Selenium transformation in ultra-low-emission coal-fired power units and its enrichment characteristics in fly ash

doi:10.11949/0438-1157.20210887

Abstract

Abstract:

Microwave digestion and hydride generation-atomic fluorescence spectrometry were used to investigate the migration and transformation of selenium (Se) in nine ultra-low emission units in service. The characteristics of fly ash from circulating fluidized bed (CFB) and pulverized coal (PC) units are compared for understanding the Se adsorption ability in fly ash. After combustion, Se in coal is essentially volatilized in gas but only a small amount is remained in bottom slag. Compared to concentration normalization method and mass distribution method, relative enrichment factor method is more suitable to evaluate the Se enrichment ability for feed coal and combustion by-products, which indicates that Se is enriched in fly ash from both CFB and PC units. Low combustion temperature and CaO additive in CFB boiler can not only reduce Se release ratio from coal but also enhance the Se adsorption ability in fly ash. As a result, Se enrichment in bottom slag and fly ash from CFB is more than that from PC, while Se in gypsum from CFB unit is less than that of PC. Moreover, Se adsorption content is heavily depended on the physical properties of fly ash. The amount of selenium adsorbed by fly ash increases with the increase of specific surface area or pore volume, but decreases with the increase of particle size or pore size. The fly ash from CFB unit has high unburned carbon content, irregular shape, rough surface and more honeycomb pores, which makes Se enriched in fly ash from CFB more than that of PC.

Key words: coal combustion, pollution, selenium migration and transformation, microwave digestion, adsorption

摘要：

采用微波消解法和氢化物发生-原子荧光光谱法考察了9台超低排放在役机组硒迁移转化规律，探究了循环流化床（CFB）和煤粉炉（PC）机组飞灰特性差异对硒吸附能力的影响。燃烧后煤中硒几乎全部呈现挥发态，底渣中残留量极低。与浓度归一化和质量分布法相比较，相对富集系数法可以客观地评价燃煤副产物中硒的富集能力，两类机组中硒均主要富集于飞灰中。CFB较低炉膛温度和添加CaO可以降低入炉煤中硒释放比例并增强飞灰对硒的吸附能力，故其底渣和飞灰中硒的富集程度均高于PC，导致脱硫石膏中硒富集程度低于PC。飞灰对硒的吸附量随比表面积或孔容积增大而增大，但随粒径或孔径增大而减小。CFB飞灰中未燃尽碳含量高、形状不规则、表面粗糙且存在较多蜂窝状孔隙，导致其对硒的富集程度高于PC飞灰。

关键词: 煤燃烧, 污染, 硒迁移转化, 微波消解, 吸附

CLC Number:

TQ 53

Xuan LIU, Yinjiao SU, Yang TENG, Kai ZHANG, Pengcheng WANG, Lifeng LI, Zhen LI. Selenium transformation in ultra-low-emission coal-fired power units and its enrichment characteristics in fly ash[J]. CIESC Journal, 2022, 73(2): 923-932.

刘轩, 苏银皎, 滕阳, 张锴, 王鹏程, 李丽锋, 李圳. 超低排放燃煤机组硒的迁移转化及飞灰对其富集特性[J]. 化工学报, 2022, 73(2): 923-932.

Figures/Tables 14

Table 1 Unit capacity， boiler type and samples of coal-fired power units in this study

机组编号	机组容量	烟气尾端污染物控制设备	取样点
CFB1	135 MW	SNCR+FF+WFGD	入炉煤+底渣+飞灰
CFB2	200 MW	SCR+FF+WFGD	入炉煤+底渣+飞灰+脱硫石膏
CFB3	300 MW	SNCR/SCR+FF+WFGD	入炉煤+底渣+飞灰+脱硫石膏
CFB4	300 MW	SNCR+FF+WFGD	入炉煤+底渣+飞灰+脱硫石膏
PC1	300 MW	SCR+ESP+WFGD	入炉煤+底渣+飞灰+脱硫石膏
PC2	330 MW	SCR+ESP+WFGD+WESP	入炉煤+底渣+飞灰+脱硫石膏
PC3	350 MW	SCR+ESP+WFGD+WESP	入炉煤+底渣+飞灰+脱硫石膏
PC4	600 MW	SCR+ESP+WFGD+WESP	入炉煤+底渣+飞灰+脱硫石膏
PC5	600 MW	SNCR/SCR+FF/ESP+WFGD+WESP	入炉煤+底渣+飞灰+脱硫石膏

