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    Separation solutions
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    With a no failure record,
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Designing a process system capable of separating oil, water, gas, and any solids, traditionally relies upon the application of sophisticated spreadsheets, based upon empirical information. The aim of the design is to meet the process operating conditions, by optimising the type, location and size of the internals within the vessel. These spreadsheet calculations provide fundamental information on the overall operating conditions within a separator vessel. However, the calculations also assume that the flow in the vessel is uniform in nature whereas, in reality, the flow field in the vessel will be strongly three-dimensional and highly turbulent.

To account for the true nature of the flow, therefore, Computational Fluid Dynamics (CFD) is used to simulate the flow conditions in the vessel, thereby providing greater detail and accuracy. These CFD predictions can be evaluated against the spreadsheet calculations to ensure the validity of the process design methods. Coupling the CFD solutions with Finite Element Analysis (FEA) of the mechanical design features of the separation internals enables the integrity of the systems to be guaranteed.

A CFD software package is simply a representation of the laws of physics in mathematical form so that the governing equations can be solved numerically. Visualisation software provides the means to interpret these results and understand the flow behaviour.

CFD enables the nature of the flow in the vessel to be illustrated so that the interaction between the separation internals and the different flow components can be understood. For example, introducing bubbles and droplets into the CFD model at any chosen position enables their trajectories to be predicted as they are transported by the turbulent flow through the vessel. Agreement between the CFD predictions and the spreadsheet results generates confidence in the design since this essentially provides an independent verification of the alternative methods.

Modelling the complex three-dimensional flow interactions with the vessel internals can provide a visual indication of the weaknesses in the process design. This greatly simplifies the trouble-shooting process.

To these ends, working closely with the client, we can offer:

  • Trouble-shooting
  • Design optimisation – reducing size and weight of separation equipment
  • Process optimisation – increasing capacity of separation equipment
  • Process optimisation – increasing efficiency of separation equipment
  • Evaluation of revamps - before and after studies
  • Anti-sloshing arrangements for Floating Production Units (FPUs)
  • Viability analyses
  • Feed studies.

To enhance our in-house CFD capabilities, Zeta-pdm purchased 100% of the shareholding of CFD specialist and consultancy company Flow Dynamics AS.

Case Studies

Demisting Cyclones Flow Assurance

The Zeta-pdm Ltd 4G-FD® Demisting Cyclones are designed to polish the gas prior to compression. The CFD model of these cyclones includes the swirl generation element. It is the modelling of swirl that allows the CFD model to accurately predict the droplet separation characteristics of these cyclones with the client’s process data. The inclusion of swirl raises the benchmark within the industry and renders obsolete the practice maintained by the competition of modelling cyclones as straight flow through a box.

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