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

对天津市某电厂循环流化床(CFB)锅炉燃用的原煤及燃烧产物底灰、飞灰、细飞灰(≤50 μm)进行痕量元素含量的测定,分析了Be、Zn、Hg、V、Cr、Mn、Co、Ni、Cu、As、Se、Cd、Pb 13种痕量元素在燃烧过程中的迁移行为,揭示了痕量元素在CFB锅炉中的分配、富集特性。结果表明,CFB锅炉中,较低的炉温对于痕量元素的迁移富集产生了较大的影响。由相对富集系数得知,Be、V、Co、Se在底灰中耗散,在飞灰中富集,Zn、Mn倾向于在底灰中富集,元素Cd、Pb、Ni、Cu挥发性较强,在底灰和飞灰中均是耗散。As受钙氧化物影响,挥发性表现并不明显。Hg在底灰和飞灰中相对富集系数均很低,表明Hg在整个燃烧过程中以气态形式排放;Hg、As、Se、V、Cr、Mn、Co、Ni、Cu、Zn、Pb均有向小颗粒物中富集的趋势。根据相对富集系数以及研究的13种元素在低温CFB锅炉中的迁移行为,将这些元素分为三类:A类(E_R<0.1),主要是以气态形式排放元素Hg;B类(0.1R≤0.85),较易挥发元素As、Be、Ni、Cu、Se、Cd、Pb、Co、V;C类(E_R>0.85),主要残留在固体产物中元素Zn、Mn、Cr。

Mobility and enrichment of trace elements in a coal-fired circulating fluidized bed boiler

Some hazardous trace elements in coal, bottom ash, fly ash and fine fly ash from a circulating fluidized bed (CFB) boiler in a power plant were examined. The distribution, enrichment and partitioning behavior of Be, Zn, Hg, V, Cr, Mn, Co, Ni, Cu, As, Se, Cd and Pb were analyzed. The results show that the distribution and enrichment characteristics of trace elements are greatly affected by the temperature of CFB. According to the relative enrichment factor (E_R), Be, V, Co and Se trend toward fly ash; Zn and Mn show a tendency into bottom ash. Some volatile trace elements like Cd,Pb,Ni and Cu show low enrichment in both bottom ash and fly ash. The element of As is affected by calcium oxide, and its volatility is not obvious. Hg is more likely discharged with flue gas. Hg, As, Se, V, Cr, Mn, Co, Ni, Cu, Zn and Pb all have an enrichment tendency toward fine particles. On the basis of E_R and behaviors of the 13 trace elements in CFB boiler, these elements are divided into 3 categories: A(E_R<0.1), Hg mainly volatilizes into the atmosphere; B(0.1R≤0.85), As, Be, Ni, Cu, Se, Cd, Pb, Co and V are more easily volatilization; C(E_R>0.85), Zn, Mn and Cr mostly stay in solid residues.