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

Part One of this text described the typical incident scenarios at tank farm fires and presented foam as essentially the most suitable extinguishing agent along with the firefighting equipment most commonly used. In เพรสเชอร์เกจnuovafima look at foam concentrate proportioning technologies, cell extinguishing systems and conclude with classes discovered.
NFPA eleven describes numerous types of foam focus proportioning tools. In the next, three systems are looked at that are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning rate must not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning price should not exceed 30% above the permitted value i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning fee is allowed to be an absolute maximum of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller worth should be used respectively).
To guarantee เกจวัดแรงดันไฮดรอลิค , the proportioner, together with the proportioning fee have to be examined no much less than every year and its correct functioning must be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a proven and cost-effective know-how. The bladder tank is a pressurized vessel with a bladder inside which is crammed with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi principle. When the fireplace pumps are activated, stress is generated by the pump, inflicting supply of froth concentrate to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the froth concentrate into the extinguishing water circulate.
The benefits of this system are its simple design with out shifting elements and its simple operation. No external energy is required, and the system is relatively inexpensive.
A disadvantage is that the system is a pressurized vessel subject to corresponding rules corresponding to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system have to be shut down and drained. The rubber bladder is sensitive; 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 move stress and quantity. Adding or changing particular person foam discharge devices is feasible solely to a really restricted extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The appropriate proportioning rate should be measured in the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus within the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam focus pump with an electronically managed valve and a move meter in the extinguishing water move line. When the fire pumps are activated, the foam focus pump drive and digital management system must be activated. The extinguishing water circulate rate is measured by the move meter and the control system adjusts the right foam concentrate quantity through the management valve. The foam focus is injected into the extinguishing water move by the foam concentrate pump. If there is a change in the move price, 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, impartial of the extinguishing water pressure or move rate. Foam concentrate 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 have to be activated; however, the delivered foam concentrate may be measured through a return line. The proportioning price is calculated from the extinguishing water/foam concentrate move price. No premix is produced; and as a end result of the foam focus is passed again into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an exterior interruption-free energy provide for the froth concentrate pump and the management system, as properly as the need for a complicated control system and the comparatively greater buying prices. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water move price and the newly adjusted foam focus amount. The foam high quality could also be compromised when constantly changing operating conditions as foam discharge units 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 focus pump which is connected directly to the water motor. Water motor and pump form one compact unit. Upon activation of the hearth pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump offers immediate foam-concentrate injection into the extinguishing water. If the circulate price changes, the amount of froth concentrate is customized instantly.
The benefit of the system is its independence from external power sources in addition to a precise and quick foam-concentrate proportioning whatever the extinguishing water stress or flow fee. If a piston or plunger pump is used, adjustment or calibration after set up isn’t essential since the water motor and the pump are volumetric units firmly related to one another. Foam focus refilling during operation is possible. The system can additionally be able to proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam concentrate may be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam focus move fee. No premix is generated; and if the foam focus is handed back into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively greater buying prices are a disadvantage of the system.
With any system, consideration ought to be taken into consideration for the annual testing prices, which can be appreciable in terms of substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge gear may be damaged in extensive fires in the tank or in the dyke area and thus lose effectiveness, cellular fireplace screens and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they have solely limited extinguishing agent circulate rates and reaches.
Firefighting monitors
Firefighting monitors are discharge devices mounted on autos or trailers and out there in lots of sizes. The extinguishing agent flow price could be as much as 60,000 litres/min and the reach may be as much as 180m if the strain of the hearth pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a floor hearth in a tank, or water, to chill 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 contained in the dyke area should always be observed to avoid an overflow of the dyke.
Mobile hearth displays may be supplied both by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the foam focus normally takes place via mobile proportioners. This clearly factors in the direction of the advantage of power independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular units out there as back-ups is proven by the following instance for the position of monitors for fireplace 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 alternatives for the monitors. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which ought to be capable of handle varying circulate rates to guarantee flexibility throughout extinguishing operations. Depending on the native conditions, the screens will want to keep a minimum distance to the burning tank or could not be capable of be positioned near to the tanks due to debris. In addition, it won’t all the time be possible to place several displays across the tank. It should be ensured the monitor has enough throwing peak in relation to the tank peak, to ship foam into the inside of the tank.
The dimensioning of the whole firefighting system is made following legal rules in addition to recommendations by associations like NFPA and isn’t checked out extra closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned
As mentioned in the introduction to Part One of this text, it seems that many authorities and companies have not realized the required lessons from disastrous hearth incidents of past years. Tank farm fires within the oil and petrochemical industry 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 fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught hearth 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 didn’t have mounted extinguishing methods put in. All 15 tanks had been surrounded by one single dyke. The owner had relied on the native fireplace service, which was on the spot very quickly however couldn’t take management over the hearth with the equipment available, partially because flammable substance was repeatedly 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 concentrate in addition to the preparation of a plan of motion took roughly thirteen hours. The hearth was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts have been revamped three days, with foam focus and water shortages occurring in the meantime. In complete, over 500,000 litres of foam concentrate had been used. Instead of a fireplace in the dyke area, 11 of the 15 tanks burnt down.
It may be very possible that the hearth would have been extinguished shortly if the warning techniques and valves had labored and a fixed fire extinguishing system had existed. It is also possible that the fireplace would have been extinguished quickly if the extinguishing operation, which succeeded finally, had been began earlier. Both circumstances would have resulted in notably less harm.
Summing up, the following points ought to be discovered at least. As far as they haven’t but been implemented, or just partly, they want to function a basis for discussions about one’s own fire-protection concept:
Have an acceptable fire-protection idea together with alternative situations which adapt to the given state of affairs regularly.
Always have a adequate variety of cell extinguishing systems as a backup to fixed extinguishing methods.
Stock an appropriate foam concentrate.
Ensure sufficient foam concentrate provide.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment obtainable in a sufficient number.
Have educated personnel out there in a adequate quantity.
Ensure a fast implementation of an acceptable plan of action.
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