碱金属/（FeO+CaO+MgO）对硅酸盐灰熔渣结构和黏度的影响机理

doi:10.11949/0438-1157.20221380

摘要/Abstract

摘要：

熔渣在高温液态炉侧壁的流动情况强烈影响高温炉的平稳运行。熔体中碱性金属对熔融灰渣的流动特性有着重要影响，且不同碱性组分对熔体的特性影响不同。通过FactSage热力学计算和分子动力学模拟，研究在SiO₂和Al₂O₃含量不变的情况下，Na₂O、K₂O和FeO、CaO、MgO的相对比例对煤灰熔体黏度和微观结构的影响。研究发现，随着M₂O/MO的增加，熔体中的高聚合度单元Q⁴占比增大，同时桥氧(BO)增加，非桥氧(NBO)减少，使熔体的聚合度增大。碱性氧化物对熔体的电荷补偿能力由大到小依次为K₂O>Na₂O>MO。当碱金属氧化物(Na₂O、K₂O)替换FeO、CaO、MgO后部分M⁺脱离NBO充当电荷补偿离子，生成BO；脱离的M⁺解聚用于维持电荷平衡的三簇氧(TO)，生成BO。这种结构上的变化增大了熔体的黏度。

关键词: 碱金属氧化物, 分子动力学模拟, 黏度, 熔渣结构, 电荷补偿

Abstract:

The flow of slag on the side walls of a high-temperature liquid furnace strongly influences the smooth operation of the high-temperature furnace. The alkali metal in the melt has an important influence on the flow characteristics of the slag and the different alkaline components have different effects on the characteristics of the melt. Through FactSage thermodynamic calculations and molecular dynamics simulations, the effects of the relative proportions of Na₂O, K₂O, FeO, CaO, and MgO on the viscosity and microstructure of coal ash melt were studied under the condition of constant SiO₂ and Al₂O₃ contents. The study found that as M₂O/MO increased, the percentage of high polymerization units Q⁴ in the melt increased, while bridge oxygen (BO) increased and non-bridging oxygen (NBO) decreased, resulting in an increase in the polymerization degree of the melt. The order of charge compensation ability of basic oxides to melt is K₂O>Na₂O>MO. When alkali metal oxides (Na₂O, K₂O) replace FeO, CaO, MgO, some of the M⁺ breaks away from the NBO to act as charge compensating ions to produce BO. The M⁺ depolymerizes to tri-cluster oxygen (TO) that maintains the charge balance to produce BO. This structural change increases the viscosity of the melt.

Key words: alkali metal oxides, molecular dynamics simulation, viscosity, slag structure, charge compensation

中图分类号:

TQ 546.4

张永泉, 玄伟伟. 碱金属/（FeO+CaO+MgO）对硅酸盐灰熔渣结构和黏度的影响机理[J]. 化工学报, 2023, 74(4): 1764-1771.

Yongquan ZHANG, Weiwei XUAN. Mechanism of alkali metal/(FeO+CaO+MgO) influence on the structure and viscosity of silicate ash slag[J]. CIESC Journal, 2023, 74(4): 1764-1771.

