Gas Flotation of Petroleum Produced Water: A Review on Status, Fundamental Aspects, and Perspectives

Abstract

Produced water is a major byproduct in oil production and the largest waste stream generated in the petroleum industry. At the Norwegian Continental Shelf, produced water is still mostly discharged to the sea, but some installations re-inject produced water into the reservoir for pressure support or disposal. Gas flotation is a separation technology widely used both onshore and offshore that generally reduces the oil concentration to <25 ppmv. It is also a promising technology for subsea water treatment. The aim of this review is to give an overview and provide a link between the industrial use and the fundamental aspects of gas flotation. The industrial analysis examines the development and design of gas flotation technologies: induced, dissolved, and compact flotation units. Several aspects of subsea water separation are also discussed. The fundamental aspects are dedicated to the fluid dynamics of bubble−droplet collisions and the phenomena involved after their encounter, i.e., film drainage, forces involved in this process, and spreading of oil on the surface of gas bubbles. Moreover, a detailed analysis of parameters that can affect gas flotation, like gas bubble and oil droplet sizes, droplet−bubble attachment mechanisms, interfacial properties, water composition, oil and gas properties, pressure, and temperature, is provided.

Interfacial Behavior and Internal Microflow of an Oil Droplet during the Process of the Oil Droplet Covering a Gas Bubble: Without and with NaCl

“…10,11 In the flotation process, there are three attachment modes of the oil−bubble aggregate, namely, full or partial encapsulation, oil lens, and point attachment. 12 If the oil droplet spreads over the bubble's surface, the oil−bubble aggregate is then more stable and strives against the upward rise better. 11 The formation of a stable aggregate can be divided into five stages: 13 (1) an approach stage, (2) a film drainage stage, (3) a spread stage, (4) an oscillation stage, and (5) an equilibrium stage.…”

“…6,13 After the film rupture event, the oil droplet can wrap the gas bubble for the positive spreading coefficient (S 0 ). 12 The coverage time is shorter than the induction time, and spreading is faster with the low viscosity of oil. The period of coverage time is on a millisecond scale.…”

“…In the flotation process, there are three attachment modes of the oil–bubble aggregate, namely, full or partial encapsulation, oil lens, and point attachment . If the oil droplet spreads over the bubble’s surface, the oil–bubble aggregate is then more stable and strives against the upward rise better .…”

Synthesis and Flotation Performance Evaluation of Polypropylene Glycol Grafted Poly N‐[(3‐dimethylamino)propyl]methacrylamide Copolymer

“…In this case, the rising velocity of the attached oil droplets is increased, which is beneficial for oil removal. [11–13] . Effective oil removal during air flotation depends on the collision frequency between bubbles and droplets, the adhesion efficiency between them, and the stability of the obtained bubble‐droplet agglomerations [14,15] …”

The effect of molecular structure on the properties of cationic polyacrylate and its flocculation‐flotation performance of oilfield oily wastewater treatment

“…10 At present, the process of oily wastewater treatment on offshore platforms is usually a three-stage process of inclined plate-air flotation-filtration. The floating oil and large dispersed oil droplets in oily wastewater can be removed in the inclined plate separator with the help of water clarifier [11][12][13][14][15][16] Small emulsified oil droplets are usually removed in the air flotation separator by using air flotation agent. [17][18][19] Filtration, such as walnut shell filter 20 and membrane filtration, [21][22][23] is performed at the end of the oily wastewater treatment because the oil, suspended solids, and potential biochemical toxicity should be removed considerably for some platforms with strict environmental protection regulations and standards.…”