COMPUTATION OF PHASE AND CHEMICAL-EQUILIBRIA IN FLUE-GAS WATER-SYSTEMS

The phase and chemical equilibria of flue-gas/water systems containing sour gases such as HCl, HF, SO2, SO3, NOx and volatile heavy metal compounds such as Hg, HgCl2, and SeO2 are calculated from thermodynamic standard data using the Gibbs free energy minimization method. The Pitzer/Debye/Huckel equation is used for the activity coefficients of the ions in the aqueous solution. The inhibition of certain oxidation reactions is considered by a proper formulation of the atom matrix. The comparison of the calculated equilibrium values to experimental data from a coal-fired power plant show that concentrations of most pollutants at the outlet of the absorbers are close to the equilibrium values of one single theoretical stage. The extension of the Gibbs free energy minimization to multistage countercurrent absorbers gives the concentration profiles of various components.