Effect of Na2O on mineral transformation of coal ash under high temperature gasification condition
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摘要: 利用XRD和FT-IR考察了高温弱还原气氛下Na2O对两种硅铝含量不同的煤灰中矿物质组成的影响, 揭示了Na2O影响煤灰熔融特性的本质.通过FactSage计算了高温下矿物质反应的ΔG, 探讨了Na2O影响煤灰中矿物质组成的机理.结果表明, Na2O对煤灰矿物质组成的影响与原煤灰的硅铝含量密切相关.硅铝总含量82.89%的煤灰, Na2O含量为5%-20%时, 钠长石和霞石的生成是煤灰熔融温度降低的主要原因; 当Na2O含量大于20%时, 导致煤灰熔融温度降低的原因是霞石的生成.硅铝总含量47.85%的煤灰, Na2O含量小于10%时, 没有含钠矿物质生成; 当Na2O含量大于10%时, 主要生成菱硅钙钠石、青金石和含钠的硅铝酸盐矿物, 导致煤灰熔融温度降低.FactSage计算表明生成含Na矿物质反应的ΔG较小, 其在高温下更容易发生.Abstract: In order to reveal the mechanism of Na2O influence on ash fusion temperatures (AFTs), effect of Na2O on mineral transformation of two coal ashes with different SiO2+Al2O3 levels were investigated by XRD and FT-IR under reducing atmosphere at high temperature. Thermodynamic software package FactSage was used to calculate the ΔG of reactions between minerals to reveal the mechanism of Na2O influence on mineral transformation. It is found that the effect of Na2O on mineral compositions depends on SiO2+Al2O3 levels of coal ash. For ash with 82.89% SiO2+Al2O3 while Na2O content is 5%-20%, albite and nepheline are formed, leading to a decrease of AFTs. However, only nepheline is formed when Na2O content is higher than 20%. For ash with 47.85% SiO2+Al2O3, when Na2O content is less than 10%, no Na-containing mineral is observed. When Na2O content is higher than 10%, Na-containing minerals such as combeite, lazurite and sodium aluminium oxide are formed, resulting in a decrease of AFTs. Furthermore, FactSage results reveal that Na-containing mineral is easily formed at high temperature due to low ΔG of the reactions.
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Key words:
- high temperature gasification /
- Na2O /
- mineral matter /
- AFTs
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图 1 煤灰熔融特征温度随Na2O含量的变化
Figure 1 Ash fusion temperatures vs Na2O contents
(a): SH; (b): ZD
图 2 不同Na2O含量时寺河煤灰在不同温度下的XRD谱图
Figure 2 XRD patterns of SH coal ash with different Na2O content at different temperatures
(a): raw ash; (b): 5% Na2O; (c): 10% Na2O; (d): 20% Na2O
1: quartz; 2: mullite; 3: anorthite; 4: illite; 5: albite; 6: corundum; 7: nepheline; 8: cordierite; 9: carnegieite
图 3 1 100 ℃时不同Na2O含量SH煤灰的FT-IR谱图
Figure 3 FT-IR patterns of mineral matters in SH coal ash with different Na2O contents at 1 100 ℃
a: raw ash; b: 5% Na2O; c: 10% Na2O; d: 20% Na2O
图 4 不同Na2O含量时准东煤灰在不同温度下的XRD谱图
Figure 4 XRD patterns of ZD coal ash with different Na2O content at different temperatures
(a): raw ash; (b): 5% Na2O; (c): 10% Na2O; (d): 20% Na2O
1: quartz; 2: lime; 3: anhydrite; 4: hematite; 5: oldhamite; 6: wollastonite; 7: iron sulfide; 8: gehlenite; 9: combeite; 10: lazurite; 11: sodium aluminium oxide
图 5 1 000 ℃时不同Na2O含量ZD煤灰的FT-IR谱图
Figure 5 FT-IR patterns of mineral matters in ZD coal ash with different Na2O contents at 1 000 ℃
a: raw ash; b: 5% Na2O; c: 10% Na2O; d: 20% Na2O
图 6 FactSage计算不同Na2O含量寺河煤灰高温下的矿物质组成
Figure 6 FactSage calculation of SH coal ashes with different Na2O contents at high temperatures
图 7 FactSage计算不同Na2O含量准东煤灰高温下矿物质的组成
Figure 7 FactSage calculation of ZD coal ashes with varying Na2O contents at high temperatures
表 1 煤样的工业分析和元素分析
Table 1 Proximate and ultimate analysis of coals
Sample Proximate analysis wad/% Ultimate analysis wdaf/% M A V FC C H O* N St SH 2.17 18.52 5.54 73.77 86.92 3.01 8.59 1.06 0.42 ZD 12.10 1.44 21.13 65.33 81.15 3.42 14.37 0.82 0.24 *: by difference; St: total sulfur 
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表 2 煤样的灰成分分析
Table 2 Chemical compositions of coal ashes
Sample Content w/% SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O SH 49.54 33.35 3.36 5.20 1.11 1.28 1.30 1.28 ZD 35.10 12.75 19.38 17.14 4.38 4.89 0.79 2.42
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表 3 煤灰的灰熔点
Table 3 AFTs of coal samples
Sample Temperature t/℃ DT ST HT FT SH 1 380 1 452 1 523 1 532 ZD 1 164 1 185 1 188 1 193 DT: deformation temperature; ST: sphere temperature; HT: hemisphere temperature; FT: flow temperature
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表 4 高温下煤灰中矿物质反应的吉布斯自由能
Table 4 Gibbs free energy of reactions among minerals at high temperature
Reaction ΔG /kJ 1 000 ℃ 1 100 ℃ 1 200 ℃ 1 300 ℃ 3Al2O3+2SiO2→3Al2O3·2SiO2(mullite) -15.40 -18.06 -20.70 -23.33 CaO+ Al2O3+2SiO2→CaAl2Si2O8(anorthite) -131.64 -133.60 -135.62 -137.71 CaO+SiO2→CaSiO3(wollastonite) -88.57 -88.34 -88.01 -87.62 SiO2+Al2O3+2CaO→Ca2Al2SiO7(gehlenite) -163.84 -166.55 -169.36 -172.23 Na2O+ Al2O3+6SiO2→2NaAlSi3O8(albite) -395.71 -397.51 -396.89 -395.08 Na2O+Al2O3+2SiO2→2NaAlSiO4(nepheline) -356.37 -357.60 -356.45 -354.80 Na2O+2CaO+3SiO2→Na2Ca2Si3O9(combeite) -442.00 -433.16 -421.93 -409.52
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