燃煤过程中砷的赋存形态及其挥发特性

选取3个国内煤样，利用自制恒温热重装置研究了燃烧过程中砷的赋存特性及其挥发规律。通过测定不同停留时间下燃烧样品中砷的含量，拟合得到砷的挥发曲线和挥发速率曲线，并采用逐级化学提取的方法对原煤和不同停留时间下的燃烧样品进行形态分析。实验结果表明：温度是影响砷挥发的重要因素，700～1000℃是砷挥发的主要温度区间。煤粉燃烧过程中，砷的挥发速率与煤粉的失重速率具有同步性；伴随着煤中水分和挥发分的快速析出，砷也具有较高的挥发速率；随着燃烧过程的深入进行，砷的挥发速率变得缓慢。煤粉燃烧结束，3种煤（五里庄、红岩和梅花井）砷的挥发比例分别为49.5%、80.7%、65.0%，且在燃烧过程中煤中残渣态、硫化物结合态和可交换态砷相互作用迁移。

Volatilization characteristics and mode of occurrence of arsenic during coal combustion

The volatilization characteristics and mode of occurrence of arsenic for three coals were studied by a customized isothermal thermogravimetric experimental system. Limited by online monitoring of gaseous arsenic, the volatilization characteristics of arsenic were determined by measuring the arsenic concentration of ash at the specified residence time in this paper. The volatilization ratio of arsenic at the various residence time was obtained and the volatilization characteristics of arsenic were fitted through B-spline curve. Mode of occurrence of arsenic in the coals and corresponding ashes at the specified residence time was measured by sequential chemical extraction method. The results showed that the volatilization ratio of arsenic increased gradually with temperature, while most arsenic volatilized in 700-1000℃ period. The volatilization rate of arsenic was correlated to the combustion rate of coal. The volatilization rate of arsenic was relative high due to the release of volatile matter, and it began to slow down with the increase of burning time. After coal combustion, the final volatilization ratios of arsenic for coals (WL, HY, and MH) were 49.5%, 80.7% and 65.0%, respectively. The residue and sulfide arsenic would be partly migrated to be exchangeable state.