PETROLEUM FIREWATER SYSTEMS DESIGN

Fire-water systems shall be installed on petroleum Plant to cover the fire-water needs of each plant. This document describes the minimum facilities and fire-water capacities required to meet the statuary requirements.

The permanent systems used for protection of equipment usually consist of a combination of deluge, water sprays and fixed monitors.

·         A water deluge system is one in which all the water is applied at the top of the vessel and allowed to run down the sides.

·         A water spray system uses many nozzles arranged in a grid pattern to distribute the water evenly over the vessel.

·         Fixed monitors are permanently connected to the fire-water grid system and directed at the protected unit.

·         Gas Turbines/Compressors/Expander

Gas turbines/compressors/expander packages are not water protected as the units are enclosed and protected by CO₂ total flooding systems.

·         Vessels

All vessels containing hydrocarbon liquids are water protected including their supporting skirts.

·         Drain System

Closed Drain Drum is deluged as well as the Closed Drain Pump.

·         Compressor Discharge Coolers

Compressor discharge coolers are not water protected as those coolers are air cooler type and contain little or no liquid.

·         Overhead and Bottoms Air Coolers

Liquid filled coolers are water protected; those with condensing liquids are not water protected.

·         Emergency Generator

The driver of the Emergency Diesel Generator and its feed vessel will be deluged only if fire is detected in its area. A dedicated deluge valve shall be provided for the skids.

·         Pressurized LPG Spheres

Each LPG storage sphere shall be protected either by a water deluge system or water spray system, to protect against pool-fire exposure, supplemented by fixed monitors.

Fire-water Flow Rates

The minimum flow rates used in determining the total fire-water flow rate are shown in Table

Flow is initiated only in the zone(s) where the fire is detected. In the remaining zones, flow can be initiated manually. Fixed sprays or deluge cover equipment and critical valves. Monitors and hydrants operation is manual.

SPRAY NOZZLE SELECTION

The spray nozzle shall be effective at the minimum discharge pressure given in NFPA 20 of 40 psig. In general spray nozzles are fully effectively from 50 psig upwards (3.5 barg).

For example: D3 Protect spray Nozzle No. 21, K = 25.9 @ 3.5 barg

Q =    Flow rate, 48.5 litter/minute

P  =    Pressure, bar

K =    Nozzle constant (by vendor)

Litters / minute

Contractor shall fully design the actual fire-water network in detail engineering and all assumed parameters in this document shall be recalculated to give the optimum fire-water system.