Effects of Xinjiang high calcium coal co-firing on melting characteristics of Ca-bearing minerals in ash

doi:10.11949/0438-1157.20200406

Abstract

Abstract:

In this study, a high-calcium coal, a high-silicon-aluminum Xinjiang coal and their blends were burnt in a drop tube furnace. The computer-controlled scanning electron microscope (CCSEM) was used to analyze the total ash mineral composition and particle size distribution after combustion. Based on CCSEM analysis, the composition data of single particle ash was obtained. The thermodynamic equilibrium method was used to calculate the liquid phase ratio of minerals in the ash, and the effect of coal blending on the melting characteristics of calcium-containing minerals in the ash was analyzed. The results show that the organically bound Ca easily interacts with other minerals in the coal. The mineral species of Ca-bearing minerals in the bulk ash mainly depend on the included minerals in coal. Co-firing will promote the conversion of calcium-containing aluminosilicate in the ash to calcium-containing complex aluminosilicate, and at the same time promote the melting of calcium-containing minerals. Under low temperature conditions, the particle size distribution of molten calcium-containing minerals in co-fired coal ash is affected by the particle size distribution of the alkali metal; however, under high temperature conditions, co-firing promotes the migration of molten calcium-containing minerals to large particle size ash.

Key words: coal combustion, reaction, slagging, mixing, CCSEM, melting characteristics

摘要：

选用一种高钙和一种高硅铝新疆煤，在沉降炉中进行不同比例的混煤和单煤燃烧实验。采用计算机控制扫描电镜（CCSEM）分别对燃烧后总灰矿物成分和粒径分布进行分析。基于CCSEM分析获取单颗粒灰成分数据，采用热力学平衡方法对灰中矿物液相比例进行计算，分析混煤燃烧对灰中含钙矿物熔融特性影响。结果表明，煤中有机结合态Ca极易与煤中其他矿物元素发生交互反应，交互反应后含钙矿物种类取决于煤中内在矿种类。混煤燃烧会促进灰中含钙硅铝酸盐向含钙复杂硅铝酸盐转化，同时促进含钙矿物的熔融。在低温条件下，混烧煤灰中熔融含钙矿物粒径分布受碱金属粒径分布影响；但是高温条件下，混烧促进熔融含钙矿物向大粒径煤灰迁移。

关键词: 煤燃烧, 反应, 结渣, 混合, CCSEM, 熔融特性

CLC Number:

TK 224

Sheng CHEN, Dunxi YU, Jianqun WU, Yimin XIA, Yueming WANG, Minghou XU. Effects of Xinjiang high calcium coal co-firing on melting characteristics of Ca-bearing minerals in ash[J]. CIESC Journal, 2020, 71(9): 4260-4269.

陈胜, 于敦喜, 吴建群, 夏祎旻, 王越明, 徐明厚. 新疆高钙煤混烧对灰中含钙矿物熔融特性影响[J]. 化工学报, 2020, 71(9): 4260-4269.

Figures/Tables 9

Table 1 Fuel properties

煤种	工业分析/%(mass,ad)				元素分析/%(mass,ad)
煤种	M	VM	A	FC	C	H	S	N	O（差值）
YK煤	3.6	30.04	36.93	29.43	39.85	3.66	0.25	0.54	15.16
EK煤	5.93	33.61	10.03	50.43	59.06	4.34	0.42	0.69	19.53
灰成分分析/%(mass)
煤种	Na₂O	MgO	Al₂O₃	SiO₂	P₂O₅	SO₃	K₂O	CaO	Fe₂O₃
YK煤	1.41	1.67	26.54	58.30	0.33	1.43	2.18	4.26	3.88
EK煤	6.24	8.26	17.45	28.00	0.78	7.87	1.03	21.64	8.73

Table 2 Distribution of Ca-bearing minerals in raw coal

煤种	含量/%（mass）
煤种	钙铝硅酸盐	碳酸钙	钙硅酸盐	有机结合钙
YK煤	22.91	2.72	2.14	72.23
EK煤	3.70	7.22	0.22	88.85

Fig.1 Distribution of CaO in Ca-bearing mineral

Fig.2 Ternary phase diagram of SiO2-Al2O3-CaO in calcium-containing aluminosilicate

