Vaporization model of arsenic during single-particle coal combustion: Numerical simulation

摘要

Arsenic emissions from coal-fired power plants has been given increasing attention due to its harmful effect on the environment and human health. The vaporization behavior of arsenic in high temperature flame zones is critical for understanding arsenic partitioning in downstream flue gas. However, the gaseous arsenic concentration in furnaces are hard to measure due to limitations in sampling technology. In this work, a novel vaporization model for arsenic was established to simulate the release behavior of arsenic during single-particle coal combustion. The temporal-spatial vaporization ratio and concentration of arsenic could also be obtained. The effects of temperature, O-2 concentration, particle size as well as the content and occurrence mode of arsenic in coal are discussed in detail. Simulation results indicate that with increase in temperature or O-2 concentration, or decrease in particle size, the vaporization rate of arsenic accelerated gradually with a higher As2O3(g) concentration peak. Meanwhile, the As2O3(g) concentration curves changed from one single peak to multiple peaks mainly due to the oxidation delay of sulfide-bound arsenic (simplified as FeAsS) in the inner shells of a single coal particle. Compared to anthracite, bituminous or lignite coal tended to have a larger vaporization ratio of arsenic with a more pronounced As2O3(g) peak. Further, the peak concentration of As2O3(g) was found to be correlated linearly to the arsenic content in the feed coal. Furthermore, model results were compared with both on-line and off-line experimental data for validation. The comparisons showed that the proposed single-particle model predicted well the vaporization kinetics of arsenic for the combustion temperatures analyzed, indicating the adaptability of the model as a potential tool for determining arsenic vaporization as well as gaseous arsenic concentration prediction.