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Cfd as a feature to optimize vacuum towers

INTRODUCTION

A study was performed to verify the refinery vacuum tower feed inlet device modifications, comparing actual configuration to a future proposal.

The study was based in a comparison between the two configurations of tower internals and a verification of the best feed nozzle angle.

Two configurations was tested with a 42" nozzle diameter: one with a penetration angle of 135° and another one with a penetration angle of 235°.

MODELING AND SIMULATION

The following condition have been used:

  • Two Fluid Model:
    1. Continuous Phase: Vapor
    2. Dispersed Phase: Liquid (Φ=100 μm)
    3. Independent Velocity Fields
  • Isothermal Model
  • Turbulence Models:
    1. Vapor : k - ε
    2. Liquid: Dispersed Phase Zero Equation
SLOP WAX COLLECTOR VELOCITY DISTRIBUTION

It must be noticed that the vapor maldistribution tends preferentially to take the streamlines to the north, northeast and the northwest region of the tower below the slop wax collector.

Despite the presence of the bed and wax collector the CFD study shows us that the vapor distribution was not uniform on the feed nozzle.

The preferential flow in the north region confirms a practical observation (present feed nozzle). This region is the hottest through the tower.

The future feed nozzel tend to avoid nonuniform vapor distribution and liquid entrainment.

CUSTOMER

Petrobras - Brazil

CONCLUSIONS

We can conclude that the high liquid entrainment level found in the refinery vacuum tower simulation is due to the high vapor speed in the flash zone, mainly in the inlet nozzle.

We can notice a better vapor distribution in the future feed nozzle of the refinery vacuum tower, it should reduce corroded regions.

Even with the vapor high velocities, the future feed nozzle concept do not allow liquid entrainment.