Fig.3 Ternary phase diagram of SiO2+Al2O3-MgO+Fe2O3+Na2O+K2O-CaO in calcium-containing complex aluminosilicate

Fig.4 Melting point of bulk ash

Fig.5 Liquid phase ratio of CaO in bulk ash

Fig.6 Distribution of CaO in liquid phase in fly ash with different particle sizes at different temperatures

Fig.7 Distribution of alkali metals in calcium-containing minerals with different particle sizes

References 30

1	裘品姬. 丝绸之路经济带背景下新疆煤炭行业发展研究[J]. 煤炭经济研究, 2015, (7): 18-23.
	Qiu P J. Study on development of Xinjiang coal industry under background of silk road economic belt[J]. Coal Economic Research, 2015, (7): 18-23.
2	Xu J Y, Yu D X, Fan B, et al. Characterization of ash particles from co-combustion with a Zhundong coal for understanding ash deposition behavior[J]. Energy & Fuels, 2014, 28(1): 678-684.
3	潘世汉, 陈勤根, 陈晓勇. 准东高碱煤特性分析及防止锅炉结渣的对策措施[J]. 能源工程, 2016, 180(1): 71-76.
	Pan S H, Chen Q G, Chen X Y. Characteristic analysis of higher-sodium coal of the eastern Jungar and countermeasures for preventing boiler slagging[J]. Energy Engineering, 2016, 180(1): 71-76.
4	Dai B Q, Wu X J, de Girolamo A, et al. Inhibition of lignite ash slagging and fouling upon the use of a silica-based additive in an industrial pulverised coal-fired boiler (Part 1): Changes on the properties of ash deposits along the furnace[J]. Fuel, 2015, 139: 720-732.
5	Li J B, Zhu M M, Zhang Z Z, et al. The mineralogy, morphology and sintering characteristics of ash deposits on a probe at different temperatures during combustion of blends of Zhundong lignite and a bituminous coal in a drop tube furnace[J]. Fuel Processing Technology, 2016, 149: 176-186.
6	Lu Y, Wang Y, Xu Y, et al. Investigation of ash fusion characteristics and migration of sodium during co-combustion of Zhundong coal and oil shale[J]. Applied Thermal Engineering, 2017, 121: 224-233.
7	Zhou H, Ma W. An experimental study on the effects of adding biomass ashes on ash sintering behavior of Zhundong coal[J]. Applied Thermal Engineering, 2017, 126: 689-701.
8	Zeng X P, Yu D X, Liu F Q, et al. Scavenging of refractory elements (Ca, Mg, Fe) by kaolin during low rank coal combustion[J]. Fuel, 2018, 223: 198-210.
9	Wang X B, Xu Z X, Wei B, et al. The ash deposition mechanism in boilers burning Zhundong coal with high contents of sodium and calcium: a study from ash evaporating to condensing[J]. Applied Thermal Engineering, 2015, 80: 150-159.
10	崔育奎, 张翔, 乌晓江. 配煤对新疆准东高碱煤沾污结渣特性的影响[J]. 动力工程学报, 2015, 35(5): 361-365.
	Cui Y K, Zhang X, Wu X J. The effect of coal blending ration on slagging/fouling characteristics of Zhundong Xinjiang high-alkali coal[J]. Journal of Chinese Society of Power Engineering, 2015, 35(5): 361-365.
11	雷煜, 于鹏峰, 喻鑫, 等. 新疆高碱煤混烧含Ca、Fe矿物分布特性的CCSEM研究[J]. 动力工程学报, 2017, 37(12): 956-962.
	Lei Y, Yu P F, Yu X, et al. CCSEM investigation on distribution characteristics of Ca and Fe containing minerals during blend combustion of Xinjiang high-alkali coal[J]. Journal of Chinese Society of Power Engineering, 2017, 37(12): 956-962.
12	Qiu J R, Li F, Zheng Y, et al. The influences of mineral behaviour on blended coal ash fusion characteristics[J]. Fuel, 1999, 78(8): 963-969.
13	Baxter L L. Ash deposit formation and deposit properties. A comprehensive summary of research conducted at Sandia’s combustion research facility[R]. New Mexico: Sandia National Laboratories, 2000.
