Modification of ash fusion behavior of high ash fusion temperature (AFT) coal by textile dyeing sludge addition and its mechanism
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摘要: 为解决煤气流床(EFB)气化过程中的结渣问题,在还原气氛下研究了染布厂污泥(TDS)对高灰熔融温度(AFT)煤的熔融特性的影响。通过X射线衍射、傅里叶变换红外光谱(FT-IR)和FactSage计算研究其变化机理。结果表明,当TDS含量添加20%−25%时,流动温度降至1380 ℃以下,满足EFB气化的液态排渣要求。随着TDS含量的增加,低熔点矿物(如铁尖晶石、钙长石和钠长石)的形成导致AFT降低。网络结构的桥氧键被金属离子(如Fe2+、Ca2+、Na+)破坏,大量的非桥氧(NBO)键生成,导致硅酸盐网络结构疏松,AFT降低。Si−O−Si键和Si−O−Al键的峰值强度逐渐降低,Fe−O键和Si−O−M(M:Ca2+或Na+)键的振动增强被FT-IR证实了NBO的形成。FactSage计算的结果与实验中灰熔融行为具有一致性。Abstract: To address the slagging problem during coal entrained-flow bed (EFB) gasification, the influences of textile dyeing sludge (TDS) addition on the fusing characteristics of high ash fusion temperature (AFT) coal were explored under a reducing atmosphere. And the change mechanisms were investigated by X-ray diffraction, Fourier Transform Infrared Spectroscopy (FT-IR) and FactSage calculation. The results showed that the flow temperature of high ash fusion temperature (AFT) coal decreased below 1380 °C when the TDS addition reached 20%−25%, which met the requirements of liquid-slag removal for EFB gasification. With the content of TDS increasing, the formations of low-melting minerals (e.g., hercynite, anorthite, and albite) decreased AFT. The bridging oxygen bonds of the network structure were destroyed by metal ions (e.g., Fe2+, Ca2+, Na+), formation of much non-bridged oxygen (NBO) bonds relaxed the silicate network, thus decreasing the AFT. The formations of NBO bonds were confirmed by gradual decreases in the peak strengths of Si−O−Si and Si−O−Al bonds and intensified the vibration of Fe−O and Si−O−M ( M: Ca2+ or Na+) bonds. FactSage calculation results were in good agreement with the experimental ash fusion behavior.
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Key words:
- ash fusion behaviors /
- textile dyeing sludge /
- high AFT coal /
- modification mechanisms
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Figure 5 XRD patterns of coal ash and mixture ashes with different TDS ash mass ratios at different temperatures (a): C; (b): C+5%; (c): C+10%S; (d): C+15%S; (e): C+20%S; (f): C+25%S; 1: Quartz (SiO2); 2: Anhydrite (CaSO4); 3: Mullite (Al6Si2O13); 4: Anorthite (CaAl2Si2O8); 5: Hematite (Fe2O3); 6: Hercynite (FeAl2O4); 7: Albite (NaAlSi3O8); 8: Alumina (Al2O3)
Figure 6 XRD patterns of mixed ashes with different TDS ash mass ratios at 900 to 1300 °C (a): 900 °C; (b): 1000 °C; (c): 1100 °C; (d): 1200 °C; (e): 1300 °C 1: Quartz (SiO2); 2: Anhydrite (CaSO4); 3: Hematite (Fe2O3); 4: Mullite (Al6Si2O13); 5: Albite (NaAlSi3O8); 6: Alumina (Al2O3); 7: Anorthite (CaAl2Si2O8); 8: Hercynite (FeAl2O4)
Figure 9 Phase assemblage-temperature curves of coal ashes and mixture ash (a): C; (b): C+5%S; (c): C+10%S; (d): C+15%; (e): C+20%; (f): C+25% 1: Mullite (Al6Si2O13); 2: Albite (NaAlSi3O8); 3: Anorthite (CaAl2Si2O8); 4: Potassium Feldspar (KAlSi3O8); 5: Hercynite (FeAl2O4); 6: Calcium Phosphate (Ca5HO13P3); 7: Cordierite (Al4Fe2Si5O18); 8: Ferrous Sulfide (FeS); 9: Quartz (SiO2); 10: Titania (TiO2); 11: Alumina (Al2O3); 12: Ilmenite (FeTiO3); 13: Protopyroxene (FeAl2SiO6); 14: Titania Spinel (Fe2TiO4); 15: Fayalite (Fe2SiO4)
Table 1 Proximate and ultimate analyses of coal and TDS samples
Sample Proximate analysis wad/% Ultimate analysis wdaf/% Mad Vad Aad FCad C H O N S Coal 6.60 12.86 10.15 70.39 92.62 3.99 1.65 1.42 0.32 TDS 14.25 28.37 58.63 1.25 21.16 2.66 1.10 9.32 2.49 Chemical composition of the ash w/% SiO2 Al2O3 CaO Na2O Fe2O3 MgO P2O5 SO3 TiO2 K2O Coal 41.15 32.10 7.03 1.07 6.76 0.60 1.10 5.77 3.68 0.74 TDS 15.37 19.65 5.33 2.38 44.90 1.86 3.40 3.93 1.78 0.47 ad-air dry basis; daf- dry ash free basis; M-moisture; A-ash; V-volatile matter; FC-fixed carbon Table 2 AFTs of the coal and TDS
Sample Temperature/℃ DT ST HT FT Coal 1481 > 1500 > 1500 > 1500 TDS 1188 1235 1267 1321 -
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