Deoiling Hydrocyclones: An Experimental Study of Novel Control Schemes

Abstract

Deoiling hydrocyclones are compact, passive devices commonly used for produced-water treatment (PWT) for oil production. The oily water enters the tangential inlet of the hydrocyclone and gets separated such that cleaned water comes out as a water-reject (underflow) stream, and concentrated oil comes out as an oil-reject (overflow) stream. For control purposes, the pressure drop ratio (PDR) across the inlet and the two outlets may be kept constant to maintain separation in the presence of disturbances. However, the PDR control scheme does not effectively reject some disturbances, such as changes in the inlet oil concentration and inlet droplet distribution. This paper proposes three novel control schemes to improve the separation with the aim to limit the oil concentration at the water reject at 30 ppm. The control schemes use concentration measurements from online oil-in-water analyzers at the inlet and water-reject (underflow) outlet. Two control schemes (a feedforward and a feedback/cascade) are used as a supervisory layer to the existing PDR control scheme. The third control scheme directly manipulates the final control element (valve position) to maintain the separation of the hydrocyclones. This paper gives experimental results to validate all three control schemes when subjected to disturbances such as changes in inflow rate, inlet oil concentration, and inlet droplet distribution.