14	Rushdi A, Gupta R, Sharma A. Mechanistic prediction of ash deposition in a pilot-scale test facility[J]. Fuel, 2005, 84(10): 1246-1258.
15	Wu J Q, Yu D X, Liu F Q, et al. Impact of oxy-fuel combustion on ash properties and sintering strength development[J]. Energy & Fuels, 2018, 32(4): 4315-4322.
16	Fan B, Yu D X, Zeng X P, et al. Occurrence of calcium and magnesium in the ash from Zhundong coal combustion: emphasis on their close juxtaposition[J]. Energy & Fuels, 2019, 33(3): 2556-2564.
17	Wu J Q, Yu D X, Zeng X P, et al. Ash formation and fouling during combustion of rice husk and its blends with a high alkali Xinjiang coal[J]. Energy & Fuels, 2018, 32(1): 416-424.
18	吴乐, 吴建群, 于敦喜, 等. O₂/CO₂燃烧对神华煤Ca和Fe交互反应影响[J]. 化工学报, 2015, 66(2): 753-758.
	Wu L, Wu J Q, Yu D X, et al. Influence of O₂/CO₂ combustion on interaction of Ca and Fe in Shenhua coal[J]. CIESC Journal, 2015, 66(2): 753-758.
19	刘芳琪, 于敦喜, 吴建群, 等. 燃煤锅炉SCR对颗粒物排放特性影响[J]. 化工学报, 2018, 69(9): 4051-4057.
	Liu F Q, Yu D X, Wu J Q, et al. Effect of SCR on particulate matter emissions from a coal-fired boiler[J]. CIESC Journal, 2018, 69(9): 4051-4057.
20	Huggins F, Kosmack D A, Huffman G, et al. Coal mineralogies by SEM automatic image analysis[J]. Scanning Electron Microscopy, 1980, I: 531-540.
21	Srinivasachar S, Helble J J, Boni A A. Mineral behavior during coal combustion (1): Pyrite transformations[J]. Progress in Energy & Combustion Science, 1990, 16(4): 281-292.
22	吴乐, 吴建群, 罗嘉, 等. 煤样不同密度组分中致渣矿物特性的CCSEM研究[J]. 化工学报, 2014, 65(8): 3221-3227.
	Wu L, Wu J Q, Luo J, et al. CCSEM investigation on slagging minerals in different density ingredients of bituminous coal samples[J]. CIESC Journal, 2014, 65(8): 3221-3227.
23	温昶. 燃煤矿物质成灰行为的CCSEM分析与PM₁₀生成特性的研究[D]. 武汉: 华中科技大学, 2013.
	Wen C. CCSEM study on mineral evolution and formation behavior of ash including PM₁₀ during coal combustion[D]. Wuhan: Huazhong University of Science & Technology, 2013.
24	Wu J Q, Wang Y M, Han J K, et al. Ash formation and deposition in oxy-fuel combustion of rice husk, coal, and their blend with 70% inlet O₂[J]. Energy & Fuels, 2020, 34(1): 890-899.
25	Raask E. Mineral Impurities in Coal Combustion, Behavior, Problems, and Remedial Measures[M]. Washington: Hemisphere Publication Corporation, 1985.
26	Bryers R W. Fireside slagging, fouling, and high-temperature corrosion of heat-transfer surface due to impurities in steam-raising fuels[J]. Progress in Energy and Combustion Science, 1996, 22(1): 29-120.
27	Dai B Q, Wu X J, De Girolamo A, et al. Inhibition of lignite ash slagging and fouling upon the use of a silica-based additive in an industrial pulverised coal-fired boiler (Part 2): Speciation of iron in ash deposits and separation of magnetite and ferrite[J]. Fuel, 2015, 139: 733-745.
28	Akiyama K, Pak H, Ueki Y, et al. Effect of MgO addition to upgraded brown coal on ash-deposition behavior during combustion[J]. Fuel, 2011, 90(11): 3230-3236.
29	Degereji M U, Ingham D B, Ma L, et al. Prediction of ash slagging propensity in a pulverized coal combustion furnace[J]. Fuel, 2012, 101: 171-178.
30	岑可法, 樊建人, 池作和, 等. 锅炉和热交换器的积灰, 结渣, 磨损和腐蚀的防止原理与计算[M]. 北京: 科学出版社, 1994.
	Cen K F, Fan J R, Chi Z H, et al. Mechanism and Calculation of Fouling, Slagging, Abrasion and Erosion in Furnace and Heat Exchanger[M]. Beijing: Science Press, 1994.

