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

Part One of this article described the standard incident situations at tank farm fires and introduced foam as the most suitable extinguishing agent together with the firefighting gear mostly used. In Part Two we look at foam concentrate proportioning technologies, mobile extinguishing methods and conclude with lessons discovered.
NFPA eleven describes varied types of foam focus proportioning gear. In the following, three systems are checked out that are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning rate must 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 should not exceed 30% above the permitted value i.e. three.9% for a 3% foam focus 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 focus or 7% for a 6% foam focus (the smaller value must be used respectively).
To guarantee correct proportioning, the proportioner, together with the proportioning fee must be tested no less than once a year and its appropriate functioning should be checked.
เกจวัดแรงดันอากาศ with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a confirmed and cost-effective technology. The bladder tank is a pressurized vessel with a bladder inside which is crammed 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 linked to a proportioner which operates using the venturi principle. When the fireplace pumps are activated, pressure is generated by the pump, causing supply of froth focus to the proportioner. The extinguishing water flows through the venturi proportioner. The resulting vacuum induces the foam concentrate into the extinguishing water circulate.
The benefits of this method are its easy design with out shifting elements and its straightforward operation. No exterior vitality is required, and the system is relatively cheap.
A drawback is that the system is a pressurized vessel topic to corresponding regulations similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system should be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the froth concentrate. At a given proportioning fee, the system is suitable just for low variations within the extinguishing water move pressure and volume. Adding or changing particular person foam discharge gadgets is feasible solely to a very restricted extent. The system can additionally be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system must be activated and premix generated at the venturi proportioner inside the extinguishing water line. The right proportioning price must be measured in the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam concentrate within the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter in the extinguishing water circulate line. When the fire pumps are activated, the foam concentrate pump drive and digital control system must be activated. The extinguishing water flow fee is measured by the circulate meter and the control system adjusts the correct foam concentrate quantity by way of the control valve. The foam concentrate is injected into the extinguishing water circulate by the foam focus pump. If there’s a change in the move rate, the amount of injected foam focus is regulated by the management valve.
The system’s advantage lies in the exact proportioning of the froth concentrate, independent of the extinguishing water stress or circulate fee. Foam focus may be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system must be activated; however, the delivered foam concentrate can be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move fee. No premix is produced; and as a outcome of the foam concentrate is handed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free vitality supply for the foam focus pump and the management system, as well as the necessity for a sophisticated management system and the comparatively larger buying costs. Furthermore, it should be accepted that a delay happens between the change of the extinguishing water circulate fee and the newly adjusted foam concentrate quantity. The foam high quality could also be compromised when continuously changing operating circumstances as foam discharge units are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the froth focus, a water motor installed within the extinguishing water flow line and a foam concentrate pump which is related on to the water motor. Water motor and pump type one compact unit. Upon activation of the hearth pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the move fee changes, the amount of froth concentrate is customized instantly.
The benefit of the system is its independence from exterior energy sources in addition to a exact and quick foam-concentrate proportioning regardless of the extinguishing water strain or move price. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t essential since the water motor and the pump are volumetric devices firmly connected to one another. Foam focus refilling during operation is feasible. The system is also able to proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nonetheless, the delivered foam concentrate can be measured via a return line. The proportioning price is calculated from the extinguishing water/foam focus move fee. No premix is generated; and if the froth focus is passed again into the tank, no foam focus must be topped up.
The bigger design and the comparatively higher purchasing costs are a drawback of the system.
With any system, consideration should be taken into consideration for the annual testing costs, which can be considerable when it comes to alternative foam concentrate, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge tools can be damaged in in depth fires within the tank or in the dyke space and thus lose effectiveness, cellular hearth screens and foam pipes may be used.
Foam pipes are normally held by firefighters, making them very versatile. Yet they’ve solely limited extinguishing agent flow charges and reaches.
Firefighting displays
Firefighting monitors are discharge gadgets mounted on vehicles or trailers and obtainable in plenty of sizes. The extinguishing agent flow price can be as a lot as 60,000 litres/min and the reach may be up to 180m if the pressure of the fire pumps is adequate. They are suitable 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 so as to prevent it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke area should always be observed to avoid an overflow of the dyke.
Mobile fire displays could be provided either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the froth focus often takes place through cell proportioners. This clearly factors towards the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cell models available as back-ups is proven by the next instance for the location of screens for fire extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several options for the monitors. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which should have the power to deal with various flow rates to guarantee flexibility during extinguishing operations. Depending on the local situations, the displays will need to hold a minimal distance to the burning tank or could not be ready to be positioned close to to the tanks due to particles. In addition, it is not going to always be potential to position a quantity of screens around the tank. It should be ensured the monitor has enough throwing height in relation to the tank peak, to ship foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following authorized rules as properly as recommendations by associations like NFPA and isn’t checked out extra closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons realized
As talked about within the introduction to Part One of this text, it seems that many authorities and companies have not realized the mandatory classes from disastrous fireplace incidents of previous years. Tank farm fires within the oil and petrochemical trade do not occur incessantly. When they do, they normally have devastating penalties. Let us keep in mind the tank farm fireplace at Deer Park, Texas in March 2019 mentioned within the introduction.
The fire developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fire for but 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 fastened extinguishing techniques installed. All 15 tanks were surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot in a short time but could not take control over the fire with the equipment available, partially as a result of flammable substance was constantly leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of apparatus and foam concentrate as properly as the preparation of a plan of motion took approximately 13 hours. The fire was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been remodeled three days, with foam focus and water shortages occurring within the meantime. In total, over 500,000 litres of foam concentrate were used. Instead of a fireplace within the dyke space, eleven 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 set fireplace extinguishing system had existed. It can be possible that the fire would have been extinguished quickly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both cases would have resulted in notably much less injury.
Summing up, the following factors ought to be discovered at least. As far as they haven’t yet been applied, or simply partly, they should serve as a basis for discussions about one’s personal fire-protection concept:
Have an acceptable fire-protection idea including alternative eventualities which adapt to the given situation regularly.
Always have a enough number of mobile extinguishing methods as a backup to mounted extinguishing systems.
Stock a suitable foam focus.
Ensure enough foam focus supply.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically placed and functioning extinguishing tools out there in a adequate quantity.
Have skilled personnel available in a enough quantity.
Ensure a fast implementation of an appropriate plan of action.
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