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Minimum Diameter For A Structured Packing Bed In A Column

structured packing distillation

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#1 gegio1960

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Posted 23 March 2019 - 01:15 AM

Dear Experts,

I'd like to obtain info about the minimum applicable / applied diameter for a distillation column filled with structured packing.

The column is part of a plant to be installed in a gas field.

The plant has a very low capacity (around 1 m3/h) because it would be only used during startup periods.

The traffic is very low and I'm specially afraid of the minimum liquid rate per surface.

The most critical section would have 2 structured packing beds of 500 mm height.

Possibly, the diameter should be 200-250 mm but I'm not sure it can be done.

I've applied structured packings to crude oil vacuum distillation towers up to 10 m diameter but I don't know the other face of the problem. I imagine that process engineers involved in pilot plants could have some hints to propose. 

Thank you in advance for any expert help / comment, that will be considered side by side with packing vendor answers on the same subject (when they will have the time to answer).

Kind regards,

gegio



#2 Dazzler

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Posted 23 March 2019 - 01:40 AM

Hello Gegio,

 

Structured packing would have a wetting rate (flow rate per unit area). It may also be called Liquid loading.  I think that with those values and your flow you can work out the minimum area or diameter of the column for particualr models of packing.  If the industrial versions are not suited you might need laboratory scale packing or even consier small random packing (which has a recommend nominal size or diameter as a ratio of column diameter, as a rule of thumb, like a wetting rate).

 

In the end though you still need to be able to fabricate the coulmn and maintain and inspect it.  So if if is too small this may be hard.  From that point of view, the minimum suggested seems about right.

 

Dazzler



#3 gegio1960

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Posted 23 March 2019 - 02:43 AM

Thank you very much, Dazzler.

Of course, I'm aware of wetting rates...my concerns are relevant to the minimum size of structured packing "modules" for the installation.

Please kindly clarify a little bit more the meaning of your statement "the minimum suggested seems about right".

Does it mean that, according to your experience, a 200 mm ID column filled with structured packing has been built and operated?

Kind regards,

gegio



#4 PingPong

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Posted 23 March 2019 - 05:11 AM

I have no experience with such small diameter but I am sure it can be done as Sulzer also delivers structured packing for even smaller laboratory columns. If you are prepared to pay, you can get almost anything.

The most critical section would have 2 structured packing beds of 500 mm height.

Possibly, the diameter should be 200-250 mm but I'm not sure it can be done.

Apparently you already have a certain type of structured packing in mind.

There is a considerable difference in required diameter depending on whether you choose 750X or 125Y.

Required bed height for given number of stages also depends heavily on chosen type.

 

I don't really understand why you would want to use structured packing in this service, as you do not seem to need many theoretical stages.

 

Try to design the column using random packing like Raschig Super-rings of Sulzer NeXRings or ......



#5 gegio1960

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Posted 23 March 2019 - 06:26 AM

Thank you very much, Ping Pong.

The main parameter for the choice of the structured packing is the available quantity of liquid.

Since it is very limited (again!), I think that a proper selected structured packing would work better than random packings... but I'm ready to correct myself.

What do you think about this specific point?

Kind regards,

gegio



#6 breizh

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Posted 23 March 2019 - 06:33 AM

Hi gegio,

Consider the document attached to support your work .

You will find some info about hydrodynamic .

good luck .

Breizh

Attached Files



#7 gegio1960

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Posted 23 March 2019 - 07:01 AM

Thank you very much, Breizh.

I'll take a good look!

Kind regards,

gegio



#8 PingPong

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Posted 23 March 2019 - 07:54 AM

The plant has a very low capacity (around 1 m3/h)
Assuming that 1 m3/h is liquid capacity then, based on a minimum wetting rate of 1 m3/h.m2 (0.4 GPM/ft2) for oily liquid on steel random packing, the maximum allowable column diameter for steel random packing would be 1100 mm.

 

The actual required minimum wetting rate in your particular design depends on the type of liquid, packing material (metal type, glass, ceramic, plastic), packing type, packing surface area, et cetera.



#9 gegio1960

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Posted 23 March 2019 - 09:18 AM

Dear Ping Pong,

regretfully, 1 m3/h is only the size of the plant (i.e. the total feed to the column).

My doubts are relevant to the upper part, where only 1/3 of the feed material will be distilled.

Moreover, recycle rate is constraneid by the available cold utility.

I thought of a structured packing because of the requirement of a min wetting rate considerably lower than 1 m3/h/m2 (about 0.2 m3/h/m2).

Thank you,

gegio






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