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摘要: 研究了不同温度条件下高硅煤中矿物组成比例下的Si-Al-Fe-Ca多元体系的碳热反应以及其影响因素。通过XRD和FESEM-EDS技术对各还原产物进行分析。结果表明,Fe2O3对含硅矿物的碳热反应起促进作用,Fe可以有效提高Si反应活性。CaO在较低温度时与灰中的Al2O3和SiO2反应形成致密的Ca-Al-Si相共熔体CaAl2Si2O8,阻碍含硅矿物碳热反应的进行。随着温度的升高,继续反应生成SiC、CaAl4O7和CaSiO3。热力学模拟计算与实验结果基本吻合。
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关键词:
- 高硅煤 /
- Si-Al-Fe-Ca四元体系 /
- 含硅矿物 /
- 碳热反应
Abstract: During coal pyrolysis and gasification, the minerals in coal undergo various transformations, which affects coal conversion and characteristics of coal ash obviously. Carbothermal reduction of Si-Al-Fe-Ca quaternary system in high-silica coal under different temperature was investigated. Composition of products obtained was analyzed by X-ray diffraction (XRD) and field emission scanning electron microscope-energy dispersive spectrometer (FESEM-EDS) technology. The results show that Fe2O3 plays a positive role in carbothermal reaction of silicon-bearing minerals, which could effectively improve activity of Si. On the contrary, CaO reacts with Al2O3 and SiO2 to form dense Ca-Al-Si eutectic, mainly CaAl2Si2O8, at lower temperature, covering surface of the reactant, which hinders the carbothermal reaction of silicon-containing minerals. With increasing temperature, CaAl2Si2O8 reacts with graphite to generate SiC, CaAl4O7 and CaSiO3. The related thermodynamic calculations are in accordance with the experiment results. -
图 3 不同比例Si-Al-Fe-Ca四元体系还原产物XRD谱图
Figure 3 XRD patterns of the products of different synthetic ashes
Q: Quartz; Cr: Cristobalite; G: Graphite; C: Corundum; A: Anorthite; H: Hematite; SC: Silicon Carbide; W: Wollastonite; P: Pseudowollastonite; Wu: Wustite; S: Silimanite; FS: Fe3Si; FS2: Fe1.34Si0.66; FS3: Fe5Si3; CA1: CaAl4O7; CA2: CaAl12O19; CS: Ca2SiO4; CF: CaFe3O5; He: CaFeSi2O6; AC: Al4Ca; FC: Fe3C; FA: FeAl3; FAS: Fe3Al2Si3; FSO: Fe2.56Si0.44O4
图 4 不同添加物的产物SEM照片
Figure 4 SEM of the product of different additives
(a): the unreacted graphite; (b): the product of SiO2 at 1 600 ℃; (c): magnification of the product of SiO2 at 1 600 ℃; (d): the product of sample mixed with CaO at 1 600 ℃; (e): the product of sample mixed with Fe2O3 at 1 600 ℃; (f): magnification of the product of sample mixed with Fe2O3 at 1 600 ℃
图 5 各点(1#-3#)的能谱图
Figure 5 EDS of the points(1#-3#) in Figure 4
表 1 Si-Al-Ca-Fe多元系比例表
Table 1 Compositions of synthetic ashes
SiO2 Al2O3 Fe2O3 CaO 1 50 30 15 5 2 50 30 5 15 3 55 30 10 5 4 60 25 10 5 5 55 30 5 10 6 60 30 5 5 7 65 30 0 5 8 65 30 5 0 9 50 35 10 5 10 100 0 0 0 1# 2# 3# Element w/% wA/% Element w/% wA/% Element w/% wA/% Si 52.14 31.84 Si 34.01 28.3 Si 13.89 16.12 C 47.86 68.19 Al 34.06 29.49 Fe 70.16 40.71 Ca 5.05 2.94 C 15.94 43.17 O 26.88 39.26 表 3 Si-Al-Fe-Ca系主要反应及相应的吉布斯-亥姆霍兹方程[21-23]
Table 3 Gibbs-Helmholtz equations of the main reactions in Si-Al-Fe-Ca system
Reaction formular ΔG0/(kJ·mol-1) (1) SiO2+3C=SiC+2CO(g) 616.56-0.353 0T (2) Fe2O3+3C=2Fe+3CO(g) 466.35-0.505 8 T (3) 3Fe+SiO2+2C=Fe3Si+2CO(g) 570.32-0.349 9 T (4) 3Fe+C=Fe3C 22.594-0.013 7 T (5) CaO+2SiO2+Al2O3=CaAl2Si2O8 -91.211+0.028 9 T (6) CaAl2Si2O8+Al2O3+6C=CaAl4O7+2SiC+4CO(g) 1 315.117-0.713 3 T (7) CaAl2Si2O8+3C=CaSiO3+Al2O3+SiC+2CO(g) 618.647-0.324 9 T (8) CaO+3C=CaC2+CO(g) 464.34-0.210 9 T (9) CaO+C=Ca+CO(g) 525.75-0.194 3 T (10) Ca+2C=CaC2 -59.413-0.017 4 T (11) Ca+SiO2+2C=CaSi+2CO(g) 539.151-0.345 9 T (12) Ca+2SiO2+4C=CaSi2+4CO(g) 1 228.926-0.694 9 T (13) 2Al2O3+9C=Al4C3+6CO(g) 2 414.4-1.066 1 T -
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