Difference of fly ash characteristics from PC and CFB boilers and its effect on mercury adsorption capability

doi:10.11949/j.issn.0438-1157.20180882

Abstract

Abstract:

The particle size distribution, surface structure property, unburned carbon content and mercury content of fly ash were investigated to understand the effect of boiler type and mercury adsorption capability on fly ash. Different samples were obtained from a circulating-fluidized bed (CFB) boiler and a pulverized coal (PC) boiler with the capacity of around 300 MW coal-fired power generation units. In this study, the mercury contents in fly ash collected from the CFB and PC boilers are 1584.0ng/g and 503.7ng/g, respectively. The results show that the mercury content in the fly ash from CFB boiler increases with decreasing particle size and reactivity temperature, but increasing surface area and unburned carbon content. For the fly ash from PC boiler, the portion with the diameter of 75—53 μm displays better mercury adsorption capability, the unburned carbon content is much lower than that from CFB boiler, and the surface area is almost independent to particle size. As a result, the adsorption capacity of the sample taken from the ash discharge port of the pulverized coal boiler dust removal equipment is much lower than that of the corresponding position of the circulating fluidized bed boiler.

Key words: coal-fired boiler, fly ash, mercury, adsorption, unburned carbon, particle size distribution, reactivity

摘要：

通过分析两台容量相近的循环流化床锅炉和煤粉锅炉飞灰样品的粒径分布、表面结构特性、未燃尽碳含量、反应性和汞含量，探究两种类型锅炉飞灰特性差异及其与飞灰汞吸附能力的关系。结果表明：循环流化床和煤粉锅炉尾端除尘设备排灰口飞灰汞的含量分别为1584.0 ng/g和503.7 ng/g，其原因与飞灰粒径、未燃尽碳含量和表面特性相关。对于循环流化床锅炉，飞灰中汞含量随其粒径和反应性温度的减小而增加，随未燃尽碳含量增加而增加，且与比表面积和吸附量呈正相关关系。对于煤粉锅炉，粒径为75～53 μm的飞灰对汞吸附能力较强，未燃尽碳含量明显小于循环流化床所产生飞灰的含量，飞灰比表面积随粒径变化不大，由此导致煤粉锅炉除尘设备排灰口所取样品对汞的吸附能力远低于循环流化床锅炉相对应位置飞灰对汞的吸附能力。

关键词: 燃煤锅炉, 飞灰, 汞, 吸附, 未燃尽碳, 粒度分布, 活性

CLC Number:

TQ 534.9

Xiaohang LI, Yun LIU, Yinjiao SU, Yang TENG, Yanjun GUAN, Kai ZHANG. Difference of fly ash characteristics from PC and CFB boilers and its effect on mercury adsorption capability[J]. CIESC Journal, 2019, 70(3): 1075-1082.

李晓航, 刘芸, 苏银皎, 滕阳, 关彦军, 张锴. 煤粉炉和循环流化床锅炉飞灰特性对其汞吸附能力的影响[J]. 化工学报, 2019, 70(3): 1075-1082.

Figures/Tables 10

Table 1 Ultimate and proximate analysis in together with Hg content in coal collected from two boilers

Source of coal	M_ad/%	A_ad/%	V_ad/%	FC_ad/%	C_ad/%	H_ad/%	O_ad/%	N_ad/%	S_ad/%	Hg_ad/(ng/g)
CFB boiler	2.82	43.04	11.96	41.82	44.27	2.33	4.60	0.80	2.14	221.40
PC boiler	1.27	30.32	11.89	56.52	58.47	2.80	4.54	1.01	1.59	236.40

Fig.1 Particle size distribution and mean particle diameter of raw fly ash collected from two boilers

Fig.2 SEM images of raw fly ash samples collected from two boilers

Fig.3 Adsorption and desorption isothermal of raw fly ash collected from two boilers

Fig.4 Surface area and UBC content in raw fly ash collected from two boilers

Fig.5 Hg content in raw fly ash samples and that in sieved fly ash samples collected from two boilers

Fig.6 Hg content and surface area in sieved fly ash samples collected from two beilers

Fig.7 Adsorption and desorption isothermal of sieved fly ash samples collected from two boilers

Fig.8 UBC content and Hg content in sieved fly ash samples collected from different boilers

Fig.9 Hg content and reactivity in sieved fly ash samples collected from two boilers

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