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

Part One of this text described the typical incident eventualities at tank farm fires and presented foam as the most suitable extinguishing agent along with the firefighting equipment mostly used. In Part Two we take a look at foam concentrate proportioning technologies, cellular extinguishing systems and conclude with classes discovered.
NFPA 11 describes numerous types of foam focus proportioning equipment. In the following, three techniques are checked out which are commonest. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning price should not be lower 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 value i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning fee is allowed to be an absolute maximum of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller value must be used respectively).
To guarantee right proportioning, the proportioner, together with the proportioning price have to be tested a minimum of once a year and its appropriate 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 expertise. 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 froth focus from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi principle. When the hearth pumps are activated, strain is generated by the pump, inflicting supply of froth concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the foam concentrate into the extinguishing water move.
The benefits of this technique are its easy design without shifting elements and its straightforward operation. No external vitality is required, and the system is comparatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding regulations 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 delicate; when broken, water will contaminate the froth concentrate. At a given proportioning price, the system is suitable only for low variations in the extinguishing water circulate strain and volume. Adding or changing particular person foam discharge units is feasible only to a really limited extent. The system can also be unsuitable for proportioning extremely viscous foam concentrates.
To conduct เกจวัดแรงดันเบนซิน required annual testing, the system should be activated and premix generated at the venturi proportioner within the extinguishing water line. The right proportioning fee should be measured within the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam focus within the bladder tank needs to 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 focus, an electrical or diesel-powered foam concentrate pump with an electronically controlled valve and a move meter in the extinguishing water move line. When the hearth pumps are activated, the froth focus pump drive and digital control system should be activated. The extinguishing water move price is measured by the circulate 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 circulate by the froth concentrate pump. If there is a change in the flow fee, the amount of injected foam focus is regulated by the control valve.
The system’s advantage lies within the exact proportioning of the froth concentrate, unbiased of the extinguishing water pressure or move rate. Foam focus can be topped up in the course of 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; nonetheless, the delivered foam concentrate may be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus circulate fee. No premix is produced; and as the foam focus is handed again into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free power provide for the froth concentrate pump and the control system, as well as the necessity for a complicated control system and the comparatively greater purchasing prices. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water move rate and the newly adjusted foam concentrate quantity. The foam quality may be compromised when constantly changing operating conditions as foam discharge devices are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam focus, a water motor installed within the extinguishing water move line and a foam focus pump which is related directly to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump gives immediate foam-concentrate injection into the extinguishing water. If the flow rate adjustments, the amount of foam focus is adapted immediately.
The benefit of the system is its independence from external power sources in addition to a precise and instant foam-concentrate proportioning whatever the extinguishing water stress or flow rate. If a piston or plunger pump is used, adjustment or calibration after set up isn’t essential for the rationale that water motor and the pump are volumetric devices firmly connected to one another. Foam focus refilling throughout operation is possible. The system can be capable of proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus may be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move fee. No premix is generated; and if the froth concentrate is handed back into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively higher buying costs are a drawback of the system.
With any system, consideration must be taken into account for the annual testing prices, which may be considerable when it comes to substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge tools could be damaged in intensive fires within the tank or in the dyke area 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 flexible. Yet they’ve only restricted extinguishing agent flow rates and reaches.
Firefighting displays
Firefighting screens are discharge units mounted on autos or trailers and obtainable in plenty of sizes. The extinguishing agent flow fee can be up to 60,000 litres/min and the reach can be as much as 180m if the stress of the fire pumps is sufficient. 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 in order to forestall it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke area ought to at all times be noticed to avoid an overflow of the dyke.
Mobile hearth screens could be supplied either by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the foam focus normally takes place through cell proportioners. This clearly factors in the course of the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of mobile items obtainable as back-ups is shown by the next example for the position of displays 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 results in a number of options for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should be succesful of deal with varying move charges to ensure flexibility throughout extinguishing operations. Depending on the native conditions, the screens might need to keep a minimal distance to the burning tank or may not be capable of be positioned close to to the tanks due to debris. In addition, it will not at all times be possible to position several monitors across the tank. It must be ensured the monitor has adequate throwing height in relation to the tank peak, to ship foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following authorized rules as well as recommendations by associations like NFPA and isn’t looked at extra carefully within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons realized
As talked about within the introduction to Part One of this text, it appears that evidently many authorities and firms have not learned the required classes from disastrous hearth incidents of previous years. Tank farm fires within the oil and petrochemical trade do not happen frequently. When they do, they usually have devastating penalties. Let us remember the tank farm hearth at Deer Park, Texas in March 2019 talked about within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fireplace for yet unknown causes. 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 have been surrounded by one single dyke. The proprietor had relied on the native fireplace service, which was on the spot very quickly but couldn’t take control over the fire with the gear available, partially as a outcome of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an exterior firefighting firm 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 fireplace was finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts have been revamped three days, with foam concentrate and water shortages occurring within the meantime. In whole, over 500,000 litres of froth focus have been used. Instead of a fireplace within the dyke area, eleven of the 15 tanks burnt down.
It could be very probable that the fire would have been extinguished rapidly if the warning techniques and valves had worked and a onerous and fast fire extinguishing system had existed. It can be possible that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded eventually, had been started earlier. Both circumstances would have resulted in notably less injury.
Summing up, the following factors ought to be learned at the least. As far as they haven’t but been carried out, or simply partly, they need to function a foundation for discussions about one’s own fire-protection concept:
Have an appropriate fire-protection concept together with different scenarios which adapt to the given situation regularly.
Always have a sufficient number of cell extinguishing methods as a backup to fastened extinguishing systems.
Stock an appropriate foam focus.
Ensure sufficient foam concentrate supply.
Ensure adequate water provide.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment available in a adequate number.
Have skilled personnel obtainable in a enough number.
Ensure a fast implementation of an appropriate plan of motion.
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