[1]	Cheng CHENG, Zhongdi DUAN, Haoran SUN, Haitao HU, Hongxiang XUE. Lattice Boltzmann simulation of surface microstructure effect on crystallization fouling [J]. CIESC Journal, 2023, 74(S1): 74-86.
[2]	Jie CHEN, Yongsheng LIN, Kai XIAO, Chen YANG, Ting QIU. Study on catalytic synthesis of sec-butanol by tunable choline-based basic ionic liquids [J]. CIESC Journal, 2023, 74(9): 3716-3730.
[3]	Erqi WANG, Shuzhou PENG, Zhen YANG, Yuanyuan DUAN. Evaluation of vapor-liquid equilibrium models for mixtures containing HFOs [J]. CIESC Journal, 2023, 74(8): 3216-3225.
[4]	Linzheng WANG, Yubing LU, Ruizhi ZHANG, Yonghao LUO. Analysis on thermal oxidation characteristics of VOCs based on molecular dynamics simulation [J]. CIESC Journal, 2023, 74(8): 3242-3255.
[5]	Mengmeng ZHANG, Dong YAN, Yongfeng SHEN, Wencui LI. Effect of electrolyte types on the storage behaviors of anions and cations for dual-ion batteries [J]. CIESC Journal, 2023, 74(7): 3116-3126.
[6]	Kexin HUANG, Tong LI, Anqi LI, Mei LIN. Mode decomposition of flow field in T-junction with rotating impeller [J]. CIESC Journal, 2023, 74(7): 2848-2857.
[7]	Ji CHEN, Ze HONG, Zhao LEI, Qiang LING, Zhigang ZHAO, Chenhui PENG, Ping CUI. Study on coke dissolution loss reaction and its mechanism based on molecular dynamics simulations [J]. CIESC Journal, 2023, 74(7): 2935-2946.
[8]	Xiaokun HE, Rui LIU, Yuan XUE, Ran ZUO. Review of gas phase and surface reactions in AlN MOCVD [J]. CIESC Journal, 2023, 74(7): 2800-2813.
[9]	Tan ZHANG, Guang LIU, Jinping LI, Yuhan SUN. Performance regulation strategies of Ru-based nitrogen reduction electrocatalysts [J]. CIESC Journal, 2023, 74(6): 2264-2280.
[10]	Xiaowen ZHOU, Jie DU, Zhanguo ZHANG, Guangwen XU. Study on the methane-pulsing reduction characteristics of Fe₂O₃-Al₂O₃ oxygen carrier [J]. CIESC Journal, 2023, 74(6): 2611-2623.
[11]	Feng ZHU, Kailin CHEN, Xiaofeng HUANG, Yinzhu BAO, Wenbin LI, Jiaxin LIU, Weiqiang WU, Wangwei GAO. Performance study of KOH modified carbide slag for removal of carbonyl sulfide [J]. CIESC Journal, 2023, 74(6): 2668-2679.
[12]	Quanbi ZHANG, Yijin YANG, Xujing GUO. Catalytic degradation of dissolved organic matter in rifampicin pharmaceutical wastewater by Fenton oxidation process [J]. CIESC Journal, 2023, 74(5): 2217-2227.
[13]	Chenxi LI, Yongfeng LIU, Lu ZHANG, Haifeng LIU, Jin’ou SONG, Xu HE. Quantum chemical analysis of n-heptane combustion mechanism under O₂/CO₂ atmosphere [J]. CIESC Journal, 2023, 74(5): 2157-2169.
[14]	Qianqian WANG, Mingyan LIU, Yongli MA. Study on the effect of ultrasonic degassing in water [J]. CIESC Journal, 2023, 74(4): 1693-1702.
[15]	Simin YI, Yali MA, Weiqiang LIU, Jinshuai ZHANG, Yan YUE, Qiang ZHENG, Songyan JIA, Xue LI. Study on ammonia evaporation and hydration kinetics of microcrystalline magnesite [J]. CIESC Journal, 2023, 74(4): 1578-1586.