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Tray Design/operating Parameter Choices To Reduce Weeping

weeping

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#1 daraj

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Posted 13 October 2019 - 01:58 AM

Hi, when designing a column using RADFRAC for a new process, for separation of hydrocarbons, after finding the minimum number of stages, feed location etc. you get to sizing of the column. When using sieve (or even valve trays) aspen plus column profile shows weeping in certain trays. I tried different tray types like Ballast trays, nutter valves etc. still weeping will not go away. the column is already converged. without changing operating conditions what handles do I have to reduce weeping or eliminate weeping messages in the software?

what are the design mode parameters you can play in column design mode to reduce weeping? The vapor/liquid traffic may be fixed prior to design, so i cannot change the operating condition sof the column much like reflux ratio etc.



#2 Zauberberg

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Posted 13 October 2019 - 04:15 AM

You can try to change the % open area on the weeping trays. Probably there is higher liquid loading in this area of the tower.



#3 daraj

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Posted 13 October 2019 - 07:00 AM

Thanks. what should should the upper limits for jet flood %(range: 25 to 250) be? can increase it to say 130% to avoid certain warning messages?

 

i get following warning messages:

 

stages 2 to 35 have mare operating above than 100% downcomer backup

stages 2 to 35 are operating above 100% jet flood limits

wet tray pressure drop for above stages are higher than specified acceptable pressure drop



#4 breizh

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Posted 13 October 2019 - 08:07 AM

Hi,

Consider the documents attached to support your work.

 

Good luck

Breizh

Attached Files



#5 Zauberberg

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Posted 13 October 2019 - 10:18 AM

It seems like tower internals are undersized for given liquid and vapor flows - the downcomers are flooded and wet tray pressure drop exceeds jet flood limit.



#6 daraj

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Posted 13 October 2019 - 12:15 PM

Thanks to all. I tried changing column dia, tray spacing, no of passes, open area etc. and the warnings came down greatly 



#7 daraj

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Posted 13 October 2019 - 01:27 PM

one more question. In aspen we arrive typically at no of equilibrium stages to effect a separation. However when I start sizing, it seems to assume no of actual trays same as no of stages. Can I leave it like this? if tray efficiency needs to be incorporated(lets say 80%) how do I do this? the column is converged using equilibrium stages. and since no Murphree eff is specified same starting and ending stages is considered during sizing as well. should i manually calculate efficiency using some correlations and then just divide my no of equilibrium stages with that to size the column and provide tangent to tangent height etc.? and is the RADFRAC design sizing doesn't get affected by this? when it displays hydraulic plots it shows stage by stage condition. but these are still equilibrium stages, that's what iam confused about



#8 Bobby Strain

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Posted 13 October 2019 - 03:10 PM

Is this an exercise? Or, are you really intent on installing this fractionator.

 

Bobby



#9 daraj

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Posted 13 October 2019 - 11:42 PM

this is a concept design at this stage






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