing atmosphere, the transformation processes of iron-bearing minerals is acceler- ated. slag samples of higher CO concentration contain the polymorphic iron-bearing minerals, and iron can be detected in slag when CO concentration reaches to 25%. With the increase of temperature, the high valence iron existed in min- erals of coal is gradually reduced at the same reducing atmosphere condition,iron precipitated from slag samples under the condition that CO concentration greater than 25% and temperature not lower than 1 200 ℃. The formation of anor- thite is closely related to the enrichment of iron-bearing minerals and iron precipitation in slag.