准东煤及配煤的矿物相变及熔融机理

Mineral Phase Transformation and Ash Melting Mechanism of Zhundong Coal and Blended Coal

准东煤储量大,但其燃烧过程中严重的结渣和沾污特性对电站锅炉的安全经济运行仍然是一个极大的挑战.本文通过对准东煤低温灰化样的TGA-DSC分析,并对不同温度段的准东煤及配煤灰样辅以XRF、XRD的矿物识别及显微形态和组分的FSEM-EDS分析,得到了主要矿物的相变温度段及发生烧结和熔融的温度.研究表明:灰中对沾污结渣有重要贡献的含钠矿物在800℃以前大部分蒸发,未蒸发的含钠矿物的存在温度小于1150℃;在1280℃存在的矿物晶相以Ca(Mg,Fe)-Al-O、Ca(Mg,Fe)-Si-O、Fe-Ca-O等三元系如钙铝石、铁钙铝石、黑钙铁石、变硅黑石、钙镁硅石和铁橄榄石等及四元系的Ca-Al-Si-O,如钙铝黄长石等为主;分解产物CaO及熔体Fe-S-O促进了低温共融体的形成;富含Al的煤样按1∶9被掺入准东煤灰中,提高了该灰样流动温度,推迟灰熔融结渣的发生.

Zhundong coal is abundant in storage.However,its serious slagging and fouling characteristics still pose a major challenge to the safe and economic operation of boilers in a power plant.In this paper,the phase transformation temperature range of main minerals and the sintering and melting temperatures were obtained via the TGA-DSC analysis of low-temperature ash samples of Zhundong coal,together with the mineral identification by XRF/XRD and FSEM-EDS analysis of the morphology and composition of Zhundong and blended coal ash samples in different temperature sections.Results show that most of the sodium minerals in ash making important contribution to fouling and slagging evaporated before 800℃,and the existing temperature of the non-evaporated sodium minerals was lower than 1 150℃;Ca(Mg,Fe)-Al-O,Ca(Mg,Fe)-Si-O,and Fe-Ca-O ternary systems( e.g.,mayenite,brownmillerite,srebrodolskite,bredigite,merwinite,and fayalite) and Ca-Al-Si-O quaternary systems(e.g.,gehlenite)were the main crystalline phases in minerals at 1 280℃.The decomposition products of CaO and melted Fe-S-O also promoted the formation of the low-temperature eutectic. The Al-rich coal sample was mixed into Zhundong coal ash at a ratio of 1∶9,which increased the flowing temperature of this ash sample and delayed its melt slagging.