Improving the removal of fine particles by heterogeneous condensation during WFGD processes

Abstract

To improve the removal efficiencies of fine particles in the flue gas, a novel process of heterogeneous condensation is proposed in a limestone-gypsum desulfurization system combined with waste heat recovery. A necessary supersaturation vapor environment was established in the SO2 absorption zone by flue gas humidification at the inlet of the desulfurization system. Humidification of the flue gas was achieved by evaporation of spraying water at the inlet of the electrostatic precipitator (ESP) and installing a low temperature heat exchanger at the wet flue gas desulfurization (WFGD) inlet. The numerical calculation results indicated that the supersaturation vapor environment could be obtained in the SO2 absorption zone during this process. In the flue gas, the fine particles were activated in the supersaturation vapor environment and acted as nucleation centers for droplet growth, and the enlarged droplets were afterwards removed by the desulfurization slurry and the demister. Meanwhile, the waste heat was recovered from the flue gas before WFGD system. The influences of the relative humidity and temperature of the WFGD inlet flue gas, liquid-to-gas ratio of the WFGD system and the desulfurization slurry temperature on the removal efficiency of fine particles are studied in this paper. The results showed that inlet flue gases with high relative humidities can remove the fine particles, and high liquid-to-gas ratios of the WFGD system are also beneficial to efficiently remove fine particles. However, particle removal was unfavorable at high temperatures of desulfurization slurry. In any case, the performance of the WFGD system for the removal of fine particles was improved significantly using this novel process, and the removal efficiency of the WFGD system was improved by 40–50%.