Abstract
The formation and decomposition of dioxins (PCDD/Fs) in combustion gas have been discussed by thermodynamic calculations for the C-O-H-Cl quaternary gas system. The effects of temperature and gas composition are briefly summarized by changing the conditions based on the following “reference gas”: O20.1 + CO 1.8 + H20.15 + HCl 0.9 + C2H3Cl 0.1 mol=O:2 + C:2 + H:1.5 + Cl: 1 mol The effects of various additions (inhibitors) on the decomposition of PCDD/Fs are evaluated by use of thermodynamic package HSC Chemistry. The changes of the reference gas composition are calculated at 300゜C by addition of inhibitors such as CaO, SO2, NH3, sodium salts, organic compounds, and metals. The amounts of PCDD/Fs decrease efficiently by the additions of these substances, but it is clarified that the decrements are always reproduced by change in basic quaternary C-O-H-Cl gas composition. Increase in O or H, and decrease in Cl result in decomposition of PCDD/Fs, and thus, the regulation of the quaternary gas composition is of primary importance to control PCDD/Fs. The derived amounts of PCDD/Fs by equilibrium calculation are much higher than those observed in practice because of kinetic reasons. Taking account of slow reaction rates of the formation of PCDD/Fs and solid carbon deposition, thermodynamic simulations for depression of the formation of PCDD/Fs are demonstrated.
