Dear Sajit,
In such cases, you can try application of insulation on external surfaces of the vessel. This will retard the fire exposure.
The following things may be noted...
In India, both BPCL and IOCL have horton sphere for LPG storage.
IOCL Horton spheres are insulated and provided with fire water sprinkler
system. In case of fire, the water from sprinklers will wet the insulation
and
consequently, the fire exposure will be less.
In BPCL, there is no insulation.
The PSV sizes differ tremendously in IOCL and BPCL horton spheres. The PSV capacity in BPCL horton spheres are much bigger.
'Hope it helps.
Regards
Chakra
-----Original Message-----
From: sviswan@technip.com [mailto:sviswan@technip.com]
Sent: Wednesday, February 27, 2008 12:17 PM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] Fire case flow rate through a vent with a flame
arrester
A rectangular atmospheric pressure, diesel fuel tank of 4 independent compartments of 50 m3 each has 2 nos of NPS 4 size vents on each compartment, with same size flame arresters on each of these vents. The tank is installed on an off-shore platform and supplies diesel to the turbines.
The intent of the flame arrester is to prevent, a flame from an external fire, from entering the vapour filled tank volume.
The vents are sized for a nominal flow of 30 Kg/h.
In the event of an external fire in the vicinity of the tank the resulting vapour flow rate is expected to be of the order of 12000 kg/h.
The vent has been sized to NPS 4 to accommodate this fire case flow also. For the fire case it is sized on similar lines as that of a PSV discharge, allowing the higher velocities.
The flame arrestor vendor has expressed reservations on the 12000 kg/h (Kilograms per hour) flow rate. But has not given a conclusive answer, such as the one desired by the process engineer. The process engineer wants to know, under the 12000 kg/h flow, what would be the resulting pressure drop across the arrester. If this is in excess of the tank's MAOP, then he will do a resize of the vent. That is not easy either as things have gone far into the job where a change of nozzle size will be difficult.
I am also told that other safe guarding means for the fire case, such as a pressure relief valve is not feasible based on other considerations.
Sajit
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[Non-text portions of this message have been removed] Received on Wed Feb 27 02:45:00 2008
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