FORMATION OF HYDROBROMIC AND HYDROCHLORIC ACID AEROSOLS IN WET FLUE GAS CLEANING PROCESSES

Abstract

The formation and behavior of hydrobromic and hydrochloric acid aerosols in a wet flue gas cleaning pilot plant were investigated. The optical three-wavelength extinction (3-WE) method was used to determine mean aerosol droplet diameters and droplet number concentrations. The experimental data are compared with theoretical results of the simulation tool AerCoDe (aerosol formation in contact devices). Results are presented for a raw gas temperature of 200°C and raw gas concentrations up to 260 mg/m3(STP) for HBr, and 2500 mg/m3 (STP) for HCl. Under these conditions aerosol formation for both species is initiated by heterogeneous nucleation. It is shown that during absorption processes HBr is forming essentially higher supersaturated gas phases in comparison to HCl, resulting in higher droplet number concentrations and smaller droplet sizes. For both species the number concentration is a strong function of the maximum degree of saturation, which corresponds to the classical theory of heterogeneous nucleation. HBr aerosol droplets cannot be detected by the 3-WE method directly after the first stage of the flue gas cleaning plant (quench column) because they are smaller than the detection limit ( ≈ 500 nm) of the 3-WE method for nonabsorbing particles. In this case the droplets are enlarged in a second step, and the number concentration is determined after enlargement. Using the actual number concentration as an input parameter, the mean diameter after the first stage can be calculated with the simulation tool AerCoDe.