Q. What do you mean by Flares and Vents?
A vent is a potential gas fuel source and a potential liquid fuel source due to carry-over from the vent. This is also true for a flare, if the pilot fails. An adequate scrubber and knock-out drum should be provided for all flares and vents to minimize the possibility of liquid carryover.
Both flares and vents may become potential sources of toxic vapors. Dispersion of gases from vents must not create a problem with air intakes for turbines.
The potential danger from radiant heat from a flare, as well as from accidental ignition of a vent, should be taken into account for all potential wind directions.
Flares, engine exhausts and other similar ignition sources shall be located to avoid ignition of normal or accidental gas releases; downwind from safe areas. Use of dispersion calculations should be considered.
The height of elevated flares is also determined by the radiant heat calculations. Noise from and visibility of, the flare needs to be considered when positioning the unit relative to the property line. Flare and vent systems shall comply with API Std 521 (Guide for Pressure-relieving and Depressuring Systems) or equivalent. The radiant heat intensities or emissions from flares and vent systems shall not exceed the following limits:
• 6.3 kW/m2(2000 Btu/hr/ft2) in areas where emergency actions lasting up to one minute may be required by personnel without shielding but with appropriate clothing 4.7 kW/m2(1500 Btu/hr/ft2) in areas where emergency actions lasting several minutes may be required by personnel without shielding but with appropriate clothing. 6 kW/m2(500 Btu/hr/ft2) at any location where personnel are continuously exposed
• Temperature rating of electrical and mechanical equipment
• 50% LEL (Lowest Explosive Limit) at any point on the installation where the gas plume from a vent could be ignited or personnel could get into contact with the gas. The most unfavorable weather and process conditions have to be taken into consideration when calculating heat radiation and dispersion.
The limits above also apply to abnormal conditions (e.g. flame out of flare system and accidental ignition of vent).