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

Part One of this article described the standard incident situations at tank farm fires and presented foam as probably the most appropriate extinguishing agent together with the firefighting equipment mostly used. In Part Two we look at foam concentrate proportioning applied sciences, cell extinguishing systems and conclude with lessons learned.
NFPA 11 describes varied kinds of foam focus proportioning tools. In the next, three methods are checked out that are most typical. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning price 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 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 price is allowed to be an absolute maximum of 1% above the permitted worth – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller worth must be used respectively).
To assure correct proportioning, the proportioner, including the proportioning rate must be examined no less than annually and its correct 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 crammed with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam focus from the bladder as required. The bladder is connected to a proportioner which operates using the venturi precept. When the hearth pumps are activated, stress is generated by the pump, inflicting supply of foam focus to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth concentrate into the extinguishing water circulate.
The advantages of this technique are its easy design with out shifting elements and its easy operation. No exterior energy is required, and the system is relatively inexpensive.
A drawback 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 delicate; when damaged, water will contaminate the froth concentrate. At a given proportioning price, the system is appropriate only for low variations within the extinguishing water flow strain and volume. Adding or altering individual foam discharge devices is feasible only to a very restricted extent. The system is also unsuitable for proportioning extremely 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 correct 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 within the bladder tank must be changed.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a flow meter in the extinguishing water flow line. When the hearth pumps are activated, the froth focus pump drive and digital management system should be activated. The extinguishing water flow rate is measured by the flow meter and the management system adjusts the proper foam focus quantity by way of the control valve. The foam concentrate is injected into the extinguishing water move by the foam concentrate pump. If there is a change in the circulate price, 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 pressure or move rate. Foam focus can be topped up during the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the aim of annual testing, the system should be activated; nonetheless, the delivered foam focus could be measured through a return line. The proportioning price is calculated from the extinguishing water/foam concentrate flow price. No premix is produced; and as a outcome of the foam concentrate is handed back into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an external interruption-free power provide for the foam concentrate pump and the management system, in addition to the need for a complicated management system and the comparatively higher purchasing costs. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water move price and the newly adjusted foam focus amount. The foam quality may be compromised when continually changing working circumstances 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 linked on to the water motor. หลักการทำงานของเกจ์วัดแก๊ส and pump type one compact unit. Upon activation of the fireplace pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the move rate modifications, the amount of foam focus is adapted instantly.
The advantage of the system is its independence from external power sources as nicely as a exact and instant foam-concentrate proportioning whatever the extinguishing water pressure or flow price. If a piston or plunger pump is used, adjustment or calibration after installation is not necessary since the water motor and the pump are volumetric units firmly related to one another. Foam concentrate refilling during operation is feasible. The system can be able to proportioning highly viscous foam concentrates. The system must be activated for annual testing; however, the delivered foam focus may be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate price. No premix is generated; and if the froth concentrate is passed again into the tank, no foam focus needs to be topped up.
The larger design and the comparatively higher purchasing costs are a drawback of the system.
With any system, consideration ought to be taken into account for the annual testing prices, which can be appreciable in terms of alternative foam focus, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge gear can be damaged in in depth fires in the tank or in the dyke space and thus lose effectiveness, cell fireplace monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they have only restricted extinguishing agent flow charges and reaches.
Firefighting monitors
Firefighting monitors are discharge gadgets mounted on vehicles or trailers and obtainable in many sizes. The extinguishing agent move price can be as much as 60,000 litres/min and the reach could be up to 180m if the stress of the fire pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a surface hearth in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to have the ability to forestall it reaching the critical temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke space should always be observed to avoid an overflow of the dyke.
Mobile fire screens could be equipped either by the extinguishing water of the stationary fire pumps or by mobile pumps. The injection of the foam focus usually takes place via cell proportioners. This clearly factors in the path of the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cell items available as back-ups is shown by the next example for the position of monitors for fire extinguishing at tanks which are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several options for the displays. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which ought to be succesful of handle varying flow charges to guarantee flexibility throughout extinguishing operations. Depending on the native situations, the monitors might need to maintain a minimal distance to the burning tank or could not be ready to be positioned near to the tanks as a result of particles. In addition, it won’t always be attainable to position a number of screens around the tank. It should be ensured the monitor has sufficient throwing top in relation to the tank top, to ship foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal laws as properly as suggestions by associations like NFPA and is not looked at extra closely within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As mentioned in the introduction to Part One of this article, it seems that evidently many authorities and corporations haven’t discovered the necessary classes from disastrous hearth incidents of past years. Tank farm fires in the oil and petrochemical business do not occur incessantly. When they do, they normally have devastating consequences. Let us keep in mind the tank farm hearth at Deer Park, Texas in March 2019 talked about in the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for 30 minutes and caught fireplace for but unknown reasons. The plant had no gas warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fastened extinguishing techniques put in. All 15 tanks were surrounded by one single dyke. The owner had relied on the local fireplace service, which was on the spot very quickly however couldn’t take management over the fire with the gear available, partially because flammable substance was constantly leaking from the tank. Thirty-six hours after the hearth had damaged 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 motion took roughly 13 hours. The fire was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts have been made over three days, with foam focus and water shortages occurring within the meantime. In whole, over 500,000 litres of foam concentrate have been used. Instead of a fire within the dyke space, eleven of the 15 tanks burnt down.
It is very probable that the hearth would have been extinguished quickly if the warning methods and valves had worked and a set fireplace extinguishing system had existed. It can additionally be probable that the fire would have been extinguished rapidly if the extinguishing operation, which succeeded ultimately, had been started earlier. Both cases would have resulted in notably less injury.
Summing up, the following points ought to be realized at least. As far as they haven’t but been applied, or just partly, they should serve as a basis for discussions about one’s own fire-protection concept:
Have a suitable fire-protection concept together with various situations which adapt to the given state of affairs frequently.
Always have a sufficient variety of mobile extinguishing techniques as a backup to fastened extinguishing systems.
Stock an appropriate foam focus.
Ensure sufficient foam concentrate provide.
Ensure sufficient water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing gear out there in a adequate quantity.
Have educated personnel obtainable in a adequate quantity.
Ensure a fast implementation of a suitable plan of action.
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