(363i) CFD Modeling of Gravity Separator with PID Interface Controller

In many industries, gravity separators play an essential role as low-cost solution separating produced fluid mixtures. Efficient separation is of critical importance to achieve the desired production rate. Separation is accomplished by the difference in densities between the oil and water. Generally, settling by gravity needs sufficient residence time, and the control of the interface levels is important to have a reliable operation. Therefore, the design and sizing of separators can be challenging.

In this study, a two-phase Eulerian computational fluid dynamics (CFD) model was developed to investigate the efficiency of a water–oil separator. A proportional integral derivative (PID) controller logic is developed to maintain the oil/water interface levels by automatically adjusting the oil and water outlet flows, respectively. Optimizing the PID controller is essential to achieve desired interface levels in response to variations in process parameters. To optimize the PID controller coefficients, a reduced order model was created using results obtained from CFD, and the PID controller coefficients are finetuned based on this reduced order model. Optimized coefficients are validated using the CFD simulation. The CFD model results are found to be in good agreement with the plant data.