The Logic Behind The Magic."Reject Oil Tank and pumps

The reject oil vessel receives recovered oil from the produced water hydrocyclone and vessel. Reject oil  pump is provided to transfer oil from the reject oil collection vessel back to the separator. The pump speed is regulated to maintain oil level in the vessel.

The control loop is typical with produced water treater vessel
Pressure Indicating Controller.
The PIC maintains a constant pressure in the reject oil vessel at set point by actuating control valve gas inlet from separator and valve in hp flare line to release excess pressure.

As the pressure falls below setpoint the controller shall open the control valves in separator gas outlet and close the control valves in HP flare to increase the pressure. The valve in separator gas outlet is fail closed type and the valve in HP flare is fail open type. The controller output shall be direct and control valve "OPDIR" is direct for the valve in separator gas outlet and reverse for the valve in HP flare.

 Level Controller
The controller maintains a constant liquid level in the reject oil collection vessel by regulating the speed of reject oil pump. The level controller shall be direct acting. When high or low liquid level threshold is reached. The alarm shall be displayed on the HMI