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

Part One of this article described the standard incident eventualities at tank farm fires and introduced foam as the most appropriate extinguishing agent together with the firefighting tools mostly used. In Part Two we look at foam concentrate proportioning applied sciences, mobile extinguishing systems and conclude with classes learned.
NFPA eleven describes numerous kinds of foam concentrate proportioning tools. In the following, three methods are looked at which are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning rate 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 price 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 price 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, including the proportioning fee should be examined at least once a 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 expertise. The bladder tank is a pressurized vessel with a bladder inside which is filled with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the froth 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, pressure is generated by the pump, inflicting supply of foam concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the foam concentrate into the extinguishing water flow.
The advantages of this system are its simple design without shifting parts and its easy operation. No exterior vitality is required, and the system is relatively cheap.
A drawback 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 broken, water will contaminate the froth concentrate. At a given proportioning rate, the system is suitable only for low variations within the extinguishing water move stress and quantity. Adding or altering individual foam discharge units is feasible solely to a really restricted extent. The system can be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system have to be activated and premix generated at the venturi proportioner within the extinguishing water line. The correct proportioning price 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 flow 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 controlled valve and a move meter in the extinguishing water flow line. When the hearth pumps are activated, the froth focus pump drive and digital control system have to be activated. The extinguishing water move fee is measured by the flow meter and the management system adjusts the correct foam focus amount via the management valve. The foam concentrate is injected into the extinguishing water flow by the foam focus pump. If there is a change within the move price, the amount of injected foam concentrate is regulated by the control valve.
The system’s advantage lies within the exact proportioning of the foam concentrate, impartial of the extinguishing water strain or circulate rate. Foam focus can be topped up through 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 concentrate can be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate circulate rate. No premix is produced; and because the foam concentrate is passed again into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an external interruption-free vitality supply for the foam concentrate pump and the control system, as properly as the necessity for a complicated management system and the comparatively higher buying costs. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water circulate rate and the newly adjusted foam concentrate amount. The foam high quality could additionally be compromised when constantly changing working situations as foam discharge gadgets are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam concentrate, a water motor installed in the extinguishing water move line and a foam concentrate pump which is connected on to the water motor. Water motor and pump type 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 spmk700 , the quantity of foam focus is tailored immediately.
The benefit of the system is its independence from external vitality sources as properly as a exact and immediate foam-concentrate proportioning regardless of the extinguishing water stress or flow rate. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t necessary since the water motor and the pump are volumetric units firmly related to each other. Foam concentrate refilling throughout operation is possible. The system is also capable of proportioning extremely viscous foam concentrates. The system have to be activated for annual testing; however, the delivered foam focus can be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam focus circulate fee. No premix is generated; and if the foam concentrate is passed back into the tank, no foam concentrate needs to be topped up.
The bigger design and the comparatively larger buying costs are a disadvantage of the system.
With any system, consideration ought to be taken under consideration for the annual testing costs, which may be considerable when it comes to substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge equipment can be damaged in extensive fires in the tank or within 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 limited extinguishing agent circulate charges and reaches.
Firefighting screens
Firefighting displays are discharge devices mounted on automobiles or trailers and out there in lots of sizes. The extinguishing agent circulate rate could be up to 60,000 litres/min and the attain could be as much as 180m if the stress of the fireplace pumps is enough. They are appropriate to discharge foam, e.g., to extinguish a floor fire in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank in order to prevent it reaching the critical temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area should always be observed to avoid an overflow of the dyke.
Mobile fireplace monitors may be equipped both by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the foam focus usually takes place through mobile proportioners. This clearly factors towards the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular items obtainable as back-ups is shown by the following instance for the position of screens 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 alternate options for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should have the power to handle various circulate charges to ensure flexibility during extinguishing operations. Depending on the native situations, the monitors might need to hold a minimal distance to the burning tank or could not be succesful of be positioned close to to the tanks due to debris. In addition, it is not going to always be possible to place a quantity of screens across the tank. It have to be ensured the monitor has enough throwing height in relation to the tank top, to ship foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following authorized rules in addition to suggestions by associations like NFPA and isn’t checked out more closely in the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned
As mentioned within the introduction to Part One of this text, plainly many authorities and companies have not discovered the necessary classes from disastrous fireplace incidents of past years. Tank farm fires in the oil and petrochemical industry don’t happen regularly. When they do, they usually have devastating consequences. Let us bear in mind the tank farm fire 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 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 mounted extinguishing methods put in. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native fire service, which was on the spot very quickly however couldn’t take management over the fire with the gear obtainable, partially because 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 company to do the extinguishing work. Mobilization of equipment and foam concentrate as well as the preparation of a plan of motion took approximately thirteen hours. The fire was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. เกจวัดแรงดันออกซิเจนราคา were remodeled three days, with foam concentrate and water shortages occurring in the meantime. In whole, over 500,000 litres of froth focus had been used. Instead of a fire within the dyke area, eleven of the 15 tanks burnt down.
It is very probable that the fireplace would have been extinguished quickly if the warning methods and valves had worked and a set fireplace extinguishing system had existed. It can also be probable that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably less injury.
Summing up, the next factors ought to be realized at the least. As far as they haven’t but been carried out, or simply partly, they want to serve as a foundation for discussions about one’s own fire-protection concept:
Have a suitable fire-protection idea together with alternative situations which adapt to the given scenario often.
Always have a sufficient number of cell extinguishing methods as a backup to mounted extinguishing systems.
Stock a suitable foam concentrate.
Ensure enough foam concentrate supply.
Ensure adequate water provide.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing equipment obtainable in a enough number.
Have trained personnel obtainable in a sufficient number.
Ensure a quick implementation of a suitable plan of motion.
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