Fig.1 Mean Se content in feed coal and by-products of coal fired power units

Table 2 Proximate analysis of feed coals from coal-fired power units

燃煤机组	入炉煤工业分析/%(质量,空气干燥基)
燃煤机组	水分	灰分	挥发分	固定碳
CFB1	2.23	41.50	29.72	26.55
CFB2	1.24	61.20	18.62	18.94
CFB3	2.36	33.96	24.94	38.74
CFB4	2.38	39.76	24.74	33.12
PC1	0.90	41.67	12.26	45.17
PC2	1.25	29.32	10.67	58.76
PC3	2.67	15.05	29.95	52.33
PC4	3.98	16.42	25.57	54.03
PC5	2.83	29.67	27.32	40.18

Fig.2 The Se content ratio of fly ash to feed coal and bottom slag to feed coal

Fig.3 Mass distributions of Se in fly ash and bottom slag

Fig.4 REF of Se in fly ash and bottom slag

Fig.5 Se content in fly ash of different sizes

Fig.6 Unburned carbon content in fly ash of different sizes

Fig.7 Adsorption and desorption isothermal curves of fly ash with different sizes from CFB4 and PC1 units

Fig.8 SEM images of fly ash samples from CFB4 and PC1 units

Fig.9 Adsorbed Se content and surface area of fly ash with different sizes from CFB4 and PC1 units

Fig.10 Adsorbed Se content and pore volume of fly ash with different sizes from CFB4 and PC1 units

Fig.11 Adsorbed Se content and pore diameter of fly ash with different sizes from CFB4 and PC1 units

Fig.12 Pore volume distribution of fly ash with different sizes from CFB4 and PC1 units

