Simplified First-Principles Model of a Compact Flotation Unit for Use in Optimization and Control

Abstract

In this paper, we develop a simplified control-oriented model of a compact flotation unit (CFU), which removes residual oil from produced water in oil and gas production systems. CFU is a class of separators that exploits the synergy between separation effects of a swirling flow and the effect of flotation, in which small gas bubbles attach to the oil droplets, and float to the top of the separator, where they are removed. The purified water flows downwards, and is removed from the bottom. Our CFU model consists of a simplified initial swirl separation part, and a flotation part, in which populations of oil droplets, gas bubbles without oil droplet, and gas bubbles with oil droplet attached are tracked spatially. After analyzing the model, we use it as a basis for designing a control structure that operates the separation system optimally.

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

“…29 Performing gas flotation in single mode would result in disadvantages: in IGF systems, the oil droplets much smaller than 100 μm may escape flotation, while in DGF systems, the oil droplets larger than 100 μm cannot be floated. 30 Vertical vessels are usually preferred, because they require less space and are less affected by wave motion. The retention time is typically less than 1 min.…”

“…Illustration of bubble generation during DGF. This figure was reproduced with permission from ref . Copyright [2019 American Chemical Society.…”

Optimal Operation of a Subsea Separation System Including a Coalescence Based Gravity Separator Model and a Produced Water Treatment Section

“…In this paper, we used a simplified first-principles based CFU model, developed by Das and Jäschke. 33 Other control oriented models for CFUs in the literature are data driven.…”

“…These variables are ppm out CFU , α gas top , and P CFU . We propose to pair P CFU and ppm out CFU with F reject and F float , respectively. The remaining degree of freedom F out is used to control the gas hold up at the top α gas top .…”

“…In this paper, we used a simplified first-principles based CFU model, developed by Das and Jaschke. 33 Other control oriented models for CFUs in the literature are data driven. Please refer to Arvoh et al, 34 Arvoh et al, 35 and Asdahl and Rabe 36 for an overview of data driven models for CFUs and their uses.…”