Evaporation of mineral oil in a mist collector

Many industrial processes generate mineral oil mist. Current control technologies focus only on removing the mist droplets from the air. However, if these droplets evaporate, the vapor can pass through a collector designed to remove droplets alone. The purpose of this study was to determine the extent of evaporation for mineral oil droplets introduced to a mist collection system. Vapor was sampled using activated carbon downstream from the collector as high concentrations (45 to 55 mg/m³) of oil mist were injected upstream. After the system was loaded with mist, additional vapor samples were taken without mist injection to determine the amount of evaporation from mist-loaded collector components. The average vapor concentration measured for all samples taken when oil mist was introduced to the system was 4.02 mg/m³, or 8.8 percent of all oil introduced. Vapor concentrations caused by evaporation from collector components declined from 3 to 5 mg/m³ as clean air initially passed through freshly loaded components to 1 to 2 mg/m³ after air had passed through the components for about 12 hours. These findings suggest that even if a collector is 100 percent efficient for droplets of all diameters, some of the incoming mass will penetrate through the collector as vapor, and that evaporation of liquid oil retained on the collector itself can cause significant concentrations of vapor even if the collector has not been exposed to oil mist recently.