Oil/Water Separation by Induced-Air Flotation

Abstract

The separation of oil, stabilized with an oil-soluble petroleum sulfonate, from brine solutions by induced-air flotation was studied in a continuous-flow pilot unit. The effects of inlet oil concentration, vessel residence time, air flow rate, bubble diameter, oil drop diameter, temperature, NaCl concentration, and cationic polyelectrolyte concentration were investigated. Oil drop and air bubble diameters, liquid residence time, and concentration of cationic polyelectrolyte were the most significant variables affecting overall flotation performance. Only drops larger than 2μm showed significant removal, while smaller drops were generated by the air-inducing rotor. The cationic polyelectrolyte improved flotation performance by increasing the number of large oil drops. The removal rate for each oil drop size was first order with respect to oil drop concentration, and an experimental procedure permitting determination of the first-order rate constants for removal only due to bubble/drop interactions was developed. The oil drop and air bubble diameters were the only variables which affected these rate constants. Inceasing oil drop diameter and decreasing bubble diameter increased the rate constants. Comparison of the experimental and theoretically predicted rate constants showed that the mechanism of oil-droplet removal by bubbles from 0.2- to 0.7-mm is one of hydrodynamic capture in the wake behind the rising bubbles.