References 33

1	Rayman M P. Selenium and human health[J]. The Lancet, 2012, 379(9822): 1256-1268.
2	张敏明, 袁林喜, 尹雪斌, 等. 人体发硒水平影响因素研究进展[J]. 生物技术进展, 2017, 7(3): 187-192.
	Zhang M M, Yuan L X, Yin X B, et al. Review on influence factors of selenium levels in human hair[J]. Current Biotechnology, 2017, 7(3): 187-192.
3	Song G C, Xu W T, Liu K, et al. Transformation of selenium during coal thermal conversion: effects of atmosphere and inorganic content[J]. Fuel Processing Technology, 2020, 205: 106446.
4	周新越, 吴洋文, 密腾阁, 等. 燃煤烟气重金属与铈改性CaO的相互作用机理研究[J]. 燃料化学学报, 2020, 48(12): 1520-1529.
	Zhou X Y, Wu Y W, Mi T G, et al. Interaction mechanism between heavy metals and Ce-doped CaO in flue gas of coal combustion[J]. Journal of Fuel Chemistry and Technology, 2020, 48(12): 1520-1529.
5	苏银皎, 刘轩, 李丽锋, 等. 三类煤阶煤中汞的赋存形态分布特征[J]. 化工学报, 2019, 70(4): 1559-1566.
	Su Y J, Liu X, Li L F, et al. Distribution characteristics of mercury speciation in coals with three different ranks[J]. CIESC Journal, 2019, 70(4): 1559-1566.
6	吴舜泽, 孙宁, 卢然, 等. 重金属污染综合防治实施进展与经验分析[J]. 中国环境管理, 2015, 7(1): 21-28.
	Wu S Z, Sun N, Lu R, et al. The progress and empirical analysis on the implementation of comprehensive prevention and control of heavy metal pollution[J]. Chinese Journal of Environmental Management, 2015, 7(1): 21-28.
7	Wang J, Nakazato T, Sakanishi K, et al. Microwave digestion with HNO₃/H₂O₂ mixture at high temperatures for determination of trace elements in coal by ICP-OES and ICP-MS[J]. Analytica Chimica Acta, 2004, 514(1): 115-124.
8	Iwashita A, Nakajima T, Takanashi H, et al. Effect of pretreatment conditions on the determination of major and trace elements in coal fly ash using ICP-AES[J]. Fuel, 2006, 85(2): 257-263.
9	Gómez-Ariza J L, Sánchez-Rodas D, Giráldez I, et al. A comparison between ICP-MS and AFS detection for arsenic speciation in environmental samples[J]. Talanta, 2000, 51(2): 257-268.
10	施正伦, 骆仲泱, 周劲松, 等. 石煤流化床燃烧重金属排放特性试验研究[J]. 煤炭学报, 2001, 26(2): 209-212.
	Shi Z L, Luo Z Y, Zhou J S, et al. Experimental research on heavy metals emission from fluidized bed with stone coal fired[J]. Journal of China Coal Society, 2001, 26(2): 209-212.
11	Zheng C H, Wang L, Zhang Y X, et al. Partitioning of hazardous trace elements among air pollution control devices in ultra-low-emission coal-fired power plants[J]. Energy & Fuels, 2017, 31(6): 6334-6344.
12	赵志锋, 杜谦, 董鹤鸣, 等[J]. 湿法脱硫装置对燃煤锅炉PM2.5排放特征的影响[J]. 化工学报, 2017, 68(11): 4261-4271.
	Zhao Z F, Du Q, Dong H M, et al. Influence of wet flue gas desulfurization devices on PM_2.5 emission characteristics of coal-fired boilers[J]. CIESC Journal, 2017, 68(11): 4261-4271.
13	徐文东, 曾荣树, 叶大年, 等. 电厂煤燃烧后元素硒的分布及对环境的贡献[J]. 环境科学, 2005, 26(2): 64-68.
	Xu W D, Zeng R S, Ye D N, et al. Distributions and environmental impacts of selenium in wastes of coal from a power plant[J]. Environmental Science, 2005, 26(2): 64-68.
14	López-Antón M A, Díaz-Somoano M, Spears D A, et al. Arsenic and selenium capture by fly ashes at low temperature[J]. Environmental Science & Technology, 2006, 40(12): 3947-3951.
15	Fu B, Liu G J, Sun M, et al. Emission and transformation behavior of minerals and hazardous trace elements (HTEs) during coal combustion in a circulating fluidized bed boiler[J]. Environmental Pollution, 2018, 242: 1950-1960.
16	陈冠益, 王钦, 颜蓓蓓. 煤中痕量元素在循环流化床锅炉中的迁移行为与富集特性[J]. 燃料化学学报, 2013, 41(9): 1050-1055.
	Chen G Y, Wang Q, Yan B B. Mobility and enrichment of trace elements in a coal-fired circulating fluidized bed boiler[J]. Journal of Fuel Chemistry and Technology, 2013, 41(9): 1050-1055.
17	Seames W S, Wendt J O L. Regimes of association of arsenic and selenium during pulverized coal combustion[J]. Proceedings of the Combustion Institute, 2007, 31(2): 2839-2846.
