4 VENT SYSTEM
The Vent System, designed for the worst credible blow-down scenario, has been designed in order to collect and disperse the continuous or emergency gas discharges in the atmosphere by means of two Cold Vents.
Vents location and stacks height design have been based on dispersion calculations to prove that the foreseen gas rates can be released without creating explosive air/gas mixtures on the installation or in its vicinity.
Further, the possibility of an unintended ignition shall be taken into account in the design, verifying that heat radiation does not exceed the limits reported below in case of accidental ignition:
Recommended Design Total Radiation
kW/m2 (Btu/hft2 ) Conditions
4.73 kW/m2
(1500 Btu/hft2) Maximum radiant heat intensity in areas where emergency actions lasting 2 min or 3 min can be required by personnel without shielding but with appropriate clothing (*).
1.58 kW/m2
(500 Btu/hft2) Maximum radiant heat intensity at any location where personnel with appropriate clothing (*) can be continuously exposed.
(*) Appropriate clothing consists of hard hat, long sleeved shirts with cuff buttoned, work gloves, long legged pants and work shoes. It minimizes direct skin exposure to thermal radiation.
Table 4.1: Recommended Design Total Radiation Limits.
The stack has been located at one far end of the installation, as far as possible from personnel and main equipment and with due regard to the location of cranes and helideck.
The Vent System has been designed to operate within all specified criteria for backpressure, velocity, noise and erosion. It is protected against flame back (e.g. water seal, flame arrestor, purging) in case of ignition of the discharged gas.
Vent System is equipped with suitable CO2 Snuffing System to be automatically activated in case of discharged gas ignition.
Manual activation devices have also been provided.
•