The Influence of Various Parameters on Petroleum Oil Removal from Produced Water with Novel Nanobubbles/microbubbles Flotation

Abstract

Produced water at offshore and onshore petroleum and natural gas extraction sites is very complex and contains many inorganic and organic contaminants. Such contaminants include free and emulsified petroleum oils and suspended solids. Gas flotation technologies are commonly used to remove finely dispersed oil droplets and suspended solids. New generation of flotation systems use nanobubbles-microbubbles generators that can produce very small bubbles ranging from 1 - 1,000 nanometers and 1-30 microns. However, influence of various parameters such as pH, salinity, temperature, pressure, type, and dosage of polymeric flocculants, mixing energy and hydraulic residence time have not been studied. In this manuscript we present detailed analysis and literature review of parameters that influence the performance of such flotation systems. High molecular weight and high charge density cationic flocculants significantly enhance the removal of dispersed oils and solids. Dual cationic-anionic flocculant approach is particularly efficient. Centrifugal hydrocylone based flotation systems where nucleation of bubbles and flocs occur at the same time are particularly effective. Higher temperature and pH enabled better emulsion flocculation and flotation. Salinity impairs flocculant activation and the performance of flotation system. Nanobubbles enhance flotation and flocculation at high NaCl concentrations. We propose a "hungry black hole" model for nanobubbles effects in flocculation and flotation: nanobubbles occasionally collapse and like black holes release a strong jet of gas that can then penetrate oil droplets, flocculant chain networks and floc pores. Secondary nano and microbubbles nucleation in those pores then creates large light flocs that float in seconds to the top of flotation units.