硫酸盐胶凝特性对飞灰板结成垢影响机理研究

Study on Influence Mechanism of Sulfate Gelation Characteristics on Fly Ash Scaling

硫酸盐加剧锅炉尾部受热面飞灰板结成垢现象,严重危害设备安全。文中对板结样品进行黏性强度、形貌和成分测试,探索硫酸盐对飞灰板结成型的影响机理;采用热力学平衡计算分析硬垢的最终产物,并对现场硬垢进行分析测试,探索硫酸盐对飞灰硬化成垢的促进机理。结果表明,硫酸盐提高了飞灰的黏结强度,灰粒间发生粘结团聚并有芦絮状、针棒状结晶析出,板结灰样含有硫酸铵、半水石膏和硅酸二钙等胶凝材料,其促进了飞灰的团聚板结。针对飞灰硬化成垢阶段,热力学计算结果表明:垢坚硬的原因是其含有芒硝盐、硬石膏和水化硅酸钙等硅酸盐水泥成分。某电厂低低温省煤器表面飞灰呈现出板结成型和硬化成垢两个阶段,硫酸盐与飞灰水化生成的二水石膏和水化铝酸三钙等胶凝硬化产物,促进垢的硬化。硫酸盐具有胶凝特性和促进飞灰水化的特性,导致飞灰团聚板结和硬化成垢。

Sulfate aggravates the fouling of fly ash plate on the heating surface of the boiler tail,which seriously endangers the safety of equipment.The bonding strength,morphology and composition of the samples are tested to explore the influence mechanism of fly ash agglomeration under the action of sulfate.The final composition of encrustations is analyzed by thermodynamic equilibrium calculation,and the field encrustations are analyzed and tested to explore the scale formation mechanism of sulfate hardening fly ash.The results show that sulfate can improve the bonding strength of fly ash.Fly ash particles are bound together,and flocculent and needle-rod crystals are precipitated.The agglomerated samples contained cementitious materials including ammonium sulfate,hemihydrate gypsum and calcium silicate.These cementing materials promote the agglomeration of fly ash.In hardened stage of fly ash,the thermodynamic calculation results show that the encrustation contains silicate cement components such as mirabilite salt,anhydrite and calcium silicate hydrate,making the encrustation hard.On the low-low temperature economizer of a power plant,the fly ash hardened into scale presents two stages of agglomeration and encrustation.The dihydrate gypsum and tricalcium aluminate hydrate are produced by the hydration of sulfate and fly ash.These cementitious hardening products promote the hardening of encrustation.Sulfate has the characteristics of cementing and it can promote the hydration of fly ash,which leads to agglomeration and encrustation of fly ash.