Fire Protection Systems - Hydrocarbon Storage Tank Deluge Systems PDF

Fire Protection Systems • Chapter 15 OBJECTIVE 7 Explain the purpose of and describe a typical deluge water system for hydrocarbon storage yesse/s. HYDROCARBON STORAGE TANK DELUGE WATER SYSTEMS Hydrocarbon storage vessels contain large volumes of flammable material that have a potential to evolve...

Fire Protection Systems • Chapter 15 OBJECTIVE 7 Explain the purpose of and describe a typical deluge water system for hydrocarbon storage yesse/s. HYDROCARBON STORAGE TANK DELUGE WATER SYSTEMS Hydrocarbon storage vessels contain large volumes of flammable material that have a potential to evolve into a BLEVE (boiling liquid expanding vapour explosion) if preventive measures are not put in place to cool and remove the heat from a fire. Deluge systems are used to prevent these fires and explosions. Prevention of Fire It is sometimes possible to use water spray to dissolve, dilute, disperse, and cool flammable or combustible materials, thus preventing ignition. Fbced water sprays are designed specifically to provide optimum control, extinguishment, or fire exposure protection for special fire protection problems. Limitations to the use of water spray include the nature of the equipment to be protected and the physical and chemical properties of the materials involved. Hydrocarbon storage tanks can be protected by deluging the tank with water if a fire occurs in the vicinity. Fixed Deluge Water Spray Systems A water spray system is a special pipe system connected to a reliable supply of fire protection water and equipped with water spray nozzles for specific water discharge and distribution over the surface or area to be protected. The piping system is connected to a water supply through a deluge valve that can be actuated automatically or manually to initiate the flow of water. Automatic system actuation valves for spray systems can be actuated electrically by the operation of automatic detection equipment, such as heat detectors, relay circuits, and gas detectors. System actuation valves can also be actuated mechanically by hydraulic or pneumatic systems, depending on the operating mode of the individual valves. Generally, each manufacturer of system actuation valves (most of which can do dual service in deluge systems) provides its own particular combination of system actuation valve, releasing mechanism, detection system, and supervisory service. 3rd Class Edition 3 • Part A2 807 ?& Chapter 15 • Fire Protection Systems Systems Application Fuced water spray systems are most commonly used to protect equipment from exposure fires in flammable liquid and gas tankage, piping, and equipment; in electrical equipment such as transformers, oil switches, rotating machinery, and cable trays; in structural supports; and in conveyor systems and the openings in firewalls and floors through which they pass. The type of water spray required for any particular hazard will depend on the nature of the hazard and the purpose for which the protection is provided. A water spray system is designed to give complete surface wetting with a specified water density, taking into consideration the following: • Nozzle types, sizes, and spacing • Influence of wind and drafts • Probability of water rundown • Prevention of the formation of difficult-to-wet deposits ofsoot or carbon surfaces • Overlap of water discharge patterns onto the surfaces • Ability of the water supply to furnish adequate pressure to all of the nozzles In most cases, it is neither desired nor expected that a water spray be used to extinguish burning gases, such as LPG (liquefied petroleum gas). However, the cooling effect of the water on the tank may reduce and control the rate of burning until the gas supply to the fire is exhausted or it can be isolated. 808 3rd Class Edition 3 • Part A2 ?& Chapter 15 • Fire Protection Systems Internal Tank Foam Distributing Devices A prime requirement for efl&cient fuel tank extinguishment by topside foam devices is that the foam must be applied to the burning surface without undue plunging into the fuel or allowing the foam to become coated with burning fuel. This gende application of foam must be accomplished at any level of the contents of the tank. Many devices have been developed to gendy apply foam from one point regardless of burning fuel level. These devices are listed as type I foam-discharge outlets for tanks and are required for some alcohol-type foams. When foam discharge into a tank is deflected to run down the inside tank shell to the burning fuel surface, it is called a type II outlet for foam application. Central Foam Distributing Systems Central foam distributing systems are systems that consist of an enclosure that houses a foam concentrate supply tank and a proportioning device, as shown in Figure 26. The foam solution is supplied under pressure from this foam house to the piping system. The foam solution is controlled by appropriate valves so that the foam chambers with foam-makers on the burning tank receive the foam solution Figure 26 - Schematic Arrangement ofAir-Foam Protection for Storage Tanks Foam made here at chambers Foam chamber Concentrate. storage Foam solution Solution Drain" Water supply hydrant Pump (Courtesy of the National Fire Protection Association) Semi-fixed systems of similar design are more frequently used with mobile foam concentrate supply from foam trucks. The truck proportions and pumps foam solution to the pipe laterals, feeding the foam-makers from a safe location outside the dike. Fbced systems that consist of automatically operated combinations of foam spray systems and foam monitors are often installed to protect chemical processing plants. Alcohol-resistant foams are usually required in these locations. In these designs, where there may be a high fire risk, process vessels, pumps, and piping are often all included within the foam distribution pattern for overall protection. The sensing of heat by fire detectors can automatically activate the system. 810 3rd Class Edition 3 • Part A2