Winterisation by-passes - noisey..

[jamesbanda]

Dear all,

I am looking for a reference which would allow me to calculate in an Orifice plate is noisy.. ?

On plant we built 5 years+ ago we installed 5/6 mm orfice plates pw pressure 4/5 barg, return pressure nearly atm.. they were very nosey we ended up placing two orfice plates on the project to stop the noise..

For our next plant we are doing the same... i want to avoid two orfice plates - it is mad!!we should be able to calculate the flows where we have a problem..

i plan to suggest we drop the flow from 500kg/hr to 20kg/hr for freeze protection based on the norwedgen standards i found on freeze protection (over the whole project this will save several tonnes of water)..

 

[SeanB]

Could you supply more information please? What are you bypassing for one thing?

 

[jamesbanda]

the winterisation bypass is for freeze protection...on process water duty

i bascially want to know how to ensure the flow is not noisey and what citeria should be applied to prevent this...

 

[rzrbk]

I would suspect that your noise is caused by cavitation and will not be affected by reducing the flow rate. With the downstream pressure at almost atmospheric, a staged pressure letdown (two restriction orifices) will likely be required.

The other option I see is to raise the return pressure by elevating the return piping outlet. (a small amount may be all that is required)

Many orifice plate sizing programs will calculate what downstream pressure would be required to eliminate cavitation.

 

[JimCasey]

If your orifice plate has a single hole, it will likely be much noisier than if it has an array of tiny holes. The characteristic frequency of the plate is defined by the hole diameter. Smaller holes-higher frequencies. most of the noise generated by a 2mm hole is above the audible range-and if you can't hear it, is it noise?

 

[sshep]

A short length of appropriate bore tubing may be an alternative to noise generated by taking the pressure drop across an orifice plate.

NOTE: The bore decrease required to go from 500 to 20 kg/hr will give so small bore diameter as to plug easily.

As to water conservation, spirax-sarco and others make a modulating freeze protection valve which will adjust the flow based on the temperature of water flowing through the freeze trap. Might be worth checking into if water conservation is a concern- install with filter and locate per manufacturer recommendation.

best wishes,
sshep