Effect of Volatile and Ash Contents in Coal on the Volatilization of Arsenic during Isothermal Coal Combustion

The effects of the temperature, volatile content, and ash content on the volatilization kinetics of arsenic were discussed. Six Chinese coals were tested in an isothermal thermogravimetric reactor at 600-1300 degrees C. Sequential chemical extraction analysis was employed to know the speciation transformation of arsenic during coal combustion. Results show that the volatilization ratio of arsenic increases with the temperature, and most arsenic volatilizes between 700 and 1000 degrees C. The volatile content has a positive effect on the volatilization rate of arsenic in the initial stage of combustion. With the same level of ash content, high-volatile coals (>30%) own a larger volatilization rate of arsenic (0.55-0.6% s(-1)) than the low-volatile coals (<12%) (0.25% s(-1)). In contrast, coals with a higher ash content tend to obtain a lower volatilization rate of arsenic during the process. Despite the effect of volatile and ash contents on the volatilization rate of arsenic, the final volatilization ratio of arsenic largely depends upon its mode of occurrence of arsenic in coal, especially on sulfide- and organic-bound arsenic. A first-order reaction kinetic model can well describe the volatilization characteristics of arsenic. A calculation shows that the activation energy of arsenic volatilization is significantly affected by the volatile content, while the ash content has a tiny effect on it. High-volatile coals have lower activation energy of arsenic volatilization than low-volatile coals.