What are the maximum allowable limits for following?
1- Jet Flooding %
2- Downcomer Flooding %
3- Downcomer Froth Backup %
4- Downcomer clear liquid (inch)
5- Weir Loading (gpm/in)
6- Pressure Drop across MV trays (psi)
Answers
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06/09/2014
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A:
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Attilio Jose Praderio-Soler, ConocoPhillips - LNG Technolgy Licensing and Process Group, attilio.j.praderio@conocophillips.com
This is an excellent summary. I would like to suggest that in order to make it even better, indicate that those values shall be used in conjunction with a selected "System De-Rating Factor" or also called "System Factor".
On the other hand, system factors may vary for the same service depending on the corelation selected or the software selected for the calculations.
Also, the results of correlations and software depend on the accuracy of the estimation of the values of the transport properties provided.
Surface tension is a very difficult transport property to be predicted in an accurate way, specially at values below 10 dynes/ct but the accuracy of the prediction becomes more critical/difficult at values below 5 dynes/ct. Additionally, the more components in a multicomponent mixture the more difficult to get an accurate value and, if CO2 is present, then an extra degree of difficulty is added.
Not all process simulators use the same correlations to estimate transport properties and the difference between the value of 1 dyne/ct and the value of 2 dynes/ct can generate in reality and practical terms an important loss in column capacity / premature flooding.
All the above is to suggest that care must be used when selecting "System De-Rating Factors" and physical properties correlations when a column design is pushed to the 80% - 85% limits and expected to be operated at that point, especially in high pressure light hydrocarbons systems and foaming systems ike amine contactors and regenerators. On the other side, to much safety margin in the "high side" can limit the expected/desired turndown, especially in large diameter columns with multi pass trays that can become unbalanced at low loads. It must be not forgotten that all the De-Methanozers are not the same, as all the packings are not the same, etc.
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26/11/2010
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Shri Sawant, Ingenero, krishnasawant@rediffmail.com
Jet Flooding % = Depends on the service: Moderate pressure & High P : 75-80%, Vacuum 70-75%
2- Downcomer Flooding % = 80%
3- Downcomer Froth Backup % = should not exceed tray spacing
4- Downcomer clear liquid (inch)
= < 50% Tray spacing and < 35% Tray spacing for high pressure applications
5- Weir Loading (gpm/in) = 4 - 8 gpm/in
6- Pressure Drop across MV trays (psi) = 5 -6 mm Hg Moderate pressure; 3-4 mmHg Vacuum Applications, up to 8 mm Hg for highpressure applications
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