Dried cracked gas from the Gas Dryers is chilled against -11ºC propylene refrigerant and is fed to the HP Depropanizer. Normally-no-flow vent streams enter into the top of the column. The HP Depropanizer is operated to meet the C4 and heavier specification in the tower overhead stream. The top of the HP Depropanizer contains a mist eliminator and sufficient disengagement height to eliminate entrainment and serve as a knockout drum for the final stage of the Process Gas Compressor. A significant portion of the C3s is *allowed to leave in the bottoms* product to reduce the bottoms temperature. This allows the tower to be re-boiled with quench water instead of steam.

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