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

Part One of this text described the typical incident situations at tank farm fires and offered foam as the most suitable extinguishing agent along with the firefighting equipment mostly used. In Part Two we look at foam focus proportioning technologies, cellular extinguishing techniques and conclude with classes discovered.
NFPA eleven describes varied types of foam concentrate proportioning gear. In the next, three techniques are looked at that are commonest. Tight limits for the proportioning of froth concentrate 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 rate should not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning rate is allowed to be an absolute most of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam concentrate (the smaller value must be used respectively).
To guarantee appropriate proportioning, the proportioner, together with the proportioning fee must be examined at least every year and its right 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 full of foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the foam focus from the bladder as required. The bladder is related to a proportioner which operates using the venturi principle. When the hearth pumps are activated, strain is generated by the pump, causing delivery of foam concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The ensuing vacuum induces the froth concentrate into the extinguishing water move.
The benefits of this system are its easy design without transferring parts and its straightforward operation. No exterior vitality is required, and the system is comparatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding regulations such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system have to be shut down and drained. The rubber bladder is delicate; when damaged, water will contaminate the foam concentrate. At a given proportioning rate, the system is appropriate just for low variations in the extinguishing water flow stress and quantity. Adding or altering particular person foam discharge devices is feasible solely to a really limited extent. The system can additionally be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system must be activated and premix generated on the venturi proportioner inside the extinguishing water line. The right proportioning rate have to be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam concentrate in the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a circulate meter in the extinguishing water circulate line. When the fireplace pumps are activated, the foam focus pump drive and digital control system should be activated. The extinguishing water flow rate is measured by the move meter and the control system adjusts the correct foam concentrate amount via the management valve. The foam focus is injected into the extinguishing water move by the froth concentrate pump. If there is a change in the flow price, the amount of injected foam focus is regulated by the control valve.
The system’s advantage lies in the precise proportioning of the foam concentrate, unbiased of the extinguishing water stress or flow rate. Foam focus may be topped up through the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the purpose of annual testing, the system should be activated; however, the delivered foam focus could be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam focus move price. No premix is produced; and as the foam concentrate is passed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free vitality provide for the foam concentrate pump and the control system, in addition to the necessity for a classy management system and the comparatively higher purchasing costs. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water circulate fee and the newly adjusted foam focus quantity. The foam high quality could also be compromised when continually altering working conditions 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 within the extinguishing water flow 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 fireplace pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the move fee modifications, the amount of froth focus is tailored instantly.
The benefit of the system is its independence from exterior energy sources as nicely as a exact 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 installation isn’t necessary for the rationale that water motor and the pump are volumetric units firmly related to one another. Foam concentrate refilling throughout operation is feasible. The system is also capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; however, the delivered foam focus could be measured by way of a return line. The proportioning rate is calculated from the extinguishing water/foam focus circulate fee. No premix is generated; and if the froth concentrate is passed again into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively larger purchasing prices are a disadvantage of the system.
With pressure gauge น้ำมัน , consideration must be taken under consideration for the annual testing prices, which may be considerable by method of substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge equipment could be damaged in extensive fires in the tank or within the dyke area and thus lose effectiveness, cell fire monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they’ve solely restricted extinguishing agent circulate charges and reaches.
Firefighting monitors
Firefighting monitors are discharge devices mounted on automobiles or trailers and obtainable in many sizes. The extinguishing agent move fee may be as much as 60,000 litres/min and the attain may be up to 180m if the pressure of the fireplace 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 be able to stop it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke space should at all times be noticed to keep away from an overflow of the dyke.
Mobile fire displays can be supplied both by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the froth concentrate often takes place via mobile proportioners. This clearly points in the path of the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of mobile items out there as back-ups is shown by the following instance for the position of monitors for hearth extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This leads to a quantity of options for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be able to handle varying circulate charges to ensure flexibility during extinguishing operations. Depending on the local situations, the screens might want to maintain a minimal distance to the burning tank or might not have the flexibility to be positioned near to the tanks as a outcome of particles. In addition, it will not always be potential to place several monitors around the tank. It must be ensured the monitor has enough throwing peak in relation to the tank height, to ship foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following authorized regulations in addition to suggestions by associations like NFPA and isn’t checked out extra carefully in the current article.
Fig. four: 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, it seems that evidently many authorities and firms haven’t learned the necessary classes from disastrous hearth incidents of past years. Tank farm fires within the oil and petrochemical business don’t occur regularly. When they do, they often have devastating consequences. Let us remember the tank farm hearth at Deer Park, Texas in March 2019 mentioned within 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 fireplace for yet unknown reasons. The plant had no fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have mounted extinguishing techniques installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the local hearth service, which was on the spot in a short time but could not take control over the fireplace with the equipment out there, partially as a result of flammable substance was constantly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of apparatus and foam concentrate in addition to the preparation of a plan of action took roughly 13 hours. The fire was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt had been made over three days, with foam focus and water shortages occurring in the meantime. In total, over 500,000 litres of froth concentrate have been used. Instead of a fireplace in the dyke area, eleven of the 15 tanks burnt down.
It could be very probable that the fireplace would have been extinguished quickly if the warning techniques and valves had labored and a set fire extinguishing system had existed. It is also possible 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 much less damage.
Summing up, the following points must be learned as a minimum. As far as they haven’t yet been carried out, or simply partly, they need to function a foundation for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection concept including various scenarios which adapt to the given scenario regularly.
Always have a enough variety of cellular extinguishing methods as a backup to fixed extinguishing systems.
Stock a suitable foam concentrate.
Ensure sufficient foam focus supply.
Ensure enough water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing gear obtainable in a adequate number.
Have trained personnel out there in a sufficient number.
Ensure a fast implementation of an appropriate plan of action.
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