烟气气氛对准东煤灰熔融特性影响的显微观察

Influence of flue gas atmosphere on Zhundong coal ash melting characteristics through microscopic observation

准东煤田预测储量高,准东煤灰具有高硫,低硅铝,高碱/碱土金属等特点,实际燃用准东煤锅炉出现了严重的沾污、结渣现象,影响准东煤的大规模开发利用。烟气气氛(含有大量SO_(2),SO3)可能影响高温下Na2SO4的生成/分解,从而影响煤灰的熔融过程。深入研究烟气气氛对准东煤灰熔融特性的影响,有助于加深对锅炉结渣过程的理解,为燃用准东煤锅炉结渣防控提供技术支持。为获得烟气气氛对准东煤灰熔融特性的影响规律,建立了单热电偶高温显微观察系统(SHTT),比较了还原性气氛、氧化性气氛、惰性气氛及模拟烟气气氛下准东煤灰的熔融特性。结果表明,建立的灰熔融温度测试方法精度较好,96.92%的灰样熔融温度与标准灰熔点仪测得的流动温度相比偏差在3%以内(≤40℃),最大偏差<50℃,测试偏差在煤灰熔融特性测试允许误差范围内。当碱酸比R<2.5时,气氛对灰熔融特性无显著影响;当R>2.5时,煤灰组分中Fe_(2)O_(3)质量分数较高,导致还原性气氛下灰熔点降低。烟气中SO_(2)对煤灰熔融温度的影响与煤灰组分相关,当R>2.5时,煤灰中碱/碱土金属及硫(AAEM/S)质量分数较高,烟气中SO_(2)会抑制煤灰中CaSO_(4)的分解,提升高温下煤灰中CaO质量分数,并减少长石,辉石等低熔点矿物的生成,进而提升煤灰熔融温度。烟气中SO_(2)是促进富含Na/Fe硫酸盐或硫化物超细颗粒生成及沉积的重要因素。

Zhundong Coal field has a high predicted coal reserve.The ash generated by Zhundong coal is characterized by high content of Sulphur,alkali/alkaline,and low content of Si and Al.Sever fouling,slagging problems occurred in Zhundong coal-fired boilers,which greatly obstruct the large-scale utilization of Zhundong coal.The formation/decomposition of Na2SO4 at high temperature may be affected by SO_(2)and SO3 in flue gas.Thereby affecting the melting process of coal ash.In-depth study on the influence of the flue gas atmosphere on the melting characteristics of coal ash will help deepen the understanding of the slag process.Which can provide technical support for the slagging prevention in real boilers.To acquire the influence of flue gas atmosphere on the melting characteristics of Zhundong coal ash,a high temperature online microscopic observation test rig based on single hot thermo-couple technique(SHTT)was constructed.The melting characteristics of Zhundong ash under the reducing,oxidizing and inert atmosphere were compared.The results show that 96.92%of the measured ash melting point through SHTT test rig is consistent with the standard melting point measurement method,and within an uncertainty of 3%.When alkali/acid ratio R is lower than 2.5,the atmosphere have little effect on ash melting point.When R is larger than 2.5,the high Fe_(2)O_(3)content causes a lower ash melting point at the reducing atmosphere.In real flue gas atmosphere,the melting point of Zhundong ash increases since the existence of SO_(2)restrains decomposition of CaSO_(4)in Zhundong ash as well as the production of low melting materials such as feldspar and augite.SO_(2)in flue gas also stimulates the production of ultra-fine particles rich of Na/Fe sulfates and thus plays a significant role on fouling and deposition.