Petrochemical Plant

Explore the equipment

Separate a multiphase hydrocarbon feed into gas, liquid and water, then fractionate the liquid — holding levels and pressures inside the envelope each downstream machine can tolerate.

Components

• Feed lineLN-301

  Brings multiphase feed into the train

  Normally: Steady flow at design rate

• Three-phase separatorSEP-301

  Splits gas, hydrocarbon liquid and water

  Normally: Interface and liquid level under control

• Fractionation columnCOL-301

  Separates the liquid into products by boiling point

  Normally: Temperature profile stable across the trays

• ReboilerREB-301

  Supplies heat to the column bottoms

  Normally: On duty, steam flow modulating

• Overhead condenserCND-301

  Condenses the overhead vapour

  Normally: Cooling water flowing, outlet temperature steady

• Compressor KO drumKOD-301

  Catches liquid before the gas compressor

  Normally: Empty, level transmitter live

• Gas compressorCMP-301

  Compresses separated gas for export

  Normally: Running, suction free of liquid

• Flare headerFLR-301

  Takes relieved and blown-down hydrocarbon to the flare

  Normally: Clear, purged

Operating states

• Normal Operation

  Separator on level control, column at steady profile, compressor exporting gas.

• Startup

  Levels established before heat is applied, compressor on recycle until suction is dry.

• Shutdown

  Feed isolated, inventory depressured to flare, column cooled under control.

Failure scenarios and safeguards

• MORELevel

  Feed and compressor trip before liquid reaches the compressor suction.

  Causes

  • Liquid outlet valve fails closed
  • Slug arriving from the feed line

  How it develops

  1. 01Liquid accumulates faster than the outlet can drain it.
  2. 02Level reaches the gas outlet and liquid begins to carry over.
  3. 03Knock-out drum fills and the compressor trips on high level.

  Safeguards

  • High level tripLSHH-301

    Trips the feed on high-high level in the separator

    If it fails: Liquid continues to accumulate towards the gas outlet

  • KO drum level tripLSHH-302

    Trips the compressor on liquid in the knock-out drum

    If it fails: Liquid reaches a machine designed only for gas

  Unmitigated: Liquid enters a gas compressor, which cannot compress it — mechanical damage and a potential loss of containment.

• MOREPressure

  The column relieves to flare and stays within its design pressure.

  Causes

  • Loss of cooling water to the overhead condenser
  • Reboiler duty left on with the overheads blocked

  How it develops

  1. 01Overhead vapour stops condensing.
  2. 02Pressure climbs through the column as vapour has nowhere to go.
  3. 03Relief lifts and the column vents to the flare header.

  Safeguards

  • Column reliefPSV-301

    Relieves the column to flare on overpressure

    If it fails: The column is exposed above its design pressure

  Unmitigated: The column is taken above design pressure with no relief path.