บทความ เกจวัดแรงดัน

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

Part One of this text described the typical incident situations at tank farm fires and introduced foam as essentially the most suitable extinguishing agent together with the firefighting equipment mostly used. In Part Two we have a glance at foam focus proportioning technologies, cellular extinguishing systems and conclude with lessons discovered.
NFPA eleven describes various forms of foam concentrate proportioning tools. In the next, three methods are checked out which are most typical. 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 concentrate or 6% for a 6% foam concentrate.
The proportioning price should not exceed 30% above the permitted value i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning fee is allowed to be an absolute most of 1% above the permitted value – i.e. 4% for a 3% foam focus or 7% for a 6% foam focus (the smaller worth must be used respectively).
To assure correct proportioning, the proportioner, including the proportioning rate have to be tested at least once a year and its right functioning must 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 froth concentrate from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi precept. When the fire pumps are activated, pressure is generated by the pump, causing supply 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 flow.
The advantages of this method are its easy design with out transferring parts and its straightforward operation. No external power is required, and the system is comparatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws such as 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 damaged, water will contaminate the froth concentrate. At a given proportioning rate, the system is appropriate only for low variations within the extinguishing water flow stress and quantity. Adding or altering particular person foam discharge units is possible solely to a really limited extent. The system can also be unsuitable for proportioning extremely viscous foam concentrates.
To conduct เกจวัดแรงดันไนโตรเจนราคา required annual testing, the system must be activated and premix generated on the venturi proportioner within the extinguishing water line. The appropriate proportioning fee have to be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus in the bladder tank needs to be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with flow 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 move meter in the extinguishing water move line. When the fire pumps are activated, the froth concentrate pump drive and digital control system should be activated. The extinguishing water move rate is measured by the flow meter and the management system adjusts the correct foam concentrate quantity through the control valve. The foam concentrate is injected into the extinguishing water flow by the foam focus pump. If there is a change in the move price, the quantity of injected foam concentrate is regulated by the management valve.
The system’s advantage lies in the exact proportioning of the foam concentrate, independent of the extinguishing water stress or move price. Foam concentrate may be topped up through the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system should be activated; nevertheless, the delivered foam concentrate can be measured through a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate rate. 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 external interruption-free power provide for the foam concentrate pump and the control system, as well as the necessity for a classy management system and the comparatively larger buying prices. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water flow price and the newly adjusted foam concentrate quantity. The foam quality may be compromised when constantly changing operating circumstances as foam discharge devices are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the froth concentrate, a water motor installed in the extinguishing water circulate 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 quick foam-concentrate injection into the extinguishing water. If the move fee modifications, the amount of froth concentrate is adapted immediately.
The benefit of the system is its independence from external energy sources in addition to a exact and quick foam-concentrate proportioning regardless of the extinguishing water stress or circulate fee. If a piston or plunger pump is used, adjustment or calibration after installation isn’t needed because the water motor and the pump are volumetric units firmly linked to every other. Foam concentrate refilling during operation is feasible. The system can additionally be able to proportioning extremely viscous foam concentrates. The system have to be activated for annual testing; nonetheless, the delivered foam focus can be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate price. No premix is generated; and if the froth focus is handed back into the tank, no foam focus must be topped up.
The bigger design and the comparatively greater buying costs are a drawback of the system.
With any system, consideration ought to be taken into consideration for the annual testing costs, which may be appreciable by means of replacement foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge gear could be damaged in extensive fires within the tank or within the dyke space and thus lose effectiveness, cellular fireplace screens and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve only limited extinguishing agent flow rates and reaches.
Firefighting monitors
Firefighting screens are discharge units mounted on vehicles or trailers and available in many sizes. The extinguishing agent move price can be up to 60,000 litres/min and the reach can be up to 180m if the pressure of the fireplace pumps is enough. They are suitable to discharge foam, e.g., to extinguish a surface fire in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to have the ability to stop it reaching the crucial temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke space should at all times be observed to keep away from an overflow of the dyke.
Mobile fireplace screens can be equipped either by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the foam concentrate usually takes place through cellular proportioners. This clearly points towards the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular units out there as back-ups is proven by the following instance for the position of monitors for fire extinguishing at tanks which are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This results in a quantity of alternate options for the screens. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which should be capable of handle varying circulate charges to guarantee flexibility throughout extinguishing operations. Depending on the native conditions, the displays might want to hold a minimal distance to the burning tank or may not be in a position to be positioned near to the tanks as a outcome of particles. In addition, it is not going to always be potential to position a number of screens across the tank. It should be ensured the monitor has adequate throwing peak in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal laws in addition to suggestions by associations like NFPA and is not checked out more intently in the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As talked about within the introduction to Part One of this text, it seems that many authorities and companies have not learned the necessary classes from disastrous fire incidents of previous years. Tank farm fires in the oil and petrochemical trade don’t occur incessantly. When they do, they normally have devastating consequences. Let us bear in mind the tank farm fire at Deer Park, Texas in March 2019 talked about within the introduction.
The fire developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for 30 minutes and caught fireplace for but unknown reasons. The plant had no gasoline warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fastened extinguishing techniques installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the local fire service, which was on the spot in a brief time however could not take management over the hearth with the tools out there, partially because flammable substance was constantly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of equipment and foam concentrate in addition to the preparation of a plan of motion took roughly 13 hours. The hearth was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt have been made over three days, with foam concentrate and water shortages occurring within the meantime. In total, over 500,000 litres of froth focus have been used. Instead of a fire within the dyke area, eleven of the 15 tanks burnt down.
It is very possible that the fire would have been extinguished rapidly if the warning methods and valves had worked and a exhausting and fast fireplace extinguishing system had existed. It can also be possible that the fireplace would have been extinguished rapidly if the extinguishing operation, which succeeded finally, had been started earlier. Both instances would have resulted in notably less injury.
Summing up, the following factors must be discovered at the least. As far as they haven’t yet been carried out, or simply partly, they should serve as a basis for discussions about one’s own fire-protection idea:
Have an appropriate fire-protection idea including various scenarios which adapt to the given situation regularly.
Always have a enough number of cell extinguishing systems as a backup to fastened extinguishing methods.
Stock an acceptable foam focus.
Ensure sufficient foam focus supply.
Ensure sufficient water provide.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing gear out there in a enough number.
Have trained personnel available in a adequate number.
Ensure a quick implementation of an appropriate plan of action.
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