18	王珲, 宋蔷, 姚强, 等. ICP-OES/ICP-MS测定煤中多种元素的微波消解方法研究[J]. 光谱学与光谱分析, 2012, 32(6): 1662-1665.
	Wang H, Song Q, Yao Q, et al. Study on microwave digestion of coal for the determination of multi-element by ICP-OES and ICP-MS[J]. Spectroscopy and Spectral Analysis, 2012, 32(6): 1662-1665.
19	张锴, 刘轩, 苏银皎, 等. 一种测定燃煤电厂煤及其燃烧副产物中砷、硒、铅的方法: 110487758B[P]. 2021-05-14.
	Zhang K, Liu X, Su Y J, et al. Method for determining arsenic, selenium and lead in coal-fired power plant coals and combustion byproducts thereof: 110487758B[P]. 2021-05-14.
20	Contreras M L, García-Frutos F J, Bahillo A. Oxy-fuel combustion effects on trace metals behaviour by equilibrium calculations[J]. Fuel, 2013, 108: 474-483.
21	韩军, 梁洋硕, 赵波, 等. 混煤燃烧过程中砷/硒与飞灰中矿物质之间的高温原位反应[J]. 燃料化学学报, 2020, 48(11): 1356-1364.
	Han J, Liang Y S, Zhao B, et al. In-situ reaction between arsenic/selenium and minerals in fly ash at high temperature during blended coal combustion[J]. Journal of Fuel Chemistry and Technology, 2020, 48(11): 1356-1364.
22	Querol X, Fernández-Turiel J L, López -Soler A. Trace elements in coal and their behaviour during combustion in a large power station[J]. Fuel, 1995, 74(3): 331-343.
23	Ma T T, Huang Y D, Deng S, et al. The relationship between selenium retention and fine particles removal during coal combustion[J]. Fuel, 2020, 265: 116859.
24	Shen F H, Liu J, Zhang Z, et al. Temporal measurements and kinetics of selenium release during coal combustion and gasification in a fluidized bed[J]. Journal of Hazardous Materials, 2016, 310: 40-47.
25	邢佳颖, 王春波, 张月, 等. Se和SeO₂在O₂/CaO(001)表面吸附反应的第一性原理研究[J]. 燃料化学学报, 2019, 47(8): 993-999.
	Xing J Y, Wang C B, Zhang Y, et al. First-principles study of the adsorption and reaction of Se and SeO₂ on O₂/CaO(001) surface[J]. Journal of Fuel Chemistry and Technology, 2019, 47(8): 993-999.
26	Liu Z, Han J, Zhao L, et al. Effects of Se and SeO₂ on the denitrification performance of V₂O₅-WO₃/TiO₂ SCR catalyst[J]. Applied Catalysis A: General, 2019, 587: 117263.
27	Shin Y, Lee D W, Choi K Y, et al. VSb(SeO₃)₄, first selenite containing V³⁺ cation: synthesis, structure, characterization, magnetic properties, and calculations[J]. Inorganic Chemistry, 2013, 52(24): 14224-14230.
28	Wang L, Zheng C H, Zhang Y X, et al. Speciation characteristics and mobility of trace elements across ultralow emission air pollution control devices[J]. Energy & Fuels, 2017, 31(12): 13963-13971.
29	刘福国. 煤粉炉燃烧效率工程预测模型[J]. 动力工程, 2004, 24(5): 636-639.
	Liu F G. Engineering forecasting model of combustion efficiency for pulverized fired boiler[J]. Journal of Chinese Society of Power Engineering, 2004, 24(5): 636-639.
30	刘建忠, 张光学, 周俊虎, 等. 燃煤细灰的形成及微观形态特征[J]. 化工学报, 2006, 57(12): 2976-2980.
	Liu J Z, Zhang G X, Zhou J H, et al. Formation and micromorphology characteristics of fine particles generated during coal combustion[J]. Journal of Chemical Industry and Engineering (China), 2006, 57(12): 2976-2980.
31	徐飞, 骆仲泱, 王鹏, 等. 不同工况和粒径下飞灰孔隙结构的实验研究[J]. 动力工程, 2007, 27(4): 620-624.
	Xu F, Luo Z Y, Wang P, et al. Experimental study on the porous structure of variously sized fly ash particles under different combustion conditions[J]. Journal of Chinese society of Power Engineering, 2007, 27(4): 620-624.
32	Barrett E P, Joyner L G, Halenda P P. The determination of pore volume and area distributions in porous substances(I): Computations from nitrogen isotherms[J]. Journal of the American Chemical Society, 1951, 73(1): 373-380.
33	Sing K S W. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)[J]. Pure and Applied Chemistry, 1985, 57(4): 603-619.