图/表 9

参考文献 41

1	Hu S H, Ni Y G, Yin Q, et al. Research on element migration and ash deposition characteristics of high-alkali coal in horizontal liquid slagging cyclone furnace[J]. Fuel, 2022, 308: 121962.
2	Heberlein S, Chan W P, Veksha A, et al. High temperature slagging gasification of municipal solid waste with biomass charcoal as a greener auxiliary fuel[J]. Journal of Hazardous Materials, 2022, 423: 127057.
3	Oh M S, Brooker D D, de Paz E F, et al. Effect of crystalline phase formation on coal slag viscosity[J]. Fuel Processing Technology, 1995, 44(1/2/3): 191-199.
4	Yuan H P, Liang Q F, Gong X. Crystallization of coal ash slags at high temperatures and effects on the viscosity[J]. Energy & Fuels, 2012, 26(6): 3717-3722.
5	Mills K C, Hayashi M, Wang L J, et al. The structure and properties of silicate slags[M]//Treatise on Process Metallurgy. Amsterdam: Elsevier, 2014: 149-286.
6	Sukenaga S, Saito N, Kawakami K, et al. Viscosities of CaO-SiO₂-Al₂O₃-(R₂O or RO) melts[J]. ISIJ International, 2006, 46(3): 352-358.
7	Kim H, Kim W H, Park J H, et al. A study on the effect of Na₂O on the viscosity for ironmaking slags[J]. Steel Research International, 2010, 81(1): 17-24.
8	Kim W H, Sohn I, Min D J. A study on the viscous behaviour with K₂O additions in the CaO-SiO₂-Al₂O₃-MgO-K₂O quinary slag system[J]. Steel Research International, 2010, 81(9): 735-741.
9	Zhang G H, Chou K C. Measuring and modeling viscosity of CaO-Al₂O₃-SiO₂ (-K₂O) melt[J]. Metallurgical and Materials Transactions B, 2012, 43(4): 841-848.
10	Higo T, Sukenaga S, Kanehashi K, et al. Effect of potassium oxide addition on viscosity of calcium aluminosilicate melts at 1673—1873 K[J]. ISIJ International, 2014, 54(9): 2039-2044.
11	Chang Z Y, Jiao K X, Ning X J, et al. Novel approach to studying influences of Na₂O and K₂O additions on viscosity and thermodynamic properties of BF slags[J]. Metallurgical and Materials Transactions B, 2019, 50(3): 1399-1406.
12	Ge Z F, Kong L X, Bai J, et al. Effect of CaO/Na₂O on slag viscosity behavior under entrained flow gasification conditions[J]. Fuel Processing Technology, 2018, 181: 352-360.
13	Wang W L, Shao H Q, Zhou L J, et al. Rheological behavior of the CaO-Al₂O₃-based mold fluxes with different Na₂O contents[J]. Ceramics International, 2020, 46(17): 26880-26887.
14	Vargas S, Frandsen F J, Dam-Johansen K. Rheological properties of high-temperature melts of coal ashes and other silicates[J]. Progress in Energy and Combustion Science, 2001, 27(3): 237-429.
15	Nowok J W. Viscosity and phase transformation in coal ash slags near and below the temperature of critical viscosity[J]. Energy & Fuels, 1994, 8(6): 1324-1336.
16	倪怀玮. 硅酸盐熔体的物理化学性质研究进展及其应用[J]. 科学通报, 2013, 58(10): 865-890.
	Ni H W. Advances and application in physicochemical properties of silicate melts[J]. Chinese Science Bulletin, 2013, 58(10): 865-890.
17	吴永全, 尤静林, 蒋国昌. 铝酸钙熔体结构的分子动力学模拟研究[J]. 无机材料学报, 2003, 18(3): 619-626.
	Wu Y Q, You J L, Jiang G C. Molecular dynamics study of the structure of calcium aluminate melts[J]. Journal of Inorganic Materials, 2003, 18(3): 619-626.
18	Zheng K, Zhang Z T, Yang F H, et al. Molecular dynamics study of the structural properties of calcium aluminosilicate slags with varying Al₂O₃/SiO₂ ratios[J]. ISIJ International, 2012, 52(3): 342-349.
19	徐利莹, 王秀丽, 吴永全, 等. 铝硅酸钙熔体中氧原子的配位性质及动力学[J]. 硅酸盐学报, 2006, 34(9): 1117-1123.
	Xu L Y, Wang X L, Wu Y Q, et al. Coordination and dynamics of oxygen in calcium aluminosilicate melts[J]. Journal of the Chinese Ceramic Society, 2006, 34(9): 1117-1123.
20	Jiang C H, Zhang H X, Xiong Z X, et al. Molecular dynamics investigations on the effect of Na₂O on the structure and properties of blast furnace slag under different basicity conditions[J]. Journal of Molecular Liquids, 2020, 299: 112195.
21	Gao L F, Liu X C, Bai J, et al. Structure and flow properties of coal ash slag using ring statistics and molecular dynamics simulation: role of CaO/Na₂O in SiO₂-Al₂O₃-CaO-Na₂O[J]. Chemical Engineering Science, 2021, 231: 116285.
