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

Part One of this article described the typical incident situations at tank farm fires and introduced foam as essentially the most suitable extinguishing agent along with the firefighting gear mostly used. In Part Two we take a look at foam concentrate proportioning applied sciences, cell extinguishing methods and conclude with classes realized.
NFPA eleven describes varied types of foam concentrate proportioning gear. In the next, three methods are looked at which are most common. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning price must not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam focus.
The proportioning fee should 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 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 worth must be used respectively).
To assure right proportioning, the proportioner, including the proportioning rate must be examined a minimum of annually 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 know-how. เกจวัดแรงดันถังลม 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 froth 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, pressure is generated by the pump, inflicting supply of foam concentrate to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the foam focus into the extinguishing water flow.
The benefits of this system are its easy design with out transferring elements and its simple operation. No external power is required, and the system is comparatively cheap.
A drawback is that the system is a pressurized vessel topic to corresponding rules such as ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, 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 suitable just for low variations in the extinguishing water move stress and volume. Adding or changing particular person foam discharge units is possible solely to a very limited extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The appropriate 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 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 electric or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter within the extinguishing water move line. When the hearth pumps are activated, the froth concentrate pump drive and digital management system have to be activated. The extinguishing water move rate is measured by the circulate meter and the management system adjusts the correct foam focus amount through the management valve. The foam focus is injected into the extinguishing water circulate by the froth concentrate pump. If there is a change within the move price, the amount of injected foam concentrate is regulated by the management valve.
The system’s advantage lies in the precise proportioning of the foam focus, independent of the extinguishing water strain or move fee. Foam focus could be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system should be activated; nevertheless, the delivered foam focus can be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate flow rate. No premix is produced; and as the foam focus is passed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free energy supply for the foam concentrate pump and the control system, in addition to the necessity for a classy management system and the comparatively larger buying prices. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water flow price and the newly adjusted foam focus amount. The foam quality could additionally be compromised when constantly 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 circulate line and a foam focus 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 gives instant foam-concentrate injection into the extinguishing water. If the flow rate modifications, the quantity of foam focus is adapted immediately.
The advantage of the system is its independence from exterior vitality sources as nicely as a precise and immediate foam-concentrate proportioning regardless of the extinguishing water stress or move fee. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t needed since the water motor and the pump are volumetric units firmly related to each other. Foam focus refilling during operation is possible. The system can be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam concentrate may be measured by way of a return line. The proportioning rate is calculated from the extinguishing water/foam focus flow fee. No premix is generated; and if the foam focus is handed again into the tank, no foam focus must be topped up.
The larger design and the comparatively greater purchasing costs are a disadvantage of the system.
With any system, consideration must be taken into account for the annual testing prices, which may be considerable by way of alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge gear can be broken in extensive fires in the tank or within the dyke space and thus lose effectiveness, mobile fire displays and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they have only restricted extinguishing agent move rates and reaches.
Firefighting monitors
Firefighting screens are discharge units 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 can be as a lot as 180m if the pressure of the fireplace pumps is adequate. 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 to be able to prevent it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space should always be noticed to keep away from an overflow of the dyke.
Mobile hearth monitors may be supplied either by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the froth concentrate often takes place via cellular proportioners. This clearly factors in path of the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular items out there as back-ups is proven by the next example for the position of screens for fire 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 number of options for the monitors. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which ought to be able to handle various flow rates to guarantee flexibility throughout extinguishing operations. Depending on the local conditions, the screens might want to maintain a minimal distance to the burning tank or may not be able to be positioned close to to the tanks as a outcome of particles. In addition, it will not all the time be potential to position several monitors around the tank. It should be ensured the monitor has adequate 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 laws in addition to suggestions by associations like NFPA and is not checked out extra carefully within the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As mentioned in the introduction to Part One of this text, it appears that many authorities and firms have not discovered the required lessons from disastrous fire incidents of past years. Tank farm fires within the oil and petrochemical business don’t happen regularly. When they do, they often have devastating consequences. Let us remember the tank farm hearth at Deer Park, Texas in March 2019 talked about within the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for half-hour and caught hearth for yet unknown reasons. The plant had no gas 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 had 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 hearth with the tools out there, partially as a outcome of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of equipment and foam focus in addition to the preparation of a plan of motion took approximately 13 hours. The fire was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been revamped three days, with foam focus and water shortages occurring within the meantime. In total, over 500,000 litres of foam concentrate had been used. Instead of a fireplace in the dyke space, 11 of the 15 tanks burnt down.
It could be very probable that the fireplace would have been extinguished quickly if the warning systems and valves had worked and a set fireplace extinguishing system had existed. It can additionally be possible that the fireplace would have been extinguished quickly if the extinguishing operation, which succeeded finally, had been started earlier. Both circumstances would have resulted in notably less damage.
Summing up, the following points ought to be realized as a minimum. As far as they have not but been carried out, or just partly, they should serve as a foundation for discussions about one’s own fire-protection concept:
Have an acceptable fire-protection concept including different eventualities which adapt to the given scenario often.
Always have a enough number of cellular extinguishing techniques as a backup to fastened extinguishing systems.
Stock an acceptable foam concentrate.
Ensure adequate foam focus supply.
Ensure sufficient water supply.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment available in a adequate quantity.
Have skilled personnel available in a adequate quantity.
Ensure a quick implementation of an acceptable plan of action.
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