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

Part One of this article described the everyday incident situations at tank farm fires and offered foam as the most appropriate extinguishing agent along with the firefighting gear mostly used. In Part Two we have a glance at foam focus proportioning applied sciences, cell extinguishing techniques and conclude with classes discovered.
NFPA eleven describes various types of foam concentrate proportioning equipment. In the next, three methods are checked out which are most typical. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning price 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 value i.e. three.9% for a 3% foam concentrate or 7.8% for a 6% foam focus; 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 concentrate (the smaller value have to be used respectively).
To assure appropriate proportioning, the proportioner, including the proportioning fee must be examined at least annually and its correct 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 full of 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 connected to a proportioner which operates using the venturi precept. When the hearth pumps are activated, strain is generated by the pump, inflicting delivery of foam 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 circulate.
The advantages of this technique are its easy design with out transferring parts and its easy operation. No exterior vitality is required, and the system is comparatively cheap.
A drawback is that the system is a pressurized vessel subject to corresponding laws such as 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 focus. At a given proportioning rate, the system is appropriate only for low variations within the extinguishing water circulate pressure and volume. Adding or changing individual foam discharge units is possible solely to a really restricted extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The appropriate proportioning rate must be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam concentrate within the bladder tank must be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the froth focus, an electrical or diesel-powered foam focus pump with an electronically controlled valve and a move meter in the extinguishing water flow line. When the hearth pumps are activated, the foam focus pump drive and digital management system have to be activated. The extinguishing water circulate fee is measured by the flow meter and the control system adjusts the right foam focus amount via the control valve. The foam concentrate is injected into the extinguishing water move by the foam focus pump. If there is a change in the move fee, the quantity of injected foam concentrate is regulated by the control valve.
The system’s advantage lies in the exact proportioning of the foam focus, impartial of the extinguishing water strain or flow price. Foam focus may be topped up through the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system must be activated; however, the delivered foam concentrate could be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam focus circulate fee. No premix is produced; and because the foam focus is passed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free power provide for the froth focus pump and the control 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 rate and the newly adjusted foam focus quantity. The foam high quality may be compromised when constantly altering operating conditions 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 foam concentrate, a water motor put in in the extinguishing water move line and a foam focus pump which is connected on to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump provides instant foam-concentrate injection into the extinguishing water. If the circulate rate modifications, the amount of foam focus is customized immediately.
The advantage of the system is its independence from external power sources in addition to a exact and instant foam-concentrate proportioning whatever the extinguishing water pressure or move rate. If a piston or plunger pump is used, adjustment or calibration after installation isn’t necessary because the water motor and the pump are volumetric gadgets firmly linked to one another. Foam focus refilling during operation is possible. The system is also able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nonetheless, the delivered foam focus could be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam focus move rate. No premix is generated; and if the foam focus is handed back into the tank, no foam concentrate must 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 prices, which may be appreciable in terms of alternative foam focus, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge tools may be damaged in extensive fires in the tank or within the dyke space and thus lose effectiveness, cellular fireplace monitors and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they’ve only restricted extinguishing agent move rates and reaches.
Firefighting monitors
Firefighting monitors are discharge units mounted on autos or trailers and available in many sizes. The extinguishing agent circulate price could be up to 60,000 litres/min and the reach may be up to 180m if the strain of the hearth pumps is enough. They are suitable 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 so as to forestall it reaching the important temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke area should all the time be noticed to keep away from an overflow of the dyke.
Mobile fireplace monitors could be provided both by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the foam concentrate usually takes place through mobile proportioners. This clearly points in the path of the advantage of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular models available as back-ups is proven by the following example for the placement of screens for fireplace 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 a number of alternatives for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should have the flexibility to handle varying circulate charges to guarantee flexibility during extinguishing operations. Depending on the native situations, the monitors will need to hold a minimum distance to the burning tank or might not be capable of be positioned near to the tanks because of debris. In addition, it is not going to at all times be potential to position several monitors around the tank. It must be ensured the monitor has sufficient throwing peak in relation to the tank height, to ship foam into the within of the tank.
The dimensioning of the complete firefighting system is made following legal laws as well as recommendations by associations like NFPA and is not checked out more closely within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned
As talked about within the introduction to Part One of this text, it seems that evidently many authorities and corporations have not realized the required classes from disastrous fire incidents of past years. Tank farm fires in the oil and petrochemical trade do not happen incessantly. When they do, they normally have devastating penalties. Let pressure gauge digital ราคา bear in mind the tank farm fireplace 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 faulty valve for half-hour and caught fire for but 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 fastened extinguishing methods put in. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the local fire 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 continuously leaking from the tank. Thirty-six hours after the fireplace had damaged out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of apparatus and foam focus as properly as the preparation of a plan of action took approximately thirteen hours. The hearth was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been revamped three days, with foam focus and water shortages occurring in the meantime. In whole, over 500,000 litres of foam concentrate have been used. Instead of a hearth in the dyke area, eleven of the 15 tanks burnt down.
It may be very probable that the fire would have been extinguished rapidly if the warning techniques and valves had labored and a set fireplace extinguishing system had existed. It is also probable that the fire would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been began earlier. Both instances would have resulted in notably less harm.
Summing up, the following points ought to be learned as a minimum. As far as they have not yet been carried out, or simply partly, they need to function a basis for discussions about one’s personal fire-protection idea:
Have an appropriate fire-protection concept together with different situations which adapt to the given scenario often.
Always have a adequate number of mobile extinguishing methods as a backup to fastened extinguishing systems.
Stock an acceptable foam focus.
Ensure enough foam concentrate supply.
Ensure sufficient water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing gear available in a enough number.
Have educated personnel obtainable in a adequate number.
Ensure a fast implementation of an acceptable plan of motion.
For extra info, go to www.firedos.com
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