calculating sound level on steam vent 1

JD327,
The answer is "it depends".
Noise level depends where source is located and where you are measuring it and what is the distance between source and control point.
The best advise I can give you to contact vent silencer manufacturer and ask your question. Usually they have a lots of practical experience with noise and also can size and give you quotation of silencer based on your requirement ( 90 dB at 3 meteres or similar).
Try to google "vent silencer".
Regards,

curtis

Well at this point we are just in a P1 DMF, where we are basically getting a project together, + or - 50% estimates, and having all the reasons (deliverables) why this project needs to be done, pleaing to the jury if you will. So if we can say that this pipe venting is 150 dB and show how we derived that number, and knowing that the compliance standard is 85dB at 10ft or 3m, this is now a major safety and compliance concern. It's so frustrating to me, seems like equating this would be so simple!

Thanks for the input though, the last time I went through a vendor on this it was a major headache, I gave him all the information we had, he said he would figure it up and call me back, but he must have forgotten. I have three other vendors quoting silencers, but they seem to only want to give the level it will drop or the maximum level it will reach.

I had somewhere noise control booklet with estimation of those. When I will get home I'll check.
The other things you have to consider is distance. If there is no special noise barriers noise level will be reduced 3 dB when you double distance.
If your vent is 50 feet above roof level, and the closest a person will get is 200 ft. from discharge point then this will be a different situation. Compliance standard will be different because in order to get 10 ft from a nozzle your employees should have wings to fly around that pipe.
Check location of exaust pipe and distance to common walkway area in the plant where people can walk. Also check the distance from source to perimetr or a wall of the plant and what is located behind the wall of the plant. It will be important if plant is located next to residential or wildlife area.
I told you "it depends".

JD327,
I've got my book.
Vent and blowdown noise is a function of upstream pressure and temperature, type of gas being vented, the valve size and type, plus the effect of downstream piping.
Vent noise is relatively broad band, and of predictable high intensity (amplitude) in the immediate vicinity of the vent.
Many theroretical aspects of vent and blowdown silencing are highly complex. Where usable theory has not yet been perfected or is not readily understood, the experience factor remains as important as scientific principles.
Silencer type and size is based upon:
- Service (continuous or intermittent)
- Aplitude (Lw or Lp) of the unsilenced noise
- Peak frequency fp of unsilenced noise
- Specified noise criteria (required silencer DIL)
- type of gas being vented
- upstream pressure and temperature
- flow rate and allowable pressure drop
- cost considerations
Your estimation 150-160 dB seams correct. I've got in a table 158 dB noise level at 100 ft from unsilenced vent with 3" valve venting air at 200 psi and 500 F. For 100 F at the same conditions table has 151 dB. This is 100 ft away from pipe venting upstream (at 90 degree)!
Now, flow rate venting to atm. You wrote 200,000#/hr. I'm a bit puzzled by this. How did you estimate this flow rate? I'm asking this question because flow rate will depend on type and size of valve (PD through valve), type and size of silencer selected (PD through silencer), and also piping layout.
I would refer you to valve supplier who can also give you a quote for valve (you have to give him your operational conditions) with nose data. In most cases they have experimental data.
You can look for more detailed data, however, based on my experience I'm afraid no one can you give precise answer to this issue. Usually, when you request silencer manufacturer to meet nose level at some level (to garantee it) they will quote one size bigger silencer in order to have some extra margin in noise attinuation. This is the case when bigger is better, but it comes with cost.

Have a fun,

curtis

Maybe you will find useful info at the link below: