8 replies to this topic

[drdave]

Hello All,

PP Pall rings are versatile tower packing for absorption / stripping operated well below recommended use temperature by suppliers. It has been observed that it lasts longer .Here, I want to know :

What are the life indicating parameters to replace PP Pall rings with fresh lot?
For example,Can we say that tensile strength / compressive strength will change from specified level to some "not acceptable" level etc.

Thanks

Dattatreya

[Ming Hooi]

Instead of checking the ring physically, why don't you check the performance of the absorption? for example, the pressure drop across the packing - has it increased drastically? or, your absorption capacity - is the output less concentrated?

[drdave]

Hello MH.C.

Here,Pressure drop across packing does not reveal much as it is significantly higher at start of run & even after end of run of more than 10 years life.
Moreover,Outgoing ammonia concentration is not much deviating .System hydraulics indicate inherent more pressure drop than normally specified. Tower contains non-conventional size PP Pall rings since inception.
Hence, We are in search of other convincing ways & means to solve without crash shut down/process disturbance.

Thanks

D.R.Dave

[siretb]

We have used for years plastic (PP) packings at temperatures in the range of 60-70°C. This is for scrubbing operation, where water is the main solvent.
We do see that the packings become a bit brittle, but performances are unaffected.
I would advise that, if you see too many fragments in the sumps, in the filters protecting the pumps, may be it's time to change the packing.
A bed lasts for years.

[drdave]

Hello Sireth,

Thanks for giving check points to decide the packing life.

May you please provide difference of pressure drops for one lot of PP Pall rings (or plastic Ring packings) for Start of Run & End of Run in your case of scrubbing operation.

Dave

[siretb]

Well, our application is somewhat special, because we also handle a lot of solids in the liquids. Despite the high solids load (> 10 grams/liter) we have no very significant pressure increase due to packing deterioration. Nor do solids accumulate, unless they become sticky because of a procees deviation problem.
So I do not have really the information you are asking me. We see that pressure drop is stable versus time.
What I can tell you is that the initial pressure drop is somewhat higher than what we would calculate from the suppliers data. We think that this is because there is a"solids holdup" in the packing.
Again, we use water as the liquid solvent and temperature is moderate. The plants usually shut down once every 18 monthes of so. we inspect the packing, check the bed heigth, and "fill up" if needed. Definitly, the rings are more brittle after 18 monthes operation.
I would be very practical: As long as you have no problems with efficiency or pressure drop, no need to replace, as MH.C stated. I would use something better than Pall rings (CMR or the like). You may also consider structured packing, like MELLAPAK plastic. Breakage is less of a problem, the pressure drop is lower. We tend to move from dumped packings to structured packing, because of the lesser pressure drop, despite a higher cost.

[drdave]

Hello Sireth,

Practically speaking,We have pressure drop problem in off gas treatment towers.
Tower hydraulic gives confirmation of more pressure drop than specified.But,There is no assurance on separation purity for top product which should not contain CO2 more than specified in PFD otherwise it can deteriorate our main process of melamine manufacturing.CMR#2 is one such option to tackle higher pressure drop problem.But, There is no way to confirm separation as desired for joint scrubber-stripper tower for NH3-CO2-H2O system.

Thanks

Dave

N.B. The base case is already discussed elsewhere separately in this forum.

Hi all,

Dont know if your still discussing this issue, maybe you can pm me if you are

Cheers

Ned