Depth of turbulence in a tank from a poured inlet stream 2

[kling]

I've encountered an interesting problem that I could use some input on. A tank at my job site has a layer of sedimentation in the bottom which, when disturbed, enters a process and causes issues with inline equipment. The tank is on a recirculating loop and has an inlet for the recirculating fluid, and the tank level varies from day to day.
I want to determine how full the tank must be to dissipate the energy from the falling fluid from the inlet to such an extent that the sediment on the bottom is not disturbed. In different words- How deep into a pool of liquid does the kinetic energy from a stream of flowing liquid penetrate before any induced turbulence is dissipated?
Any help is appreciated.

 

[bimr]

Little information is provided.

From experience, you can expect currents in a tank to be as deep as 10-12 feet.

The current dissipation will depend on the residence time in the tank, the specific gravities of the fluids and sediment, the size of the flows, the tank geometry, etc.

Installing some type of baffle or flow distributor may be of some help to minimize the turbulence.

 

[Compositepro]

So how long are you going to allow sediment to accumulate in the tank? How about using a filter.

 

[kling]

Thanks for the input, a baffle is a good idea. We will be installing a filter in a few months during a scheduled shutdown but in the interim maintaining a high enough fluid level to avoid turbulence is an easy way to mitigate issues. I did manage to find some information specific to the calculation I needed after some searching- for reference:

http://eprints.hrwallingford.co.uk/1127/1/SR63.pdf

 

[bimr]

Not sure that paper is going to help you at all.

Try a google search for "flow patterns in water treatment tanks".

Most of the equipment manufacturer's have already visited this subject extensively.

 

[Compositepro]

You can let the fluid cascade down a chain or extend a dip pipe close to the bottom and elbow it upwards at the end. A small hole in the side of the dip pipe, at the top, will prevent siphoning, if that is a concern.

 

[cvg]

the Wallingford paper deals with alluvial river scour caused by discharges from dam outlet structures. The "sediment" size was 0.25 meters, corresponding to a small size of riprap. not at all relevant to your tank, but a good addition to my dam safety library.

 

[kling]

The gold in the Wallingford paper is in his references, in case you want to flesh out your library some more

 

[cvg]

agreed

 

[itsmoked]

Doesn't seem like a great solution worrying about "how deep" if you don't remove the sediment. Eventually it will reach any level and be disturbed.

Why not put in a polishing filter to continually remove all sediment from the tank. Then maintenance becomes closing some valves and replacing a filter element occasionally.

Keith Cress
kcress -

http://www.flaminsystems.com