Real-Time Automatic Operation and Optimization of Produced-Water Treatment

Abstract

In general, the operation of produced water treatment systems is often based on manual sampling, visual observations, operator judgment and manual tuning by operation of valves. Work has been conducted to automate the operation of a Compact Flotation Unit (CFU). The objective was mainly to reduce the overall amount of discharged of Oil-in-Water (OiW). As discharge peaks often govern the overall OiW percentage in discharge, a real-time operated and optimized CFU system could immediately detect and reduce the effect of such peaks. Furthermore, the waste generated and utility consumption should both be reduced. The CFU operation would not require operating personnel which is an absolute requirement for an unmanned installation or subsea operation. The work was conducted in a produced water test rig. Manual sampling and visual observations were successfully replaced with online analyzing- and flow measuring technology. This replacement ensured better process overview and allowed implementation of Integrated Operations (IO) philosophy. Advanced control algorithms for real-time CFU operation and optimization were developed based on implementation of this technology. The work has resulted in a new automatically operated CFU system. Testing in the produced water test rig met the goals: increasing OiW content was detected and effective corrective actions were taken without the need for operating personnel. In addition to reducing the OiW content, the waste generation and utility consumption were simultaneously minimized.

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

“…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.…”

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

“…These relationships helped them to develop a control system for CFU that optimizes separation efficiency and reject flow rate, and minimizes flotation gas usage using an automatic empirical approach. 5 However, to the authors' knowledge, there has been no analysis of CFU operation based on modelsa gap we fill in this paper.…”

“…14 At the top of the CFU, the collected oil and gas along with some water is removed through the reject stream. The liquid flow in the reject stream at the top is typically maintained at around 1% of the incoming water flow, 5 and the purified water typically has an oil concentration below 30 ppm.…”

“…Due to a low residence time in compact separation equipment and due to several degrees of freedom in operation, these compact systems, in comparison to conventional separation technologies, are more difficult to operate, and require more advanced control strategies. , Control of CFUs has been studied experimentally by Asdahl and Rabe and Arvoh et al, , who analyze the effect of changing the reject valve position and CFU pressure on gas and liquid reject flow rates. These relationships helped them to develop a control system for CFU that optimizes separation efficiency and reject flow rate, and minimizes flotation gas usage using an automatic empirical approach . However, to the authors’ knowledge, there has been no analysis of CFU operation based on modelsa gap we fill in this paper.…”