Simultaneous volatilization characteristics of arsenic and sulfur during isothermal coal combustion

Abstract

Six coals that with different rank and sulfur contents were chosen for the isothermal combustion experiments at 900°C and 1300°C. By changing the residence time, the volatilization ratio and rate of arsenic with time were obtained. Effects of residence time, temperature, coal type and sulfur content on arsenic volatilization characteristics were discussed. The emission concentration of SO2 was also obtained through online monitoring by flue gas analyzer. Furthermore, the curves of arsenic volatilization, SO2 emission and mass loss of coal were compared together to study the simultaneous volatilization characteristics of arsenic and sulfur. Results show that coals with higher sulfur content tend to have a larger proportion of sulfide bound arsenic, which could have a positive effect on arsenic volatilization. With the increase of residence time, the volatilization ratio of arsenic increases gradually with various volatilization rate. One volatilization peak of arsenic is observed for all the coals. The volatilization peak of arsenic moves forward with higher temperature and lower coal rank. The peak rate of arsenic increases with higher temperature while varies much in different coals. At 900°C, coals with lower coal rank tend to have a higher peak rate of arsenic, while at 1300°C, coals with larger proportion of sulfide bound arsenic tend to have a higher peak rate of arsenic. As for SO2, all the coals have one emission peak at 900°C while two emission peaks at 1300°C, which is similar to the mass loss characteristics of coals. The simultaneous releasing behavior of arsenic and sulfur is observed at 900°C due to the moderate mass loss of coal and at 1300°C due to the decomposition of As-bearing sulfides.