22	马志斌, 白宗庆, 白进, 等. 高温弱还原气氛下高硅铝比煤灰变化行为的研究[J]. 燃料化学学报, 2012, 40(3): 279-285.
	Ma Z B, Bai Z Q, Bai J, et al. Evolution of coal ash with high Si/Al ratio under reducing atmosphere at high temperature[J]. Journal of Fuel Chemistry and Technology, 2012, 40(3): 279-285.
23	Bai J, Li W, Li B Q. Characterization of low-temperature coal ash behaviors at high temperatures under reducing atmosphere[J]. Fuel, 2008, 87(4/5): 583-591.
24	付子文, 王长安, 车得福, 等. 成灰温度对准东煤灰理化特性影响的实验研究[J]. 工程热物理学报, 2014, 35(3): 609-613.
	Fu Z W, Wang C A, Che D F, et al. Experimental study on the effect of ashing temperature on physicochemical properties of Zhundong coal ashes[J]. Journal of Engineering Thermophysics, 2014, 35(3): 609-613.
25	李文, 白进. 煤的灰化学[M]. 北京: 科学出版社, 2013: 46.
	Li W, Bai J. Chemistry of Ash from Coal[M]. Beijing: Science Press, 2013: 46.
26	Kieffer J, Angell C A. Structural incompatibilities and liquid–liquid phase separation in molten binary silicates: a computer simulation[J]. The Journal of Chemical Physics, 1989, 90(9): 4982-4991.
27	Belashchenko D K, Ostrovskii O I. Computer simulation of noncrystalline ionic-covalent oxides CaO-P₂O₅ [J]. Inorganic Materials, 2002, 38(2): 146-153.
28	Guillot B, Sator N. A computer simulation study of natural silicate melts (Ⅱ): High pressure properties[J]. Geochimica et Cosmochimica Acta, 2007, 71(18): 4538-4556.
29	Xuan W, Wang H, Yan S, et al. Exploration on the steam gasification mechanism of waste PE plastics based on ReaxFF-MD and DFT methods [J]. Fuel, 2022,315: 123121.
30	Zhang Z, Xie B, Zhou W, et al. Structural characterization of FeO-SiO₂-V₂O₃ slags using molecular dynamics simulations and FT-IR spectroscopy[J]. ISIJ International, 2016, 56(5): 828-834.
31	Zhang S F, Zhang X, Liu W, et al. Relationship between structure and viscosity of CaO-SiO₂-Al₂O₃-MgO-TiO₂ slag[J]. Journal of Non-Crystalline Solids, 2014, 402: 214-222.
32	Wu T, He S P, Liang Y J, et al. Molecular dynamics simulation of the structure and properties for the CaO-SiO₂ and CaO-Al₂O₃ systems[J]. Journal of Non-Crystalline Solids, 2015, 411: 145-151.
33	Xuan W W, Wang H N, Xia D H. Depolymerization mechanism of CaO on network structure of synthetic coal slags[J]. Fuel Processing Technology, 2019, 187: 21-27.
34	Grundy A N, Jung I H, Pelton A D, et al. A model to calculate the viscosity of silicate melts (Ⅱ): The NaO_0.5-MgO-CaO-AlO_1.5-SiO₂ system [J]. International Journal of Materials Research, 2008, 99(11): 1195-1209.
35	Kim W Y, Pelton A D, Decterov S A. A model to calculate the viscosity of silicate melts (Ⅲ): Modification for melts containing alkali oxides [J]. International Journal of Materials Research, 2012, 103(3): 313-328.
36	Cormier L, Neuville D R, Calas G. Structure and properties of low-silica calcium aluminosilicate glasses[J]. Journal of Non-Crystalline Solids, 2000, 274(1/2/3): 110-114.
37	Ganster P, Benoit M, Kob W, et al. Structural properties of a calcium aluminosilicate glass from molecular-dynamics simulations: a finite size effects study[J]. The Journal of Chemical Physics, 2004, 120(21): 10172-10181.
38	Xuan W W, Wang H N, Xia D H, et al. Quantitative study of Si structural units in coal slags and their influence on viscosity[J]. Energy & Fuels, 2019, 33(11): 10593-10601.
39	Wu T, Wang Q, Yu C F, et al. Structural and viscosity properties of CaO-SiO₂-Al₂O₃-FeO slags based on molecular dynamic simulation[J]. Journal of Non-Crystalline Solids, 2016, 450: 23-31.
40	Xuan W W, Wang H N, Xia D H. Deep structure analysis on coal slags with increasing silicon content and correlation with melt viscosity[J]. Fuel, 2019, 242: 362-367.
41	Chen Y, Pan W J, Jia B R, et al. Effects of the amphoteric behavior of Al₂O₃ on the structure and properties of CaO-SiO₂-Al₂O₃ melts by molecular dynamics[J]. Journal of Non-Crystalline Solids, 2021, 552: 120435.