[1]	Baiyu YANG, Yue KOU, Juntao JIANG, Yali ZHAN, Qinghong WANG, Chunmao CHEN. Chemical conversion of dissolved organic matter in petrochemical spent caustic along a wet air oxidation pretreatment process [J]. CIESC Journal, 2023, 74(9): 3912-3920.
[2]	Bingchun SHENG, Jianguo YU, Sen LIN. Study on lithium resource separation from underground brine with high concentration of sodium by aluminum-based lithium adsorbent [J]. CIESC Journal, 2023, 74(8): 3375-3385.
[3]	Ruihang ZHANG, Pan CAO, Feng YANG, Kun LI, Peng XIAO, Chun DENG, Bei LIU, Changyu SUN, Guangjin CHEN. Analysis of key parameters affecting product purity of natural gas ethane recovery process via ZIF-8 nanofluid [J]. CIESC Journal, 2023, 74(8): 3386-3393.
[4]	Yan GAO, Peng WU, Chao SHANG, Zejun HU, Xiaodong CHEN. Preparation of magnetic agarose microspheres based on a two-fluid nozzle and their protein adsorption properties [J]. CIESC Journal, 2023, 74(8): 3457-3471.
[5]	Longyi LYU, Wenbo JI, Muda HAN, Weiguang LI, Wenfang GAO, Xiaoyang LIU, Li SUN, Pengfei WANG, Zhijun REN, Guangming ZHANG. Enhanced anaerobic removal of halogenated organic pollutants by iron-based conductive materials: research progress and future perspectives [J]. CIESC Journal, 2023, 74(8): 3193-3202.
[6]	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.
[7]	Jie WANG, Xiaolin QIU, Ye ZHAO, Xinyang LIU, Zhongqiang HAN, Yong XU, Wenhan JIANG. Preparation and properties of polyelectrolyte electrostatic deposition modified PHBV antioxidant films [J]. CIESC Journal, 2023, 74(7): 3068-3078.
[8]	Shaoyun CHEN, Dong XU, Long CHEN, Yu ZHANG, Yuanfang ZHANG, Qingliang YOU, Chenglong HU, Jian CHEN. Preparation and adsorption properties of monolayer polyaniline microsphere arrays [J]. CIESC Journal, 2023, 74(5): 2228-2238.
[9]	Caihong LIN, Li WANG, Yu WU, Peng LIU, Jiangfeng YANG, Jinping LI. Effect of alkali cations in zeolites on adsorption and separation of CO₂/N₂O [J]. CIESC Journal, 2023, 74(5): 2013-2021.
[10]	Chenxin LI, Yanqiu PAN, Liu HE, Yabin NIU, Lu YU. Carbon membrane model based on carbon microcrystal structure and its gas separation simulation [J]. CIESC Journal, 2023, 74(5): 2057-2066.
[11]	Ruiheng WANG, Pinjing HE, Fan LYU, Hua ZHANG. Parameter comparison and optimization of three solid-liquid separation methods for washed air pollution control residues from municipal solid waste incinerators [J]. CIESC Journal, 2023, 74(4): 1712-1723.
[12]	Xiangning HU, Yuanbo YIN, Chen YUAN, Yun SHI, Cuiwei LIU, Qihui HU, Wen YANG, Yuxing LI. Experimental study on visualization of refined oil migration in soil [J]. CIESC Journal, 2023, 74(4): 1827-1835.
[13]	Yin XU, Jie CAI, Lu CHEN, Yu PENG, Fuzhen LIU, Hui ZHANG. Advances in heterogeneous visible light photocatalysis coupled with persulfate activation for water pollution control [J]. CIESC Journal, 2023, 74(3): 995-1009.
[14]	Xuanjun WU, Chao WANG, Zijian CAO, Weiquan CAI. Deep learning model of fixed bed adsorption breakthrough curve hybrid-driven by data and physical information [J]. CIESC Journal, 2023, 74(3): 1145-1160.
[15]	Yu PAN, Zihang WANG, Jiayun WANG, Ruzhu WANG, Hua ZHANG. Heat and moisture performance study of Cur-LiCl coated heat exchanger [J]. CIESC Journal, 2023, 74(3): 1352-1359.