Effects of coexistent gases (HCl, SO2, O2, CO 2, and H2O) in simulated coal combustion flue gas on mercury removal by a commercial activated carbon (coconut shell AC) were investigated in a laboratory-scale fixed-bed reactor at 80 °C. To clarify the contribution of the Deacon reaction 2HCl+1/2O2=Cl 2+H2O on the mercury sorption mechanisms, the experiments were also conducted in the presence of Cl2 (in the absence of HCl). The characteristics (thermal stability) of the mercury species formed on the AC under the various sorption conditions were investigated by the temperature-programmed decomposition desorption (TPDD) technique. It was found that O2 promoted mercury removal in the presence of SO2; however, SO2 suppressed mercury removal irrespective of the presence of O2. The promotion of mercury removal by the presence of O 2 may result from the Deacon reaction. However, SO2 seemed to inhibit the Deacon reaction. It is thought that mercury species formed on AC through the Deacon reaction was HgClx (including HgCl2), which decomposed and desorbed at around 300 °C. This was supported by confirmation of the presence of HgCl2 vapor in the reactor effluent gas in TPDD experiments. From the comparison of mercury removal in the gas containing 1 ppmv HCl and gas containing 0.5 ppmv Cl2 system in the presence of SO2, O2, CO2 and H2O, it was suggested that Cl2 enhances mercury removal more efficiently than HCl. Therefore, efficient removal of mercury with AC is possible to achieve via promoting the Deacon reaction. The high-temperature TPDD peaks were observed at around 500 °C in TPDD spectra of the spent sorbents used in mercury removal in the presence of Cl2 (or high concentrations of HCl), SO2, O2, CO2, and H2O. This TPDD peak temperature range is very close to the decomposition temperature of HgSO4. We suggest that the high-temperature mercury desorption peaks are related to the decomposition of mercury species similar to mercury sulfate containing chlorine (HgSxOyClz) on AC.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology