Migration characteristics of heavy metals during co-combustion of dehydrated sludge with straw
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摘要: 在一台实验室规模的内循环流化床中，研究了700−850 ℃下脱水污泥与玉米秸秆的掺烧反应。目的是研究不同温度、污泥掺混比、二次风比率对掺烧后NO排放以及各种重金属在底灰、飞灰、烟气中迁移规律。结果表明，在实验工况下，随着温度升高，NO排放上升，底灰中V、Cr、As、Sb、Hg含量先增大后减小，Zn、Cu、Se、Cd与之相反，且大部分重金属的转折点在800 ℃；随着污泥掺混比的增加，NO排放先减少后增加，底灰中Cu、Hg、Tl含量均先增加后减小，Cr与之相反，且转折点均在污泥掺混比为10%时；随着二次风比率的增加，NO排放降低，底灰中重金属Zn、Cu、Se、Hg含量减少，As、Cd与之相反。Abstract: Sludge incineration technology has significant advantages such as capacity reduction and energy utilization, but it will cause heavy metal pollution. Therefore, the co-combustion of dewatered sludge with corn straw at 700−850 ℃ was studied in a laboratory scale internal circulating fluidized bed. The effects of different temperature, sludge mixing ratio and secondary air ratio on the NO emission and the migration of different heavy metals in bottom ash, fly ash and flue gas after co-combustion were examined. The results show that under the experimental conditions, with the increase in temperature, the NO emission concentration increases, and the concentrations of V, Cr, As, Sb and Hg first increase and then decrease in the bottom ash, while the concentrations of Zn, Cu, Se and Cd vary to the contrary. The turning point of most heavy metals concentration is at 800 ℃. However, with the increase in the sludge mixing ratio, the NO emission concentration first decreases and then increases, and the Cu, Hg and Tl concentrations all increase first and then decrease in the bottom ash, while the Cr concentration change is the opposite, with turning points all at the sludge mixing ratio of 10%. Also, with the increase in the secondary air ratio, the NO emission concentration decreases, and the Zn, Cu, Se and Hg concentrations in bottom ash decrease, on the contrary, the As and Cd concentrations increase.
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Key words:
- fuel /
- pollution /
- fluidized bed /
- co-combustion /
- heavy metal
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图 1 内循环流化床实验装置示意图
Figure 1 Schematic diagram of internal circulating fluidized bed experimental device system
图 2 不同污泥掺混比在不同掺烧温度下NO排放
Figure 2 NO concentration at different temperatures and sludge mixing ratios
图 3 10%污泥掺混比下不同温度、二次风比率的NO排放
Figure 3 NO emission concentrations at different temperatures and secondary air ratios under 10% sludge mixing ratio
图 4 10%污泥掺混比在不同掺烧温度下各重金属的分布
Figure 4 Distribution of heavy metals with different temperatures at 10% sludge mixing ratio
图 5 10%污泥掺混比在不同温度下飞灰的XRD谱图
Figure 5 XRD patterns of fly ash at 700 ℃, 750 ℃, 800 ℃, 850 ℃ with 10% sludge mixing ratio
1-SiO2；2-NaAlSi3O8；3-KAlSi3O8；4-CuFeS2；5-KCl
图 6 800 ℃时不同掺混比下各重金属的分布
Figure 6 Distribution of heavy metals with different mixing ratios at 800 ℃
图 7 800 ℃时污泥掺混比5%、10%、15%、20%下飞灰的XRD谱图
Figure 7 XRD patterns of fly ash with sludge mixing ratio of 5%, 10%, 15%, 20% at 800 ℃
1- SiO2；2-NaAlSi3O8；3-KAlSi3O8；4-CaCl2；5-KCl
图 8 污泥掺混比为10%时不同温度、二次风比率下各重金属的分布
Figure 8 Distribution of heavy metals at different temperatures with varying secondary air ratios at a 10% sludge mixing ratio
图 9 10%污泥掺混比在700、750、800、850 ℃下飞灰的XRD谱图
Figure 9 XRD patterns of fly ash with 10% sludge mixing ratio at 700, 750, 800, 850 ℃
1- SiO2；2-NaAlSi3O8；3-KAlSi3O8；4-CuFeS2；5-KCl；6-Ca(Al2Si2O8)；7-Al2O3；8-K2FeO4；9-FeSO3；10-CaCl2；11-HCl(H2O)
表 1 样品的元素分析和工业分析
Table 1 Proximate and ultimate analyses of samples
Sample Ultimate analysis wad/% Proximate analysis wad/% C H ${\rm{O} }^*$ N S M V A FC Sewage sludge 18.03 2.85 13.81 2.07 0.60 3.84 32.66 58.80 4.70 Corn straw 48.73 6.65 33.20 0.92 0.28 4.81 76.56 5.41 13.22 *: by difference 
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表 2 原料的重金属及Cl含量分析
Table 2 Concentration of heavy metals and Cl in raw materials（mg·kg−1）
Sample As Cr Hg Ni Cu Zn Sb Pb Cl Sewage sludge 44.60 227.87 35.24 52.21 104.83 1158.88 3.74 41.72 411 Corn straw 221.86 6.36 0.07 3.63 6.14 314.01 1.53 5.75 1520
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表 3 10%污泥掺混比在不同温度下掺烧后飞灰中主要物质含量
Table 3 Concentration of main substances in fly ash at different temperatures with a 10% sludge mixing ratio
t/℃ w/% SiO2 Na(AlSi3O8) KAlSi3O8 CuFeS2 KCl 700 39.7 52.5 5.5 2.2 − 750 41.3 − 58.7 − − 800 94.4 5.4 − − 0.2 850 24.0 76.0 − − −
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表 4 800 ℃时不同污泥掺混比下掺烧飞灰中主要物质浓度
Table 4 Main substances concentration in fly ash with different sludge mixing ratios at 800 ℃
Concentration w/% SiO2 Na(AlSi3O8) KAlSi3O8 CaCl2 KCl Mixing ratio 5% 16.6 68.4 15.0 − − Mixing ratio 10% 94.4 5.4 − − 0.2 Mixing ratio 15% 60.2 − 39.8 − − Mixing ratio 20% 23.2 − 76.5 0.3 −
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表 5 不同二次风比率下掺烧飞灰中主要物质浓度
Table 5 Concentration of main substances in fly ash with different secondary air ratios
t/℃ w/% SiO2 Na(AlSi3O8) KAlSi3O8 Ca(Al2Si2O8) Al2O3 K2FeO4 FeSO3 CaCl2 HCl(l) 700 37 − 57.6 − − − − − 5.4 750 41.2 − 6.8 − − − − 52 − 800 64.1 − 18.9 − 1.5 13.4 2.1 − − 850 1.6 91.7 − 6.7 − − − − −
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