样品	含量/%(质量)
样品	SiO₂	Al₂O₃	FeO	CaO	MgO	Na₂O	K₂O	M₂O/MO	T_liq/K
S1	48.00	30.00	5.00	15.00	2.00	0.00	0.00	0.00	1744.80
S2	48.00	30.00	4.09	12.27	1.64	4.00	0.00	0.22	1701.53
S3	48.00	30.00	3.18	9.55	1.27	8.00	0.00	0.57	1645.07
S4	48.00	30.00	2.27	6.82	1.19	12.00	0.00	1.20	1556.46
S5	48.00	30.00	4.09	12.27	1.64	0.00	4.00	0.22	1727.32
S6	48.00	30.00	3.18	9.55	1.27	0.00	8.00	0.57	1693.18
S7	48.00	30.00	2.27	6.82	0.91	0.00	12.00	1.20	1667.59
S8	48.00	30.00	2.27	6.82	0.91	6.00	6.00	1.20	1590.18

样品	含量/%(质量)
样品	SiO₂	Al₂O₃	FeO	CaO	MgO	Na₂O	K₂O	M₂O/MO	T_liq/K
S1	48.00	30.00	5.00	15.00	2.00	0.00	0.00	0.00	1744.80
S2	48.00	30.00	4.09	12.27	1.64	4.00	0.00	0.22	1701.53
S3	48.00	30.00	3.18	9.55	1.27	8.00	0.00	0.57	1645.07
S4	48.00	30.00	2.27	6.82	1.19	12.00	0.00	1.20	1556.46
S5	48.00	30.00	4.09	12.27	1.64	0.00	4.00	0.22	1727.32
S6	48.00	30.00	3.18	9.55	1.27	0.00	8.00	0.57	1693.18
S7	48.00	30.00	2.27	6.82	0.91	0.00	12.00	1.20	1667.59
S8	48.00	30.00	2.27	6.82	0.91	6.00	6.00	1.20	1590.18

原子个数									密度/(g/cm³)	盒子长度/Å
Si	Al	Fe	Ca	Mg	Na	K	O	总数	密度/(g/cm³)	盒子长度/Å
1722	1268	150	576	107	0	0	6179	10002	2.75	50.66
1702	1254	122	466	87	275	0	6098	10004	2.69	50.84
1683	1240	94	359	66	544	0	6017	10003	2.64	51.00
1665	1226	66	253	47	807	0	5939	10003	2.64	51.00
1727	1272	124	473	88	0	183	6139	10006	2.68	51.14
1732	1276	96	369	68	0	368	6095	10004	2.62	51.61
1736	1280	70	264	49	0	554	6052	10005	2.55	52.09
1700	1252	68	259	48	412	271	5995	10005	2.57	51.62

原子个数									密度/(g/cm³)	盒子长度/Å
Si	Al	Fe	Ca	Mg	Na	K	O	总数	密度/(g/cm³)	盒子长度/Å
1722	1268	150	576	107	0	0	6179	10002	2.75	50.66
1702	1254	122	466	87	275	0	6098	10004	2.69	50.84
1683	1240	94	359	66	544	0	6017	10003	2.64	51.00
1665	1226	66	253	47	807	0	5939	10003	2.64	51.00
1727	1272	124	473	88	0	183	6139	10006	2.68	51.14
1732	1276	96	369	68	0	368	6095	10004	2.62	51.61
1736	1280	70	264	49	0	554	6052	10005	2.55	52.09
1700	1252	68	259	48	412	271	5995	10005	2.57	51.62

原子对	电荷	A_ij /eV	ρ_ij /Å	C_ij /(eV•Å⁶)
Si—O	1.89	50307.43	0.161	46.3
Al—O	1.4175	28539.14	0.172	34.58
Fe—O	0.945	13033.26	0.19	0
Ca—O	0.945	155671.6	0.178	42.26
Mg—O	0.945	32653.47	0.178	27.28
Na—O	0.4725	120307.1	0.17	0
K—O	0.4725	2284.8	0.29	0
O—O	-0.945	9023.03	0.265	85.09