The structure design and offshore oilfield experiment study of industrial compact flotation unit

Abstract

The Compact Flotation Unit is widely used in the offshore oilfield produced water treatment based on the characteristics of relatively small footprint and high oil removal efficiency, but the structure details of the Compact Flotation Unit have been rarely described up to now. Few literature is talking about the Compact Flotation Unit design process and systematically analyzing the influence of operating parameters on the oil removal efficiency, especially on the large-capacity industrial-level Compact Flotation Unit products. In this paper, the working principle and structure design process of the Compact Flotation Unit from Beijing Institute of Petrochemical Technology cooperated with China National Offshore Oil Corporation Research Institute were systematically introduced. Furthermore, the single-stage Compact Flotation Unit from Beijing Institute of Petrochemical Technology of industrial scale with a treatment capacity of 120 m³/h was manufactured and tested on floating production storage and offloading unit located in the South China Sea. When the inlet average oil content was 280.3 mg/L, the outlet average oil content was 39.9 mg/L, and the corresponding average oil removal efficiency was 85.8%. The flow split ratio, back pressure, and inlet flow rate have a significant impact on the oil removal efficiency, while the effect of the gas-liquid ratio and outlet water recycle ratio are not sensitive. The main reason can be attributed to the dissolved gas components in the produced water. A large quantity of microbubbles is generated after depressurization which directly participates in the flotation process. Besides that, the single-stage Compact Flotation Unit prototype can tolerate the fluctuation of inlet flow rate and oil content.