11 replies to this topic

[Root]

Hi Al's,
We are facing a hammering problem in our fractionator column at reflux inlet point, actually hammering is inside the column. Hammering is started when we reduced the feed to 80% and reflux is 70% and TPA IR remained same and temperature is 50~ 45⁰C.
we check water contents are very less just 800ppm and composition is same only. Reflux line dia is 8" and inlet nozzle is 10" . I am assuming about the velocity has reduced to 2.5 ft/sec instead of 3 or 3+ and this is the main reason?
Can any one please explain or give some clue about this problem.
Thanks
Toor

[AngieD]

Just a thought. Have you tried modeling the surrounding system?
This is a software I'm currently learning and it would seem useful for determining hammer effects in water systems...

http://www.flowmaster.com/water.html

[Himanshu Sharma]

Sir ,

This is interesting as there is practically no water in the system.

If all other process parameter are running constant???,i am more concerned about the temperature of the top tray with feed reduced and IR maintained at same mass flow.

from my vantage point,hydraulic hammering may also result because of a hot vapors collapsing on a a cooler reflux

[theleftcoast]

Hello everyone,

This excerpt is from the Troubleshooting chapter of Carl Branan's "Rules of Thumb for Chemical Engineers.

Hammer

Problem: There was a severe water-hammer type pounding at a column feedpoint.
Cause: The feed was subcooled and at a rate of 30% design. The hypothesis for the problem proved true, namely that the oversized feed sparger allowed all the liquid to run out of the first several upstream orifices. Consequently vapor would enter the remaining orifices and condense in the cold sparger. This caused hydraulic hammering.
Solution: The sparger (feedpipe) was turned so that the holes were on top rather than the bottom. This ensured that the sparger remained full of liquid even at low feed rates. A deflector was installed above the orifices to keep feed from impinging on the tray above. This solution was better than the alternate of plugging holes, because the hole area would then have been undersized at the higher design feed rates.
Moral: Collapsing vapor can produce severe hammering.

Hope this helps with your problem.

-JT

[Milutin]

We faced identical problem during crude unit startup, when TPA temperature drop below 45degC severe hammering started. Solution was simple, we increased TPA temperature. By design TPA heat exchanger has by-pass valve.

Regards,

[chimistul]

Hammering ocure due to boiling/vaporization and increasing localy the presure. Many times it is because of big diference of temperature beetwen wapours and liquid phase in the same vessel or beetwin spaces in exchangers.. What substances do you have in this column?I

Edited by chimistul, 18 November 2010 - 02:19 PM.

[Root]

We faced identical problem during crude unit startup, when TPA temperature drop below 45degC severe hammering started. Solution was simple, we increased TPA temperature. By design TPA heat exchanger has by-pass valve.

Regards,

Milutin,
I agree with you, by increasing temperature of TPA reflux this problem is going off, Main problem is sub-cooling of TPA reflux due to reduced feed.
Thanks for your input.
Toor

[Milutin]

Toor,

As you said the main problem is sub-cooled TPA return. Although not specified, suppose this is atmospheric distillation column, with TPA and two other pumparounds.

You can try increase duty on two other pumpoaroundas with aim to unload TPA duty and get higher return temperature.

Regards,

[Zauberberg]

Back to the original post, it seems like there was no change in the TPA return temperature ("usual" vs. actual case)?

Hammering takes place in the TPA line/distributor, and it may happen that lower flow has caused the same phenomenon as the one described in Branan's handbook: collapsing of uprising vapors in the TPA distributor itself. If that's the case in your system, maintaining the TPA flow - regardless of the return temperature - should eliminate hammering, as there will be no vapor entrainment into the distributor. This is an interesting opportunity to determine what actually causes hammering.

Maintaining TPA flow and unloading MPA should do the work - assuming that these are the only heat removal circuits in the column.

[Root]

Back to the original post, it seems like there was no change in the TPA return temperature ("usual" vs. actual case)?

Hammering takes place in the TPA line/distributor, and it may happen that lower flow has caused the same phenomenon as the one described in Branan's handbook: collapsing of uprising vapors in the TPA distributor itself. If that's the case in your system, maintaining the TPA flow - regardless of the return temperature - should eliminate hammering, as there will be no vapor entrainment into the distributor. This is an interesting opportunity to determine what actually causes hammering.

Maintaining TPA flow and unloading MPA should do the work - assuming that these are the only heat removal circuits in the column.

Zauberberg,
Henry kister also mentioned same in his book distillation operation and he also pointed out same as you scribed here, but sub-cooling of the TPA reflux looks more favorable in this situation because when we increased TPA reflux temperature problem is going off. Milutin is given very good suggestion for increasing the BPA and TPA flow helped more.
Thanks

[Zauberberg]

I understand and agree with your point. What I would personally like to try further - if I were at your place - is to confirm whether the hammering occurs at design flow rate of TPA, regardless of the return temperature. Basically, I can't see any other possible location where hammering could take place, except the distributor itself. Keeping it fully flooded with liquid, no matter how cold it is, should prevent vapor phase from entering the distributor and subsequently collapsing. That would be a sort of evidence that hammering occurs due to low flow, and probably not so much due to lower return temperature. If you experience something else, that would point out at different cause(s) of hammering.

[Milutin]

To get hammering you need both conditions:
- distributor which is not full of liquid (TPA low flow)
- cold temperature of reflux

Distributor which is not full of liquid will allow hot vapors to enter, cold liquid will cause sudden condensation of hot vapors, liquid in distributor will hit side opposite to liquid enter.
If any of these two conditions is missing, no hammering occurs.


Regards,

Edited by Milutin, 21 November 2010 - 06:08 PM.