Dust collector filter extractor fans and cyclone separators can generate high levels of noise and are a common cause of complaints. Conventional silencing can be difficult as the dust in the air will clog the attenuator, reducing the performance and requiring regular cleaning and maintenance. Installing silencers can also reduce the efficiency of baghouse filter systems. In some cases, structural vibration or acoustic resonances can also cause noise problems.
Given the problems with conventional dust extraction fan silencers, how can you reduce the noise from dust collectors and cyclone separators without the maintenance and efficiency compromises associated with attenuators?
Fortunately, there are solutions in the form of elegant, low-cost alternative engineering noise control methods for these traditionally difficult applications. We've also developed the technology to diagnose and solve these noise problems remotely by email - a much faster and lower-cost process than commissioning noise reports.
The following is a detailed explanation of the best practice dust collection, cyclone separator, and bag filter fan noise reduction technique options with examples.
Dust extract noise control
Email us a video from your smartphone for an evaluation of best practice
Filter and cyclone fans often generate low-frequency (LF) tones (hum or drone) that can vary in level substantially depending on the backpressure in the filter bags (how often they are cleaned). These tones travel long distances, causing noise complaints. These LF tones at the blade passing frequency of the fan (fan speed x number of blades) are very poorly attenuated by conventional mufflers as absorptive silencers are only effective at mid-to-high frequencies (above about 300Hz).
The best solution is to use aerodynamic fan noise reduction techniques:-
Scrap and dust extract chopper fan and cyclone example
In the example shown here, the 147Hz tonal noise from this tyre remould scrap and dust extract chopper fan and cyclone was reduced by 32dB and the overall noise by 19dB(A) by fitting an aerodynamic insert at a cost of c £2k instead of the proposed enclosure at a cost >£30k - and that would not have attenuated the tone...
The mid to high-frequency noise can be generated by airflow through the extract fan or cyclone separator, by material and scrap impacts on ducts and cyclone surfaces, by system vibration radiated as noise or by reverse jet filters - or by all four. The noise reduction options for these sources are detailed below.
Reducing airflow noise from fans
Residual airflow noise can be reduced by:-
Material impact noise and vibration
This takes the form of mid-high frequency "rattling" sounds from the impacts of, for example, wood or metal fragments in duct walls. As the walls are thin material, they behave as very efficient loudspeakers that convert the impact vibration into sound. The same applies to motor, fan or other vibration source radiated by panels as noise. There are 2 fundamental noise control techniques, the choice of which depends on the application.
Reverse jet filter noise control
The intermittent high-frequency pulsations from reverse jet air filters are another potential cause of complaints. There are 2 effective noise control techniques:-
The noise from cyclone separators is usually created by the filter system or baghouse fans. Where that is the case, the noise reduction techniques described above provide the best solution. However, in some instances, there can be acoustic resonances in the cyclone or structural vibration that is radiated as noise (particularly if a vibrator is used to move the contents).
Cyclone acoustic resonance
The noise from a number of cyclone separators that were used to transport and filter PVC granules from the waste plastic included a shrill, penetrating whistle at 4975Hz that dominated the entire production area. As well as being extremely annoying, the overall 110 dB(A) noise level posed a very high risk of hearing loss.
The noise control measures under consideration were high-cost acoustic enclosures.
We diagnosed the cause to be a flow-induced resonance that was eliminated by inserting a small shaped steel sheet, tuned to provide the maximum attenuation. As shown here, this reduced the tone by 50dB and the overall noise level by 25dB(A) at a cost of <£1. Potentially a world record for cost-effective noise control...
All you need is a smartphone and 30 minutes. Send us a few photos and recordings, we will then analyse the data and send you the optimum (and costed) noise attenuation options. The details of the information we need are provided on the Remote control of noise page. This process typically reduces noise control project costs by 50% - 90%.