Study on the gas dissolution performance and bubble generation characteristics of a jet flow type pressurized tubular microbubble generator

Microbubble generation technology has the potential to significantly enhance the separation efficiency of offshore oilfield produced water flotation treatment devices, which currently display unstable performance. In this study, we developed a jet flow type pressurized tubular microbubble generator, comprising a jet-dissolved gas tube (JDGT) and a standard ball valve. The JDGT was designed based on the principle of intensifying bubble breakup through jet nozzles and enhancing gas dissolution via up-down circulation vortex. We proposed an innovative Computational Fluid Dynamics (CFD) model that utilizes User Defined Functions (UDF) to predict the flow pattern and dissolved oxygen (DO) distribution within the tube. The relative error between numerical simulations and experimental results was 5.25 %. Under identical operating conditions, the JDGT can efficiently produce gas-dissolved water in 3.5 s, achieving a dissolved gas efficiency of 80.24 %, compared to 58.31 % for a conventional jet vertical vessel with a hydraulic retention time of 30 s. High-quality microbubbles can be generated through decompression via a standard ball valve. The oxygen volumetric mass transfer coefficient increases with the inlet water flow rate, the gas–liquid volume ratio, and increased dissolved pressure. As the inlet water flow rate increases, the Sauter mean bubble diameter initially increases before decreasing. Both the gas–liquid volume ratio and dissolved gas pressure are exponentially related to the Sauter mean bubble diameter. An engineering prototype with a treatment capacity of 35 m³/h was successfully field-tested on a platform in the South China Sea. The test results indicated that when the microbubble generator was connected to a vertical air flotation unit with a 10 % reflux flow system, the average oil concentration at the unit’s outlet was 13 mg/L. The calculated average oil removal efficiency was 72.38 %, which is 12.8 % higher than that achieved without a tubular microbubble generator.