Effect of MgO content on the ash fusibility of high sodium coal

doi:10.16085/j.issn.1000-6613.2017-1224

Abstract

Abstract: In order to study the effect of MgO content on the ash fusibility of high sodium coal,high sodium synthetic coal ash samples with different MgO content were prepared and the ash fusion temperatures were measured. A multicomponent system including SiO₂-Al₂O₃-Fe₂O₃-CaO-MgO-Na₂O was established by the thermodynamic database FactSage 7.0 to simulate the ash melting process. X-ray diffraction(XRD) and scanning morphology microscope(SEM) were applied to investigate the mineral composition and surface morphology of synthetic coal ash samples. The results show that the ash fusion temperatures dropped first and rose later with the increase of MgO content. When the MgO content increase from 0 to 5%,a large quantity of diopside with low melting point was generated in ash at high temperature. Diopside could form eutectics with minerals such as nepheline,and thus reducing the ash fusion temperatures. When the MgO content was further increased,minerals with high melting point such as akermanite,forsterite and merwinite were generated in ash at high temperature,and thus improving the ash fusion temperatures. The results of binary phase diagram and analogous ternary phase diagram indicated that the variation of liquid temperature was consistent with the ash fusion temperatures with the increase of MgO content. For the coal ash samples in this study,the ash fusion temperatures could be improved efficiently and the formation of molten slag could be suppressed significantly when the MgO content reached to 30%.

Key words: ash fusibility, high sodium coal, MgO content, mineral conversion, thermodynamic, phase equilibria

摘要： 为研究MgO含量对高钠煤灰熔融特性的影响，配制了不同MgO含量的高钠合成灰并对灰熔融温度进行了测试。利用FactSage 7.0提供的热力学数据库建立了SiO₂-Al₂O₃-Fe₂O₃-CaO-MgO-Na₂O多元体系，模拟不同MgO含量的高钠合成灰的熔融过程。使用X射线衍射（XRD）和扫描电子显微镜（SEM）对合成灰的矿物质组成及微观形貌进行了研究。结果表明，随着MgO含量的增加，灰熔融温度先降低后升高。当MgO质量分数由0增加到5%时，高温下灰中生成大量低熔点的透辉石，透辉石会与霞石等矿物质形成低温共熔体，导致灰熔融温度降低。进一步增加MgO含量，高温下灰中生成镁黄长石、镁橄榄石和镁硅钙石等高熔点矿物质，使灰熔融温度升高。二元相图和似三元相图的结果表明，全液相温度随MgO含量的变化趋势与灰熔融温度相同。对本研究中的煤种，当MgO质量分数为30%时，可以有效提高灰熔融温度并抑制熔融液渣的生成。

关键词: 灰熔融特性, 高钠煤, MgO含量, 矿物变化, 热力学, 相平衡

CLC Number:

TK536.4

WANG Dongxu, CHEN Yuhui, WANG Yang, LI Wenyan, XIAO Haiping, KANG Zhizhong. Effect of MgO content on the ash fusibility of high sodium coal[J]. Chemical Industry and Engineering Progress, 2018, 37(04): 1392-1401.

王东旭, 陈裕辉, 王洋, 李文艳, 肖海平, 康志忠. MgO含量对高钠煤灰熔融特性的影响[J]. 化工进展, 2018, 37(04): 1392-1401.

