Effect of silicon oxide additive on the transformation characteristics of sodium and sulfur in Zhundong coal ash under atmospheric and elevated pressure
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摘要: 本实验研究了常压和加压条件下氧化硅添加剂对准东煤灰中钠和硫转化特性的影响。结果表明，氧化硅添加剂在高压下对钠的释放具有更强的抑制作用。0.1 MPa下，添加比为4%时，灰中钠含量比无添加剂时高3.5%。而4 MPa、添加比例为0和4%时，灰中钠含量比0.1 MPa、无添加剂时分别高5.4%和6.9%。在0.1 MPa时，钠主要以NaAlSiO4 和 NaAlSi3O8的形式存在。随添加比的升高灰中NaAlSiO4的含量增加，这有效地减弱了灰的团聚。在4 MPa时，添加剂含量的增加，抑制了低熔点矿物CaSO4的分解，并且显著促进了NaAlSiO4与CaSO4反应生成Na6Ca2Al6Si6O24(SO4)2的反应。本实验提出了高压下氧化硅抑制煤灰中钠和硫释放的机理。Abstract: The effects of silicon oxide additive on the transformation characteristics of sodium and sulfur in coal ash under atmospheric and elevated pressure were investigated in this study. The results indicated that silicon oxide additive significantly inhibited the release of sodium under high pressure. The sodium content in ash with 4% of silicon oxide additive was 3.5% at 0.1 MPa, which was higher than that without additive. However, the sodium content increased to 5.4% without additive and 6.9% with 4% additive at 4 MPa, respectively. The sodium mainly existed in the forms of NaAlSiO4 and NaAlSi3O8 at 0.1 MPa, and the content of NaAlSiO4 increased with increasing additive dosage, which weakened the agglomeration of ash. The decomposition of low melting point mineral CaSO4 was inhibited at 4 MPa, and the formation of Na6Ca2Al6Si6O24(SO4)2 from NaAlSiO4 and CaSO4 was promoted significantly with increasing additive dosage. Furthermore, the inhibition mechanism of sodium and sulfur released from coal ash by silicon oxide under high pressure was proposed.
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Key words:
- Zhundong coal ash /
- elevated pressure /
- silicon oxide additive /
- sodium /
- sulfur
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Figure 2 Morphology of ash samples under different pressures and addition ratios at 1000 °C
Figure 4 Residual rate of Ash-1000 for excluding additive under various pressures and addition ratios
Figure 5 Content of Na, S, and Ca in Ash-1000 excluding additive at different pressures and addition ratios
Figure 6 XRD patterns of raw Ash-500 and Ash-1000 with different addition ratios under 0.1 MPa
a- CaSO4; b- Ca2Al2SiO7; c- NaAlSiO4; d- CaMgSi2O6; e- CaCO3; f- CaO; g- NaCl; h- Fe2O3; i- NaAlSi3O8; n- Al2SiO5; q- SiO2; r- MgCaSiO4; t- Na6Ca2Al6Si6O24(SO4)2; u- MgFe2O4
Figure 7 XRD patterns of Ash-1000 with various addition ratios under 4 MPa
a- CaSO4; b- Ca2Al2SiO7; c- NaAlSiO4; d- CaMgSi2O6; h- Fe2O3; i- NaAlSi3O8; q- SiO2; r-MgCaSiO4; t- Na6Ca2Al6Si6O24(SO4)2; u- MgFe2O4
Figure 9 Transformation pathways of sodium and sulfur under 0.1 and 4 MPa with or without SiO2 (Thickened solid and dashed lines represent the processes promoted under the operating pressure)
Table 1 Proximate and ultimate analyses of HSQ coal
Sample Proximate analysis wad/% Ultimate analysis wad/% M A V FC C H O N S HSQ 14.18 4.06 24.60 57.16 63.19 2.90 15.34 0.51 0.39 
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Table 2 Ash compositions of HSQ coal sample
Composition Na2O Al2O3 Fe2O3 MgO TiO2 SiO2 SO3 K2O CaO P2O5 Content/% 6.41 4.58 8.28 11.09 0.20 0.28 27.72 0.31 40.46 0.07
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Table 3 Ash-500 mass with different addition ratios
Addition ratios w/% 0 1 2 3 4 Mass /g 0.2500±0.0005 0.3500±0.0005 0.4000±0.0005 0.4500±0.0005 0.5000±0.0005
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Table 4 Element contents of Ash-1000 with different addition ratios by EDS under 0.1 and 4 MPa
Element w/% O Na Ca Al Si Fe S Mg 0 0.1MPa Area-A 36.82 4.48 17.31 9.98 14.95 11.29 − 5.18 4MPa Area-B 36.79 4.73 17.11 12.76 14.19 9.08 − 5.34 0.1MPa Spot-a 44.70 16.61 − 15.52 20.53 − − 2.64 4MPa Spot-b 49.07 8.97 9.49 14.24 13.59 − 1.78 2.86 4% 0.1MPa Area-C 40.82 4.57 10.91 12.92 19.19 6.32 − 5.28 4MPa Area-D 35.81 3.81 13.52 10.75 19.41 10.94 1.10 4.67 0.1MPa Spot-c 42.86 4.59 11.21 13.94 19.09 5.30 − 3.02 4MPa Spot-d 53.30 8.44 7.72 13.54 15.24 − 2.84 1.92 4MPa Spot-e 23.80 − 43.40 2.01 2.57 2.95 24.41 0.873 “−”: indicates that no relevant crystalline phase was detected
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