Effect of kaolin on the ash fusion characteristics of high alkali Zhundong coal: A quantum chemistry and experimental study
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摘要: 采用量子化学理论计算与实验表征相结合的方法, 研究了高岭土对准东高碱煤煤灰熔融特性及其熔融过程中矿物质演变规律的影响, 并从矿物质微观结构特性角度阐述了高岭土对改变准东煤煤灰熔融特性的影响机制。结果表明, 准东高碱煤煤灰熔融温度随高岭土的添加呈现先快速升高后逐渐变缓的趋势, 当高岭土添加比例大于10%时, 其提高煤灰熔融温度的趋势变缓; 准东高碱煤添加高岭土后, 其在1 000-1200 ℃下的低熔融矿物钙长石、硬石膏等量明显减少, 1 200-1 300 ℃下有一定量的莫来石生成, 是其煤灰熔点升高的主要原因; 高岭石分子结构中的O (26)、O (22)、Si (6)、Si (8) 的反应活性较高, 能够与灰中的Fe2+等金属离子成键, 促使高岭石的铝氧键断裂。煤中的碱金属或碱土金属(Na或Ca) 氧化物中的的O2-, 作为亲核试剂, 与高岭石的Si (6) 和Si (8) 发生亲核反应, 使桥氧键S-O-Si断裂。Abstract: The effect of kaolin on the ash fusion characteristics of high alkali Xinjiang Zhundong coal was investigated by quantum chemistry calculation and experimental measurement methods. The results show that the ash fusion temperature is increased significantly by adding kaolinite; the ash fusion temperature increases rapidly at first with the increase of kaolinite content added in the Zhundong coal and then levels off when the fraction of kaolinite exceeds 10%. By adding kaolin in the Zhundong coal, the content of minerals with a low melting point (1 100-1 200 ℃), such as anorthite and anhydrite, is reduced, whereas mullite is found at 1 200-1 300 ℃. O (26), Si (6), O (22) and Si (8) atoms in the kaolinite molecular structure exhibit relatively high reactivity; Al-O bond, which is connected with O (26) and O (22), can be ruptured by reacting with Fe2+ or other metal ions in ash as an electrophilic reagent. The O2- of alkali oxides in ash, such as Na2O and CaO, can react as a nucleophilic reagent with Si (6) and Si (8) in kaolinite, breaking the oxygen bridge bond of Si-O-Si in kaolinite.
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Key words:
- Zhundong coal /
- kaolin /
- density functional theory /
- ash fusion characteristics /
- high alkali coal /
- reactivity
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图 1 添加高岭土对准东高碱煤煤灰熔融温度的影响
Figure 1 Effect of kaolin on the fusion temperature of high-alkali Zhundong coal ash
图 2 不同温度下不同灰样的XRD谱图
Figure 2 XRD patterns of samples at different temperatures
(a): high-alkali Zhundong coal; (b): Zhundong coal with 5% kaolin; (c): Zhundong coal with 10% kaolin
Q: quartz; H: hematite; A: anhydrite; Tri: tridymite; An: anorthite; Mu: mullite; CAS: calcium aluminum silicate
图 4 高岭石的HOMO、LUMO示意图
Figure 4 HOMO and LUMO schematic of kaolinite
(a): HOMO; (b): LUMO
图 5 高岭石的优化结构、静电势及其Fukui函数在0.2 a.u.等值面上的映射图
Figure 5 Optimized structure, ESP isosurface and Fukui function of kaolinite (0.2 a.u.)
(a): optimized structure; (b): electrostatic potential (ESP); (c): electrophilic Fukui Function; (d): nucleophilic Fukui function
表 1 实验煤样与高岭土分析数据
Table 1 Properties of coal and kaolinite
Project Zhundong coal Kaolin Proximate analysis Mar/% 20.48 0.0 Mad/% 8.86 0.0 Aar/% 14.23 100 Vdaf/% 35.98 0.0 Qnet, ar/(MJ·kg-1) 18.3 0.0 Elemental analysis Cdaf w/% 78.77 - Hdaf w/% 4.59 - Odaf w/% 15.06 - Ndaf w/% 0.84 - Sdaf w/% 0.74 - Melting temperature (reducing atmosphere) DT t/℃ 1 070 > 1 500 ST t/℃ 1 080 > 1 500 HT t/℃ 1 090 > 1 500 FT t/℃ 1 110 > 1 500 Chemical compositions of coal ash SiO2 w/% 35.95 61.99 Al2O3 w/% 14.60 21.73 Fe2O3 w/% 16.32 1.39 CaO w/% 11.72 0.61 MgO w/% 5.69 0.48 K2O w/% 0.78 0.61 Na2O w/% 4.46 0.21 TiO2 w/% 0.96 0.59 SO3 w/% 9.10 0.83 
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表 2 高岭石Mulliken原子布居数及简缩Fukui函数(f -和f+)
Table 2 Atomic charges (q) and condensed Fukui Functions (f- and f+) of Kaolinite
Atom q f- f+ atom q f- f+ Al (1) 1.441 0.047 0.058 O (18) -0.967 0.011 -0.023 Al (2) 1.463 0.044 0.047 O (19) -0.793 0.042 -0.020 Al (3) 1.441 0.047 0.058 O (20) -0.775 0.056 -0.010 Al (4) 1.464 0.044 0.047 O (21) -0.811 0.037 -0.008 Si (5) 1.884 0.036 0.158 O (22) -0.787 0.061 -0.013 Si (6) 1.853 0.037 0.168 O (23) -0.793 0.042 -0.020 Si (7) 1.884 0.036 0.158 O (24) -0.775 0.055 -0.010 Si (8) 1.853 0.037 0.168 O (25) -0.811 0.037 -0.008 O (9) -0.994 0.017 -0.015 O (26) -0.787 0.062 -0.013 O (10) -0.982 0.017 -0.014 H (27) 0.335 0.012 0.076 O (11) -0.992 0.012 -0.023 H (28) 0.337 0.017 0.050 O (12) -0.952 0.015 -0.030 H (29) 0.393 0.015 0.032 O (13) -0.967 0.011 -0.023 H (30) 0.347 0.025 0.064 O (14) -0.994 0.017 -0.015 H (31) 0.335 0.012 0.077 O (15) -0.982 0.017 -0.014 H (32) 0.337 0.017 0.050 O (16) -0.992 0.012 -0.022 H (33) 0.393 0.015 0.032 O (17) -0.952 0.015 -0.030 H (34) 0.347 0.025 0.065
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