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

Part One of this text described the standard incident situations at tank farm fires and introduced foam as essentially the most appropriate extinguishing agent along with the firefighting gear most commonly used. In Part Two we take a glance at foam concentrate proportioning applied sciences, mobile extinguishing methods and conclude with classes discovered.
NFPA eleven describes varied forms of foam concentrate proportioning gear. In the following, three methods are looked at which are most common. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning rate should not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning fee should not exceed 30% above the permitted worth 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 maximum of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller value should be used respectively).
To assure appropriate proportioning, the proportioner, together with the proportioning rate should be examined no much less than every year and its right functioning should be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a proven and cost-effective technology. The bladder tank is a pressurized vessel with a bladder inside which is crammed with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the froth focus from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi precept. When the hearth pumps are activated, pressure is generated by the pump, causing delivery of froth focus to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water flow.
The benefits of this system are its easy design with out moving parts and its straightforward operation. No exterior vitality is required, and the system is relatively inexpensive.
A disadvantage is that the system is a pressurized vessel subject to corresponding regulations similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system have to be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam focus. At a given proportioning price, the system is suitable just for low variations within the extinguishing water circulate pressure and volume. Adding or changing particular person foam discharge units is possible solely to a very limited extent. The system can additionally be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system have to be activated and premix generated on the venturi proportioner inside the extinguishing water line. The appropriate proportioning price have to be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus in the bladder tank needs to be replaced.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam concentrate pump with an electronically managed valve and a move meter in the extinguishing water circulate line. When the fireplace pumps are activated, the froth focus pump drive and digital management system should be activated. The extinguishing water circulate fee is measured by the circulate meter and the management system adjusts the correct foam focus quantity by way of the control valve. The foam focus is injected into the extinguishing water flow by the foam focus pump. If there is a change within the circulate rate, the amount of injected foam focus is regulated by the management valve.
The system’s benefit lies within the precise proportioning of the froth focus, independent of the extinguishing water stress or move fee. Foam concentrate could be topped up through the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system should be activated; however, 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 a end result of the foam concentrate is passed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free vitality provide for the froth focus pump and the management system, in addition to the need for a classy management system and the comparatively higher purchasing prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water move price and the newly adjusted foam focus quantity. The foam quality may be compromised when continually altering working situations as foam discharge devices are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam concentrate, a water motor put in in the extinguishing water flow line and a foam concentrate pump which is linked directly to the water motor. Water motor and pump type one compact unit. Upon activation of the hearth pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the move fee adjustments, the amount of foam concentrate is tailored instantly.
The advantage of the system is its independence from exterior energy sources in addition to a precise and quick foam-concentrate proportioning whatever the extinguishing water pressure or circulate rate. If a piston or plunger pump is used, adjustment or calibration after set up isn’t essential for the explanation that water motor and the pump are volumetric devices firmly linked to each other. Foam focus refilling throughout operation is feasible. ตัววัดแรงดันน้ำมัน is also capable of proportioning highly viscous foam concentrates. The system must be activated for annual testing; nonetheless, the delivered foam focus may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate fee. No premix is generated; and if the froth focus is passed back into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively larger purchasing prices are an obstacle of the system.
With any system, consideration must be taken into consideration for the annual testing costs, which can be considerable when it comes to substitute foam focus, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge tools could be broken in intensive fires within the tank or within the dyke space and thus lose effectiveness, cell fireplace monitors and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they have only limited extinguishing agent move rates and reaches.
Firefighting screens
Firefighting monitors are discharge units mounted on vehicles or trailers and obtainable in many sizes. The extinguishing agent circulate fee may be up to 60,000 litres/min and the reach can be as a lot as 180m if the stress of the fire pumps is sufficient. They are appropriate to discharge foam, e.g., to extinguish a floor hearth in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank so as to forestall it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke space should all the time be noticed to keep away from an overflow of the dyke.
Mobile fireplace displays may be provided both by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the froth focus often takes place through mobile proportioners. This clearly factors in direction of the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular items obtainable as back-ups is shown by the next example for the location of monitors for fireplace extinguishing at tanks which are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This results in a quantity of alternatives for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should be in a position to deal with varying circulate rates to guarantee flexibility during extinguishing operations. Depending on the local situations, the screens might need to hold a minimum distance to the burning tank or could not have the power to be positioned near to the tanks due to particles. In addition, it is not going to at all times be attainable to place a quantity of displays around the tank. It should be ensured the monitor has enough throwing peak in relation to the tank peak, to deliver foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following authorized regulations as nicely as recommendations by associations like NFPA and isn’t checked out more intently within the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned
As talked about in the introduction to Part One of this text, plainly many authorities and corporations have not discovered the necessary classes from disastrous fireplace incidents of previous years. Tank farm fires in the oil and petrochemical trade do not happen incessantly. When they do, they usually 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 half-hour and caught fireplace for yet unknown reasons. The plant had no fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fixed extinguishing systems put in. All 15 tanks have been surrounded by one single dyke. The owner had relied on the local fire service, which was on the spot very quickly however could not take control over the fireplace with the gear 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 external firefighting company to do the extinguishing work. Mobilization of apparatus and foam focus in addition to the preparation of a plan of action took roughly thirteen hours. The fire was finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts have been revamped three days, with foam concentrate and water shortages occurring in the meantime. In complete, over 500,000 litres of froth focus were used. Instead of a hearth in the dyke space, eleven of the 15 tanks burnt down.
It may be very probable that the fireplace would have been extinguished shortly if the warning methods and valves had worked and a set fireplace extinguishing system had existed. It is also possible that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably much less damage.
Summing up, the following points ought to be discovered at least. As far as they have not but been implemented, or just partly, they should serve as a foundation for discussions about one’s own fire-protection concept:
Have an acceptable fire-protection idea including alternative eventualities which adapt to the given situation frequently.
Always have a adequate number of mobile extinguishing techniques as a backup to fastened extinguishing techniques.
Stock an acceptable foam concentrate.
Ensure sufficient foam focus supply.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically placed and functioning extinguishing gear out there in a adequate quantity.
Have educated personnel obtainable in a sufficient number.
Ensure a quick implementation of a suitable plan of motion.
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