Online estimation of reject gas flow rates in compact flotation units for produced water treatment: A feasibility study

Abstract

The largest waste water stream from oil and gas production wells is referred to as produced water (PW). One way of treating PW to limits acceptable for discharge into sea is by the use of compact flotation units (CFU). Currently, CFUs' are operated manually due to lack of advanced monitoring solutions. The main areas of interest in the current operation of the flotation unit are to provide online measurements of both liquid and gas flow rates through the reject stream of the flotation unit. A full scale feasibility study on the application of acoustic measurements and partial least squares regression as a tool for online estimation of the reject gas flow rate was investigated. From the experiments conducted to determine the optimal sensor location, it was concluded that there were no significant differences between the four sensor locations investigated. Several reject gas flow rate models were calibrated and validated with fully independent data. The average root mean square error of prediction (RMSEP) was 7.5% within the experimental range (0.07–2.5 Sm3/h). The RMSEP for experiments with varying salt concentration was 0.25% (within the range of 0–5.5%) whilst that for varying temperature was 1.8°C (within the range of 30–60°C). The model for reject liquid flow rates through the CFU had a RMSEP of 16.86l/h (within the range of 225–485l/h). These promising results will form the basis for further development and implementation of the technique in flotation units.