REDUCTION OF DIOXIN EMISSIONS FROM WAELZ PROCESS OPERATED IN ACIDIC OR BASIC MODE

摘要

Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) concentration measured in stack gas of the Waelz plant investigated was as high as 150 ng-TEQ/Nm3 in 2005 due to its relatively high dioxin formation potential and low PCDD/F removal efficiency (<70%) achieved with the bag filter (BF). In 2006, activated carbon injection (ACI) technology was adopted in the Waelz plant investigated to reduce PCDD/F emission. Flue gases samplings were conducted at different sampling points to evaluate the removal efficiency and the partitioning of PCDD/Fs between vapor/solid phases in this facility. By applying ACI + BF, the PCDD/F concentrations of stack gas was dramatically decreased to 3.38 ng-TEQ/Nm3 as the activated carbon injection rate was controlled at 40 kg/h. With adsorbent injection + dual baghouse filter (DBF) system being adopted in 2007, the PCDD/F concentration in stack gas was significantly reduced to 0.235 ng-I-TEQ/Nm3 with the adsorbent injection rate at 16 kg/h. In practice, the carbon-type adsorbent is mixed with part of the fly ash collected by cyclone and then injected into the flue gas. In 2008, Ca(OH)2 was applied to replace SiO2 as part of the input material of this facility and its operation was converted from acidic mode to basic mode. In the meantime, the PCDD/F concentration measured at stack gas was further reduced to 0.123 ng-TEQ/Nm3. With this operation mode, the total PCDD/F emission flow on the basis of treating one kg of EAF dust in this facility was dramatically decreased from 1,925 to 269 ng-I-TEQ/kg EAF-dust treated.