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 eventualities at tank farm fires and presented foam as probably the most appropriate extinguishing agent together with the firefighting equipment most commonly used. In Part Two we have a look at foam focus proportioning technologies, mobile extinguishing systems and conclude with lessons discovered.
NFPA eleven describes various kinds of foam focus proportioning tools. In the following, three systems are looked at that are most common. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning fee must not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning rate must 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 most of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam focus (the smaller worth must be used respectively).
To guarantee appropriate proportioning, the proportioner, together with the proportioning price must be tested at least annually 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 technology. The bladder tank is a pressurized vessel with a bladder inside which is filled with foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the froth concentrate from the bladder as required. The bladder is connected to a proportioner which operates using the venturi precept. When the fire pumps are activated, pressure is generated by the pump, causing delivery of foam concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the froth concentrate into the extinguishing water flow.
The advantages of this technique are its easy design without moving components and its easy operation. No exterior power is required, and the system is relatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding laws similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system should be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam concentrate. At a given proportioning fee, the system is suitable only for low variations within the extinguishing water circulate strain and volume. Adding or changing particular person foam discharge gadgets is feasible only to a really restricted extent. The system can be unsuitable for proportioning extremely 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 should 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 must be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the foam focus, an electric or diesel-powered foam focus pump with an electronically controlled valve and a move meter within the extinguishing water move line. When the hearth pumps are activated, the froth focus pump drive and electronic management system have to be activated. The extinguishing water circulate price is measured by the move meter and the control system adjusts the proper foam concentrate amount via the control valve. The foam concentrate is injected into the extinguishing water circulate by the froth concentrate pump. If there’s a change within the move rate, the quantity of injected foam concentrate is regulated by the management valve.
The system’s advantage lies in the precise proportioning of the froth focus, impartial of the extinguishing water pressure or move price. Foam focus may be topped up in the course of the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system must be activated; nevertheless, the delivered foam concentrate can be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate flow price. No premix is produced; and as the foam concentrate is handed back into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an exterior interruption-free energy provide for the foam focus pump and the control system, as properly as the need for a complicated control system and the comparatively higher buying prices. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water flow fee and the newly adjusted foam focus amount. The foam high quality may be compromised when constantly changing operating conditions as foam discharge gadgets are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam focus, a water motor put in within the extinguishing water flow line and a foam concentrate pump which is related directly to the water motor. Water motor and pump kind one compact unit. Upon activation of the fireplace pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump offers immediate foam-concentrate injection into the extinguishing water. If the flow price adjustments, the amount of foam concentrate is adapted immediately.
The advantage of the system is its independence from external energy sources in addition to a precise and immediate foam-concentrate proportioning regardless of the extinguishing water stress or flow rate. If a piston or plunger pump is used, adjustment or calibration after installation isn’t needed since the water motor and the pump are volumetric devices firmly related to each other. Foam concentrate refilling throughout operation is possible. The system is also capable of proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nonetheless, the delivered foam concentrate can be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate flow price. No premix is generated; and if the froth concentrate is handed again into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively larger purchasing costs are a disadvantage of the system.
With any system, consideration must be taken under consideration for the annual testing prices, which can be appreciable when it comes to replacement foam focus, disposal of premix and labour costs.
Mobile extinguishing methods
As the stationary foam discharge tools may be broken in extensive fires within the tank or within the dyke space and thus lose effectiveness, cellular fire screens and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they’ve only restricted extinguishing agent move charges and reaches.
Firefighting screens
Firefighting monitors are discharge devices mounted on vehicles or trailers and available in many sizes. The extinguishing agent circulate price could be up to 60,000 litres/min and the reach could be as much as 180m if the pressure of the fireplace pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a surface fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank to find a way to prevent it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke area ought to always be observed to avoid an overflow of the dyke.
Mobile hearth monitors could be supplied either by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the foam focus normally takes place through mobile proportioners. This clearly points in course of the advantage of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cell units available as back-ups is proven by the following instance for the position of monitors for hearth extinguishing at tanks which are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This leads to a number of alternate options for the screens. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which should have the ability to handle varying circulate charges to ensure flexibility during extinguishing operations. Depending on the native circumstances, the screens might need to keep a minimal distance to the burning tank or might not be able to be positioned close to to the tanks as a outcome of particles. In addition, it will not all the time be potential to position several monitors across the tank. It must be ensured the monitor has enough throwing top in relation to the tank height, to deliver foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal rules in addition to recommendations by associations like NFPA and isn’t looked at more intently within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As mentioned within the introduction to Part One of this text, plainly many authorities and companies haven’t discovered the necessary lessons from disastrous fire incidents of previous years. Tank farm fires in the oil and petrochemical business do not occur incessantly. When they do, they usually have devastating penalties. Let us keep in mind the tank farm fire 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 fireplace for but unknown causes. The plant had no gas warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fastened extinguishing systems installed. All 15 tanks had been surrounded by one single dyke. เกจวัดแรงดันpcp had relied on the native hearth service, which was on the spot very quickly however could not take management over the hearth with the equipment available, partially as a result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire had damaged out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of equipment and foam focus as nicely as the preparation of a plan of action took approximately 13 hours. The fire was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt were made over three days, with foam concentrate and water shortages occurring within the meantime. In complete, over 500,000 litres of froth focus were used. Instead of a fireplace in the dyke area, 11 of the 15 tanks burnt down.
It may be very possible that the fire would have been extinguished quickly if the warning techniques and valves had labored and a fixed hearth extinguishing system had existed. It can also be possible that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded finally, had been began earlier. Both instances would have resulted in notably less injury.
Summing up, the following points should be realized as a minimum. As far as they have not but been implemented, or simply partly, they want to function a foundation for discussions about one’s own fire-protection concept:
Have an acceptable fire-protection concept including various scenarios which adapt to the given scenario frequently.
Always have a sufficient variety of cellular extinguishing systems as a backup to fixed extinguishing techniques.
Stock a suitable foam concentrate.
Ensure sufficient foam focus provide.
Ensure sufficient water supply.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing equipment obtainable in a enough number.
Have educated personnel out there in a sufficient number.
Ensure a quick implementation of an appropriate plan of motion.
For more data, go to www.firedos.com
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