Online estimation of reject gas and liquid flow rates in compact flotation units for produced water treatment

Production from oil and gas wells results in a large quantity of waste water which is referred to as Produced Water (PW). One way of treating produced water to limits acceptable for discharge into sea is by the use of a compact flotation unit (CFU). Acoustic measurements combined with partial least squares regression (PLS-R) was applied as a tool for online estimation of the reject gas and liquid flow rates from the CFU. The results from investigating the effect of varying CFU pressure showed that the CFU pressure was the dominating variation in the acoustic measurements. In the case of experiments with varying reject valve openings the results again showed that the reject valve opening was the dominating variation but in experiments with varying PW flow rate, the reject gas flow rate was the dominating variation. The root mean square error of prediction of the model validated with a fully independent data for reject gas and liquid flow rates were 0.178 Sm3/h (in the range of 0.3 Sm3/h–1.8 Sm3/h) and 47.93 l/h (in the range of 300 l/h–900 l/h) respectively. The promising results from these experiments made it clear that acoustic measurements combined with PLS-R can provide the necessary information required to automatically control these compact flotation units.

► Monitoring reject gas and liquid flow rates in compact floatation units for produced water treatment.
► Two-phase (gas/liquid) flow characterisation based on acoustic chemometrics.
► Online estimation of reject gas and liquid flow rates.
► The accurate prediction results showed a huge potential for implementing this technique on the floatation unit.