Noise Reduction

[sampi]

We use "modified" compressors to pump our process gasses through the plant. We have about 22 compressors that makes quite a lot of noise. ~ 130dB for one, then you add about 6dB for every compressor, thus in total more or less 256dB.

We definitely need to provide ear protection for our operators. An we consulted a acoustic engineer and he said that the only way to shield noise is by surrounding the unit that makes the noise with mass & density (concrete, steel, ect) and that putting soft tissue on the walls will, if that much, only absorb ~6dB in total.

Please comment!

If anyone knows about an alternative way to reduce noise instead of surrounding our compressors with cement/steel or to put them underground, I will appreciate your input.

 

[sshep]

sampi,

256dB sounds impossibly high, but even 130bB or above is serious noise. I think you should review your noise calculations including your interpretation of the attenuation estimates supplied by your acoustic engineer. A plot plan with actual noise survey data is the best way to capture the distance impact of noise in the work area, a factor which you don't mention when citing your noise levels. You may be better off than you think once your engineering controls are installed.

In the USA you would be required by OSHA code to implement some engineering and administrative controls- hearing protection is personal protective equipment and cannot alone bring you into compliance.

Generally you only have two noise control choices at the compressor itself, lag the compressor directly or put it inside an enclosure. For multiple units an enclosure is usually more economical. It has not been my experience that these enclosures are solid concrete, but rather a metal frame with panels designed for noise control. On the otherhand, even a solid concrete barrier wall would be a welcome relief if the situation is as bad as you describe.

best wishes,sshep

 

[Guidoo]

Your noise figures cannot be right. A sound pressure level of 130 dB(A) results in immediate hearing damage to the unprotected ear. Even double hearing protection (earplugs in combination with earmuffs) will not be sufficient. Also combination of two noise sources results in an additional 3 dB(A), not 6. 256 dB(A) is just not possible.

When you use noise enclosures, note that you also have to provide forced ventilation, gas detection in order to protect against explosions (assuming you have a flammable gas in your plant).

 

[epoisses]

256 dB is a nonsense figure. You can't just add all the noise up becasue you can't stand right next to 22 compressors at the same time. What you ought to do first of all is do noise measurements in the plant, map them and then develop a specific plan for the few locations where the level is too high. 130 dB is very high and in my experience is encountered either not at all or very close to a very noisy compressor.

I guess burying compressors underground is not very cost-effective and makes maintenance a pain in the butt, but before discussing preventive measures futher, go out there and collect more detailed data.

 

[dan21703]

Agree that most if not all of your numbers are suspect. Easy to get turned around in noise calculations. Noise is measured as flux xxx dB at yyy ft. Normally the noise is rated at 3-5 feet 1-2 meters. Noise will dissapate by free air by the cube rule. Since dB is a log scale the free air attentuation is lower but significant nonetheless.

As suggested here and in other replies you must consider geometry first then attenuation. I do not doubt however that your compressors are not too noisy. There are many ways to attenuate noise and there are some very effective commericial products. Depending on the frequency of the noise concrete and/or steel can be as much a transmittor of noise as an attenuator. No simple answers with noise engineering. However the commerical products do work and you can get significant reduction using this or adding insulation lagging to the source. If possible the easiest way to significantly reduce the noise may be to modify these "modified" compressors however.

good luck.

 

[sampi]

Ok! Did some measurements. ~104dB per compressor. And I have 22 of them. The acoustic guy estimates the noise levels to be about 116dB for the plant (still trying to figure out how he got to that).

Can you comment on the use of white noise? The alternative would be lagging (and personel protection for the operators).

If white noise is a suitable solution, it would make communication on the process floor much easier.

How advanced/effective is white noise apparatus currently?

 

[epoisses]

Please note that dB is a logaritmic scale. Each time you add X dB, you multiply the noise by Y. I believe 3 dB is a factor ~2 or so, so a factor Y=22 corresponds to 2 log 22 times 3 which is X=13.4, which takes you from 104 to 117.4. You should be able to find more accurate data to verify that.

104 dB sounds like a much more reasonable number. I guess most chemplants solve the local problem (for the operators and maintenance people) with earplugs. That of course provides no solution for the surrounding communities if you have a problem with those. I wouldn't be able to advise further on that, I'm really not an acoustic expert.

 

[sidassy]

we have customers that use electric driven compressors together with large generators in locations where noise is an issue..

 

[Guidoo]

At this point the only good advice is that you should contact an acoustic consultant to do a study and make a report. Your question goes beyond what can be expected from a forum such as this.

When I look at the description of white noise on

http://science.howstuffworks.com/question47.htm

, I don't think this will help you. You can mask a specific noise by adding noise at other frequencies, but you cannot make it disappear... It will not make communication on the process floor easier as you suggested.