The formation and removal characteristics of aerosols in ammonia-based wet flue gas desulfurization

Abstract

The characteristics of aerosol generation were studied experimentally in an ammonia-based wet flue gas desulfurization process. Particle size distributions and concentrations, morphologies and compositions before and after desulfurization were measured using an electrical low pressure impactor and scanning electron microscopy, respectively. The results show that aerosols can be generated between ammonia and sulfur dioxide resulting in gas-phase reaction and the aerosol concentration at the outlet of scrubber is significantly higher than at the inlet. Before desulfurization the particles are primarily silica-alumina minerals including O, Al, Si and C, while after ammonia-based desulfurization aerosol particles have smooth surfaces with regular structures, such as cubic and prismatic crystals, and contain principally O, S and N. Particle sizes up to 10 μm were measured, but the majority of the aerosol particles are in the submicron range. Separation of submicron particles from flue gas is difficult by conventional desulfurization scrubber; however high removal efficiency can be achieved based on the enlargement of the particles by heterogeneous condensation. The influence of the supersaturation degree and liquid–gas ratio on the removal efficiencies of the particles are demonstrated additionally. It indicates that aerosols generated in ammonia-based desulfurization process can be deliquesced and gradually enlarged in a high humidity flue gas, but the supersaturation degree higher than 1.2 is required for heterogeneous nucleation of water vapor with ash particles from coal combustion.