10 replies to this topic

[A mukherjee]

Hi everyone,
In our plant there is a packed tower where air is cooled by water.Water enters from top & air feed nozzle is at bottom.Water is distributed by pipe arm type distributor.
I just want to know how to calculate the optimum distance between distributor & top of packing support,so that the top part of packed bed does not get flooded & distribution becomes even.

[Art Montemayor]

The distance between distributor & top of packing support is irrelevant. It plays no role in determining if the packed bed gets flooded or liquid distribution becomes even.

I have, in the past operated absorbers and other towers where the distributor (mostly trough types) were resting on the packed bed itself – and no negative effects were ever noticed or claimed. Do not get my statement wrong. I am not advocating that you not dedicate a reasonable distance between the distributor & the top of your packing support. On the contrary, I believe you should leave some distance there in order to allow for inspections, packing support maintenance, distributor maintenance, etc., etc.

But the proximity of the distributor to the packing will not be the cause of any tower flooding. Flooding is caused by other factors. It will also not cause any increase in liquid entrainment. The critical height dimension to pay attention to in the top section of a packed tower is the distance between the liquid distributor and the top vapor outlet nozzle. This height represents your disengagement space and it is related to the type of distributor you employ. This height is dependent on the liquid, the superficial velocity, and densities of the gas and liquid.

[A mukherjee]

Thnxx a lot ART.
Is there any guideline for determining the disengagement space height?
There are actually two such zones in the tower.
1.From the water distributor to demister pad
2.From demister pad to air outlet nozzle.

[Zauberberg]

See attached.

Attached Files

•  Clearance.pdf   75.73KB   155 downloads

[A mukherjee]

Thnxx a lot Zauberberg...but how can these rule of thumbs be deduced?

[Art Montemayor]

Please refer to the attached workbook for detailed comments.

This thread started out with a simple question about liquid distribution and tower flooding. Now it introduces vapor disengagement – a totally different topic. It starts to go in different directions at the same time and is confusing.

What – exactly – is your concern with this water scrubber tower? Is is flooding or is it water entrainment? The two subjects are the matter of diferent design principles and criteria. Let us go back to basic data:

• Is this tower existing and operating? ( I assume it is)
• Is it operating satisfactorily? If not, what is the problem with its operation? Is there any water entrainment taking place?
• Are you proposing to change the original design basis?

If it is an existing, operating tower with a mist eliminator it obviously was designed and supplied that way. The design of the tower obviously included an incorporated mist eliminator design. What has been designed and supplied must have fulfilled the original specifications and was accepted. If this has now changed, what has taken place? The original calculations and design should reveal what the capacities are and what are the design limits. The original designer and fabricator should be consulted if there are any operating faults or deficiencies – or if there is a desire to increas or modify the original specifications.

Attached Files

•  Water Distributor distance to Packing.xls   1005.5KB   133 downloads

[A mukherjee]

Thnxx a lot ART for the post...But I am having some difficulty in opening ur attachment.

In reply to ur qstns ,
1.The tower is not existing.It is currently in design stage.
2.I want to calculate that distance(liquid distributor to vapour outlet nozzle) to minimise entrainment only.
3.As this is currently in designing stage,so there is no qstn of changing original design.

[Zauberberg]

Here you can see the recommended distances for a vertical demister-type of separator. It is equally applicable for columns as well.

As Art has explained, these guidelines were derived after a lot of theoretical (CFD) and empirical (plant) studies have been done. They also concur with common sense, i.e. the demister pad cannot be located immediately above the inlet distributor as it would suffer from entrainment and low efficiency.

If you are asking us to show you the Sun we can do that. But if you ask us to confirm at which steps and which way the Sun has been there on the sky from day No.1, I'm afraid the true answer you can get only from the Creator himself.

Attached Files

•  Layout.pdf   45.58KB   117 downloads

[A mukherjee]

Thnxx a ton...

[Supriyo Mukherjee]

Hi,

I have one question regarding it.

If we are dealing with an packed bed in which air is getting cooled by water from top.

What will be distance between the water distributor and the mist eliminator at the top before air outlet.
Is there any guidelines for fixing these distance(some empirical equations )
Generally we are using minimum 0.5*ID od the tower as an thumb rule.
This distance is recommended as some entrained water is presumed to settle down before mist eliminator?
Kindly advise

[breizh]

Hi ,

Let you try google ( tower disengagement height ) or Perry chemical handbook or ludwig or manufacturers like Glistch/Koch or others.
Hope this helps

Breizh