Hammer/Vibration in vacuum flashing tank 1

[Franklinchem]

Hi, We are suffering from the vibration problem in our vacuum flashing tank. This tank is used to cool down the process fluid(water dissolving slight amount oraganics) to precipitate these solids. The inlet temperature is 100°C, inlet pressure is around 2 kg/cm2G, the flowrate is about 100 M3/H, the pipe size is 6'', there is a control valve just before the vacuum flashing tank to control the upstream tank level(this valve is located in minimum distance to the vacuum tank). The vacuum tank works at -0.35 KG/cm2G and around 89°C. We found the the vacuum tank shakes a lot when the tank level reaches 40-70%(2.0M-3.5M above the feed nozzle.This vibration prevents us from lowering the pressure further to recover more solids. has anyone any idea about the vibration mechanism and the solution? thank in advance

 

[reena1957]

Dear Franklinchem,
Why do you hold a level above the feed nozzle? That seems to be the problem.
Best wishes

 

[Franklinchem]

Dear Reena1957,

We have to swing the level from 20% to 80%,required by the process. there is a filter downstream, this filter works in batch by sequence, so this vacuum tank should buffer the liquid volume when the filtration stops.

In fact, there is a agitator in the vacuum tank, I don't know if the un-adequate agitation can cause this hammer?

Best regards

 

[reena1957]

Dear Franklinchem,
If possible, change the location of feed Nozzle above the highest level. Secondly, vary the agitator speed and see if the vibration stops. Stop the agitator totally before the feed is filled in the vessel and then run it.
Best wishes

 

[JimCasey]

Thank you for all the data you supplied.
I ran some calculations and the water is flashing. The velocity into the empty vessel is nearly 100 meters/sec. As the vessel fills there is more back pressure and the fluid both flashes less and the velocity decreases. I suspect that at higher fluid levels, you are getting slug flow causing the water hammer you mention. At the high levels you are almost at the boiling pressure of the liquid as it exits the valve....only 0.2% of the mass shows that it remains as steam.

If you discharge into the vessel above the level you will need a mist separator, but it will likely limit how much you suffer from the slugs of flow.

 

[25362]

Reena1957 is right. The mechanism: vapor slugging through a deep liquid layer. The cause: series operations not balanced out.

Other possible solutions that came to mind:

[•] to smoothen the downstream batch operation, possibly by duplicating it, or
[•] to use a parallel vacumm vessel to absorb the added
volume.

 

[Franklinchem]

Thanks, Guys,
I appreciate the suggestions you guys gave, they are very intereasting. Before making any conclusion, there are still some points to clarify:
1) To increase the inlet nozzle above the the liquid level(On the top of the tank)may solve the hammer problem. And the mist elimation is not a problem, there is a scrubber betwen the vapour outlet and the condenser, the return condensate can wash the discharge vapour.
My concern is the solid buidup, since there are some dissolved solid in the feed, after flashing and cooling, the solid will precipitate, if the feed in above the liquid level, the flashing will splash the solid on the wall, and the buildup will happens.
2)To duplicate the tank or vacuum cooling system, means a lot of investment, I need to prove my boss that there no other way to solve the problem.

Let's keep on the efforts to find the optimized solution

Best regards

 

[reena1957]

Dear Franklinchem,
Put an impingement baffle in front of the feed nozzle to direct flow downwards.
Best wishes