Quench water represents about 80% of the total waste streams generated from the operations of an ethylene plant. It is also by far the most polluted, containing oil, benzene, styrene, butadiene, and other volatile organic compounds (VOC). Separate waste streams such as wash water and decoking water, along with spent caustic, represent minor flows compared to the volume of quench water that is generated from ethylene cracking.
Polymers such as polyethylene are manufactured in pellet form, using ethane and propane as feedstock. The formation of pellets takes place after the resin has been polymerized via catalyst in the reactor vessel with hexane as a solvent. The product is centrifuged, washed with carbon tetrachloride, centrifuged again, washed with acetone, water washed, extruded through a pelletizer, and washed with quench water.
Quench water has a key role in pellet formation. To maintain a high quality polymer pellet, quench water must be conditioned through advanced filtration to prevent water contaminants such as sand, iron, and organic material from flashing onto the pellet surface. Poor treatment techniques can result in a lower quality pellet with reduced market value.