燃烧温度对煤中汞析出特性及形态分布的影响

Effects of coal combustion temperature on mercury emission and speciation

在管式炉实验装置上研究了燃烧温度对燃煤汞析出特性的影响,利用在线烟气分析仪和EPA Method 26A湿化学法对燃煤烟气中O_2/SO_2/NO/CO/HCl/Cl_2等进行同步定量分析,探讨不同燃烧温度下烟气组分的变化及其在烟气降温过程中对汞形态迁移转化的影响规律。结果表明:在高温燃烧条件(≥750℃)下,煤中汞基本全部逸出,析出率≥97.9%,且随燃烧温度升高而递增;基于氧量分析,煤中汞的析出在挥发分燃烧阶段即开始发生;随着燃烧温度的升高,烟气中元素态汞(Hg0)份额逐渐降低,而氧化态汞(Hg^(2+))份额相应增大,900℃时接近50%;燃烧温度对烟气中各组分浓度影响较大,随温度升高,烟气中NO、HCl及Cl_2呈现不同程度的上升趋势,SO_2含量基本持平,而CO含量逐渐降低;对痕量元素汞而言,NO、HCl及Cl_2通过直接或间接氧化作用在烟气降温过程中促进Hg0向Hg^(2+)转化,烟气中还原性气体组分CO对Hg0的氧化有一定抑制作用,SO_2对汞形态分布的影响则不甚明显。

The effects of different temperature on mercury speciation and transport during coal combustion were studied in a tube furnace device. EPA（Environmental Protection Agency）Method 26 A and flue gas analyzer were used to determine the content of HCl/Cl2/NO/CO/O2/SO2 in flue gas. The change of flue gas components at different combustion temperature and the oxidation mechanism of Hg0 at flue gas cooling process were also investigated. The results indicated that mercury in coal was completely released and the discharge rate reached 97.9% at high combustion temperature（〉750℃）. Based on the analysis of oxygen,mercury began to release in coal combustion stage. The content of Hg0 became lower,while the content of Hg^2＋ was higher with increasing combustion temperature and close to 50% in flue gas at 900℃. Different temperature led to an obvious change in the flue gas components. The concentration of CO decreased gradually and the concentration of SO2 remained stable,while the concentration of NO/HCl/Cl2 became higher at elevated temperatures. NO/HCl/Cl2 can promote the oxidation of Hg0 at flue gas cooling process,but CO had the opposite effect. In addition,SO2 had unconspicuous effect on mercury speciation.