Emergency relief discharge from a chemical reactor or a process storage vessel will often need treatment before it can be vented to atmosphere. The discharge of flammable and/or toxic materials can create fire and explosion hazards as well as toxicity hazards both on site and off site. Potential environmental impact can also lead to large cleanup and restoration costs. Two-phase discharges are more challenging than all other vapor discharges.
Two-phase discharges can lead to the formation of aerosols and heavier than air clouds. More mass is airborne and as a result the resulting dispersion footprints are larger. Rainout of toxic and/or flammable materials (small liquid droplets) can occur near the release point and/or downstream of the release point.
Two-phase relief from chemical reactors and process vessels must be discharged to a safe location. This can be particularly challenging for plants that are congested and/or that are near population centers. Although it is possible in some cases to eliminate two-phase relief by design or to discharge a two-phase effluent directly to the atmosphere, the use of vent containment can provide a more versatile approach to reducing two-phase relief risks.
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