Enhanced Oil-Water Separation Using Cyclonic Dissolved Gas Flotation Unit (CDFU) for Produced Fluid Treatment
Shenzhen Clear Science & Technology Co., Ltd (SINOKLE)’s patented product - CDFU (Cyclonic Dissolved Gas Flotation Unit) is a technology that innovatively integrates centrifugal cyclone separation and dissolved gas flotation separation into a unified system, forming a synergistic treatment system. The device enhances the collection and removal of oil droplets and suspended solids significantly by the combined effects of the cyclone field and dissolved micro-nano bubbles. This not only greatly improves flotation efficiency but also shortens the hydraulic retention time, thus enabling efficient and rapid purification of oily wastewater, especially suitable for various types of industrial oily (and suspended solids) wastewater that are difficult to treat.
The simplified process diagram is shown in Figure 1 below.
Figure 1: Process Diagram for Oilfield Produced Fluid Treatment
1. Produced Fluid Treatment Process Principle
Gas flotation technology is a mature physical-chemical separation process. Its core mechanism involves injecting a large number of highly dispersed micro-nano bubbles into the water to be treated, which then act as carriers to effectively adsorb oil droplets or flocculent substances suspended in the water, forming "bubble-particle" complexes. These complexes, due to their overall lower density than the water, rise rapidly to the surface under buoyancy, where they aggregate into a floating sludge layer that is easy to remove mechanically, thereby achieving efficient separation of oil and water, solid and liquid phases, and purifying the water.
Gas flotation technology is a physical purification method that achieves high-efficiency separation of oil, water, and solids in a multi-phase system. It has been widely applied in various wastewater treatment processes, including dissolved gas flotation, electroflotation, dispersed gas flotation, and vortex-flotation. In recent years, with ongoing innovations combining multiple technologies, new hybrid processes such as coagulation-gas flotation, flotation-magnetic separation, and cyclone-gas flotation have emerged, significantly enhancing treatment efficiency and adaptability. Among these, Cyclonic Dissolved Gas Flotation (CDFU) integrates the advanced EDUR gas-liquid two-phase pump from Germany and a high-precision gas flow control system, achieving 100% gas saturation dissolution. The system is compact and highly reliable, excelling in improving gas dissolution efficiency and energy utilization. The gas dissolution effect is shown in Figure 2 below.
Figure 2: Gas Pump Fluid Dynamics Model and Gas Dissolution Effect
The dissolved gas water is released via a specially designed pipeline release device, which efficiently generates large quantities of micro-nano bubbles. The device uses a large-size pipeline release structure, ensuring the generation of uniformly sized, fine ultrafine bubbles (with a diameter range of 5–30µm), while effectively preventing internal clogging and significantly improving gas release efficiency. The effect of the efficient release device in gas dissolution is shown in Figure 3.
Figure 3: Microbubble Effect
Water carrying micro-nano bubbles (diameter 5–30 microns) enters the high-efficiency cyclone dissolved gas flotation unit’s inlet pipeline. After mixing with the incoming water, it enters the container tangentially from the bottom, forming a weak cyclone field. This flow field causes the oil droplets and bubbles to migrate toward the central area while enhancing the collision and adhesion probability between them. Then, under the flotation effect, the multiphase mixture of oil-bubble-suspended solids rises to the surface and is removed via a pressure oil discharge system. The purified clean water is discharged from the bottom outlet. Figure 4 shows a schematic diagram of the cyclone separation structure.
Figure 4: Cyclone Dissolved Gas Flotation Separation Schematic
To further enhance the synergistic effect of cyclone and flotation, a dedicated cyclone barrel is installed inside the container to precisely control the centrifugal force field strength. The combined action of cyclone separation and flotation results in a significant increase in efficiency, allowing the CDFU device to achieve pollutant removal rates far exceeding those of single technologies in a very short residence time.
2. Produced Fluid Treatment Process Flow Diagram
After pre-treatment by a three-phase separator, the produced fluid enters the two-stage high-efficiency cyclone dissolved gas flotation unit for further treatment. During this process, emulsified oil is captured by ultra-fine bubbles, which then continuously aggregate, coalesce, and demulsify under the cyclone effect, forming oil clusters that are quickly separated from the wastewater. The demulsified and coalesced oily sludge is returned to the front-end three-phase separator for secondary treatment, while the treated wastewater enters downstream treatment equipment for further processing.
3. Produced Fluid Treatment Effectiveness Analysis
After the new CDFU treatment equipment was put into operation, the oil-water separation efficiency of the produced fluid improved significantly, and the appearance of the treated water was greatly enhanced. Taking the produced fluid treatment project at an offshore oil platform in the Bohai Sea, China, as an example, the comparison of the main water quality parameters for the inlet and outlet water is shown in Table 1 and Figure 2 below.
Table 1: CDFU Operation Detection Data Table
Figure 5: CDFU Operation Detection Data Chart
