污泥与高碱煤协同燃烧中碱金属与重金属竞争机制研究

Study on Competition Mechanism of Alkali Metals and Heavy Metals in Collaborative Combustion of Sludge and Alkali Coal

在CFB锅炉燃烧温度下研究了低品质燃料(高碱煤)与生物质燃料(污泥)协同燃烧中重金属元素Pb、Ni和As的迁移特性。结果表明:燃烧温度对重金属元素热力学平衡分布起到重要的作用,温度越高,Pb、Ni和As在气相中的摩尔分数越高;当温度超过1 300℃时,Pb将全部以单质形态迁移至气相中,在CFB锅炉燃烧温度区间里大部分以PbCl2(g)、少量以PbCl的形态固集于飞灰颗粒上;当温度高于1 800℃时,系统中主要成分为Ni(g);在整个燃烧温度区间,As以单质的形态存在于系统中,其摩尔分数随着温度的升高而上升;碱金属Na主要竞争燃料中的Cl和O元素,实现重金属化合物形态的转化;与Na相比,K的竞争是微弱的,在700℃时K竞争Ni化合物中的CrO4^2-,导致NiO摩尔分数下降,而在850℃时,K与Ni竞争系统中的O元素,这与700℃的反应过程不同。

The migration characteristics of heavy metal elements Pb,Ni and As in the co-combustion of low-quality fuel(high alkali coal)and biomass fuel(sludge)were studied at the characteristic temperature of a CFB boiler.It is found that the combustion temperature plays an important role in the thermodynamic equilibrium distribution of heavy metals.The higher the temperature is,the higher the molar ratios of Pb,Ni and As would be in the gas components.When the temperature exceeds 1300℃,Pb would migrate to the gas components in the element state.In the CFB temperature range,Pb deposits on the surface of fly ash particles,with most part in the form of PbCl2and a small amount in the form of PbCl.When the temperature gets above 1800℃,Ni exists mainly in the form of Ni(g)in the system.Throughout the combustion temperature range,the mass fraction of As increases with the rise of temperature in the form of a single substance.The alkali metal Na mainly competes for the elements Cl and O in the fuel to achieve morphological conversion to heavy metal compounds.Compared with Na,the competitiveness of K is weaker,and K competes for ion CrO4^2- in the Ni compound at 700℃,resulting in an decrease in the mole fraction of NiO,while K competes with Ni for element O in the system at 850℃,when the reaction process is different from that at 700℃.