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

Part One of this text described the everyday incident situations at tank farm fires and offered foam as probably the most appropriate extinguishing agent together with the firefighting equipment mostly used. In Part Two we look at foam focus proportioning technologies, cell extinguishing methods and conclude with classes discovered.
NFPA 11 describes various forms of foam concentrate proportioning gear. In the next, three systems are looked at that are commonest. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning fee should not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning fee 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 fee is allowed to be an absolute most of 1% above the permitted worth – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam concentrate (the smaller value have to be used respectively).
To assure correct proportioning, the proportioner, together with the proportioning fee must be tested at least every year 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 confirmed 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 linked to a proportioner which operates using the venturi principle. When the fireplace pumps are activated, strain is generated by the pump, causing delivery of froth concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The ensuing vacuum induces the froth concentrate into the extinguishing water circulate.
The benefits of this method are its easy design with out transferring parts and its simple operation. No exterior energy is required, and the system is relatively inexpensive.
A drawback is that the system is a pressurized vessel subject to corresponding rules corresponding to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system must be shut down and drained. The rubber bladder is delicate; when damaged, water will contaminate the foam concentrate. At a given proportioning fee, the system is appropriate only for low variations in the extinguishing water circulate pressure and quantity. Adding or changing individual foam discharge devices is possible solely to a very restricted extent. The system can be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system should be activated and premix generated on the venturi proportioner within the extinguishing water line. The right proportioning price must be measured in the premix by laboratory analysis. The generated premix should 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 circulate meter
The system consists of an atmospheric tank for the foam concentrate, 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 foam concentrate pump drive and electronic management system have to be activated. The extinguishing water circulate rate is measured by the move meter and the control system adjusts the proper foam concentrate amount via the management valve. The foam concentrate is injected into the extinguishing water move by the froth focus pump. If there is a change in the move fee, the quantity of injected foam concentrate is regulated by the management valve.
The system’s benefit lies within the exact proportioning of the froth concentrate, impartial of the extinguishing water stress or flow rate. Foam focus may be topped up through the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nevertheless, the delivered foam concentrate may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate fee. No premix is produced; and as the foam concentrate is handed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an external interruption-free power supply for the froth focus pump and the control system, as nicely as the need for a complicated control system and the comparatively greater buying prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water move fee and the newly adjusted foam focus quantity. The foam quality could also be compromised when constantly changing operating 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 foam concentrate, a water motor installed within the extinguishing water flow line and a foam concentrate pump which is connected directly to the water motor. Water motor and pump type one compact unit. Upon activation of the hearth 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 flow fee modifications, the amount of froth focus is adapted immediately.
The benefit of the system is its independence from external energy sources in addition to a precise and quick foam-concentrate proportioning whatever the extinguishing water pressure or move rate. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t necessary because the water motor and the pump are volumetric gadgets 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 have to be activated for annual testing; nevertheless, the delivered foam concentrate can be measured via a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate price. No premix is generated; and if the foam concentrate is passed back into the tank, no foam focus must be topped up.
The larger design and the comparatively larger buying prices are a disadvantage of the system.
With any system, consideration should be taken under consideration for the annual testing costs, which can be considerable in terms of alternative foam focus, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge equipment can be broken in in depth fires within the tank or in the dyke space and thus lose effectiveness, cell fireplace displays and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet เกจวัดแรงดันpressuregauge ‘ve solely limited extinguishing agent flow charges and reaches.
Firefighting displays
Firefighting monitors are discharge devices mounted on vehicles or trailers and obtainable in many sizes. The extinguishing agent move price can be as a lot as 60,000 litres/min and the reach can be as much as 180m if the pressure of the hearth pumps is sufficient. 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 forestall it reaching the crucial temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke space ought to all the time be observed to keep away from an overflow of the dyke.
Mobile fireplace monitors could be supplied either by the extinguishing water of the stationary hearth pumps or by cellular pumps. The injection of the foam focus often takes place through cellular proportioners. This clearly points in the direction of the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cell items obtainable as back-ups is proven by the next example for the placement of displays 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 results in a quantity of alternate options for the screens. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which ought to be able to deal with varying move charges to ensure flexibility during extinguishing operations. Depending on the native circumstances, the displays might need to hold a minimum distance to the burning tank or might not be in a position to be positioned near to the tanks because of particles. In addition, it won’t always be possible to place a number of displays across the tank. It should be ensured the monitor has sufficient throwing height in relation to the tank height, to deliver foam into the inside of the tank.
The dimensioning of the whole firefighting system is made following legal rules as nicely as recommendations 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 concentrate tank.
Lessons discovered
As talked about within the introduction to Part One of this text, it seems that many authorities and companies haven’t discovered the mandatory lessons from disastrous fireplace incidents of previous years. Tank farm fires in the oil and petrochemical business don’t occur incessantly. When they do, they usually have devastating penalties. Let us keep in mind the tank farm hearth at Deer Park, Texas in March 2019 talked about in the introduction.
The fire developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for half-hour and caught hearth for but unknown causes. The plant had no gasoline warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fixed extinguishing techniques put in. All 15 tanks were surrounded by one single dyke. The owner had relied on the native fire service, which was on the spot very quickly but couldn’t take management over the fire with the gear obtainable, partially as a outcome of flammable substance was continuously leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of equipment and foam focus as nicely as 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 were revamped three days, with foam focus and water shortages occurring within the meantime. In total, over 500,000 litres of foam focus have been used. Instead of a fire within the dyke area, eleven of the 15 tanks burnt down.
It could be very probable that the hearth would have been extinguished quickly if the warning techniques and valves had worked and a fixed fire extinguishing system had existed. It can be possible that the fire would have been extinguished shortly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both instances would have resulted in notably less injury.
Summing up, the next factors should be discovered at the least. As far as they haven’t yet been implemented, or simply partly, they should function a basis for discussions about one’s own fire-protection concept:
Have an appropriate fire-protection idea together with various situations which adapt to the given scenario frequently.
Always have a sufficient number of cellular extinguishing methods as a backup to fastened extinguishing techniques.
Stock an acceptable foam concentrate.
Ensure enough foam focus provide.
Ensure enough water provide.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing gear obtainable in a sufficient quantity.
Have trained personnel obtainable in a sufficient quantity.
Ensure a fast implementation of an acceptable plan of motion.
For extra info, go to www.firedos.com
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