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ACOUSTIC CLEANING SYSTEMS...BLACK MAGIC, OR DO THEY REALLY WORK?
The principle behind acoustic cleaning is very simple: sound is a vibration through air that can be heard. Vibrations are effective at dislodging dust from surfaces, and the source of the vibration doesn’t matter. If a vibration is imparted to a dust-coated surface with enough intensity, dust will be dislodged from that surface, whether the vibration is caused by sound waves or a mechanical impact. Nothing magical about acoustic energy...it’s just a source of vibratory energy.
The frequency and intensity of the vibration are critical factors in acoustic cleaning. To be effective, the frequency should be low, but not too low, and the intensity of the sound (decibel level) must be great enough to remove the collected particulate. BHA’s Powerwave acoustic horns are scientifically designed to produce powerful
pulses of sound energy that will resonate and dislodge dust from fabric filters, boiler tubes and heat exchangers, precipitator collecting plates and high voltage discharge electrodes, hoppers and dust lines, even SCR catalyst. Acoustic energy has been used successfully for more than 20 years to improve the efficiency of air pollution control equipment in many applications, and has even enabled some plant operators to use acoustic horns as their sole cleaning devices!
THE ROLE OF FREQUENCY AND INTENSITY
Typically, the lower the frequency, the more effective a horn will be at dislodging dust or particulate. However, extremely low-frequency sound waves (produced by infrasonic devices) can be dangerously close to the resonate frequency of the structure or vessel and can cause damage to the structure or loosen or crack welded or bolted connections. Powerwave acoustic horns operate at 75 hertz or above, well above the frequency of the structure, and cannot damage structural components. Low frequency, high decibel sound is proven to be the most effective at removing particulate, without damaging the equipment.
Acoustic cleaning is accomplished through particle displacement, changes in pressure that break the bond of the particles from themselves and the structure. Lower frequencies produce greater displacement (or changes in air pressure) and will clean a larger cross sectional area. BHA’s family of acoustic products are engineered and tested to produce the cleaning power you need, with moderate cost, low maintenance, and high efficiency. We publish the frequency and intensity ratings of our horns, so you know what you're getting.
PROVEN APPLICATIONS FOR BHA POWERWAVE ACOUSTIC CLEANING SYSTEMS
BOILER TUBES/HEAT EXCHANGERS
Powerwave horns can be used to supplement or replace steam sootblowers in industrial or utility boilers. Many boiler operators have found that they can reduce or eliminate opacity spikes associated with sootblower use by using Powerwave horns to keep the tubes clean. The horns can be operated more frequently than sootblowers, and keep the tubes cleaner without parasitic steam use. Annual maintenance expenses are much lower than for retractable sootblowers, as Powerwave horns have just one moving part, a tough titanium diaphragm plate. Powerwave acoustic horns are also extremely effective for removing particulate from rotary or tubular heat exchanger surfaces.
BAGHOUSE FABRIC FILTERS/ELEMENTS
Traditional fabric filter cleaning methods (shaking, air flow reversal, or pulsing) create motion in the filters that can shorten filter life by causing abrasion and flexing of the fibers. Acoustic energy is gentle to the fabric, but effectively resonates and dislodges dust accumulations from the filters. Acoustic energy can allow reduced frequency of traditional cleaning cycles, and in some cases can eliminate the need to use any other method of cleaning. (Pulse-jet baghouses usually require some traditional pulsing, unless BHA-TEX membrane filters are used.)
Precipitator internals are cleaned using either externally-mounted rappers, or internally-mounted rotating hammers. Both types of conventional cleaning systems literally “hammer” the dust free from the surfaces, allowing it to fall into the hoppers. Cleaning cycles often result in some re-entrainment of the dust, and the effect of the mechanical impacts used tend to cause cracks, distortion, and fatigue of the collecting surfaces, along with failures of the discharge electrodes. Powerwave horns clean these surfaces without imparting mechanical stress and fatigue, and sometimes prove to be so effective that the conventional rapping systems are no longer necessary.
SELECTIVE CATALYTIC REDUCTION (SCR) EQUIPMENT
Historically, SCR cleaning was done using steam sootblowers, although the parasitic steam usage could cost many thousands of dollars per year, and sootblower maintenance costs were often high. Because sootblowers are operated infrequently, the amount of ash dislodged is excessive, and can result in re-entrainment and "puffing" at the stack, as well as reduced catalytic reaction between sootblowing cycles. Moreover, the action of steam sootblowers tends to erode and shorten the life of SCR catalyst. Acoustic energy is a viable, effective, and comparatively inexpensive method for cleaning SCR catalyst. Advantages: lower cost and operating expense, low maintenance cost, and very small size compared with steam sootblowers.
MATERIAL HANDLING (HOPPERS, FANS, SILOS, DUCTWORK)
Powerwave horns are designed in many different configurations that allow them to be used in hoppers, I. D. fans, bins, and ductwork. The more compact models can be used to fluidize dust in pneumatic conveyor lines and hopper emptying valves, while specialized models are used to keep fan blades clean, balanced, and vibration-free. Acoustic horns can eliminate the need for sledgehammering, rodding out hopper poke holes, or dangerous work unclogging ash vessels.