Effect of O2/CO2 combustion atmosphere on the mineral inter-reaction of blended coal ashes
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摘要: 对蒙煤与平七煤两种单煤及其按照不同比例组成的混煤，分别在O2/CO2和O2/N2气氛下，采用管式炉燃烧制取灰样；对灰样进行灰熔点、XRD及同步热分析（TG/DSC）测试，并进行相关热力学计算，分析了O2/CO2燃烧方式对混煤灰中矿物质间反应的影响。结果表明，常规灰熔点测试方法测得的两种气氛下的混煤灰熔点没有明显差别。O2/CO2气氛促进了煤灰/混煤灰中钙的碳酸化，且明显抑制了高温下CaCO3的分解。气氛的改变影响了含钙矿物的转化，进而影响了混煤中钙与莫来石反应生成低温共熔物；O2/CO2气氛下钙更易于与莫来石发生反应生成低温共熔物，从而会增加结渣倾向。当混煤中蒙煤比例达到或大于75%时，随着蒙煤比例的逐渐增加，莫来石含量减少，O2/CO2气氛对钙与莫来石之间的反应影响减弱，但对含铁矿物的影响更加明显，使其更易于生成含铁玻璃体，从而也会增加结渣倾向。Abstract: The mineral inter-reaction of blending coals during O2/CO2 combustion was studied. Two coals, Meng coal and Pingqi coal, were blended by certain ratios. The blending coals were burned in a tube furnace with O2/CO2 or O2/N2. Ash fusion temperature test, XRD, TG/DSC and thermodynamic calculation were employed to examine the melting behavior and mineral reactions of blending coal ashes during O2/CO2 and O2/N2 combustion in detail. The results show that:there is no a pronounced difference in the blending coal ash fusion temperature between O2/CO2 and O2/N2 combustion. More CaCO3 produced during O2/CO2 combustion suggests that O2/CO2 atmosphere significantly prevents the decomposition of CaCO3. The changing of atmosphere has an impact on the transformation of Ca-containing minerals, and the reaction between Ca and mullite occurs significantly, which is easier in O2/CO2 combustion to produce more low-melting phase that will aggravate the boiler slagging. When the blending ratio of Meng coal in blends with Pingqi coal is 75% or more, less mullite is present in blending coals, and thus the impact of atmosphere on Ca-mullite reaction is weaker. However, the atmosphere has a more impact on Fe-containing minerals and more Fe-glass phase will be formed during O2/CO2 combustion, which will aggravate the boiler slagging.
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Key words:
- pulverized coal /
- coal blending /
- O2/CO2 atmosphere /
- mineral transformation /
- boiler slagging
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图 3 蒙煤灰在N79和C79气氛下的TG-DTG-DSC曲线
Figure 3 TG-DTG-DSC results of Meng ash in N79 and C79 atmospheres
图 4 M75煤灰在N79和C79气氛下的TG-DTG-DSC曲线
Figure 4 TG-DTG-DSC test of M75 ash heating in N79 and C79 atmosphere
图 5 M50煤灰在N79和C79气氛下的TG-DTG-DSC曲线
Figure 5 TG-DTG-DSC tests of M50 ash in N79 and C79 atmospheres
图 6 M25煤灰在N79和C79气氛下的TG-DTG-DSC曲线
Figure 6 TG-DTG-DSC tests of M25 ash in N79 and C79 atmospheres
图 7 平七煤灰在N79和C79气氛下的TG-DTG-DSC曲线
Figure 7 TG-DTG-DSC tests of Pengqi coal ash in N79 and C79 atmospheres
图 9 蒙煤815℃灰的XRD谱图
Figure 9 XRD patterns of Meng coal ash prepared at 815℃
Q: quartz-SiO2; S: anhydrite-CaSO4; H: hematite-Fe2O3; C: calcite-CaCO3
图 13 平七煤815℃灰的XRD谱图
Figure 13 XRD patterns of Pingqi ash prepared at 815℃
Q: quartz-SiO2; S: anhydrite-CaSO4; H: hematite-Fe2O3; C: calcite-CaCO3
图 16 M50煤1100℃灰的XRD谱图
Figure 16 XRD patterns of M50 ash prepared at 1100℃
Q: quartz-SiO2; An: anorthite-CaO·Al2O3·2SiO2; M: mullite-2Al2O3·SiO2
图 17 M75煤1100℃灰的XRD谱图
Figure 17 XRD patterns of M75 ash prepared at 1100℃
An: anorthite-CaO·Al2O3·2SiO2; H: hematite-Fe2O3; Ma: magnetite-Fe3O4
图 18 蒙煤1100℃灰的XRD谱图
Figure 18 XRD patterns of Meng coal ash prepared at 1100℃
Au: augite-Ca(Mg, Fe, Al)[(Si, Al)2O6]; Ge: gehlenite-2CaO·Al2O3·SiO2; He: hedenbergite-CaFeSi2O6; Ba: bassanite-CaSO4·0.5H2O; Ma: magnetite-Fe3O4
表 1 实验用煤的煤质特性
Table 1 Properties of coal samples
Coal sample Ultimate analysis wd/% Proximate analysis w/% Q (net, ar) /(kJ·kg-1) C H N S O Mad Ad Vd FCd Meng coal 71.23 4.80 0.75 0.49 15.19 3.51 7.54 34.07 58.39 21543 Pingqi coal 62.06 4.50 0.87 0.54 10.61 1.42 21.42 30.28 48.30 21505 
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表 2 煤灰成分分析
Table 2 Ash composition of coal samples
Coal Composition w/% Na2O Al2O3 SiO2 SO3 K2O CaO Fe2O3 MgO TiO2 Meng coal 2.88 13.74 32.03 22.31 0.71 19.83 5.55 0.71 0.95 Pingqi coal 1.47 34.13 50.29 4.27 0.80 3.26 1.97 1.80 1.04
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表 3 HSC模拟计算工况
Table 3 Cases of HSC calculation
Case 1 (O2/N2 atmosphere) Case 2(O2/CO2 atmosphere) Reactants SiO2 Al2O3 CaSO4 SiO2 Al2O3 CaCO3 CaSO4 Amount /kmol 5.22 1.32 3.46 5.22 1.32 2.08 1.38 Products 3Al2O3·2SiO2、CaO·Al2O3·2SiO2
2CaO·Al2O3·SiO2、CaO、SO3(g)3Al2O3·2SiO2、CaO·Al2O3·2SiO2
2CaO·Al2O3·SiO2、
CaO、SO3(g)、CO2(g)
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