温度和赋存形态对燃煤过程中砷迁移和释放的影响

选取3个煤阶共6个国内典型煤种,利用水平管式炉在不同温度下进行煤的燃烧实验,研究燃煤过程中砷的迁移和释放特性。利用热分析的相关理论和方法,将煤的热重分析手段运用于煤燃烧过程中砷的质量变化,通过对实验结果进行拟合得到砷的失重曲线和失重速率曲线,并采用逐级化学提取的方法对原煤及不同温度下煤灰中砷的赋存形态进行分析。25～1100℃的实验结果表明:随着温度升高,煤中砷的释放比例逐渐增大,1100℃下砷的释放比例变化范围为30%～67%。不同温度区间下砷的失重速率存在差异,800～900℃区间出现显著的砷失重峰,主要原因是以硫化物形式存在的砷在800～900℃区间发生剧烈的分解/氧化分解。此外,相同温度下褐煤的失重比例和失重速率较大,无烟煤的失重比例和失重速率较小,烟煤则介于无烟煤和褐煤之间。温度升高后,煤中的有机物结合态砷向气相迁移,酸溶态砷和残渣态砷共同作用,减少的砷主要进入气相中,还有一部分向可交换态砷迁移。

Effect of temperature and occurrence form of arsenic on its migration and volatilization during coal combustion

Migration and volatilization features of arsenic in combustion processes for six coal samples selected from three different ranks were studied in a horizontal tube furnace at various temperature ranges. The mass change of arsenic in the combustion process was tracked and analyzed using the instruments and theoretical method of thermal analysis (TG/DTG) and coal analysis for these selected coal samples. The curves of arsenic mass loss and its rate were obtained by fitting these experimental results. The occurrence form of arsenic in the coals and corresponding ashes was determined by using a sequential chemical leaching method. The experimental results show that arsenic volatility and the releasing proportion increase with temperature, and the proportions varied from 30% to 67% at 1100℃. The mass loss rate of arsenic varies for different temperature regions, and a peak value of arsenic loss rate is observed at 800-900℃, mainly due to decomposition/oxidation of arsenic in sulfide form. Furthermore, lignite shows the highest mass loss ratio and rate of arsenic under the same temperature, followed by bituminous coals and anthracite. With temperature increases, organic arsenic volatiles easily into gas phase, and the interaction between acid-soluble and residual arsenic makes them migrate mainly into gas phase, and only a small part is transferred to its exchangeable form.