EnginSoft Partnership
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Numerical simulation of demister equipment for application in gravitational separators

MIST-ELIMINATOR = DEMISTER
  • Internal devices designed to collect liquid droplets from gaseous streams:
    1. Used in separators, columns, etc;
    2. Avoids losses of liquid material;
    3. Protects the gas stream equipment from hydraulic damage.
  • Usually designed using manufacturers tables/formulas:
    1. These tables/formulas work with averaged and ideal conditions;
    2. Average velocities, droplets diameters, gas flow homogeneously distributed, etc.
  • Vane Pack and wire-mesh models:
    1. Different ranges of liquid loads, velocities and (mainly) droplets diameter.
VANE-PACK MIST ELIMINATOR
  • Vanes forming tortuous "paths"
  • Particles collide against walls (inertia)
  • Good efficiency for large droplets
  • Can be used in series with the wire-mesh model
WIRE-MESH MIST ELIMINATOR
  • Wires forming a mesh with high void fraction and high surface (contact) area
  • Small particles collide against the wires and are collected
  • Good efficiencies for small droplets
OBJECTIVES

Create a methodology to simulate such equipment:

    1. Preview the actual efficiency of the device;
    2. Acquire detailed information on the gas/liquid distribution over the demister surface;
    3. Compare with manufacturers data.

Simulate the equipment for a given separator geometry:

    1. Horizontal and vertical separators;
    2. Horizontal and vertical demister configurations.

Wire-mesh demister only!

MODELING

Demister modeled as a thin surface using the "porous jump" condition:

    1. Behavior similar to a porous media;
    2. Good approximation for thin porous equipment.

Efficiency calculated locally (per control volume) via UDF!

    1. Using local conditions (gas velocity, droplet diameter, etc.);
    2. "Raffles" the particles collected based on local calculated efficiency!
    3. Stores on demister volumes information of number and mass of droplets collected and the averaged collected diameter.
CUSTOMER

Petrobras - Brazil

CONCLUSIONS

Methodology available!

  • Calculates the "local" efficiency – local flow/droplet properties!

  • Manufacturers correlations adapted for local variables and to consider efficiency reduction for velocities higher than the ideal value.