References

[1] WANG X,XU Z,WEI B,et al. The ash deposition mechanism in boilers burning Zhundong coal with high contents of sodium and calcium:a study from ash evaporating to condensing[J]. Applied Thermal Engineering,2015,80:150-159.
[2] 陶玉洁,张彦威,周俊虎,等. 准东煤在燃烧过程中的矿物演变过程及Na、Ca释放规律[J]. 中国电机工程学报,2015,35(5):1169-1175. TAO Y J,ZHANG Y W,ZHOU J H,et al. Mineral conversion regularity and release behavior of Na,Ca during Zhundong coal's combustion[J]. Proceedings of the CSEE,2015,35(5):1169-1175.
[3] 张守玉,陈川,施大钟,等. 高钠煤燃烧利用现状[J]. 中国电机工程学报,2013,33(5):1-12. ZHANG S Y,CHEN C,SHI D Z,et al. Situation of combustion utilization of high sodium coal[J]. Proceedings of the CSEE,2013,33(5):1-12.
[4] AKIYAMA K,PAK H,UEKI Y,et al. Effect of MgO addition to upgraded brown coal on ash-deposition behavior during combustion[J]. Fuel,2011,90(11):3230-3236.
[5] 陈晓东,孔令学,白进,等. 高温气化条件下Na₂O对煤灰中矿物质演化行为的影响[J]. 燃料化学学报,2016,44(3):263-272. CHEN X D,KONG L X,BAI J,et al. Effect of Na₂O on mineral transformation of coal ash under high temperature gasification condition[J]. Journal of Fuel Chemistry and Technology,2016,44(3):263-272.
[6] WANG Y,XIANG Y,WANG D X,et al. Effect of sodium oxides in ash composition on ash fusibility[J]. Energy & Fuels,2016,30:1437-1444.
[7] WANG Y,WANG D X,DONG C Q,et al. The behaviour and reactions of sodium containing minerals in ash melting process[J]. Journal of the Energy Institute,2017,90:167-173.
[8] 高峰,马永静. Mg²⁺和Na⁺对高熔点煤灰熔融性的影响[J]. 燃料化学学报,2012,40(10):1161-1166. GAO F,MA Y J. Study on the effect of Mg²⁺ and Na⁺ on the fusibility of coal ash with high ash fusion point[J]. Journal of Fuel Chemistry and Technology,2012,40(10):1161-1166.
[9] 毛军,徐明厚,李帆. 碱性矿物质对煤灰熔融特性影响的研究[J]. 华中科技大学学报(自然科学版),2003,31(4):59-62. MAO J,XU M H,LI F. The effect of alkali mineral matter on the ash melting characteristic[J]. Journal of Huazhong University of Science & Technology(Nature Science Edition),2003,31(4):59-62.
[10] 姚星一. 煤灰熔点与化学成分的关系[J]. 燃料化学学报,1965(2):61-71. YAO X Y. Relationship of coal ash fusibility to chemical composition[J]. Journal of Fuel Chemistry and Technology,1965(2):61-71.
[11] 王洋,李慧,王东旭,等. 煤灰熔融特性与灰成分之间关系的矿物变化研究[J]. 燃料化学学报,2016,44(9):1034-1042. WANG Y,LI H,WANG D X,et al. Relationship between coal ash fusibility and ash composition in terms of mineral changes[J]. Journal of Fuel Chemistry and Technology,2016,44(9):1034-1042.
[12] LIU B,HE Q,JIANG Z,et al. Relationship between coal ash composition and ash fusion temperatures[J]. Fuel,2013,105(105):293-300.
[13] YAN T,BAI J,KONG L X,et al. Effect of SiO₂/Al₂O₃ on fusion behavior of coal ash at high temperature[J]. Fuel,2017,193:275-283.
[14] 王洋,李慧,王东旭,等. 煤和生物质灰中氧化钾含量对灰熔融特性的影响[J]. 化工进展,2016,35(9):2759-2765. WANG Y,LI H,WANG D X,et al. The effect of K₂O in coal and biomass ash on ash fusibility[J]. Chemical Industry and Engineering Progress,2016,35(9):2759-2765.
[15] VASSILEV S V,KITANO K,TAKEDA S,et al. Influence of mineral and chemical composition of coal ashes on their fusibility[J]. Fuel Processing Technology,1995,45(1):27-51.
[16] AKIYAMA K,PAK H,TAKUBO Y,et al. Ash deposition behavior of upgraded brown coal in pulverized coal combustion boiler[J]. Fuel Processing Technology,2011,92(7):1355-1361.