Use of froth for firefighting in tank farms of the oil and petrochemical business – Part 2

Part One of this text described the typical incident scenarios at tank farm fires and introduced foam as probably the most appropriate extinguishing agent together with the firefighting tools mostly used. In Part Two we take a glance at foam focus proportioning applied sciences, cell extinguishing techniques and conclude with lessons learned.
NFPA eleven describes various types of foam concentrate proportioning equipment. In the following, three systems are checked out that are most common. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning rate should not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning price must not exceed 30% above the permitted value i.e. three.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; respectively, the proportioning rate is allowed to be an absolute most of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller worth must be used respectively).
To guarantee correct proportioning, the proportioner, together with the proportioning fee must be examined no less than once a year and its appropriate functioning have to be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a proven and cost-effective know-how. The bladder tank is a pressurized vessel with a bladder inside which is filled with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is linked to a proportioner which operates utilizing the venturi precept. When the fire pumps are activated, stress is generated by the pump, inflicting supply of froth focus to the proportioner. The extinguishing water flows via the venturi proportioner. The ensuing vacuum induces the froth concentrate into the extinguishing water flow.
The advantages of this system are its simple design without shifting components and its easy operation. No exterior vitality is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic to corresponding laws such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system must be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the foam focus. At a given proportioning rate, the system is suitable only for low variations within the extinguishing water circulate stress and quantity. Adding or changing particular person foam discharge units is possible only to a very restricted extent. The system can be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated at the venturi proportioner within the extinguishing water line. The appropriate proportioning fee should be measured in the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam concentrate in the bladder tank must be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the foam focus, an electric or diesel-powered foam focus pump with an electronically managed valve and a move meter within the extinguishing water move line. When the fire pumps are activated, the foam focus pump drive and digital management system should be activated. The extinguishing water circulate price is measured by the circulate meter and the control system adjusts the proper foam focus amount by way of the control valve. The foam concentrate is injected into the extinguishing water move by the foam concentrate pump. If there’s a change within the move fee, the quantity of injected foam concentrate is regulated by the control valve.
The system’s advantage lies within the exact proportioning of the foam focus, impartial of the extinguishing water strain or move fee. Foam focus could be topped up through the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the purpose of annual testing, the system should be activated; nevertheless, the delivered foam focus may be measured via a return line. The proportioning price is calculated from the extinguishing water/foam focus flow price. No premix is produced; and as the foam concentrate is passed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free energy supply for the foam concentrate pump and the management system, in addition to the necessity for a complicated management system and the comparatively larger buying prices. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water move fee and the newly adjusted foam focus quantity. The foam quality could additionally be compromised when continually changing working situations as foam discharge gadgets are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the froth concentrate, a water motor installed in the extinguishing water flow line and a foam concentrate pump which is related on to the water motor. Water motor and pump form one compact unit. Upon activation of the hearth pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump gives immediate foam-concentrate injection into the extinguishing water. If the circulate price adjustments, the quantity of foam focus is customized instantly.
The advantage of the system is its independence from exterior vitality sources in addition to a precise and immediate foam-concentrate proportioning whatever the extinguishing water stress or flow fee. If a piston or plunger pump is used, adjustment or calibration after set up is not needed since the water motor and the pump are volumetric devices firmly related to each other. Foam focus refilling during operation is possible. The system can also be able to proportioning highly viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus could be measured via a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate fee. No premix is generated; and if the foam concentrate is handed back into the tank, no foam concentrate must be topped up.
The larger design and the comparatively greater purchasing prices are an obstacle of the system.
With any system, consideration must be taken under consideration for the annual testing costs, which may be appreciable by way of substitute foam concentrate, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge gear may be damaged in intensive fires in the tank or within the dyke area and thus lose effectiveness, cell fireplace displays and foam pipes could also be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have solely restricted extinguishing agent move charges and reaches.
Firefighting monitors
Firefighting screens are discharge units mounted on automobiles or trailers and out there in many sizes. The extinguishing agent move price can be up to 60,000 litres/min and the reach could be as much as 180m if the stress of the fireplace pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a floor fire in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank in order to forestall it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space should at all times be noticed to keep away from an overflow of the dyke.
Mobile hearth monitors could be supplied both by the extinguishing water of the stationary fireplace pumps or by mobile pumps. The injection of the foam concentrate normally takes place through cell proportioners. This clearly factors in the direction of the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular models available as back-ups is shown by the following instance for the position of monitors for hearth extinguishing at tanks that are 45m in diameter and 15m excessive.
According to เกจวัดแรงดันออกซิเจนราคา , 32,000 litres of premix per minute are required. This leads to a number of alternatives for the displays. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which ought to be ready to deal with various flow charges to ensure flexibility during extinguishing operations. Depending on the native conditions, the displays will want to keep a minimum distance to the burning tank or might not be ready to be positioned close to to the tanks because of particles. In addition, it won’t at all times be potential to place several displays around the tank. It must be ensured the monitor has adequate throwing peak in relation to the tank peak, to deliver foam into the inside of the tank.
The dimensioning of the whole firefighting system is made following legal regulations as well as recommendations by associations like NFPA and is not checked out more intently in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned
As talked about within the introduction to Part One of this text, plainly many authorities and corporations haven’t discovered the necessary classes from disastrous fire incidents of previous years. Tank farm fires within the oil and petrochemical industry don’t happen regularly. When they do, they often have devastating consequences. Let us bear in mind the tank farm hearth at Deer Park, Texas in March 2019 mentioned within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fire for yet unknown causes. The plant had no gasoline warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have fixed extinguishing methods put in. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the local hearth service, which was on the spot in a short time however couldn’t take management over the hearth with the tools obtainable, partially as a outcome of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of kit and foam focus as nicely as the preparation of a plan of action took approximately thirteen hours. The fire was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt were remodeled three days, with foam concentrate and water shortages occurring within the meantime. In whole, over 500,000 litres of froth focus had been used. Instead of a fireplace in the dyke space, eleven of the 15 tanks burnt down.
It may be very possible that the fireplace would have been extinguished quickly if the warning techniques and valves had labored and a exhausting and fast fireplace extinguishing system had existed. It is also probable that the fire would have been extinguished shortly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both circumstances would have resulted in notably much less harm.
Summing up, the next points should be discovered at the least. As far as they haven’t but been implemented, or simply partly, they need to serve as a foundation for discussions about one’s own fire-protection concept:
Have an appropriate fire-protection concept including alternative scenarios which adapt to the given situation regularly.
Always have a enough number of cell extinguishing techniques as a backup to fixed extinguishing systems.
Stock a suitable foam focus.
Ensure adequate foam focus supply.
Ensure adequate water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing tools obtainable in a enough quantity.
Have trained personnel available in a sufficient number.
Ensure a fast implementation of a suitable plan of motion.
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