Fate of heavy metals during fluidized-bed thermal treatment of municipal solid waste
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摘要: 在流化床实验装置上研究模拟生活垃圾热解、气化、焚烧等热处置过程中重金属Cd、Pb、Zn及Cu的迁移转化, 分析氧化还原气氛及温度对重金属挥发特性的影响。结果表明, 高温及还原性条件促进了Cd、Pb及Zn的挥发; 而氧化性气氛有利于Cu的迁移。热力学平衡模拟结果表明, 金属在氧化和还原气氛下的转化途径不同。在还原性气氛下, 金属主要以元素态单质或硫化物的形式存在, 其熔沸点高低决定了金属挥发程度。反之, CuCl3等氯化物的生成促进了Cu在氧化性气氛下的挥发。金属基反应在氧化性气氛下得到加强, 提高了Cd、Pb及Zn向气相产物转化的起始温度。进一步考察重金属在不同组分的分布及富集规律, 大部分以气相形式挥发的重金属易在降温过程中冷凝并富集于飞灰。气流夹带亦是导致重金属迁移的重要原因, 流化床的高气速特性对重金属分布有显著影响。Abstract: Municipal solid waste pyrolysis, gasification and incineration experiments were conducted in a fluidized bed reactor to investigate the effect of redox atmosphere and temperature on the fate of heavy metals (Cd, Pb, Zn and Cu). The results show that higher temperature and reductive atmosphere are effective for the evaporation of Cd, Pb and Zn; while the oxidative condition favors the migration of Cu. Thermodynamic equilibrium calculation confirms that the metal species differ a lot under redox conditions. Metals are mainly existed as elemental forms or sulfide under reductive atmosphere; and their volatility depends on the metal boiling point dominantly. On the contrary, the formation of metal chlorides such as CuCl3 increases the volatilization of Cu in an oxidative atmosphere. Besides, the evaporation of Cd, Pb and Zn is postponed under oxidative condition due to the metal-matrix reactions. The distribution of heavy metals in different fractions was further examined. The majority of the vaporized metals are condensed and enriched in the fly ash upon cooling. Entrainment also poses a significant influence on the migration of metals, which is determined by the characteristics of high gas velocity used in fluidized bed.
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Key words:
- heavy metals /
- municipal solid waste /
- fluidized bed /
- redox atmosphere /
- distribution
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表 1 模拟生活垃圾组分及特性
Table 1 Components and characteristics of simulated-MSW
Component Rice Cabbage Cardboard PE PVC Wood Fabric Tire Content war /% 29 29 13 17 3 5 2 2 Ultimate analysis wad/% Proximate analysis wad/% Calorific value Q/(MJ·kg-1) C H O N S Cl V M A 48.4 6.3 29.2 0.8 0.3 1.6 73.8 9.2 4.2 22.5 -
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