超低排放燃煤机组硒的迁移转化及飞灰对其富集特性

doi:10.11949/0438-1157.20210887

摘要/Abstract

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

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

中图分类号:

TQ 53

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.

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.

图/表 14

表1 所选燃煤机组容量、类型及取样类型

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

图1 燃煤电厂入炉煤及副产物中硒平均含量

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

表2 燃煤机组入炉煤工业分析

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

图2 飞灰和底渣与入炉煤中硒含量的比值

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

图3 飞灰和底渣中硒质量分布

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

图4 飞灰和底渣中硒相对富集系数

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

图5 不同粒径飞灰中硒含量

Fig.5 Se content in fly ash of different sizes

图6 不同粒径飞灰中未燃尽碳含量

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

图7 CFB4和PC1机组不同粒径飞灰吸附和脱附等温曲线

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

图8 CFB4机组和PC1机组飞灰SEM图

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

图9 不同粒径飞灰中硒吸附含量与其比表面积关系

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

图10 不同粒径飞灰中硒吸附含量与其孔容积关系

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

图11 CFB4机组和PC1机组不同粒径飞灰中硒吸附含量与其孔径关系

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

图12 CFB4机组和PC1机组不同粒径飞灰孔容积分布图

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

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