Control valve vs silencer

[Mike4chemic]

Hi,
I have a vaporizer with a constant blow-down to the atmosphere of CO2 and Steam.
The standard design for this blow-down is using silencer downstream of a control valve (attached case 1)
I wondering whether I can use another control valve instead of the silencer (attached case 2) and still maintaining the original performance (noise level of 85 dB).
Is it feasible?
What should I be concerned of?

Blow-down stream properties:
Pressure [bara] 6.9
Temperature [°C] 145.5
Flow [kg/s] 7.5
Water: 60% vol.
CO2: 40%vol.

Appreciate your help.

 

[zdas04]

My experience with acoustic modeling is that it won't tell you much that is valid about your idea. If I were you I'd see if there was any way to try it and measure the noise. I'm pretty confident that you won't get a closed-form answer to the noise propagation through two control valves situation. I may be overstating the primitiveness of state of the art sound modeling, but I am consistently disappointed in the performance.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[EnergyMix]

It depends on whether you're in an area where you need the accoustic reduction in noise. In other words, to be blunt, are you in the US and will you violate an OSHA requirement, either state or federal, if you don't have a silencer installed? (If you're in a different country, they may have a similar regulation, it just wouldn't be OSHA.)

 

[zdas04]

I haven't seen the regulation that required a "silencer", mostly I've seen "noise level must be below ___dBA at 3m" or whatever distance. With language saying "what" needs to be achieved instead of "how" to achieve it, then the kit you use to reach the goal is up to you. Has OSHA started going to regs that specify certain kit by category?

I am starting to see more and more regulations specifying "how" and they really piss me off because the regulators are effectively killing any chance of a better mouse trap being developed. I worked on the new Subpart OOOO of the Clean Air Act last year for the API an we identified dozens of places where the "how" regulation would result in dirtier air than just telling us the target. Mostly they listened (for once) and we got an awful lot of that garbage exorcised.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[EnergyMix]

David, I don't know that OSHA requires a silencer; I haven't read them recently I agree with your assessment that they most likely set a minimum standard of "noise level must be below x" and companies end up using a silencer to get below "x." And that's not necessarily a bad thing. It protects people's hearing and the older I get the more valuable I find that (after years of working in power plants, I find my hearing degenerating, and I assiduously wore ear protection. Heck, I wore ear protection to the health club, even though I got strange looks. I'm not against having silencers, hearing protection, and quiet zones. Different working environment.)

I was trying to let Mike4chemic know that, presuming he was in the US which might be a bad presumption on my part, that there are reasons for silencers and a control valve might not meet those reasons.

 

[zdas04]

When I worked in Power Plants real men didn't wear hard hats or hearing protection. As my hair thins the results of no hard hat and rising stem gate valves becomes evident. There is a band in the noise spectrum that I "hear" as pain. Your way is better.

The reason for silencers is to lower noise level. Million ways to do that. The last time I read 1910 it said "what" not "how". The two control valves idea might be an effective silencer since you can set it to adjust for changing conditions.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[steamdog]

The noise is created in the valve due to the pressure drop. By using a second control valve, each valve will take 1/2 the drop and the noise created will be less. Will it be low enough for your code/application? - I could not tell you. However, if you do put in that second valve it will reduce the capacity of the first valve you have installed now.

 

[Mike4chemic]

Hi,
The application is designated to EU power plant. We do have restrictions on the noise level.
I can't do an experiment to check it.

my concern is, whether the pressure drop on the second valve and the release of vapours will cause high noise level.

with the valve vendor's software it looks that i am on the safe side (<80 dB).
Do you have any more suggestions, on how else can i check it?

 

[EnergyMix]

Mike, there's a NASA paper on acoustic monitoring. I thought I had it bookmarked, but I'm not finding it quickly. Try doing a search on the site using the words "acoustic monitoring" and see if it comes up. If I have time today (not really likely) I'll look for it, but don't hold your breath.

 

[rmw]

There are valves made to mitigate valve noice. Google the terms (without the parenthis) "whisper trim", "hush trim" and "drag valve" and see where that takes you.

rmw

 

[hacksaw]

a lo-db plate (multihole restriction) and a vent stack with silencer

a 16" valve say 3 bar drop is not cheap and is likely noisey it self, use a single valve and treat the noise

regs are fine, they're good for business, remember when the noise restrictions first arose in the 70's...everyone thought the end of the world,...

not really, the valve suppliers were delighted...and the valve ended up providing better control with longer life,

we had a valve in a plant designed in the 50's, it went through 30K of inconel trim every month! OSHA noise restrictions did not exist when designed,

since when did engineers start complaining about "homework"

 

[Mike4chemic]

For now, I will design for case 2 (two valves).
I am still concerned about the high velocity flow through the blow-down pipe to the atmosphere.
What do you recommend the vapours' max velocity criteria of design should be, to avoid the noise restrictions?

 

[hacksaw]

the discharge pressure at the vent exit must be held below 2 barA and
the deltaP/P at each valve must be held less than 0.5 with the fluid mach number at each valve exit held less than 0.3...

your valve supplier, will advise as to the generated noise in the valves and you'll have to consult the vent silencer supplier as to un-treated vent noise

we expect a full report of your piping and valve cost options next week...