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Multiphase Desander – Separation Size and Collection Efficiency (B-FSM088)

Note: The solids separation efficiency model for a multiphase desander builds on the methodology presented for a liquid desander as detailed in post B-FSM-059. I recommend strongly to read the previous material first.

Much like the fluid throughput approach previously describe, solids separation relationship is built from hydraulic and pneumatic cyclone models. These are listed below.

Hydraulic Model

  • Based on Arterburn liquid cyclone model (reference below)
  • Same correction factors (Cn) applied as liquid model – but based on fluid mixture properties
  • Use D50 and alpha to plot graded efficiency curve and determine separation size (D98)
  • Recovery curve applied to inlet particle size distribution, then sum of recovery of each particle size provides total solids recovery and particle removal
  • Used for liquid-dominant operating regime

Pneumatic Model

  • Based on Leith-Licht relationship (referenced in Benitez below)
  • Incorporates specific geometric constants for the cyclone model
  • Uses “heavy” gas – which is fluid mixture density and viscosity
  • Sum the individual particle size collection to total recovery – then calculate D50 and D98
  • Used for gas-dominant operating regime

Multiphase Model

Flow regime determines model

  • Hydraulic model for liquid dominant
  • Pneumatic model for gas dominant
  • Use mixing rules for fluid properties

Rule-of-thumb: Wellhead desander will remove solids that settle within a production separator

  • Particles collecting at oil-water interface or passing into oil phase not captured

An example of these models will be presented in the next article.

References

  1. Arterburn, R.A. 1978. The Sizing and Selection of Hydrocyclones, FL Smidth, flsmidth.com.
  2. Benítez, J. 1993. Process Engineering and Design for Air Pollution Control. Upper Saddle River, NJ: PTR Prentice Hall.
  3. Rawlins, C.H. 2017. “Separating Solids First – Design and Operation of the Multiphase Desander”, paper 185658-MS presented at the SPE Western Regional Meeting, Bakersfield, CA, 23-27 April.
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