Fire Protection System for Sphere Tanks

Rayan H. Al-SuraihiBachelor of International Business Administration.Saudi Aramco ExxonMobil Refinery (SAMREF)Fire ChiefWork experience 14 years in Fire field.Aramco - Petro Rabigh – SamarfCertified Fire instructor from Texas A & M University, United States.

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Overview:

• Key Features of a BLEVE.

• Fire and Special Safety Systems.

• Gas detectors system.

• linear heat detectors.

• Water Spray system .

• Water Injection System.

LPG

Definition :

• Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), also referred to as simply propane or butane, are flammable mixtures of hydrocarbon gases used as fuel in heating appliances, cooking equipment, and vehicles. AS its boiling point is below room temperature, LPG will evaporate quickly at normal temperatures and pressures and is usually supplied in pressurized steel vessels.

Storage :

• In a refinery or gas plant, LPG must be stored in pressure vessel These containers are either cylindrical and horizontal or spherical.

When a tank containing LPG is exposed to an external fire, the hot content inside the tank causes an excessive increase in tank pressure opening the pressure relief valve and allowing the compressed gas to leak out.

The volume of the liquid inside the tank decreases while the volume of the empty dry part of the tank expands over the level of liquid inside the tank. In this case, the liquid begins to boil and the gases expand, which may cause the explosion.

BLEVE Overview :

Vessel Damaged

Vapor Cloud Exposed by Pressure Relief

Vessel Damaged Due to Corrosion

Vessel Damaged By Hot Temperature, Exposed By

External Fire

Key Features of a BLEVEKey Features:• Flame impingement or radiant above liquid level .• Success of pressure relief valve does not prevent BLEVE.• Sudden and catastrophic destruction of the vessel- mechanical failure

of vessel.• Impulse overpressure wave.• Fireball far larger than the vessel rising into the air creates immense

radiant heat for large distances.• Large vessel fragments can travel long distances in unpredictable

directions.• Delay between onset of fire and BLEVE occurrence:

o Gives firefighters a chance to prevent BLEVE.o Creates the opportunity for a large number of onlookers to gather at

unsafe distances.

BLEVE Video

Beaumont Refinery had a BLEVE in the 1970’s:

This was from a C4 Scrubber on Gas Plant. Flame impingement on scrubber caused vessel to BLEVE Had it been a large LPG sphere, it would have been worse.

Gas Detectors System:

Sphere tanks will be surrounded by two types of gas detectors :

• Open-path IR detectors:

IR Beam Sender and receiver station are Surrounding the tank on ground level and all four direction.

• Point detectors:Located on tank bottom and near tank PSV at the top.

Linear heat detectors:

Two-core cable terminated by an end-of-line resistor The two cores are separated by a polymer plastic, that is designed to melt at a specific temperature which causes the two cores to short and correspondingly send alarm signal to fire panel .

The cable will be rapped on tank surface.

Water spray system:An automatic or manually actuated fixed pipe system connected to a water supply and equipped with water spray nozzles designed to provide a specific water discharge and distribution over tank or vessel.

Operating mechanism:

• Automatic (By linear heat detectors):

The water spray system will be activated when liner detector melt at the designed temperature. Sequentially , A signal will be send to solenoid valve to actuate deluge valve and discharge water into spray system.

• Manual :

When gas detectors detect flammable gas at the area an alarm signal will be received on distributed control system (DCS) notifying the console operator . The operator will have the option to activate the spray system on the individual tank via pushbutton at control panel.

Water Injection System:

it is a dry pipe connected from tank bottom and fitted with valves and hose connection allows firefighters to pump fire water into sphere tank via fire apparatus . By pumping the water with higher pressure than the tank will fill the tank with water and increase its level till reach to leaking point.This operation will convert a gas leak into a water leak

stopping vapor production and providing time to mitigate the incident.

Thank You