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, NOx, 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.