Emission and local ventilation control of droplets generated by condensation and bubble-bursting during pickling

Abstract

• The mass and C HCl of acid drops generated during pickling were measured. • The mass and C HCl of acid drops generated in different ways were compared. • The effects of the variables on the emission rate of droplets were investigated. • The efficiency of a jet-assisted exhaust hood in capturing droplets was discussed. Acid droplets emitted during pickling are a typical airborne pollutant. To remove the acid droplets efficiently, a local ventilation system should be designed according to the characteristics of the droplets emitted through different pathways. In this study, the mass and HCl concentration (C HCl-d ) of the droplets generated by condensation and bubble burst during pickling were experimentally compared. The effect of parameters on the emission rate of bubble-bursting droplets was then analyzed. Finally, the droplets capture efficiency of a jet-assisted exhaust hood was discussed. It was found that the bubble-bursting droplets were the main component of the acid droplets based on both their mass and C HCl-d . The emission rate of bubble-bursting droplets depended on the reaction intensity, gravity of large droplets, and heat convection around the droplets. Within the scope of this study, almost all droplets within 50 μm were captured by the jet-assisted exhaust hood. The ventilation system needs to be optimized due to the low capture efficiency for capturing the droplets larger than 75 μm in diameter, and evaporation was advantageous to improve the droplet capture efficiency. The conclusions can be applied for optimizing strategies of controlling acid droplets to improve the indoor environment of industrial buildings.