ABSTRACT
The design of a separator is a very extensive and stepwise procedure. Overall, the most important thing is knowledge about the entire system and the present case, which is most likely a unique one. This starts with the determination of the characteristics, composition and fluid properties of the crude petroleum, water and other impurities in the mixed well stream. Additionally, the phase behaviors need to be clearly understood for the phase separation afterward. Fluid samples are sources, that are more reliable than mathematical approaches and therefore, they are crucial in order to come up with valid input parameters, which are the basis for a proper result of the design in the end. The detailed application and configuration for the desired task and function of the separator needs to be clarified in advance and for this and the present media, the ideal operating conditions need to be determined in the laboratory.
All these parameters are then considered and included in the sizing procedure of the pressure vessel and its inlet, gravity settling, liquid collection and mist extraction sections. As presented in detail, this process is based on the gas and liquid capacities and governed by the droplet settling theory and liquid retention times. While the former can still be perfectly described by Archimedes’ Principle and Stokes’ Law, the latter need to be estimated in the laboratory, measured in a test separator or determined by means of particle tracking in computational fluid dynamics simulations. With the seam-to-seam length and diameter, being the outcome of the sizing and the defining dimensions, the wall thickness of the pressure vessel can then be designed according to the ASME code.
Sloshing and slugs, foaming, liquid carry-over, gas carry-under, wax appearance, sand, corrosion and emulsions are all possible issues, which can occur during the lifetime of the field and the separator. Therefore, it is important to prevent or at least counteract and mitigate the effects of those undesired happenings by means of internals. Health, safety and environment, including safety elements and waste management of the accruing and undesired byproducts, have to be considered as well.
To sum up, the motto Garbage In, Garbage Out, mentioned at the very beginning, definitely applies to the separator design and therefore, it is essential to determine and define all the input parameters as good as possible at the start. Computational fluid dynamics is a strong design tool that can be used to optimize and improve the separator design and the efficiency of the separator itself. On the one hand, opensource software solutions as SALOME, OpenFOAM and ParaView can be used, however, high expertise is required to implement all the details in order to come up with useful and insightful results. On the other hand, commercial programs as ANSYS would be simpler for companies to use, since an ANSYS training center is available for support.
