Study on the mineral transformation and heavy metal distribution during high-silicon coal combustion
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摘要: 选取云南宣威地区高硅煤，对其在燃烧过程中矿物转化特征及重金属分布富集规律进行了研究。高硅煤中的矿物主要由石英、高岭石、黄铁矿和锐钛矿组成。飞灰中莫来石可能来自煤中石英、高岭石的转变，而石英主要来自煤中原始石英组分或由SiO2-Al2O3系统转化形成。分析高硅煤和高硅飞灰中部分重金属的富集特性，发现高硅煤中富集的元素有Cr、Cu和As，电厂ESP各级电场中富集的重金属有Mo元素，而Se元素在高硅煤和飞灰中分别都低于世界煤和飞灰的平均值。放射性元素Th和U含量在细粒径的高硅飞灰中都高于世界煤灰平均值，在ESP的4电场飞灰中富集系数分别为1.51和1.59。Abstract: The high-silicon coal in Xuanwei area of Yunnan is selected to study the transformation behavior of minerals and the distribution and enrichment of heavy metals during the combustion process. The minerals in high-silicon coal are mainly composed of quartz, kaolinite, pyrite and anatase. The mullite in fly ash may come from the transformation of quartz and kaolinite in coal; the quartz in fly ash mainly comes from the original quartz component in coal or is formed by the conversion of SiO2-Al2O3 system. Analyzing the enrichment characteristics of several heavy metals in high-silicon coal and its fly ash, it can be found that Cr, Cu, and As are enriched in the high-silicon coal, and Mo is the heavy metal enriched in the electric fields of the ESP, while Se contents in high-silicon coal and fly ash in China are both lower than the world average level. The contents of radioactive elements of Th and U in the fine-particle high-silicon fly ash are higher than the average of world coal ash, and the enrichment factors in the fly ash in the four electric fields of the ESP are 1.51 and 1.59, respectively.
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Key words:
- high-silicon coal /
- coal combustion /
- fly ash /
- mineral transformation /
- heavy metals
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图 1 高硅煤(a)及其高温灰(b)的XRD谱图
Figure 1 XRD patterns of the high-silicon coal
(a) and its high temperature ash (b) Q: quartz; K: kaolinite; P: pyrite: A: anatase; H: hematite
图 3 不同粒径的DD电厂粉煤灰的XRD谱图
Figure 3 XRD patterns of the fly ash of the DD power plant with different particle sizes
(a): unsized; (b): 38.5-74 μm; (c): < 30.8 μm; Q: quartz; M: mullite
图 4 DD电厂高硅飞灰的ESEM-EDX
Figure 4 ESEM-EDX images of the high-silicon fly ash in the DD power plant
(a): overall morphology of coarse fly ash; (b): overall morphology of fine fly ash; (c), (d): hollow spherical particle; (e): Fe-bearing particle; (f): unburned carbon
图 5 高硅煤重金属的富集系数(DD煤/世界硬煤平均值)
Figure 5 Enrichment factors of heavy metals in the high-silicon coal (DD coal/average of world hard coal)
图 7 高硅飞灰中重金属富集系数
Figure 7 Enrichment factors of heavy metals in the high-silicon fly ash
图 8 煤燃烧过程中矿物转化和重金属迁移富集关系
Figure 8 Relationship of mineral transformation and heavy metal migration and enrichment during coal combustion
表 1 工业分析和元素分析
Table 1 Proximate and ultimate analyses
Proximate analysis wad/% Ultimate analysis wad/% N C S H M V A FC 1.07 62.44 1.42 2.70 1.70 12.17 28.70 57.43 ad: air-dry base; M: moisture; V: volatile matter; A: ash; FC: fixed carbon 
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表 2 高温灰的主要元素组成
Table 2 Major elemental composition of high temperature ash
Composition w/% SiO2 Al2O3 Fe2O3 CaO MgO Na2O SO3 TiO2 P2O5 MnO 54.99 29.87 4.32 3.63 1.12 0.93 3.24 1.71 0.16 0.03
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表 3 高硅煤及其高温灰中的矿物含量
Table 3 Mineral contents in the high-silicon coal and its high temperature ash
Sample Content w/% quartz kaolinite pyrite anatase hematite DD high-silicon coal 46 26 20 8 - High temperature ash 66.37 - - - 33.63
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表 4 不同粒径的高硅粉煤灰中矿物质的定量
Table 4 Mineral contents of the high-silicon fly ash with different particle sizes
Sample Content w/% quartz mullite Fly ash (unsized) 70.45 29.55 Fly ash (38.5-74 μm) 68.31 31.69 Fly ash (< 30.8 μm) 79.78 20.22
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表 5 高硅煤中的重金属含量和富集系数
Table 5 Heavy metal contents and enrichment factors (EF) of the high-silicon coal
Heavy metal Content/(μg·g-1) Average of world hard coal EF Cr 35.40 17 2.08 Cu 48.70 16 3.04 As 18 9 2 Se 0.56 1.60 0.35 Mo 2.97 2.10 1.41 Pb 14.60 9 1.62 Th 8.85 3.20 2.77 U 3.29 1.90 1.73
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表 6 ESP各级电场飞灰中重金属含量(μg/g)及富集系数
Table 6 Heavy metal contents (μg/g) of each ESP electric field and enrichment factors (EF) of the high-silicon fly ash
1 electric field 2 electric field 3 electric field 4 electric field World average content EF content EF content EF content EF Cr 101 0.84 117 0.98 122 1.02 129 1.08 120 Cu 159 1.45 174 1.58 199 1.81 205 1.86 110 As 33.20 0.72 46.4 1.01 53.10 1.15 60.20 1.31 46 Se 2.45 0.25 3.38 0.34 6.90 0.69 8.69 0.87 10 Mo 20 1.43 30.50 2.18 35.90 2.56 42.40 3.03 14 Pb 53 0.96 66.70 1.22 81.90 1.49 89.60 1.63 55 Th 28.20 1.23 29.60 1.29 32.50 1.41 34.70 1.51 23 U 14.10 0.94 17.80 1.17 20.60 1.37 23.80 1.59 15
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