5 replies to this topic

[process engineer2002]

Hi all,


I need to put a vortex breaker in a horizontal vessel.

How do i determine the distance from the outlet nozzle to the low liquid level ?

I found the way calculating Minimum submergence with an equation. but that equation is not for vortex breaker but for without vortex breaker.

-the process conditions are as follows

1. outlet nozzle size : 30"

2. oultet nozzle will be located on the bottom of hori. vessel.

3. Cross type vortex breaker should be used(as per requirment)

4. horizontal vessel size : dia 5m / length : 20m

5. outlet pipe is conneted to pump. flow rate : 2300 m3/h

now my questions are as follows

Q1) how much distance(min. submergence) could i reduce by using vortex breaker?

Q2)"Cross type vortex breaker(on 30" outlet nozzle) width shall be nozzle dia. but not less than 100mm" as per
requirement. that means the vortex breaker width will be 30"

the low liquid level should be above top of vortex breaker? if the top of vortex breaker is above low liquid level,
the vortex breaker doesn't work?

i would like to lower the low liquid level as long as the vortex breaker works well.
if the low liquid level is 30" from the bottom of the horizontal vessel, the volume under the low liquid level will be dead volume. This means the volume will be loss.

Is there any standard for determining the distance from the outlet nozzle to the low liquid level with a vortex breaker?



Your guidence is much appreciated.
thanks,
nick

[Pilesar]

To determine the minimum height required to avoid a vortex, there is a simple equation from "Hydraulic Institute's Pump Intake Design" ANSI/HI9.8-1998 manual:

S = D + 2.3DFr

where:

S is the minimum height above the outlet nozzle to avoid a vortex.
D is the outlet nozzle diameter.
Fr is the Froude number.

For your large nozzle, the equation indicates a submergence of greater than 5 feet is required to avoid a vortex. This is about a third of your drum, so use a vortex breaker.

Do you have a level bridle on the drum? The lower tap of the level bridle will usually set the low low level. I would set the lower tap about 25 inches from the bottom for a 5 meter horizontal drum considering mechanical constraints.

Your drum seems designed for a liquid holdup of about five minutes between high level (HLL) and low level (LLL). Consider that in a horizontal vessel, the volume per inch of level is lower as you get near the bottom. At a liquid level of 25 inches there is less than one minute of holdup.

[process engineer2002]

Thank you for your detail response,

there will be a level bride with side/bottom connection. Anyway, if i set the low low liquid level(LLLL) about 25 inches from the bottom for

a 5 meter horizontal drum considering mechanical costraints, the vortex will not occur near 25inches from bottom?

At LLLL, the pump will be stoped. that means the pump will be still running while liquid level go down from LLL to LLLL.

in my opinion, vortex should not occur while liquid level go down from LLL to LLLL

So i want to know the way to set LLLL with vortex breaker.


tanks in advance,
nick

[Pilesar]

Most engineers assume there will be no vortex if there is a
vortex breaker installed. I do not know of any way to easily
confirm this with hand calculations. Fluid flow device
designs seem to be primarily based on experimental data. If
your four-blade design is specified by the client, you
should probably install one to meet specs. Why come up with
a new method to operate at a lower liquid level when the
benefits are so small? It is more important to be able to
justify your design based on client specs and accepted
industry practices. Make certain you have a properly
designed pump suction line and the proper suction head.

There are other designs of vortex breakers, including
minimal three-blade baffles and more complex grid plates in
alternating orthogonal layers. One process engineer I worked
with was convinced that the cross-shaped vortex breaker he
installed in a deaerator resulted in four smaller vortexes
instead of one large one. I am still a little skeptical,
but he replaced it with a grid design and the problem
disappeared.

[process engineer2002]

I appreciate very much.

as your advices, I agree on that there will be four vortex.

I think i should come up with a new method, like a grid design.



thank you very much.


nick.

[breizh]

To be considered :

http://www.gouldspum...m/pag_0007.html

Breizh