BOILER MAINTENANCE Sonic cleaner does job of multiple blowers in clearing soot deposits
With nearly 140 Infrafone sonic cleaners installed on a variety of maritime vessels since 1982, Stockholm-based Infrafone is now promoting its patented boiler cleaning system offshore. The company's first award in this sector has come from Petrobras for the Cairu FPSO which is being rebuilt in Spain.
The basis of the Infrafone sonic cleaner is to prevent soot flakes and soot deposits building up in boilers, air pre-heaters and precipitators by generating a high intensity, low frequency (20-35Hz) sound which activates soot particles and forces them to follow the same path as air particles. With no sooty deposits slowing down the exhaust flow, efficiency is increased considerably.
The key element of the system lies in its patented acoustic feedback principle which generates infrasound that is always at a resonant frequency. The slightest departure from resonant frequency would have a highly detrimental effect on efficiency, but the system's reliability means that the activating power will always be at an optimum level.
Low operating costs
According to Infrafone vice president Harold von Matern, operating costs for the Infrafone sonic cleaning system are very low. "The blower uses 2-8kW on average with the system working intermittently by insonating 8-20 seconds every five minutes. Existing soot blowers need steam corresponding to a fuel consumption from 0.5-1.5 tons/day: with one Infrafone system replacing all soot blowers, pay-off time is very short."
The sonic cleaner consists of a quarter-wave resonance tube which is fitted to a positive feedback pulsator. The air supply is led into the resonance tube via a feeder tube that has a number of slots. These are partially covered by a surrounding slotted sleeve connected to a diaphragm which senses the dynamic pressure at the back end of the resonance tube.
A standing wave is then generated in the resonance tube with a wave length four times the length of the tube. The pressure variations of the sound wave set the diaphragm in corresponding motion at a frequency of about 20Hz. Because the diaphragm is connected to the moveable sleeve, the air supply is pushed into the resonance tube so that the standing wave is amplified.
The Infrafone equipment comprises:
- a pulsator that generates pulses into a 2.5-3.5 meter long resonance tube equipped with a diffuser. A compensator prevents vibrations from the sonic cleaner from being transmitted to the wall of the boiler.
- an air blower with silencers consisting of a two-speed motor and air blower built into the frame. The two speeds, insonating' when cleaning is being performed and `idling' when cleaning is over, are controlled from an electronic insonating controllers that monitors the generation of infrasound.
- the insonating controller, with meters for acoustic power output and pressure in the surge tank, is also supplied with an alarm in the event of insonate failure.
Easy installation and maintenance
Von Matern points out that the system can be easily installed by the customer's own personnel in one day, including commissioning. Only one penetration of the boiler wall made in the duct between the boiler and air pre-heater is needed, so no tubes have to be moved during installation.
Maintenance of the Infrafone system is also very simple, requiring only a few hours every year. "There is only one moving part in the pulsator and the special equipment we provide with the system means that maintenance can be carried out while the boiler is in service," says von Matern.
For more information contact Harald von Matern, Infrafone: telephone +46 8 661 3310 or fax +46 8 661 3360.
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the infrafone boiler cleaner system.
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Main components of the sonic cleaning system.
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