Equilibrium inside a three-phase separator from simple to complex

Understanding the functioning of every element used in industrial installations, including the oil industry, is an important target of the education process in engineering study programs. Treatment of fluids coming from a hydrocarbon well is quite complex. The first process applied to these fluids is to separate their phases (liquid and gas) so further processes can take place. In the case of the oil industry, the fluid can be further separated in heavy liquid (water and other heavy elements) and light liquid (hydrocarbons and other elements). The equipment responsible for this work is the three-phase separator. The following work presents a wide approach to a three-phase separator that covers the progression from a parallelepiped to a horizontal cylinder shape, including the use of a weir plate. A gravity three-phase mixture is simulated as two immiscible liquid and gas. The model focused on the liquid behaviour inside the tank, the movement of the gas is assumed to be at constant pressure, equal to atmospheric pressure. During this work, a comprehensive model was built using MatLab Simulink®. A horizontal parallelepiped model is used to introduce the concepts of height limits and control strategies and a horizontal cylindrical model is used to show an actual geometry. Design calculations are done using steady-state conditions and control strategies are normally introduced afterwards. However, the decision of using MatLab Simulink® is because we can introduce from the beginning the concepts of the transient phenomena, allowing the student to understand that the equations used in the design corresponding to the stable solution of the system. Nevertheless, the intention of this work is not introducing controllers to the system yet but to set the bases for their functioning as students can identify the physical limits for the variables that will be used later, such as set point and alarm levels. Validation of the model is done against a laboratory equipment at UiT campus Narvik. Results show that the model can successfully reproduce the functioning of the equipment.