Formation, Reduction and Emission Behaviors of CBzs and PCDD/Fs from Cement Plants

ABSTRACT

The formation, reduction and emission behaviours of chlorobenzenes (CBzs) and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) were studied in a typical dry cement kiln in China. The operating conditions were scrutinized at various positions by monitoring the concentrations of CO, NO_x, HF and HCl in the flue gas. Furthermore, the concentration, gas/particle partition and congener distribution of CBzs and PCDD/Fs were analyzed at the outlet of cyclone pre-heater, suspension pre-heater, raw mill and stack. The main PCDD/F formation zone was proven to be the first stage of pre-heater and the congener distribution of PCDD/Fs was significantly affected by the recycling ash. Specially, the concentration of CBzs continually increased with the flowing of flue gas. The final emissions of PCDD/Fs and CBzs in the flue gas were 0.016 ng I-TEQ Nm^–3 and 26 µg Nm^–3, respectively. Moreover, the reduction efficiency of I-TEQ via bag filter was up to 81% and 86% for gas and particle phase PCDD/Fs, respectively. Most importantly, the mass balances indicated that raw meal was the dominant input and the rotary kiln incinerating waste was clearly a weighed PCDD/F and CBz sink. Furthermore, HCBzs correlated well with the total I-TEQ during the whole process of cement production.