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

Part One of this article described the typical incident situations at tank farm fires and offered foam as probably the most appropriate extinguishing agent along with the firefighting equipment mostly used. In Part Two we take a look at foam concentrate proportioning technologies, mobile extinguishing techniques and conclude with classes learned.
NFPA eleven describes varied kinds of foam focus proportioning gear. In the following, three systems are looked at that are commonest. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning fee 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 rate must not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; respectively, the proportioning fee 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 should be used respectively).
To assure appropriate proportioning, the proportioner, together with the proportioning price should be examined a minimal of annually and its right functioning should be checked.
Fig. 1 Bladder tank with proportioner.
เกจวัดแรงดันลม10bar with proportioner
The bladder tank with a proportioner is a confirmed and cost-effective know-how. 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 foam concentrate from the bladder as required. The bladder is linked to a proportioner which operates utilizing the venturi precept. When the hearth pumps are activated, stress is generated by the pump, causing supply of froth focus to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the foam concentrate into the extinguishing water flow.
The advantages of this method are its simple design with out moving elements and its easy operation. No exterior energy is required, and the system is comparatively inexpensive.
A disadvantage 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 must be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the foam concentrate. At a given proportioning price, the system is appropriate only for low variations within the extinguishing water flow stress and volume. Adding or altering individual foam discharge devices is feasible solely to a very restricted extent. The system can also be unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system should be activated and premix generated at the venturi proportioner inside the extinguishing water line. The appropriate proportioning rate should be measured in the premix by laboratory analysis. 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 move meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the froth focus, an electrical or diesel-powered foam concentrate pump with an electronically managed valve and a circulate meter in the extinguishing water flow line. When the hearth pumps are activated, the froth focus pump drive and electronic control system must be activated. The extinguishing water move rate is measured by the flow meter and the control system adjusts the correct foam concentrate quantity through the management valve. The foam focus is injected into the extinguishing water flow by the froth focus pump. If there is a change in the circulate fee, the quantity of injected foam concentrate is regulated by the management valve.
The system’s advantage lies within the exact proportioning of the froth focus, unbiased of the extinguishing water strain or flow price. Foam focus could be topped up during 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 can be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move price. No premix is produced; and because the foam concentrate is handed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free vitality provide for the froth concentrate pump and the control system, in addition to the need for a sophisticated management system and the comparatively higher purchasing prices. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water circulate price and the newly adjusted foam concentrate quantity. The foam quality could additionally be compromised when continuously altering operating 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 move line and a foam concentrate pump which is related directly to the water motor. Water motor and pump form one compact unit. Upon activation of the hearth pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump gives quick foam-concentrate injection into the extinguishing water. If the move fee modifications, the quantity of froth concentrate is tailored instantly.
The benefit of the system is its independence from exterior energy sources in addition to a precise and quick foam-concentrate proportioning regardless of the extinguishing water pressure or flow fee. If a piston or plunger pump is used, adjustment or calibration after installation is not necessary for the rationale that water motor and the pump are volumetric gadgets firmly connected to each other. Foam focus refilling throughout operation is feasible. The system can also be able to proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam concentrate may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus move fee. No premix is generated; and if the froth focus is passed back into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively higher buying prices are a drawback of the system.
With any system, consideration ought to be taken into consideration for the annual testing costs, which can be appreciable in terms of alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing methods
As the stationary foam discharge gear can be damaged in intensive fires in the tank or within the dyke space and thus lose effectiveness, mobile hearth screens and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they’ve only limited extinguishing agent move charges and reaches.
Firefighting monitors
Firefighting screens are discharge units mounted on autos or trailers and available in many sizes. The extinguishing agent circulate fee can be as a lot as 60,000 litres/min and the attain can be as much as 180m if the pressure of the fire pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a floor fireplace 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 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 observed to avoid an overflow of the dyke.
Mobile fireplace displays may be provided both by the extinguishing water of the stationary fire pumps or by cellular pumps. The injection of the foam focus usually takes place via cell proportioners. This clearly points towards the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular items out there as back-ups is shown by the next instance for the position of displays for fire extinguishing at tanks which are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This ends in a quantity of alternatives for the displays. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should have the flexibility to deal with varying circulate charges to ensure flexibility throughout extinguishing operations. Depending on the native circumstances, the monitors might need to hold a minimal distance to the burning tank or may not be capable of be positioned near to the tanks because of debris. In addition, it won’t at all times be potential to position several monitors across the tank. It should be ensured the monitor has adequate throwing peak in relation to the tank height, to ship foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following legal rules as nicely as suggestions by associations like NFPA and is not checked out more 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 in the introduction to Part One of this article, it appears that many authorities and corporations haven’t learned the required classes from disastrous fireplace incidents of previous years. Tank farm fires in the oil and petrochemical business do not happen incessantly. When they do, they often have devastating penalties. Let us remember the tank farm fireplace at Deer Park, Texas in March 2019 mentioned in the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for half-hour and caught hearth for yet unknown reasons. The plant had no fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have mounted extinguishing systems installed. All 15 tanks were surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot very quickly but could not take control over the fire with the gear out there, partially as a end result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of kit and foam concentrate in addition to the preparation of a plan of motion took approximately 13 hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt have been made over three days, with foam concentrate and water shortages occurring within the meantime. In complete, over 500,000 litres of froth concentrate were used. Instead of a fire in the dyke space, 11 of the 15 tanks burnt down.
It is very probable that the fire would have been extinguished quickly if the warning methods and valves had labored and a hard and fast hearth extinguishing system had existed. It can be probable that the fire would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been began earlier. Both instances would have resulted in notably much less injury.
Summing up, the next points must be learned at least. As far as they haven’t yet been applied, or simply partly, they should function a foundation for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection idea together with different situations which adapt to the given state of affairs regularly.
Always have a adequate number of cell extinguishing systems as a backup to fixed extinguishing techniques.
Stock an appropriate foam focus.
Ensure adequate foam concentrate supply.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing tools out there in a sufficient number.
Have educated personnel obtainable in a adequate number.
Ensure a quick implementation of an acceptable plan of motion.
For more data, go to www.firedos.com
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